ESS/HASS effectiveness model for yield and screen profile optimization

Environmental Stress Screen (ESS) and Highly Accelerated Stress Screen (HASS) have been used extensively to screen defects in manufacturing electronic products throughout various industries. To improve the screen effectiveness, an ESS and HASS optimization model has been developed that uses defect Precipitation Effectiveness (PE) and defect Detection Effectiveness (DE) to calculate Screening Strength (SS) over combinations of screens and tests. The model accepts actual or projected manufacturing workmanship and infant mortality defect densities at 4 levels of screening/testing within an ESS regime. Using these defect density estimates with the SS, the remaining defects and yields are calculated at each screening level. Visibility of SS and yields at each screening level allows identification of the optimum ESS regime with respect to test durations, escaped defects and consumption of life and cost of screening. The ESS/HASS Optimization model provides a fast comparison for identification of the most effective screening with respect to the percentage of life consumption.