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.

Thanks for any replies.

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