How to Improve Parylene Adhesion

Through the deposition process, Parylene does not adhere chemically, only mechanically, to any given substrate. In order to improve Parylene adhesion for a wide variety of substrates, different methods of surface modification via adhesion promoters must be used. Adhesion promotion methods are typically used before the actual coating process. However, some can be integrated during the process itself.

The largest factor affecting Parylene adhesion is surface cleanliness. Contaminants on the substrate that have accumulated during all phases of manufacturing, as well as handling and transportation, can cause very poor adhesion and lend to poor overall coating quality. It is highly recommended that substrates be cleaned prior to coating. Contrary to popular belief, this includes no-clean fluxes. Cleaning can be done via manual methods, inline, batch or ultrasonic means.

One common surface modification method to improve Parylene adhesion is the use of A-174 silane. This adhesion promoter is usually applied after the masking operation, either by a manual spray, soaking, or a vapor phase silane process, depending on each individual application. The A-174 silane molecule forms the chemical bond to the surface enabling Parylene’s mechanical property to form improved adhesion characteristics.

However, in some applications, materials remain to which Parylene coatings may not achieve optimal adhesion. Developed by SCS’ industry-leading team of research and development engineers, AdPro Plus® and AdPro Poly® increase adhesion between Parylene coatings and difficult substrates, including titanium, stainless steel, gold, chromium, solder mask and many polymeric materials. When looking to improve Parylene adhesion, a close review of all of the current processes, including handling, is a necessity. Once best adhesion practices have been established, it is important to enforce strict adherence to the processes. If adhesion becomes an issue, any deviation from a process can be a good troubleshooting start-point.

Using industry best practices, such as substrate cleaning and an adhesion promotion application, combined with standard, repeatable processes will ensure strong adhesion for Parylene coating.