RETRACTED ARTICLE: Effect of grain size on the interface structure and shear behavior of lead-free solder joints

This paper investigates the effect of grain size on the evolution and shear behavior of lead-free solder joints. The grain size of the solder is 2-11 μm, 5-15 μm, 15-25 μm, respectively. The interface structure of the solder joint and the microstructure of the inferred surface are analyzed. The void ratio of the flip-chip solder layer is tested. In order to study the change of shear strength and fracture surface, the solder/copper joint was subjected to isothermal aging treatment (1000 h) under the environment of relative humidity of 85 °C/85%. The results show that the smaller the solder crystal grains, the larger the surface area of the crystal grains per unit mass. Because of the action of the liquid bridge force, tin powder agglomeration is prone to occur, which leads to a high void rate of the solder layer. At this time, a higher activity flux is required to remove oxides. Highly active flux (NC559-TPF) was added and verified. When the grain size is 5-15 μm, the solder paste has the best soldering performance. After the filament is aged for 1000 h, the junction temperature is the lowest. Secondly, the blue light flux is the highest.