I would like to try my hand at reflowing emitters and I have some basic questions.
First, what method is recommended for occasional reflowing ? I have seen videos of people using a hot pan, soldering iron, BIC lighter, reflow station, heat gun, etc. It seems to me that a cheap heat gun would be ideal. Is that a good solution ?
Second, when you heat the MCPCB, do you heat it from the LED side or the bottom (for both removing and reflowing) ?
Third, what is an proper temperature for reflowing ?
Fourth, is there anything that I should watch out for when making my first attempt ?
I use the same exact method. It is the best method i have found for getting enough heat. An 80 - 100 watt iron works well also.
I use solder paste on the mcpcb and just place the led in its correct orientation and heat until it starts to bubble around the edge. Once it settles in remove heat and let cool slowly for a min or two.
I have a small copper plate from an old computer heatsink (about 2” x 2” x 1/”) and I put that in a vise.
I put the star on top of the plate, and use solder paste and put a thin bead across (perpindicular to) the pads.
I place the emitter on the star, then I use a small torch (I used to use one of those “jet” propane lighters) and heat the plate from the bottom until the solder paste turns shiny and the emittter moves and seats itself (you’ll see what we mean when you try it).
Then I remove the heat and let it cool.
I’ve been meaning to buy one of those electric burners, to try that, but what I do now seems to work fine, and I don’t do enough reflowing to justify (as if that was needed :)!).
Later,
Jim
P.S. Before I tried this for the first time, I took an old emitter on a star and practiced removing the emitter from the star and then reflowing it back onto the star.
I haven’t done one yet but instead of using solder paste I was just going to apply some flux to the pads on the star together with a tiny bit of solder, heat it from underneath with a small butane gun until the solder flows out. I would put some more flux on the led, place it in position and heat again until the solder flows and the led settles itself down.
I’m just not sure if the solder flux is absolutely necessary, I don’t have any?
I use a heat gun, it has 3 settings and you can also adjust the heat with distance.
1) clean and prepare copper base with a tiny layer of no clean flux (if there is residue of solder I would remove it)
2) place small amount of soldering paste onto the pads
3) place emitter onto soldering paste
4) preheat copper base from the bottom with heat gun on low setting
5) put heat gun on higher setting and go closer
6) after a few seconds the solder melts
this can be done in a vise or any other (heat resistant) installation
I try to stay close to the temperature profile of parts, pcb, flux and check in between with an old temperature probe. I don’t have a IR thermometer but ordered one today
I use a small torch with the LED star hanging off the table in a vice grip. Temperature is regulated by how far the flame is from the bottom of the star (and how big you set the flame too.) . Hot enough is when the solder melts, and if you can’t see that point, when the star smokes, it’s too hot. lol. Personally I prefer the torch over lighter because of a cleaner flame however, it wouldn’t be the end of the world if one has to take a napkin and wipe the star off before installation.
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If you want to be a little cautious and reduce the chances of overcooking the LED, take a fine nose tweezers and try to pic up the LED every few seconds. Don’t keep the tweezers in contact with the LED or star all the time or else heat will be transferred to it prolonging the process and possibly burning your fingers.