Printed circuit board (PCB) is the support of circuit components and components in electronic products. It provides electrical connections between circuit elements and devices. With the rapid development of electronic technology, PCB density is getting higher and higher. The ability of PCB design to resist interference makes a big difference. Practice has proved that even if the circuit schematic design is correct and the printed circuit board design is improper, the reliability of electronic products will be adversely affected. For example, if two thin parallel lines on a printed board are close together, there will be a delay in the signal waveform, resulting in reflected noise at the end of the transmission line. Therefore, when designing printed circuit board, we should pay attention to the correct method, comply with the general principle of PCB design, and should meet the requirements of anti-interference design.

General principles of PCB design

The layout of components and wiring is important for optimal performance of electronic circuits. In order to design PCB with good quality and low cost, the following general principles should be followed:

1. The wiring

The principles of wiring are as follows:

(1) Parallel wires at the input and output terminals should be avoided as far as possible. It is better to add ground wire between wires to avoid feedback coupling.

(2) The minimum width of PCB wire is mainly determined by the adhesion strength between wire and insulating substrate and the value of current flowing through them. When the thickness of copper foil is 0.5mm and the width is 1 ~ 15mm, the current through 2A, the temperature will not be higher than 3℃. Therefore, the wire width of 1.5mm can meet the requirements. For integrated circuits, especially digital circuits, 0.02 ~ 0.3mm wire width is usually selected. Of course, whenever possible, use wide wires, especially power and ground cables. The minimum spacing of wires is mainly determined by the insulation resistance and breakdown voltage between wires in the worst case. For integrated circuits, especially digital circuits, the spacing can be less than 5 ~ 8mil as long as the process permits.

(3) Printed wire bend generally take circular arc, and right Angle or included Angle in high frequency circuit will affect the electrical performance. In addition, avoid using large copper foil as far as possible, otherwise, when heated for a long time, copper foil is easy to expand and fall off. When large areas of copper foil must be used, it is best to use a grid. This is conducive to the removal of copper foil and substrate bonding between the heat produced by the volatile gas.