Stephen -

The condition you describe suggests a localized "hot spot" which kept the
solder in a liquified state for a prolonged period of time following reflow,
rather than a contaminant.  Eutectic solder which cools rapidly generally has
a "bright/shiney" appearance.  (Excuse me, All, for using this phrase.)  The
same solder, cooled at a very slow rate has the tendency to form crystalline
clumps, for lack of a better description, which give a highly textured
appearance to the solder surface.

The "hot spot" I mentioned can be the product of anything which produces a
high thermal mass area on the object being soldered, ie., heavy circuitry,
ground plane areas, a larger than normal component, a part which has a higher
IR absorbtion rate than the others around it, etc.

Fine tuning the profile will probably help this condition.  Recommend you
instrument this part location and compare it to other areas on the board to
confirm that the cooling rate is slower.   I have also seen small pieces of
foil placed on top of parts prior to reflow to reduce IR absorbtance.


Good luck - Kelly

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