There are various types of conformal coatings for PCBs and they all have their pros and cons. Picking the proper type for your use case is based on what components are used, the level of protection needed, cost guidelines, and usability. The main types of coatings are acrylic, silicone, and urethane resin. Less common coatings are epoxy and parylene conformal coating, and nano coatings.
PCB Conformal Coating Types
Acrylic Resin Coating is the most common and basic type of coating. This is fairly cheap and gives a good amount of protection to PCBs and their components. The coating protects printed circuit boards from dirt, moisture, dust, but can be damaged by solvents or other chemicals that can eat away at acrylic. This is also a benefit as an acrylic coating can be easy to remove with solvents. Acrylic coating is known for good insulation with a high dielectric withstanding voltage. It is generally cheap and fast drying. Another benefit is that inspecting the coating is easy with a UV light as it glows. Acrylic coating is also able to be applied by spray, brush, or dip tank.
Silicone Conformal Coating is also a good choice but has different benefits and negatives. The coating is more flexible due to being silicon and is able to handle vibrations very well. Many can also handle high heat, salt spray, and chemicals well. The biggest issue with silicone conformal coating is that removing the coating takes specialized solvents and long soak times. This type of coating also can be seen under a UV light for inspection.
Urethane Resin has good properties in blocking out moisture and chemicals. This causes the same issue as silicone conformal coating where it is hard to remove after applied. Unlike the silicone coating, it is much more scratch and abrasion resistant.
Epoxy Conformal Coating is a two part compound that has high resistance to chemicals and salt. They have high abrasion and chemical resistance but are very hard to remove after applied. Epoxy coating is fairly stiff and provides the best hardness. Reworking and repairs are fairly difficult but can be done using the proper chemicals. A methylene chloride based solvent and an acid activator can be used to spot chemical strip.
Parylene Conformal Coating is a strong coating and can be applied very thin. The coating has to be applied through a vapor deposition process. Different types of parylene are heated up together at over 100C in which is sprayed as a monomer gas after the mixture becomes sublimated in the heated vacuum. The PCB assemblies are put inside a coating chamber and after being sprayed, a cooling phase occurs which is used to remove the residual parylene materials. This process is much more involved than the others on this list, pricier, and has the ability to limit throughput.
PCB conformal coatings have many benefits but in order to choose the right one, your team must analyze the boards usage. This guide should act as a good starting point for your decision. If your project has a specialized use case, contact us and we’ll see what we’d recommend.