Ken,

I consider what you are describing as being a cyclic burn-in and not ESS.  ESS is not
achieved until the unit is pushed beyond its regular operating parameters .  I feel
true ESS is a great tool to use during design qualifications and that's about it.

 I personally agree with the statements made by Smith /Whitehall in their book
"Optimizing Quality in Electronics Assembly: A Heretical Approach" that "any rational
reason why ESS should be anything other than a costly exercise in degradation of
dependability is certainly not clear....... it is impossible for us to accept that a
unit which survives being run oven by a truck is more dependable for the experience."

Just my opinion,
Gary Camac

Chafin, Ken G. wrote:

> 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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