# Cree XR-E Thermal Concerns



## cmacclel (Nov 12, 2006)

Many have you have been asking about the thermal condictivity of the Cree round and star bases so here are your pics.

As you can see there is a thin layer of PCB between the thermal pad of the Cree and the actual aluminum heatsink base. Not a very effecient solution in my opinion. Lumileds emitters are directly thermal epoxied directly to the aluminum for you would think a much better thermal path.


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## LumenHound (Nov 12, 2006)

Nice photos!
Looks like an inexpensive phase change adhesive "thermal pad" between an emitter and bare metal heatsink would give the same so-so results of those round and star shaped bases.


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## frenzee (Nov 12, 2006)

I think that's how Lux I's are attached too. Not an efficient way IMO either.


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## Anglepoise (Nov 12, 2006)

Thanks for taking the time to chop up and photograph.
I will let others, more knowledgeable than I, tell us what this will mean in real world terms.


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## IsaacHayes (Nov 12, 2006)

Not good for 1amp drive level that's for sure. Luxeons are durable but I've killed one with the stock star at 1amp drive. The thermal resistance of the pcb was too high.

700ma the cree will probably survive, but won't run well. 350ma should be ok. That's why luxeon1s at 350ma use the pcb, and lux3 at 700ma dont.

I personally like a max of TWO thermal interfaces in my lights, and that's with thermal epoxy. Emitter to heatsink, and heatsink to flashlight. One would be awesome.

A copper star would be excellent, with a pcb cut out for the center to attach to the copper directly, and pads above for the connections. Sure the solder would be a bit thicker but I think it would conduct heat better than even a thin layer of thermal epoxy...


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## NewBie (Nov 12, 2006)

FYI, those stars and rounds are **NOT** produced by CREE, but by other companies, and some distributors. The ETGTech version is a very common one. Unfortunately, it is lacking.

All MCPCBs are most definitely not created equal, and I most definitely applaud your taking one apart to show us all the short commings of the first round of MCPCBs produced by various third parties for the CREE LED. You get what you pay for.

They buy the CREE LEDs and mount them on the boards themselves.

The FR-4 you see there is a great insulator (epoxy and fiberglass), and it has to be made extremely thin just to get modest thermal transfer. 

An example of the problems this causes is shown here:






Directly soldered to copper, for comparision:


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## cmacclel (Nov 12, 2006)

So Newbie what boards be it round or star provides the best thermal transfer?

Mac


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## wquiles (Nov 12, 2006)

Nice photos Mac - thanks 

Will


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## chimo (Nov 12, 2006)

Yes, LumiLEDs changed their star heatsinks as well. Here is an old LuxIII vs a new LuxI heatsink. Note that they made the copper under the slug as large as possible for heat spreading.




 



Paul


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## davidefromitaly (Nov 12, 2006)

IsaacHayes said:


> Not good for 1amp drive level that's for sure. Luxeons are durable but I've killed one with the stock star at 1amp drive. The thermal resistance of the pcb was too high.
> 
> 700ma the cree will probably survive, but won't run well. 350ma should be ok. That's why luxeon1s at 350ma use the pcb, and lux3 at 700ma dont.
> 
> ...



yeah a copper star!!! some modder can start to di it  solder it with tin mean to have 10 times more heat tranfer vs. the best arctic product.


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## NewBie (Nov 12, 2006)

cmacclel said:


> So Newbie what boards be it round or star provides the best thermal transfer?
> 
> Mac




Well, thats a tough one to call. They do function, but why would these distributors purposefully throw the cat in with the wash?

Here we have a really nice XR-E product that CREE worked so hard at minimizing thermal resistance, so you could pull the heat out of the die, in order to maximize the light output (lumen output drops as the LED heats up), then some distributor comes up with a cheap hack that works the opposite way, and launches them off to yet another board house for mounting. I don't know what nutcase designed these things.

They could have very easily put 150 copper vias under the thermal pad area, which would have given direct thermal transfer thru the board directly to the aluminum (common in RF designs), and also flooded the copper from the thermal pad across the surface of the board, to also act as a heat spreader. This would have resulted in a thermal resistance well under 0.5 C/W. Instead of using what looks to be 0.000707" thick copper (1/2 oz.), they could have easily used 4 oz copper to help maximize the spreading across the entire surface of the board. Sure, so it would have actually cost nothing for the vias as well as nothing for the copper flood. If they were wanting to maximize performance, they could have spent another 0.04 dollars for the thick copper, but it sure would have helped further. I don't know, but this just reeks of cheap.

If I'd spend some of my own hard earned cash on these myself, you bet I'd be on the phone and someone's ears would be on fire...this isn't rocket science, just Thermal Management 098.

It would be cool if CREE were to take the mess these distributors made out of these and make something proper. Though, I don't think there are any plans for this- but I've never asked CREE about it.

Which works better? Harumpf, neither?

In reality, if you don't care much for getting great performance, and don't mind loosing some of your lumens due to die temperature rise, as well as color shift due to higher temps, I guess they work adequately.


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## Erasmus (Nov 12, 2006)

Interesting post and good to know for those who buy mounted Cree's. But maybe the threadstarter can change the title. It's no thermal concern about the Cree LED but about the third party PCB's. I hope there will be better PCB's soon!


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## chesterqw (Nov 12, 2006)

maybe there is some super secret formula for a thermal conductive pcb?


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## rgbphil (Nov 12, 2006)

Just to throw something in to this thread, check out :
http://www.instructables.com/id/E1HN1KQHG6ETVPN5PT/
basically a way to solder underneath a chip (or LED) on a homemade PCB. Sort of a thermal via.

perhaps someone can make use of this to play with interesting thermal designs with PCBs and the newer higher junction temp LEDs. If you do, please post results.

Phil


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## NewBie (Nov 12, 2006)

chesterqw said:


> maybe there is some super secret formula for a thermal conductive pcb?



Nah, the techniques have been pretty common for the past decade, nothing new to see here. Usually, where the FR-4 is used in the ones ETGTech supplies, you use instead, a thermally conductitive dielectric material, instead of an insulator material.

I'm looking at one of these and the FR-4 layer they use looks to be about 12 mils thick, but I do not have one that is unmounted for measurement. If this is in fact correct, the thermal resistance would be about 25 C/W.

Typical MCPCB's from way back when used to use 3 mil thick FR-4, which results in a thermal resistance of about 7 C/W.

Something that came out a few years ago, was a special thermal dielectric material that enhanced the thermal conductivity of the dielectric layer (typically the board material was black in color inside), which has a 3 C/W thermal resistance.

Just simply using 150 vias (which is 100% free in volume manufacturing) under the part can lower the thermal resistance to way below 0.5 C/W. This can be lowered even further by utilizing top and bottom copper layers, flooding from the thermal pad (the copper spot you solder to) across the board surface.

Using vias as thermal transfer points can be quite effective. You could make the board 39 mils thick (1mm), and do nothing more than put only 9 vias of 0.5mm in diameter, and still end up with a thermal resistance of 9 C/W. If you reduce the board thickness to one of the standard pre-preg board materials, like the 3 mil thick material (0.0762 mm), you end up with a thermal resistance of only 0.69 C/W.

Keep in mind, with the CREE, the ceramic material used is not the best for thermal spreading. As such, one would most definitely want to put the vias right under the die area.


So, how does it work in the overall scheme? I took a A19 head with a 2x123 cell body, and with the surface area, very roughly estimate the flashlight has a 30C/W thermal resistance to the ambient air. Using the 12 mil thick FR-4 MCPCB would end up nearly doubling the thermal resistance of the overall solution from the LED die to the ambient air.

However, if one were to carry the flashlight in their hand, as most people do, you always sweat a little, causing a very good thermal path from the hand, to the blood steam, which then pumps the heat away, much like a coolant system does for the engine in a car. Unfortunately, I do not know the exact C/W of this interface, but in this case, the use of the ETGTech MCPCB would be by and far be the highest thermal resistance point, and have a highly significant impact on the overall thermals.


On another note, if you want to go high tech instead:

There have been some developments in the past few years where they use graphite as a thermal spreader (done right, it has a lower spreading thermal resistance than even copper, about 20% better), then use the area advantage to lower thermal transfer thru the board. 

An example of one of these newer technologies:
http://www.graftechaet.com/Technical-Documents/Technical-Bullitin/EG-ZS-PP-098.pdf


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## chimo (Nov 13, 2006)

I just sacrificed a blank ETG board (not the same as above). The FR4/copper layer on that one is around 4-5 mil. I may have to hang on to these.

I checked the FR4 layer on new LumiLED star and it measured 5 mil.

Paul


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## cmacclel (Nov 13, 2006)

Last night I did a quick test with the MCPCB's I ran the mounted cree for about 1 minute while measuring the LED die temp then the back of the MCPCB the difference in temp was ony 15 degrees so they seem like they are working ok.

Mac


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## SemiMan (Nov 13, 2006)

*Best MCPCB Material*

As NEWBIE has pointed out, there are vast differences between MCPCB materials. The best in my experience is LAIRD THERMAGON 4mil thermal pre-preg with 2ounce copper. I have only used it on an Aluminum core, but I hear it is even better on a copper core. It is not as good as mounting directly to copper, but it is probably as close as you are going to come with current products where you need isolation. It appears to be as almost if not as good as some of the esoteric methods such as Anotherm where they place traces right on the heat sink. The material is 0.053C in2/W so for a 5mm*5mm conduction path, you can get about 1.3C/W. With some extra copper for spreading you can get this down to about 1/2 of that.

As Newbie has pointed out though, using lots of vias, especially if they are filled, will be even better. However, if you need isolation, the Thermagon is one of the best options.

Semiman


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## Anglepoise (Nov 13, 2006)

Things are getting a bit technical and above my head.

Where can we buy these 'good' MCPB's?

Are they generally available for sale or as I rather suspect, have to be custom made for each application. 

If the later, how does one go about getting 1000 or more made up just for us.


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## NewBie (Nov 13, 2006)

cmacclel said:


> Last night I did a quick test with the MCPCB's I ran the mounted cree for about 1 minute while measuring the LED die temp then the back of the MCPCB the difference in temp was ony 15 degrees so they seem like they are working ok.
> 
> Mac




Good deal.

How did you go about measuring the die temperature on yours?

I hope it wasn't an IR thermometer, they are not that accurate in this situation.

I'm seeing 10-20C rise just from the aluminum of the MCPCB to the body of the CREE, which means the die is much hotter than that.


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## cmacclel (Nov 13, 2006)

NewBie said:


> Good deal.
> 
> How did you go about measuring the die temperature on yours?
> 
> ...




Yup it was an IR thermometer  Hey I tried 

Mac


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## ViReN (Nov 13, 2006)

One more reason NOT to buy mounted Cree XR-E


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## cmacclel (Nov 13, 2006)

Well hey does my finger count?? My finger thermometer said it was close 

Mac


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## chimo (Nov 13, 2006)

Here's another reason not to buy a mounted emitter. This is a 1W Cree emitter from an earlier group buy (It is NOT an XR-E). It is mounted on an ETG heatsink. I removed the emitter from the board today. That little dab of solder is certainly not the best method for transferring heat!





Paul


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## NewBie (Nov 13, 2006)

cmacclel said:


> Yup it was an IR thermometer  Hey I tried
> 
> Mac




Well, hey, thanks a bunch for trying!

If you go up a few posts, up to my IR pictures, you will note the one that is on the ETGTech MCPCB. Note that the hotspots on the LED body are about 13C above the MCPCB temperature. So for surface temp, it basically agrees nicely with the IR camera. Also notice, how you see the surface temperature of the lens, and not the die, you can't even make it out...


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## IsaacHayes (Nov 14, 2006)

Chimo, wow!!! crazy, even looks like air bubbles under the solder. How did you pop it off?


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## ViReN (Nov 14, 2006)

the best I would suggest is file off the base contacts (not to remove the base Heat sink contact) and then directly epoxy it (with a very thin layer) over the copper heat sink (for those who do not have expertise on direct soldering to copper plate). this should give much better results.

oh use upper contacts


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## IsaacHayes (Nov 14, 2006)

or clip the corners then the bottom are no longer connected! too easy.


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## NewBie (Nov 14, 2006)

chimo said:


> Here's another reason not to buy a mounted emitter. This is a 1W Cree emitter from an earlier group buy (It is NOT an XR-E). It is mounted on an ETG heatsink. I removed the emitter from the board today. That little dab of solder is certainly not the best method for transferring heat!
> 
> 
> 
> ...




I've seen some really **** poor soldering in my days, but dang ETGTech did a really poor job on those.

Definitely click on the picture link, it tells a thousand words...

Outstanding find chimo!


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## chimo (Nov 14, 2006)

IsaacHayes said:


> Chimo, wow!!! crazy, even looks like air bubbles under the solder. How did you pop it off?




- Held it vertically in a vise
- Applied heat with a mini-torch on the back of the heatsink
- Grasped the sides of the emitter with pliers and pulled gently until the solder was soft enough to release the emitter

Paul


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## Kryosphinx (Nov 14, 2006)

You don't even need a mini-torch. Any ordinary lighter is hot enough to do it. The only problem is that it can leave a black film on the bottome of whatever you're heating up.


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## 45/70 (Nov 15, 2006)

I have a "what if" idea.

What if you unsolder the emitter, as chimo did. Take an exacto knife, cut around the thermal "pad" (_*not the elecrtical contacts!*_) on the board and peel this section up and remove it. Clean up the heatsink that is now exposed. Then, either of two things,

Put solder paste on the MCPCB electrical contacts. Put _*thermal epoxy*_ in the area you cut out, where the thermal pad goes. Mount the emitter and clamp it together, untill the epoxy sets. Then, heat the assembly up to reflow the solder at the electrical contacts.

_*OR,*_

Same as above _*but*_, cut a piece of thin copper sheet to the dimensions of the cut out area. Place thermal epoxy in the cutout area, place the copper sheet on the board and clamp it in a jig to assure flatness, untill the epoxy sets up. Then, apply solder paste to the electrical contacts _*and*_, the thermal pad area. Heat the the assembly up to reflow the solder.

