Drawbacks of Parylene Coating

Parylene has a well-deserved reputation as one of the leading choices for conformal coatings. For many applications, it is the best choice. However, there are some Parylene disadvantages as well.

Coating Cost and Logistics

A major downside of Parylene is its cost. The Parylene dimer used for coating varies in price and is usually purchased by the pound. Since a single run necessitates a pound of Parylene, the material cost can soar, particularly when only a few components require coating.

In addition, Parylene can only be deposited one way — as a vapor in a vacuum. This requires highly-specialized equipment that has limited capacity, making it hard to handle very large quantities of items. At the same time, since the coating process requires extensive preparation before it can start, the labor cost of coating makes Parylene doubly unsuitable for small runs.

Other coatings can be applied in small or large batches using a range of different methods. Furthermore, many of these coating materials are substantially less expensive. This makes it easier and less costly to coat both very small and very large jobs.

Total Coverage… No Matter What

Parylene covers everything, everywhere. Since it is deposited as a vapor, it coats anything that air touches. While this can be a highly desirable feature, it also means that items that are not intended to be fully coated need to go through a masking process that adds time and expense. Acrylic coatings, on the other hand, can be sprayed or brushed on by coating operators or automated equipment. This makes it easier to only apply the coating where it needs to go.

Thin and Clear

Parylene is optically clear and ultra-thin. While these characteristics are often desired, they may be a disadvantage is some instances. A thicker conformal coating, like silicone can provide, can add an additional layer of cushioning and shock protection to the coated item. While Parylene protects the items that it coats, especially given its cost, it is more likely to be applied in a thin coating.

Parylene’s optical clarity makes it suitable for coating lenses and optical elements. However, this also means that anything coated with it is visible to anyone that looks at it, including someone that is interested in reverse engineering the item. Pigmented epoxy and polyurethane coatings can be used to completely cover the item, hiding its components. They also have roughly similar toughness to Parylene, making it hard for someone to remove them.

Total Protection

Parylene is very difficult to remove. It is hard, solvent-resistant and relatively heat-resistant. This means that the only practical way to remove it is with time-consuming and inconvenient micro-abrasion. Reactive coatings like acrylic can be removed by something as simple as a cotton swap dipped in solvent. Other stripping solutions work on silicone-coated items and some even work to remove polyurethane coatings.

UV Resistance

Many of the less expensive Parylene dimers have relatively weak resistance to ultraviolet light. This means that if they are used on a component that is mounted outdoors, they could yellow. While some Parylene dimers have UV resistance, they are typically the most expensive formulations, costing thousands of dollars per pound. For comparison, both silicone and acrylic coatings can be applied in a UV-resistant formats that allow them to be used outdoors for extended periods of time without any degradation or yellowing. This property also makes them more effective at protecting the items that they coat from UV radiation.

Although Parylene comes with its share of drawbacks, it boasts notable advantages as well. Ultimately, various coatings are tailored to specific products. It is crucial to assess the distinct protective properties required for each application in order to identify the most suitable coating solution.