Electrical Rules Should Be Paid Attention To In PCB Design

1. Treatment of power supply and ground wire

Even if the wiring in the entire PCB board is completed very well, the interference caused by the improper consideration of the power supply and the ground wire will reduce the performance of the product, and sometimes even affect the success rate of the product. Therefore, the wiring of the electric and ground wires must be taken seriously, and the noise interference generated by the electric and ground wires should be minimized to ensure the quality of the product. Every engineer engaged in the design of electronic products understands the cause of the noise between the ground wire and the power wire, and now only the reduced noise suppression is expressed. It is well-known to add coupling capacitor between the power supply and the ground wire. Widen the width of the power and ground wires as much as possible, preferably the ground wire is wider than the power wire, their relationship is ground wire>power wire>signal wire. Usually the signal wire width is 0.2～0.3mm, the smallest width can reach 0.05～0.07mm, the power cord is 1.2～2.5mm. For the PCB of the digital circuit, a wide ground wire can be used to form a loop, that is, to form a ground net to use (the ground of the analog circuit cannot be used in this way). Use a large area of ​​copper layer as the ground for wire use, connect the unused places on the printed board to the ground as a ground wire. Or it can be made into a multi-layer board, and the power supply and ground wire occupy one layer each.

2. Common ground processing of digital circuit and analog circuit

Nowadays, many PCBs are no longer single-function circuits (digital or analog circuits), but are composed of a mixture of digital and analog circuits. Therefore, it is necessary to consider the mutual interference between them when wiring, especially the noise interference on the ground wire. The frequency of the digital circuit is high, and the sensitivity of the analog circuit is strong. For the signal line, the high-frequency signal line should be as far away as possible from the sensitive analog circuit device. For the ground line, the whole PCB has only one node to the outside world, so the problem of digital and analog common ground must be dealt with inside the PCB, and the digital ground and analog ground inside the board are actually separated, they are not connected to each other, but at the interface (such as plugs, etc.) connecting the PCB to the outside world. There is a short connection between the digital ground and the analog ground. Please note that there is only one connection point. There are also non-common grounds on the PCB, which is determined by the system design.

3. The signal line is laid on the electric (ground) layer

In the multi-layer printed board wiring, because there are not many wires left in the signal line layer that have not been laid out, adding more layers will cause waste and increase the production workload, and the cost will increase accordingly. To solve this contradiction, you can consider wiring on the electrical (ground) layer. The power layer should be considered first, and the ground layer second. Because it is best to preserve the integrity of the formation.

4. The place where the legs are connected in the large area conductor

In large-area grounding (electricity), the legs of commonly used components are connected to it, and the treatment of the connecting legs needs to be considered comprehensively. In terms of electrical performance, it is better to connect the pads of the component legs to the copper surface. There are some undesirable hidden dangers in the welding and assembly of components, such as ① Welding requires high-power heaters. ②It is easy to cause virtual solder joints. Therefore, both electrical performance and process requirements are made into cross-patterned pads, which are called heat shields, commonly known as thermal pads. In this way, virtual solder joints may be generated due to excessive cross-section heat during soldering. In this way, it is possible to greatly reduce the possibility of virtual solder joints due to excessive cross-section heat during welding. The processing of the electrical connection (ground) leg of the multilayer board is the same.

5. The role of the network system in cabling
In many CAD systems, the wiring is determined according to the network system. Although the grid is too dense and the path has increased, the step is too small and the amount of data in the map field is too large, which will inevitably have higher requirements for the storage space of the equipment, and also have a great impact on the operation speed of the object computer electronic products. Some paths are invalid, such as those occupied by the pads of the component legs or by mounting holes and fixed holes. Too sparse grids and too few channels have a great impact on the distribution rate. Therefore, there must be a well-spaced and reasonable grid system to support the wiring. The distance between the legs of standard components is 0.1 inches (2.54mm), so the basis of the grid system is generally set to 0.1 inches (2.54 mm) or less than an integral multiple of 0.1 inches, such as 0.05 inches, 0.025 inches, 0.02 Inches etc.

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