In the PCB design, wiring is an important step to complete the product design. It can be said that the previous preparation work is done for it. In the whole PCB, the wiring design process is the highest, the trick is the finest, and the workload is the largest.
PCB wiring has single-sided wiring, double-sided wiring, and multilayer wiring. There are also two ways of wiring: automatic routing and interactive wiring. Before automatic routing, you can use interactive pre-wired lines that require more stringent requirements. The edges of the input and output should avoid adjacent parallel to avoid reflection interference. If necessary, ground wire should be isolated. The wiring of two adjacent layers should be perpendicular to each other, and parasitic coupling is easy to occur in parallel.
The routing rate of automatic routing depends on a good layout, and the wiring rules can be preset, including the number of bending of the traces, the number of vias, and the number of steps. Generally, the exploratory warp line is firstly connected, and the short lines are quickly connected, and then the labyrinth wiring is performed. First, the wiring to be cloth is optimized for the global routing path, and the laid line can be disconnected as needed. And try to re-route to improve the overall effect.
For the current high-density PCB design, it has been felt that the through-hole is not suitable. It wastes a lot of valuable wiring channels. To solve this contradiction, blind hole and buried hole technology have emerged, which not only completes the function of the via hole. It also saves a lot of wiring channels to make the wiring process more convenient, smoother and more perfect. The PCB board design process is a complicated and simple process. To master it well, it also needs extensive electronic engineering design. When people go to their own experience, they can get the truth.
1, power, ground processing:
Even if the wiring in the entire PCB board is completed well, the interference caused by the inconsistency of the power supply and the ground line may degrade the performance of the product, and sometimes even affect the success rate of the product. Therefore, the wiring of the power supply and the ground wire should be taken seriously, and the noise interference generated by the power supply and the ground wire should be minimized to ensure the quality of the product.
For every engineering engineer engaged in the design of electronic products, the reason for the noise between the ground and the power line is known. Now only the reduced noise suppression is stated:
It is well known to add a decoupling capacitor between the power supply and the ground.
Try to widen the power supply and ground line width. It is better to ground the ground line than the power line. Their relationship is: ground line > power line > signal line. Usually the signal line width is 0.2~0.3mm, and the finest width is up to 0.05 to 0.07 mm, the power cord is 1.2 to 2.5 mm.
For the PCB of a digital circuit, a wide ground wire can be used to form a loop, that is, a ground net is used for use (the ground of the analog circuit cannot be used in this way).
Use a large area of copper for grounding, and connect the unused areas to the ground on the printed board for grounding. Or make a multi-layer board, power supply, ground line each occupy a layer.
2. Co-processing of digital circuits and analog circuits:
Many PCBs are no longer single-function circuits (digital or analog circuits), but rather 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.
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 is as far as possible away from the sensitive analog circuit device. For the ground line, the whole human PCB has only one node to the outside, so The number of processing and the common ground must be handled inside the PCB, and the digital ground and the analog ground inside the board are actually separated from each other, but only at the interface where the PCB is connected to the outside (such as a plug). The digital ground is slightly shorted to the analog ground. 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.