What are the six principles of PCB wiring?

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What are the six principles of PCB wiring?
1. Power supply, ground processing
Both the wiring in the entire PCB board is completed well, but the interference caused by poorly considered power and ground lines will degrade the performance of the product, and sometimes even affect the success of the product. Therefore, the wiring of electric and ground lines should be taken seriously to minimize the noise interference generated by electric and ground lines to ensure the quality of products. For each of the engineers engaged in the design of electronic products understand the reasons for the noise generated between the ground and power lines. Now only to reduce the type of noise suppression to express: the well-known is in the power supply, between the ground line plus decoupling capacitors. Try to widen the power supply, ground line width, preferably wider than the power line, their relationship is: ground line > power line > signal line, usually the signal line width: 0.2 ~ 0.3mm, the most by fine width up to 0.05 ~ 0.07mm, power line for 1.2 ~ 2.5 mm on the digital circuit PCB available wide ground wire to form a circuit, that is, constitute a ground network to use (analog circuit of (analog circuit ground can not be used in this way) with a large area of copper layer for the ground, in the printed circuit board is not used in the place are connected to the ground as the ground. Or make a multilayer board, power supply, ground each occupy a layer.
2. digital circuits and analog circuits for common ground processing
Nowadays, many PCBs are no longer a single-function circuit, but a mixture of digital and analog circuits. Therefore, in the wiring will need to consider the problem of mutual interference between them, especially noise interference on the ground. Digital circuits are high frequency, analog circuits are sensitive, for signal lines, high-frequency signal lines as far away as possible from sensitive analog circuit devices, for ground, the whole PCB to the outside world only a junction, so the PCB must be processed inside the digital and analog common ground, and the board is actually separated from the digital and analog ground they are not connected to each other, only in the PCB and the outside world connection The interface between the PCB and the outside world. Digital ground and analog ground have a short connection, please note that there is only one connection point. There is also no common ground on the PCB, which is determined by the system design.
3. signal lines laid on the electrical (ground) layer
In the multilayer printed circuit board wiring, due to the signal line layer is not finished cloth line left has not much, and then add more layers will cause waste will also add a certain amount of work to the production, the cost has increased accordingly, in order to solve this contradiction, you can consider wiring on the electrical (ground) layer. The first consideration should be to use the power layer, followed by the ground layer. Because it is best to retain the integrity of the ground layer.
4. Handling of connecting legs in large-area conductors
In the large-area ground (electrical), commonly used components of the leg and its connection, the processing of the connection leg requires comprehensive consideration, in terms of electrical performance, the pad of the component leg and copper surface full connection is good, but the welding assembly of the components there are some undesirable pitfalls such as: ① welding requires high-power heaters. ② easy to cause false solder points. So take into account the electrical performance and process needs, made of cross flower pads, called thermal isolation commonly known as hot pads, so that the possibility of false solder points due to excessive heat dissipation in the cross-section during welding is greatly reduced. Multi-layer board of the grounding (ground) layer leg of the same treatment.
5. The role of network systems in wiring
In many CAD systems, wiring is based on the decision of the network system. The grid is too dense, the pathway is increased, but the step is too small, and the amount of data in the figure field is too large, which inevitably has higher requirements for the storage space of the equipment, and also has a great impact on the computing speed of computer-type electronic products. And some of the pathway is invalid, such as the pad occupied by the component leg or by the installation hole, fixed their holes occupied by the. The grid is too sparse, too little access to the cloth through the rate of great impact. So there should be a reasonable grid system to support the wiring process. The distance between the two legs of the standard components is 0.1 inch (2.54 mm), so the basis of the grid system is generally set at 0.1 inch (2.54 mm) or an integer multiple of less than 0.1 inch, such as: 0.05 inch, 0.025 inch, 0.02 inch, etc.
6. Design Rule Check (DRC)
After the wiring design is completed, it is necessary to carefully check whether the wiring design conforms to the rules set by the designer, and also to confirm whether the rules set meet the requirements of the production process of the printed circuit board, generally checking the following aspects: line and line, line and component pad, line and through-hole, component pad and through-hole, whether the distance between through-hole and through-hole is reasonable and whether it meets the production requirements. Is the width of the power and ground lines appropriate, and is there tight coupling (low wave impedance) between the power and ground lines? Are there still places in the PCB where the ground line can be widened. Are the best measures taken for critical signal lines, such as the shortest length, adding protection lines, and input and output lines are clearly separated. Whether the analog and digital circuit sections have their own separate ground lines. Whether the graphics (e.g. icons, note labels) added later to the PCB can cause signal shorts. Modification of some undesirable lineshapes. Is there a process line added to the PCB? Does the solder resist meet the requirements of the production process, is the size of the solder resist appropriate, and are the character marks pressed on the device pads so as not to affect the quality of the electrical installation. Is the outer frame edge of the power ground layer in the multilayer board reduced, such as the power ground layer of copper foil exposed outside the board is prone to short circuit. Overview The purpose of this document is to explain the use of PADS printed circuit board design software PowerPCB for printed circuit board design process and some considerations for a working group of designers to provide design specifications to facilitate communication between designers and mutual check.