What Are Conformal Coatings?
Conformal coatings are clear, flexible topcoats that conform to the intricate geometries of PCBs. They are applied over circuit boards to ruggedize them and thereby extend product life.
Conformal Coating Material Types
There are currently eight distinct families of conformal coatings, as designated in the IPC-CC-830C Standard. These comprise acrylic, polyurethane, silicone, epoxy, UV curable, parylene, ultra-thin and styrenated block-copolymer types. The table below summarizes the pros and cons associated with each coating type.
|Acrylic||Ease of use, low cost||Poor solvent resistance|
|Polyurethane||Abrasion resistance||Long cure times|
|Epoxy||Chemical and scratch resistance||Difficult to use and rework|
|Silicone||High temperature resistance||Poor solvent resistance|
|UV Cure||Very fast cure time||Expensive, high capital cost|
|Parylene||Completely conformal and uniform||Expensive, difficult to apply|
|Ultra-Thin||Fast cure, good hydrophobicity||Less surface protection than other coatings|
|Styrenated Block-copolymer||Superior moisture protection||Poor solvent resistance|
Choosing the right technology will depend principally on considerations like: What (if any) certifications do I require? What are the main environmental concerns I need protection from? And, what are my processing capabilities? Ultimately, proper material selection comes down to knowing all of your requirements.
How Are Conformal Coatings Used?
Conformal coatings are used to help extend the life of circuit boards by providing a layer of protection against common environmental elements, such as moisture, dust, dirt, and fungus. These coatings have excellent dielectric properties that help prevent flashover, which allows traces to be placed closer together and thereby facilitates the design of smaller, more powerful electronics components.
Conformal Coating Standards
There are two main standards for conformal coatings: UL746E and IPC-CC-830. The UL746E Conformal Coating Standard comprises a series of dielectric tests that measure the coating’s insulation properties following environmental stress, as well as its flame retardancy. The IPC-CC-830 standard was created by the Institute for Printed Circuits (IPC) to replace the MIL-I-46058C Standard, which was declared inactive in 1998. This standard test the coating’s durability against thermal shock, hydrolytic aging, moisture saturation, fungal resistance and flame retardancy.
We have provided more specific details concerning both the UL746E and IPC-CC-830 Standards in these two articles.