Investigation of jet printing performance of lead-free solder paste

Surface Mounted Technology (SMT) is a universal technology used in electronics packaging industry. Electronic manufacturing industries have utilized advanced Integrated Circuits(IC) packages to achieve the manufacture of smaller, lighter, faster and cheaper products. However, the assembly of these surface mounts packages and the reliability of the products are challenged by solder paste printing process. A novel solder paste jet printing technology can solve the problem well, which demands a new-type solder paste suitable for jetting process. The solder paste is the homogeneous mixture of alloy solder powder and flux. In this paper, the viscosity and stability properties of Sn-3Ag-0.5Cu lead-free solder pastes have been systematically investigated by viscosity test, slump test and other material analysis methods. The impacts of different metal content, alloy type, and size distribution on the viscosity, thixotropy and slump properties have also been discussed. The requirements of solder powder used for jet printing have also been concluded by jet printing test. In addition, the rheology and jet printing performance of solder pastes with different kinds of flux have been compared and the influence of thixotropic agents was explored preliminarily.