Suspect that you may be taking a long time to get from plating of Tin to
stripping of Tin, or perhaps the panels are seeing some heat.  Either
situation will give you a lot of intermetallic Copper/Tin formation.  When
this happens, and you strip, you need virtually a chemical polish to restore
brilliance of Copper, and if your Copper contains high enough level of
organics this may not be possible at all.

Suggest that you investigate either processing faster or without baking to
prevent problem, or if that is not possible, try immersing panels in second
part of the old style 2 part solder strippers, before plating.  These
strippers had "anti-tarnish" additives which made them function like a
virtual chemical polish.

And if you cannot find this type of stripper available, contact me directly,
I sell them.

Rudy Sedlak

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