PCB Tech - The type of EMC interference of PCB copy board?

To reach the level of electromagnetic interference control of the original PCB board, the PCB copy board must have a full understanding of the electromagnetic interference (EMI) related technology of the circuit board. Whether the PCB copy board can effectively control electromagnetic interference affects whether the copy board can reach or exceed the function of the original board. standard. This article analyzes the main types of PCB electromagnetic interference and the commonalities and differences between different types.

Causes of electromagnetic interference Electromagnetic interference (EMI) refers to the stray energy emitted by the PCB board or the stray energy entering the PCB board from the outside, which includes:

Conducted (low frequency) electromagnetic interference;

Radiation (high frequency) electromagnetic interference;

ESD (electrostatic discharge);

Electromagnetic interference caused by lightning.

Conducted and radiated electromagnetic interference has differential mode and common mode manifestations. When dealing with various forms of electromagnetic interference, specific problems must be analyzed in detail. For electromagnetic interference caused by ESD and lightning, electromagnetic interference suppression devices must be used to eliminate ESD and lightning before entering the system to prevent the resulting system from working abnormally or damage. For conductive or low-frequency electromagnetic interference, whether it is receiving or transmitting, filtering measures must be taken on the power line and the transmission line of the PCB board input/output port. There are three basic forms of radiated electromagnetic interference suppression: electronic filtering, mechanical shielding and interference source suppression.

Among all forms of electromagnetic interference, radiated electromagnetic interference is the most difficult to control, because the frequency range of radiated electromagnetic interference is 30MHz to a few GHz. In this frequency range, the wavelength of energy is very short, even if it is very short on the PCB. The wiring can become a transmitting antenna. In addition, the inductance of the circuit in this frequency band increases, which may lead to increased noise. When the electromagnetic interference is high, the circuit will easily lose its normal function.

Although the control and shielding of radiated electromagnetic interference can be controlled by mechanical shielding technology, electronic filtering or interference source suppression, and electronic filtering and mechanical shielding technology are very effective in electromagnetic interference suppression, these two methods are usually the first to control radiated electromagnetic interference. Second line of defense. Due to the need for additional components and increased installation time, the cost of electronic filtering technology is relatively high. In addition, users often open the shielding door of the equipment or remove the back panel to facilitate the maintenance of internal components or PCB boards. Therefore, mechanical shielding technology is often in vain.

Therefore, the main way to control electromagnetic interference is to reduce the energy of the radiation source and control the size of the electromagnetic field generated by the voltage and current on the PCB. Most of the circuits are installed within the range of the PCB board, so the inductance, capacitance, transient voltage and current path can be controlled through careful design of the PCB board, thereby controlling the size of the electromagnetic field.

In the process of PCB copying, attention should be paid to the measures to reduce electromagnetic interference in the original PCB design. It is consistent with the function and performance of the original board.