Louis:
This is a very common problem, particularly if you are stripping in a tank.
There exists a mechanism to completely stop this, which is available in some strippers, like ours for instance.
Other things you can do to minimize the problem, over time:
The current Tin plating baths usually have a high load of (Stannic) Tin oxide dispersed in the bath. This is the enemy. This oxide is co-deposited with the metal, then dissolves in the stripper, and immersion plates on the exposed Copper.
Put a VERY fine filter on the bath, to filter out the Tin oxide. Monitor dissolved Tin oxide levels by taking a 250 ml cylinder of bath out once a week, and allowing to settle overnight, and noting level of settled oxide.
Make sure anode area is high. Too low an anode area promotes the Tin going to Stannic Tin oxide, instead of going into solution as Stannous, as it "should".
Further info on photoresist strippers that prevent this problem available off-Technet.
Rudy Sedlak
RD Chemical Company
--- On Fri, 9/11/09, Louis Hart <[log in to unmask]> wrote:
From: Louis Hart <[log in to unmask]>
Subject: [TN] tin redeposit???
To: [log in to unmask]
Date: Friday, September 11, 2009, 8:57 AM
Technetters, hoping this question is not too arcane, has anyone experienced sporadic tin redeposit on exposed copper surfaces during the photoresist stripping process prior to final ammoniacal etching? In this case electroplated tin is used as an etch resist.
Thanks for any comments.
Louis Hart
Compunetics
Monroeville, PA
USA
[log in to unmask]<mailto:[log in to unmask]>
412-858-1272
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