# Reflow Soldering MC-E



## kuksul08 (Jan 31, 2010)

I am going to be soldering a an MC-E to a parallel star board soon, and I set up this little temperature adjustable 'hot plate'. It's just bigger than the star board. I can dial in the temp of the soldering iron so it just melts the solder. I know it's weak haha...









My question is - should I put solder between the board and the center of the LED (where the heat goes through)? I did this before using thermal paste. I heated it up, melted the solder onto all the electrical pads, then dropped the emitter on. It's been working fine.. but who knows how well that paste works.






Thanks


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## J_C (Jan 31, 2010)

If you're not going to use solder, I don't see the point of using the heat plate instead of soldering the pins with an iron. Am I missing something (getting late at night...)?

I do know you can't effectively solder the heatsink on LEDs with aluminum backplates, at least not with regular solder as it won't cut the oxide layer.


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## kuksul08 (Jan 31, 2010)

J_C said:


> If you're not going to use solder, I don't see the point of using the heat plate instead of soldering the pins with an iron. Am I missing something (getting late at night...)?
> 
> I do know you can't effectively solder the heatsink on LEDs with aluminum backplates, at least not with regular solder as it won't cut the oxide layer.



Okay, and the MC-E has an aluminum backplate? That makes sense. I need to figure out how to solder these leads individually.


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## J_C (Feb 1, 2010)

I don't remember what metal the backplate is, I just recalled that issue with a different LED.

Soldering individually shouldn't be hard, especially with solder paste you can just drag the iron, even with a huge tip, across the leads. If you have no paste, putting some flux down and dragging a pre-tinned tip across would also, usually suffice. If you have neither, are only going to use solder with flux in it, you'll probably need a finer tip/finer-iron/whichever.


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## bshanahan14rulz (Feb 1, 2010)

JC, if you can solder the thermal pad, solder it. I don't see any reason why you wouldn't be able to, since the thermal pad was designed to be soldered down anyways...

Thermal greases and adhesives are for those who aren't able to solder to the star, reasons like soldering iron isn't powerful enough, don't know how to, etc.

Basically tin the entire surface of the solder pads with as little solder as possible, float the emitter on there, push down on it (not on the dome, only on the black part, and not hard, just hard enough to squeeze out the excess melted solder. LED will be hot!) and let it cool. Once cool enough, you can release pressure.


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## mudman cj (Feb 1, 2010)

bshanahan14rulz said:


> JC, if you can solder the thermal pad, solder it. I don't see any reason why you wouldn't be able to, since the thermal pad was designed to be soldered down anyways...
> 
> Thermal greases and adhesives are for those who aren't able to solder to the star, reasons like soldering iron isn't powerful enough, don't know how to, etc.
> 
> Basically tin the entire surface of the solder pads with as little solder as possible, float the emitter on there, push down on it (not on the dome, only on the black part, and not hard, just hard enough to squeeze out the excess melted solder. LED will be hot!) and let it cool. Once cool enough, you can release pressure.



+1 for the reason that solder will provide a better thermal path than paste or epoxy at the same thickness. Plus, if you have a setup to reflow solder, it's easier to just do all of the connections at the same time.


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## kuksul08 (Feb 1, 2010)

okay, so I bought some solder paste. If I understand this correctly, I should apply it thin and evenly to both the electrical contacts as well as the center thermal path.

Then should I:

a) Set the emitter on the paste, then heat everything up until it flows, or 
b) Allow the solder to flow then set the emitter on the molten solder?

I want to do this as right as I can with what I have


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## bshanahan14rulz (Feb 1, 2010)

I would say allow the solder to flow first, then drop the emitter on there, give it a second, maybe two, to reflow (when you drop the emitter on there, it may solidify the solder on contact for a short time), then remove heat and cool down. I push down on my emitters, but that's just increasing the chance that I'll knock off a dome or something..


