I'm having a rather perplexing problem with shorts on inner layers.  The
short is very small, and occurs mainly on fine line jobs (5/5 mils and less).
 It also occurs primarily on layers with one ounce copper, although I've seen
it on half ounce.

The short is very very small; in fact, it is rarely seen at AOI.  Usually, it
is discovered at final electrical test.  Failure analysis exhibits a very
fine sliver of copper that appears to have broken loose from a trace; it
remains attached at one end and flips across the adjacent circuit.

Cross sections and SEM's of both developed resist and etched layers show a
near vertical sidewall.  Has anyone seen this phenomenon?  Any suggestions?

Eric

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