Electronic shield manufacturer, shell shield EMC shielding technology + 15 years shield manufacturer

Electronic shield manufacturers, a project must consider the shielding problem in the planning stage, so that the cost of shielding measures will be low. If the problem is exposed and then the leakage is checked, it will often cost a considerable price. Shielding measures often increase the cost and weight of the instrument. If it can be solved by other EMC methods, try to reduce the shielding cover as much as possible. Pay attention to the following two points for PCB: 　　 (1) Make the wires and components as close as possible to a large metal plate (this metal plate does not refer to the shield) 　　 (2) Keep the electrical components and lines as close to the ground as possible (to reduce the electromagnetic signal between the layers (Interference, the ground layer can absorb part of the interference) In this way, even if a shielding cover is needed, the demand for SEshiedling effectiveness (SEshiedling effectiveness) can be reduced.　　The concept of shielding　　The shielding cover is equivalent to a filter, placed on the propagation path of electromagnetic waves, forming a high impedance to a part of the frequency band. The greater the impedance ratio, the better the shielding effectiveness. For general metals, a thickness of 0.5mm can produce a good shielding effect on electromagnetic waves of 1MHz, and a very good shielding effect on 100MHz. The problem is that thin-layer metal shielding is not effective for those below 1MHz or pores. , This article focuses on this aspect. 1. Larger spacing and rectangular shielding will be better (1) Larger spacing between circuits and shields can reduce mutual interference; 　　 (2) Rectangular (or irregular) shielding shape can avoid frequency resonance as much as possible; square The outer shell is often easy to cause resonance; 　　 But in general, the circuit board is generally located in the shielding body, and its components, wiring, etc. will change the expected resonance frequency point, so don't worry too much.　　2, skin effect　　Skin depth: Engineering defines the thickness from the surface to the current density down to 0.368 (ie 1/e) of the surface current density as the skin depth or penetration depth. In the formula: 　　μ－permeability of wire material; 　　γu003d1/ρ－conductivity of material; 　　k-temperature coefficient of material conductivity (or resistivity); High, the shallower the depth, the more skin); from the perspective of conduction, the skin effect is expected to be deep, which means that the utilization rate of the wire is high; but for the shield, it is hoped that the skin depth is shallow, so It can shield more electromagnetic frequency bands with thinner metal; the skin depth of 50Hz is 5～15mm, which is difficult to shield...　　The metal used for shielding should have good electrical and magnetic properties, and the thickness depends on the frequency of interference. The skin depth is determined. Generally 1mm low carbon steel sheet or 1μm galvanized layer can meet general applications. (This is also the reason why we often see galvanization on the cabinet wall in practice) 　　3. Porosity　　 If the entire shell of the shield is seamless and non-porous, it is not difficult to achieve 100dB attenuation for 30MHz electromagnetic waves. The problem is that they are not seamless and holeless: 　　 a hole in a perfect shielding shell is equivalent to forming a half-wave resonant slot antenna. The relationship between the shielding effectiveness SE and the large size of the hole d and the electromagnetic wave wavelength λ is as follows: 　　 then For the previously mentioned 30MHz, wavelength 10m, assuming a USB port (diagonal aperture size 10mm), the converted SE is 54dB, the larger the d, the smaller the SE.　　To achieve a 40dB SE, it is usually necessary to use conductor washers and alligator fingers to seal. Pay attention to the distance between the internal components and the shield, and the distance between the data bus and the openings and gaps.　　 It should also be noted that when there is a current in the shield and there are holes in the forward direction of the current to block the way, forcing the current to go around, it will cause the holes to resemble antennas and emit a magnetic field, which is generated by the changing voltage of the holes.　　4. Shielding of low-frequency magnetic field 　　 uses high permeability alloy materials (such as amorphous alloys, permalloy), and shields are made according to certain specifications, which can greatly reduce the influence of magnetic fields.　　5. The gasket 　　 uses good conductors for filling joints, which can withstand certain extrusion deformation, is corrosion-resistant and durable. 6. The shielding of the vent holes. The vent holes are made into two forms: 　　 (1) metal grid (similar to honeycomb aluminum plate) 　　 (2) (up to) waveguide 7. Painted or electroplated plastic is beautiful and light, so it is often In this case, conductive material is generally sprayed on the surface of the plastic cup, because the thickness of the conductive layer cannot be too thick (micron level), the actual effect is not very good. For class II electrical appliances (class II), electrostatic discharge (ESD) ) Possibility.　　 Class II electrical appliances: This type of electrical appliances adopt double insulation or reinforced insulation, and there is no grounding requirement.　　 8. Non-metallic shield 　　 such as carbon fiber or conductive polymer (conductive plastic), but in any case its SE is not as good as metal. Hardware, 15 years of focusing on electronic shield manufacturers, 20,000+ sets of customized stamping die production experience, monthly processing of 100+ sets of molds, hundreds of precision processing production equipment, daily production capacity of 3 million punches, and silk-like stamping accuracy up to 0.01 mm, the raw materials are imported and the original national standard factory, and 16 quality inspections are strictly controlled.