I would be very much interested to know whose process your are
  evaluating. I have seen this problem with the conventional electroless
  process, where the electroless deposit will literally crack and flake off
  the the hole wall resulting in pin hole voids and sometimes ring voids.
  As for the inconsistent results you are experiencing with your direct
  metalization, I would suggest you look into the cleaners and to make sure
  you are getting a good wetting in the holewall. Another issue you may
  want to investigate is hole wall preparation prior to thru-hole. Do you
  use plasma or permanganate desmear.  The plasma is the preferred in most
  cases.


  To:       TechNet @ ipc.org at Internet@CCMAILEXCHANGE
  cc:        (bcc: Ramoodit Kimal/CDev/Ceridian)
  From:     TechNet @ ipc.org at Internet@CCMAILEXCHANGE
  Date:     04/22/96 04:40:00 PM
  Subject:   Direct metalization of Flex Rigid PWBs




We are working on developing direct metalization process for flex-rigid
pwbs using palladium based process.   Currently we are very early in the
development stage and are experiencing inconsistent results.  Some of the
test results were very good others failed.  The failures exhibited rough
hole walls and voids.  The roughness appears to be caused by something
flaking off of the hole wall and plating.  The appearance is similar to
blistered or peeling electroless.  Does anyone run flex-rigid through a
direct metalization process?  If so, has anyone
experienced similar problems and what is the cure?