Hi Joe,
You ask: "Is standoff distance considered a good indicator of correct solder
ball

collapse?  Is there a formula for calculating what the theoretical standoff

distance should be after reflow based on package weight, solder ball

diameter, # of balls, etc...?"

Standoff height is the major geometric parameter besides component size
determining solder joint reliability. Observed height variations are
indicative of BGA warpage during reflow soldering. BGA warpage during reflow
is a fuction of unequal heating and thermally asymmetric design. If the
corner solder joints are the ones with the shorter standoff height
reliability is reduced.

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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