Investigation of reflow soldering under nitrogen atmosphere

Oxidation reaction, poor wettability and high peak temperature during reflow soldering will do harm to the electronic welding. In order to solve these problems, the welding performance in a nitrogen atmosphere was studied. Nitrogen atmosphere can improve the wettability of solder, reduce the degree of oxidation, and accelerate the welding speed of soldering reaction. A series of soldering experiments were conducted in a small reflow soldering oven. The copper slices and the silicon slices were used to imitate the welding of substrate and chip, and a typical lead-free solder, Sn96.5Ag3.5, was used in our experiment. After the soldering experiment was completed, the differences in quality of welding in the air and nitrogen were compared. A tensile experiment of the welded parts was used to measure the mechanical properties of the samples. The welding layer was observed by electron microscope for the three-dimensional morphology of the alloy. The tensile force under nitrogen welding is 72.715N, and the tensile force under air welding is 15.612N, showing a significant improvement of welding strength. There are fewer gas induced voids in the nitrogen welding than in the air welding. The experimental results show that welding in the nitrogen has more advantages than wending in the air.