Abstract: SMT (surface mount technology) is the most popular technology and process in the electronic assembly industry, and solder paste is the key auxiliary material in the surface mount technology, and the cold welding phenomenon often appears in the welding process is also related to solder paste. Through the analysis of solder paste material, confirmation of application parameters (solder reflow curve), microscopic observation of solder paste on chip pin pad and comparative analysis of solder paste on PCB with different surface treatment, the aim is to find out the root cause of "cold soldering" phenomenon in SMT welding process, and adjust the application process conditions, avoid welding defects and ensure the reliability of electronic products.

Key words: SMT, Solder paste, Welding, Cold welding