A comparative investigation of the electromigration behavior between wedge-type and line-type Cu/Sn3.0Ag0.5Cu/Cu interconnects

With the increasing miniaturization of electronic devices and products, the size of solder joints becomes smaller and smaller, the current density in the solder interconnects gets higher and higher, accordingly the electromigration (EM) has become a serious reliability issue for the solder interconnects. The studies on flip chip have shown that the configurable change of solder joints and current crowding effect are the main cause of electromigration. In this study, the microscale joint with an irregular solder geometry (i.e., wedge-type joint) was designed and the electromigration behavior under a direct current of a density 1.5×10⁴ A/cm² was investigated by both experiment and finite element simulation. For a comparison, the line-type joint with the same sectional area was also studied. The results show that there are some similar features between two types of solder joints, which include, hillocks grew near the anode side of the joints, voids and micro-cracks formed near the cathode side, the intermetallic compound (IMC) become coarsening at both interfaces of the joints. The results also show that there are some obvious differences, for example, the local melting easily occurred at the bottom corner of the wedge-type joint, this means the current crowding effect existing in the joint. Furthermore, the micro-cracking gradually became severe from top to bottom at the cathode side of the wedge-type joint, this implies that the bottom corner may be the weakest interfacial part in service.