# Question on XR-E instalation and soldering.



## Anglepoise (Nov 8, 2006)

This post asks a question and hopefully will open up some discussion.

I think/hope I have my facts correct.

The base of the new Cree XR-E is a ceramic substrate with 3 copper 'pads' recessed into it. The large center pad is for thermal management and the 2 side pads are + and -, and these 2 connection points are duplicated on the top side. The center pad is electrically isolated from the others.

As in the LUX III , the bottom of the emmmiter gets hot instantly and we need to remove this heat.

Now Cree suggests that soldering via a method called 're flow' will connect the center 'pad' to its host. However for this to work, the host has to be a very thin bit of copper .

Now for my question. Does anyone know how efficient the aluminum based star is. I think it has been established that a few MCPCB's are not efficient but there has been no mention of the star. 

I don't want to mod a nice light only to find that the XR-E has a sandwich of non conductive material between the 'pad' and the light's aluminum heat sink.

I am experimenting with epoxying the LED directly to its heat sink and not using any intermediate MCPCB. The problem then is that the electrical connections are very close to shorting out the heat sink ( flashlight body ) and the metal reflector as it seats on the metal 'reflector ring'.

All comments appreciated.


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## cmacclel (Nov 8, 2006)

Newbie's post

https://www.candlepowerforums.com/posts/1673515&postcount=12

Mac


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## Anglepoise (Nov 8, 2006)

Just discovered something else that is interesting and potentially useful.

The electrical connection from the yellow emmiter first goes to the upper electrical pads. Then it connects to the bottom pads by two tiny copper tracks at the very edges of the rectangle substrate.
See below 






This little copper track is exposed when the very edge of the board ( ceramic ) is touched to a diamond wheel. 

Now if one caries on and grinds a few thou deeper, one severs the connection to the base.
Remember to grind both sides or all 4 corners if you want to completely disconnect the top and bottom 
electrical paths and have complete isolation of bottom and top.






Now all electrical connections must be to the top pads and the emitter can be epoxied to a 'base' without worry on shorting.


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## cmacclel (Nov 8, 2006)

Awesome find! Now I need a diamond wheel 


Mac


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## wquiles (Nov 8, 2006)

I like that - thanks David!

Will


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## Amonra (Nov 8, 2006)

i too sever the connection but only on the positive side.
There is no need to use a diamond wheel, i just snip the corners off with a pair of wire cutters, fast and easy.


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## greenLED (Nov 8, 2006)

Thanks for the pics and the tips! I realized the pads were connected as I sanded off the bottom contacts last night. I was wondering how to deal with those - I'm off to snipping the corner, then. 

Amonra, that's cool. I can still keep the (-) connection to the bottom.

Can anybody confirm it's safe to solder directly onto the contacts. I have no clue about this "reflow" soldering hoopla.


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## Anglepoise (Nov 8, 2006)

greenLED said:


> Thanks for the pics and the tips! I realized the pads were connected as I sanded off the bottom contacts last night. I was wondering how to deal with those - I'm off to snipping the corner, then.
> 
> Amonra, that's cool. I can still keep the (-) connection to the bottom.
> 
> Can anybody confirm it's safe to solder directly onto the contacts. I have no clue about this "reflow" soldering hoopla.



I think we should be all right soldering on the top pads. Cree did not have to have them there and the fact that they are.....well lets try.

My only concern is the two wires will be very close to the reflector as it sits on the LED shoulder and if metal, will have to be insulated with a Teflon washer, Kaptan, nail polish etc.

Have not tried 'Amonra's' idea of snipping but sounds logical if one lacks a diamond wheel.


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## Meduza (Nov 8, 2006)

Ok... now i have cut of the corners and AA Epoxied it to a old Lux star 

Now i want to see if it lights up... if only the epoxy could cure a little faster...


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## Anglepoise (Nov 8, 2006)

Well I got my XR-E epoxied to a chunk of Aluminum
with AA. Then soldered to the two pads.
With 600ma going to the LED, the heat sink gets hot ( good) 
and so far so good.


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## dabiscake (Nov 8, 2006)

Great stuff guys, keep the tips and finds coming!!


