Rudy,
One of the things I saw whilst at CSL was that we would sometimes see
corrosion on inner layer traces when they were placed very close to the
edge of a board.  If the panels had been scored rather than routed, as was
the case, the mechanical flexing would open the edge of the laminate, or
the rough edge would allow moisture ingress, such that the inner layers
could corrode.  So one thing I would look at would be the flexibility of
the oxide.  I would also look at how well oxide coated inner traces, placed
near the edge of the board, resisted corrosion.  If you are convinced that
the vendor has adequate inner layer cleanliness before lamination, then you
might want to use some external contaminant source, such as salt spray/fog
testing or some of the mixed flowing gas tests done at UL.  Susan Mansilla
had a good test and would be dramatically faster and easier than the tests
I suggest, but probably would not address the corrosion issues.

The whole point of the inner layer oxide is protect the metal.
a.  Does the oxide interfere with good plating in vias?
b.  Does the oxide have sufficient flexibility to protect the metal in high
G or high shock environments?
c.  Does the oxide have sufficient chemical resistance to protect the metal
against corrosive elements?

Doug Pauls
Rockwell Collins

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