Introduction to the welding principle of electric soldering iron
The electric soldering iron uses tin to carry out the welding operation. Its working principle is to heat and melt the solid solder wire through the heated soldering iron. With the help of the flux, it flows into the metal to be welded, and forms 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, and with the occurrence of wetting, the solder gradually diffuses to the copper metal, forming an adhesion layer on the contact surface between the solder and the copper metal, making the two are firmly combined.
Therefore, soldering is accomplished by combining three physical and chemical processes of wetting, diffusion and metallurgy.
1. Wetting
The wetting process means that the melted solder flows around along the fine bumps and crystal gaps on the surface of the base metal by capillary force, forming an adhesion layer on the surface of the base metal to be welded, so that the atoms of the solder and the base metal are close to each other , to reach the distance at which the gravitational force of the atoms acts.
Environmental conditions that cause wetting: The surface of the base metal to be welded must be clean and free from oxides or contaminants.
Image metaphor: Drop water on the lotus leaves to form water droplets, that is, the water cannot moisten the lotus. Drop water on the cotton, and the water will penetrate into the cotton, that is, the water can moisten the cotton.
2. Diffusion
With the progress of wetting, interdiffusion between solder and base metal atoms begins to occur.
Usually the atoms are in a state of thermal vibration in the lattice lattice, once the temperature rises. The atomic activity intensifies, so that the atoms in the molten solder and the base metal cross the contact surface and enter the lattice lattice of each other. The moving speed and quantity of the atoms are determined by the heating temperature and time.
3. Metallurgical combination
Due to the interdiffusion between the solder and the base metal, an intermediate layer ~ metal compound is formed between the two metals. To obtain a good solder joint, a metal compound must be formed between the base material to be welded and the solder, so that the base metal achieves a firm metallurgical bond. combined state.
