I do not know which 'thermal shock issue' you investigated; heating too fast
or cooling too fast? Chip components, unless already defective, do not crack
on fast heating, but can do so on fast cooling. That can happen in
combination with pad designs that allow exessively large solder fillets. When
these large solder volumes cool, they shrink at ~25 ppm/C and the ceramic
chip components at only ~6 ppm/C. When you cool too fast the solder can not
creep fast enough to relax the stresses and component cracking can result.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]

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