Hi Bev,
Brian is correct on all points, and just because people (that is who write
Nortel or Telecordia or Bellcore or IPC specs, after all) established
definitions does not make it a "fait accompli"; only sloppy use of language
and a perfect source for miscommunication.
Also, please do not misquote 'almost' ancient (I was part of it) work by Bell
Labs; there indeed was a significant difference how one ramped up--the
temperature increase had to precede the humidity increase and conversely, the
humidity had to be decreased before the temperature was reduced. Crazy data
resulted when condensation occurred.
In both SIR and ECM it is very important, that only the areas to be measured
contribute to the reduction in resistance. It thus becomes very important how
the test leads are attached to the test vehicles and how much distance there
is between attachment points.
We have found, that for boards for which CAF paths are created PTH-to-PTH
during T/RH/V exposure, such path are also created even if no bias is applied
during the T/RH exposure; this path turn quickly into CAF upon application of
the sensing voltage.
One other thing we found was, that unless we supplied water to the internal
wet-bulb reservoir via a peristaltic pump rather than an external refill
reservoir, the internal reservoir can run dry.
All in all, this is a rather complex subject matter.

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

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