Current density dependent shear performance and fracture behavior of micro-scale BGA structure Cu/Sn–3.0Ag–0.5Cu/Cu joints under coupled electromechanical loads

The shear performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu joints under coupled electromechanical loads with the increasing current density (from 6 × 10 3 to 1.1 × 10 4 A/cm 2 ) were investigated systematically. Severe Joule heating and current crowding effects on actual temperature, shear strength, damage and fracture behavior of the joints under coupled electromechanical loads were studied by theoretical formulation and experimental characterization, as well as finite element simulation. Results demonstrate that severe Joule heating and current crowding effects lead to significantly increased temperature in the joints, which is much higher than the ambient temperature. The shear strength of joints under coupled electromechanical loads shows strong dependence on current density, in terms of a relatively rapid monotonic decrease with the increasing current density. Moreover, a fully coupled finite element model was developed to characterize the degree of damage of joints under coupled electro-mechanical loads. The results show that electric current leads to aggravated damage in the joints, and damage occurs and accumulates much more easily in joints subjected to high density current stressing. The maximum viscoplastic dissipation energy density increases monotonically with current density. With increasing current density, there is a transition in fracture position (path) from the solder matrix to the solder/IMC interface of the joints, which corresponds to a shift in fracture mode from ductile fracture to brittle fracture.