Vibration resistance of conformal coated axial-lead components on printed wiring assemblies

The conformal coating applied to the printed wiring assemblies of military and aerospace electronics both prevents electrical insulation property degradation by moisture and other environmental contaminants and supports small components in a way that increases their resistance to vibration-induced lead fatigue failures. Attention is given to the results of a test program aimed at the compilation of engineering data on the fatigue resistance of axial lead components which have been conformally coated with typical epoxy, polyurethane, and silicone formulations. The development of a test method for the determination of fatigue resistance in conformally coated, filleted, or bonded axial lead components is described.