The research of lead-free dispensing solder paste

The process of solder paste dispensing is considered as a popular coating method in solder paste applications currently. The properties of dispensing solder paste are easily effected by the changes of proportions. The research of Sn-Ag-Cu lead-free dispensing solder paste mainly focuses on the ratios of Sn-Ag-Cu alloy powder and flux, and the ratios of components in flux. In this paper, the mass ratio of alloy powder and flux in dispensing solder paste was 86:14wt %. On the basis of multi-ingredient in flux, the study had adopted four-factor and three-level of L-9 (3(4)) orthogonal designing method to design the mass percent of four main ingredients in flux, and achieved a set of optimizing parameters quickly. The four selected factors were rosin, thixotropic agent, solvent, and surfactant. Their effects on viscosity were investigated in this study. With formula of the flux optimized by orthogonal designs and range analysis, investigations on property of the dispensing solder paste had been made. The experiments of viscosity, spreading and slump showed that the methods were effective and feasible to form parameter optimization of dispensing solder paste. The experimental results indicated that the Sn-Ag-Cu lead-free dispensing solder paste would gain moderate viscosity and excellent spreadability when the mass percent of rosin, thixotropic agent, solvent, and surfactant in the flux was 40%:5%:25%:6%.