In the course of our business applying parylene to a range of different products, our clients ask many questions. They also have a few consistent misconceptions. Here are the five biggest ones -- and the facts to clear things up.
1. Parylene Doesn't Stick to Metal
This misconception is based in truth. One of this coating's drawbacks is that its chemical structure doesn't always adhere as well to metal as it does to other materials. However, there are two ways to rectify the challenge. Metal surfaces that aren't perfectly smooth will provide enough surface area for the parylene to flow in and adhere to the substrate. If your product has smooth surfaces, you can also improve parylene adhesion via silane or other surface modification methods, which adheres to both the coating and the metal, giving you the protection you desire.
2. Once Applied, It's Essentially Indestructible
In the world of conformal coatings, parylene is one of the toughest. It has a broad temperature range, can withstand most normal types of abrasion and is chemically inert, making it unlikely to corrode away. It can be removed, though. Extreme heat will eventually melt it, although it carries the risk of damaging the components underneath. Instead, the most effective removal methods usually require a mechanical approach, with the use of tools providing micro abrasion typically providing the best results.
3. Every Type is the Same
Parylene dimer comes in two primary types -- C and N formulations. The most popular type -- C -- offers better performance across most metrics. Parylene N has three key advantages that may apply to your application, though. It has a higher melting point, it is a more effective dielectric, and because of its more active molecular structure, it is better able to permeate very small cracks and crevices, making it a better compound for coating extremely complex surfaces. Other types of the dimer are also available, although the C and N variants are, by far, the most commonly used.
4. Parylene is Always the Best Choice
For many applications, parylene is the best choice. It offers a package of attributes that make it generally more attractive than other coatings. However, it might not be the best coating for your exact needs.
For example, epoxy is harder, providing even better protection against damage or against having your product reverse-engineered. Acrylic is easier to remove. Silicone can be applied in a layer so think that it serves as a shock absorber as well as a coating. Finally, most coatings are also usually less expensive and are usually easier to apply quickly to large quantities of product.
5. Parylene Is Too Expensive for My Application
Parylene conformal coatings are usually expensive choices due to both the high cost of the underlying chemical and the unique demands of their vapor deposition process. However, you can manage their costs to make them more affordable than the material cost on its own might indicate.
First, you typically need less of the dimer to coat an item than you might think. This is because it is effective at thickness levels measured in microns instead of mils. Using less means that you are able to stretch your materials further.
Second, the unique way that the coating gets applied both creates opportunities for waste and for minimizing that waste. Vapor deposition means that you have to fill an entire coating machine with the material and that the material will coat the chamber as well as the products. In a relatively empty chamber, the waste rate will be high. However, if your run includes enough product to fill the coating chamber, you will reduce the waste per unit, lowering your cost.
Lastly, the cost benefits of failure must be weighed against the cost of coating. Often times, on critical devices the higher price is worth the potentially life savings benefits that parylene offers.
If you have additional questions about parylene or other conformal coatings, contact us. Our expert staff can answer your questions, clear up your misconceptions and help you find the right coating for your next project.