Nice tutorial with some good additions.
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But, doesn't adding the emitter to the hot board and "wet" solder shock the emitter? Unless it's sitting on the hot plate, warming up in time with the board itself, then getting picked up and placed, that would have it at or very near the same temperature as the board when placed, correct? Hmmmm......
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You are correct, and I omitted the preheat info. LED is placed at the far end of the plate, away from the direct heat source. While the preheat times are toward the lower end of recommended (ts min to ts max) the crucial temp and time guidelines (tl and tp) are largely followed.
I also keep the bare LEDs in a bag with silica gel to minimize moisture absorption. This has worked out so far, but I'm always open to suggestions on how to improve the process.
I don't know why everything is now in bold; I am posting this from an iPad, and cannot seem to remove the formatting. :)
Thanks ChicagoX, very interesting.
Your suggestions helped a BUNCH! 
While I don’t have the components to implement your procedure precisely, I did use the SS plate on a glass top stove for even heat dispersal. I also switched from the copper bearing solder paste I used before to silver bearing solder paste. And this time, after squeezing out the non-uniform mix that was nearest the tube end, I squeezed out some more to get the goods. It looked a bit thick so I added a little of the clear flux back into it to get a bit thinner mixture. Fed it onto the boards in a more minimalistic fashion, placed the boards on a pre-warmed plate, set the emitters atop them, (2 XP-G2, 2 Nichia 219…with one of these on a board cut down to 10mm pinsnneedlestime) And then turned the heat up to 6 on the control panel. The emitters sat atop a mix that started bubbling a bit, then set right down where they belong with no more assistance needed! The 10mm and 219 is the best one of the bunch! Relief, happiness, joy, joy.
I was worried about that slab of stainless holding the heat too long, even after moving it off the burner, so after about 15 seconds I placed the star boards on the glass top next to the burner I had used and let it pull heat from the stars a little faster. They all look great, very little spill out from under them, and even have a nice little showing of silver solder at the outlets on either side, for the most part…a couple don’t show any excess at all.
And now I get to hook up a 219 and see if it’s got the tint I hope it has, or I put the wrong emitter on the 10mm board!
Thanks very much for your explanation on this, it’s more scary than it is hard, one just has to proceed delicately!
seriously, you must be a bunch of closet manicurists - I can sand at least 1/2in of the end of each finger without noticing it
I just use the kitchen table, it’s flat enough for my purposes. Don’t forget the Mother’s Magic Aluminium polish step to get it nice’n’shiny!
I’m no expert on reflowing by any measure, but I have heard people saying that you shouldn’t cool the reflowed LED down too quickly for some reason, so it might be worth just moving it to the other end of the alu bar after the heat is removed, instead of putting it on a large cold lump of metal. I’m really not sure how critical cool down rate is for what we do (probably not very), but it might be worth thinking about.
Years ago I assisted my friend, the gunsmith, hand polishing guns. In those days, I had no fingerprints! lol
Ever sand the Tenifer finish off a Glock slide by hand? Tain’t easy! But the competition shooter I did it for was madly in love with his Glock19C with extended barrel after it was blued Colt Python Blue! Hand sanded my Caspian SS slide for my own Glock 23 to a mirror finish as well, sure made clean-up a breeze. Ahh, those were the days…used to go the the gravel pits with my buddy and help him sight in rifles, then play around at the various water holes in the pits trying to shoot dragon flies with handgun, from a snubby .357 to a handloaded .45 Long Colt putting out more energy than a .44 Mag. Those little buggers can move, let me tell you! lol (in fair disclosure, I only managed to hit one of those little daredevils twice)
But, I digress……
EDIT: No, not the same one! 
That's probably good advice.
Cree recommends a 6C/sec max cool down rate in the doc linked above.
I deliberately set the LED on the pad rotated a bit from where it should be... if it doesn't snap itself into place there's too much solder.
I've used a hotplate before, but most times just use a butane torch with the soldering adapter but no tip installed, so it's just hot air. No flame and no direct contact. Takes about 5-10 seconds with the torch held about an inch underneath the board.
First off, a belated thanks to ChicagoX for this post! Now a few noob questions...
1. Instead of heating to the star with solder paste separately from the LED, can you place the LED on the paste on the star and heat it all together until the paste flows? Or would that result in too much heat being applied to the LED?
2. What prevents the solder from flowing between the thermal base and the contact points, especially if the emitter is pressed down? Just the fact that there isn't enough solder to squeeze out and flow across? Actually, if it's pressed down it seems like it would prevent any solder from bridging the gaps.
