Corrosion can occur when a continuous layer of water condenses on the
electronic circuitry. The water needs only a few dissolved ions to become
conductive and allow electrochemical reactions to start, resulting in
corrosion of metals on the circuit or the creation of electrical leakage
between conductors, especially with bias voltages that are present in the
circuitry. Protecting the circuit with silicone, however, has been found to be
one of the most effective ways to extend the life of the electronics in harsh
use environments. This has been documented over decades of use in the industry
in many different applications and use situations.
One of the keys for providing protection to underlying circuitry and other
metallic surfaces is attaining good wetting and adhesion of the cured silicone
to all surfaces of the electronic device or module. Liquid water is easily
excluded at the cured surface of silicone gels, but water vapor, present as
humidity in the air, can permeate to the interface. However, without a place
to collect, it causes no ill effects. Whether it’s from the enhanced adhesion
additives of toughened gels or the naturally tacky nature of most gels, good
adhesion is attained to many common surfaces, which eliminates even microgaps
where liquid water could condense.
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