PCB News - What is the shielding concept of PCBA board

What is the shielding concept of PCBA board
The shielding concept of the PCBA board is to isolate the metal between two space areas to control the induction and radiation of electric fields, magnetic fields and electromagnetic waves from one area to another. Specifically, it is to use a shield to surround the interference source of components, circuits, assemblies, cables or the entire system to prevent the interference electromagnetic field from spreading out; use the shield to surround the receiving circuit, equipment or system to prevent them from being exposed to the outside world. The influence of electromagnetic fields. Because the shielding body absorbs energy, reflects energy and offsets energy from external interference electromagnetic waves and internal electromagnetic waves from wires, cables, components, circuits or systems, etc., the PCBA board shielding body has the function of reducing interference.

1. When the frequency of the interference electromagnetic field is high, the eddy current generated in the metal material with low resistivity is used to form the cancellation effect of the external electromagnetic wave, so as to achieve the shielding effect.
2. When the frequency of the interference electromagnetic wave is low, materials with high magnetic permeability should be used, so that the lines of magnetic force are limited to the inside of the shielding body and prevent spreading to the shielded space.
3. In some cases, if a good shielding effect is required for both high-frequency and low-frequency electromagnetic fields, different metal materials are often used to form a multi-layer shielding body.
Many people do not understand the principle of electromagnetic shielding, and think that as long as a box is made of metal, and then the box is grounded, it can play the role of electromagnetic shielding. Under the guidance of this concept, the result is failure. Because the electromagnetic shielding has nothing to do with whether the shielding body is grounded or not. There are only two factors that really affect the shielding effectiveness of the shield: one is that the entire surface of the shield must be conductive and continuous, and the other is that there can be no conductors directly penetrating the shield. There are many conductive discontinuities on the shield, the most important one is the non-conductive gap formed at the junction of different parts of the shield. These non-conductive gaps produce electromagnetic leakage, and PCBA board manufacturing is like fluid leaking from the gap on the container. One way to solve this kind of leakage is to fill the gap with conductive elastic material to eliminate non-conductive points. This is like filling rubber in the gaps of fluid containers. This elastic conductive filling material is an electromagnetic sealing gasket.

In many documents, the electromagnetic shielding body is likened to a liquid-tight container. It seems that only when the gap is sealed to the degree of dripping with a conductive elastic material, the electromagnetic wave can be prevented from leaking. In fact, this is inaccurate. Whether the gap or hole will leak electromagnetic waves depends on the size of the gap or hole relative to the wavelength of the electromagnetic wave. When the wavelength is much larger than the size of the opening, no obvious leakage occurs. Therefore, when the frequency of interference is high, the wavelength is short at this time, and electromagnetic sealing gaskets are needed. Specifically, when the frequency that interferes with the PCB board exceeds 10MHz, it is necessary to consider the use of electromagnetic sealing gaskets. Any material with elasticity and good conductivity can be used as electromagnetic sealing gasket.