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Date: | Fri, 29 Feb 2008 22:02:31 +1100 |
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Hi all.
I'm trying to solve a problem of pitting around the holes after
ammoniacal etching. I suspect my problem is insufficient deposits of
electroplated tin resist around the holes, which is making it more
susceptible to attack by the etchant. The reason I think its a tin
problem is because prior to etching, the tin deposits appear solid and
smooth when viewed under a microscope. However after etching there is
evidence of pitting around many holes.
The problem seems to go away with excessive plating, about 8um or more.
Normally I've not had a problem at only 2~3um.
Also is it normal to have a small amount of white foaming hydrogen gas
above the PCB while tin plating ? The tin bath is an acid stannous
sulfate type with brighteners, and has always been a milky yellow
appearance.
Adam Seychell
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