Hi 'kgchafin,'
Provided that your product is indeed "designed and qualified to operate from
-40 degrees C to +70 degrees C" (did you use IPC-D-279 'Design for
Reliability'-procedures and IPC-SM-785 accelerated reliability testing?), 6
cycles -40<->+71C will not do significant damage.
However, this ESS will not "screen out those assemblies with workmanship
faults... involving solder connections"; it may cause inadequately wetted
solder joints to separate, but without in situ monitoring you are not likely
to find those SJs.
A generic 'do-everything' ESS typically does not work very effectively; ESS
needs to be aimed at the suspected defects. For SJs (inadequately wetted,
forget cosmetic-type workmanship faults; they are not a reliability problem)
you are better of with vibration preferably at -40C; very effective and no
damage to good SJs.

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

>A proposal has been made that all our recently designed surface mount
>printed circuit board assemblies be subjected to the following thermal
>cycling process:
>
>1) Heat chamber to +71 degrees C as rapidly as chamber allows (but not
>to
>exceed 15 degrees C per minute).
>
>2) Dwell at +71 degrees C for 2 hours.
>
>3) Ramp temperature down as rapidly as chamber permits to -40 degrees C
>(but
>not to exceed 15 degrees C per minute).
>
>4) Dwell at -40 degrees C for 2 hours.
>
>5) Ramp temperature from -40 degrees C to +71 degrees C as rapidly as
>chamber allows (but not to exceed 15 degrees C per minute).
>
>6) Conduct the above +71>-40>+71 thermal cycle 6 times.
>
>7) Retest PCB assemblies.
>
>Note: No power or signal is applied to units during thermal cycling.
>
>View #1:  The thermal cycling described above will tend to screen out those
>assemblies with defective components and/or workmanship faults--including
>those involving solder connections.  It will help identify likely infant
>mortalities and assemblies likely to fail prematurely in field operation.
>
>View #2:  The thermal cycling described above is likely to create more
>defects than it identifies.  The cost of performing this screening process
>outweighs its benefits.
>
>
>Our electronic equipment is generally designed and qualified to operate
>from
>-40 degrees C to +70 degrees C.
>
>I would appreciate any references to personal experience or literature
>which
>would help determine whether View #1 or View #2 is more credible.

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