John:

You wrote asking about mechanical scrub vs. chemical clean on outlayers.


Today, most shops use a chemical clean on outerlayers prior to photoresist.
 The chemical clean line usually consists of an acid clean followed by a
microetch.   Some people have used alkaline clean followed by microetch.  The
trick, or difficulty, is making sure that your microetch is REAL controlled
so that it does not get through the electroless Copper.  The way to do that
is to make sure that the cleaning prior to the microetch is real real good,
and then make the microetch real light.  Most folks target about 30
microinches, but this is more than is necessary if the pre-clean is done
right.

The use of the microetch on the electroless Copper is a major reason why the
industry went to medium and heavy deposition electroless Copper plating
baths.

If we may be of assistance, please do not hesitate to let us know.

Rudy Sedlak
RD Chemical Company
Phone:  1-888-RDCHEM1