Hi Steve
What you are describing is exactly what will happen with electromigration.
Of course after the material migrates and shorts out completely, it will
work for a while then finally won't at all.

1)  Horizontal microsections will some times be able to let us see the
dendrites within the board.

2)  If you have the condition in one location it is probably present in other
locations across the board.

3)  To get electromigration you have to have moisture and contamination.
So what kind of environment do these assemblies see?  Conf Coating?

4)  Hind sight would suggest some sort of cleanliness requirements for
inner layers prior to lamination - Bellcore requires process qualification
with SIR type tests.  IPC specs and military specs do not.

Susan Mansilla
Technical Director
Robisan Lab

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