The first method you mentioned has several advantages but the design is
incorrect. I assume that if you are going to use a feed and bleed that you
will be using a nitic based system. If this is the case you want the fresh
chemistry to go into the first module not the second. The most active
chemistry (higher normality, lower SG) will then be stripping the tin or tin
lead. Less active chemistry will be removing any excessive tin or
intermettallic. Feeding fresh chemistry into the second module will increase
your copper attack and shorten your bath life. Nothing kills a nitirc solder
stripper like copper over 15g/l.

The second method is very good from a cost stand point but of course the
productivity is lost because you can't use a feed and bleed system. Typically
two parts are more apt to give you a less astethic pleasing copper surafce
because the second step is typically ferric chloride based.
 Regards,
Chris McGary
Dexter Electronic Materials

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