EFFECT OF LOAD-MIX ON FATIGUE-CRACK GROWTH IN 63SN-37PB SOLDER JOINTS

Fatigue crack growth at the interface between Sn-Pb solder and Cu was examined under various mixed-mode conditions. The load-mix, in terms o f the ratio of Mode-II to Mode-1 stress intensities, was systematicall y changed by varying the thickness ratio of Cu layers in the flexural- peel specimens made from Sn-Pb/Cu joints. Fatigue crack growth experim ents 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 lo ad-mix, with the effect of the load-mix being more pronounced in the n ear-threshold regime. The effect of the load-mix on fatigue crack grow th is shown to result from shear-enhanced frictional sliding of fatigu e crack surfaces.