Environmental stress screening strategies for multi-component systems with Weibull failure-times and imperfect failure detection

Environmental stress screening (ESS) is employed to reduce, if not eliminate, the occurrence of early field failures. In this paper, a general two-level ESS model is presented for a multi-component electronic system. Screening is performed at the component and unit level. Components and connections are assumed to come from good and substandard populations and their time-to-failure distributions are modeled with mixture distributions. ESS models currently found in the literature assume that time-to-failure distributions are mixtures of exponentials. This paper extends previous work by examining mixtures of Weibull distributions for all assembly levels. The mixed Weibull distribution is used to examine how screening strategies change when wear-out mechanisms are present, Also, this paper relaxes the assumption that all failures precipitated by the screening process are found before being used in subsequent assembly levels. Numerical examples are provided to illustrate the screening model. Significant changes in screening strategies are found when the assumptions of perfect failure detection and exponentiality are relaxed.