Hi Adam!

Do any of the holes look like this:

http://stevezeva.homestead.com/AnnularRing3.jpg

 
http://stevezeva.homestead.com/AnnularRing.jpg

http://stevezeva.homestead.com/AnnularRing2.jpg

Steve Gregory

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Adam Seychell
Sent: Friday, February 29, 2008 5:03 AM
To: [log in to unmask]
Subject: [TN] acid tin plating question

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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