PP PET PI PEN Chemical Gold Plating Vacuum Gold Plating Sputtering Gold Plating Metal Melting Spray Coating Metal Foil Surface Coating Material

With the development of modern high-tech, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) caused by electromagnetic waves are becoming increasingly serious. Therefore, exploring efficient solutionselectromagnetic shielding materialPreventing electromagnetic interference and compatibility issues caused by electromagnetic waves is of great significance for improving the safety and reliability of electronic products and equipment, enhancing international competitiveness, preventing attacks from electromagnetic pulse weapons, and ensuring the safe and smooth operation of information communication systems, network systems, transmission systems, weapon platforms, etc. Given the significant role of electromagnetic shielding materials in social life, economic development, and national defense, their research and development have become increasingly important topics of concern.

（1） Ferromagnetic materials and metal good conductor materials

Ferromagnetic materials and metal good conductor materials are commonly usedShielding materialFerromagnetic materials are suitable for shielding low-frequency (below 100kHz) magnetic fields. Their principle of action is to use the high magnetic permeability of ferromagnetic materials to guide magnetic lines through high penetration materials and reduce magnetic flux density in nearby space to achieve magnetic shielding. Commonly used ferromagnetic materials include pure iron, silicon steel, and Permalloy (iron nickel alloy). The electromagnetic shielding effect of Pomo alloy is much superior to other types. Pomo alloy has three main components, namely 78% Ni, 65% Ni, and 50% Ni. Among them, the magnetic permeability of 78% Ni Pomo alloy is much higher than the other two, reaching the order of 3 × 104~1.2 × 105. Pomo alloy is sensitive to stress, and its magnetic properties are closely related to heat treatment. However, the material used is not heat-treated, so it is necessary to understand and master the heat treatment process when using it. The newly emerged iron cobalt (Fe Co) alloys and iron aluminum alloys are also soft magnetic alloy materials that can be used for shielding low-frequency magnetic fields.

Due to the low conductivity of ferromagnetic materials, they are not suitable for shielding high-frequency electromagnetic fields. Metal conductors with good conductivity are suitable for shielding high-frequency electromagnetic fields and electrostatic fields. Conductivity is the main criterion for selecting shielding materials in electromagnetic shielding, and the most commonly used materials are steel plates, galvanized steel sheets, copper plates, aluminum plates, and other materials with good conductivity. Metal shielding materials also have excellent mechanical properties, but their disadvantages such as high density, susceptibility to corrosion, and difficulty in processing are obvious, and they have significant limitations.

（2） Surface coating film shielding material

Surface coating film shielding material is a type of shielding material that attaches a conductive layer to the surface of insulating materials such as plastics, in order to achieve shielding. It belongs to the category of shielding materials mainly based on reflection loss. Common preparation methods include chemical gold plating, vacuum spraying, sputtering, metal melting, and pasting metal foil. This type of surfaceConductive thin film shielding materialIt generally has the advantages of good conductivity and obvious shielding effect, but its disadvantages are low adhesion of the surface conductive film, easy peeling, and poor secondary processing performance.

(1) Chemical gold plating

Chemical gold plating is the process of depositing metals such as Ni, Fe Ni, or Cu/Ni onto the surface of engineering plastics such as ABS using non electrolytic electroplating. This method is currently the most widely used and effective method for surface metallization of plastics, and it is also the only method that is not limited by the shape and size of the shell material and can obtain a uniformly thick conductive layer. The commonly used plastic at present is electroplated ABS engineering plastic, with nickel or copper nickel composite coating as the coating. In the range of 30MHz to 1.0GHz, chemical nickel plating is generally used, and the shielding effect has reached about 60dB. For higher requirements, a composite coating with copper plating as the bottom layer and nickel plating as the surface layer can be used. A single copper coating can also achieve good shielding effect. However, due to the easy oxidation of copper in air and poor corrosion resistance, it cannot be used alone. The shielding effect of this composite coating can reach over 90dB. The advantages of chemical gold plating are good effect, not limited by the shape and size of the shell, uniform coating, strong adhesion, mass production and low cost; The disadvantage is that there are fewer plastic varieties suitable for electroplating. Improvement methods include using blending modification techniques to form plastic alloys between ABS and other plastics, surface grafting of plastics, and surface chemical treatment to enable electroplating of certain plastics that are difficult to electroplate, thereby expanding the application range of such materials.

(2) Vacuum gold plating

Vacuum gold plating is the process of vaporizing low boiling point metals such as Al, Gr, Cu, etc. in a vacuum container and condensing them on the surface of plastic to form a uniform metal conductive film. Vacuum gold plating can be applied to various plastics, with good conductivity and fast deposition speed of the coating. However, the size of the vacuum container limits the size of plastic products, and it has a good effect on flat surface treatment. For complex shaped surfaces, it is difficult to control the uniformity of the film thickness. In order to improve the adhesion between the coating and the plastic, it is necessary to keep the plastic surface highly clean and free from contamination. Usually, the plastic surface is pre treated to remove impurities and make the treated surface rough, in order to improve the adhesion of the metal coating. There are generally three pre-treatment methods: spraying iron sand for cleaning, chemical etching, and applying primer. The primer coating method is a good pre-treatment method, which does not require special sandblasting equipment, has a fast production speed, and does not cause significant chemical pollution. For polyolefin plastics, corona treatment is required before spraying to increase the content and polarity of surface oxidation groups.

(3) Sputter gold plating

Sputtering gold plating is the process of using high-energy argon ions to impact a metal in a vacuum container, causing the metal to vaporize, and then forming a metal thin film on the surface of plastic fabrics, etc. Sputtering gold plating can also be applied to various plastics. Compared with vacuum gold plating, the adhesion between the plated metal and plastic is generally stronger. However, the equipment cost is high, and there are also advantages and disadvantages of vacuum gold plating.

(4) Metal melting

The metal spraying method is to instantly melt the metal under high temperature of an arc, and then immediately use high-pressure air to blow the molten metal into a mist and spray it onto the surface of the plastic. Metal Zn is melted by an arc at high temperature and blown into extremely fine granular powder on the surface of plastic using high-speed airflow, forming a very thin metal layer with a thickness of about 50 μ m. It has good conductivity, a bulk resistivity of up to 10-2 Ω· cm, and a shielding effect of about 60-120dB. The disadvantage of the metal spraying method is that the adhesion between the Zn coating and the plastic is poor, and the coating is prone to detachment, requiring a special spraying device.

(5) Stick metal foil

Paste metal foil composite shielding materialIt is to bond metal foil or composite metal foil with plastic sheet, thin film or thin film with adhesive first, and then press it into shape by laminating method, which can produce soft and hard shielding materials. Metal foil can be attached to the surface or between two layers of plastic. Its advantages are that the method is simple and easy to implement, the adhesive strength is high, it is not easy to partially detach, and the conductivity is good. The shielding effect can reach more than 70dB, but for complex shapes, the construction operation is very difficult.