Effects of Cu Opening Size on the Mechanical Properties of Epoxy-Contained Sn-58Bi Solder Joints.

Abstract

The effects of Cu opening size on the mechanical properties of epoxy-contained Sn-58Bi solder joints were investigated by a low-speed shear test. Eight sample types were fabricated with various Cu opening sizes and solder pastes. The Cu opening sizes of the component and substrate were 200 μm or 380 μm, respectively, and the component formed a Sn-3.0Ag-0.5Cu (SAC305) solder bump which was placed on the Sn-58Bi solder paste or epoxy Sn-58Bi solder paste printed on the substrate and then reflowed. The microstructures of the solder joints were observed using scanning electron microscopy (SEM), and the chemical compositions were analyzed by energy-dispersive X-ray spectroscopy (EDS) and electron probe X-ray micro-analyzer (EPMA). Epoxy was formed around the solder joints after the reflow process, improving the bonding strength of the epoxy-contained solder joints. Specifically, the bonding strength of the epoxy Sn-58Bi solder joints increased about 2.9 times in the 200 μm (opening size of component)/380 μm (opening size of substrate) sample. When the opening size of the component and substrate differed, a fracture occurred at the smaller opening size. On the other hand, a fracture occurred at the substrate side for the SAC305 (solder paste of component)/Sn-58Bi (solder paste of substrate) solder joints, while a fracture occurred at the interface between SAC305 and Sn-58Bi at the SAC305/epoxy Sn-58Bi solder joints for samples with the same opening size between the component and substrate.