Skills of Using Circuit Board Soldering Tools
The circuit board soldering technology mainly uses tin-lead solder for soldering, referred to as tin soldering.
The welding mechanism of the circuit board: In the process of soldering, the solder, the weldment and the copper foil are subjected to the action of welding heat, the weldment and the copper foil do not melt, the solder melts and wets the welding surface, relying on both the weldment and the copper foil The movement of atoms and molecules causes the diffusion between the metals to form a metal alloy layer between the copper foil and the weldment, and connects the copper foil and the weldment together to obtain a firm and reliable welding point.
If you want to realize the soldering of circuit boards, you can't do without soldering tools. The following introduces the soldering tools for circuit boards and how to use them.
Circuit board welding tools mainly include: electric soldering iron, solder and flux and auxiliary tools.
1. Soldering iron
The electric soldering iron is the most important welding tool in circuit board welding. Different electric soldering irons have different structures. The external heating electric soldering iron is generally composed of a soldering iron tip, a soldering iron core, a shell, a handle, a plug, etc. The soldering iron tip is installed in the soldering iron core and is made of a copper alloy material with good thermal conductivity as the matrix; the internal heating electric soldering iron The soldering iron is composed of five parts: a connecting rod, a handle, a spring clip, a soldering iron core, and a soldering iron tip (also called a copper tip). There are many types of electric soldering irons, which can be divided into direct heating type, induction type, energy storage type and temperature adjustment type from the heating method; from the power size can be divided into 15W, 2OW, 35W...300W and so on.
The temperature of the soldering iron tip of a low-power electric soldering iron is generally between 300 and 400 °C. Generally speaking, the greater the power of the electric soldering iron, the greater the heat, and the higher the temperature of the soldering iron tip.
Welding integrated circuits, printed circuit boards, and CMOS circuits generally use 20W internal heating electric soldering iron. The greater the power of the soldering iron used, it is easy to scald the components (generally, the junction temperature of the diode and triode will burn out if it exceeds 200°C) and the printed circuit board wires will fall off from the substrate; the power of the soldering iron used is too small, and the solder cannot be fully melted , The flux cannot be volatilized, the solder joints are not smooth and firm, and it is easy to produce false welding.
2. Solder and flux
When soldering, tin and flux are also required.
Tin material: It is a fusible metal that can connect the component leads to the connection points of the printed circuit board. Tin (Sn) is a soft, malleable silver-white metal with a melting point of 232°C. 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 soft light blue-white metal with a melting point of 327°C. High-purity lead has strong atmospheric corrosion resistance and good chemical stability, but it is harmful to the human body. Adding a certain proportion of lead and a small amount of other metals to tin can make it with low melting point, good fluidity, strong adhesion to components and wires, high mechanical strength, good conductivity, not easy to oxidize, good corrosion resistance, bright and beautiful solder joints Solder, commonly known as solder. Solder can be divided into 15 according to the amount of tin content, and divided into three grades of S, A, and B according to the chemical composition of tin content and impurities. Soldering electronic components, generally using a rosin core wire solder wire. This solder wire has a low melting point and contains rosin flux, which is easy to use.
Soldering flux: According to the function, it is divided into two types: flux and solder resist.
①Flux
The use of flux during the soldering process can help us remove the oxides on the metal instant noodles, which is not only conducive to soldering, but also protects the tip of the soldering iron. It can dissolve and remove oxides on the metal surface, and surround the metal surface during welding heating to isolate it from the air and prevent the metal from oxidizing during heating; it can reduce the surface tension of the molten solder and facilitate the wetting of the solder. Flux can generally be divided into inorganic flux, organic flux and resin flux. At present, the commonly used flux is rosin or rosin water (dissolve rosin in alcohol); when soldering larger components or wires, solder paste can also be used, but it is corrosive to a certain extent, and the residue should be removed in time after soldering.
②Solder resist
The solder resist can cover the board surface of the printed circuit board that does not need to be soldered, so that the solder can only be soldered on the required solder points, and can protect the panel so that it is less heat-shocked during soldering and is not easy to foam. It can prevent bridging, tipping, short circuit, false welding and so on.
When using flux, it must be applied in an appropriate amount according to the area size and surface state of the workpiece to be welded. If the amount is too small, the welding quality will be affected. If the amount is too much, the flux residue will corrode the components or deteriorate the insulation performance of the circuit board.