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## greenLED (Nov 8, 2006)

Amonra said:


> ...just snip the corners off with a pair of wire cutters, fast and easy.


wait, I just thought about this - wouldn't that possibly crack the ceramic plate somewhere under the emitter itself?


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## Morelite (Nov 8, 2006)

Not my best soldering job, but it works. Those top contacts are rather tricky to solder to. 

Cree XR-E Aleph LE


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## Monolith (Nov 8, 2006)

How much does the location of the top contacts interfere with a reflector?


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## Amonra (Nov 8, 2006)

greenLED said:


> wait, I just thought about this - wouldn't that possibly crack the ceramic plate somewhere under the emitter itself?



I have done it to 8 XR-E's so far and no cracking yet.

Soldering to the top contacts is a very tricky job and the solder seems to want to stick to the aluminium ring rather than the pads but i have managed to find a way kind of. i lightly tinned the bare wires and dipped them in soldering grease ( not too much ) then placed the wire on top of the pad and press it there with the hot iron for a few seconds until the grease has bubbled off and the solder starts flowing. being careful not to move the wire i remove the iron whilst blowing and it's done and not too bad.


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## Anglepoise (Nov 8, 2006)

Monolith said:


> How much does the location of the top contacts interfere with a reflector?



Due to the upper contacts being on the same plane as the bottom of the reflector there will definitely be problems with metal reflectors coming dangerously close to shorting.

Some sort of heat resistant, non conductive, 'washer' under the reflector might be the ticket.


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## kenster (Nov 8, 2006)

Anglepoise said:


> Due to the upper contacts being on the same plane as the bottom of the reflector there will definitely be problems with metal reflectors coming dangerously close to shorting.
> 
> Some sort of heat resistant, non conductive, 'washer' under the reflector might be the ticket.


 
I have been using a thin plastic washer between the reflector & LED and haven`t had a problem yet.


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## IsaacHayes (Nov 8, 2006)

If the metal ring around these XRE's are like the UV cree's, it's actually plated copper....

Good tips everyone!

Also, couldn't one file the edge of the top trace to break the connection that goes down the edges?

I'm going to AA epoxy mine to a Pentium heatsink which is anodized. I'm tempted to just throw it on there and not worry about shorts since anodize is an insulator, as well as AA. I will have the AA on there thin though. I got my 2.5" aspherical lens in today, tommorow I will play!!! :naughty:


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## Anglepoise (Nov 8, 2006)

IsaacHayes said:


> If the metal ring around these XRE's are like the UV cree's, it's actually plated copper....
> 
> Good tips everyone!
> 
> ...



Well that explains why solder is so keen to stick to the ring<g>

I did not want to muck about with the top pads/trace as that is where the connection comes from the die.


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## Ganp (Nov 8, 2006)

Yesterday I was filing the edge of the circular heatsink of pre-mounted Cree. Some masking tape which I had used to hold a protective pad over the LED stuck to the lens during my clumsy handling. When I eased the tape off, the lens came off with it.  

I guess it can't be very serurely fixed compared to a Luxeon lens as it separated from the tape really easily.

I placed it back over the die and luckily the LED still works....  

Colin.


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## IsaacHayes (Nov 8, 2006)

Luxeons dome's can come off easy too. It's not a part you want to apply any force to.


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## Anglepoise (Nov 8, 2006)

Another thing I noted. Although we all have early examples, the forward voltage is a little high and a fully recharged C-R123a could only direct drive my XR-E to 780ma. Now the same test got a TYOH LuxIII up to 1.2 amps. 
Forward voltage was 3.64 volts for the XR-E and 3.38 for the LUX.

And the combination XR-E and its aluminum heat sink got hot fast.


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## PEU (Nov 8, 2006)

Anglepoise said:


> Now all electrical connections must be to the top pads and the emitter can be epoxied to a 'base' without worry on shorting.



EXCELLENT find, thanks for sharing! Just in time my 1st XR-Es arrived today 


Pablo


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## chimo (Nov 9, 2006)

Here's a post  that goes a little further back (with an earlier Cree LED).  

Paul


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## Morelite (Nov 11, 2006)

here is my first attemp at re-flow soldering. I reflowed the cree on the cree PCB that is available at the Shoppe. This PCB is very thin and is ideal for my application, where the extra thickness of the stock cree MCPCB's are too thick. 

