PCB wiring is very important in the entire pcb design, how to do fast and efficient wiring, and make your PCB wiring look tall, is worth studying. Sorted out the 7 aspects that need to be paid attention to in PCB wiring, come and check the gaps!
1. Common ground processing of digital circuit and analog circuit
There are now many PCBS that are no longer single-function circuits (digital or analog circuits), but are composed of a mixture of digital and analog circuits. Therefore, when wiring, it is necessary to consider the interference between them, especially the noise interference on the ground wire. The frequency of the digital circuit is high, the sensitivity of the analog circuit is strong, for the signal line, the high-frequency signal line is as far away from the sensitive analog circuit device as possible, for the ground line, the PCB has only one node to the outside world, so it must be processed inside the PCB, the problem of the number and mode common ground, and the digital and analog inside the board are actually separated from each other. Only at the interface between the PCB and the outside world (such as plugs, etc.). There is a bit of a short connection between digital and analog, but note that there is only one connection point. There are also common on the PCB, which is determined by the system design.
2. the signal line is distributed on the electrical (ground) layer
In the multi-layer printed board wiring, because there is not much left in the signal line layer, more layers will cause waste and will increase a certain amount of work for production, and the cost will increase accordingly, in order to solve this contradiction, you can consider wiring on the electrical (ground) layer. The power layer should be considered first, followed by the formation. Because it is better to preserve the integrity of the formation. Baioneng belongs to Qinji Group, is the leading electronic industry service platform in China, providing online components, sensor procurement, PCB customization, BOM order, material selection and other electronic industry supply chain solutions, one-stop to meet the comprehensive needs of small and medium-sized customers in the electronics industry.
3. power supply, ground processing
Even if the wiring in the entire PCB board is completed well, the interference caused by the inconsiderate power supply and ground wire will reduce the performance of the product, and sometimes even affect the success rate of the product. Therefore, the wiring of the power supply and ground wire should be taken seriously, and the noise interference caused by the power supply and ground wire should be reduced to a minimum to ensure the quality of the product. For every engineer engaged in the design of electronic products, it is understood that the cause of the noise between the ground line and the power line is only expressed by reducing the noise suppression: it is well known that the coupling capacitor is added between the power supply and the ground line. Try to widen the width of the power supply and ground wire, it is best that the ground wire is wider than the power line, their relationship is: ground wire > power line > signal line, usually the signal line width is 0.2 ~ 0.3mm, the most fine width can reach 0.05 ~ 0.07mm, the power line is 1.2 ~ 2.5mm. The PCB of the digital circuit can be composed of a wide ground wire to form a loop, that is, to form a ground network to use (the ground of the analog circuit can not be used in this way) with a large area of copper layer as a ground wire, and the place that is not used on the printed board is connected with the ground as a ground wire. Or make a multi-layer board, the power supply, the ground line occupy a layer.
4. the role of the network system in wiring
In many CAD systems, the wiring is determined by the network system. The grid is too dense, although the path has increased, the step is too small, and the amount of data in the graph field is too large, which inevitably has higher requirements for the storage space of the device, and also has a great impact on the computing speed of the object computer electronic products. Some paths are invalid, such as those occupied by the pad of the component leg or those occupied by the mounting holes and fixing holes. Too sparse grid and too few channels have great influence on the distribution flux. Therefore, it is necessary to have a reasonable grid system to support the wiring. The distance between the legs of the standard components is 0.1 inches (2.54mm), so the basis of the grid system is generally set at 0.1 inches (2.54mm) or an integral multiple of less than 0.1 inches, such as: 0.05 inches, 0.025 inches, 0.02 inches, etc.
5. Processing of connecting legs in large area conductors
In a large area of grounding (electrical), the legs of commonly used components are connected to them, and the treatment of the connecting legs needs comprehensive consideration. As far as electrical performance is concerned, the welding pad of the components' legs is fully connected with the copper surface, but there are some bad hidden dangers in the welding assembly of components, such as: ① welding requires high-power heaters. ② Easy to cause virtual solder joints. Therefore, taking into account the electrical performance and process needs, make a cross welding pad, called heat shield, commonly known as Thermal pad, in this way, the possibility of virtual solder joints caused by excessive heat dissipation in the welding section is greatly reduced. The treatment of the electrical (ground) leg of the multilayer board is the same.
6. Design Rule Check (DRC)
After the wiring design is completed, it is necessary to carefully check whether the wiring design meets the rules formulated by the designer, and it is also necessary to confirm whether the rules formulated meet the needs of the printed board production process, the general inspection has the following aspects: Whether the distance between wire and wire, wire and component pad, wire and through hole, component pad and through hole, through hole and through hole is reasonable, whether it meets the production requirements. Whether the width of the power cord and ground wire is appropriate, whether the tight coupling between the power supply and the ground wire (low wave impedance) is there a place in the PCB where the ground wire can be widened. Whether the best measures are taken for the key signal lines, such as the shortest length, the protection line, the input line and the output line are clearly separated. Whether the analog circuit and the digital circuit have their own ground lines. Whether the graphics (such as ICONS, marking) added to the PCB will cause signal short circuit. Modify some undesirable lines. Is there a process line on the PCB? Whether the solder resistance meets the requirements of the production process, whether the solder resistance size is appropriate, whether the character mark is pressed on the device pad, so as not to affect the quality of Denso. Whether the outer frame edge of the power supply formation in the multi-layer board is reduced, such as the copper foil of the power supply formation is exposed outside the board, it is easy to cause short circuit.
7. Design of via
Through hole (via) is one of the important components of multi-layer PCB, and the cost of drilling usually accounts for 30% to 40% of the PCB board cost. Simply put, every hole on the PCB can be called a pass hole. From the function point of view, the hole can be divided into two categories: one is used as an electrical connection between the layers; The second is used as the fixing or positioning of the device. If from the process, through the hole is generally divided into three categories, namely blind via, buried via and through via.
English
Chinese