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## J_C (Feb 1, 2010)

^ I second that, no need to expose LED to high temp while you wait for the other part to heat up, especially if/when it's not a tightly temperature controlled scenario.


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## kuksul08 (Feb 1, 2010)

Cool thanks!! I'll update this thread with how it goes, my procedure and all for future reference.


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## Linger (Feb 1, 2010)

Dissenting view - dropping a 'cool' emitter on the melted solder isn't going to create the proper bond.

After pre-cleaning all appropriate parts
Add a swabbing of paste on all contact pads (the electrical + slug), the barest minimum that, when melted, would 'tin' the entire pad area. (you can test this with-out emitters)
Precisely place emitter on top of pads. It will be resting up slightly on the small particles in the solder paste (but to the untrained eye should almost look like it is already fixed in place)
Heat applied under the star with your iron, and when solder liquefies you will see the emitter sucked down and in and settle all by itself. Capillary action between pads on star and emitter. The tiniest bit of solder will weep out the side of emitter, remove heat.


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## mudman cj (Feb 1, 2010)

I will side with Linger on this one. I use this method with great success, and can't imagine dropping the LED in just the right spot for it to go well. If you preheat the assembly as per the datasheet by placing a piece of metal on your high temp heating surface (I use a socket with a small square of sheet metal on top of it), you can get this second surface to the right temperature (in my case by selecting the proper socket size) for the preheating step. Then, the actual high temperature phase of the soldering takes only a few seconds and no harm done to the emitter.


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## J_C (Feb 1, 2010)

It'll create the proper bond because the thermal capacity of the LED is so small, a couple seconds after dropping it on it will have been brought up to the melting point of the solder. I would spear a dab of paste on the bottom of the LED too, just in case heating the star makes the flux flow off to the side of the solder pad.


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## usLEDsupply (Feb 1, 2010)

Cree recommends a warm up and cool down rate but I think even without fancy controls you could get close just by using a timer


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## kuksul08 (Feb 1, 2010)

That picture is too small, I can't read the text^^ 

lol


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## J_C (Feb 1, 2010)

mudman cj said:


> I will side with Linger on this one. I use this method with great success, and can't imagine dropping the LED in just the right spot for it to go well. If you preheat the assembly as per the datasheet by placing a piece of metal on your high temp heating surface (I use a socket with a small square of sheet metal on top of it), you can get this second surface to the right temperature (in my case by selecting the proper socket size) for the preheating step. Then, the actual high temperature phase of the soldering takes only a few seconds and no harm done to the emitter.



The LED will center itself, the solder pulls it into position. The issue with what you describe is no matter what control you have of the heating surface temperature, this will result in variable temperature of the solder depending on what you are reflowing. I suppose you could use an infrared thermometer to determine that, but it starts getting more and more elaborate and complex than necessary to just do an LED or two.


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## Illum (Feb 1, 2010)

Now its much too large... 1836px × 2109px violates the 800px x 800px forum rule


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## kuksul08 (Feb 1, 2010)

Illum said:


> Now its much too large... 1836px × 2109px violates the 800px x 800px forum rule



:laughing: Yeah it always was. (previous sarcasm)


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## usLEDsupply (Feb 1, 2010)

is this better? i sized it for your iphone


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## Linger (Feb 2, 2010)

J_C said:


> this will result in variable temperature of the solder depending on what you are reflowing.



Hrm? I use digital 80watt soldering station (which is only important to say I can turn up the heat by each degree as I feel fit)

I was taught this method by a very very popular CPF builder/seller. I've used it for singles, doubles, and triples. With a 20mm triple star, temp rises and the flux above my iron is activated (begins vapourizing), the heat spreads remarkably evenly and I only need shift the iron a little bringing the tip under each emitter for the flux to activate the solder to liquify and the emiter to be sucked down into place. I let it sit a second or to while looking that all seems are flush before adjusting the tip slightly to center it under the next emitter. Less then a minute (40s? in truth I haven't timed it) from room temp start to heating to triple finished.