These will be going into Aleph light engines. This cree PCB can than be expoxied to the E-screw with a thin layer of AA, and the lead wires can be soldered to the PCB pads instead of the cree top pads. Soldering directly to the cree top pads can be done but it is very tricky, as you can see in my previous post.


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## IsaacHayes (Nov 11, 2006)

The vias in that cree board are much like what are found on the ceramic of the Cree itself. I know useless info but interesting to me none the less.


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## Anglepoise (Nov 11, 2006)

Morelite,
Thanks for posting the two pics. I personally have not yet attenped the soldering. Will try.

However my question for you is this. Can you tell us a little about the makeup of the MCPCB. I am getting the feeling from reading between the lines that these boards consist of a micron thin layer of copper, a center vias ( think that is what its called )of some non electrical material and then another layer of copper.
If this is the case then I suspect we are all going to experience some very hot Crees.


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## LumenHound (Nov 11, 2006)

Anglepoise said:


> Another thing I noted. Although we all have early examples, the forward voltage is a little high and a fully recharged C-R123a could only direct drive my XR-E to 780ma. Now the same test got a TYOH LuxIII up to 1.2 amps.
> Forward voltage was 3.64 volts for the XR-E and 3.38 for the LUX.
> 
> And the combination XR-E and its aluminum heat sink got hot fast.


I wonder what the Vf of that XR-E would be after a 24 hour burn in at 350mA?
How much would it drop by?


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## Morelite (Nov 11, 2006)

Anglepoise said:


> Morelite,
> Thanks for posting the two pics. I personally have not yet attenped the soldering. Will try.
> 
> However my question for you is this. Can you tell us a little about the makeup of the MCPCB. I am getting the feeling from reading between the lines that these boards consist of a micron thin layer of copper, a center vias ( think that is what its called )of some non electrical material and then another layer of copper.
> If this is the case then I suspect we are all going to experience some very hot Crees.


 
I haven't messed around with the MCPCB yet, but it is my understanding that they have a solid copper core with silver plating connecting the top and bottom center pad, the outer contact pads only have a thin trace core connecting them. I haven't found any info from Cree to support that theory other than they state that the "MC" in MCPCB stands for metal core. I guess someone that has a MCPCB that they don't need could sand or grind away at it and find out for sure.


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## MillerMods (Nov 12, 2006)

It's also possible to fit a Cree in the same space that a Lux fits. For example, after trimming the ceramic down, I fit one in an L1P. The only bad thing is that there is just enough pad left to solder some 30 gauge magnet wire to. I used a bored out, trimmed down IMS reflector to get a nice hotspot.


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## IsaacHayes (Nov 12, 2006)

magnet wire, lol dang. MM, is the hotspot brighter than the stock lux?

I just swapped a SX0H lux1 into an ultrafire, which has a constant current driver in it, no matter what VF led you use, it delivers 250ma to the led. Brightness is up a lot but not double. I'm thinking about cree-ing it next. But the ultrafire heatsink has a round centering depression for the luxeon, and the cree is flat.... so I'm gonna have to dremel it I guess...


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## Anglepoise (Nov 12, 2006)

Morelite said:


> I haven't messed around with the MCPCB yet, but it is my understanding that they have a solid copper core with silver plating connecting the top and bottom center pad, .........



Thanks,
If that center pad is metal right the way through, then no worries.


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## cmacclel (Nov 12, 2006)

Here you go

http://candlepowerforums.com/vb/showthread.php?p=1687859#post1687859

Mac


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## Anglepoise (Nov 13, 2006)

Due to the tests made by Newbie and others, it seems that the MCPCB is not the way to go for users contemplating 350 ma and above.

So if you are like me, then the other option is to Arctic Alumina the emitter directly to the light heatsink.

The only problem I see in this is that the wire connections will interfere with the base of the reflector. As one shaves metal off the base of the reflector, the hole increases in size. So the reflector has nothing to rest against except the solder points ( not good) .

I think I need a small adapter that fits over the Cree reflector but does not bottom out. It would have a large flat surface to accept the base of the reflector and at the same time allow a little air space underneath for solder connections.




