Conformal Coatings Guide and Overview
This article is based on an original publication by Chemtronics.
Engineered to protect circuit boards and other electronic components from adverse environmental conditions, conformal coatings adhere to irregular surfaces to ensure dielectric resistance and operation integrity.
Conformal Coating Resin Types
There are five main categories of conformal coatings:
- AR - Acrylic Resin
- SR - Silicone Resin
- UR - Polyurethane (Urethane) Resin
- ER - Epoxy Resin
- XY - Parylene
AR - Designed for moderate elasticity and general protection, this one-part system offers hight dielectric strength, high abrasion resistance, and easy application and removal.
SR - With an extensive temperature range and good chemical resistance, silicone resin offers excellent protection and flexibility but may require longer soaking times or special solvents for removal.
UR - Known for moisture, abrasion and chemical resistance, polyurethane coatings are also resistant to many solvents and are therefore difficult to remove.
ER - Engineered for high resistance to chemicals, abrasion and humidity, two-part epoxy resin compounds are not generally flexible and are very difficult to remove once cured.
XY - Highly resistant to solvents and temperatures, this uniquely durable coating is applied through vapor phase deposition.
Fluorocarbon Conformal Coatings - Formulated of conformal coating dissolved in a fluorocarbon-based carrier solvent, this material offers good moisture resistance but is easily rubbed off.
Varnish and Alkyd Coatings - Generally hard and moisture-resistant, these types of coatings tend to lack flexibility.
Conformal Coating Cure Types
Conformal coatings are also classified by cure mechanism. While some methods are foolproof, others leave room for error in an uncontrolled application process.
Evaporative Cure - To achieve this cure, a liquid carrier evaporates to leave a conformal coating behind. Although simple in theory, a surface must generally be dipped two or more times to accumulate adequate coating.
Moisture Cure - Generally employed with silicone and urethane materials, this process involves a reaction with ambient moisture to form a coating and is often used in conjunction with an evaporative cure.
Heat Cure - Typically used as a secondary mechanism for a UV, moisture or evaporative cure, the addition of heat speeds up the cure of a system.
Two-Part Systems - Designed for use with epoxy systems, this method begins to cure when two substances are mixed and ratios are strictly observed.
UV Cure - Coatings that are cured by ultraviolet light deliver fast production results and do not contain carrier solvents. While the need for a secondary curing system is eliminated, UV cured coatings can be difficult to repair and require protective considerations for workers exposed to UV radiation.