Abstract
Improving mechanical strengths of solder joints is a crucial issue in electrons packaging, and using composite solders is one of the potential methods to increase the joints strengths. In this study, Cu6Sn5-contained solder paste was produced by mechanical mixing Cu6Sn5 nano powder into commercial SnAg solder paste. The Au/Ni-P/Al UBM was first deposited onto the silicon wafer, and the Cu6Sn5-contained solder paste was then stencil printed on the UBM and reflowed at 240°C. The interfacial morphology and microstructure of solder bumps were evaluated by FE-EPMA. With different reflows, the microstructures of solder matrixes and IMCs at interface of solder/UBM joint in both Cu6Sn5-contained solder and commercial Sn3.0Ag0.5Cu solder were evaluated and discussed. Besides, the elemental distribution of Cu6Sn5-contained solder was detected by X-ray color mapping in a newly developed FE-EPMA. To realize the effect of Cu6Sn5 nano powder doping, the creep characteristics and ball shear strengths of the joints were further investigated. Nanoindentation was employed to measure the creep characteristics of solder alloys. It was revealed that the creep strain rate sensitivity of Cu6Sn5-contained solder was higher than that of SnAgCu solder although the creep hardness of both solders was identical. Ball shear strengths of both solder joints were applied at two different shear speeds. In addition, the ball shear strengths of Cu6Sn5-contained solder and SnAgCu solder joints were probed with respect to the fracture surfaces, interfacial morphologies, and fracture modes. The effects of nano-sized Cu6Sn5 additive were summarized and the feasibility of this composite SnAgCu solder in electronic packaging was discussed.