On the Implications of R&M 2000 Environmental Stress Screening

The US Air Force R&M 2000 ESS policy differs little from that of the other armed services in that the same two primary screens, temperature cycling and random vibration, are employed at the module and end-item levels. Two of the screening parameters, 25 cycles and 30 °C/minute, for module-level temperature-cycling exceed the norm. What is different is the requirement for part defect rates, 1000 parts per million (ppm) beginning in 1986 October and 100 ppm in 1989 October. Defense contractors will have to figure out how to work with their part suppliers, or develop in-house screening methods to get part defect rates down to 100 ppm. The Air Force has published a handbook [1] and a companion guideline document [3] for implementing the ESS policy. The handbook contains procedures for addressing the four problems: 1) estimating the fraction of defects entering the manufacturing process, 2) estimating the fraction of defects generated during manufacturing, 3) assessing the effectiveness of stress screens, and 4) determining an acceptable level of defects remaining on delivery. The ESS policy and guidelines can result in effective application of ESS and improved field reliability.