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Jeff Urban Jeff Urban is offline
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Default contaminated soldering surfaces

Well if it's under the solder of course it was during manufacture, but
it could be earlier in the process as well. Right now I assume when
you say tags you mean pads, the copper surface on the board right ?

It may have well been the photo resist. I worked for a PCB
manufacturer for a short time when I was younger and I know
cleanliness is esential. Somebody screwed up, and now I would wonder
if the problem is not just a one time occurance. If it is on the same
part of the board in more than one unit, the process was faulty. It's
more likely though that it was just a one time thing, or maybe just a
few. When they run these things through a bath maybe the fluid got low
or something like that.

In this case I guess the photoresist was conductive enough to let the
unit work, and the thermal mass of the solder during the wave
soldering was enough to make some kind of bond. It obviously didn't
last forever but a soldering iron simply cannot do what a pool of
molten solder can.

I would be VERY interested to know if the same problem is found again
on different specimens of the same model.

J