Rapid Evaluation Methods for Thick-Film Multilayer Conductor Systems for Hybrid Microcircuits

Palladium-silver and copper thick-film conductors are now being widely used instead of gold in the fabrication of multilayer hybrid microcircuits, with a possible consequent increase in the risk of conductor crossover failure. Because of the potentially very large number of thickfilm material combinations available for the construction of such crossovers, evaluation methods more rapid than the 85°C/85 percent relative humidity (RH) test (currently used by British Telecom) have been investigated. A measurement of insulation resistance made after boiling in salt water and drying has been found to correlate with the results of an 85°C/85 percent RH test. A room temperature insolation resistance greater than about 3 x 10¹¹ cm2 indicates a suitable materials combination for Pd/Ag crossover systems, while a somewhat lower value may be acceptable for copper. Measurements at high temperatures of insulation resistance and time-to-failure under bias did not, however, correlate with the 85°C/85 percent RH results and were only useful for predicting time-to-failure under dry conditions.