How to strengthen anti-interference ability in PCB design

Printed circuit boards (PCBs) are the supporting components for circuit components and devices in electronic products in smt assembly. It provides electrical connections between circuit components and devices. With the rapid development of electronic technology, the density of PCBs is getting higher and higher. The quality of PCB design has a significant impact on its anti-interference ability. Practice has proven that even if the circuit schematic design is correct and the printed circuit board design is inappropriate, it can have adverse effects on the reliability of electronic products. For example, if two thin parallel lines of a printed circuit board are placed very close together, it will cause a delay in the signal waveform and generate reflected noise at the terminals of the transmission line. Therefore, when designing printed circuit boards, attention should be paid to adopting the correct methods, following the general principles of PCB design, and meeting the requirements of anti-interference design

To achieve optimal performance in electronic circuits, the layout of components and the placement of wires are crucial. In order to design high-quality and low-cost PCBs,

the following general principles should be followed:

Firstly, consider the size of the PCB. When the PCB size is too large, the printed lines are long, the impedance increases, the noise resistance decreases, and the cost also increases; If it is too small, the heat dissipation is poor, and adjacent lines are easily disturbed. After determining the PCB size, determine the position of special components. Finally, layout all components of the circuit according to its functional units.

When determining the position of special components, the following principles should be followed:

Try to shorten the wiring between high-frequency components as much as possible, and try to reduce their distribution parameters and electromagnetic interference with each other. Components that are susceptible to interference should not be too close to each other, and input and output components should be kept as far away as possible.

There may be a high potential difference between certain components or wires, and the distance between them should be increased to avoid accidental short circuits caused by discharge. Components with high voltage should be arranged in areas that are not easily accessible by hands during debugging.

Components weighing over 15g should be fixed with brackets and then welded. The components that are large, heavy, and generate a lot of heat should not be installed on the printed circuit board, but on the chassis bottom plate of the entire machine, and heat dissipation should be considered. The thermal element should be kept away from the heating element.

For the layout of adjustable components such as Potentiometer, adjustable inductance coil, variable capacitor, microswitch, etc., the structural requirements of the whole machine shall be considered. If it is adjusted internally, it should be placed in a convenient place on the printed circuit board for adjustment; If it is adjusted externally, its position should match the position of the adjustment knob on the chassis panel.

The position occupied by the positioning holes and fixing brackets of the printed board should be reserved.

According to the functional units of the circuit. When PCB layout is applied to all components of a circuit, the following principles should be followed:

Arrange the positions of each functional circuit unit according to the circuit flow, making the layout convenient for signal flow and keeping the signal in the same direction as much as possible.

Layout around the core components of each functional circuit as the center. The components should be evenly, neatly, and compactly arranged on the PCB. Minimize and shorten the leads and connections between various components as much as possible.

For circuits operating at high frequencies, consideration should be given to the distribution parameters between components. The general circuit should arrange the components in parallel as much as possible. In this way, not only is it aesthetically pleasing, but it is also easy to assemble and weld, making it easy for mass production.

The components located at the edge of the circuit board are generally not less than 2mm away from the edge of the circuit board. The optimal shape of a circuit board is a rectangle. Both length and width are 3:2 or 4:3. Circuit board size greater than 200 × At 150mm, the mechanical strength of the circuit board should be considered.

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