John Gully,

We do not recommend chem clean for outerlayer unless the process is a panel
or flash pattern plate with pth electroless followed by electrolytic plating
since the chemical etch will remove too much electroless and there is a
possibility of increasing pth voids. 

Non scrub electroless is okay if the panel hold time is not longer than 24
hours and antitarnish is used after electroless. Otherwise an alternative is
brush pumice or jet pumice or jet alum oxide (expensive machines, though).

Feel free to call if you would like to talk over the situation.

John Ganjei
MacDermid Imaging
302-995-3562