Assuming you mean high build electroless copper and pattern plate I would
look at your electroless process, in particular the e copper bath.  We have
in the past experienced noduling of the plated copper within the holes when
the air aggitation of the bath was insufficient and caused localized areas of
little or no air aggitation. A small amount of "sanding" on the panel
surfaces or racks was present to tip off the problem usually, but a time or
two we had no sanding but the problem. Copper noduling became very evident
after pattern plating. Increasing the air supply to the electroless bath
along with modifications to the air spargers fixed the problem.  Other causes
of instability may be at work also,  too high operating temperature, high
caustic, formaldehyde concentrations, or low chelator, stabilizer
concentration. (Check bath chemistry to be sure it is within the recommended
operating ranges for all components).

Phil Dam

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