3. Can I just use a hot plate? Maybe a dual one like this? One plate to heat the heatsink or star and the other to warm up the LED if it's not best to heat both together.
4. I was going to buy the Kester paste that was linked to in other threads. How long will that last in my fridge after use? I don't want to buy too much and end up only doing one reflow with it.
Thanks! I'm moving into a house in a month and I can't wait to have a flashlight workshop in the basement with lathe, drill press, soldering station, and reflow station :)
Hi Jonny,
I'm glad you found this thread to be of use. I'll try to answer your Qs, but hope that others with more experience will jump in as well.
1) Many do this very thing. I chose the other method, as I was still figuring out how much paste is "too much." If using appropriate amounts, there doesn't seem to be a reason to not go this route.
2) The solder mask helps out, as does the correct quantity of paste/solder.
3) Many here use a hot plate/hob to reflow.
4) I don't know, but given my usage, most of it will spoil before being used up. There is enough in the $20 syringe to do hundreds of LEDs (if not more!)
I can't wait to see your new setup !
I’m new at this too and have success reflowing XP-G2’s, Nichia 219’s and XM-L2’s onto copper SinkPADs by placing a 1/8” thick SS plate on top of the glass cooktop to ensure even heating and pre warming it a bit. Then I put the star/stars on the plate with paste applied with a needle and after they’re on the plate I carefully place the emitter on top of the paste. Then turn the heat back on to a 5 or 6 on our glass cooktop and watch closely. When the solder liquifies and the emitter settles I give it a few more seconds then slide the plate off the burner. After about 10 more seconds I remove the stars carefully to a 3” cube of 6061 to pull the heat off of em. This has worked without burning the white mask and with just a tiny bit of solder showing from under the emitters, so I wonder if I’m not using quite enough paste. But they’re working!
It’s really not that difficult, just have to be careful and watch em closely. And this is coming from the experience of only a few times, so I’m no expert to be sure.
Moving up next to stacking chips!
Good Luck!
Edit: Thought I’d add that I got my solder paste at Lowe’s for like $4.00! It’s made by Solder-It and is the Silver bearing version, works nicely even if it’s not the big name Kester or stored in the fridge. It’s a bit thick which makes it kinda difficult to get it spread onto the tiny copper strips with a needle so it might actually be a good idea to mix just a bit more flux into it. Although, once heated I’ve noticed that flux flows out onto the mask which has to be cleaned up after it cools so there appears to be plenty of flux present.
The tip of a ordinary flathead pocket screwdriver is about the perfect size/shape to apply the paste to the pads.
hey JonnyC, welcome to the BLF rabbit hole no. 3547 - reflowing your own LEDs! Good questions to ask and pretty simple to answer, much the same as above:
1) I put the star-paste-LED on the hob all together. They all stick together nicely so there’s less chance I’m going to drop something, plus the set up is more relaxing - you can figure out which way round it goes before heating things up to scorchio. It’s also possibly better for the LED as most reflow temperature profiles show a gradual heat and cool.
2) Solder mask. No metal = no solder. In fact, when you use paste (and really not very much of it either), it going liquid will actually suck the LED down onto the star in almost perfect alignment and squeeze the excess out of the side. You can then just pick it off with a toothpick.
3) I use my hob with old style ring burners. ChicagoX kindly pointed out that using a flat piece of aluminium will stop the stars accidentally falling through the rings into whatever lies below No. 3 or 4 on the dial works for me!
4) For commercial stuff, most say a year at 4C, but for what we do I wouldn’t worry. If it gets thick, just add flux to thin it down again. Afterall, it’s just flux and solder particles. You can even make your own with the cheesegrater, although the missus might be a bit unhappy with that next time she grates some nutmeg 
I still find it faintly terrifying, even though I’ve had a 100% success rate even with triples, but it really is very straightforward.
So absolutely true. There have been so many times where I was thinking of getting out of the game, then something else sucks me back in.
Thanks for all of the responses guys! It doesn't seem so scary now.
well, compared to fast cars and racy women, flashlights are a pretty cheap hobby (on BLF at least). That’s what I tell the wife anyway, just before she tells me to sleep on the sofa
Wow - totally missed this thread - thanx Chicago X for this. I'm another one with bleeding fingers (also finger tips numb by the way) - the drill/flat head screw/glue method looks outstanding. Have to study this thread more.
This is my idea of a good lapping station: 