Parylene can be successfully applied to almost any substrate, common materials include metals, elastomers, plastics, paper and glass. A key factor to this success is adhesion which can vary quite considerably unless the right pre-treatment procedures are followed.
As Parylene adheres mechanically to the substrate cleanliness is the first step. The substrate must be free of contaminants. Many post manufacturing cleaning leaves residues, so a further cleaning process must be carried out so ensure coating adhesion can take place. These include sources such as mould release agents on plastic and elastomeric components and ‘no clean’ flux on PCBs.
Once the parts to be coated are clean, the next step is to determine the correct adhesion promotion method. Where there is micro porosity in the surface such as with many elastomers or where a metal substrate has a high RA, little or no adhesion promotion may be required. However, most other substrates need adhesion promotion of some sort.
Common methods include:
Mechanical abrasion: This is where a very fine grit is used to lightly abrade metal surfaces therefore creating a mechanical key for the CW Parylene to attach to. This is commonly used in the production of Parylene coated wire mandrels, manufacturing aids used in the Medical Device industry.
Plasma activation: As a pre-treatment this method activates the surface of many substrates including polymers, ceramics, glass and metals. As the activation is short lived this is usually carried out just before the coating process takes place.
Chemical bond pre-treatment: The most commonly used silane solution for pre-treatment is A-174 which is applied by various methods including spray, dip and within the chamber by vapour deposition. CW Parylene’s adhesion can be greatly improved by pre-treating the surface in this way as it creates a chemical bond to the surface, improving the ability of CW Parylene to mechanically attach to the substrate.
At Curtiss-Wright, we apply the most effective methods to clean and pre-treat the parts to ensure excellent adhesion, with thorough testing to ensure consistency of the results. We have proprietary silane’s that are specifically formulated to ensure excellent adhesion with more challenging substrates such as noble metals and many polymeric materials.
Through our own development and external centres of excellence we continually strive to advance our adhesion promotion methods to handle the most challenging substrates, providing high reliability to customer applications operating in the harshest environments.