Our acid copper plating racks constantly plate with copper and tin in
random locations.  The plating racks are coated with Plastisol and we
are certain there are no pin holes in the racks.  Freshly coated racks
last approximately 150 hours before the build up starts. After the racks
are cleaned, the build up begins in about 50 hours.

We have two automatic plating lines.  Each line has six copper tanks and
one tin tank.  Copper plating time is 55 minutes and tin plating is 9
minutes.  There are seperate spray rinse tanks for the copper and the
tin.  There is no micro-etch in the line.  Prior to copper plating the
panels are mounted on the racks and soaked for 5 minutes in an acidic
cleaning solution.

We suspect that the rack plating is initiated by an "electroless"
deposit of a tin compound which remains on the rack after rinsing.  Once
this deposit builds up, it cannot be removed.  On one line we typically
run 600-900 amps per rack for copper.  The other larger line runs
800-1500 amps per rack.  The plating deposits are much worse on that
line.

I would like to know if anyone is doing pattern plating, using tin as
and etch resist and is not have a build-up of copper/tin on their
plating racks.  I would also like to hear from anyone who has this
problem and has come up with a solution to the problem

Hans Rohr