Effect of the Solder Powder Size of Sn-Bi-Ag-In Lead-Free Solder on the Wettability and Microstructure of Cu Substrate

In this study, tin-bismuth-silver-indium (Sn-Bi-Ag-In) lead-free solder powders are prepared by the consumable-electrode direct current arc (CDCA) method. Without agglomeration, the satellite-free solder powders show good sphericity. The effect of solder powder sizes on the wettability and microstructure of Sn-Bi-Ag-In solder alloy on copper substrate is systemati-cally investigated. The solder joints prepared by solder powder in a size of 53-120 mu m exhibit relatively small wetting angles. In addition, the microstructure of the solder joints is com-posed of bismuth-rich phases, tin-rich phases, and Ag3Sn phases. A continuous intermetallic compound (IMC) layer with a thickness in the range of 0.64-0.70 mu m is formed at the inter-face between the solder and the copper substrate. The results show that the formation and morphology variety of the IMC layers for different solder joints are unobvious, reflecting the good wettability of the Sn-Bi-Ag-In lead-free solder powders on the copper substrate in a wide size range.