Stochastic finite element modeling of fatigue damage evolution for visco-plastic materials in micro-electronics

Thermo-mechanical fatigue is one of the main failure mechanisms of solder joints in electronic devices. Deterministic approaches that are typically used to predict the life of joints, may predict the life far different from the test results and field environment. This difference is caused by uncertainties introduced in finite element and damage modeling with different random variables such as material properties, geometry, damage model constants and many others. This paper presents a methodology to include these uncertainties in the life prediction approach for solder joint materials. Non-linear stochastic finite element modeling is used to evaluate the sensitivity of the life prediction results to uncertainties in elastic and inelastic material properties and damage model constants. The analyses show that from material properties, creep coefficient and activation energy are two factors that have significant effect in fluctuating the prediction results. Coefficient of Thermal Expansion was also found to have a strong effect. Analyses also show that damage model constants have more pronounced effect than material properties.