Parylene vs. Potting

If you have a component that needs protection, you typically have a choice between potting and conformal coating. While potting offers the largest and most powerful barrier against external harm, it also carries some significant drawbacks. Conformal coating, especially with Parylene, also offers a protective barrier, but does it without the challenges that potting poses.

Potting

Potting is a two-step process. First, you put the item that you want to protect into a case or shell. That shell is the “pot.” Then, you take a liquid potting compound, such as certain types of epoxy resins, and pour it into the pot. This completely seals, or embeds, the item in the pot. With colored compound, you can even obscure the appearance of the device that you are protecting.

Parylene Conformal Coating

Parylene conformal coatings are, in many ways, the exact opposite of potting. With this method of protection, the technician places the item to be protected in a special deposition chamber. Vaporized Parylene dimer is deposited onto the item, creating a protective coat that covers it entirely, even under parts and inside gaps. The coating provides a high degree of protection, is ultra-thin, typically measured in microns, and remains virtually invisible.

Common Benefits

Potting and Parylene coating both provide some similar benefits. Either choice delivers a degree of dielectric protection. Coatings and potting also block moisture, preventing it from infiltrating the device. While the compounds used in potting can differ, both Parylene and the epoxies that are usually used in potting are also chemically inert, protecting against corrosion, salt, acids, bases and most solvents.

Common Drawbacks

Both methods have notable drawbacks. First, it takes time, effort and money to add the additional protection to the item. This increases production costs and turnaround time, slowing time to market. In addition, once an item is coated, the coating needs to be removed to allow access to it for any sort of additional work or repair. Unfortunately, potting and Parylene coatings are both hard, if not impossible, to remove.

Choosing a Method

Given that both methods have similar benefits and drawbacks, the choice might seem complicated. Often the faster and cheaper method is potting. In addition, because potting involves an exterior case and a large quantity of additional protective material, it is the best choice for items that need protection from abrasion or impact. Given that most potting materials are epoxy resins and most PCB’s are glued with epoxy resins, most efforts to remove the potting would also destroy the printed circuit board.

Parylene coatings are appropriate in certain instances, as well. Because they are ultra-thin and pinhole-free when applied, they are the best choice when tolerances are tight. The invisibility of the coating makes it a good choice when the item needs to be visible. Potting an indicator light wouldn’t make any sense, for example. Finally, Parylene coatings are biocompatible, allowing for them to be used within the human body.