Thermal Environmental Stress Screen Optimization

Abstract

A multi parameter optimization process is created to minimize test time for thermal environmental stress screening (ESS), while meeting the minimum desired strength of screen level. The ESS variables affecting the test time include the maximum and minimum soak temperatures, the maximum and minimum overshoot temperatures, the dwell time at soak temperature, the dwell time at overshoot temperature, the thermal chamber ramp rate, and the number of ESS cycles. Factors affecting the hardware strength of screen include the total temperature range experienced by the hardware, the hardware thermal ramp rate, and the number of ESS cycles. The Matlab based optimization routine includes a two node thermal model to generate a thermal chamber temperature profile and a resulting hardware temperature response given the known time constant of the hardware under test. Additionally, the optimization process also includes custom functions that specify necessary constraints, the most important of which is the desired minimum precipitation efficiency of 88.7%. For the case study presented herein, the optimization process produces a significant reduction in necessary test time while maintaining the desired minimum precipitation efficiency. Actual test time improvements depend on many factors including the hardware time constant, strength of screen requirements, and thermal chamber capabilities. The primary purpose of this study is to demonstrate a process by which thermal environmental stress screening can be optimized.