What are the various kinds of conformal coatings?
Conformal coatings are applied to printed circuit boards (PCBs) to protect them from environmental stress such as salt, corrosion, humidity, and moisture, mitigate tin whiskers, and provide a barrier to electrically insulate components. They enable design of smaller electrical assemblies, while increasing mechanical support for components, and improving the fatigue life of solder joints.
A wide variety of conformal coating types are available, including silicones, acrylics, polyurethanes, epoxies, poly-para-xylylenes, and light-cure chemistries. It can be difficult to know which coating is right for the required application, but below is a summary of their pros and cons to get you started.
Acrylic Conformal Coatings: Liquid coatings that require the use of solvents for application. The products excel on printed circuit boards for moisture protection. In applications with possible exposure to solvent vapor, acrylic conformal coatings do not provide the best protection. They have poor chemical resistance, so they are easy to remove and rework.
Epoxy-Based Conformal Coatings: Usually the materials are two-part systems with limited pot life. Like polyurethanes, they provide good moisture and chemical resistance. A major downfall is that they are almost impossible to remove chemically for rework.
Poly-para-xylylenes: Coatings that are applied at very high temperatures with a vacuum-coating process. Therefore, they cost significantly more compared to other technologies.
Polyurethane Conformal Coatings: These coatings come in single-component, two-component, UV-curable, and water-borne systems. Although polyurethanes provide good chemical and moisture resistance, they are often hard to rework and have low tolerance in humid environments.
Silicone Conformal Coatings: Often used for very high- or low-temperature environments, these coatings provide high humidity and corrosion resistance along with good thermal endurance but require thermal curing and have short pot lives. Silicone coatings are also prone to abrasion (low cohesive strength) and have high coefficients of thermal expansion.
Urethane Conformal Coatings: These materials are more durable and rigid than other types of coatings. They are widely used for printed circuit boards since they provide excellent protection against chemicals and moisture. Although urethanes have a high tolerance against solvents, removal of the coating to rework is possible. These coatings typically take much longer to cure than acrylated urethane coatings.
LINK:https://dymax.com/resources/news-and-media/blog/conformal-coating/the-different-types-of-conformal-coatings
