Lou, here is what I know about black oxide.

Compunetics here has been putting black oxide on some outer layers.  
Solder mask adhesion was a concern.  It is being used mostly for DFSM, 
but some LPI boards also get it.  Without data to provide convincing 
evidence, the belief is that adhesion is better.  My understanding is 
that at least one LPI supplier advised against black oxide.

Problems in solder resist adhesion have arisen because of uneven plating 
across the board surface.  Some regions are higher than others, so dry 
film doesn't always conform or the silk-screened LPI is not deposited 
with enough thickness.

Some time back, I found a copy of IPC-SM-839.  It had a lot of 
interesting comments on adhesion promoting treatments.  I don't think 
black oxide was mentioned.

Lou Hart
412-858-6117


.

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