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June 2002

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 21 Jun 2002 07:24:06 EDT
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Hi Bev, David & All T's,
While I concur with David's "big enough" statement, I also assume he does not
include in "if you can detect it, it is too big!" cross-sectioning.
On the other hand, Bev writes "Shades of voids in BGAs...   How big of a
crack in thermally cycled solder joints is too big of a crack?"
Cracks in thermally cycled solder joints have nothing to do with voids;
therefore why "Shades of voids in BGAs...". Solder exhibits micro-voids
[having nothing to do with voids] at grain boundary intersections after about
25 to 30% of the fatigue life having been consumed, and micro-cracks along
grain boundaries after about 40%. That means about 60% of life is still
available when 'observable' micro-cracks are present.
David then says: "A better question would be how do you distinguish between a
crack and a void?"
That one is easy, voids a roughly spherical, cracks are fractures.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 386-437-8747, Fax: 386-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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