I had a similar experience using MSA tin lead plating.
The coating started as a tin salt deposit in and on the coating.
It could be seen under a 400X microscope. Then, during
copper plating, the deposit would eventually cover the racks.
We found that a weak caustic dip tank would leach out (off)
the deposit and we could continue plating without the condition
taking place. Our concern was drag in to the cleaning line / plating
line. Good rinsing took care of that.
But it was a manual line.

The above comments are of my own opinion, and
not necessarily that of my employer.

Dave Hoover (aka, Groovy)
NPI Mgr HADCO TC2
Watsonville, CA

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From: Hans Rohr <[log in to unmask]>
To: [log in to unmask]
Subject: [TECHNET] FAB:Copper/Tin Build-up on Plating Racks