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The
indirect effects are numerous. Some components
are sealed to prevent moisture of any type from
entering a device. Electronic components such as
electrolytic capacitors and integrated circuits
all are sealed to prevent this moisture
intrusion. In both cases, moisture breaching the
seal usually results in failures over time. As
humidity testing normally involves high heat, this
serves to aid in forcing water vapor through
weakly sealed components. High temperature and
humidity also work to promote the growth of fungus
and other forms of contamination. These effects
may only be the first step in that they may weaken
structures or connections eventually leading to
failure of the device over time.
With all of
this discussion, it must be pointed out that
humidity is considered a very weak stress in
general for electronic devices. It does have its
uses for specific component failure modes, and
verification of cleaning processes. It is
typically combined with high temperature and may
also be used in conjunction with altitude and
electrical power effects.
A final
note is that humidity is only applicable at
temperatures above freezing. This may seem
obvious as water freezes out of the air below 0
degrees C, but requests have been received for testing
involving humidity at –40 degrees C. Note also
that some environmental chambers require that the
humidity system be shut off when transitioning
below 0 degrees C. Failure to shut off the humidity
system results in the chamber being constrained to
temperatures above freezing thus not meeting the
desired profile.
Test
Specification Template (Static
Temp/Humidity/Altitude/Power)
Test
Specification Template
(Temp/Humidity/Altitude/Power Cycling)
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