Reliability of Conductors and Crossovers for Film Integrated Circuits

Evaluation of the reliability of thin film conductors and crossovers is essential for the determination of the life expectancy of circuits containing these elements operating under various conditions in the telephone plant. In the present study thin film conductor and crossover test circuits were encapsulated with RTV 3145 and exposed to dry temperature cycling and temperature cycling in a high humidity environment. The encapsulant effectively prevented corrosion and the crossover structures were not damaged by the mechanical stresses caused by the differential in thermal expansion coefficients of gold and RTV. The main failure mode was found to be the increase in leakage current through the encapsulant of the crossovers with a strong dependence on the thickness of the encapsulant and the applied bias voltage. It was concluded that the crossover and conductor life will be adequate for almost all applications, even under the most stringent environment conditions.