Study And Evaluation On Lead-Free Solder Paste For Surface Mount Technology

With the development of electronic industry and surface mount technology (SMT), solder paste has become one of the most important electronic joining materials in electronic-industry. This paper analyzed the properties of the SYS305 lead-free solder paste and flux. A new type flux has been developed by adjusting the elements of flux, the proportion of solder power and the reliability of residues. The solder ball test, wettability test and slump test have been carried on. The results show that:1 The original solder paste could form welding spots, but the spots have been oxidized seriously, the residues after welding can not be curdled, and surface insulation resistance was too low. The reason is that the ratio of activator is unreasonable, the solvent's melting point is excessively low, the rosin content is excessively high in the original flux.2 Through changing the ratio of activator, the corrosion of flux has been reduced; Good solvent component systems which can improve the flux's wettability, increace its surface insulation resistance and higher dissolving ability was brough out. Choosing new ratio of rosin components to decrease the solid content, enhance the viscosity of flux and make the residues solidification.3 Accoding to the new flux system, when the solder power was account for 88.0% of the solder paste, it can be better printed than the other ones. The influence of the solder power's proportion to rheological properties and print capability has been studied.4 Through assessing the standard of solder paste, the solder ball test and the wettability test have reached the first grade; the slump rate is 0.10; the welding spots have good appearance ; the residues solidify well.