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Conformal Coatings Options
For conformal coatings, the most competitive options are materials based on:
acrylics, epoxies, urethanes, parxylenes or silicones.
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Acrylic
Acrylic coatings are typically solvent based and are easily repaired.
Traditionally they were low cost but have become less competitive with rising
regulation requirements and safety concerns with solvent usage. They were
tough, hard, and transparent - but lacked stress relieving capability. Pot
life was good since additional solvent could be added to keep the bath
viscosity low and they exhibited low moisture absorption and had short drying
times when volatile solvents were used.
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Epoxy
Epoxy coatings are very hard, usually opaque and are good at resisting the
effects of moisture. They possess excellent chemical and abrasion resistance,
but can cause stress on components during thermal extremes. Cure chemistries
can sometimes require extra precaution for safe handling. Fluctuating
temperatures can cause considerable drift in viscosities and difficulties in
controlling cure times and coating thicknesses.
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Urethane
Urethane coatings are tough, hard and exhibit excellent resistance to
solvents. Along with excellent abrasion resistance and low moisture
permeability, they offer good low temperature flexibility.
Their use is often prevented by their limited high-temperature capability and
lack of repairability.
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Paraxylylene
Paraxylylene coatings are very uniform and yield excellent pin coverage. Their
limitations include high cost, sensitivity to contaminants and the need for
vacuum application technique.
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Silicone
Silicone coatings range from elastoplastic (tough, abrasion-resistant) to
soft, elastomeric (stress-relieving) materials.
They possess the following characteristics:
Heat cure or RTV cure
Usefulness over a very wide temperature range
Good moisture and humidity resistance
Processing versatility
Easy
repairability
Low toxicity
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