Thermal reliability investigation of Ag-Sn TLP bonds for high-temperature power electronics application

Transient liquid phase (TLP) bonding is a potential joining technology for high-temperature power electronics packaging. In this study, the thermal reliability of Ag-Sn TLP bond was investigated through high-temperature storage test, in which the relationship between microstructure evolution and mechanical property was developed during 350 °C aging. After aging for 120 h, the Ag3Sn or ζ phase within the joint evolved totally into Ag(Sn) solid solution, which fractured with a ductile characteristic during shear test. The Ag-Sn TLP bond was confirmed to operate at ambient temperature of 350 °C for nearly 1000 h without serious failure, still possessing high shear strength of about 40 MPa. During thermal aging, a great amount of irregular Ni-Sn intermetallic particles were precipitated and dispersed adjacent to the interface between the Cu substrate and the Ag-Sn phases once the Ag metallization layer was consumed entirely. Moreover, a relatively thick Ni buffer layer should be carefully considered to prevent continuous cracks propagating along the Cu/Ag(Sn) interface, which was induced by the significant outflow of Cu flux from the interfacial zone, like a Kirkendall voiding process.