Growth Behavior of Ni-Sn Intermetallic Compounds in Microbumps During Long-Term Aging Process

With downward scaling of bump size in advanced electronic packaging, it is urgent to understand Sn/Ni interfacial reaction in a limited volume. In this paper, the growth behaviors of Ni-Sn intermetallic compounds (IMCs) in Cu/Ni/Sn-Ag microbumps aged at 150 degrees C for 2000 h were investigated. The diffusion of Sn atoms across Ni3Sn4 layer caused constant nucleation of Ni3Sn4 grains near the Ni barrier. The thickening of Ni3Sn4 layer was contributed by grain nucleation and coarsening, leading to a vertical difference of grain size inside the Ni3Sn4 layer. Another kind of IMC, Ni3Sn2, was formed at the Ni/Ni3Sn4 interface. A growth model of Ni-Sn IMCs comprising diffusion, nucleation, grain coarsening and phase transformation was proposed based on experimental results. These findings provided insights into advanced electronic packaging reliability.