[


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## greenLED (Nov 13, 2006)

Angle, I've actually been thinking about fitting a plastic ring/washer around the metallic ring surrounding the XR-E's dome. The height of the ring could be sized for reflector focus and still allow space between the wires and the bottom of the reflector.

Just an idea, not sure how to implement it yet...


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## cmacclel (Nov 13, 2006)

The ring would be tough as it would definetly insulate but then you would be dealing with muliple heights with the variances in the wire soldered.


Mac


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## greenLED (Nov 13, 2006)

cmacclel said:


> The ring would be tough as it would definetly insulate but then you would be dealing with muliple heights with the variances in the wire soldered.


I was thinking most of the heat is already conducted by the base plate at the underside of the ceramic base, and a thin washer/ring around the metal ring wouldn't present much of a problem. 

Yes, it does seem that every reflector (obviously) has different focus heights, so this washer I'm thinking about must be custom sized.


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## MillerMods (Nov 13, 2006)

greenLED said:


> I was thinking most of the heat is already conducted by the base plate at the underside of the ceramic base, and a thin washer/ring around the metal ring wouldn't present much of a problem.
> 
> Yes, it does seem that every reflector (obviously) has different focus heights, so this washer I'm thinking about must be custom sized.



I think he means if the wire is soldered to the top side of the emitter.


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## cmacclel (Nov 13, 2006)

GreenLED you got me all wrong. 


I was just stating if the reflector rested on the insulating washer it would be most likely be cocked as you would never be able to solder the wires the same height.

Mac


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## greenLED (Nov 13, 2006)

Nah, I'm following you, but I see now that you're thinking of a rather thick outer ring. The supporting ring I had in mind wouldn't be resting on the wires at all. This means that it has to be around/less than credit card thickness. Sure, that's awful thin of a washer, but that's what I had in mind.

You have the fancy machines, you could actually machine a "stepped" ring, where the smaller diameter would be small and deep enough as to not interfere with the wires and still support the reflector. Something like this (sorry, no time to get on a drawing program right now):

reflector sits here

```
__________
!		 !
!		 !
--!    !--
  !    !  
O---------O
this is the board
```

the "O" are the wires

yup, tiny. 

_
Dang it!! Stupid drawing doesn't come out as I want it to. Imagine two rings, one on top of the other. The smaller ring sits lower: its height and OD is such that it clears the wires, and serves as base for the upper, larger ring that supports the reflector (only that the 2 rings are a single piece). OK, gotta run now._


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## CodeOfLight (Nov 13, 2006)

Why dont you guys just solder a short copper standoff plate underneath the cree, then solder that to the heatsink plate? Make sure the standoff plate is just large enough to cover the heat transfer plate and not the connector points underneath. Think of it like the cree sitting on a mesa. The wires could still be attached underneath, and the heat would travel through the standoff into the base. All you would need would be a piece of 1/8th or 3/16 inch copper plate cut into a rectangle that is as wide as the heat transfer area under the cree and as long as the base plate. The cree would sit astride this "beam" of copper. Picture a postage stamp sitting on a stick of dentyne gum.


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## greenLED (Nov 13, 2006)

That's a good idea, COL. It may work, and help "fill in" the space lost when sanding down the opticalware (relative to Luxeon). It adds a layer of complexity trying to complete the (-) path again, though.

Mac, you're the one with the fancy tools: make a "pedestal" for the Cree.


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## Anglepoise (Nov 13, 2006)

That would certainly help and allow space for soldering on the bottom two tabs, thereby allowing the reflector a flat plane to rest against.


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## CodeOfLight (Nov 13, 2006)

But don't just make it a pedestal, extend the ends of the pedestal so that it is like a beam. That will give more structural support, and a greater thermal fan-out. The only parts of the led that will overhang the beam to the left and the right will be the contact points of the led.

If you really wanted to get fancy, you could cut two rectangular holes under the contact points in a solid plate of metal, and line up the cree contacts so that they are entirely within the rectangular hole areas. Pre solder the wires onto the emitter, then insert a small segment of silicone tubing into the rectangular holes. Run both wires through the tubing and pull the emitter down until it is lined up right, then solder or thermal epoxy it together.

