Effect of Fatigue on Individual SAC305 Solder Joints Reliability at Elevated Temperature

Abstract

Failure due to thermal cycling is common at the solder joint level of electronic assemblies due to the mismatch in the coefficient of thermal expansions between the carrier and printed circuit board. Combined damage mechanisms of creep and fatigue are presented in thermal cycling conditions. Recent studies showed that fatigue damage is dominant during ramps, while creep damage is dominant during dwell times. The amount of damage is highly aggregated when the temperature is elevated. So, it is essential to explore the effect of both damage mechanisms on solder joint reliability, especially at elevated temperatures. In this work, an accelerated shear fatigue test on individual solder joints is used to study the effect of elevated temperature at different stress levels on fatigue life. Individual SAC305 solder joints were cycled in stress-controlled fatigue at various temperature levels of 25°C, 60°C and 100°C using Instron micro-tester machine with a customized fixture. The stress amplitudes include 16, 20, and 24MPa. Hysteresis (stress-strain) loops were generated at different testing conditions, and the inelastic work per cycle is calculated. The results showed that increasing the stress level leads to increasing the inelastic work per cycle and decreasing fatigue life. The fatigue life of the solder joint is reduced significantly with increasing temperature at certain stress levels. Also, the inelastic work per cycle is significantly increased with increasing temperature. The effect of temperature found to create more damage than increasing stress levels. Further experiments with different testing conditions are in progress to study the effect of both creep and fatigue. It would help in quantifying both damages at several temperatures and stress levels.