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February 2008

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Subject:
From:
Adam Seychell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Adam Seychell <[log in to unmask]>
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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