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Plating Spark - How to prove it's a real issue

Looking for help with an issue I've got here, 0.50 MM thick copper heatsink coated with 60/40 tin lead 8-10 microns, I'm seeing what looks like a spark mark in one corner causing our solder not to reflow - any help ? Also on the same part ( 6 months old ) the shine has gone and the parts will not reflow in the same manner as new stock - is this an example of copper leeching ?

Kevin O'Brien
Artesyn Technologies - Youghal, Cork, Ireland
2002

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2002

The loss of shine and poor reflow after 6 months is usually because the solder oxidized from contact with the air. If the storage atmosphere is particularly dirty, you may also have some organic deposits on the surface. In either case, dipping the pieces in a liquid flux will probably be adequate cleaning. I had one case where I had to use an ultrasonic degreaser followed by a mild acid dip on some VERY old printed circuit boards.

(As a demonstration, if you have a chunk of lead (Pb) around, the surface is probably a dark gray color. Shave off a little of the surface with a knife and you see the nice shiny, silvery color of lead. You see the same thing with solder, only not as pronounced.)

Tom Gallant
- Torrance, California, USA

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