Most of you guys know a lot more about all this than I do but, I thought I wouild present my idea for comment. 

Dave


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## NewBie (Nov 15, 2006)

Sounds like a lot of work to fix these MCPCB.


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## McGizmo (Nov 15, 2006)

chimo said:


> - Held it vertically in a vise
> - Applied heat with a mini-torch on the back of the heatsink
> - Grasped the sides of the emitter with pliers and pulled gently until the solder was soft enough to release the emitter
> 
> Paul



That does look like a bunk solder job but can we be certain that's what it looked like before you softened the solder and had it reflow to some extent? The solder under the LED leads is nice and rounded and full making me think that it had reflowed and reformed after you removed the LED. :thinking:

I am no expert at all but I have reflowed some of these LED's and watched the process. I have also dabbled a bit with jewlery soldering and learned to use the heat to pull the solder towards it. It would be interesting to take a component that you know has been flowed properly and see what you get when you remove it in the manner this was done.

I guess I don't know enough to make a judgement on this solder job so I defer to others.


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## chimo (Nov 16, 2006)

Don,

It appears that was as far as the solder paste reflowed under the emitter body. 

If you will note the emitter, you can see that a significant portion of the center pad never had any solder - the same is true for the heatsink. I was applying tension to the emitter while I was heating the underside of the heatsink. 

Pretty well all the solder came off with the emitter. Perhaps that's because of the heat transfer direction - the solder touching the heatsink would have softened before the solder at the emitter interface, so it would have released first (especially while tugging on the emitter).

An explaination for the anode/cathode contacts having better reflow would be that they would have heated first and would have been at reflow temperature for a longer period. This one just may not have been in the oven long enough. It seems like the most likely explaination.

Paul



McGizmo said:


> That does look like a bunk solder job but can we be certain that's what it looked like before you softened the solder and had it reflow to some extent? The solder under the LED leads is nice and rounded and full making me think that it had reflowed and reformed after you removed the LED. :thinking:
> 
> I am no expert at all but I have reflowed some of these LED's and watched the process. I have also dabbled a bit with jewlery soldering and learned to use the heat to pull the solder towards it. It would be interesting to take a component that you know has been flowed properly and see what you get when you remove it in the manner this was done.
> 
> I guess I don't know enough to make a judgement on this solder job so I defer to others.


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## McGizmo (Nov 16, 2006)

Paul,
I agree with the appearance as you have stated it. From watching the parts I reflowed and using some solder paste myself, I would say it looks like the solder never _really_ flowed in the first place. It doesn't look like the part snugged down to the MCPCB. As you suggest, it doesn't look like the center pad ever had a complete film of solder on it. :shrug: Havingnever removed parts in this manner, I won't pretend to know what it should look like but I agree that this sample doesn't look right!


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## IsaacHayes (Nov 16, 2006)

yup, looks like the surface tension never was broke and the solder never spread out and covered everything. Once it does, it's near impossible to have the tension rise up and the solder come cleanly off of something like that from my experience. It won't want to ball up after it's been spread and contacted everything.


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## 45/70 (Nov 16, 2006)

NewBie said:


> Sounds like a lot of work to fix these MCPCB.


Yeah, well, I need to use a star for my application. I don't have my Q2 bins yet, as they won't be coming for a few weeks.

Whether or not the reflow job is good (my impression of chimo's example is, it obviously wasn't hot enough), if NASA/JPL oversaw the reflow process and it was perfect, these MCPCB's still wouldn't be worth a crap anyway. Just trying to find a solution. 

Dave


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## McGizmo (Nov 16, 2006)

45/70 said:


> .......... if NASA/JPL oversaw the reflow process and it was perfect, these MCPCB's still wouldn't be worth a crap anyway. Just trying to find a solution.
> 
> Dave



I am not sure why these MCPCB's aren't worth crap but like you, I too need a solution. My present one is using these MCPCB's. 

So far, they seem to work fine so I am really feeling stupid here! :green:
According to ETG and a spec sheet they provided me, the isolation layer used on the MCPCB's is rated at less than .6 C/W resistance. Now the whole LED package is bonded to the MCPCB with this isolation layer and this means that the area under the LED lead pads as well have this thermal connection. From messing with these LED's, it is clear to me that this LED package has great heat transfer throughout and this includes the lead "wings". I like the idea of the center pad and the two lead pads all solder flowed to copper which then has this isolation barrier of reasonable thermal resistance and then on to the core of the MCPCB. In a more perfect world, the MCPCB would be silver and the center portion would be somehow raised up directly to the plane of the center pad of the LED and only the lead pads would have an electrical isolation layer and perhaps only the positive pad for that matter. Well If such a board is available or any board with marked improvement over the ETG board, sign me up. 

In the mean time, I will stick with the crap I have available and the crap that seems to work pretty well to me.


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## NewBie (Nov 16, 2006)

Well, something is quite wrong with their spec, to say the least, unless you are driving the A19 at 20 Watts?

It is extremely clear the package does not have good thermal spreading in it, and something is wrong with the ETGTech board.








Possibly their process is partially to blame. I took Chimo's picture of the ETGTech MCPCB and blew it up, to look at things closer. Notice how the solder didn't flow, as well as the grain of the CREE surface in the solder area:


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## ViReN (Nov 16, 2006)

One Alternate solution some one had recently posted (was it milkey?) is to put Cree on New Generation Luxeon's (they have much better copper below the surface) solder able? not sure, but it can be epoxied (like the luxeon slug)... legal? may be not, but certainly more efficient than the ETG and Third Party MCPCB

It would be best if Cree themselves come out with Star's and Rounds, they would hopefully be doing much better job, wonder what's stopping them? is it some thing with Luxeon Patents???


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## Calina (Nov 16, 2006)

Nevertheless, is there something better available?


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## 45/70 (Nov 16, 2006)

Well Don, I hope you are correct.  As I pointed out earlier, you guys are way ahead of me! As NewBie has pointed out, these boards just don't seem right, and the fact that Lumileds mounts their higher power LED's directly onto the aluminum heatsink, I just have to wonder?

I was planning on trying one (mine will be mounted on stars) and seeing what happens. I would like to be able to run them, at least intermittently, at 1000mA+ and be able to continuosly run them at 750mA in a brass (not as heat friendly as aluminum) light. What I'm seeing here just doesn't look too good. :sigh:

Again, I hope your right. :thumbsup:


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## Calina (Nov 16, 2006)

Viren, this solution has not been proven yet to be any better than ETG's MCPCB.

It look fine in theory but before it is tested we don't know!


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## NewBie (Nov 16, 2006)

McGizmo said:


> According to ETG and a spec sheet they provided me, the isolation layer used on the MCPCB's is rated at less than .6 C/W resistance.



Their numbers do not add up.

3 mil thick FR-4, has a thermal resistance of 7.4 C/W, as measured by Flomerics and OSRAM.

To work out, ETGTech's FR-4 layer would have to be 0.00025" thick.

It is not.

For a sanity check take another look at the photos, and note the temperature scale on the side for various points, like the LED near the metal ring, towards the ends, and then look a surface of MCPCB area.








Next, take a look at this one, note the scale for temperatures on the side, and compare the LED metal ring, the various areas of the flat spot on the CREE body, and then also the copper surface that the XR-E is mounted to:







I'm looking at the blown up version of Chimo's photo of the ETGTech's MCPCB again, and I'm wondering if the solder was even reflowed at all in the center of the CREE thermal pad. It could be just as likely that Chimo melted the solder under the thermal pad, and it never even got reflowed there in the first place:


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## McGizmo (Nov 16, 2006)

Newbie,
Both images present a good case for questioning. :shrug:

ViRen,
The direct mount of the Luxeon to the Al core of the star is fine if your LED leads are in a plane above the sink plane. (it's a shallow hole there) If you mount a XR-E to this board, you have a gap to fill and with what?!?! 

I have mounted someof these directly to Al and had the lead pad areas relieved to avoid electrical contact. This is fine but I am also avoiding thermal passage from the package to the sink here. 

In terms of Luxeon's being mounted to the bare core of the boards, consider the fact that the K2 is the first Luxeon that even has the reflow option. Any K2's mounted on stars by Lumileds?

There are theoretical ideal methods where cost and effort are not factored in and then there are commercialy viable methods which compromise based on cost and time. 

We have seen some examples here where it looks like QC may be more of a problem than materials or design even.

None of our lights are going to perform as well as a LED mounted to a big hunk of copper unless the design includes that big hunk of copper. There will likely be some loss in efficiencies but the important thing to consider is the magnitude of these losses and whether they are acceptable when it is all said and done. 

Clamp one of these to a 10kt emerald cut diamond and you are on your way!


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## Calina (Nov 16, 2006)

You might be glad to know that the price of diamonds is way down since they started producing artificial gems.

Hey don't rush to get some; I'm just teasing.


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## IsaacHayes (Nov 16, 2006)

Don, if you snipe the corners with wire cutters you sever the electrical connection of the bottom of the pads and they become neutral. Solder to the top then for connection. Attach with AA epoxy, or solder to copper. No need then to make reliefs/depressions in the heatsink to prevent a short. It's really easy and effective.

IIRC Newbies copper was a very thin copper sheet. Not the most perfect setup either, but good enough for showing what a direct solder to copper can do.

Right now I'm torn between just AA'ing it to aluminum, or soldering it to a copper disc the thickness of a penny, and AA'ing the "penny" to the aluminum light. The former would only be 1 thermal interface, but the later would help spread the heat better so it had a larger area to go through the less efficient thermal interface of AA epoxy... :shrug:


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## ViReN (Nov 16, 2006)

> ViRen,
> The direct mount of the Luxeon to the Al core of the star is fine if your LED leads are in a plane above the sink plane. (it's a shallow hole there) If you mount a XR-E to this board, you have a gap to fill and with what?!?!



Dear McGizmo,

I was referring to the chimo's Luxeon Pictures mentioned in the following post.
https://www.candlepowerforums.com/posts/1688325&postcount=9

of course, direct mounting on solid aluminum / soldering to copper would be much preferred

perhaps Cree could change LED design so as to easily mount on heat sink.


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## NewBie (Nov 16, 2006)

Even a thick, I think it was 39.3701 mils (1mm) FR-4 board in their example, glued to aluminum, with only 9 vias in it has a thermal resistance of 9.7C/W. If one reduces the thickness of the board to a standard pre-peg FR-4 thickness of 3 mils, *AND* keeps the same nine thermal vias, the thermal resistance drops to 0.746 C/W. There is a tremendous reduction of thermal resistance, just by adding vias to nothing more than standard FR-4. A person can easily decrease the thermal resistance further, by utilizing smaller vias, and more of them, to increase the copper area that goes thru the board. This doesn't count solder that partially fills the vias, which lowers if further. I'd seriously consider putting the vias under the LED die area and filling the whole thermal pad area with them.
http://www.flomerics.de/Produkte/Osram/Golden_Dragon_LED.pdf


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## Christexan (Nov 16, 2006)

Speaking of copper sheets etc, a common issue I've seen (but haven't seen this solution to) is soldering wires to the top contacts of the Cree. The common issues seem to be:
#1 - Difficult to solder cleanlyi
#2 - Wires interfere with reflector/optics placement to a larger or smaller degree...

Solution to both of these, get some very thin copper sheet / heavy copper foil... cut the sheet into a thin strip (roughly the size of the Cree contacts, with a little extended part either off the short or long edge depending on desired wire routing...)
tin the Cree contacts, and the copper sheet, then lay the copper sheet over the contact as desired (with a dab of flux to improve the process, as desired). Apply soldering iron briefly to top of sheet (should heat up very quickly considering thickness)... and remove... probably would only take a second or two to make the joint. Now you have a "solder tab" off the edge of the package, you can solder to directly (flat), or roll/fold into a tube shape, and insert wire then solder for a stouter joint. 
Tweak sheet thickness, overhang, etc, as desired for your needs, but now the entire LED package "top" is still flat (a few mils higher, but still flat and level for the most part).
Hope someone finds the tip handy, if it works (can't imagine why it wouldn't).


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## 45/70 (Nov 16, 2006)

McGizmo said:


> In terms of Luxeon's being mounted to the bare core of the boards, consider the fact that the K2 is the first Luxeon that even has the reflow option. Any K2's mounted on stars by Lumileds?


Well, no but, there are no XR-E's mounted on stars by Cree either. Hummm. :thinking:

Dave


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## 45/70 (Nov 16, 2006)

McGizmo said:


> Newbie,
> Clamp one of these to a 10kt emerald cut diamond and you are on your way!


Group Buy? 

Dave


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## 45/70 (Nov 16, 2006)

NewBie said:


> Even a thick, I think it was 39.3701 mils (1mm) FR-4 board in their example, glued to aluminum, with only 9 vias in it has a thermal resistance of 9.7C/W. If one reduces the thickness of the board to a standard pre-peg FR-4 thickness of 3 mils, *AND* keeps the same nine thermal vias, the thermal resistance drops to 0.746 C/W. There is a tremendous reduction of thermal resistance, just by adding vias to nothing more than standard FR-4. A person can easily decrease the thermal resistance further, by utilizing smaller vias, and more of them, to increase the copper area that goes thru the board. This doesn't count solder that partially fills the vias, which lowers if further. I'd seriously consider putting the vias under the LED die area and filling the whole thermal pad area with them.
> http://www.flomerics.de/Produkte/Osram/Golden_Dragon_LED.pdf


Sounds good to me, NewBie. When can you start? :naughty:

Dave


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## McGizmo (Nov 16, 2006)

Soldering to the top is a PITA and the fact that the lens retaining ring is tinned and more than happy to receive solder doesn't help!! :green:

Instead of nipping the corners off to remove the vias feeding the bottom side, has anyone tried just taking a burr to the vias themselves to break continuity?

ViRen,

The current XR package mounts easily to a heat sink using reflow technology. The issue here is more in regards to quality control, quality and effective thermal relief of various MCPCB's and what have you.

