Partially ionized beam deposition of parylene

Conventionally deposited parylene C polymer thin films have excellent properties, including moisture barrier, toughness and electrical insulation characteristics. However, their use has been restricted by poor adhesion to most smooth or non-porous substrates characteristic of earlier deposition processes [H. Yasuda, B.H. Chu, D.L. Cho, T.J. Lin, D.J. Yang, J.A. Antonelli, Corros. Sci. 52 (3) (1996) 169. [1]]. In spite of this adhesion problem, parylene C has the proven ability to provide excellent environmental protection on electronic circuit boards for computer and general industrial products for which adhesion is enhanced by separate means. In addition to environmental protection, parylene will also encapsulate any solders that may be present and prevent them from causing shorting problems, and it is effective in very thin layers [R. Olson, Society of Vacuum Coaters, in: Proceedings of 31st Annual, May 2–6, 1998. [2]]. The work here shows that the adhesion between parylene C films and substrates can be greatly improved by ion-assisted deposition in which the parylene monomers are ionized and accelerated to the substrate during film growth. Solid parylene C is vaporized at 134 °C to a dimeric gas, and pyrolized to cleave the dimer to a monomer at 680 °C. The monomeric gas is ionized and accelerated toward the substrate by an electric field, and finally parylene is polymerized with some penetration into the substrate surface to improve the adhesion.