Preparation of metal film resistors on laminated plastics

Some properties of metal resistance films on resin-bonded glass cloth have been investigated. Plastics laminates bonded with different polymers were coated with films of nickel-chromium alloy by vacuum evaporation and with sandwich films of gold between bismuth oxide layers deposited by sputtering. Glow discharge cleaning was essential before evaporation to make adherent films. Silicone resin bonded laminates were unsuitable for preparing stable resistors, because they had a large number of surface defects produced by strains arising during the curing process. Melamine bonded laminates were decomposed by ion bombardment during discharge cleaning or sputtering. The resistors were tested under a load of 1 W/in.2 of film area over a period of 3 months. Resistors which became non-conducting during the test were found to break down invariably along surface scratches in the base material. The most stable resistors on plastics bases were produced with epoxy or polyester resin bonded laminates, and with the metal films protected by a melamine lacquer. Nickel-chromium films up to 800 Ω/square and gold films up to 50 Ω/square reached a stable resistance value after an ageing period of about eight weeks.