Epoxy Conformal Coatings

Epoxy-based coatings are usually two-part systems with limited pot life. Similar to polyurethanes, they provide good moisture and chemical resistance. A major downfall is that they are almost impossible to remove chemically for rework.

Strengths

Useful to 150°C [302°F]
Harder Durometer
Abrasion Resistance
CTE Closer to Epoxy PCB Substrates
Higher Tg
Dielectric Properties

Weaknesses of Cure Type

Solvent Evaporation

Higher chloride contamination potential
Process intensive, difficult to maintain viscosity, complex mix ratios
Potential for high stress during temperature cycling conditions
Difficult to rework
High probability of reversion under temperature and humidity stress conditions

Heat Cure

Cure is dependent on thickness
Component mass affects time and temperature of cure process
Susceptible to cure inhibition
Selective coating quality (edge definition) could be impacted
Shrinkage (3% - 10%), potential for damaging fragile (e.g. glass) components
Should be used with caution for low temperature components

UV Cure

One-component coatings require accurate application material to avoid shadowed areas
Two-part systems require meter mix equipment
Some coatings are more difficult to rework
UV intensity and wavelength effects cure
Some secondary cure mechanisms require heat exposure

Catalyzed

Cure inhibition
Short work life
Contamination sensitive
Difficult to rework
Pungent order

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