Abstract
Ni/Sn-2.5Ag/Ni samples were used to simulate the microbumps in three-dimensional (3D) packaging. The annealed test was adopted to observe the microstructure of intermetallic compound formation at 100°C, 125°C, and 150°C up to 1000 h. In the Ni/Sn-2.5Ag/Ni, predominant phases of layer-type Ni3Sn4 and Ag3Sn particles could be seen under the thermal treatment. The formation of Ni3Sn4 followed a parabolic rate law at each aging temperature. Due to the limited solder volume, the remaining solder of the microbump was completely exhausted after long-time annealing at 150°C. The activation energy for Ni3Sn4 formation in the Ni/Sn-2.5Ag/Ni microbump was 171.8 kJ/mol. Furthermore, the consumption of the Ni under bump metallization (UBM) was estimated based on the mass balance of Ni atoms during the interfacial reaction.
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