You could even just hollow out fairly deep cavities where the contact points would come into contact with the metal of the heatsink. Pre-solder the wires onto the bottom of the LED, coat (insert into) the cavities with 1/2 of a piece of silicone tubing and mount the led like above.


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## chris_m (Nov 13, 2006)

Some good ideas coming out here - I may just change my Q2 order to emitters after all. Question is, how do you solder the LED onto the standoff, and then the standoff onto the heatsink? It doesn't seem that would be easy to hand solder. Would using thermal epoxy (a very thin layer of, by squeezing the parts together) be OK for this, or would this be worse than the PCB?


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## MillerMods (Nov 13, 2006)

chris_m said:


> Some good ideas coming out here - I may just change my Q2 order to emitters after all. Question is, how do you solder the LED onto the standoff, and then the standoff onto the heatsink? It doesn't seem that would be easy to hand solder. Would using thermal epoxy (a very thin layer of, by squeezing the parts together) be OK for this, or would this be worse than the PCB?



Arctic Silver thermal epoxy is something like 60% micronized silver. It has excellent thermal transfer characteristic; especially in thin layers. Shoot, even as it is, it almost has the heat transfer ability of steel. I know steel isn't that great, but in very thin layers a delta in temperature from one side to the other will be very negligible; probably less than a few degrees C.


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## NewBie (Nov 19, 2006)

MillerMods said:


> Arctic Silver thermal epoxy is something like 60% micronized silver. It has excellent thermal transfer characteristic; especially in thin layers. Shoot, even as it is, it almost has the heat transfer ability of steel. I know steel isn't that great, but in very thin layers a delta in temperature from one side to the other will be very negligible; probably less than a few degrees C.



Artic Silver Epoxy Greater than 7.5 W/m-°K
http://www.articsilver.com/arctic_silver_thermal_adhesive.htm

I am seeing nearly a 10x difference between Artic Silver Epoxy and Steel, with Steel being much better.


Thermal Conductivity is the inverse of Thermal Resistance. You want to have a high Thermal Conductivity, and a low Thermal Resistance.

W/m-°K = W/m·°C

Substance	Thermal Conductivity (W/m·°C)
Air (still)	0.03
Helium (liquid)	0.0307
Nitrogen (liquid)	0.1411
Epoxy	0.2
Mylar	0.2
Phenolic	0.2
Silicone Grease	0.2
Silicone Rubber	0.2
Teflon	0.2
FR-4* (G-10)	0.3
Heatsink Compound	0.4
Water	0.55
Mica	0.7
Epoxy (thermally conductive)	0.8
Glass	0.8
Silicon Dioxide (amorphous)	1.4
Silicon Dioxide (quartz, a-axis)	5.9
Invar	11
Silicon Dioxide (quartz, c-axis)	11
Alumina (85%)	11.8
Stainless Steel (321)	14.6
Kovar	17
Monel	19.7
Silicon Nitride	16-33
Titanium	21.9
Stainless Steel (410)	24
Alumina	27.6
Sapphire (a-axis)	32
Lead	34.3
Sapphire (c-axis)	35
Boron Nitride	39.4
GaAs	59.1
Tin	63
Iron	66.9
*Steel (low carbon)	66.9*
Platinum	73.4
Silicon Carbide	90
Nickel	90.6
Zinc	102.4
Beryllium-Copper	106.3
Beryllia (95%)	116.1
Brass (70/30)	122
Molybdenum	129.9
Silicon (pure)	145.7
Silicon (0.0025 W-cm)	145.7
Beryllia (97%)	157.5
Magnesium	157.5
Beryllium	177.2
Beryllia (99.5%)	196.9
Tungsten	196.9
Aluminum	216.5
Gold	291.3
Copper	393.7
Silver	417.3
Diamond (room temp)	629.9



