Correct way to solder Cree LED's?

This is how I've been doing it:

I glue the emitter down to the heatsink with Arctic Alumina.

Set my soldering station on high.

Touch the tip of the iron to the corner of the LED pad, then touch the solder to the LED/tip junction. A small amount of solder will melt and flow right onto the LED pad.

All of this takes maybe 4 seconds.

Then I lay the pre-soldered wire onto the pad, hold it in place with some tweezers, place the tip of the iron on top of the wire and when the solder between the pad and the wire flow together I remove the tip. Again, a few seconds is all it takes.

I do this with an eye towards using as little heat as possible.

I was talking to someone today while ordering some LED's, a man with good credentials, that said I was hurting the brightness of the LED by up to 30% by doing it that way. Told me that if I wasn't reflow soldering I needed to order the LED's mounted on boards. So I did.

Is it really true that I could be killing off that much brightness the way I've been soldering my Cree's? :thinking:

I don't believe it. How do you think they get the emitters mounted to stars? They heat up the whole setup in an oven at 255˚C for a short period. Using an iron competently, the junction temperature shouldn't get as high as during reflow soldering. IMO, he's trying to sell you star boards.

You already had the emitter thermally linked to a heat sink, which will act to limit the LED junction temperature. From your description of the process, it sounds like your heat sink would not even be too hot to touch. I personally don't like boards because they use aluminum and introduce a layer of comparably low thermal conductivity in the form of paste or bare surface contact with the heat sink. I want my LEDs mounted to a massive slug of copper. Call me :tinfoil:.

I don't think the gentleman was trying to sell me something I didn't need. I believe he was telling me his honest opinion.

That said tho', I don't see how the way I'm doing it is wrong. I don't even "tin" the pad until it's Arctic Alumina'd to the heatsink, and I use a hot iron so I can get in there and get out without saturating the LED with much heat.

I think I may change my order to bare emitters. I don't know what to do........ : pullinghairout:

I am in the process of soldering 12 Crees XR-E to a copper disk.
First I made a PCB to connect the Crees together
Then snipped the corners of the Leds to remove the connection between top and bottom and soldered the top of the Crees to the PCB which has holes to take the lens and ring through the board

Then using SMD past and a heat gun place the board on the copper disk and heat the other side of the copper disk to give the required temperatore profile given in the Cree brochure.

I am measuring the temperature using a K thermocuple and a DMM. After doing a few tests I found it was easy to keep to the temperature profile but lowered the temp by about 20degC as the thermocouple seemed to read low. Checked this by using the know melting point of the SMD solder.

matthew

Greg G said:

Touch the tip of the iron to the corner of the LED pad, then touch the solder to the LED/tip junction. A small amount of solder will melt and flow right onto the LED pad.

Then I lay the pre-soldered wire onto the pad, hold it in place with some tweezers, place the tip of the iron on top of the wire and when the solder between the pad and the wire flow together I remove the tip. Again, a few seconds is all it takes.

Click to expand...

I don't think you're overheating the LED. However, I think you might get a "technically" better solder joint if you don't pre-tin the pad and then re-melt the solder. If possible, I'd just solder the wire to the pad. If necessary, clean and flux the pad first. (Ignore this if I'm misunderstanding the process you're using due to other considerations.) Generally, you want to heat the metal parts to be connected and melt the solder on them. A good solder joint likes fresh solder melted once. Not that we haven't all fudged a lot of joints

PS if it works, don't fix it. If it doesn't work, remove the old solder, clean, and resolder.