What principles should be followed in PCB layout design

PCB circuit board is the support of circuit components and devices in electronic products. Even if the circuit schematic design is correct, the printed circuit board is not properly designed, which will adversely affect the reliability of electronic products. When designing printed circuit board, we should adopt correct method, abide by the general principle of PCB design, and meet the requirements of anti-interference design.

• The principle of PCB layout design should be followed:

Firstly, the size of PCB should be considered. When the size of PCB is too large, the printing line is long, the impedance is increased, the ability of resisting noise is decreased, and the cost is also increased; if the size is too small, the heat dissipation is not good, and the adjacent lines are liable to be interfered. After determining the PCB size, determine the location of the special components. Finally, all the components of the circuit are arranged according to the function unit of the circuit.

The following principles should be followed when determining the location of special components:

1. Shorten the connection between high frequency components as much as possible, and try to reduce their distribution parameters and electromagnetic interference. The easily disturbed components should not be too close to each other and the input and output components should be as far away as possible.

2. Some components or wires may have a high potential difference, so the distance between them should be increased to avoid accidental short circuit caused by discharge. Components with high voltage shall be arranged as far as possible in places not accessible by hand during commissioning.

3. Components weighing more than 15g should be fixed with brackets and then soldered. Those components that are large, heavy, and have a lot of heat should not be mounted on the printed board, but should be installed on the chassis of the whole machine, and heat dissipation should be considered. The thermal element should be kept away from the heating element.

4. For the layout of adjustable components such as potentiometer, adjustable inductor, variable capacitor and micro switch shall take into consideration the structural requirements of the whole machine. If the inside adjustment, it should be placed on the PCB to facilitate the adjustment; if the outside adjustment, the position of the adjustment knob on the chassis panel should be appropriate.

5. The position occupied by the positioning holes of the printed board and the fixed bracket should be left.

• The PCB layout of the circuit components should meet the requirements of anti-interference design:

1. Arrange the position of each functional circuit unit according to the flow of the circuit so that the layout is convenient for the signal circulation and the signal keeps the same direction as possible.

2. Take the core components of each functional circuit as the center, and make layout around it. The components should be uniformly, neatly and compactly arranged on the PCB. Minimize and shorten the lead and connection between the components.

3. For circuits operating at high frequencies, the distribution parameters between components should be considered. General circuits should be as close to parallel as possible. In this way, it is not only beautiful, and easy to install welding, easy to mass production.

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