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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