Now for custom or modded lights where production and assembly costs are not of primary concern, there are other alternatives that are likely more efficient interms of thermal resistance. This is one link in the chain of the complete light package. Efficiencies are compromised at many levels. The key is to consider the total package and determin if the summation of losses are at a permissible level or not, or so I would think. The more we understand each link in the chain, the better we can control and dictate the eventual strength and nature of the full chain.

Newbie's IR image here is contrary to what one would expect from the MCPCB. A similar image may be contrary to what one would expect from another solution that looked good in print. :shrug:

This image is of a hand assembled part that does not have a good and complete thermal path from MCPCB to can (view the delta from LED to the perimeter which I believe is the can lip which is above the contact plane). The LED is being driven beyond spec. This is a sample of one. It looks like a 10C difference and this is with a drive current of 825 mA or about 3 watts? Does that mean we are looking at a delta of about 3C/Watt from source across the MCPCB itself (including not only the boundaries from LED pad through the isolator film to Al core but spread through the core and then back up through the boundary layer and into the white paint of film that is the surface finish on the MCPCB and actually being photographed)? Some of these thermal epoxies have a great thermal conductivity when used in very thin films but those numbers are also based on surface area. What do we get with a real IR photo like this when the part is mounted on a sink?

I won't pretend that this thermal image is an image I can understand or properly interpret. Had Newbie scrapped a spot on the MCPCB to show the raw Al core of the MCPCB, would we see this as a hot spot in the image? What is with the streak from right to left that shows a much cooler section across the whole image? I assume I am to disregard this portion of the image but why disregard this but accept the balance and pretend to understand what I am seeing? Just what _am_ I seeing here? How am I to read this? GlowBug has done a number of IR images of complete flashlights and I recall one he did of a chrome Aleph that was just bunk. It seems that chrome is not a reasonable surface to get an IR image from. The chrome seems to hide the IR energy from the camera. :shrug: 

Newbie has stated that he coated the part with some material that will provide the same emmisivity (sp) to the camera. This makes me think that the camera is imaging the surface and not the core beneath. Isn't the core beneath insulated by both the isolation layer as well as some top film? If yes, perhaps this insulation is not significant.

I have learned from personal experience that an IR thermometer is not to be trusted for absolute temperature readings. However, an IR image is? :thinking: I can imagine that an IR image is viable for relative comparison but for absolute measure I need some coaxing.


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## IsaacHayes (Nov 16, 2006)

I've had no problem soldering on the top. I use very fine teflon wire prebent where I want it to go. :shrug: This is even after the corners have been snipped off so there is even less to solder to. Christexan's idea of making LED leads is pretty good too, but might be hard when you solder the wire, it might unsolder from the LED at the same time. But would make it look more like a luxeon lead package.

Don, yes at first people were grinding the pads off the bottom, but clipping seems so much faster. 

Yes it's hard to tell exactly whats going even with the IR picture, but it's easy to see that the cree runs about 2x more hot with the pcb. Weither or not you have much actual lumen loss is another thing to ponder as if you don't then all this worry is moot point. Unless it shortens the life of the led considerably.

A test with a cree on MCPCB, to measure lumens with a ceiling bounce or light box, then take the same cree off, re-flow it to a copper disc/sheet metal, and re-test would be needed to see how much of an improvement we get I think is the next logical step.


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## Anglepoise (Nov 16, 2006)

McGizmo said:


> Instead of nipping the corners off to remove the vias feeding the bottom side, has anyone tried just taking a burr to the vias themselves to break continuity?



Yes Don. I have done this with a diamond grinder.
See this post. 3rd one in. Click


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## Christexan (Nov 16, 2006)

I thought about my "solder tab" idea unsoldering itself when connecting the wires to the "tab" part of it shortly after I posted it, but 2 thoughts on that...

#1 - Once soldered directly to the package, the package itself will act as a heatsink for any heat applied to the "tab" part (open to ambient), so the temperature gradient from hanging tab part to package soldered part should be dramatic (meaning, the solder to the package itself is unlikely to heat up across the width enough with brief "end tab" soldering to loosen completely from the package (the heat being "sunk" into the unit itself). 
#2 Once the "tab" is fixed to the Cree package, a simple alligator clip or other "solder heat sink" method (putty, etc) can be used to isolate the free-hanging end from the rest of the tab/package contact joint. Again, with copper this thin, any soldering should be momentary, at most 1-2 seconds contact probably to make a good connection, so the heat isn't likely to have time to heatup the package/contact top and break the connection before the iron is removed from the wire connection being made. Anyhow, those were my post-posting thoughts.


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## McGizmo (Nov 16, 2006)

David,
I meant going into the via itself with like a ball burr and just removing enough copper (think counter sink or divet) to break the connection. This would leave full pad and surface contact of LED to sink. That ceramic is a great thermal conductor!

Isaac,
I believe much of the 2X temp is due to the small LE trying to compete with thermal relief against the larger and more massive copper plate. I think it reasonable to look at the two images in terms of thermal differentials across the components but not to draw conclusions on the absolute temp of the LED in both cases. A full and clear picture may be worth 1000 words but what is the value of a partial or misintrepreted picture? :thinking:

I leave it to the qualified to draw the proper conclusions.


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## Anglepoise (Nov 16, 2006)

Christexan said:


> I thought about my "solder tab" idea unsoldering itself when connecting the wires to the "tab" part of it shortly after I posted it, but 2 thoughts on that...
> 
> #1 - Once soldered directly to the package, the package itself will act as a heatsink for any heat applied to the "tab" part (open to ambient), so the temperature gradient from hanging tab part to package soldered part should be dramatic (meaning, the solder to the package itself is unlikely to heat up across the width enough with brief "end tab" soldering to loosen completely from the package (the heat being "sunk" into the unit itself).
> #2 Once the "tab" is fixed to the Cree package, a simple alligator clip or other "solder heat sink" method (putty, etc) can be used to isolate the free-hanging end from the rest of the tab/package contact joint. Again, with copper this thin, any soldering should be momentary, at most 1-2 seconds contact probably to make a good connection, so the heat isn't likely to have time to heatup the package/contact top and break the connection before the iron is removed from the wire connection being made. Anyhow, those were my post-posting thoughts.



I tried your idea and it worked but did not really help at all. As far as I can see, any soldering done to the top is potentially going to interfere with the reflector. 
However I have a photo somewhere of Don's new McR-17EX and it looks as if he has machined a shoulder inside the back of the reflector so when it sits on the tinned Cree reflector ring, it is proud of the connection plane.

From the photo it looks like there might be enough room to solder some 24 gauge wire to the top pads. 

My next test is going to mount the LED on a machined pedestal with AA in the traditional way , and solder the + and - underneath. 

I have been running a P2 , XR-E Cree epoxied directly to a 3/4" X 3" aluminum rod with a thin layer of AA. Steady state temp stabilized at 37° C ( Fluke Thermocouple ) with 350 ma going to the LED. Think that is a bit hot?


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## milkyspit (Nov 16, 2006)

ViReN said:


> One Alternate solution some one had recently posted (was it milkey?) is to put Cree on New Generation Luxeon's (they have much better copper below the surface) solder able? not sure, but it can be epoxied (like the luxeon slug)... legal? may be not, but certainly more efficient than the ETG and Third Party MCPCB
> 
> It would be best if Cree themselves come out with Star's and Rounds, they would hopefully be doing much better job, wonder what's stopping them? is it some thing with Luxeon Patents???




* ViReN, *yup, that was me.  I neither epoxy nor solder the heatsinking area but rather apply a thin layer of Arctic Silver 5 thermal compound. I have no hard quantitative data to support anything one way or the other, but the empirical data suggests that decent thermal transfer is taking place... the underside of the star warms up pretty quickly once power is applied to the Cree emitter. It does seem to do the job.

Is it the best possible solution? Probably not. Is it at least as good as other starlike approaches, possibly a little better? Again I'm not sure, but my guess would be yes. Is it legal? I don't see why not... after all, I did buy the Luxeon stars in the first place... I'm using scrap parts from previous builds... in essence I've already paid for the stars AND the Luxeon emitters that were on them... now they're mine!

Just seemed like a decent idea in that the Luxeon I star is flat and has an exposed copper pad for the heatsinking area.
:shrug:


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## chimo (Nov 16, 2006)

Although it's evident from the pic, I just wanted to remind everyone that the pic was a 1W Cree an not an XR-E. I have no information on the pre-mounted XR-Es. They may be the same quality or they may be properly re-flowed. 



chimo said:


> Here's another reason not to buy a mounted emitter. This is a 1W Cree emitter from an earlier group buy (It is NOT an XR-E). It is mounted on an ETG heatsink. I removed the emitter from the board today. That little dab of solder is certainly not the best method for transferring heat!


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## Amonra (Nov 16, 2006)

does a thin copper sticker with electrically insulated sticky side exist ? if so it can be cut in a small strip and put under the bottom electrical pads of the emitter and the emitter can then be reflow soldered onto a diy copper 'star'


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## NewBie (Nov 16, 2006)

McGizmo said:


> Newbie's IR image here is contrary to what one would expect from the MCPCB. A similar image may be contrary to what one would expect from another solution that looked good in print. :shrug:
> 
> This image is of a hand assembled part that does not have a good and complete thermal path from MCPCB to can (view the delta from LED to the perimeter which I believe is the can lip which is above the contact plane). The LED is being driven beyond spec. This is a sample of one. It looks like a 10C difference and this is with a drive current of 825 mA or about 3 watts? Does that mean we are looking at a delta of about 3C/Watt from source across the MCPCB itself (including not only the boundaries from LED pad through the isolator film to Al core but spread through the core and then back up through the boundary layer and into the white paint of film that is the surface finish on the MCPCB and actually being photographed)? Some of these thermal epoxies have a great thermal conductivity when used in very thin films but those numbers are also based on surface area. What do we get with a real IR photo like this when the part is mounted on a sink?



The image also agrees with thermocouple measurements, when utilizing fine 42 guage K-type thermocouples.

It isn't much of an issue, once the heat gets to the aluminum of the MCPCB, it is getting the heat there in the first place, that is an issue.



McGizmo said:


> I won't pretend that this thermal image is an image I can understand or properly interpret. Had Newbie scrapped a spot on the MCPCB to show the raw Al core of the MCPCB, would we see this as a hot spot in the image?



Unfortunately no.

Remember, the ETGTech MCPCB does not have the PCB portion of it covering the Aluminum core all the way to the edge, so you are actually seeing the Aluminum substrate with the highly emissive coating I put on it, at the edges.

If you look carefully in the IR picture, you can see the threaded hole portion.







Here is one of the module types I used in the photo, note a number of areas where it is bare aluminum:








McGizmo said:


> What is with the streak from right to left that shows a much cooler section across the whole image? I assume I am to disregard this portion of the image but why disregard this but accept the balance and pretend to understand what I am seeing? Just what _am_ I seeing here? How am I to read this?



This "streak" is one of the wires I installed on the module, blocking the image.




McGizmo said:


> GlowBug has done a number of IR images of complete flashlights and I recall one he did of a chrome Aleph that was just bunk. It seems that chrome is not a reasonable surface to get an IR image from. The chrome seems to hide the IR energy from the camera. :shrug:



No, chrome doesn't really hide the IR energy, it just is a very poor radiator of heat, and thus you cannot see it. Most shinny looking metals are quite poor thermal radiators, but something as simple as Hard Anodize is many times more emissive. A very interesting thing is that you can take aluminum or titanium, and sandblast it, etch it, and scratch it all up, and in the 7-14um spectrum, it looks like a perfect mirror, as it also reflects heat. It is one of the reasons that aluminized mylar works great both for keeping heat in, and also reflecting the heat in the summer, and the properties are often taken advantage of in fire fighting suits and "space blankets" Thats why I coat items with a high emissivity material. If all the surfaces were the same, one could simply adjust the thermal emissivity settings for many shots, but it still doesn't work well with bare metals. Heatsinks that are designed to radiate are even anodized black, to radically raise the emissivity, and allow a substanial amount of heat to be released into the air/space as IR radiation. 




McGizmo said:


> Newbie has stated that he coated the part with some material that will provide the same emmisivity (sp) to the camera. This makes me think that the camera is imaging the surface and not the core beneath. Isn't the core beneath insulated by both the isolation layer as well as some top film? If yes, perhaps this insulation is not significant.



Actually, the material conducts heat better than Arctic Alumina, is very thin, and is not even close to being significant.




McGizmo said:


> I have learned from personal experience that an IR thermometer is not to be trusted for absolute temperature readings. However, an IR image is? :thinking: I can imagine that an IR image is viable for relative comparison but for absolute measure I need some coaxing.



I certainly can understand why folks often have issues with IR temperature measurement systems. Having worked for FLIR Systems, I worked with the IR camera systems on a daily basis for a number of years. I also understand some of the gotchas, and how they actually work, better than many folks.

Thats why I used the highly emissive coating, and had the wire going down to the surface, to allow me to measure the actual temperatures present. I'd also taken a number of other temperature measurements on various surfaces.

If you have your emissivity dialed in properly, the system used is accurate to +/- 2 degrees C, and the delta temperatures are accurate to 0.08 degrees C.

Remember, I actually worked for FLIR Systems (a world leader in IR imaging systems) for a number of years, and also worked on the AN/AAS-33 Detecting and Ranging (FLIR imaging based) weapons systems when I was in the military for the A6-E TRAM (Target Recognition and Attack Multisensor) Intruder, so I know a little more than your average joe about IR, and have many years of actual on hands IR experience (since 1987).


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## McGizmo (Nov 17, 2006)

Thanks Newbie for the added info, insight and explainations. To isolate the effect of the MCPCB, would a better comparison be one where such a MCPCB were secured to a similar plate of copper as the discrete LED and then images made of both LED's driven at the same current (assuming the LED's are close in flux bin)?

