How to Improve Parylene Adhesion
Parylene, through its deposition process, does not adhere chemically, only mechanically, to any given substrate. In order to improve parylene adhesion to its best possible levels for a wide variety of substrates, different methods of surface modification via adhesion promoters must be used. Adhesion promotion methods are typically used prior to the actual coating process, however some can be integrated during the process itself.
The largest factor affecting parylene (or any conformal coating) 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.
The most common surface modification method to improve parylene adhesion is the use of A-174 silane. A-174 silane 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.
When looking to improve parylene adhesion, a close review of all of the current processes, to include handling, is a necessity. Once best adhesion practices have been established, it is of utmost importance 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 A-174 silane application, combined with standard, repeatable processes will ensure strong adhesion for parylene coating.