Janice

I have limited experience with solder balls but I have seen a 'wrinkling' of the surface.  If
you let me have a picture then I can tell you whether it is the same as I saw.

I have come across a number of hypotheses as to the cause - oxidation and differential cooling
of the solder being two.  I do not think that it causes any problems that might be associated
with  the physical properties of the ball.

Michael McInerney

"Pelchat, Janice" wrote:

> 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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