Rheological Properties And Printing Properties Of Nano TiO₂ Doped Solder Paste At Different Temperatures

With the rapid development of electronic products,steel screen printing has reached its limits and is not suitable for the current 3D packaging,flexible electronics and customized electronic products production.The spray printing of solder paste can well meet the needs of current development,but the coating process was prone to gags,satellite droplets.For nano-modified solder paste with excellent performance,the influence of particle size effect on the modification was still to be further studied.The parameter adjustment efficiency of modified solder paste was low when introduced into printing,and there was no efficient guidance means.In the past,the mechanical properties,rheological properties and printing properties of SAC105 solder paste modified by nano Ti O₂ particles with different particle sizes were studied under particle size effect.The 7 kinds of paste were successfully prepared by mechanical mixing method,including undoped SAC105 paste and nano-Tio₂ particle modified SAC105 paste with particle size of 150nm,100nm,60nm,30nm,10-25nm and 5-10nm.The mechanical properties were studied from the aspects of post-welding shear resistance,nano-pressing property and microstructure.The study of mechanical properties included post-welding shear resistance,nano-pressing properties and microstructure observation.The results showed that compared with the unoppanted SAC105 solder paste,with the decrease of modified particle size,the shear resistance after welding continued to increase,with an increase range of 12%-54%;the nano-pressing hardness continued to increase,the increase range was 12%-23%,and the nano-penetration depth continued to decrease.By observing the morphological changes of post-welding tensile fractures,the changes in IMC thickness,and the size,orientation and phase distribution of Sn-based grains,the main mechanisms of action on solder paste modification at different particle sizes were studied.The rheological properties were studied by variable temperature viscosity,variable temperature amplitude sweep,variable temperature thixotropic ring and cold/hot collapse experiments.It was found that the seven kinds of solder paste were pseudoplastic Newtonian fluids.The viscosity,flow point（G’=G’）and thixotropic ring area of the modified solder paste decreased first and then increased with the decrease of particle size at room temperature.With the increase of temperature,the viscosity of 7 kinds of solder paste decreased continuously.Except for the modified solder paste with the particle size of 150nm and100nm,the flow point of other modified solder paste showed a trend of increasing,and the thixotropic ring area of 7 kinds of solder paste decreased continuously.All 7 kinds of solder paste can print with fine spacing of 0.2mm.A 2D printing simulation model was established based on VOF mode to simulate the effects of printing pressure,cavity of temperature and pulse time on solder paste spray printing.It was found that the spray printing pressure has a significant effect on the thick and long liquid trailing,the temperature has a significant effect on the thin liquid trailing,and the pulse time has a significant effect on the amount of solder paste spraying.Rapid calculation of particle size of 10-25nm and 5-10nm Ti O₂ particle modified SAC105 paste by drip spray printing pressure range,calculated the appropriate pressure range is 45kpa-68kpa.In this paper,the mechanical properties,temperature rheological properties and printing properties of SAC105 solder paste modified by nano Ti O₂ particles with different particle sizes were studied,and the high quality nano-modified solder paste with excellent mechanical properties and rheological properties was obtained.The main mechanism of solder paste modification under the effect of particle size was studied.Combined with the simulation model,the paper provides a model for calculating the process parameters of spray printing paste according to the drop.The study provides theoretical basis and experimental guidance for the selection of nano-particle size and the application of spray printing equipment,which has very important engineering application value.