Befor I ruin another Q5....

This was to be my first attempt at actually building something.

I am trying to mount a Q5 on a heatsink to go in a cutdown M*g 1D.

I carefully route my wires through the sink and to the pads of the Q5. Using a Hakko soldering station and a good quality fine Kester solder, I tin my leads.

I then place the tinned leads on the LED pads and touch with the iron. No solder flow. I touch again, this time longer. No solder flow. A little longer...

Now I notice that the (-) pad on the LED is gone. Apparently lifted by the heat - except I don't see it on my iron tip or anywhere.

I am doing this all under a magnifying light and am being really careful. I did some MIL SPEC soldering about 40 years ago, so had the illusion that I was still good at it. Guess not.

Any tips for me about getting the solder to flow to the LED pad? Recommended iron temperature?

The LED's are too expensive for me to experiment further without experienced input.

Thanks for any suggestions,
Bill

Edit: Mods - not sure if this is in the correct forum. Please move if not - sorry.

Bill,
This style works for me. Get some fingernail polish and put it on the area of the LED that you don't want solder (just past the pad and aluminum ring) Take some solder flux and put some on the Cree pad. Crank the soldering iron up to around 600+F and pre-tin the wires. Pre-tin the LED pad quickly as the flux will let it flow quickly and stick to the pad. Then cook the wire and press it against the LED pad for two seconds and remove. Blow on the connection to cool it down quickly.

This is how I do it...flux is your friend! I find it much easier to solder two things together that are pre-tinned than trying to get the wire to stay by just tinning it. Good luck!

Many thanks! Off to Ratshack to get some flux! Hoping the next LED survives my efforts.

Cheers,
Bill

as BentHead said, you should pre-tin the pads on the emitter. it sounds to me like that was the only issue with your method.

If the LED is already attached to the heatsink, the heat might have gone to the heatsink instead of melting the solder.

Gunner12 said:

If the LED is already attached to the heatsink, the heat might have gone to the heatsink instead of melting the solder.

Click to expand...

It is possible to directly solder to the larger CREE emitters directly, but it's a little tricky.

The problem is that if the LED is already mounted on it's heatsink with arctic silver or some other highly heat conductive material, then you are trying to bring the whole underlying heatsink up to soldering temperature.

As someone already noted, the best bet is to pre-solder the leads to the CREE before it is attached to the heat sink, but this risks 'thermal shock' issues because then the LED tends to heat up super quickly because it doesn't have much thermal mass. Use a small tip on a low power 12 to 15 watt iron. (we are working with the unmounted LED, so massive watts are not needed, and will add to the possibility that you will 'shock' the LED thermally by heating it too quickly).

Be sure to use light gauge very soft flexible stranded wire so the LED can be handled later, and the wires routed without putting to much stress on the pads (which have a tendency to break off).

Pre-Tin each wire first. Then, to tin your Q5 emitter's pads, start by making sure the tip of your iron is very clean by giving it a wipe on a wet sponge, then apply a tiny bit of fresh solder to the tip and immediately apply it to the Q5's pad and try to feed some fresh solder to the 'heat bridge' formed at the point where the freshly tinned iron is touching the Q5's pad.

This is the secret to nice clean solder connections, first you form a 'heat bridge' to surface to the surface of the pad using the tiniest bit of fresh solder on the iron you can manage, then feed the rest of the solder directly onto the the pad at the junction with the iron, as the pad comes up to temperature (trying to catch that magic point where it has JUST reached soldering temperature).

After you have tinned both the wires and pad with nice fresh shiny solder, you should be able to just hold the wire on the pad and press it down lightly with the iron to re-flow the solder and attach the wire to the pad permanently (if you went to rat-shack and got some flux, a tiny dab of flux on the wire at this point will help).

Hope this helps.

These types of problems are why I aways recommend getting emitters premounted on a 'star' type board.

It's possible to direct solder to a CREE, but with some emitters like the Rebel, it's damn near impossible without destroying the LED.

Gunner12 said:

If the LED is already attached to the heatsink, the heat might have gone to the heatsink instead of melting the solder.

Click to expand...

Bingo!