When you say the image agrees with the thermocouples, were the thermacouples measuring the coated surface of the MCPCB or the core itself? I think you are saying that the difference is not that great anyway. I am still confused here (no doubt obvious). If the laminate surface of the MCPCB is essentially the same temp as the core then the resistance through this laminate must not be too great?!? :thinking:

If the MCPCB itself were thermally relieved in a better manner (I.E. bonded to a hunk of copper) then I believe the steady state temp would be lower than is seen in the example. With a lower steady state, would the delta be as great?

Coming from another angle, if a LED were to be thermally epoxied to an Al sink the same size as the MCPCB and then compared to the MCPCB with FLIR imaging of both driven at the same current, wouldn't this be a better means of viewing the effect of the MCPCB's composition and thermal relief? Better yet, put a thermacouple on the underside edge of both samples and the hotter unit is the more efficient?

*EDIT: I am not doubting your credentials or use of the FLIR. I do somewhat question the isolation of key factors in the two examples shown and most assuredly question what it seems some are taking away from this discussion as conclusions.  

Perhaps you are better at identifying the differences in a basket of mixed fruit than the casual reader?
*


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## NewBie (Nov 17, 2006)

McGizmo said:


> Thanks Newbie for the added info, insight and explainations. To isolate the effect of the MCPCB, would a better comparison be one where such a MCPCB were secured to a similar plate of copper as the discrete LED and then images made of both LED's driven at the same current (assuming the LED's are close in flux bin)?



Of course, maybe even with both LEDs wired in series, on the same plate, so they get exactly the same current, and are working against the same plate temperature.




McGizmo said:


> When you say the image agrees with the thermocouples, were the thermacouples measuring the coated surface of the MCPCB or the core itself? I think you are saying that the difference is not that great anyway. I am still confused here (no doubt obvious). If the laminate surface of the MCPCB is essentially the same temp as the core then the resistance through this laminate must not be too great?!? :thinking:



Think about the amount of heat being transferred thru the board. The thermal resistance of the board low enough to replace what is lost to thermal radiation. There is no actual thermal "load" on it. Kind of like a battery. Take a CR2032 battery and measure the voltage unloaded. Then put a 300mA load on the battery and you will see the voltage drop. Or even a CR123 cell, which is ~3.2V open circuit, then put a 1.5A load on it and watch the cell voltage drop to 2.7V or lower. The voltage is still present inside the cell in both cases, but the internal resistance of the cell, undler load, causes the voltage at the terminals to drop. 



McGizmo said:


> If the MCPCB itself were thermally relieved in a better manner (I.E. bonded to a hunk of copper) then I believe the steady state temp would be lower than is seen in the example. With a lower steady state, would the delta be as great?



Actually, the delta would increase.




McGizmo said:


> Coming from another angle, if a LED were to be thermally epoxied to an Al sink the same size as the MCPCB and then compared to the MCPCB with FLIR imaging of both driven at the same current, wouldn't this be a better means of viewing the effect of the MCPCB's composition and thermal relief? Better yet, put a thermacouple on the underside edge of both samples and the hotter unit is the more efficient?



No, there is no thermal loading, see my comment/example a few back. 




McGizmo said:


> Perhaps you are better at identifying the differences in a basket of mixed fruit than the casual reader?
> [/b]



When I have items in hand, it will be very easy to sort out the fruit, to make it easier to do a direct comparison between the bananas.


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## McGizmo (Nov 17, 2006)

Thanks Newbie. I am lost but need to be elsewhere. Carry on......... :wave:


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## yaesumofo (Nov 17, 2006)

Why not simply make some heat sinks for the emitter from copper. lapped smooth. tin them with solder. flow the solder with the emitter in place. Complicated issue. making a run of stars an an edm machine shouldn't be that difficult. 
I am not in any kind of league as you guys are when it comes to this stuff. But I know that when using a little arctic alumina between a LUX III and an O-Sink worked pretty well.
Attaching the emitter to a lapped smooth Copper star really should do the trick. The problem then becomes what to do with the heat from the star. So my mind tells me to solder the emitter directly to the sink which will be used to mount the emitter into the light. Is this not possible?
Yaesumofo


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## ViReN (Nov 17, 2006)

NewBie said:


> Even a thick, I think it was 39.3701 mils (1mm) FR-4 board in their example, glued to aluminum, with only 9 vias in it has a thermal resistance of 9.7C/W. If one reduces the thickness of the board to a standard pre-peg FR-4 thickness of 3 mils, *AND* keeps the same nine thermal vias, the thermal resistance drops to 0.746 C/W. There is a tremendous reduction of thermal resistance, just by adding vias to nothing more than standard FR-4. A person can easily decrease the thermal resistance further, by utilizing smaller vias, and more of them, to increase the copper area that goes thru the board. This doesn't count solder that partially fills the vias, which lowers if further. I'd seriously consider putting the vias under the LED die area and filling the whole thermal pad area with them.
> http://www.flomerics.de/Produkte/Osram/Golden_Dragon_LED.pdf




now some one needs to design 1/2 mm and 3mil thick boards with 9 heat conductive vias with Cree's Reflowed, these would help Modders and manufacturers to directly implement things on the Luxeon Based lights. we already have Heat sinks in many of the lights already.

CPF has the expertise in creating small PCB's with thruhole via's... only some one needs to come up and make them in star's and round shape...


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## McGizmo (Nov 17, 2006)

I'm still lost but dropped by for a quick look see. Not that it matters but Cree *is* aware of the MCPCB's its authorized distributors are providing their LED's mounted on. Now Cree is also stipulating drive currents of 350 mA and 700 mA in their specs. I have been using the ETG MCPCB's in the protos I have built and will be using them in the Ti lights (525 mA - thermal issues? ) 

I am not aware of a real problem here and I have to defer to experts where I am not. The contact I have at Cree as well as ETG don't consider the MCPCB a problem but then maybe they don't know any better. :shrug:




QUESTION:

If you make a mountain out of a mole hill, what happens to the poor mole! :thinking:


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## NewBie (Nov 17, 2006)

McGizmo said:


> I'm still lost but dropped by for a quick look see. Not that it matters but Cree *is* aware of the MCPCB's its authorized distributors are providing their LED's mounted on. Now Cree is also stipulating drive currents of 350 mA and 700 mA in their specs. I have been using the ETG MCPCB's in the protos I have built and will be using them in the Ti lights (525 mA - thermal issues? )
> 
> I am not aware of a real problem here and I have to defer to experts where I am not. The contact I have at Cree as well as ETG don't consider the MCPCB a problem but then maybe they don't know any better. :shrug:
> 
> ...




From way back in the thread, Post #12:



NewBie said:


> In reality, if you don't care much for getting great performance, and don't mind loosing some of your lumens due to die temperature rise, as well as color shift due to higher temps, I guess they work adequately.



In your A19 flashlight, the hottest spot I've been able to find, as close as I could get the thermocouple to the backside of the XR-E, was 84 degrees C after 30 minutes, at the package edge basically, by the board. BUT, I can't get to the backside under the die, but for this exercise, we will use the 84C. You have roughly 3W going to the Emitter. We know the spec for the LED is 8 C/W. Ambient temperatures were 25C. 3W * 8 C/W = 24C. So, the die temperature would be roughly, 84 C + 24 C = 108 C.

From the XR-E datasheet, the maximum die temperature is 145C, so you are good to go, as far as exceeding the specs, and if it was 50C outside, the die temperature would only rise to 133C, so you'd be okay too. You'd loose 30% of your lumen output vs. a die temperature of 25C, but you'd be just fine.

More robust, or lower thermal resistance in your path could buy one 10% more lumens- thats all I was trying to point out earlier.

More agressiveness in the overall system thermal path to the flashlight body could buy one further gains in the lumen area, as well as using more efficient converters to reduce overall system temperatures- to get even further lumen gains.

Of course, there is the other monkey to chase down, the reflector coating itself, which is typically in the ~20% loss range, but may be a little less for loss contribution with the CREE XR-E, as typically, more of the CREE XR-E lumens (percentage) don't hit the reflector, as compared to a Luxeon in the same reflector.

Now, if the ETGTech MCPCB, had some of the CREE XR-E LEDs that were not soldered on them properly, the situation could be much worse...kinda like what Chimo showed in his pictures of the ETGTech MCPCB.


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## 45/70 (Nov 17, 2006)

NewBie said:


> From way back in the thread, Post #12:


I remember that post, and was thinking at the time, "Gee, that pretty much describes 99.999% of flashaholics, we don't care if it works right, we just want a neato flashlight!".

I'm kidding, of course. McGizmo has relieved some of my fears about these. The poor reflow example still bothers me though. We'll see. 

Dave


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## Kinnza (Nov 17, 2006)

Is there anyway to do vias? Drilling holes?


Newbie said:


> Even a thick, I think it was 39.3701 mils (1mm) FR-4 board in their example, glued to aluminum, with only 9 vias in it has a thermal resistance of 9.7C/W. If one reduces the thickness of the board to a standard pre-peg FR-4 thickness of 3 mils, *AND* keeps the same nine thermal vias, the thermal resistance drops to 0.746 C/W.


 
For example, im thinking on use cheap thinest FR4 and drill vias in the area where slug seat. It would be possible? A thermal resistance below 1C/W is good enough for me.

If its possible, please explain how to do the vias.


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## McGizmo (Nov 17, 2006)

Newbie,
Thanks for pulling this back into the perspective of the overall picture. Realistically, I think all of the lights we currently have as well as lights we will make or acquire in the future will have losses in efficiency all along the train of energy conversion from stored electrical potential to photons delivered on target. These losses will add up to a percentage we wish weren't the case and this difference will continue to be a tool of marketing where some will cite the potential and others the reality.

As an exercise in theory, application of theory and in the pursuit of design goals and execution of the design in actual construction, an awareness and understanding of the nature of these losses and feasible attempts to minimize these losses should be pursued. This is my opinion but I expect it is shared by most.

There is a gap between ideal and realistic. This gap can be narrowed if not bridged by identifying its nature and understanding its dynamics and the parameters within one's control. Threads such as these are very illumination and instructive towards such a goal.

I dare say even a poorly designed flashlight is more efficient in energy conversion than we are efficient in using our brains, to their full potential. :green: Whether by intent or not, there is always room for improvement. You just have to find that room and be willing to pay for it.

----------

Regarding the example of the ETG MCPCB that doesn't look like a proper solder mount, I have some background info to share. 

ETG has loose emitters in inventory as well as blank MCPCB's. In the case of a small or sample order of mounted LED's and when these are not in stock, ETG will mount the emitters locally with the use of a hot plate and per instructions laid out by Cree. This sample was likely one such case and I suggest it was one in which the process was not very successful. 

When there is a reasonable size order for mounted LED's, they are done by the the MCPCB factory and done with reflow equipment which dispenses the proper amount of solder paste and does perform a succesful solder reflow.

I took the liberty of sharing the above example with ETG and I would like to think that it will be taken into consideration in the future when they provide a locally mounted assembly. :shrug:


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## IsaacHayes (Nov 17, 2006)

I still want to see a test with a lightbox/ceiling bounce with the same led. First on the MCPCB, and then unsolder and re-flow to the copper. See how much of a difference that heat makes in the real world.

As we get higher flux leds, 10% or whatever can become a decent amount of lumens to gain. Especially if used in a flashlight with multiple leds, the gains you get can add up quite fast. Back in the day of 30lumens from the led, 10% would only mean a measly 3 lumens lost.


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## 45/70 (Nov 17, 2006)

IsaacHayes said:


> As we get higher flux leds, 10% or whatever can become a decent amount of lumens to gain. Especially if used in a flashlight with multiple leds, the gains you get can add up quite fast. Back in the day of 30lumens from the led, 10% would only mean a measly 3 lumens lost.


I don't know, Mr. Hayes. 10% is 10%. The actual quantity, really makes no difference. If it's a 10% increase though, I'll take it! 

I have a question, on the poor reflow issue. Would it not be proper to see solder along the edge of the emitter package, in the thermal pad area, where its mounted to the MCPCB? In the few high resolution photographs I've seen of MCPCB mounted XR-E's, there doesn't seem to be any visable solder on the edge of the thermal pad. Flux is present but, no solder. Does this, perhaps, indicate a cold reflow?

Dave


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## NewBie (Nov 18, 2006)

Okay, we mentioned thermal vias.

So, what is the effect of a thermal via?

Lets say we take a very low cost standard FR-4 prepeg material, to keep the prices down.

Lets use 100 13 mil vias, with 2 oz. copper plating.

Punching in 13 mil diameter vias, putting in 2 oz (and remembering to change the copper from mils to oz.) and 3 mil thick board, you get:

2.16 C/W for one single via.

Online calculator for this is found here:
http://circuitcalculator.com/wordpress/2006/03/12/pcb-via-calculator/

Since we are using vias in parallel (using more than one in the board), you then just take the C/W for one via by number of vias, to get to C/W:

2.16 / 100 = 0.022 C/W

So, it gets pretty easy and low cost, using commonly available practices, to get the C/W down to incredibly low numbers.

If you use fewer vias, placing the vias directly under the die area will typically benefit you the most. 

Keep in mind, I did not include the additional C/W reduction of any solder that is inside the via barrel, nor the further reduction due to the FR-4.


The additional nice thing about the CREE XR-E, is that it's thermal pad is electrically isolated (thank you!), so there are no worries there.


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## Doug S (Nov 18, 2006)

NewBie said:


> Okay, we mentioned thermal vias.



Speaking of vias, in the XR-E package itself, is the thermal conduction from the die pedistal to the backside of the package entirely through the ceramic material or does the ceramic material contain hidden thermal vias?


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## McGizmo (Nov 18, 2006)

Hi Doug! :wave:  If you want some of these LED's to play with, send me an e-mail.


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## NewBie (Nov 19, 2006)

Doug S said:


> Speaking of vias, in the XR-E package itself, is the thermal conduction from the die pedistal to the backside of the package entirely through the ceramic material or does the ceramic material contain hidden thermal vias?



Entirely thru the Alumina Ceramic. Note I didn't say Aluminum Nitride ceramic, Boron Nitride ceramic, nor Beryllium ceramic. Yes, thermal spreading resistance comes into play..

