Microstructure and mechanical properties of Co/Sn-10Bi couple and Co/Sn-10Bi/Co joint

- The transient liquid phase bonding process of Co/Solder/Co structure was first conducted in this investigation.
- The shear strength of Co/Sn-Bi/Co and Co/CoSn3 + Bi/Co joints was tested.
- The fracture mechanism of non-TLPB and TLPB joints was first investigated.

The growth behavior of interfacial intermetallic compounds (IMCs) layer of Co/Sn-10Bi and Co/Sn-10Bi/Co couple has been studied by scanning electron microscope. The critical temperature and shear strength of Co/Sn-10Bi/Co joints were tested by universal testing machine. The results showed that the thickness of CoSn3 IMCs layer increased as the increase of aging time and temperature. The growth rate of CoSn3 IMCs layer of Co/Sn-10Bi/Co couple was suppressed and was lower than that of Co/Sn-10Bi couple as the decline in Sn concentration of residual Sn-Bi layer. The critical temperature of Co/Sn-10Bi/Co joint that could hold a load of 1 N changed as the chemical composition of residual Sn-Bi layer changed. The shear strength of Co/Sn-10Bi/Co joints bonded at 240 °C for 20 min, 30 min, 40 min, and 50 min was between 58 MPa and 82 MPa. The shear strength of Co/Sn-10Bi/Co joint bonded at 240 °C for 60 min was only about 17 MPa. The damage in shear strength of Co/Sn-10Bi/Co joint bonded for 60 min was led by the crack in residual Bi layer.