FE simulation of size effects on interface fracture characteristics of microscale lead-free solder interconnects

Understanding of interface fracture behavior of the solder joints has long been significant in reliability evaluation of electronic components and packages. The experimental and finite element methods were employed to characterize the fracture performance of "Cu wire/solder/Cu wire" sandwich structured butt microscale solder joints with different sizes (75 to 425 mum in thickness and 200 to 300 mum in diameter). In particular, linear elastic and elastic-plastic fracture mechanics approaches were used to quantitatively characterize the fracture performance of the predefined crack at the solder/IMC interface of both Pb-free (Sn-3.0Ag-0.5Cu) and Pb-contained (Sn-37Pb) solder joints. The simulation results show that the crack tip stress intensity factors (SIFs) for the crack at the solder/IMC interface, both K_II and K_I, decrease with decreasing thickness of the solder joint and increasing the loading rate; and this is coincident with the experimental results. Also, it has been seen that K_II is greater than K_I probably owing to the effect of Poisson contraction of the solder metal near the interfaces. It has also been shown that with increasing thickness of the solder joint, the orientation evolution of the high energy release rate area may result in the change in fracture position from the solder/IMC interface to the middle part of the joints.