Abstract: The size effect of mechanical behaviors and performance evolution of micro-scale interconnects prepared by lead-free Sn-Ag-Cu solder with different joint sizes are investigated by a sophisticated micro-tension experiment and finite element simulation. The results show that the tensile strength and fracture strain of the joints increase with decreasing joint diameter (475~200 μm) while keeping joint thickness constant (225 μm), and strength values of the joints are obviously higher than that of the bulk solder. For the joints with large diameter, the fracture occurs in interfaces of the joints and shows low ductility, in contrast to necking type fracture with large deformation happened in the mid of the joints having small diameter. Numerical simulation results show that due to the different levels of mechanical constraint in the solder joints, the small diameter joint has relatively low interface stresses and the maximum stress locates in the mid of the joint where the final fracture usually occurs, thus the joint would exhibit high fracture strength; while for the large diameter joint, the maximum stress locates in the interfaces where cracks easily initiate and grow in intermetallic compound layer through the interfaces at a low level of applied stress, and consequently the strength of the joint will be low.

Key words: Finite element simulation, Lead-free solder, Mechanical properties, Micro-interconnect joints, Size effects