Microstructure and mechanical properties of Sn3Ag0.5Cu3Bi0.05Cr/Cu joints

The mechanical properties and interfacial microstructure of Cu/Sn3Ag0.5Cu3Bi0.05Cr/Cu (Cu/SACBC/Cu) and Cu/Sn3.0Ag0.5Cu/Cu (Cu/SAC/Cu) joints were comparatively investigated after isothermal aging at 85 °C, 120°C and 150°C for 24, 168, 500 and 1000 h, respectively. The mechanism of Bi addition affecting the intermetallic compounds (IMCs) growth was discussed. Results show that the tensile strength of Cu/SACBC/Cu and Cu/SAC/Cu joints both decreased exponentially with aging time at any temperature and declined linearly with the increased temperature, while the rate of strength decrease for the former joint was lower with an order of magnitude. The SEM observation on the tensile fracture surfaces for Cu/SACBC/Cu joints shows that the tensile fracture mechanism transformed from a quasi-cleavage fracture to a cleavage-like brittle fracture after aging at 150 °C, while quasi-cleavage fracture is the main fracture mode for 120 °C and 85 °C. The relative stable tensile strength for Cu/SACBC/Cu joints can be attributed to thinner interfacial layer and strengthened Sn matrix with the solution strengthening and precipitating effects of Bi. The growth behaviors of interfacial IMCs were similar after aging at 150°C, 120°C and 85°C.