Keep in mind, that these numbers below are in W/cm·°C, not W/m·°C

Substance	Thermal Conductivity (W/cm·°C)
Air (still)	0.0003
Helium (liquid)	0.000307
Nitrogen (liquid)	0.001411
Epoxy	0.002
Mylar	0.002
Phenolic	0.002
Silicone Grease	0.002
Silicone Rubber	0.002
Teflon	0.002
FR-4* (G-10)	0.003
Heatsink Compound	0.004
Water	0.0055
Mica	0.007
Epoxy (thermally conductive)	0.008
Glass	0.008
Silicon Dioxide (amorphous)	0.014
Silicon Dioxide (quartz, a-axis)	0.059
Invar	0.11
Silicon Dioxide (quartz, c-axis)	0.11
Alumina (85%)	0.118
Stainless Steel (321)	0.146
Kovar	0.17
Monel	0.197
Silicon Nitride	0.16 - 0.33
Titanium	0.219
Stainless Steel (410)	0.24
Alumina	0.276
Sapphire (a-axis)	0.32
Lead	0.343
Sapphire (c-axis)	0.35
Boron Nitride	0.394
GaAs	0.591
Tin	0.63
Iron	0.669
Steel (low carbon)	0.669
Platinum	0.734
Silicon Carbide	0.9
Nickel	0.906
Zinc	1.024
Beryllium-Copper	1.063
Beryllia (95%)	1.161
Brass (70/30)	1.22
Molybdenum	1.299
Silicon (pure)	1.457
Silicon (0.0025 W-cm)	1.457
Beryllia (97%)	1.575
Magnesium	1.575
Beryllium	1.772
Beryllia (99.5%)	1.969
Tungsten	1.969
Aluminum	2.165
Gold	2.913
Copper	3.937
Silver	4.173
Diamond (room temp)	6.299


Yes, Millermods is right, keeping the Artic Silver Thermal Epoxy absolutely as thin as possible is quite important, due to it's high thermal resistance.


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## Kinnza (Nov 19, 2006)

Hey Newbie, any idea of thermal conductivity and emissivity of Barium Sulphate (BaSO4)? I was looking for it, but i cant find it:scowl: 

Im working in a mix of Barium Sulphate with latex flat white paint to paint reflectors, its a very reflective mix (over 96%, near 98-99% between 430 and 650nm) and cheap, with pure lambertian reflexion. Ive found the fusion point of BaSO4 over 1500ºC, but not thermal properties. Im worry about penalizing thermal conductivity and emissivity by covering with BASO4.

Any thoughs about are much apreciated.


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## MillerMods (Nov 19, 2006)

Newbie, I stand corrected.

My memory didn't serve me too well in what I had remembered finding when I researched thermal epoxies, but now I remember that certain types of stainless steel is the closest metal in terms of thermal conductivity to Artic Silver. Although stainless steel (14.6 W/m·°C) is still a better conductor thermally, the Arctic Silver epoxy (7.5 W/m·°C) is the best that I know of and is much better than the thermal epoxy called out on the list. 

321 stainless is almost 2 times better than Silver Epoxy, but in short distances, with enough surface area of the Arctic Silver bonding to a good thermal conductor such as aluminium, it's an amazing product. I've been unable to find any thermal epoxy that beats it's performance.


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## NewBie (Nov 19, 2006)

MillerMods said:


> Newbie, I stand corrected.
> 
> My memory didn't serve me too well in what I had remembered finding when I researched thermal epoxies




Hey, no sweat.

The more common metals we use, in reference to 7.5 of the Artic Silver epoxy: 

Titanium 21.9
Stainless Steel (321) 14.6
Stainless Steel (410) 24
Steel(low carbon) 66.9
Aluminum 216.5
Copper 393.7


Of course, they all pale in comparison to heatpipes. Wonderful critters for spreading heat out, or moving it from point A to B. Note they use Thermal Resistance instead of Thermal Conductivity:
http://www.acktechnology.com/Heat Pipe.htm
http://www.avc.com.tw/products/nb-thermal/66.htm

Local reps for AVC can be found here (and many of them don't know they sell heatpipes):
http://www.avcamerica.com/Sale/index.htm


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## MillerMods (Nov 19, 2006)

BTW Newbie, thanks for all the great research, pictures, and charts. You've taken the time to provide data that many of us have been curious about. Your posts are great references for Cree based flashlight designs.


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## NewBie (Nov 19, 2006)

You are most welcome MillerMods.

And Thank you.


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## Erasmus (Nov 20, 2006)

Great post indeed. Cheers to everyone who made a contribution to this post, it's a good overview when you start modding with these LEDs. Right now I'm going to try the trick of removing the 4 corners to I can put the Cree into my L2P with some adhesive thermal paste.

