Assessment of Environmental Screening for Improved Component Reliability

A multiple phase, high reliability test program for discrete semiconductor devices, recently completed for the Polaris missile program is described. The role of the electronics subcontractor as equipment designer and manufacturer, test and failure analysis laboratory, and technical liaison during concurrent supplier, subcontractor, prime contractor testing is discussed. Approximately 400, 000 production parts comprised of twenty-two discrete device types, were assigned as the subcontractor´s responsibility for procurement of screened parts, evaluation of fest results, verification testing, failure analysis and lot disposition. These parts included NPN and PNP transistors, general purpose, zener and reference diodes, varicaps, SCR´s and dual junction FET´s. The basic concept of using only a precap visual, environmental screening, and subsequent assessment testing to bring common parts up to a high reliability level is discussed. The relative effectiveness of each test phase is evaluated in terms of yield and early detection of failure modes.