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October 2004

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Subject:
From:
"Whittaker, Dewey (AZ75)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Whittaker, Dewey (AZ75)
Date:
Tue, 19 Oct 2004 06:29:10 -0700
Content-Type:
text/plain
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text/plain (95 lines)
He's back! The old Doug we all know and love.
See you in Minneapolis.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Douglas O. Pauls
Sent: Monday, October 18, 2004 2:55 PM
To: [log in to unmask]
Subject: Re: [TN] Moisture on PWB and Conformal Coating


Wellllll, ya shoulda said so in the first place.  Your failure in humidity
testing may have nothing to do with the conformal coating.  Do you, by
chance, sell solder mask?  It is usually the solder mask vendors who point
the finger first at the conformal coating (IPC meetings upcoming, must warm
up).

Your failure may be due to pinholes in the coating, or incompleteness of
coverage, incompleteness of cure, uncured coating under parts, you might
have ionic contamination present that causes leakage when humidity sets in,
you might have an organic contaminant that absorbs water and induces other
failures.  Hell, you might have a chipmunk running around in your test
chamber gnawing on the cables.

I have seen humidity related failures in the past (not here of course) and
the engineering response (not ours, of course) is to try to pot the
assembly with conformal coating.  Then the drawings get to production and
the operators wonder how long it will take to apply 25 mils of acrylic
coating.  My theory is that if we gave our manufacturing operators small
baseball bats and let them run through the engineering cube farms in search
of the worst offenders, products would get better by a thinning of the
stupid from the herd.  And I'm considered a loose cannon.  Go figure.

Contact me off line, I think you have other problems beside pre-coating
dryness.

Doug Pauls




                      "Shoda, Stephen J
                      (US SSA)"                To:
<[log in to unmask]>, <[log in to unmask]>
                      <steve.shoda@baes        cc:
                      ystems.com>              Subject:  RE: [TN] Moisture
on PWB and Conformal Coating

                      10/18/2004 04:33
                      PM






Doug,
We are only a medium sized mid-west corn growing state, so I'm certain the
ambient moisture failure mode is now ruled out!

I working on a development product which failed humidity qualification
test. Upon return testing, the board was baked out for numerous hours. As
it dried out it failed less electrical tests, but it took over 8 hours of
baking.

I want to make sure the modules are very dry prior to conformal coating the
retest samples.


Steve

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