In order to improve and ensure the high-quality welding of electronic circuits, and prevent false welding and virtual welding in circuit welding, it is the key to correctly operate the soldering iron and reasonably select soldering tin and flux, and the treatment of the lead pins of the electronic components to be welded, the proper temperature of tin on the printed circuit board and the flexible replacement of wattage power of the soldering iron are also the key points. Generally speaking, in the welding process of electronic circuits, the following specific points and measures to ensure the welding quality can be summarized.
1. Flexible control of wattage power of soldering iron: soldering iron is a special welding tool in electronic circuit welding. At present, the power of various types of internal heating soldering iron and external heating soldering iron is different. In the actual welding process, when the power used is too low and the welding temperature is too low, it is easy to produce false welding between components and circuits, while when the welding temperature is too high when the power used is too high, it will also lead to overheating and damage of wiring and components on the printed circuit board, and the welding head will be easily oxidized and burned to death. Therefore, generally speaking, low-power internal heating soldering irons of about 20 w, 25 w, and 40 w are often used in electronic circuits, and their welding head is in the shape of a slope, which is very suitable for components with slightly larger distance between soldering points, and the welding head will not often be oxidized and ablated. For components with relatively narrow distance between soldering points, such as integrated modules and arrayed microswitches, it is more appropriate and flexible to use pointed welding head.
2. Self-modification and renovation of soldering iron head: In daily circuit welding, sometimes we slightly modify the existing welding head or process the old welding head, which makes it more practical and convenient to use and reuse the waste head. First, cut off the slope plane of the original internal heating welding head with a hacksaw, then flatten the welding head with a file, and then drill a small hole with a depth of about 2mm in the central part of the plane with a 1.5mm Zuo Zuo drill. Thus, the reformed welding head is not only easy to tin, but also convenient and quick to disassemble the component pins, and the solder joints of its solder joints are burr-free and bright and smooth. 2. Reuse and processing of waste welding head. For the burned waste internal heating welding head, we will add a section of brass rod with the same diameter at the front residual head (the brass rod can be welded with welding head by gas-oxygen welding tool), then grind and round the welding scar on a grinding wheel, and finally grind the brass rod head into a slope surface. According to the practice, the brass welding head is easier to tin than the original copper welding head, and it is more resistant to oxidation and ablation in use, thus effectively prolonging the reuse life of welding head to a great extent.
3. Cleaning and decontamination of circuit boards and components before welding: In some failures that cause virtual welding and false solder joints, some of them should be desoldered at the components, and some of them are desoldering at the circuit boards, all of which are caused by the failure of cleaning and decontamination in the early stage before welding. There is a layer of oxide at the solder joints of copper foil of printed circuit boards. However, when the solder joints of copper foil that have been welded and disassembled for several times will have converging oil stains, once they are not cleaned, they will rush to solder components, which will easily lead to the failure of virtual soldering and false soldering. Therefore, the printed board should be wiped clean with alcohol before soldering, and the remaining oil stains should be scraped clean with a knife or sandpaper. The important point to grasp in the specific welding is that the welding head should be circled around the root of the lead pin of the component, and the stop for a minute should be moved away from the soldering iron, so that the welded spot is round, burr-free and bright. At the same time, attention should be paid to the lead pins of various electronic components, which should be polished and decontaminated with diamond sand paper before welding, then plated with a little tin, and then inserted into the printed board for welding. This is a quite necessary operation link. Of course, some electronic components have been tinned at the factory, but because of the storage time, the surface of the components’ leads is also prone to produce oxide layer, so it is better to decontaminate and tin before welding, so as to ensure the absolute reliability of welding quality. When welding some thin wire covered leads, enameled leads, yarn covered leads, etc., if we use the scraping method for the insulating paint layer of the leads, it is easy to scrape or damage the thin leads. For this reason, we can lay the thin lead head to be welded on a glass plate, and then dip a little rosin in the welding head, which can be pressed on the lead head and dragged back and forth. Due to the heat and rosin, the insulation layer of the lead head is quickly wiped off and the tin can be applied quickly. When welding multi-strand yarn covered wire leads, it is often necessary to polish the yarn layer wrapped outside the wire with fine sandpaper before tinning. However, because the diameter of the yarn covered wire is very small, it is easy to break the wire when polishing. The best way is to put the yarn-wrapped thread end on a lighter, burn it instantly, and then put it on a glass plate, and then use welding head dipped in rosin to drag the tin onto the thread end, so as to ensure the continuous strand of the thread end and fully ensure the even and smooth tin coating.
4. Characteristics and Selection of solder wire and Flux: At present, the commonly used special soldering tin for electronic circuits is a hollow tubular solder wire strip, and the hollow cavity of its welding wire contains rosin and active substances, which can ensure sufficient mechanical strength and reliable conductivity after the solder joints are solidified. There are many diameters of solder wire, such as 0.5, 0.8, 1. 2, 1.5, 2.0, 2.5, 3.0mm, etc. The selection can be determined according to the actual demand of solder joints and the welding area. When welding commonly used electronic components, it is advisable to choose a solder wire with a diameter of about 1.2mm, of course, it can be flexibly selected in actual use. However, some other hardware solder bars and solder blocks should not be used in electronic circuit welding because they contain too many impurities, so as to ensure the absolute reliability of solder quality. The function of flux is to prevent the metal surfaces (points) of components from being oxidized at high temperature, which is not easy to be welded. At present, the commonly used types of flux are rosin, rosin water, solder paste, solder oil, etc. In the use of electronic circuit welding, we should try our best to avoid using corrosive acid-base flux such as solder paste. Although sometimes using solder paste can reduce false soldering, the problem of corrosion of components and circuit boards will occur over time. For soldering, rosin and rosin water are the best soldering fluxes for electronic circuits, which are non-corrosive and have good electrical insulation properties. It is best to choose rosin with light yellow color and higher transparency. Generally, pine perfume is a mixture of rosin powder and alcohol, which can be debugged and configured by itself, and its configuration ratio is about 1: 3. In use, in order to prevent alcohol from evaporating too fast, a little kerosene can be added appropriately, and the effect is better.
