Soldering is a science. The principle is to heat and melt the solid solder wire with a heated soldering iron, and then make it flow between the metals to be welded with the help of flux, and form a firm and reliable solder joint after cooling.
When the solder is a tin-lead alloy and the soldering surface is copper, the solder first wets the soldering surface. With the occurrence of the wetting phenomenon, the solder gradually diffuses into the metal copper, forming an adhesion layer on the contact surface of the solder and the metal copper, so that The two are firmly combined, so the solder is completed through the three physical and chemical processes of wetting, diffusion and metallurgical bonding.
1. Wetting: The wetting process means that the melted solder flows around the surface of the base metal by the capillary force along the fine bumps and crystal gaps on the surface of the base metal, thereby forming an adhesion layer on the surface of the base metal to be welded, so that the solder and the base metal The atoms of are close to each other, reaching the distance at which atomic gravity works.
Environmental conditions that cause wetting: The surface of the base metal to be welded must be clean and free of oxides or contaminants. (Wetting can be visually compared as: water drops on the lotus leaf to form water drops, that is, water cannot wet the lotus. When the water drops on the cotton, the water penetrates into the cotton, and the water can wet the cotton.)
2. Diffusion: With the progress of wetting, the phenomenon of mutual diffusion between the solder and the metal atoms of the base metal begins to occur. Usually atoms are in a state of thermal vibration in the lattice lattice, once the temperature rises. The intensification of atomic activity causes the atoms in the molten solder and the base material to cross the contact surface and enter each other's lattice lattice. The moving speed and number of atoms are determined by the heating temperature and time.
3. Metallurgical bonding: due to the mutual diffusion of the solder and the base metal, an intermediate layer is formed between the two metals-a metal compound. To obtain a good solder joint, a metal compound must be formed between the base metal and the solder to make the mother The material reaches a strong metallurgical bonding state.