There are many types of electromagnetic shielding materials, and the most widely used electromagnetic shielding material is conductive paint. Electromagnetic waves will interact with electronic components and cause interference, which is called EMI (Electromagnetic Interference). For example, the common "snowflakes" on TV screens indicate that the received signal is disturbed. Magnetic shielding materials mainly include three categories: 1) Metal: directly select metal materials, such as beryllium copper, stainless steel, etc.; 2) Filling: adding a certain proportion of conductive fillers to non-conductive substrates to make the material conductive, The material can be silica gel, plastic and other materials, and the conductive filler can be metal sheet, metal powder, metal fiber or metalized fiber; 3) Surface coating and conductive coating: electroplating the substrate, such as conductive cloth.
The conductive paint is sprayed and brushed to make the completely insulated non-metallic or non-conductive surface have the characteristics of absorbing, conducting and attenuating electromagnetic waves like metal, thereby playing the role of shielding electromagnetic interference. The principle of electromagnetic shielding of conductive coatings .
There are many conductive discontinuities on the conductive paint of 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 cause electromagnetic leakage, just as fluid leaks from a gap in a container. One way to solve this 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 conductive paint of the electromagnetic shielding body is likened to a liquid sealed container. It seems that only when the gap is sealed with a conductive elastic material to the extent that water does not leak, the leakage of electromagnetic waves can be prevented. Actually this is not exact. 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 interference frequency is high, the wavelength is short at this time, and an electromagnetic sealing gasket is required. Specifically, when the frequency of interference exceeds 10MHz, it is necessary to consider the use of electromagnetic sealing gaskets.
Recently, a new conductive coating shielding technology-conformal shielding has emerged, which is different from the traditional mobile phone EMI shielding method that uses metal shields. The conformal shielding technology completely integrates the shielding layer and the package, and the module itself With shielding function, after the chip is mounted on the PCB, there is no need to add a shielding cover, and does not occupy additional equipment space. It is mainly used for PA, WiFi/BT, Memory and other SiP module packages to isolate and package internal circuits Interference with external systems.