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Copper bar soldering problem

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s3rkan:
Hello everyone. I have just received this copper bar from AliExpress:

 http://s.aliexpress.com/3iQrQFBz

I want to make a mosfet switched spot welder and will use this bar for mosfet drain and source. But even I have tried all I have, like soldering paste, Flux, grinding the surface and HCl, I couldn't make stick the solder to the "copper" bar. I tried it between 320-350 C degrees. Does any one have any idea what I am doing wrong?

Dave:
Copper is an outstanding conductor of heat. My bet is that even though your iron is set to 350°C, the copper bar does not get anywhere close to that temperature.
A really big iron would be my only idea. :-//

Gyro:
Don't forget to check them with a magnet.  ;)

You probably have issues with oxide formation during the heating time (you are heating the whole bar aren't you?) try abrading and fluxing while hot. If the temperatures you're quoting are just for a soldering iron, then you need to pre-heat the bar too.

The Soulman:
there is a lot of thermal mass and on top of that copper is a great heat conductor.
In order make a solder connection almost the entire thing needs to be brought up to temperature.
Best chance is a oven and low melting temp. solder.
Last option is blowtorch, but your mosfets probably wont like that.

filssavi:
It’s hard to tell for shure without seeing anything but my guess is not even remotely enough heat/power

Try with 400 degC, if it still doesn’t work you could try to preheat the bar with a heat gun so that the delta T is lower

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