For those that do not have solder paste you can tin the lads with wire solder and then slide it over a file to remove the excess, (almost back to bare copper) add flux and reflow. I’ve done this a number of times on single and triple boards and the LEDs snap to attention. The right amount of paste may be better but it can be done other ways successfully.
Thanks for all the help, guys!
I guess that I’ll be as well prepared as I can be by the time things arrive, the emitters and PCB from IS, and the Kester paste from Ebay, and a small butane torch from Ebay. Keep practicing till then, but I wish I had some PCBs with bare pads, because I think working with the ones where I removed the emitters is kind or cheating. Plus, that’s only one large XM-L, rather than 3 tiny XP-E2s.
FYI, if I get successful reflows, this is going into another el-cheapo S5 with a Qlite 3.04A IOS driver. That, 1000mA per emitter, should be about right (not overdriver, but right) for the XP-E2s, right?
I’m curious how this will work vs. an earlier Luxeon triple that I made!!
I like to do it anyhow as liquid (solder in this case) has surface tension, even when the led looks flat I tend to get just the slightest overflow on the polarity traces.
Also I havent damaged any leds, at least not with the naked eye, by pusing on the outer corners of the emitter base.
If you think cheating will help, then go ahead and reflow some junk emitters to the new board then remove them. I’m all for cheating Murphy.
Alas, I don’t have any junk XP-E/E2s or XP-G/G2s :(….
BTW, one other question: I’ve been assuming that I should reflow all 3 emitters simultaneously, rather than one at a time.
Is that correct?
I originally was thinking to use a small butane torch to do the reflow, holding it under the star, which was held in a vise.
The torch arrived today, so I was trying to practice with it tonight. Earlier (this past weekend), I had just been using a small torch-style lighter, which seemed to work ok, but it got really hot.
Anyway, here’s what I ended up with (two XM-L stars) 
:
Both of them burst into flames, and the result is above.
What did I do wrong?
It looks like there’s a think layer of plastic or something on top of the star that started burning.
Should I have had the star on top of some kind of metal plate and heated the plate from underneath with the toarch (I don’t have any metal plate, actually)?
Also, maybe my original idea, of just heating the star from underneath with the torch, is not viable?
Should I try the “reflow in a frying pan on top of a gas stove” instead?
EDIT: How’s about a cookie sheet on top of a gas stove? Would that work?
Reflow methods from best to not as best, IMO.
Reflow oven
Heat gun
Stove top
Soldering iron under star
Open flame torch
I tried a soldering iron (an Aoyue) under the star, and it never heated it up enough to remove the emitter :(…
So, maybe stove top would be my best best? That’s in a pan on top of the stove, right?
Soldering iron method is hard to rank because the effectiveness varies on the quality of the iron. I’d probably rank it ahead of the stove top method if the iron is a good, temp controlled unit. If the iron can’t get the star hot enough, then I guess it would rank last.
I use an old frying pan over a stove. I dunno about using a cookie sheet.
I tried again with a cheap 50W pen type iron, and was able to remove, then reflow the emitter a couple of times.
So then I tried the Aouyue again, and this time, set it to max, 480C, and was able to remove and reflow the emitter.
Both times, the star was clamped in a vise.
I’m thinking that I wasn’t patient enough the 1st time I tried it with the Aouyue iron this past weekend.
Is 480C too hot for this? The Kester solder past I have coming in is 183C solder past, so maybe the iron temperature should be lower for that, to do the reflow?
I think that this is the way I’ll try, as I feel a lot more in control than with the torch under the star approach.
It doesn’t take a large flame using a butane torch. If its adjustable (most are) set it to a low flame and keep the tip of the flame under the pcb. With a 20mm star it doesn’t take long or a hot torch to do the job. I find the torch easier to control and access than the stovetop method and I can clap the star in a vise and be seated and steadied more readily but that’s just me.
Do you think that the top layer burn and delaminate because the flame wasn’t “under” the PCB. I had the star in a vise, but was holding the torch at a kind of angle, pointing at the bottom of the star, to direct the flame towards the bottom of the star, so it’s possible that the entire flame wasn’t under the star.
Those look like mine did before I learned that I didn’t need so much heat. I have two small butane torches, one, a BernzOmatic and the other is a glorified lighter that tail stands and both are adjustable. as long as the traces haven’t become detached you can keep practicing with those boards but you should be able tI do it without even discoloring the solder mask just a little darkening from the flux that can be cleaned off.
When using an iron, I clamp my pcb in a vise-grip type C-clamp with leather glued to the clamp pads. That way the clamp isn’t stealing away your heat. I tin the pads and apply flux with a Kester flux pen to the tinning and the underside of the emitter.
Next, I crank up my iron to 840°F and hold it under the emitter using small circular motions. It takes no time at all. Use a fat tip for better heat.
The triple XP-G board I’m working on will already be attached to a copper slug, and because of the way I am trying to improve the thermal path on the aluminum PCB the LEDs will have to be left til last. I’m going to use PilotPPKs Method of floating the emitters into place.
I wouldn’t want you to think this method is better just available. If you can, once you’ve gotten comfortable with this method, try another that you have the equipment for and once you can do both then you can decide for yourself which works best for you.
Use the lowest temp it takes to melt the solder on the pads. Practice with your XML boards and try to get the solder to melt within a reasonable time. You don’t want to have the iron on there too long.
Another quick question: Do I put solder on the center pad(s)?
Also, I am still wondering if I should reflow all 3 emitters at the same time?
yeah, without solder it would transfer the heat horribly
What he said. The center pad is for conducting heat away from the diode junction and needs to be soldered. It’s not an electrical connection but a thermal one.