Basic knowledge of electric soldering iron welding (welding principle and welding process)
With the acceleration of packaging updates for electronic components, the original direct insertion type has been changed to flat mount type, and the connecting cables have also been replaced by FPC soft boards. The resistance and capacitance of components have gone through 1206080506030402 and have now moved to 0201 flat mount type. After BGA packaging, Bluetooth technology has been used, which without exception indicates that the development of electronics has moved towards miniaturization and miniaturization, and the difficulty of manual welding has also increased, Any carelessness during welding can damage components or cause poor soldering.
Therefore, frontline manual welding personnel must have a certain understanding of welding principles, welding processes, welding methods, welding quality assessment, and electronic fundamentals.
1、 Welding principle of electric soldering iron
Tin welding is a science that uses a heated soldering iron to melt the solid solder wire, and then, with the help of soldering flux, it flows into the metal to be welded. After cooling, it forms a solid and reliable welding point.
When the solder is made of tin lead alloy and the welding surface is made of copper, the solder first wets the welding surface. With the occurrence of wetting phenomenon, the solder gradually diffuses towards the metal copper, forming an adhesion layer on the contact surface between the solder and the metal copper, making the two firmly bonded. Therefore, soldering is accomplished through three physical and Chemical process: wetting, diffusion and metallurgy.
1. Wetting: The wetting process refers to the use of capillary force to diffuse the melted solder along the fine concave convex and crystalline gaps on the surface of the base metal, forming an adhesion layer on the surface of the welded base metal, making the solder and the atoms of the base metal close to each other, reaching the distance at which atomic force acts.
Environmental conditions that cause wetting: The surface of the welded base material must be clean and free from oxides or pollutants.
Image metaphor: Dropping water onto lotus leaves to form water droplets means that water cannot moisten the lotus. Drop water onto the cotton and it will penetrate into the cotton, which means that water can moisten the cotton.
2. Diffusion: With the wetting process, the mutual diffusion phenomenon between the solder and the base metal atoms begins to occur. Usually, atoms are in a thermal vibrational state in the lattice lattice, once the temperature increases. The intensification of atomic activity causes the atoms in the melted solder and base metal to cross the contact surface and enter the lattice of each other. The speed and number of atoms' movement depend on the heating temperature and time.
3. Metallurgical bonding: Due to the mutual diffusion between the solder and the base metal, an intermediate layer - a metal compound - is formed between the two metals. In order to obtain good solder joints, a metal compound must be formed between the welded base metal and the solder to achieve a solid metallurgical bonding state of the base metal.
