How to set shielding for PCB layer in Xi ‘an PCB design

In product development, from the perspective of cost, schedule, quality and performance, it is usually best to carefully consider and implement the correct PCB design as early as possible in the project development cycle. Add-ons and other “quick” patches implemented later in the project are usually not ideal solutions in function, their quality and reliability are poor, and the cost is higher than those implemented earlier in the process. Lack of foresight in the early design stage of a project usually leads to delayed delivery and may lead to customer dissatisfaction with the product. This question applies to any design, whether analog, digital, electrical or mechanical.
Compared with shielding a single IC and part of PCB, the cost of shielding the whole PCB in Xi ‘an PCB design is about 10 times, and the cost of shielding the whole product is 100 times. If the whole room or building needs to be shielded, then the cost is really astronomical. The “nested” shielding method is a possible solution. Nesting method is a method of applying masking at every lowest level of product design. For example, shielding is first applied to: Partial area of a single IC/PCB Entire PCB Subassembly All products Nested shielding method can minimize the total cost of manufacturing high-quality products on time and within performance specifications. Use a low shielding level. For various reasons, it makes sense to shield at the lowest possible level (single IC, small area of PCB and PCB level): Shielding can’t help attenuate the interference between individual ICs on PCB, but PCB level shielding can help attenuate the interference between individual ICs. From the practical/cost-effective point of view, the typical shell shielding technology can’t provide significant attenuation performance at higher (GHz) frequencies, while PCB shielding can indeed provide this function. By effectively using shielding on PCB layer, the cost and weight of shielding layer can be reduced to the greatest extent. From the perspective of susceptibility, modern integrated circuits have shrinking silicon characteristics, faster rise time and lower noise margin. As long as the PCB layer is shielded, it can work efficiently in noisy environment. The integration of wireless communication module with noise in the product will lead to harmful inference to other sensitive analog and digital components in the immediate vicinity. This noise can also be reduced by using PCB level shielding. Because it is necessary to add holes and slots to penetrate input/output cables, displays, ventilation, contact removal media, etc., the shielding of the housing is usually compromised to the point of complete failure. If PCB-level shielding is used, this situation will not be so serious. Effective shell shielding usually requires that all cables entering and leaving the product should be accurately filtered at the position where the cables pass through the shell shielding. If PCB level shielding is used, the need for additional filtering can be reduced. Whether designing mobile phones, tablets, portable computers or other forms of electronic products, besides PCB level shielding, good PCB layout is essential to minimize EMI. Ground plane and power plane can be used as EMI shielding for high-threat noise signals. This technology is a good first step towards minimizing the noise in these high-threat signals. There will be a problem with this method, and RF energy will still radiate out of the component leads and packages, so a more complete solution is needed. Here, PCB level shielding (also called “shielding can”) can be used to attenuate the noise emitted by these noisy devices. To provide maximum benefits, PCB horizontal shield must form a complete six-sided metal shell. This is achieved by welding the shielding layer to a solid ground plane under all components that need to be shielded. To maximize efficiency, there must be no substantial gaps or openings in the ground plane. The actual performance of all shielding layers and grounding layers will always be affected by openings (such as adjustment holes, indicators, wires, structural joints and gaps between grounding layer connections of shielding tanks). Therefore, it is necessary to avoid using these items as much as possible. The goal of EMI shielding is to create a faraday cage around the enclosed RF noise components using six sides of the metal box. The top five sides are made of shielding cover or metal can, while the bottom side is made of ground layer in PCB. In an ideal housing, no emissions will enter or leave the box. Harmful emissions from these shields do occur, such as being released from holes punched into tin cans, which allow heat transfer during solder reflow. These leaks may also be caused by defects in EMI gaskets or solder accessories. Noise may also escape from the space between the ground vias used to electrically connect the shield cover to the ground layer. Traditionally, PCB shielding is connected to PCB using through-hole solder tails, which are manually soldered after the main assembly process. This is a time-consuming and expensive process. If maintenance is required during installation and maintenance, the circuits and components under the shielding layer must be removed. In a dense PCB area containing highly sensitive components, there is a risk of expensive damage. Typical properties of PCB liquid level shielding tank are as follows: The floor area is small; Low-key configuration; Two-piece design (fence and cover); Through hole or surface mount; Multi-cavity pattern (using the same shielding layer to isolate multiple components); Almost unlimited design flexibility; Vent hole; Removable cover for quick maintenance of components; I/O hole Connector notch; RF absorber enhanced shielding; ESD protection with insulation pad; Use the firm locking function between the frame and the cover to reliably prevent shock and vibration. Typical shielding materials Generally, various shielding materials can be used, including brass, nickel silver and stainless steel. The most common types are: The floor area is small; Low-key configuration; Two-piece design (fence and cover); Through hole or surface mount; Multi-cavity pattern (using the same shielding layer to isolate multiple components); Almost unlimited design flexibility; Vent hole; Removable cover for quick maintenance of components; I/O hole Connector notch; RF absorber enhanced shielding; ESD protection with insulation pad; Use the firm locking function between the frame and the cover to reliably prevent shock and vibration. Generally, tinned steel is the best choice for shielding below 100 MHz, while tinned copper is the best choice for shielding above 200 MHz. Tin plating can achieve the best welding efficiency. Because aluminum itself has no heat dissipation characteristics, it is not easy to weld to the ground plane, so it is usually not used for PCB level shielding. According to the regulatory burden of the final product, all materials used for shielding may need to meet RoHs standards. In addition, if the product is used in a hot and humid environment, it may cause electrical corrosion and oxidation.