Effect of Sn grain orientation and strain distribution in 20-mu m-diameter microbumps on crack formation under thermal cycling tests

Abstract

The thermo-mechanical properties of microbumps serving as interconnects between Si chips in three-dimensional integrated circuits were examined in this study. Arrays of SnAg microbumps were subjected to temperature cycling tests up to 2500 cycles. Extensive cracks formed in the microbumps, and some of them propagated across the entire microbump. A microstructural analysis by electron back scattering diffraction indicated that the cracks propagated along two paths: Sn grain boundaries with high misorientation angles and SnAg/Ni3Sn4 interfaces. The average Sn grain size was only 7.4 mu m, implying a large proportion of grain boundaries per unit volume, which facilitated crack propagation across the microbump of 20 mu m in diameter.