Also of note, the ESD diode is SiC.

No hidden thermal vias in the XR-E, just the ones on the corner, for the electrical contacts.

The magnification effect of the lens used on the CREE makes it look much bigger than it really is.

BTW, it is great to see you again DougS.


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## IsaacHayes (Nov 19, 2006)

Hey Doug S! Now there's an old familiar face! 
Newbie: Interesting! So what is with the holes in the silver/metal thing on the thermal pad of the led? It looks like vias. Is it just to help hold the metal on there?


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## AilSnail (Nov 19, 2006)

I was just doing a search to see when you last stopped by, Doug_S. 

How important are the connectors for the thermal conduction?


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## NewBie (Nov 20, 2006)

IsaacHayes said:


> Hey Doug S! Now there's an old familiar face!
> Newbie: Interesting! So what is with the holes in the silver/metal thing on the thermal pad of the led? It looks like vias. Is it just to help hold the metal on there?



Those make electical connections on the ends of the LED, from the bottom pad up to the top. There is one in each corner.


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## IsaacHayes (Nov 20, 2006)

You misunderstood me. The bottom of the cree I had looked like it had holes underneath the thermal pad... (center pad)

EDIT: hmm looked like evenly spaced dots. I didn't look that hard, and now it's epoxied to a heatsink... oh well I'll look at the other ones when I get em in the mail.


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## NewBie (Nov 20, 2006)

IsaacHayes said:


> You misunderstood me. The bottom of the cree I had looked like it had holes underneath the thermal pad... (center pad)


 
It doesn't. Those don't go thru to the other side, and they are actually squares.

With the right lighting and magnification, one can see the ceramic surface thru the holes.

Sorry about poor picture quality.


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## IsaacHayes (Nov 20, 2006)

Interesting. I guess it helps secure it to the ceramic? :shrug:


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## ViReN (Nov 20, 2006)

now one question, is it possible to file off all the base material (including the copper) and make the ceramic thinner and then place it over a silver (heat sink) coin/slug for better (than copper) heat sinking?


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## ViReN (Nov 20, 2006)

and what's that green thingy between the ceramic and the contacts/heatsink area ...


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## NewBie (Nov 20, 2006)

ViReN said:


> and what's that green thingy between the ceramic and the contacts/heatsink area ...



Soldermask.




ViReN said:


> now one question, is it possible to file off all the base material (including the copper) and make the ceramic thinner and then place it over a silver (heat sink) coin/slug for better (than copper) heat sinking?



You are off into unchartered territory here. Anything is possible, beyond that, who knows.


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## Anglepoise (Nov 20, 2006)

ViReN said:


> now one question, is it possible to file off all the base material (including the copper) and make the ceramic thinner and then place it over a silver (heat sink) coin/slug for better (than copper) heat sinking?



I have treated mine just like a LUXIII.
I sanded the bottom absolutely flat (exposed smooth copper ) and then did the same thing to the bulkhead. Then a thin layer of AA and glue together under spring pressure till set. 

Then I grind the edges to disconnect the bottom electrical connections and solder to the top pads.

Now I have no way of measuring and comparing analytically, but my feeling is that heat transfers perfectly and that this will not cause any future problems.

I feel certain that this method will move heat to the bulkhead heat sink better and more efficiently than having a poor quality MCPCB in there as well.


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## 45/70 (Nov 20, 2006)

In the original post,


cmacclel said:


> Not a very efficient solution in my opinion.


refers to the MCPCB's as possibly being problematic. There have been suggestions of several solutions for their redesign, and later, some ways to redesign the emitter package as well. Reinventing the wheel and the cart it goes on, so to speak. Fascinating reading, for sure!





However, my question is, what can be done to the existing emitter/MCPCB setup? I don't have my stars yet, but feel one of the most important problems that might be faced is a poor reflow job, as I suspect they are done "in house". A few posts back, I mentioned a possible way to tell. In the first post, fifth picture of this thread, ArsMachina posted a very good picture that shows what I was referring to. What I see is solder around the + and - pads and only flux around the thermal pad. Would this not indicate that the reflow was incomplete on the thermal pad?

Dave


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## Amonra (Nov 20, 2006)

has anyone tried these: http://theledguy.chainreactionweb.com/product_info.php?products_id=649 instead of the ETG star ?
Would they be any good ?


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## McGizmo (Nov 20, 2006)

Anybody who has handled these LED's or soldered to them realizes that the ceramic package of the XR-E doe a magnificent job of distributing theheat well and throughout. I believe the FLIR images also show this. SO, the perfect thing to bond a XR-E to would obviously be another XR-E! :nana:











If there were room on the Z axis, this is a perfect application for Newbie's heat pipes!  I used a diamond bur to remove the trace on the top corners of the LED facing you to open the "loop" for inputs. The thermal transfer to the brass pedestal seems to be quite good! ( A little more info)

(Doug S, not quite what you had in mind but I believe illustrative of the possibility?!)


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## NewBie (Nov 21, 2006)

I've been working with these CREE parts for over two years now and find the ceramic package most definitely does not do that great of a job for heat spreading. 

In the photo below, you can very clearly see a 7 degree Celcius delta, just across the ceramic, next to the metal center, then out to the end of the ceramic pad. It is even hotter inside, under the dome- especially in the center at the die, where you cannot see (glass does not transmit IR in the 7-14um wavelength range).







Sorry, I am most definitely not going to buy into that idea, and if I did, I'd have to be quite blind and ignorant to say the least...







Then you take the same LED, and mount it to a copper slab, such that you can pull the heat out of the center, and look how the pad temperature looks much uniform:






It is the copper that is helping tremendously.


The ceramic does a decent job of transferring heat, but not excellent.

I have an old image of a CREE with the dome and ring remove, just the die on the substrate, and the poor thermal spreading becomes quite clear. I'll need to do this to an XR-E, and put pictures up. This is why it is so important to pull the heat out from the center of the die well- but the area of the whole CREE does help in theory.


Isaac-

I took some more shots of the squares in the thermal pad of the CREE, see the ceramic under them?







The square hole in the thermal pad copper:






The electrical via on the electrical connection pad:


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## McGizmo (Nov 21, 2006)

Newbie,
In the two FILR shots where you can see the LED and its surrounds, I assumed I was seeing a rectangle that represented the whole package. It also seems that the temperature is consistent across this rectangle. In the close up you just provided, there seems to be a greater contrast in color change and the color representing 78C which before seemed outside the package and on the MCPCB is now seen to be on the package? Is this a close up of the same image or a different image?


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## NewBie (Nov 21, 2006)

Maybe this would help to see what I've been trying to show. Something that is obvious to me, isn't always evident to others. I've tried to "ghost" the image of the visible picture over the IR picture of the same item. Scaling isn't perfect:


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## IsaacHayes (Nov 21, 2006)

Jar, great pics! yeah the squares aren't really holes in the ceramic but "holes" in the thin metal. Who know why they are there?? Cool pic of the via for the electrical connection!

Don: yes it's hard to solder to these things vs a luxeon, as luxeon is just a thin lead. This thing you gotta almost heat the whole package up as the solderpad is part of the led. I feel your pain!! I resoldered mine today and thought I was doomed! I almost torched the heatsink so it would help hold the heat.


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## Doug S (Nov 21, 2006)

NewBie said:


> Maybe this would help to see what I've been trying to show. Something that is obvious to me, isn't always evident to others.


Jar, the pictures are great! I am, however, in the camp that is having a bit of trouble interpreting them. I have a couple of questions whose answers might be buried in this thread but I failed to see them. 
1. What is the drive level for the MCPCB thermal images? 
2. For those MCPCB thermal images is the MBPCB in turn mounted on a heatsink or is it just in free space? It would seem that the former configuration would be the one most revealing of the MCPCB performance relative to having the package mounted directly on a massive heatsink.
3. In the thermal images is the cursor location showing the peak temperature located over a portion of the package where the coating which equalized thermal emissivity *has not* been applied? 
4. You seem to have an almost endless supply of great Cree emitter pics! One I'd love to see if you already have it is a XR or XR-E sectioned in a vertical plane.

Thanks for sharing your great work!


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## glire (Nov 21, 2006)

Just wondering, what is the wattage that the XR-E can dissipate without any heatsink under an environment of 40°C ?
I guess about 300mW.


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## chimo (Nov 21, 2006)

Doug, while waiting for Newbie's response, perhaps I can hazard a guess at some of the questions:

1, 2: See post #64 above. I believe the MCPCB is the light engine mounted with a 825mA drive current.

4. Same here.

Cheers,


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## MillerMods (Nov 21, 2006)

Newbie, is it possible to guesstimate what the thermal conductivity of the ceramic is? 

Also, what would the average delta (die to center on the back of the ceramic) be @ 350mA?

Thanks for your time.


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## Anglepoise (Nov 21, 2006)

Newbie,
In your opinion, would it be fair to presume that a round post directly under the die, soldered or glued ( AA) to the XR-E would offer the same or better heat movement that a rectangle post that covered the whole base ( not including the electrical connections pad)

My thinking here is that it is easier to machine a round post than mill a rectangle post. 

I am trying to use the data ^^^^ to formulate a strategy that will move heat, allow electrical connections, and not interfer with reflectors.


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## ViReN (Nov 21, 2006)

NewBie..... since it's a LED's Thermal Image, shouldn't the die itself be hotter than the surrounding? looks like the die portion is cooler than the Max Temperature Point.... wondering why....


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## mudman cj (Nov 21, 2006)

MillerMods - The ceramic is almost certainly Al2O3, which has a thermal conductivity of about 25-30W/m*K. Compare that with copper which has a conductivity of 385W/m*K and you can see why NewBie is not impressed.

Thanks for the great data, pics, and explanations NewBie. I too have worked with FLIR cameras and I understand what you are accomplishing. You may find it interesting to know that I work where the cryocoolers are made that go into those cameras.


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## McGizmo (Nov 21, 2006)

If I understand correctly (dubious since I am likely one of the blind and ignorant), the heat from the die is passing through the ceramic to get to the metal sink pad and this resistance is inherent in the package design. In the pursuit of optimal, why don't we filed down the whole package until we approach the die itself? 

Since one can easily break the LED lead connections from the botom solder pads, I don't see an advantage in putting the LED on a pedestal when you can mount it with full bottom surface contact; either with reflow to your large hunk of copper or via thermal epoxy to Al? If less surface contact is better then take it to the limit of no surface contact?!? Or is it the case that we just need to match the surface foot print of the die under the LED and any surface contact beyond this is less important? It goes against my intuition to think that reducing contact with a material that _*is*_ thermally conductive makes sense in terms of thermal relief, even if the thermal conduction of the material is not fantastic. 

I was under the impression that the XR-E has reached an improvement in terms of thermal conduction over previous 7090 packages. Anyone soldering to copper trace on these LED's has experienced the effect of the ceramic wicking away the heat applied!

In real world applications of flashlights and at drive levels at or below spec, how does the various means of installing the LED in the light effect the projected flux output? If one method has an advantage of say 5C/ watt over another, what is the result in flux difference?

Well this blind and ignorant person will leave this thread because of said conditions and further, I really don't have any "Cree XR-E thermal concerns".


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## IsaacHayes (Nov 21, 2006)

In discussion with Newbie, he told me that there are better ceramic types (I think he listed some in this thread) that conduct heat better than what they are using. And that they likely will change over to them to make the led better once there is demand and more competition out there. They are still holding some cards, and close to their chest for when the time is right as he said. 

I can't wait for when they decide to go ahead and release a package with all the best stuff and bells and whistles without holding back. But then I'll have to re-mod all my lights!


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## Anglepoise (Nov 21, 2006)

McGizmo said:


> Since one can easily break the LED lead connections from the botom solder pads, I don't see an advantage in putting the LED on a pedestal when you can mount it with full bottom surface contact;



My experimenting with the pedestal is purely to see if I can solder reliably to the bottom connections, so that the reflector and a very thin insulating washer does not have wire, solder, spatter etc to get in the way. Re flowing without the special equipment and my lack of knowledge bothers me a bit.


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## NewBie (Nov 22, 2006)

As far as soldering to the package, I see zero difference in how well they wick the heat away, as compared to the old XL7090 part.

Don,
The old XR7090 part also has a thermal resistance of 8 C/W as shown here:
http://www.cree.com/products/pdf/XLamp7090XR.pdf

The die itself is larger than the old die from the older XL7090. It is 1mm by 1mm, instead of 0.9mm by 0.9mm. This means the area of the die is increased by 1.24 times larger than the old die, which would be likely to reduce the thermal resistance. Possibly they increased the area of the SiC ESD diode that they mount the die upon, which would also help thermals.

When you solder things down, and if you only had a 5C/W difference, the temperature on the die would be 15C difference. This would work out to a 5% loss in light output. However, this die is not mounted on solid copper, and has a thermal spreading resistance. So, one could reduce the thermal spreading resistance in the system, by getting the area under the die closer coupled to the heatsink and utilizing something with a very high thermal conductivity to reduce the thermal spreading resistance.


As I presently understand it, the ceramic that is used is an Alumina based ceramic. 


Here is a comparision chart of the thermal conductivities (higher is better) for a few metals, and the various ceramic fillers, that primarily comprise the ceramics or compressed ceramic fired forms:


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## NewBie (Nov 22, 2006)

Doug S said:


> Jar, the pictures are great! I am, however, in the camp that is having a bit of trouble interpreting them. I have a couple of questions whose answers might be buried in this thread but I failed to see them.
> 1. What is the drive level for the MCPCB thermal images?



If you look back in the thread, you will see the A19 XR-E flashlight converter measured 800mA to the LED on the ETGTech MCPCB that is mounted in the A19 XR-E flashlight.

The direct copper plate soldered one is also at 800mA.




Doug S said:


> 2. For those MCPCB thermal images is the MBPCB in turn mounted on a heatsink or is it just in free space? It would seem that the former configuration would be the one most revealing of the MCPCB performance relative to having the package mounted directly on a massive heatsink.



