Plasma Deposition and Modification of Electrical Barrier Coatings

Abstract

Water damage is one of the leading causes of failure of smart phones and other personal devices, and as such protective coatings are of great importance in this field. The application of an electrical barrier coating to the internal circuit boards of an electronic device can protect it from corrosion and damage, and in this thesis new barrier coatings were developed for this purpose. An introduction to the use and types of electrical barrier coatings is provided in Chapter 1, and the experimental techniques used to evaluate the coatings developed herein are described in Chapter 2. Chapter 3 describes the process of preparing a barrier coating which provides complete protection from water damage to a circuit board. Allyl mercaptan was plasma deposited onto unsaturated polymer base layers resulting in a two-fold process of thiol-ene bonding between the plasma polymer layer and the base layer, and the formation of a highly crosslinked top layer arising from the thiol-ene reactions between the thiol and vinyl groups in the allyl mercaptan. An extremely superhydrophobic coating is described in Chapter 4, which as well as functioning as a wet electrical barrier coating had an extremely high water contact angle combined with low contact angle hysteresis. This coating was prepared by the deposition of a polyisoprene layer which was then functionalised by plasma fluorination. Gas pulsing was used to deposit a silane containing base layer, which significantly improved the barrier performance of the fluorinated polyisoprene coating. Plasma deposited thiol-acrylate coatings were applied as wet electrical barrier coatings in Chapter 5. Based off the findings of Chapter 3, it was posited that the dual deposition of allyl mercaptan with an acrylate could also be used to form a highly crosslinked layer imparting water protection to circuit boards. Although a composite coating was formed little improvement was seen over the thiol-ene coating of Chapter 3. Chapter 6 summarises the conclusions arising from this thesis, highlighting the areas where significant improvements in the wet electrical barrier performance were found.