Optimal acceleration of cyclic THB tests for plastic-packaged devices

The authors develop a model for calculating the effective acceleration of a temperature-humidity-bias (THB) stress which alternates between two environmental conditions. A key element of the model is a one-dimensional mathematical description of the moisture-retention properties of the plastic package. The model can be used to find the duty cycle and period of cyclic THB stress which maximizes the cycle-averaged THB acceleration. The authors demonstrate the model by applying it to hypothetical cases in which cyclic bias might be used. The demonstration provides guidelines for application of power cycling for 85/85 and 130/85 HAST stressing. The model requires knowledge of the THB acceleration factor of the die-level failure mechanism as a function of the local temperature, humidity (RH), and bias at the die. The authors use an experimentally determined acceleration factor model for moisture penetration through passivation microcracks.<>