Abnormal Shear Performance of Microscale Ball Grid Array Structure Cu/Sn-3.0Ag-0.5Cu/Cu Solder Joints with Increasing Current Density

The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn-3.0Ag-0.5Cu/Cu solder joints with increasing electric current density (from 1.0 x 10(3) to 6.0 x 10(3) A/cm(2)) at various test temperatures (25 degrees C, 55 degrees C, 85 degrees C, 115 degrees C, 145 degrees C, and 175 degrees C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 degrees C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.