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## kuksul08 (Feb 2, 2010)

Hmm, a lot to take in...


Who knows what the black surface is in the first picture?


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## mudman cj (Feb 2, 2010)

J_C said:


> The LED will center itself, the solder pulls it into position. The issue with what you describe is no matter what control you have of the heating surface temperature, this will result in variable temperature of the solder depending on what you are reflowing. I suppose you could use an infrared thermometer to determine that, but it starts getting more and more elaborate and complex than necessary to just do an LED or two.



I have had XP-E packages self-align very well, but the heavier MC-E does not move as freely. Hey, I'm not saying dropping the LED onto the MCPCB won't work or can't be done; I just want the OP to be aware of their options. Again I have to side with Linger in having difficulty understanding your point about controlling the temperature of the solder. Either method under discussion would have the same solder melting temperature. The difference is that the method I described adds a second, lower temperature surface for preheating the emitter as shown in the graph that is posted above.


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## bshanahan14rulz (Feb 2, 2010)

mudman cj said:


> The difference is that the method I described adds a second, lower temperature surface for preheating the emitter as shown in the graph that is posted above.



Ah, I misunderstood you I think. Yes, it is always best to follow the manufacturer's suggested soldering times.


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## kuksul08 (Feb 16, 2010)

*UPDATE:*

I followed your guys' instructions and attempted to reflow solder the MC-E for the first time just now. I will try to list exactly my steps so someone can follow them in the future.

1. First I bought the bare LED emitter, star boards, and solder paste. I used:
-MC-E M bin from digikey, http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MCE4WT-A2-0000-000M01CT-ND
-individual star boards from DX, http://www.dealextreme.com/details.dx/sku.16545
-Mechanic solder paste from DX, http://www.dealextreme.com/details.dx/sku.7952

2. Then I waited a long time 

3. I used a small straight-slot screwdriver to carefully spread the solder paste onto all the pads like this. I tried to keep it on the designated pad (not touching eachother) and a relatively thin layer. I also applied a very very thin layer to the bottom of the emitter thermal pad to ensure it adheres properly.






4. Then I carefully placed the emitter on the board and pressed down gently, so the paste squeezed out a little bit, making sure the chamfer on the LED was facing the positive terminals.





5. I prepared this piece of aluminum with thermal paste on it, so I could place the emitter/board on it to cool quickly after the heating process





6. I used a little piece of 1/16" aluminum atop my space shuttle tile (insulating material) and touched my soldering iron to it. There is some solder in between to help conduct the heat.





7. I placed the board on and watched carefully. After about 15 seconds, the paste started moving, then suddenly it all liquified. The emitter was sucked down onto the board and centered itself perfectly. Excess solder from underneath flowed out of the side and formed balls. I removed the soldering iron, and moved the emitter/board to the heatsink and began blowing on it to cool it down.

8. That was that. It looks really good, and all the connections are solid. The little balls of solder were removed easily.











I hope this helps someone!! Thanks for the help so I could do it!


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## J_C (Feb 17, 2010)

Good to see it turned out well, it looks good.

One caution though, be careful moving the assembly to the heatsink, be sure the solder has solidified before doing so as movement can upset the alignment and (especially if the solder is non-eutectic) cause fractured solder joints if it is still in a molten state when being moved manually.

I've even had Cree XR-E LEDs that became intermittent on the LED die-module (factory integrated PCB baseplate) from an intermittent joint, but I wasn't following best practices at the time, had been soldering a wire to that PCB baseplate itself instead of using a star and had to go back and reflow one side again to restore the factory solder connection.


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## kuksul08 (Feb 17, 2010)

J_C said:


> Good to see it turned out well, it looks good.
> 
> One caution though, be careful moving the assembly to the heatsink, be sure the solder has solidified before doing so as movement can upset the alignment and (especially if the solder is non-eutectic) cause fractured solder joints if it is still in a molten state when being moved manually.
> 
> I've even had Cree XR-E LEDs that became intermittent on the LED die-module (factory integrated PCB baseplate) from an intermittent joint, but I wasn't following best practices at the time, had been soldering a wire to that PCB baseplate itself instead of using a star and had to go back and reflow one side again to restore the factory solder connection.



