Reflow Soldering MC-E

[kuksul08]

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 🙂

 

[J_C]

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.

 

[kuksul08]

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.

 

[J_C]

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.

 

[bshanahan14rulz]

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.

 

[mudman cj]

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.

 

[kuksul08]

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 🙂

 

[bshanahan14rulz]

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..

 

[J_C]

^ 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.

 

[kuksul08]

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

 

[Linger]

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.

 

[mudman cj]

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.

 

[J_C]

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.

 

[usLEDsupply]

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

 

[kuksul08]

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

lol

 

[J_C]

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.

 

[Illum]

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

 

[kuksul08]

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

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

 

[usLEDsupply]

is this better? i sized it for your iphone

 

[Linger]

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.