Introduction to the principles of soldering with electric soldering iron
Soldering is a science, and the principle of soldering with an electric iron is to heat and melt the solid solder wire with a heated iron, and then use the effect of flux to make it flow into the metal to be soldered. After cooling, it forms a firm and reliable soldering point.
When the solder is tin lead alloy and the welding surface is copper, the solder first wets the welding surface. With the occurrence of wetting phenomenon, the solder slowly diffuses towards the copper metal, forming an adhesion layer at the contact surface between the solder and the copper metal, making the two firmly bonded. So soldering is accomplished through three physical and chemical processes: wetting, diffusion, and metallurgical bonding.
1. Wetting: The wetting process refers to the flow of melted solder along the fine concave convex and crystalline gaps on the surface of the base metal by capillary force, forming an adhesion layer on the surface of the welded base metal, so that the atoms of the solder and the base metal are close to each other, reaching the distance where atomic gravity acts.
Environmental conditions that cause wetting: The surface of the welded base material must be clean and free of oxides or contaminants.
Metaphorically speaking, when water drops onto lotus leaves to form water droplets, it means that water cannot wet the lotus. When water drops onto cotton, the water seeps into the cotton and wets it.
2. Diffusion: With the progress of wetting, the phenomenon of mutual diffusion between solder and base metal atoms begins to occur. Usually, atoms are in a thermal vibrational state in the lattice, once the temperature rises. Atomic activity intensifies, causing the melted solder and atoms in the base material to cross the contact surface and enter each other's lattice. The speed and quantity of atomic 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 a good solder joint, a metal compound must be formed between the welded base metal and the solder to achieve a strong metallurgical bonding state of the base metal.
