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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 coatings, but water vapor, present as humidity in the air, can permeate to the interface. However, without a place to collect below the coating, it causes no ill effects. Good adhesion eliminates gaps where liquid water could condense.
Besides humidity, conformal coatings provide protection from vibration and a wide variety of contaminants such as vapors, some solvents, and salt spray.
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