Hi Scott,
What you are describing is thermal shock, not thermal cycling, even though T-
shock is performed cyclically as well. The basic diference is that in T-
cycling, the loading comes from the differences in thermal expansion at the
temperature extremes, whereas T-shock is a confounded loading condition where
on top of the differences in thermal expansion at the temperature extremes,
temporary differences in thermal expansion due to transient temperature
gradients cause warpages. The warpage induced loading gets more severe with
more rapid changes in temperature: T-shocking liquid-to-liquid is more severe
than air-to-air T-shock. Typically, the damage mechanism(s) in T-shock and/or
the failure modes are different from T-cycling. You can be perfectly adequate
in terms of product reliability and still fail T-shock miserably. I define T-
shock as having a rate of temperature change above 30oC/minute; below this, it
is T-cycling.

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]

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