The A19 flashlight has an overlapping rim where the edge of the MCPCB is attached with thermal epoxy, and behind the board, they also filled the ecan with thermal epoxy. They staked MCPCB into the ecan by squishing the MCPCB Aluminum material edges up against the ecan wall at sixteen points.

I have further tests underway now to learn more. On the same exact copper plate, three LEDs are wired in series, so they will each get the same exact current.
-One, direct solder to copper plate.
-One, AA thermal epoxy'd to copper plate, cured under heavy weight.
-One, ETGTech MCPCB AA thermal epoxy'd to copper plate, cured under heavy weight.




Doug S said:


> 3. In the thermal images is the cursor location showing the peak temperature located over a portion of the package where the coating which equalized thermal emissivity *has not* been applied?



The cursor is on the peak (85 degrees C). The peak is on a surface where +98% thermal emissivity material has been applied. Correction factors for the coated areas have been already applied. This peak temperature is on the ring, as well immediately around the copper metal lens holder at the base of the LED. As I did not want to get the emissivty material on the lens, only parts of the copper ring were coated on accident. The line across the photo is a connection I made, and a wire is blocking the IR "light".

See the ghosted image of the visible part overlayed upon the IR Image. Notice how abruptly the temperatures transistion near the ring, and then drop on out to the edge of the electrical pad area (this is a IR image of the part mounted on the ETGTech MCPCB):









Doug S said:


> 4. You seem to have an almost endless supply of great Cree emitter pics! One I'd love to see if you already have it is a XR or XR-E sectioned in a vertical plane.
> 
> Thanks for sharing your great work!



I'll see if I can find the cross-sectioned device photos I have done. It was a pain, and I ended up having to use diamond to cross-section the hard ceramic.


Isaac,

As I have mentioned before, glass does not pass 7-14um wavelengths, and thus you will not see the die temperature, or an image of it. This is just one of the reasons, that attempting to use a low cost IR thermometer is nearly worthless for measuring die temperatures, and is a lesson in futility. However, you can measure the surface temperature of the dome, if you know the emissivity of the surface.


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## Moat (Nov 22, 2006)

This is all some wonderful and interesting information, Newbie... even if I never get the opportunity to touch soldering iron to a Cree LED. Thankyou - this "nobody" lurker appreciates your efforts here, and in so many other threads over the years!!



NewBie said:


> I have further tests underway now to learn more. On the same exact copper plate, three LEDs are wired in series, so they will each get the same exact current.
> -One, direct solder to copper plate.
> -One, AA thermal epoxy'd to copper plate, cured under heavy weight.
> -One, ETGTech MCPCB AA thermal epoxy'd to copper plate, cured under heavy weight.



The results of this test will likely provide some very useful answers/insight for many folks here. Bravo... and looking forward to it!


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## Anglepoise (Nov 22, 2006)

Newbie,
Look forward to see the 3 way test results.
Your hard work on this is appreciated

Below is a section of an XR-E.
What looks like a copper connection between top and bottom in the photo
is just the copper 'smearing'.Second photo is a little clearer.
There is no visible to me connection between the die and the bottom rectangular copper pad.


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## AilSnail (Nov 22, 2006)

Quote:Originally Posted by McGizmo
If the MCPCB itself were thermally relieved in a better manner (I.E. bonded to a hunk of copper) then I believe the steady state temp would be lower than is seen in the example. With a lower steady state, would the delta be as great?



> Actually, the delta would increase.



How come? If the led is colder, it is more efficient, producing less heat..



> This peak temperature is on the ring, as well immediately around the copper metal lens holder at the base of the LED.



so, would it be effective to use the reflector to draw out heat from this metal ring, or is the thermal resistance from the die too low that it would matter?

That ceramic plate looks awfully thick, I wonder why? Must be a lot of C/W just through this millimeter(?) of useless(?) spacer?


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## LightBright (Nov 22, 2006)

I believe Cree is trying to electrically isolate the LED substrate with that ceramic layer, where on the Luxeons, the copper slug is NOT electrically isolated.

The ceramic may be a manufacturing/engineering cost saving measure or a way of getting their LEDs to market in the shortest amount of time.


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## ViReN (Nov 22, 2006)

Anglepoise said:


> Newbie,
> Look forward to see the 3 way test results.
> Your hard work on this is appreciated
> 
> ...



Now we have one more way of heat sinking (atleast to some extent). i.e. through Al Reflector.

One more worry, it is learnt that Creamic is not _'that good'_ (compared to copper) conductor of heat, which kind of Ceramic is being used by Cree? any ideas?

it would have been great if they could have extended copper slug directly to the base, I am sure the thermal resistance will drop much further.

I will be seriously looking at getting multiple Cree's if they come up with a well designed product....

From My Point of View, it's True, it's bright, but's it's still a _'shabby' _design (especially after looking at the C/S).. Yes I have already signed up for a GB for Q3, let's see how they perform when I get my hands over em


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## ViReN (Nov 23, 2006)

NewBie said:


> <SnIp>
> 
> As I presently understand it, the ceramic that is used is an Alumina based ceramic.
> 
> ...



how about Epoxy + Boron Nitride... i think...many IC packagers use this for a better heat transfer (not sure how it compares to Ceramic)

it would be great if you could compare Cremic+Alumina with Epoxy+Boron Nitride


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## NewBie (Nov 23, 2006)

Here is the setup with no emissivity coating, the temperatures are **HIGHLY INACCURATE**







Here is the same setup, with a high thermal emissivity coating on all parts, so we can see the actual temperatures accurately (NOTE, TEMPERATURE SCALE ON SIDE HAS CHANGED!):







The parts that were mounted with Arctic Alumina were bonded under weight for over 12 hours.

The copper sheet metal that the parts were mounted to was placed upon another plate to help get rid of the ~9W produced.

As you can see, the Arctic Alumina Thermal Epoxy to the copper plate nearly works as well as soldering directly to the plate. The ETGTech MCPCB doesn't work nearly as well as the other two options.

The AA Thermal epoxy XR-E has a dome temperture of 42 degrees C.
The direct solder XR-E has a dome temperature of 39 degrees C.
The ETGTech MCPCB has a dome temperature of 54 degrees C.

Notice the wire going from the MCPCB to the direct copper soldered one, and how the wire is conducting heat from the MCPCB mounted XR-E, and how it fades along the wire length.


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## KWillets (Nov 23, 2006)

Can't you deduce the die temperature from the output spectrum? You can even calibrate if you heat the whole assembly to known temperatures and run at, eg, a 1% duty cycle.


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## McGizmo (Nov 23, 2006)

Newbie,
Thanks for your work and effort here. In this test set, what would you estimate the relative light output differences to be between the LED's? I can't find a graph on the XR-E in any of the data sheets I have showing the reduction in relative light output based on junction temperature. In a possibly related graph I have access to, there seems to be a 3% reduction in output per 10 degrees of C. Does that sound about right?


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## NewBie (Nov 23, 2006)

McGizmo said:


> Newbie,
> Thanks for your work and effort here. In this test set, what would you estimate the relative light output differences to be between the LED's? I can't find a graph on the XR-E in any of the data sheets I have showing the reduction in relative light output based on junction temperature. In a possibly related graph I have access to, there seems to be a 3% reduction in output per 10 degrees of C. Does that sound about right?



Using my calipers on the graph off their website datasheet, I see ~4% per 10 degrees.

Keep in mind, the case temp is only relative to the die temperature. And we cannot see the case temperature directly underneath the die.

The best thing to take away from this is to note the differing case temperature from LED to LED, and note the changes in case temperature at different points on the LED.

On the photo with the thermal emissive coating (the only accurate one), the dome hot spot is 54C. The average temp of the ceramic base is roughly 44C.
The delta here is 10C. (don't get mislead on the LED case, due to the solder pads on the MCPCB).

On the direct solder one, the dome hotspot is about 39C. The ceramic base temp is about 34C. The delta here is 5C.


Odd...the power input is nearly the same, within 2%, accounting for differing Vf and equal currents.


If you think about it a bit more, if there was no spreading thermal resistance, the deltas should have been about the same, with the same power input. But they are not. This would lead me to consider the idea that the die is even more proportionally hotter on the MCPCB mounted one, than what the LED case temperatures are showing.


The copper sheet metal temperature is about 31.5C.


When I get a chance at some point in the future, and I have plenty of extra XR-Es, I have some 42 guage K-type thermocouples, and it might be interesting to place them directly on the dies.

With everything already mounted on the copper sheet metal (oops), soldering on the MCPCB one was immensely easier to solder on, as compared to the other two.


KWillets,
Your technique works great for amber, decent for red, okay for green, but blue die used in the white LEDs do not shift their wavelength that much with temperature. An example, for one of the Luxeon power type LEDs dies at ~15.5C the peak wavelength of the blue was 463nm, but at 82.2C it was 469nm. One would need a method of measuring rather fine shifts, as it works out to only 0.135nm per degree C. This is an entirely different matter as compared to Amber LEDs which shift all over the place (or even red LEDs in comparision). If you had a full optics lab at your disposal, one could probably accomplish this, or build up a diffraction grating/prism, some known precise spectal sources, and take advantage of distance across a room (or optics), in order to calibrate and then measure the shift. Now, if you characterized a particular lot of LEDs, you could do what Nandaren(sp) did, as the phosphor helps amplify this, when looking at the whole spectrum. One could use the CIE co-ordinates or Kelvin temperature(less accurate). You'd do a very narrow duty cycle, to minimize heating, measure that LED every 5C change in ambient temperature (after allowing the temperatures to stabilize), and build up a chart with the LED and a thermal chamber. Not all LEDs track the same though, so there would be some errors if you didn't use the same LED. One could also use the old HP method, where you look at the Vf change (they stated something like 2.8mV change per degree C, if memory serves correctly, for blue). 

Each of these methods is a project by itself to do properly.

It isn't too hard to actually do, it just takes time and care. I'd love to read the write-up, look at the photos, and see the results- if you'd like to take that project on.

As it stands, we were just looking to see if the MCPCB works as well as direct soldering, and how well Arctic Alumina epoxy the emitter to a copper plate works, when compared to direct soldering.


Results are pretty simple, MCPCB is the worst, and direct soldering is the best, with AA epoxy being close to soldering. No surprises here.


Do not forget, that these measurements do not include heat generated by converters, heat generated by batteries, and the various thermal resistances typically found in an actual flashlight.


Anyhow, it is the next day here, and it is time to hit the sack now.


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## chimo (Nov 23, 2006)

Great work Newbie! I was waiting for this one. It's nice to see the comparison between the three. 

You've already answered a question I had re power to each LED. They seem to be fairly closely matched (2%). The heat flow on the interconnect wire is quite telling as well.

On the MCPCB, is there any thermal compound between it and the copper sheet?

BTW, thanks for doing this.

Paul


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## Kinnza (Nov 23, 2006)

:goodjob: Newbie!

Yes, result are how previosly expected, but it measures accurately the differences, so each one can decide the best way to mount the XR-Es, as the thermal behavior is opposite to mounting confort, and each person can decide depending on the application.

Im glad the AA not penalize thermal transfer too much in relation to direct solder, when the AA layer is thin.

In the first pic, without high emissivity coating, there is two cold areas at the sides of direct soldered. I suppose its where is the kapton. With the coating, it dissapear, so it means the kapton has little influence in overall temp, but have little emisivity, very near the LED, so i think it would be better retire the excess kapton after soldering, especially when the thermal path between the copper plate and heatsink isnt perfect.

For me, your comparision is enough. If anybody wants to do the same but with accurate die temperature measurement, i believe the best way is Vf checking. But its a tough work for little increase in knowledge, as having accurate measurement of lead's temperature allows to compute with little error margin the die temp (knowing the power used (If+Vf) and junction-board thermal resistances, both well known).

For estimating board temperature more accurately, a pic of the copper plate in the other side would be very helpfull.


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## Kinnza (Nov 23, 2006)

Newbie said:


> If you think about it a bit more, if there was no spreading thermal resistance, the deltas should have been about the same, with the same power input. But they are not. This would lead me to consider the idea that the die is even more proportionally hotter on the MCPCB mounted one, than what the LED case temperatures are showing.


 I didnt read well this paragraph. Nice observation. People not used to FLIR analysis, as me, dont notice this.

So some of my previous statements can be wrong. Maybe the tough work of further research on accurate die temp measurement worth the effort


----------



## NewBie (Nov 23, 2006)

Kinnza said:


> :goodjob: Newbie!



Thank you




 Kinnza said:


> Im glad the AA not penalize thermal transfer too much in relation to direct solder, when the AA layer is thin.



Keeping it thin as possible is key. I put a good amount of weight on it, to make it squish out, to make it thin as possible. I used a piece of pipe with a flat lapped end, over the XR-E, to avoid weight on the dome. Then I put the mass of weight on top of that.




Kinnza said:


> In the first pic, without high emissivity coating, there is two cold areas at the sides of direct soldered. I suppose its where is the kapton. With the coating, it dissapear, so it means the kapton has little influence in overall temp, but have little emisivity, very near the LED, so i think it would be better retire the excess kapton after soldering, especially when the thermal path between the copper plate and heatsink isnt perfect.


 
Actually, it is the Kapton that has much higher emissivity than solder, copper, or aluminum. There is a pre-tinned area on the copper sheet metal, a band that runs left to right. So, if you are trying to radiate the heat, the Kapton works much better. Most bare metals are extremely **** poor thermal radiators at this range of temperatures. In the picture, the Kapton is in the shape of the letter I. I've taken another picture, under different operating conditions, and labeled it (which I had to redo for the later photos, since I found a reflection of me off the surfaces which affects the image). Bare metals also make wonderful mirrors in the true IR regions. See more items labeled below.




Kinnza said:


> For me, your comparision is enough. If anybody wants to do the same but with accurate die temperature measurement, i believe the best way is Vf checking. But its a tough work for little increase in knowledge, as having accurate measurement of lead's temperature allows to compute with little error margin the die temp (knowing the power used (If+Vf) and junction-board thermal resistances, both well known).



