5 steps to correctly solder with a soldering iron
Welding technology, as a fundamental skill, plays a crucial role in electronic manufacturing. When manually soldering with an electric soldering iron, it is necessary to master certain skills, which are actually included in the entire soldering process of the 10 key points - "one scraping, two plating, three testing, four soldering, and five checking".
1. One scratch
Clean the surface of the welded metal object by scraping off the oxide layer, oil stains or insulation paint on the welding surface with a small knife, scrap steel saw blade, etc. (or polishing with fine sandpaper, wiping off with coarse rubber) until a new metal surface is exposed. Before soldering, homemade printed circuit boards also need to be carefully polished with fine sandpaper or water sandpaper on the side covered with copper foil. Scraping is a key step to ensure welding quality, but it is often overlooked by beginners. If scraping is not done properly, it will result in poor tin plating and welding. It should be noted that some component leads have been silver plated, gold plated, or tinned. As long as there is no oxidation or peeling, there is no need to scrape them again. If there is dirt on the surface, it can be wiped off with a coarse rubber as shown in Figure 3 (c). The choice of thick rubber is best when using a large rubber for drawing. Some gold-plated transistor pins and leads may be difficult to tin after scraping off the coating. No matter what form of "scraping" is used, attention should be paid to constantly rotating the pins of the components to ensure that the entire circumference of the pins is clean.
2. Second plating
Tin the area to be welded. The soldering parts of the scraped component pins, wires, etc. should be immediately coated with an appropriate amount of solder and a thin layer of tin should be plated with an electric soldering iron to prevent surface oxidation and improve the solderability of the component. The plated solder layer should be thin and uniform, so the amount of solder on the soldering iron tip should not be too much each time. For components such as crystal diodes and transistors that are sensitive to heat, they must be clamped at the root of the lead pins with tweezers or pointed pliers as shown in Figure 4 (b) to help dissipate heat, and then tin plated. Tin coating of electronic components is an important process step in welding technology to prevent hidden dangers such as virtual soldering and false soldering, and must not be taken lightly.
3. Three tests
Testing is the inspection of components that have been tinned, to see if there is any damage, deformation, or soldering (short circuit) on the appearance of the components under high temperature of an electric soldering iron. For components such as capacitors, transistors, and integrated circuits, a multimeter should be used to check their quality for reliability. Components found to be unreliable or damaged must not be reused.
4. Four welding
Welding is the process of soldering qualified components onto a printed circuit board or designated location as required. When welding, it is important to control the temperature and welding time of the soldering iron. If the temperature is too low or the welding time is too short, the solder surface will have a burr like tail like shape as shown in Figure 5 (a), and the surface will not be smooth, even resembling tofu residue as shown in Figure 5 (b). It is possible that due to incomplete evaporation of the solder flux, there is a certain amount of solder flux left between the solder and metal. After cooling, the solder flux (rosin) will stick to the metal surface and can be pulled apart with a little force, which is called false soldering.
