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May 2001

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Subject:
From:
David Hillman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 2 May 2001 17:58:07 -0500
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Hi Jan! Steve G. posted the photo of your "stars" - my guess is that the
star pattern is a "witness mark" which is due to a test probe leaving an
indentation during electrical testing of the BGA component. The "stars"
might be due to solidification shrinkage but typically surface physics does
not behave in such a repeatable, crisp pattern! Ask your BGA supplier if
they conduct electrical test on the BGA components. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Pelchat, Janice" <[log in to unmask]>@IPC.ORG> on 05/02/2001
07:26:24 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Pelchat, Janice" <[log in to unmask]>

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:

Subject:  [TN] Seeing STARS!  (BGA solderball anomaly)


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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