I'd definitely have to agree, especially for the flashlight hobbyist folks. The relative comparisons are very useful for checking out different mounting techniques and the relative worthiness of each approach.




Kinnza said:


> For estimating board temperature more accurately, a pic of the copper plate in the other side would be very helpfull.



Already tried that, it doesn't work well, as the copper, being a great thermal spreader, you see maybe a 1 degree C delta total, once you have a high emissivity coating. Remember, I am using thicker copper sheet metal, at 0.165" (4.191mm). Otherwise you only see a nice mirror. By the time you get to the backside, on thin sheetstock aluminum, it works decent. What you end up seeing, on previous testing, is the one that has the highest thermal resistance shows cooler spot when looking at the backside.








I can't go too much deeper on things/ideas in this area, as I start getting into proprietary information that I use in my designs at work. Lets just say that I've spent years looking at things, comparing stuff, testing, and I have to be kinda vague on a lot of stuff, or I'm just handing out information to competitors for free.

(And no, I do not work in the flashlight, general lighting, or other related industries. Nor do I have investments or connections in this area)


I've just been spending time here as a "hobbyist", sharing information. knowledge, and ideas with folks to advance the "State of the Art" in flashlights. It is a great way to unwind and relax from much more technical work.

.


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## McGizmo (Nov 23, 2006)

After thinking about this some, I was curious about the Vf of the LED's and the actual power each was handling. Thanks for adding that info. It is clear that the unknown insulating bondary on the MCPCB adds thermal resistance to the relief of the LED. Had the other two LED's been mounted to an Al disk of similar size, the resistance attributed to the construction of the MCPCB might be better isolated and viewed, I would think.

In one flashlight design for instance, I might have the options or choices of say an integral Al bulkhead (anodized) or the inclusion of this MCPCB seated on a shelf. On the integral bulkhead, I might mount the LED directly via a thermal epoxy or I might use a thin emitter PCB designed for good thermal transfer (double sided copper with filled vias). The thin PCB would likely be bonded with a thermal epoxy. In these examples, I would guess a good test for thermal comparison would be to make a cross section of the light head at the LED location that would like a short cylindar section. One would have the MCPCB shoulder and two would have the integral bulkhead. The three short stacks could then be mounted to a larger common sink, copper or Al. Driving the three LED's in series and confirming near match in Vf of the LED's would then show me the relative thermal differences of these means of LED hosting in isolation of other influences.

I checked the graph on the Cree site and the slope of the curve looks prety constant (flat) to me. From 25C to what looks like 145C you have a drop in relative photomeric output of 30% (100% - 70%). This is a 30% drop across 120C or .25%/C. I take this as a 2.5% drop per 10C.

If the MCPCB results in a die temp that is 20C higher than the other methods of LED mounting then there will be a 5% reduction in photometric output as a result. If the die temp is 10C higher because of the resistance in the MCPCB, there is a 2.5% reduction in photometric output as a result.

It seems to me that with the inability to actually measure the die temp itself, we need to identify a point for measure that will be consistent for the LED's and independent of the system beyond them? Not really possible I take it because of the spreading thermal resistance, I take it. Perhaps the lens retaining ring is close enough? It is accessible and as close to the die as we can get it seems. 

In the examples of possible construction I gave above, there is an addition of an anodized layer of Al in the LED's thermal path in the non MCPCB cases. These would likely add some resistance to the program which is not accounted for in the FLIR image above. I doubt this additional resistance would be that significant but it would be present.

What I take presently from this thread is the consideration that it is likely my present plan of using MCPCB's mounted with XR-E LED's in some lights carries a likely cost of about 5% loss in photometric output as compared to other more ideal means of LED hosting. If I were concerned about the absolute photometric output of the light and wanted to make up for this loss, I could increase the drive current to a level gaining this 5% and take the loss in runtime instead of light. My planed drive level is well below max and this would be an option. However, I don't have such precise control of drive current to dial in this fine adjustment. I could also design the light in such a manner that the steady state temp of the light were lowered enough to make up for this difference. Given the variations in Vf across the population of LED's I will be using as well as the variations in converter output across the population of converters I will use and of course the actual flux variation of the LED's themselves across the population I will use, this 5% loss will be a constant contribution but hardly stick out. 

In a competitive population of lights, high flux and or low VF LED's would more than surmount the handicap of the MCPCB itself. In the future, I will take this handicap into consideration but also in consideration are other greater and more significant handicaps and areas of present inefficiencies.


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## NewBie (Nov 23, 2006)

McGizmo said:


> What I take presently from this thread is the consideration that it is likely my present plan of using MCPCB's mounted with XR-E LED's in some lights carries a likely cost of about 5% loss in photometric output as compared to other more ideal means of LED hosting.




Yes, if one takes a very huge leap and tries to assume that case temperatures = die temperatures.

As I pointed out, *there are certainly some very major issues with this assumption.*


As far as the ring and thermal spreading, take a gander at this picture, realizing that there is quite a bit of magnification of the die image in the XR-E due to the lens effect. The die is only 0.1mm larger in the XR-E vs. this image of the XR7090. Notice how tiny it actually is, the die is the item mounted on top of the much larger ESD diode:






.


Adding this picture, I cleaned the part up a little:


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## PEU (Nov 23, 2006)

:goodjob: Newbie!!!


Pablo


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## NewBie (Nov 23, 2006)

Oh, I forgot to mention...

This test is at 700mA.

If you drive it beyond that, the differences become even greater, and there is porportionately more light loss due to the extra heat rise caused by the thermal resistance.

Conversely, as you drive them below 700mA, the loss is less.


Don-

Please note on the XR-E datasheet, that the light output drop with temp is done at only 350mA. Keep that in mind.


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## Kinnza (Nov 23, 2006)

I computed the slope of the photometric light output vs die temp 2,58% per 10C. But take in mind its refered to photometric output: part of the loss in radiometric efficiency is compensated for the spectral shift to longer wavelenghts, with slighty more photometric efficacy. You can see this on how cyan XR has an almost constant photometric output against die temp, due to spectral shift (very relevant in the cyan range).

Although spectrum shift is often associated to die heating, its necessary to distinguish, because using PMW, for example, is obtained a longer wl spectrum emission (higher current density in die) without aditional heating (if duty cycle is well computed). I believe the radiometric loss due to heat must be near 10%.

Agree with you, Mc Gizmo, many times a 5% of loss output is reasonable and assumible, depending of the design.

But is good to take in mind this thermal concerns. And its specially relevant when using red or amber leds in RGB designs, as red leds have and larger radiometric loss with temp, and spectral shift works against photometric output in AlInGap dies, giving large photometric losses with increasing temp.

Aditionally, red XRs have a junction board resistance of 15C/W, higher than blue/white XRs or XR-E (8C/W).

But it would be good check the Vf behavior with heating, as the XR-E report a high negative coefficient of Vf agaist temp (2,8mV/C, while K2 is 2mV/C and Golden Dragon 2,5mV/C), so 15C higher temp in the MCPCB mouted means about 5% less photometric output but with 2,8*15=42mV less Vf (1,1% less at 700mA, for a typical 3,75Vf, and 1,3% at 350mA), so the loss in efficiency isnt so great, just about a 3%:

15C difference at 700MA results in:

-2,58%*1,5=3,87% less output
-42mV/3,75V=1,1% less power

So about 2,8% less efficiency due to the bad thermal path, and less working at lower currents. It isnt dramatic. But after seeing the ETG MCPCB bad soldered, i prefer to use copper directly and attach LEDs myself, either AAd or soldered. Supposing 15C higher die temp with the MCPCB, with a 2,6W load, it only mean a average thermal resistance 5,7C/W higher, nothing critical, but who knows how the LED is soldered to the MCPCB? After seeing the examples reported, i would prefer avoid them, except if a good reflow soldering process is guaranteed.

PS: i see the last Don's post after post mine:


> Please note on the XR-E datasheet, that the light output drop with temp is done at only 350mA. Keep that in mind.


 
Good point, Newbie. I used it at 700mA and isnt valid. Sure the slope is higher at 700mA


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## McGizmo (Nov 23, 2006)

Newbie,
I don't want to assume anything if I don't have to. I do not assume that case temp = die temp but I guess I am assuming that the delta in case temp and die temp would be similar in these examples?

I concede that if I were to build a flashlight from copper with an integral bulkhead that it would be a brighter light than lights I currently have in the works; ceteris pairibus. Further, I could use a better and more thermally efficient heat sink than the MCPCB and see more light produced. 

I have no thermal concerns for my present design and parts already made and intended for use. I do have thermal considerations for the future, to keep in mind. 

With the extent that this thread has delved into the thermal issues of the MCPCB, it seems we are still at a place requiring a huge leap in asumption to get to the core of the matter? :thinking: Now is this huge leap just something I have to face or is it there for others as well? What is worse case? Is that POS MCPCB going to cause the LED to self destruct? 

Newbie, I have production parts in hand and an assembly scheme that precludes the inclusion of a large hunk of copper plate. 

I have working production piece lights that seem to be completely functional and out lux and out flux anything else I have built to date by a quantum margin, IMHO. Yes, there is room for improvement. Dare I point out that I use sapphire windows that rob considerably more light from the output than the MCPCB does? :duck:

As you well know, I have made a number of false assumptions regarding MCPCB's and the competence of those entrusted with mounting them! This goes beyond the CR-E and ETG MCPCB. I have certainly learned from this thread and your willingness to educate some of us. Thanks! Please don't take it personally if I don't elect to scrap my current projects due to thermaly related light losses you have pointed out. I am not proposing that you are suggesting I scrap these projects either. I don't take it that you are making any suggestions beyond considering the facts and information at hand. I do plan to take such into consideration and again, thank you.


----------



## NewBie (Nov 23, 2006)

Kinnza said:


> PS: i see the last Don's post after post mine:
> 
> 
> 
> ...




Actually, that was my comment to Don, not his.


Since you are "calculating" things, I though you might be interested in actual measurements:
http://candlepowerforums.com/vb/showthread.php?t=70073&page=1&pp=40

http://candlepowerforums.com/vb/showthread.php?t=138503&page=1&pp=40


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## SemiMan (Nov 23, 2006)

Newbie, have you had a chance to try out really good MCPCB such as a good Berquist or Thermagon board? I am curious to see how that would do in your tests. I think I may have some Thermagon material if you want to play around with it.

Semiman


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## NewBie (Nov 24, 2006)

I've checked out a number of materials in the past, thanks very much for the offer.


Figured I'd light up the LED shown above, for anyone that is interested:


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## glire (Nov 24, 2006)

For the love of LEDs :twothumbs


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## Concept (Nov 24, 2006)

As usual thanks Newbie. You do good work my friend.


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## NewBie (Nov 24, 2006)

Thanks for the kudos!


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## Doug S (Nov 29, 2006)

NewBie said:


> Don-
> 
> Please note on the XR-E datasheet, that the light output drop with temp is done at only 350mA. Keep that in mind.



Jar, are you intending to imply that the percentage photometric loss with increasing junction temperature would differ significantly at differing drive currents? 
I don't recall ever seeing a reference that suggested this.


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## NewBie (Dec 1, 2006)

Doug S said:


> Jar, are you intending to imply that the percentage photometric loss with increasing junction temperature would differ significantly at differing drive currents?
> I don't recall ever seeing a reference that suggested this.




Well, lets think about it a bit.

We all know that LEDs get less efficient at higher current levels, and the produce less light at higher currents, and more of the energy leaves the LED die as heat, instead of light.

This is quite apparent in LEDs that are less efficient, such as the Luxeon K2, and the OSRAM OSTAR. The light output vs. current curve starts flattening earlier, than a die mounted in a package with lower thermal resistance, or if the LED itself in the system is mounted such that the thermal resistances are higher in relation to ambient (which causes the heat to "accumulate"). Even the thermal emissivity of the heat "radiator" surface comes into play, as it all is part of the system.

Some times the equation changes, sometimes a lot, like in a small flashlight, where if you hold it in your hand, your own body acts as a pretty decent liquid cooling system, to pull the flashlight, but then you set it on the counter, floor of the tent, or whatever, where there isn't that much convection nor conduction of the heat, and you have a flashlight with a polished metal finish (low emissivity), and the little light gets amazingly hot.

So, going back, if less light is leaving the die due to lower efficiencies at higher currents, quite obviously the die will be producing more heat.

In the past, where the leading LED efficiencies were rather low, the effect of the additional losses was quite low, since the majority of the power put into the LED left as heat. As LEDs now and especially in the future, get more and more efficient, the contribution of losses in the die at various currents starts to affect the amount of heat generated, which has to travel out of the LED thru a given thermal resistance.


The older CREE 7090 chips set records back in 2005, when it was verified they had in fact achieved the 65 lm/W barrier. 
http://www.netl.doe.gov/SSL/highlights_cree2.html

Then a little later in SEPTEMBER 2, 2005 it was then announced they had even surpassed that, managing to improve the LED such that they were hitting 70lm/W.
http://www.cree.com/press/press_detail.asp?i=1143571750984


If you go back to the first one, where the Department of Energy announced that CREE had hit 65lm/W.
"A key modification to Cree's experimental LED chip design resulted in a 17-20% increase in brightness and, in addition, the demonstration of packaged blue LEDs with external quantum efficiency of 40%."

The packaged blue LED (white LEDs utilize blue LED die in them), in the finished package is actually hitting a 40% quantum efficiency! (yes, I know there are some phosphor losses due to the Stokes effect and other losses)

Several scientists/authors use the maximum perfect theoretical efficiency of a YAG Phosphor + blue LED based White LED (the kind we all use in flashlights) to be 330lm/W. At one of the conferences, they estimated by applying a few known techiques, and with the development of some improvements, white LEDs will reach 155 lm/W- and they felt this was actually realistic.

Anyhow, CREE is getting 70-90 lm/W on parts they are shipping now. Okay, so, why is this important? Well, lets take 80lm/W and divide it by 330 lm/W and you quickly realize the XR-E is running in the range of 24% efficiency! 

