How to solder circuit boards and the skills to use circuit board soldering tools
The soldering technology of circuit boards mainly uses tin lead solder for soldering, abbreviated as tin soldering.
Welding mechanism of circuit board: under the action of welding heat, solder, weldment and copper foil will not melt, solder will melt and wet the welding surface, relying on the movement of atoms and molecules between solder and copper foil, which will cause diffusion between metals to form a metal alloy layer between copper foil and weldment, and connect copper foil and weldment to obtain a solid and reliable welding point.
To achieve the soldering of circuit boards, soldering tools are indispensable. Below are the soldering tools for circuit boards and their usage methods.
Circuit board welding tools mainly include: electric soldering iron, solder and flux, and auxiliary tools.
1. Electric soldering iron
Electric soldering iron is the most important welding tool in circuit board welding. The structure of different electric soldering irons is also different. Externally heated electric soldering irons are generally composed of soldering iron head, soldering iron core, shell, handle, plug, etc. The soldering iron head is installed inside the soldering iron core and is made of copper alloy material with good thermal conductivity as the substrate; An internally heated electric soldering iron is composed of five parts: a connecting rod, a handle, a spring clamp, a soldering iron core, and a soldering iron head (also known as a copper head). The soldering iron core is installed inside the soldering iron head (with fast heating and a thermal efficiency of over 85% -%%). There are many types of electric soldering irons, which can be divided into direct heating, induction, energy storage, and temperature regulation methods; The power can be divided into various types such as 15W, 2OW, 35W, and 300W.
The temperature of the soldering head of a low-power electric soldering iron is generally between 300~400 ℃. Generally speaking, the higher the power and heat of an electric soldering iron, the higher the temperature of the soldering iron head.
Welding integrated circuits, printed circuit boards, and CMOS circuits generally use a 20W internally heated soldering iron. The higher the power of the soldering iron used, the easier it is to burn out the components (usually when the temperature of the transistor junction exceeds 200 ℃, it will burn out) and cause the printed circuit board wires to detach from the substrate; The power of the soldering iron used is too small, the soldering tin cannot be fully melted, the flux cannot be volatilized, and the solder joints are not smooth and firm, which is prone to faulty soldering.
2. Tin and flux
When welding, solder and flux are also required.
Tin material: It is a fusible metal that can connect component leads to the connection points of printed circuit boards. Tin (Sn) is a soft and ductile silver white metal with a melting point of 232 ℃. It has stable chemical properties at room temperature, is not easily oxidized, does not lose its metallic luster, and has strong resistance to atmospheric corrosion. Lead (Pb) is a relatively soft light blue white metal with a melting point of 327 ℃. High purity lead has strong atmospheric corrosion resistance and good chemical stability, but it is harmful to human health. Adding a certain proportion of lead and a small amount of other metals to tin can make solder with low melting point, good flowability, strong adhesion to components and wires, high mechanical strength, good conductivity, low oxidation resistance, good corrosion resistance, and bright and beautiful solder joints, commonly known as solder. Solder can be divided into 15 grades based on its tin content, and into three grades: S, A, and B based on its tin content and the chemical composition of impurities. Welding electronic components usually uses wire shaped solder wire with a rosin core. This type of soldering wire has a low melting point and contains rosin flux, making it easy to use.
Solder flux: divided into two types according to function: flux and solder resist.
① Flux
The use of flux during the welding process can help us remove oxides from the metal surface, which is beneficial for welding and also protects the soldering iron head. It can dissolve and remove oxides from the metal surface, and surround the metal surface during welding and heating, isolating it from air and preventing metal oxidation during heating; It can reduce the surface tension of molten solder, which is beneficial for the wetting of solder. Fluxes can generally be divided into inorganic flux, organic flux, and resin flux. At present, the commonly used flux is rosin or rosin perfume (dissolving rosin in alcohol); When welding larger components or wires, solder paste can also be used, but it has a certain degree of corrosiveness, and residues should be removed in a timely manner after welding.
② Solder resist
Solder blocking flux can cover the board surface of printed circuit boards that do not need to be soldered, so that the solder can only be soldered on the required solder joints, which can protect the panel from small heating impact during welding and is not easy to blister, and can also prevent bridging, tip pulling, short circuit, faulty soldering, etc.
When using flux, it must be properly applied according to the area size and Surface states of the weldment. If the amount is too small, the welding quality will be affected. If the amount is too large, the flux residue will corrode the components or make the insulation performance of the circuit board worse.