Yes, I worry about upsetting the solder as it is still cooling. I made sure to remove heat, then wait a moment before moving it. The surface tension (?) of the solder does a good job of holding the LED in position either way.

I wanted to cool it down quickly so the emitter didn't sit there at such a high temperature for so long, it can't be very good for it.


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## VanIsleDSM (Feb 17, 2010)

We shouldn't be trying to heat and cool the LED so quickly.

Thermal shock is what will kill the LED during reflow soldering, from being heated too quickly, that's why CREE recommends a maximum of 3C/s on warmup, and 6C/s on cool down.

It should take a minimum of 2 minutes to get to the point where solder melts, 6 minutes max. Don't rush this step, the part needs to be heated gradually.

Same goes for cooling, moving the emitter and star to a heatsink after the solder melts is not what you want to do, you want it to cool gradually as well.

Just look at the datasheet and try to simulate the relflow table already posted.


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## trout (Feb 17, 2010)

Here is a little video of a heat gun set up I used to replace some xpes 

watch carefully at 4.30 and you can see the leds self align as the solder melts .

http://www.youtube.com/watch?v=NN3tXzrJUE0


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## mudman cj (Feb 17, 2010)

VanIsleDSM said:


> We shouldn't be trying to heat and cool the LED so quickly.
> 
> Thermal shock is what will kill the LED during reflow soldering, from being heated too quickly, that's why CREE recommends a maximum of 3C/s on warmup, and 6C/s on cool down.
> 
> ...



I always set the just-soldered assembly onto a piece of glass to cool slowly. It will still cool rather quickly from the danger zone that damages the LED die while reducing the thermal shock, though I can't say that it complies with the 6C/min specification because I haven't measured it.


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## kuksul08 (Feb 17, 2010)

VanIsleDSM said:


> We shouldn't be trying to heat and cool the LED so quickly.
> 
> Thermal shock is what will kill the LED during reflow soldering, from being heated too quickly, that's why CREE recommends a maximum of 3C/s on warmup, and 6C/s on cool down.
> 
> ...



I can see how the rapid heating and cooling could be bad for it. If you go at 3C/s warm-up though, then it should take about 1 minute to get to the melting point of the solder.


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## HarryN (Feb 17, 2010)

Hi, thanks for all of the posts and pics on reflow soldering. I am following this as I have some SMT LEDs that need to be reflowed as well. It is quite an interesting, and remarkably simple concept.

Just an FYI, if the goal is just to get some premium MC-Es on a star board, I ordered some from etgtech, and they mounted them on a star board for me for 50 cents. I had them in about 1 week. Unfortunately, I decided to use a different LED for this project, so they are still sitting in a box with no good home.


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## kuksul08 (Feb 17, 2010)

HarryN said:


> Hi, thanks for all of the posts and pics on reflow soldering. I am following this as I have some SMT LEDs that need to be reflowed as well. It is quite an interesting, and remarkably simple concept.
> 
> Just an FYI, if the goal is just to get some premium MC-Es on a star board, I ordered some from etgtech, and they mounted them on a star board for me for 50 cents. I had them in about 1 week. Unfortunately, I decided to use a different LED for this project, so they are still sitting in a box with no good home.



I looked on their site and don't see where to actually buy them?

The goal was partially to get a premium MC-E on a star board, but it's also fun learning about the process. I can only learn so much by reading stuff online. When you actually do it yourself, a lot of other questions arise, so you learn more.


In the future if I were to do this again, I would do the same thing, except move it to a smaller heatsink afterward, with no thermal paste. Everything else seemed to work great. I tested the LED and all 4 dies function.


