Effect of thixotropic agents on the rheology of SnAgCu lead-free solder pastes used for jet printing

Solder paste is the most important strategic bonding material for surface mounting components in electronics manufacturing field. The aim of this study was to investigate the effect of thixotropic agents on the rheology of SnAgCu lead-free solder pastes and grope for materials suitable for jet printing process. The rheological behaviors consisting of viscosity, oscillation, creep recovery and thixotropy of solder pastes added with four thixotropic agents were investigated. The jet printing test was carried out at room temperature. In this paper, it is found that thixotropic agents ST and CVS can reduce the G ''/G' ratio of solder pastes calculated by the oscillation stress curve. Besides, ST and CVS can effectively improve the area of thixotropic loop and the value of unrecovered stress, which is suitable for the jet printing. T4 samples with CVS can be jetted continuously for more than 5000 points with a minimum diameter of 372.3 mu m. As the demand for solid-liquid two-phase fluid materials applied to jet printing increases, rheological methods can assist with the exploration of new high viscosity lead-free solder pastes.