How to design PCB for electromagnetic interference

The frequency of electronic signals and processors of electronic equipment is constantly increasing, and the electronic system has become a complex device containing multiple components and many subsystems. High density and high speed will increase the radiation of the system, while low voltage and high sensitivity will reduce the anti-interference of the system. Therefore, electromagnetic interference (EMI) is a real threat to the safety, reliability and stability of electronic equipment. When we design electronic products, the design of PCB boards is crucial to solving EMI problems. This article mainly explains the points to pay attention to when designing PCBs, so as to reduce the electromagnetic interference problems in PCB boards.

Definition of electromagnetic interference (EMI)

Electromagnetic interference (EMI, Electro Magnetic Interference) can be divided into radiation and conduction interference. Radiated interference is the interference source using space as a medium to interfere with its signal to another electrical network. And conducted interference is the interference of the signal on one electrical network to another electrical network using a conductive medium as a medium. In high-speed system design, integrated circuit pins, high-frequency signal lines and various plugs are common radiation interference sources in PCB board design. The electromagnetic waves they emit are electromagnetic interference (EMI), which will affect the normal operation of themselves and other systems.

PCB design tips for electromagnetic interference (EMI)

There are many solutions to EMI problems in PCB design tips today, such as EMI suppression coatings, suitable EMI suppression parts and EMI simulation design. The above video introduces methods to reduce EMI. Now let’s briefly explain these tips.

Tip 1: Common-mode EMI interference source (such as the voltage drop formed by the transient voltage formed on the power bus at both ends of the inductor of the decoupling path)

• Use low-value inductors on the power layer, and the transient signals synthesized by the inductors will be reduced, thereby reducing common-mode EMI.
• Reduce the length of the connection from the power layer to the IC power pin.
• Use 3-6 mil PCB layer spacing and FR4 dielectric material.

Tip 2: Electromagnetic shielding

• Try to put the signal traces on the same PCB layer, and close to the power layer or ground layer.
• The power layer should be as close to the ground layer as possible

Skill 3: Layout of parts (different layouts will affect the interference and anti-interference ability of the circuit)

• Block processing according to different functions in the circuit (such as demodulation circuit, high-frequency amplification circuit and mixing circuit, etc.), in this process, separate strong and weak electrical signals, and separate digital and analog signal circuits
• The filter network of each part of the circuit must be connected nearby, which can not only reduce radiation, but also improve the anti-interference ability of the circuit and reduce the chance of being interfered.
• Parts susceptible to interference should be avoided as much as possible during layout, such as interference from the CPU on the data processing board.

Skill 4: Consideration of wiring (unreasonable wiring will cause cross interference between signal lines)

• No routing should be close to the border of the PCB board to avoid disconnection during production.
• The power line should be wide, and the loop resistance will be reduced.
• The signal line should be as short as possible, and the number of vias should be reduced.
• Corner wiring cannot be done at right angles, and a 135° angle is preferred.
• Digital circuits and analog circuits should be isolated by ground wires, and both digital ground wires and analog ground wires should be separated and finally connected to the power ground

Reducing electromagnetic interference is an important part of PCB board design. As long as you think more about this aspect during design, it will be easier to pass product tests such as EMC tests.