[Edit] works great


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## MillerMods (Nov 20, 2006)

Erasmus said:


> Great post indeed. Cheers to everyone who made a contribution to this post, it's a good overview when you start modding with these LEDs. Right now I'm going to try the trick of removing the 4 corners to I can put the Cree into my L2P with some adhesive thermal paste.
> 
> [Edit] works great



You'll also need to modify an IMS 20 reflector to fit the L2P and the Cree. Otherwise it may be possible to modify the stock Fenix reflector.


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## Kryosphinx (Nov 20, 2006)

MillerMods said:


> You'll also need to modify an IMS 20 reflector to fit the L2P and the Cree. Otherwise it may be possible to modify the stock Fenix reflector.



Actually, it's the IMS 17. the 20 is too big. The stock fenix reflector is moddable, but a huge PITA.


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## mosport (Nov 21, 2006)

I cut the corners too close on my first XRE and needed to find another way to connect the wires, so I made some tabs to move the hook up points over to the side. Combined this with soldered copper rectangle cut from a sanded penny to raise it up slightly, now a non-conductive reflector can sit directly over the top pads.


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## NewBie (Nov 21, 2006)

Kinnza said:


> Hey Newbie, any idea of thermal conductivity and emissivity of Barium Sulphate (BaSO4)? I was looking for it, but i cant find it:scowl:
> 
> Im working in a mix of Barium Sulphate with latex flat white paint to paint reflectors, its a very reflective mix (over 96%, near 98-99% between 430 and 650nm) and cheap, with pure lambertian reflexion. Ive found the fusion point of BaSO4 over 1500ºC, but not thermal properties. Im worry about penalizing thermal conductivity and emissivity by covering with BASO4.
> 
> Any thoughs about are much apreciated.




Ultra pure Barium Sulphate has high reflectivity, it is often used for reflectance standards and for coating the insides of integrating spheres. Usually they do multilayer emulsion (like 13-20 coats), as it doesn't do very well mixed into normal paints, especially when the paints have cheap fillers like calcium compounds and zinc oxide.

Thermal emissivity:
Barium Sulphate with Polyvinyl Alcohol 0.88 

So, like many white materials, it not only emits IR well, it also reflects IR pretty decent. Carbon black emits well and absorbs well.

KoolKote and other highly Titanium Dioxide laden paints often have thermal emissivities in the 94% range.

Highly polished aluminum usually has a thermal emissivity of only 3.9-5.7%
However, black anodize is in the 80's, and just chromated is in the 55% range. These numbers can vary, depending on the process utilized.

I don't see the thermal conductivity either.


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## Kinnza (Nov 21, 2006)

Thanks a lot, Newbie:thanks: 

Im still unable to find it, but at less i know it has a decent conductivity, ive found Barium sulphate mixed with elastomeres in electronic coatings, and its description always include a "good thermal transfer" for no flamable coatings.

Ive thought in mixing it with Titanium Dioxide paint, so it might work pretty well.

With latex, the 88% figure of BaSO4+Polyvinyl Alcohol must be a good refference. Is more than i expected :rock: . Now, i have no fear on penalizing too much thermal transfer or emissivity from using it.


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## MillerMods (Nov 21, 2006)

Kryosphinx said:


> Actually, it's the IMS 17. the 20 is too big. The stock fenix reflector is moddable, but a huge PITA.



The IMS 20 will fit with trimming but it's a real pain too. You lose about 2mm of depth but it still throws very far with the Cree.


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## Morelite (Nov 21, 2006)

mosport said:


> I cut the corners too close on my first XRE and needed to find another way to connect the wires, so I made some tabs to move the hook up points over to the side. Combined this with soldered copper rectangle cut from a sanded penny to raise it up slightly, now a non-conductive reflector can sit directly over the top pads.


 
I'm not sure how that is going to work with the corners cut off. The bottom pads will no longer be connected to the LED die. Your tabs will still need to be soldered somehow to the top pads for current to travel to the die.


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## mosport (Nov 22, 2006)

True Morelite, as-is there would need to be a solder connection to the top pads. I clipped off too much material so there is not much top pad remaining, but if the corners were intact this would be workable.


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