Microstructures and properties of joints formed by Ni-Cu TLP bonding process at low temperature

In this study, pure Sn foil with a thickness of 40 μm was used as a solder interlayer in the low-temperature transient liquid phase (TLP) bonding process between Ni and Cu substrates, and joints completely composed of (Cu, Ni)₆Sn₅ and Cu₃Sn intermetallic compounds (IMCs) phases were achieved by prolonging the isothermal reaction time. During the soldering process, the interfacial (Cu, Ni)₆Sn₅ formed on the Ni side and Cu side. However, the grain morphology of the (Cu, Ni)₆Sn₅ compounds subsequently exhibited fine rounded, needlelike and coarse rounded shapes from the Ni side to the Cu side. On the other hand, the growth of the Cu₃Sn compounds was suppressed. The IMCs joint had a remelting temperature of 418.4℃ and an average shear strength of 49.8MPa, which can fulfill the requirement for thermal stable joints in high-temperature power electronics packaging and promote the reliabilities of devices operated in harsh environment.