ok, is it ok to use regular solder instead of paste?
You think heating with a mini torch is too much? What do you suggest? A small hotplate?
So reflowing badly could cause premature failure? But why did it work for a few weeks fine?
Could I reflow using a cloth iron? Do I need solder paste or can I melt solder on to the board first?
paste or solder wire makes no difference, just make sure enough is below the LED and it bounces, then give the LED a tap to push out too much solder
if you use a small torch that’s OK, but you need to add some mass to heat up slowly like a small plate of aluminum 7x7cm 6mm thick turned out OK for me before I bought a temperature controlled heat plate
best also check temperature with an IR thermometer, so you see how fast temperature is rising and you don’t overheat the LED
how about torch directly under board ? That's what I did. How about using a cloths iron?
A method to kill or badly damage the XHP70 LED in 100% of the cases
The thermal stress on this big LED is way too much if you heat the star with a torch
If you heat the LED up slowly to 200dC within 2-3 minutes and let it cool down slowly the same time, this wont hurt the LED
And never put a cold LED on a hot star
Never tried a cloth iron. I made a heatblock from two heating-elements made for 3D-printers, and a block of aluminium (link).
You can melt some common solder on the board, but you will have to pre-tin the led as well, or at least put flux on the pads. Using solder paste makes life way easier though…
I use a hot reflow station. Initially, I thought the expense would be a waste. After reflowing my first LED I was sold! It literally takes seconds. 100% temperature control (you can use a lot less heat with hot air) and you just add enough flux and paste.
edit: you can also pre-tin with an iron and then use hot air/flux. I recommend Louis Rossmann and similar youtube channels. They do this kind of work every day and their techniques can be helpful.
Yeah, I've seen those too, might be on my list to buy aswell...
7A at 6v or 12v?
If it was at 12v then no wonder it burned up, you need a proper CPU heatsink with fan to cool that.
A Thorfire S70 uses 2 - 26650’s
6v, yeah 12v would be insane at 7amps haha.
yes i know, I use liitokala 26650's
my educated guess is your hard to control mini torch greatly exceeded the safe heating rate and peak temp the led can take and damaged it.
while none of the accepted methods we often use in the forums are 100% correct in reflow temp profile the torch is the worst.
and any solder voids in the thermal pad are deadly.overheating can also damage the die attachment to the ceramic base.
a failure here causes a near instant burnup.
Yeah it was dumb of me to do. I wonder why it worked fine for a few weeks though? Maybe it worked fine but had some unvisible damage that lead to failure? Could I reflow using a cloth iron next time? That seems to work too?
if you can use a ir thermometer or better yet a thermocouple meter yes.
set the peak temp via its control.start cold with the paste applied and the led placed.
when everything is showing correct like in the video just pull the plug and let it cool.
I dont see any problem in your heating device (torch).
If you dont want to buy prof equipment, you can use it this way:
-take a flat piece of metall (block). (see djozz link)
-buy cheap 300 degree C thermometer from ebay. Mount it on block near pcb place.
-found out proper position for led star and torch flame to folow requirements that are mensioned by Lexel in every second thread (nothing bad IMO).
Important:
You need to use good (good condition, not old, not laying several years, never heaten over 40 deg C etc) solder paste. It has lower soldering temperature than most usual wire solder. With right temperature raise curve, you will have lots of time to see how it is melting due process. After some practice, you wont need to check temperature. Surface structure of solder paste will say you what it going on right now and you will aprox know how much extra time you need.
If you cant see solder paste around led, you can always put same paste on wire pads and use them as indicator.
I tried the cloth iron and works good. i also have a thermal coupler.
Modern cloth irons are too delicate. It is hard to get them hotter than 200 degrees.
well I tried and it works to reflow the led just fine!