Silicone Conformal Coating vs Parylene
Posted by Sean Horn
Friday, August 7, 2015 9:46
@ 9:46 AM
Silicone and Parylene conformal coatings are a lot like humans and dogs. At first glance, we are very different from our canine friends. However, we have a lot in common — noses, two eyes, hearts, dreams. In fact, we share 84 percent of our DNA with Rover (or Spot). So too with the two coatings. While both have some functional differences — which we’ll explore here — they also have an important similarity. Parylene and Silicone are both some of the best choices for conformal coatings of your company’s products.
Both Silicone and Parylene are technically polymers. However, there is a fundamental difference between the two. Parylene dimer is a hydrocarbon molecule, chemically related to just about every other plastic on the market. Silicone, on the other hand, is based on a blend of silicon and oxygen atoms instead of carbon and hydrogen. This makes it chemically unique among conformal coatings.
While Silicone’s chemistry is unique, its method of deposition is not. Silicone comes as a liquid and can be applied via spraying, dipping or brushing, like most other conformal coatings. Unlike other conformal coatings, silicone typically needs to be applied in a relatively thick coat to be effective per IPC Standards, between .003″-.008″.
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 touch — and coat — anything that air can touch. Unlike Silicone, Parylene coatings are extremely thin.
Both materials provide physical protection, but do it differently. Parylene forms a thin coating aqnd does not offer strong abrasion resistance. Silicone, on the other hand, is roughly 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 impacts.
Parylene supports a broad range of temperatures. In normal conditions, it can withstand cold as intense as -165 degrees Celsius without physical damage. Day-to-day heat is not a challenge for it, either. Parylene can withstand temperatures as high as 200 degrees Celsius in a vacuum, while it can remain stable at a constant temperature of 80 degrees Celsius for 10 years.
For more intense settings, there is a very good reason that many non-metallic bake ware products are made of Silicone. It is uniquely good at withstanding high temperatures. 200 degrees Celsius is a baseline operating temperature for most Silicones. Some can withstand temperatures as high as 600 degrees Celsius.
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 strongest chemicals on the market for resisting water. However, it does not resist solvents as well as others. If you need that property, this can pose a challenge.
Parylene is the conformal coating industry’s gold standard for resisting moisture and chemicals. Almost nothing gets through it. It resists water, corrosive materials, acids, bases and solvents. In fact, it is so effective at resisting these materials that it not only enjoys USP Class VI certification for biocompatibility but that it is also used to coat implantable devices — including those made of Silicone.
Both conformal coatings provide excellent and long-lasting protection. However, they serve different purposes. When you need to put PC board in an extremely tight space on a device meant for use at sea, Parylene is the best option. A component going in an engine compartment where it will be exposed to vibration and heat should probably be Silicone coated.
Ultimately, what your company needs is an expert in both coatings to help you decide which one to use for your intended application. Contact us to learn more about how Diamond-MT can help you.
Download our guide on Parylene 101
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