Now you just have to learn how to reflow from the aluminum board to the copper one. Yet another place we’ve all wasted a few LEDs.
What tint are you looking for?
Well I guess that’s why I’m getting 4.1A now 
is 4.1A with a U2 going to be noticeably brighter than a U3 at 3.2A though?
Tint doesn’t really worry me, as long as it isn’t blue like you get with cheap aliexpress lights 
Yeah I’ve already wrecked one, I don’t have any solder paste which doesn’t help!
Meh. Probably not really. You need big differences in output to notice it. But ~3Amps on an XM-L2 U2 is actually sustainable for a little while since it doesn’t start below the minimum input voltage for regulation. ~3Amps on your XM-L2 U3 is with the driver already out of regulation - therefore it will fall continuously. That’s why I’d want the lower Vf part.
Solder paste does help but before I had that it helped to pretin the mcpcb pads and use the same method, heat it up until the led slides into place. Practice on the dead one. The copper mcpcb will take more heat than the aluminum one to reflow.
Well based on that I think I’ll drive a XM-L2 U2 at 4.2A in one C8 and put a U3 in my other (2.8A) C8.
No, that’s just flux. Solder paste is gray. It has has tiny tiny balls of solder mixed with flux.
If you’re in the usa RMM / mtnelectronics.com has solder paste and ships fast. Fasttech also carries it.
There’s rosin(a type of flux), solder, and solder paste. The paste is a mix of flux and ground solder. That link is for flux and is what is used with wire solder.
FT solder paste http://www.fasttech.com/products/0/10003546/1261003-chips-repair-tool-soldering-paste-grease
I use kester but there are plenty of other options that I don’t have experience with.
Right thanks, so that Fasttech stuff will work well for reflowing?
Is solder paste better than solder for reflowing?
It should work fine, but not having it in a syringe is a pain and will guarantee a lot of extra effort.
This is the exact product which I use: Kester EP256 Solder Paste, No-Clean 63/37, Syringe Dispenser
Sorry, I forgot that the conversation was about reflowing emitters, not drivers. The little tub is probably OK for that. I have trouble getting the right mount of solder on the pads, even using a stencil (Any interest in a CREE LED solder paste stencil?), it doesn’t matter whether it comes out of a syringe or a tub in that case.
Before I started using solder paste and stencils for emitters I often ended up pre tinning the star pads and sanding off the excess as it was very difficult for me to get the right amount of wire solder in place. Still, most members into modding have most likely done more of this more frequently than I so I remain somewhat unskilled at this. I like stencils and paste.
Looks like this will do the job then? http://www.mtnelectronics.com/index.php?route=product/product&path=25_91&product_id=255
Sounds like yes.
After a recent scare with our 30 month old having elevated lead levels after a test I’ve switched to Pb-free, both solder and solder paste.
Currently I’m using Kester NXG1 paste but I wasnt satisfied with how it flowed once heated nor how it dispensed so I got it all out of the syringe and mixed it about 10:1 (just a guess, not measured) with kester liquid no-clean flux and shoved it back down in the syringe (a hell of a job) and now I’m pretty happy with it, tho there was a new learning curve where I was having some fit’s with it. Its surprisingly easy to get it to stick to pin’s, getting it to adhere to the pad’s is a little more of a job than lead solder. If I was using bottom heat it would probably be the other way around (I’m using hot air).
Thanks very much for all the help guys! I will get some of that fasttech stuff and try that… I’ll just be careful not to get lead poisining