Parylene (XY)

Co-Authors and contributors

  • Dr Lee Hitchens, Nexus

Parylene (XY) is the trade name for a variety of chemical vapour deposited poly(p-xylylene) polymers used as moisture and dielectric barriers.

Parylene can be further divided into typically four chemical types. These are Parylene C, D, F and N.

They are vacuum deposited coatings. That is they are not like the liquid coatings.

They are applied in a vacuum chamber and deposited as a gas onto the surface of the circuit board.

Hence, this is a very different process application technique to the liquid conformal coatings.

Parylene Properties

The material properties of the XY coating are very different to the liquid coatings.

  • Parylene coatings are completely conformal to the surface of the Printed Circuit Board (PCB) or product. This means that the coating has a uniform thickness and is pinhole free. As a result, component configurations with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.
  • Parylene coating provides an excellent barrier that exhibits a very low permeability to moisture and gases. This means that products coating in parylene generally are more “waterproof” than the same products coated in a liquid conformal coating.
  • Parylene is unaffected by solvents, has low bulk permeability and is hydrophobic. Coatings easily pass a 100hr salt-spray test.
  • Parylene has excellent electrical properties. These include low dielectric constant and loss with good high-frequency properties, good dielectric strength, and high bulk and surface resistance
  • Parylene is chemically and biologically inert and stable and make excellent barrier material.
  • Parylene has good thermal endurance: Parylene C performs in air without significant loss of physical properties for 10 years at 80°C and in the absence of oxygen to temperatures in excess of 200°C.

There are a few key points to consider with Parylene since it performs as a superior product to most other coatings.

  • The parylene process is a batch process. This means it does not lend itself easily to low cost high volume processing.
  • Parylene require masking of components that are not to be coated just like other liquid coatings. However, since this is a vapour being applied, the masking must be 100% effective or the coating will penetrate into the wrong areas.
  • There is no pigment or UV trace in a Parylene coating. This means inspection of the coating can be more challenging.
  • Rework of Parylene is normally achieved with abrasion techniques since it is chemically resistant.

Further information can be found on Parylene by clicking Alternative Coatings: Parylene