Microstructure and Intermetallic Growth Characteristics of Sn-Bi-In-xGa Quaternary Low Melting Point Solders

In the field of microelectronics, particularly at high temperatures, thermal stress presents a challenge to chip integration and packaging reliability. The exploration of low melting point solders has become crucial in addressing this issue and advancing next-generation low-temperature interconnect technologies. In this study, quaternary low melting point solders based on Sn-Bi-In-xGa (x = 0.5., 1.0., 1.5, wt%) were developed. The melting point of the Sn-Bi-In-xGa solders decreases with the increase in Ga content. The study explored the influence of Ga content on the microstructure and failure mechanism of solder joints. Upon forming solder joints through a 30 min reflow process at the temperature of 100°C with Cu substrates, inter metallic compounds at the interface included CU9Ga4 and CuGa2. The shear strength gradually decreases from 19.58 MPa to 7.45 MPa with the increasing Ga content. The fractography reveals that the interface of the Ga-rich phase is prone to brittle fracture.