Any electronic instrument, meter or electronic product is assembled by connecting various components, electronic modules, connectors and cables. Welding is an important part of the electronic installation process. Although mechanical automated welding equipment and advanced welding technology play a very important role in the assembly and welding of electronic products, when repairing, assembling, debugging, and repairing electronic circuits, Manual welding technique is a basic skill.

The printed circuit board can realize the wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits, provide the required electrical characteristics, and provide identification characters and graphics for component insertion, inspection, and maintenance.

When soldering the circuit board, the component installation sequence should be flexibly operated according to the actual situation of the circuit, neat and beautiful, and the model value is outward, which is convenient for inspection. In general, the principles of first low then high, first light then heavy, and priority heat resistance should be followed, followed by resistors, capacitors, diodes, transistors, integrated circuits, and high power tubes.

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Component welding sequence

Component molding

According to the distance between the solder joints and the layout of the circuit board components, the installation methods of the components are determined. There are two types: vertical and horizontal. Vertically mounted components occupy a small area and are generally used when components are densely arranged. Horizontal installation machinery has good stability, neat arrangement, and large component span. It is generally used when there is enough space. Do not bend the lead of the component from the root to prevent damage to the component. Use tweezers to clamp the lead of the component and bend it to form 2~3mm from the root. When placing components at the same time, do not make the components and the circuit board close to each other, leaving a gap of 1~2mm, which is conducive to heat dissipation of the components.

Precautions for component welding:

• Welding of resistors: The mark is required to be upward, and the direction of the text is the same. After installing the same specification, install another specification, and try to make the resistance level consistent.

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• Welding of capacitors: Please note that the "+" and "-" poles of polarized capacitors must not be connected in the wrong direction. The marking direction on the capacitors should be easy to see. Install glass glaze capacitors, organic dielectric capacitors, ceramic dielectric capacitors first, and electrolytic capacitors last.

• Diode welding: The diode has positive and negative polarities. Pay attention to the positive and negative poles of the diode when placing it. When soldering a vertical diode, the soldering time to the shortest lead should not exceed 2 seconds.

• Transistor welding: Note that the three pins b, c, and e are correctly connected, and the welding time is as short as possible. When welding, pinch the pin with tweezers to facilitate heat dissipation.

• Welding of integrated circuits: According to the requirements of the drawings, check whether the chip model, pins and placement locations meet the requirements. When soldering, the two diagonal pins should be soldered to position them, and then soldered one by one from left to right and top to bottom. When soldering CMOS integrated circuits, in order to avoid damage to components due to electrostatic induction, the soldering iron must be grounded well. The soldering time should not exceed 5 seconds. It is best to use a 20~25W internal heating soldering iron.

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