As a point of reference, if you managed to hold the die temperatures of the first Luxeon I devices down at 25C (not going to happen in a typical flashlight) we were actually seeing efficiencies in the 20lm/W range. 20 lm/W divided by 330 lm/W results in an efficiency of only 6%. Down at these levels, minor changes in the efficiency of the die had very little effect on the overall performance. Even when you you start driving the K2 parts at their rated 1.5 Amps you start getting back into this range very quickly (the OSRAM OSTAR driven at spec has much of the same problem).

However, with the CREE XR-E, with it's 24% efficiency, things that used to be minor insignificant items really start to stand out. As the future brings even better devices, with yet higher efficiencies, some of the assumptions that were quite valid and true in the past (since they didn't add up to diddly squat), all of a sudden become outdated and lead folks down the wrong path (a number of old wives tales started this way...)

So, in a way, yes, we need to begin to start and think about a more complex model, if one really want to take full advantage of everything possible. Failure to do so will start leading to extra errors from the assumptions, which can....


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## Kinnza (Dec 2, 2006)

In order to calc the real efficiency, the centroid wavelenght would be the more accurate. The 330lm/w figure is a theoretical calc of a white source with CRI over 80. But to calc the efficiency of one LED, what we need is the centroid wavelenght, as the CIE coefficient associated to that wavelenght is the max lm/w that led can achieve (converting 100% of energy in light). Dividing the lm/w emission between the max possible, gets the real efficiency.

I can calc the centroid wl from the spectral plots you linked, but its a tough work (need to digitalize the plot and introduce each wl emission in a datasheet). When i saved the spectral plot (the one of the A19, of 6402K), i noticed there is a blank cell in the pic called "WLc" wich must correspond to the centoid wavelengh (below WLd). Its because its unactivated? or the program is unable to calc it for wide spectrum sources?

If you cant get this data, ill calc it.

PD:The 330lm/W usually correspond to 3500-4000K white light sources.


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## Kinnza (Dec 2, 2006)

I already calculated it. The plot of the XR, tint XO, have a luminous efficiency of 310,7 lm/w (507.5 nm centroid wavelenght) (about 3% margin error).

So at 75,4 lm/w (reported by NIST in continous mode) , mean efficiency of 24,25%. At 85 lm/w, wich Q2 bins probably reach, means 27,35%.

I think this is not just relevant when considering the slope of the lm degradation at each current. Its very relevant when designing the thermal path. Until now, all LEDs manufacturer consider the light emission negligible when calculating the total thermal load, because it was below 10%, but when efficiencies reach 25%, it means 1/4 less heat to dissipate, and probably more, as the blue led is emiting at higher efficiency, as part of its emission is lost at phosphor conversion.


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## NewBie (Dec 7, 2006)

Very nice!

Thank you very much for all the effort.


Wavelength precision ±0.3nm (median wavelength: 546.1nm Hg lamp)
Wavelength resolution 0.9nm/pixel 
Repeatability (σ )
(For Illuminant A)
Normal Mode Luminance: 0.1%, +1 digit
Chromaticity xy: 0.0002 over the Luminance range

The relative shape is correct here, but not the absolute value. This is in *WATTS*/sr*m^2*nm (NOT Photopic numbers, so you'll need to adjust for that)

380	8.24E-05
381	3.64E-06
382	2.14E-05
383	0.00E+00
384	3.90E-05
385	4.48E-06
386	1.55E-06
387	6.45E-07
388	2.60E-05
389	1.49E-05
390	2.22E-05
391	2.99E-05
392	7.21E-05
393	0.00E+00
394	0.00E+00
395	0.00E+00
396	0.00E+00
397	0.00E+00
398	0.00E+00
399	0.00E+00
400	0.00E+00
401	0.00E+00
402	0.00E+00
403	9.19E-06
404	1.28E-05
405	0.00E+00
406	7.39E-05
407	1.01E-04
408	2.12E-05
409	1.41E-04
410	2.30E-04
411	4.15E-04
412	5.01E-04
413	7.24E-04
414	9.76E-04
415	1.36E-03
416	1.70E-03
417	2.17E-03
418	2.82E-03
419	3.59E-03
420	4.51E-03
421	5.73E-03
422	7.28E-03
423	9.00E-03
424	1.08E-02
425	1.28E-02
426	1.51E-02
427	1.76E-02
428	2.06E-02
429	2.40E-02
430	2.75E-02
431	3.15E-02
432	3.57E-02
433	4.05E-02
434	4.55E-02
435	5.10E-02
436	5.68E-02
437	6.30E-02
438	6.95E-02
439	7.65E-02
440	8.40E-02
441	9.21E-02
442	1.01E-01
443	1.09E-01
444	1.19E-01
445	1.29E-01
446	1.40E-01
447	1.51E-01
448	1.63E-01
449	1.74E-01
450	1.86E-01
451	1.97E-01
452	2.07E-01
453	2.15E-01
454	2.22E-01
455	2.27E-01
456	2.29E-01
457	2.29E-01
458	2.27E-01
459	2.22E-01
460	2.16E-01
461	2.08E-01
462	1.98E-01
463	1.87E-01
464	1.76E-01
465	1.66E-01
466	1.57E-01
467	1.48E-01
468	1.39E-01
469	1.31E-01
470	1.24E-01
471	1.19E-01
472	1.14E-01
473	1.09E-01
474	1.04E-01
475	9.96E-02
476	9.53E-02
477	9.11E-02
478	8.72E-02
479	8.34E-02
480	7.97E-02
481	7.61E-02
482	7.27E-02
483	6.97E-02
484	6.70E-02
485	6.46E-02
486	6.25E-02
487	6.07E-02
488	5.92E-02
489	5.80E-02
490	5.70E-02
491	5.62E-02
492	5.55E-02
493	5.49E-02
494	5.46E-02
495	5.45E-02
496	5.46E-02
497	5.49E-02
498	5.53E-02
499	5.59E-02
500	5.67E-02
501	5.77E-02
502	5.87E-02
503	6.00E-02
504	6.15E-02
505	6.29E-02
506	6.47E-02
507	6.63E-02
508	6.80E-02
509	6.99E-02
510	7.18E-02
511	7.36E-02
512	7.55E-02
513	7.74E-02
514	7.93E-02
515	8.12E-02
516	8.30E-02
517	8.49E-02
518	8.65E-02
519	8.83E-02
520	9.00E-02
521	9.17E-02
522	9.32E-02
523	9.48E-02
524	9.63E-02
525	9.78E-02
526	9.91E-02
527	1.00E-01
528	1.02E-01
529	1.03E-01
530	1.04E-01
531	1.05E-01
532	1.06E-01
533	1.07E-01
534	1.08E-01
535	1.08E-01
536	1.09E-01
537	1.10E-01
538	1.10E-01
539	1.11E-01
540	1.12E-01
541	1.12E-01
542	1.13E-01
543	1.13E-01
544	1.13E-01
545	1.14E-01
546	1.14E-01
547	1.14E-01
548	1.14E-01
549	1.14E-01
550	1.14E-01
551	1.14E-01
552	1.14E-01
553	1.14E-01
554	1.14E-01
555	1.14E-01
556	1.14E-01
557	1.14E-01
558	1.14E-01
559	1.14E-01
560	1.14E-01
561	1.14E-01
562	1.14E-01
563	1.14E-01
564	1.14E-01
565	1.13E-01
566	1.13E-01
567	1.13E-01
568	1.13E-01
569	1.12E-01
570	1.12E-01
571	1.12E-01
572	1.11E-01
573	1.11E-01
574	1.11E-01
575	1.10E-01
576	1.10E-01
577	1.09E-01
578	1.09E-01
579	1.08E-01
580	1.08E-01
581	1.07E-01
582	1.06E-01
583	1.06E-01
584	1.05E-01
585	1.04E-01
586	1.04E-01
587	1.03E-01
588	1.02E-01
589	1.01E-01
590	1.01E-01
591	9.98E-02
592	9.90E-02
593	9.82E-02
594	9.73E-02
595	9.64E-02
596	9.56E-02
597	9.47E-02
598	9.39E-02
599	9.30E-02
600	9.21E-02
601	9.13E-02
602	9.04E-02
603	8.96E-02
604	8.87E-02
605	8.78E-02
606	8.70E-02
607	8.61E-02
608	8.53E-02
609	8.45E-02
610	8.38E-02
611	8.31E-02
612	8.22E-02
613	8.14E-02
614	8.04E-02
615	7.94E-02
616	7.85E-02
617	7.76E-02
618	7.67E-02
619	7.59E-02
620	7.50E-02
621	7.42E-02
622	7.33E-02
623	7.24E-02
624	7.15E-02
625	7.06E-02
626	6.98E-02
627	6.89E-02
628	6.79E-02
629	6.70E-02
630	6.61E-02
631	6.52E-02
632	6.42E-02
633	6.32E-02
634	6.23E-02
635	6.13E-02
636	6.03E-02
637	5.94E-02
638	5.85E-02
639	5.76E-02
640	5.67E-02
641	5.58E-02
642	5.49E-02
643	5.40E-02
644	5.31E-02
645	5.22E-02
646	5.13E-02
647	5.04E-02
648	4.95E-02
649	4.86E-02
650	4.77E-02
651	4.68E-02
652	4.59E-02
653	4.51E-02
654	4.44E-02
655	4.41E-02
656	4.33E-02
657	4.25E-02
658	4.17E-02
659	4.09E-02
660	4.01E-02
661	3.94E-02
662	3.86E-02
663	3.80E-02
664	3.72E-02
665	3.65E-02
666	3.57E-02
667	3.50E-02
668	3.43E-02
669	3.36E-02
670	3.29E-02
671	3.23E-02
672	3.16E-02
673	3.09E-02
674	3.03E-02
675	2.97E-02
676	2.91E-02
677	2.85E-02
678	2.79E-02
679	2.73E-02
680	2.68E-02
681	2.62E-02
682	2.57E-02
683	2.51E-02
684	2.45E-02
685	2.40E-02
686	2.36E-02
687	2.31E-02
688	2.27E-02
689	2.21E-02
690	2.16E-02
691	2.11E-02
692	2.05E-02
693	2.01E-02
694	1.96E-02
695	1.92E-02
696	1.88E-02
697	1.85E-02
698	1.81E-02
699	1.77E-02
700	1.72E-02
701	1.68E-02
702	1.65E-02
703	1.62E-02
704	1.58E-02
705	1.55E-02
706	1.51E-02
707	1.49E-02
708	1.45E-02
709	1.41E-02
710	1.38E-02
711	1.35E-02
712	1.31E-02
713	1.28E-02
714	1.25E-02
715	1.22E-02
716	1.19E-02
717	1.16E-02
718	1.14E-02
719	1.11E-02
720	1.10E-02
721	1.07E-02
722	1.04E-02
723	1.02E-02
724	1.00E-02
725	9.83E-03
726	9.58E-03
727	9.41E-03
728	9.19E-03
729	8.92E-03
730	8.72E-03
731	8.61E-03
732	8.39E-03
733	8.21E-03
734	8.01E-03
735	7.86E-03
736	7.71E-03
737	7.49E-03
738	7.42E-03
739	7.25E-03
740	7.09E-03
741	6.93E-03
742	6.75E-03
743	6.61E-03
744	6.47E-03
745	6.29E-03
746	6.16E-03
747	6.10E-03
748	5.98E-03
749	5.87E-03
750	5.74E-03
751	5.52E-03
752	5.54E-03
753	5.44E-03
754	5.32E-03
755	5.14E-03
756	5.10E-03
757	4.87E-03
758	4.90E-03
759	4.84E-03
760	4.73E-03
761	4.58E-03
762	4.51E-03
763	4.47E-03
764	4.46E-03
765	4.32E-03
766	4.31E-03
767	4.24E-03
768	4.14E-03
769	4.03E-03
770	3.97E-03
771	3.79E-03
772	3.82E-03
773	3.86E-03
774	3.77E-03
775	3.64E-03
776	3.70E-03
777	3.50E-03
778	3.55E-03
779	3.58E-03
780	3.50E-03

If you get the conversion correct, the 2 degree CIE observer should put you at x= 0.3105 and y= 0.3241, Kelvin Temp 6660.


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## Benjammin22250 (Dec 7, 2006)

I wish I was as smart as Newbie! I guess thats why I'm going to college.


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## Kinnza (Dec 8, 2006)

I calculated again with the more accurate data you provided, Newbie. I obtain 276,5 lm/w of luminous efficacy. I dont know if the last data correspond to a slighty different spectrum. I used a pic of a XR-E spectrum with a color temp of 6402K, and obtained the 310,7lm/w figure, but getting the data directly from the graph (obviously, less accurate). If i understood well, the new data is from a XR-E with a 6600K color temp, corresponding to 276,5 lm/w, so for this more bluish color, same photopic emission correspond to higher efficiency.







This is a pic showing the luminous efficacy obtained depending of chromaticity coordinates. Mixing it with each tint coordinates can provide the range of luminous efficacy of any tint.

I made a Excel sheet to compute the luminous efficacy. Can anybody suggest me a good file server to put it? Anyway, i can send it for mail to anybody wanting to check the procedure used (or just to get the CIE photopic curve per nm values).

BTW, yesterday i saw this: New LED junction temperature tester.

At the bottom, there is a link to the product page, wich explain the procedure used.


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## NewBie (Dec 10, 2006)

If you poke around on the Aglient site (it may have moved over to Avago's site now), they have a paper on how to measure the internal junction temperature with an electrical setup.
Found it:
http://www.molalla.net/~leeper/ledtherm.pdf

Another method:
http://www.elecdesign.com/Articles/Print.cfm?AD=1&ArticleID=11676


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## NewBie (Jan 6, 2007)

Anglepoise said:


> Newbie,
> Look forward to see the 3 way test results.
> Your hard work on this is appreciated
> 
> ...



BTW, I wanted to thank you for sacrificing that LED! Nice


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