Help. The XHP70 positive on board won't stay soldered on

Hi,
Help. The XHP70 positive on board won’t stay soldered on.

The light has big heatsink but after 1-2 min of being on the positive wire on copper board comes off and consequently no light.

I put flux and big wires and it seems the heat makes the wire pop off.

Anyway to fix this?

Thank you
BigC

Does the reflector push against the wire or solder joint? I had that once on a C8.
alternatively try the copper sheet method (where you solder on a slim sheet of copper and then solder wire to copper)

No. Ironically the negative side is perfect. Just one side comes off

Sometimes it’s hard to get heavy wires to stay soldered onto copper boards. The wire and board steal a lot of heat, let alone the pill. Had that problem once with a copper triple.
Lots of heat and flux. Try pressing down on it with a wide tip.
Also, You may have lost the solderable surface from the contact. Try using the other pad.

That’s what it looks like to me

It looks like the solder is not getting hot enough.

The star needs to be isolated from the heatsink to get it hot enough.

With such short wires this can be difficult, but shimming it up off the heatsink with a couple of paper clips will isolate it from the main pill/heatsink and allow the star to heat up much more quickly, then slip out the paper clips when finished.

A good soldered wire wont come off easily.

+1 With my 25W solder iron it is sometimes a pain to get the wires soldered to a well heatsinked copper board, the solder does not melt and mix well, and with some force it comes off. To help that, I always tin the solder pad on the ledboard well with a blob of solder, tin the wire also first, then fuse them with the solder iron. But even then I sometimes do not get it done. Just two weeks ago I bought an extra solder iron for that (a 80W Antex :evil: ), so that will not happen me me again.

I’d be concerned that the MCPCB is getting hot enough to (I assume) melt the solder holding that wire. To me that’s a warning sign the heat is not being transferred away fast enough. Its also possible the solder you’re using has too low a melting point… do you have any details on the one you’re using?

When I’m soldering heavy gauge wires onto copper sink pads that are already glued down on the pill, I use lots of heat. I crank my temp up as high as it goes with a wide tip and hold it down on the wire until I feel a “crunching” as the wire strands separate from the tinning and start to flatten out and melt into the solder on the pad. You can feel the whole wire sink down. If I don’t feel that flattening, sinking down of the wire, I keep the tip depressed until I do. It kinda feels like breaking through ice.

Am I the only one who never solders emitters last?

Sometimes it can’t be helped. Especially in large multi emitter lights where the reflector has to be seated on all the emitters while the glue dries. You just can’t line up a bunch of emitters with the wires attached.

I guess I can understand, but I never glue anything either. :stuck_out_tongue:

Ok. So I took the star off the heatsink. Soldered the cable and then epoxy back star to heatsink. Now it works. I have done several 3 minute runs and it’s a success

I always pre tin the solder pads and wire ends before installing the star. The traces are isolated from the star core but when the star is in the host it takes much more heat to get it to wet properly. Put a short piece of drinking straw over the LED to protect it from flux spatter.

Thanks for the straw over the led tip! :beer:

You’re welcome. :beer: it’s the hap-happiest time of the year.

One other problem I came across having to use a lot of heat is that due to the amount of hot copper the wire lifts slightly before the solder solidifies, what I do now is to use something heat resistant (ceramic tipped tweezers in my case) and press the wire down, apply the iron then keep it pressed down after removing the iron until the solder is solid.

Cheers David

Edited for clarification, edit in italics.

Yes, it’s important to hold the wire down with something besides just the iron so when you remove the iron off the wire stays flat. Too much solder will draw a peak (like whipping cream) that is likely to cause shorts, use just enough to raise a low bump on the pad and wet the strands of the wire(no large bumps or hanging blobs).

sounds like your sinkpad is doing its job.