You are working with very small holes for an 8 layer flexible circuit. The alkaline pretreatment, if you can get them into the hole adequately, will cause adhesive swelling and resulting in void problems. Plasma is good but getting a uniform treatment of that small a hole over a decent area can be tough. The metal at the surface of the holes has a tendency to attenuate the plasma reaction. Reactive Ion Etching, directed plasma to state simply, might help.

Have you tried the direct metalization? For RIE you could send samples to March instruments in Concord California.

Chuck Brummer
Acuson
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P.S. Water break tests are helpful when determining if copper surface preparation is working. Better is Contact Angle Measurement, a inexpensive unit is available from March Instruments for this too.

Brent Mayfield wrote:

I am having some difficulty plating .008" holes in an 8-layer polyimid flex. I am using Dupont Pyralux, and the board thickness is ~.025. I have tried numerous alkaline pre-treaments in addition to Dupont's recommended plasma cycle, but cannot seem to get rid of electroless copper voids. Anyone have experience with this? Brent Mayfield
Flexible Circuit Products Manager
Compunetics, Inc.
Advanced Interconnect Products Division
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www.compunetics.com
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