Werner,
1) So if the IPC spec is wrong, why did we leave it as such in the last round of discussions?
2) I agree crazy data would be measured with condensation on the boards. However, wasn't the whole idea of the 96 hour latent period put in there because that was the time found that it would take to lose any condensation that might form during an uncontrolled ramp-up, where both temperature and humidity controls were turned on at the same time?

3) I agree that the spacing and method of attachment of test wires is important.  I never said otherwise.
4) I have never had the failure of an external reservoir on a humidity chamber - once I made sure the floats were able to freely go up and down because the float arms were no longer bent!  :)

5) I am only 46 and have only been in the industry for 10 years, so the 80's are ancient to me.   :)

regards,
Bev
Nortel Networks

-----Original Message-----
From:   Werner Engelmaier [SMTP:[log in to unmask]]
Sent:   Sunday, November 28, 1999 8:20 PM
To:     [log in to unmask]
Subject:        Re: [TN] SIR

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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