Thank you very much!
Sorry for the vagueness. It's one of the problems with
wanting to know about a subject but having no idea where to
start. That's what I like about this TechNet - "There's no
such thing as a stupid question." Well, at least I haven't
been blamed for that yet!
Doug McKean
____________________ Reply Separator _______________________
Subject: Re: Moisture Testing
Author: [log in to unmask] at internet-mail
Date: 5/11/96 12:00 AM
Doug.
I suspect that one of the reasons you have not gotten an
adequate response is that your question is somewhat vague.
"Humidity" testing can mean a wide range of tests, and will
mean different things to different people. The tests you
illustrate on the nylon screw, I would have called a
materials compatibility test or a materials characterization
test.
For PCBs and PWAs, there is a great deal of testing done
which utilizes high humidity to estimate deleterious
effects, either from fabrication or assembly. Most of the
temperature-humidity tests fall into the classifications of
burn-in tests (for assemblies), electromigration tests, or
surface insulation resistance (SIR). Tests like hydrolytic
stability use exposure to high humidity to test for
polymeric reversion on solder masks, potting compounds, etc.
Burn in tests are usually done on finished assemblies.
Power is applied and the environment cycles from low temp to
high temp under high humidity conditions for anywhere from
24 to 48 hours. A unit which fails such a test would soon
fail in the field. If large scale failures start to occur
in such a test, it is a sign that the process ist kaput.
Kind of an expensive process indicator.
Electromigration tests are often done on the materials used,
such as laminate, solder masks, conformal coatings. This
test incorporates high humidity to test a material systems
propensity for metal migration. SIR testing is similar in
it's approach.
For more information, you could look in the Bellcore TR-78
specification. Chapters 13 and 14 cover electromigration
and SIR. The IPC will soon have the final version (as soon
as I mail it to Dave Bergman) of the SIR Handbook, which
covers the applications of SIR to PCBs and PWAs. You can
look in the IPC-TM-650 manual. There are 4 methods under
2.6.3 that cover SIR testing. Several more cover
electromigration.
Man, I get long winded when I get rolling!
You can take a look at IPC-TR-580, 581, 582, TP-1043,
TP-1044 as documents that use SIR to test the effects of a
high humidity environment on PWAs.
Burn in tests are usually company specific, so IPC may not
have standards or specs on this. (Do they, Mike Buetow?).
MIL-STD-202 has a variety of specifications on high humidity
testing. MIL-STD-810 covers the methodology for
environmental stress screening, which uses high humidity.
Well, gotta stop, my wrists are starting to unhinge.
Doug Pauls
CSL
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