Printed Circuit Boards and Parylene

While Parylene can be applied as a uniform coating across a wide variety of applications, one of its most common uses is for protecting printed circuit boards (PCBs). Product engineers utilize Parylene because it offers a unique blend of capabilities.

Thin and Complete

Parylene is the only commonly used conformal coating that is deposited in a vapor state. While vapor deposition is a relatively complicated process, it offers two fundamental differences over the liquid deposition processes used for other conformal coatings.

First, because it is a vapor, it can occupy any space that air can reach. This means that the coating is truly conformal. Thick liquid coatings can have trouble reaching the small gaps between parts. Parylene has no problem covering these small gaps, since it is applied as a vapor.

Second, because of the combination of the vapor deposition and Parylene’s unique chemical makeup, the coating protects the application even when applied in an extremely thin coating. It can be applied ultra-thin as to have almost no impact on the total thickness or weight of a coated item. This has the benefit of protecting products that require lightweight properties.

Tin Whisker Mitigation

Tin whiskers are small crystals of tin that come out from soldered joints. Given enough time, the whiskers can become long enough to touch other connections, creating short circuits. Since PCBs usually have a significant number of solder points, tin whiskers are extremely likely to form.

Typically, there are two ways to mitigate tin whiskers. One is to use solder containing lead. Unfortunately, lead solder is a major environmental and health hazard and is almost always unsuitable for applications where the item will be used in a consumer or health care system. The other solution is to conformally coat the PCB with Parylene, which prevents the whiskers from crossing with other connections.

Parylene as a Dielectric

While electric signals are necessary for printed circuit boards to function, interference from outside signals can also make them fail. Parylene coatings provide an excellent dielectric barrier to overcome this obstacle. Coated boards are better equipped to resist outside electrical and radio frequency signals, leading to better-operating and longer-lasting electronic devices.

Parylene not only insulates PCBs from the outside, it also insulates PCBs from within. Every printed circuit board has traces, or circuits, that carry signals from place to place. However, because those traces are originally uninsulated, they leak RF or EMI signals into the air and into each other. Parylene coatings don’t just protect the board from the outside world, it also protects the application from itself, letting designers build smaller boards with closer-together traces that resist interference.

Resisting (Almost) Everything

Parylene also protects printed circuit boards from harsh environments. Moisture, acids, bases, solvents, corrosive materials and most other chemicals and liquids cannot permeate it. This makes it an excellent candidate for protecting PCBs that will be used in varying atmospheric conditions. Parylene’s chemical and moisture protection barriers are so strong that it is approved for use in the moisture laden in vivo environment.

Workable and Reworkable

Parylene provides a comprehensive and strong coating, which is what most PCBs need. When repairs and rework are necessary on a coated PCB, Parylene is able to be re-applied or reworked.

Masking allows you to control where the Parylene deposits. For instance, you might want to coat a PCB, but leave its contacts uncoated so that data or power signals can flow through them. Putting a masking down before coating the board will allow you to do this.

Once the item has been coated, Parylene can also be removed through mechanical means. Microabrasive tools gradually remove Parylene in small areas, allowing access to exactly what is needed without compromising the rest of the PCB’s coating integrity.

An increasing number of manufacturers are choosing Parylene as their preferred PCB protectant, due to its multitude of unique benefits. Contact SCS learn how to use Parylene in your next PCB application.