Heat resistant Bi-Ag-X solders for power IC die attachment

One of the urgent issues in electronic packaging is the die-attachment technique for high power ICs, which needs to withstand high operation temperature up to 250°C. In this study, the microstructure and mechanical properties of the joints between high temperature Pb-free solders (Bi-11Ag, Bi-Ag-X, Zn-30Sn and Sn-18Sb-5Ag) and Cu substrates were investigated. To evaluate the mechanical performance at elevated temperatures, shear tests from room temperature to 250°C were carried out. Experimental results show that for all the test temperatures, Bi-Ag-X joints exhibited superior shear strength than Bi-11Ag and the others. This can be ascribed to the higher solidus temperature of Bi-Ag system, and the strengthening effect of intermetallic compounds on the joints and the interface as well.