Abstract: The finite element simulation and experimental method are used to study the fracture behavior of different-sized micro-joints of “Cu wire/solder/Cu wire” butted structure under quasi-static micro-tension load, and the influence of electromigration and thermal aging on the fracture properties thereof. The results show that the interfacial crack growth driving force in the joints decreases and the anti-fracture performance improves with the decrease of the micro-joint thickness; at the interfacial crack tip the shear mode stress intensity factor KII is obviously greater than the opening mode stress intensity factor KI; both KII and KI for Sn-Ag-Cu lead-free solder joints are much lower than that for Sn-Pb solder joints, and Sn-Ag-Cu solder joints exhibit better fracture performance than Sn-Pb solder joints. Furthermore, the simulation results show that the increase of thickness of intermetallic compound (IMC) layer induced by electromigration has negligible influence on fracture properties of the joints, and propagation of a pancake-shaped void along the joint interface brings about obvious increase in stress concentration factor while the region of the maximum Von Mises stress is at the IMC/Cu interface. In addition, it is shown that the increase of IMC layer thickness due to thermal aging results in the decrease of Von Mises stress at the interfacial crack tip following an exponential function.

Key words: Electromigration, Interfacial fracture, Lead-free micro-joint, Size effects, Thermal aging