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Date: | Wed, 27 May 2009 07:15:14 -0500 |
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Hi Wayne - I recommend you determine just how much flux and/or flux
residue remains under the component after processing. Your solvent
cleaning process may not be removing all or enough flux residue to allow
for the specific pwa circuit to function in a high humidity environment.
Carefully, without using flux, remove several other capacitors in that
region to see what is underneath. In some high humidity environments,
conformal coating is necessary due to circuit spacing and functionality.
Good Luck.
Dave Hillman
Rockwell Collins
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[TN] humidity test failure
Hi Technet Gurus!
I have attached a picture of a part responsible for excess current draw
during an extended humidity/temperature cycling test. (I copied Steve so
he can hopefully post!)
The board was carefully solvent cleaned, but no SIR test validating the
process strips all ionic contamination. The board is in an enclosure
where plenty of ionic contaminants are available.
Humidity was supposed to not exceed 90% and was to be non-condensing
during cycling. There were a handful of components which displayed
similar deposits on the same circuit board. These were the only parts
biased during the humidity test. I believe the evidence suggests at least
some condensation occurred. To me the deposits look like salts. But
what do "the experts" think?
Is there any rule of thumb as to humidity levels where we are nuts to try
to survive without conformal coating? Part of the adjacent circuitry
contains RF devices and those guys get panic-stricken when told we
probably need to conformal coat!
Wayne Thayer
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