Development of low temperature solder alloys for advanced electronic packaging: Assessment of In-Bi alloys on Cu substrates

When the advanced electronic packaging technology involves the processes that are incorporated with bio-related devices or integrating the chips on flexible substrate, low temperature materials are needed to reduce the risk of damaging the devices during assembly. This study focuses on developing new alloys that have the melting temperatures not exceeding 120 °C. The new alloys should have comparable functionality to the traditional Pb-free solder alloys. Three In-Bi alloys, 33InBi, 50In50Bi and 68In32Bi, were used to study the interfacial reactions with Cu substrates. Grazing incidence X-ray diffraction (GIXRD) and electron probe X-ray microanalyses (EPMA) were used to characterize the intermetallic compound (IMC) formed at the interfaces. A low-temperature metastable phase, CuIn2, was identified during long-time aging in 68In32Bi/Cu. Shear tests were conducted on the joints of 17Sn-26In-57Bi/Cu and 50In50Bi/Cu due to the similar melting point of the two alloys. Due to high indium content, the deformation energy of 17Sn26In57Bi/Cu drastically decreased while the deformation energy of 50In50Bi/Cu decreased slightly. 50In50Bi/Cu also exhibits higher shear strength than the 17Sn-26In-57Bi/Cu at high-speed shear test.