Hello! so I recently bought some bare xhp50.2 leds from lht flashlightstore(kaidomain of aliexpress). I mounted them on an mcpcb put them in a flashlight. They were both fine up to 3amps, but once I put about 5amps through them, they both failed, burned out. So is it essential to use a good mcpcb? I think the problem is that the board is not good enough at cooling more than 3 amps. So it seems I need better cooling is that right? I hear these new xhp50.2 should handle 10 amps fine. I bought the xhp70.2 from the same place and that seems fine at well over 7 amps. What do you guys think about this? Thanks!
What kind of MPCB did you use? How did you reflow the led to the MPCB, How did you mount the MPCB to the heatsink?
cheap chinese copper board just the usual ones, reflowed it using a small butanetorch heating the board from bottom. Mounted it in an ultrafire u-f19 similar to courui d07. Mounted it with screws and arctic silver mx4
Maybe there was too little solder between the led and the MPCB, have you tried reflowing in an electric skillet? It is way easier and less prone to over heat or under heat, I learned about the electric skillet method from AdventureSportFlashlights video here…
I think you need DTP copper board for 5A with XHP50.
yeah, probably! Well... lesson learned I guess haha
Also if you have XHP50 and 70 you should slowly heat and cool the LEDs
Cree specifies 1.2°C per second above 170°C
so if you do a reflow get something as base you heat up slowly
Fast reflows with gas burner on the star are reported to die way too early
especially XHP50.2 and XPG3 seem to be critical with separation of the flip chip if handled not well
if on a non DTP the LED gets over 150°C on the die it gets damaged pretty fast
yeah could be, I've resoldered using a butane torch many times and never had a problem but who knows, maybe I overheated it in the flowing process? Thanks for the tip!
Do you know if it can survive 5A in the first place on non DTP?
oh I see well, better buy one already mounted on a board then? How about kdlight boards any good? suppose to be dtp copper, looks thick too
overheat is of course the dangeroust thing to do doing a reflow , so the LED die solder also gets liquid
I am telling about thermal shock with gas torch heating the star within 10 seconds or so
a good reflow should take a few minutes heat up slowly
with the LED already on the star, never put a cold LED on a hot star
then let it cool slowly
This exactly the answers I was looking for thank you so much guys! Very helpful!
never even thought about that haha. Well lesson learned, you learn something new everyday. Just sucks I wasted 20bucks ruining the ledsboh well...Thanks!
I would consider 3A the top current on a standard copper non DTP star
It depends if they use a thick or better very thin dielectric if you can go to 5A
Usually I would say on a XML2 Footprint better go DTP above 10W, the LED also gets more light out if it stays cooler
Yeah that sounds about right! Do you know if the kdlight boards are any good sold on lht flashlightstore and on kaidlmain?
The KD DTP-boards perform very well, just care must taken not to reflow or solder too hot because the layers tend to delaminate at (excessive) high temperatures. But that was not good for the leds anyway 
I ordered an already re-flowed xhp50.2 from mtn and it worked perfectly on arrival. But in testing, I hit it with the leads from a 2x18650 holder loaded with two protected tenergy 18650’s in series (limited to 5a each I think), thinking the protection circuits would save me from hurting anything. After three or so 1 second tests just to see if the led lit up, only half of the dies light up now.
My point is, like Lexel said, I think some of these newer Cree’s can be fragile and less noob-proof than previous ones. I have a bunch of xp-g2’s, xm-l2’s, xp-l’s etc that I’ve never had this problem with except one xm-l2 that was more than likely user error.
As well, I installed an xp-l2 from kaidomain that I reflowed on noctigon myself in a convoy l2, and during the process it was also direct driven by a protected tenergy a handful of times. Now the hotspot has a noticeably bluer color in about one quarter of the beam, but the entire die lites up and the phosphor looks normal to me. I haven’t tried to dome-slice it and I doubt it’s physically damaged, but it just seems to have crapped out for some reason, and I haven’t had this problem before. Far from an expert modder, but it’s something to consider if you’re a non-expert like myself.