Help soldering wire to a copper heatsink

Hi all

Every time i try to solder any wire to a copper heat sink with solder iron it doesn’t stick what should i do ?

i did clean the copper very good but still no sticking

there are few things involved that you did not tell us.
do you use flux?
what size is the copper slug?
what wattage is your soldering iron?

based on the short story, I would guess you need flux. Copper (or basically any metal) begins to tarnish as soon as it is exposed to open air. The flux should remove the small invisible layer of tarnish and allow the solder to take.

Hi gamezawy,

There are a few things you can do to make the job go better. As mentioned before you will need some flux, but that alone may not do the job.

I have a 60 watt variable soldering iron and even that has trouble soldering to copper slugs. I always heat the slug by either setting it an electric skillet or using a torch and warming it to just under the solder melting point, then come in with my iron. This makes a HUGE difference.

Buy a kester flux pen.

Yep, if the iron is not capable of heating the heatsink to soldering temperature, the solder will drip off like rain on a windscreen. :wink:

The very reason we have the copper slug (it’s ability to remove massive quantities of heat from the emitter) are what makes it so difficult to solder to. It drains your iron faster than your iron can recover, so the spot you’re trying to solder doesn’t get hot enough to actually melt the solder. Screw it.


I always need a blow torch to get solder stick to any sizable piece of copper/brass, it takes a lot of heat to get the whole piece to the 180 degC needed for soldering to.

looks like my problem is a heat problem since i am using 30 watt solder iron ill try to heat the copper 1st , Now give me a FLAME THROWER >)

Time to bring out the acetylene torch! LOL

yes looks like it is your problem, you can use plumbers torch to heat it up, or one of those butane lighters tourches.

or put it on a frying pan, and let it get hot, (i kid you not, i reflow all my leds using frying pan and gas oven) than soldering will be a lot easyer.

If you have a nice powerful soldering iron with the right tip (wider tips can transfer heat faster) + flux, I think you’ll be able to get it to stick. The trick is to get your iron HOT so that once the copper is touched, the local region is hot enough for solder to stick. If it doesn’t work, blowtorch it and put solder on it.

I’ve done it with small butane jet lighters before I finally got the right tip on my iron.

before mounting a led/star i heat the copper slug up with a butane torch

I do just like you

I’m curious, why solder a wire to the heatsink? :davie:

Ground to driver