Influence of thickness of interfacial IMC layer and solder mask layer on mechanical reliability of micro-scale BGA structure interconnects

Linear elastic fracture mechanics (LEFM) approach was used for studying the influence of the interfacial IMC layer thickness and solder mask layer thickness on fracture behavior of ball grid array (BGA) structure solder interconnects using finite element numerical simulation. The stress intensity factors (SIFs, K
_I
and K
_II
) at the crack tip of a predefined face-crack in the IMC layer of BGA joints were analyzed. The simulation results show that, increasing the thickness of the IMC layer results in high values of SIFs at the crack tip, so the crack may be most likely to propagate in the BGA structure interconnect with a thicker IMC layer. Moreover, for the BGA structure solder interconnect having a predefined crack with a certain distance to the IMC/solder interface, the kink angle of crack propagation increases with the increasing thickness of the IMC layer. Furthermore, a thicker solder mask layer leads to the decrease in both values of the maximum Von Mises stress and maximum tensile stress in the solder matrix, as well as a lower Von Mises stress in the IMC layer of the BGA joint, and this means that the increase in thickness of solder mask layer will improve the mechanical reliability of BGA structure interconnects.