Effect of glow discharge treatment of substrates on parylene‐substrate adhesion

A detailed investigation of the effect of argon, oxygen, and methane glow discharge (plasma) treatment of substrates on the adhesion characteristics of parylene polymer to a variety of substrates is reported. It is found that methane glow discharge treatment, which results in the deposition of a glow discharge polymer of methane on the substrate surface, is most effective in improving the bonding strength of the parylene polymer, while the oxygen glow discharge treatment which produces a hydrophilic substrate surface with no or insignificant polymer deposition is detrimental to parylene adhesion. The effect of argon glow discharge treatment may vary from true cleaning of the substrate surface to deposition of a thin layer of a polymeric coating produced by the simultaneous glow discharge polymerization of the ablated organic materials existing in the reactor and may or may not improve parylene adhesion. These results are supported by the Auger electron spectroscopy and contact angle measurements of the glow discharge‐treated surfaces. Model studies using substrates of different surface free energies indicate that water‐resistant adhesion of parylene polymer increases with the hydrophobicity of the substrate material and is in harmony with the above findings. From the viewpoint of adhesion the most advantageous and dependable effect is obtained with the methane plasma treatment. The treatment results not only in the formation of a more compatible, hydrophobic surface but also produces radical sites for covalent bonding with the parylene.