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
[log in to unmask]

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
> [log in to unmask]
> www.compunetics.com
> Phone: (412) 858-6148
> Fax: (412) 373-4184 If a man has come to that point where he is so
> content that he says; I do not want to know any more, or do any more
> or be any more, he is in a state of which he ought to be changed into
> a mummy.
> Henry Ward Beecher