Parylene Adhesion to Noble Metals

Parylene adhesion can be difficult to manage. Unlike other coatings that adhere to the surfaces they coat, Parylene sticks to itself. This can cause issues when it needs to be applied to smooth surfaces, like areas made of stainless steel or noble metals like gold or silver. Given Parylene’s numerous advantages, investigating methods to enhance adhesion is a worthwhile undertaking.

Introduction to Parylene Adhesion

There are two primary types of adhesion — chemical and mechanical. Chemical adhesion occurs when a compound bonds to another compound. For this to happen, the two compounds must be chemically active enough to bond with each other. Because Parylene is inert, it adheres using the other method — mechanical adhesion.

Parylene adheres by bonding with itself rather than directly to surfaces, effectively coating and filling them. Most coated items have small microscopic pits and cracks that the Parylene fills. In essence, it works like snaps on clothing except that, once the Parylene is snapped in, it does not come out. However, if Parylene is deposited on a perfectly smooth surface, there there are not any pits and cracks for it to fill, and it may not form a reliable coating.

Masking

When noble metals are chosen for their superior conductivity in applications, Parylene adhesion becomes irrelevant. If you intend to leave the metal exposed in a connection, avoiding Parylene coating is crucial, particularly due to its exceptional dielectric properties. By masking off these specific areas, you prevent Parylene from adhering (or not adhering) during the deposition process, effectively bypassing the issue.

The Silane Solution

While maintaining a perfectly clean surface may be enough to solve Parylene adhesion issues on most materials, some surfaces, including noble metals, require additional treatment. Coating those surfaces with a compound like A-174 silane can solve the problem.

Technically referred to as Methacryloxypropyltrimethoxysilane, A-174 is a colorless compound related to silicone. When applied to surfaces like noble metals, it provides an uneven surface to which the Parylene can bond. The silane chemically adheres to the metal, providing a tight bond between it and the surface. When the Parylene is deposited, it adheres to the uneven surface of the A-174 silane.

Silane is relatively easy to apply. If an entire item needs to be coated, it can be soaked or applied in its vapor phase. The compound can also be selectively sprayed on to the surface.

The addition of A-174 silane effectively solves Parylene’s primary adhesion challenge. This makes it a suitable choice for products containing noble metals that also need to leverage Parylene’s other beneficial properties. To learn more about how SCS can help manage Parylene adhesion issues, contact us today.