It looks very close to those photos, except most of the pits are near 
inner ring of the pads. There is also pitting near the some straight 
edges. It appears low current density areas are most susceptible. Many 
smaller pits are not completely etched through, leaving the underlying 
copper visible. Unfortunately I don't have a digital microscope to send 
you photos.
Are those photos taken after solder reflowing the boards ?

Adam Seychell.

Steve Gregory wrote:
> 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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