Hi All,
I am not aware of any studies, or product experiences, that indicate that
voids constitute a significant reliability problem--mostly BGAs. There has
been some work indicating that some voids [emphasis on some] locally and
temporarily retard crack propagation [so do not try to have more
voids]--again BGA-type solder joints. When you have highly non-uniform
loading, as with gullwing-leads, this may no longer be true--however, since
these leads are highly compliant [QFPs] it still does not make any practical
difference.  If however, you have rigid stubby leads [TSOPs, SOTs],
particularly if the foot-length is short [< 3x foot-width], then voids,
particularly in the heel fillet, could lead to earlier failure.
Whether flux residues or any other inclusions in solder voids have a
deleterious effect, I do not know.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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