Lead-free solder development is critical for semiconductor package. The properties of solder determine the process temperature and joint strength. SnAgCu and SnAg are the leading lead-free solder. However, the melting point is about 220oC, which is higher than former SnPb melting point. It is urgent to find low-temperature lead-free solder. The benefits of reducing process temperature include protection of device damage and energy-saving. Low carbon footprint reduces greenhouse effect that is friendly to environment. In this study, we choose Sn, Bi, and In elements as low-temperature solder candidates. Bi or In addition can reduce the melting point. In addition, In has good ductile and anti-corrosion. Observation of microstructure between low-temperature solder and Cu during solid-liquid and solid-solid reactions in this study. Reducing the process temperature is important for temperature-sensitive devices in order to avoid thermal damage. The composition of intermetallic compounds, phase transformation and mechanical properties are main objectives in this study.
