When the hot liquid solder dissolves and penetrates the surface of the metal to be welded, it is called metal dip or metal dip. The molecules of the mixture of solder and copper form a new alloy partly made of copper and partly soldered. This solvent action is called tin dip, which forms an intermolecular bond between each part to form a metal alloy eutectic. The formation of good intermolecular bonds is the core of the welding process, which determines the strength and quality of the welding joint. Only the surface of copper is not polluted, and there is no oxide film formed by exposure to the air to be wetted with tin, and the solder and working surface need to reach an appropriate temperature.