Silicone Conformal Coating vs Parylene

Silicone and Parylene conformal coatings may appear worlds apart initially. However, beneath the surface disparities, remarkable similarities exist. Despite their functional differences, Parylene and silicone share a crucial commonality as two of the finest options for safeguarding your company’s products.

Makeup

Both silicones (Type SR) and Parylenes (Type XY) are technically polymers. However, there is a fundamental difference between the two. Parylene is an organic hydrocarbon molecule, chemically related to just about every other plastic on the market. Silicone, on the other hand, is an inorganic molecule based on a blend of silicon and oxygen atoms instead of carbon and hydrogen. This makes silicone chemically unique among other conformal coatings.

Deposition

While silicone’s chemistry is unique, its method of deposition is not. Silicones come as a liquid and can be applied via spraying, dipping or brushing, like most other liquid conformal coatings. Unlike other conformal coatings, silicones need to be applied in a relatively thick coat, 25.8 – 203.2 microns, to meet the requirements of J-STD-001.

The only commonly used conformal coating to be deposited as a vapor in a vacuum is Parylene. Its vapor-based deposition means that it offers the best possible coverage of any conformal coating material since it can access — and coat — anything that air can access. Unlike silicones, Parylene coatings can be applied extremely thin, < 1 micron. In order to meet J-STD-001 requirements, Parylene coatings must be applied 10.2 – 50.8 microns.

Physical Protection

Both materials provide physical protection but do it differently. Parylene forms a thin coating and does not offer strong abrasion resistance. Silicone, on the other hand, is roughly an equivalent to a very soft rubber. When applied in a thick enough coat, it can actually serve as a shock absorber for the coated item, helping to protect it against impact and vibration.

Temperature Resistance

Parylene supports a broad range of temperatures. In normal conditions, it can withstand cold as intense as -165°C without physical damage. Day-to-day heat is not a challenge for it either. Parylene C can withstand temperatures as high as 200°C in a vacuum, and it can remain stable at a constant temperature of 80°C for 10 years. Parylene HT^® can withstand 350-450°C, depending on the exposure time.

There is a very good reason that many non-metallic bake ware products are made of silicones. It is uniquely suited for withstanding high temperatures. Most silicones have a baseline operating temperature of 200°C. Some can withstand temperatures as high as 600°C.

Chemical and Moisture Resistance

It is likely that your kitchen and bathroom — the two wettest areas of most houses — are sealed, at least in part, with silicone caulk. It is one of the best chemicals on the market for resisting water. However, it does not resist chemicals and solvents as well as other coatings. If you need chemical resistance properties, this can pose a challenge for silicones.

Parylene is the conformal coating industry’s gold standard for resisting moisture and chemicals. There are no known solvents or chemicals at room temperature that permanently degrades Parylene. It is an extremely good barrier against water, corrosive materials, acids, bases and solvents. It is so effective at resisting these materials that it is USP Class VI certified for biocompatibility and has also been tested to ISO 10993 requirements. Parylene is often used to coat implantable devices, including those made of silicones. Parylene C is the only conformal coating tested that survived the nuclear, biological, chemical (NBC) decontamination process that used decontamination solution number 2, DS2.

Both conformal coatings provide excellent and long-lasting protection. However, they serve different purposes. When PCBs need to be placed in an extremely tight space on a device meant for use at sea, for example, Parylene is the best option. Silicone coatings would be a good choice for a component going in an engine compartment where it will be exposed to vibration and heat.

Ultimately, an expert in both Silicone and Parylene is needed to help you decide which coating is best for your intended application. Contact us to learn more about how SCS can help meet your coating requirements.