Effect of Fe Content on the Interfacial Reliability of SnAgCu/Fe–Ni Solder Joints

Fe–Ni films with compositions of Fe–75Ni, Fe–50Ni, and Fe–30Ni were used as under bump metallization (UBM) to evaluate the interfacial reliability of SnAgCu/Fe–Ni solder joints through ball shear test, high temperature storage, and temperature cycling. The shear strengths for Fe–75Ni, Fe–50Ni, and Fe–30Ni solder joints after reflow were 42.57, 53.94 and 53.98 MPa, respectively, which were all satisfied the requirement of industrialization (>34.3 MPa). High temperature storage was conducted at 150, 175 and 200 °C. It was found that higher Fe content in Fe–Ni layer had the ability to inhibit the mutual diffusion at interface region below 150 °C, and the growth speed of intermetallic compound (IMC) decreased with increasing Fe concentration. When stored at 200 °C, the IMC thickness reached a limit for all three films after 4 days, and some cracks occurred at the interface between IMC and Fe–Ni layer. The activation energies for the growth of FeSn2 on Fe–30Ni, Fe–50Ni, and Fe–75Ni films were calculated as 246, 185, and 81 kJ/mol, respectively. Temperature cycling tests revealed that SnAgCu/Fe–50Ni solder joint had the lowest failure rate (less than 10%), and had the best interfacial reliability among three compositions.