Hi Richard ,
I sure am getting tired of all the acronyms floating around, particularly
since they are hardky ever properly defined and/or applied.
What you described as your ESS procedure in not ESS, but a burn-in. ESS has to
be much more severe to screen-out (bring to failure) latent defects, whiule at
the same time not significantly damage good product.
What you describe as HARASS', is thermal shock—any procedure involving rates
of change above about 40C/min, note: not 40C/sec, is dominated by thermal
shock which involves the loading of your product by severe warping due to the
large thermal gradients. It certainly will fail bad solder joints,
but—depending on the T extremes—also good ones.
The best ESS for solder joints is vibration, preferably at cold temperatures
like -40C.
Latent defects in solder joints means inadequate wetting—in essence no real
solder joint with a metalurgical bond has been formed. Most other so-called
(latent) defects have no significant impact on reliability.
In all ESS testing of solder joints, the monitoring for failures has to be
done during loading, because the opens are intermittent and the
fractured/separated surfaces make typically good electrical contact at rest.

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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