Effect of Load-Mix on Fatigue Crack Growth in 63Sn-37Pb Solder Joints

Abstract

Fatigue crack growth at the interface between Sn-Pb solder and Cu was examined under various mixed-mode conditions. The load-mix, in terms of the ratio of Mode-II to Mode-I stress intensities, was systematically changed by varying the thickness ratio of Cu layers in the flexural-peel specimens made from Sn-Pb/Cu joints. Fatigue crack growth experiments were conducted using a sinusoidal waveform at a frequency of 5 Hz and a load-ratio of zero. Fatigue crack growth rates were measured as a function of the total strain energy release rates for a given load-mix. Fatigue crack growth resistance was found to increase with the load-mix, with the effect of the load-mix being more pronounced in the near-threshold regime. The effect of the load-mix on fatigue crack growth is shown to result from shear-enhanced frictional sliding of fatigue crack surfaces.