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## Linger (Feb 18, 2010)

Glad you gave it a go.
It _is_ fun, isn't it? The moment the emitter is sucked down into place is so gratifying, nothing like a perfectly centered emitter to make you feel you've really up'ed your game.

Before you do too many more, consider a practice with a bit of wire and on a board - maybe start with 1/2 as much paste and work down. I'd like you to get a feel for how much of the solder paste is flux and how much joint remains after cooling. Using too much paste could compromise electrical isolation and may bridge an unwanted connection.


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## kuksul08 (Feb 18, 2010)

Linger said:


> Glad you gave it a go.
> It _is_ fun, isn't it? The moment the emitter is sucked down into place is so gratifying, nothing like a perfectly centered emitter to make you feel you've really up'ed your game.
> 
> Before you do too many more, consider a practice with a bit of wire and on a board - maybe start with 1/2 as much paste and work down. I'd like you to get a feel for how much of the solder paste is flux and how much joint remains after cooling. Using too much paste could compromise electrical isolation and may bridge an unwanted connection.



Haha yes, quite gratifying. I experimented with the paste a little bit on an old star board before doing it to a good emitter. It seems about half of the paste is flux. I was surprised how much it flattened out once the flux separated.

It was strange on the MC-E how the excess solder was squeezed out and formed those balls. There's no way to tell what it looks like underneath the emitter, but as it sits there is no electrical continuity between the heatsink and electrical contacts.


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## HarryN (Feb 18, 2010)

kuksul08 said:


> I looked on their site and don't see where to actually buy them?
> 
> .



Hi - it is not listed, I found out when I was talking to them. I have a couple if you want them - I will send a PM.

Harry


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## blesbok (Feb 19, 2010)

Just adding my DIY reflow experience to the mix.... I first tried the toaster oven approach, but couldn't consistently get the ramp rate and dwell right. I now heat the boards by holding them with pliers or tongs a few inches over an electric range on med high. I tack a thermocouple to an unused pad near the LED using high temp solder, so it will stay in place during reflow, and modulate the heat by moving the board closer or further from the burner. Works well every time for single and multi emitter boards.


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## sigsour (Feb 19, 2010)

Keep in mind that the profile is more or less for the paste and not for the LED. The soak zone is for the paste to get rid of certain volatiles and to begin the activation of the flux. When anyone receives the solder paste be sure to stir it up for 30 seconds or so for everything to be mixed properly. Also remember that is very critical to stay in liquidous state for at least 45 to 60 seconds so no cold solder is formed. The maximum temperature is what needs to be monitored for the LED but most SMT devices can withstand 225 C without any issues.


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## kuksul08 (Feb 19, 2010)

sigsour said:


> Keep in mind that the profile is more or less for the paste and not for the LED. The soak zone is for the paste to get rid of certain volatiles and to begin the activation of the flux. When anyone receives the solder paste be sure to stir it up for 30 seconds or so for everything to be mixed properly. Also remember that is very critical to stay in liquidous state for at least 45 to 60 seconds so no cold solder is formed. The maximum temperature is what needs to be monitored for the LED but most SMT devices can withstand 225 C without any issues.



45-60 seconds seems pretty excessive. The solder clearly liquified almost instantly. I gave it about 5 seconds to ensure the flux was removed and everything seated properly, but there's no doubt all the solder particles melted.


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## HarryN (Feb 19, 2010)

blesbok said:


> Just adding my DIY reflow experience to the mix.... I first tried the toaster oven approach, but couldn't consistently get the ramp rate and dwell right. I now heat the boards by holding them with pliers or tongs a few inches over an electric range on med high. I tack a thermocouple to an unused pad near the LED using high temp solder, so it will stay in place during reflow, and modulate the heat by moving the board closer or further from the burner. Works well every time for single and multi emitter boards.




Thanks for that useful insight. I was wondering about something like this, or the alternative - putting the board in an aluminum frying pan. Since my wife is probably slightly less excited about stove-top soldering, I was even wondering about doing it out on the gas gril.


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