Hi ?,
>I have heard that solid solder balls offer better reliability on an area
array device (BGA) >than a plated stamped lead. If true, what are the reasons?
Not very likely, those leads would have to be very stiff to make this true.
>Another question, are the solder balls on a BGA supposed to reflow and lose
their >spherical shape? Or are they supposed to stay round after reflow with
the substrate >pad and solder paste?
It depends. High-melt solder balls will not reflow and therefore remain
spherical; near-eutectic solder balls wil reflow and depending on component
weight and orientation, pad sizes and geometries, solder volume and surface
tension, assume geometries other than the original one. These geometries can
vary from a squashed pancake to an hourglass, circular to rectangular in
cross-section.

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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