Mr. Brummer:

(Thanks for asking the kind of question I love to answer)
Double treated foil is Copper covered with layers of a mix of Chromium and
Copper compounds.  These compounds react with the photoresist forming utterly
insoluble organo-metallic compounds, that cannot be readily removed.  The
ONLY way to get these demons off the panel is to destroy the compound, and
the ONLY easy way to do that is to use strong chelates.   And strong chelates
require powerful precipitants (like the carbamates) to precipitate the
complexed Copper.

There may be two ways out of this dilemma.

1. Use Sodium Sulfide, instead of Thiocarbamates.  This is dangerous, because
if the pH of the sump gets acidic, you release Hydrogen Sulfide, which makes
Hydrogen Cyanide seem like a gentle walk in the park....

2. Alternately, use a double sump stripping system, take off MOST of the
resist in a non-chelated stripper, and finish with a heavily chelated
stripper.  The good part of this is that the heavily chelated stripper should
last for many many times longer than the non-chelated stripper, and thus,
could be disposed of as a hazarodous waste.

This industry is not getting easier, and we are all between a rock and a hard
place, wish I had better news.

Rudy Sedlak
RD Chemical Company

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