A 2-level environmental-stress-screening (ESS) model: a mixed-distribution approach

Environmental stress screening (ESS) is used to reduce, if not eliminate, the occurrence of some types of failures from the field by fixing them before the product is deployed. This paper models a 2-level ESS program where screening is performed at the part and unit levels. The parts are screened for a specified duration before being assembled into a unit. Defects induced during the assembly process are screened at the unit level. These parts and connections are assumed to come from either a good or a substandard population, and their times-to-failure distributions are modeled by mixed distributions. The optimal screening durations are obtained by minimizing the life-cycle cost. The model is simple to use and its viability is illustrated using mixed exponential distributions. The implementation of screens at various levels depends on costs and failure distribution characteristics