Conformal coatings are generally made of a polymeric resin and, when necessary, thinned in one or more solvents to allow the material to be dispensed and flow properly.
The best type of resin to choose depends on the required protection needed for the electronic device and the particular environment it will be located. How the coating will be applied and ease of repair and rework are also important factors.
Typical Conformal Coatings
“Typical” conformal coatings are 1-part systems that have a resin base, and maybe diluted with either solvent or (in rare cases) water. These coatings are semi-permeable, so do not fully water-proof or seal the coated electronics. They protect from environmental exposure, improving the durability of the electronic device, while still being practical to apply and repair.
Coatings are categorized by their base resin:
Acrylic Resin (AR) – AR coatings are relatively economical, provide good overall protection, and are easy to apply and repair. They have high dielectric strength, and fair moisture and abrasion resistance. Acrylic coatings are easily and quickly removed by a variety of solvents, often without the need of agitation. This makes rework and even field repair practical and economical. Acrylic coatings are not effective at protecting against solvents and solvent vapors, like jet fuel fumes common in aerospace applications.
Konform AR Acrylic Conformal Coating is easy to use, offers great protective properties, and is IPC-CC-830B and UL certified.
Silicone Resin (SR) – Silicone conformal coating provides excellent protection in a very wide temperature range. SR provides good chemical resistance, moisture and salt spray resistance, and is very flexible. Silicone conformal coating isn’t abrasion resistant because of its rubbery nature, but that property does make it resilient against vibrational stresses. Silicone coatings are commonly used in high humidity environments, like outdoor signage. Removal can be challenging, requiring specialized solvents, long soak time, and agitation like from a brush or an ultrasonic bath.
ChemtronicsChemtronics offers Konform SR Silicone Coating, which provides great protection and flexibility. It is based on Dow 1-2577 resin, and is IPC-CC-830B and UL certified. Konform SR-X is a new silicone coating that is harder, clearer, with great salt-spray testing performance. Konform LED is a silicone conformal coating that is optically clear, so it can be applied directly over LEDs without causing a reduction of light intensity or color shift.
Urethane (Polyurethane) Resin (UR) – Urethane conformal coatings are known for their excellent moisture and chemical resistance. They are also very abrasion-resistant. Due to this and their solvent resistance, they are also very difficult to remove. Like silicone, full removal generally requires specialized solvents, long soak time, and agitation like from a brush or an ultrasonic bath. Urethane conformal coatings are commonly specified for aerospace applications where exposure to fuel vapors is a common concern. Chemtronics does not offer any urethane coatings.