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Does your PCB's EMI meet the standard?

o-leading.com o-leading.com 2017-06-19 10:50:58
Electronic device electronic signal and the frequency of the processor continues to improve, the electronic system is a multi-component and many subsystems of complex devices. High density and high speed will cause the system to increase the radiation, and low pressure and high sensitivity will reduce the system immunity. Therefore, EMI is a threat to the safety of electronic equipment, reliability and stability. Our design of electronic products, PCB board design to solve the EMI problem is essential. This article mainly explains the PCB design should pay attention to the place, thereby reducing the PCB board electromagnetic interference problem.

EMI, Electro Magnetic Interference, can be divided into radiation and conduction interference. Radiation interference is the source of interference to space as a media to interfere with its signal to another electrical network. And the conduction interference is to use the conductive medium as a medium to interfere with the signal on an electrical network to another electrical network. In the high-speed system design, the integrated circuit pins, high-frequency signal lines and various types of plugs are common radiation interference sources in PCB board design. They emit electromagnetic waves is electromagnetic interference (EMI), itself and other systems will be affected normal work.

Today's PCB with imedance control design techniques have a lot of solutions to solve the problem of EMI, such as: EMI suppression coating, the appropriate EMI suppression parts and EMI simulation design. Now let's take a brief look at these tips.

Tip1: Common mode EMI interference source
- In the power layer with a low value of the inductor, the inductance of the synthesis of the transient signal will be reduced, the common mode EMI to reduce.
- Reduce the length of the power supply to the IC power supply pin.
- Use 3-6 mil PCB layer spacing and FR4 dielectric material.

Tip2: Electromagnetic shielding
- try to put the signal on the same PCB layer, and close to the power layer or ground plane.
- The power plane should be as close as possible to the ground plane

Tip3: the layout of the parts (different layout will affect the circuit interference and anti-jamming capability)
(Such as demodulation circuits, high-frequency amplifying circuits and mixing circuits, etc.), which separates the strong and weak electrical signals in this process, and the digital and analog signal circuits are separated
- The filter network of each part of the circuit must be connected in the near future, which not only can reduce the radiation, which can improve the anti-interference ability of the circuit and reduce the chance of being disturbed.
- Disruptive parts should be avoided in the layout of the interference source, such as data processing board CPU interference and so on.

Tip4: wiring considerations (unreasonable wiring will cause cross-interference between signal lines)
- can not have the border close to the PCB board frame, so as to avoid disruption caused by the production.
- the power cord should be wide and the loop resistance will be reduced.
- the signal line is as short as possible and the number of vias is reduced.
- Corner wiring can not be used in the right angle method, should be 135 ° angle is better.
- digital circuits and analog circuits should be ground isolation, digital ground and analog ground to be separated, and finally connected to the power ground

Reduce the electromagnetic interference is an important part of pcb manufacturer in china and the PCB board design, as long as the design of more to this point of thinking, the product naturally in the test, such as EMC test more qualified.