Semi-Analytical Fatigue Life Model for Reliability Assessment of Solder Joints in QFN Packages under Thermal Cycling
Authors: Maxim Serebreni, Nathan Blattau, Gil Sharon, Craig Hillman, Patrick McCluskey Company: DfR Solutions and University of Maryland Date Published: 6/6/2017
ICSR (Soldering and Reliability)
Abstract: As trends in electronic packaging evolve to accommodate more complex components, solder joints are placed under increasing mechanical loads that arise from the combination of package configuration and material behavior during temperature changes. Predicting the reliability and performance of solder joints in QFN (Quad Flat No lead) devices during thermal cycling often require extensive computer simulations along with empirical damage models to correlate strain energy density and cycles to failure. In this paper, a semi-analytical model is presented to calculate the strain energy density of solder joints in QFN packages. The model offers direct parametrization to better assess the impact of geometry and material parameters on the fatigue life of solder joints. Model results fit empirical failure data for packages with sizes ranging from 4x4 mm to 12x12 mm and dual-row packages. Die size and solder fillet effect on fatigue life is capture based on geometric dependency of material properties. A hyperbolic function is used to fit material behavior across the glass transition temperature to account for the fatigue life reduction with decrease in the mold compounds coefficient of thermal expansion. The model correlates well with a wide range of experimental data for various package configurations, mold compound properties and thermal cycling conditions. This model allows for simple reliability assessment of solder joints in a variety of QFN components.