We have some ceramic BGAs that are giving us problems with fractures at the
ball/package interface after reflow.

In the process of failure analysis, we inspected unassembled parts under
high power and have seen two anomalies.  One is an apparent shaving of the
outside perimeter balls from what appears to be fixturing at the
manufacturer - that is being F/Ad by the manufacturer.  The other anomaly is
what I can only term a "star" shaped appearance on the surface of the
solderballs.

Under very high power, this "star" effect seems (to me at least) to be the
result of the solidification process of the solderball during manufacture.
It looks as though the solder surface separated - then the separations
formed crevices in a star pattern.  Think of the appearance of crevices
formed on crusty breads when they bake and cool.  (Sorry for the analogy -
in my other life - I bake).

I have a fair picture for those wanting to see a visual.  Does this sound
familiar to anyone?  Is it part of the normal BGA solderball appearance?

Jan Pelchat
Benchmark Electronics

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