Hi Hakan,
No, there are no theories indicating that one can tolerate higher percentage
as the balls get smaller. There is also very little in data. The data that do
exist indicate that voids result in a temporary localized retardation of
crack propagation, but no data exist to my knowledge that
the info in IPC-7095:

Class I: 60% of dia = 36% of area

Class II: 45% of dia = 20.25% of area

Class III: 30% of dia = 9% of area
is based on any real experience.

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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