We are experiencing a type of contamination on completed board
assemblies (we don't have access to bare boards). Under microscopic
inspection, some surface mount parts have a brown "gun powder" like
substance appearing on part of the solder joint. Scrubbing with a solvent is
required to remove it.
        1)  Has anyone experienced this?
        2)  What could it be - and what could be the root cause?
        2)  Is it something we should worry about?
        3)  Is there a cure?

Possibly related- all boards with this defect also have a number of traces
which appear to be over etched.

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