Analysis of lead-free solder paste based on performance degradation

The solder paste has become one of the most indispensable brazing and soldering materials in surface mount technology (SMT), and its performance affects the quality of welding directly. The independently-designed lead-free solder paste in the lab has the fine performance when synthesized initially. However, the performance of solder paste degraded during the storage. So the aim of the article is to analyze solder paste based on performance degradation. In the paper, the independently-designed Sn-0.3Ag-0.7Cu solder paste in the lab was compared with commercial Senju solder paste based on the observation of wettability and viscosity during being stored at room temperature. Subsequently, the solder paste was divided into solder power and flux after 1, 3 and 5 months' storage. The solder power was analyzed by scanning electron microscopy. The results show that during the solder paste was sealed at room temperature, the wettability of solder paste became worse. And the viscosity was tend to increase, which lead solder paste to become dry, sticky, and even fail in welding. In addition, solder powder would be corroded and oxidized during the storage. So the activation component of the solder paste reacts chemically with the solder powder, which results in the performance degradation of solder paste.