Werner, I'm sorry to disagree with you but most of our customer requirements
specify a minimum number of cycles, either air-to-air or liquid-liquid, at
specified temperatures. "Acceptable" results depends on customer bias, but
could be electrical resistance measurement, microsection quality after
stress or both.

For internal purposes, we usually cycle to failure using a prescribed
thermal profile and determine root cause(s) of failures, implement
corrective action(s) and retest the modified process using the same profiles.

Dave
___________________________

>Dave,
>Unfortunately, there is no 'acceptable number of cycles' either in
> air-to-air and
>one liquid-liquid thermocycling nor IST. There can be a 'minimum threshold'
>that would assure no failures as the result of the assembly processes, but
>there is further loading (less severe but more cycles) that during
>operational use in the field. Many applications are benign, but severe uses,
>e.g. automotive and military, could experience field failures on boards that
>would have no problems in benign uses e.g. computer, telecom. 
>Thus, we do need the capability to numerically correlate IST results to
>equivalent air-to-air and liquid-liquid cycles, and more importantly to
>cycles at a given use environment. Therefore, any data that would allow
>arriving at such a correlation would be very welcome.
>
>Werner Engelmaier
>Engelmaier Associates, Inc.
>Electronic Packaging, Interconnection and Reliability Consulting
>23 Gunther Street
>Mendham, NJ  07945  USA
>Phone & Fax: 201-543-2747
>E-Mail: [log in to unmask]
>
>regards
>Dave
>
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