PCB Technical - How to make PCB wiring completed quickly

PCB wiring is very important in the PCB design of the entire circuit board factory. How to achieve fast and efficient wiring and make your PCB wiring look tall is worth studying. This article sorts out several aspects that need to be paid attention to in PCB wiring. Come and check the missing parts!

Common ground processing of digital circuit and analog circuit

Nowadays, many PCBs are no longer single-function circuits, but are composed of a mixture of digital circuits 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 and 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.

The signal line is laid on the power layer or ground layer

When wiring a multi-layer PCB printed board, 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 a certain amount of work in production, and the cost will increase accordingly. To solve this contradiction, you can consider wiring on the power layer or 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.

Treatment of connecting legs in large area conductors

In large-area grounding or power supply, the legs of common components are connected to it. 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 assembly, such as: welding requires high-power heater; it is easy to cause virtual solder joints.

Therefore, both electrical performance and process requirements are made into cross-patterned pads, called thermal isolation, commonly known as thermal pads, so that the possibility of virtual solder joints due to excessive cross-section heat during soldering can be greatly reduced. The processing of the power connection or the ground leg of the multilayer board is the same.

The role of the network system in cabling

In many CAD systems, wiring is determined by the network system. The grid is too dense and the path has increased, but the step is too small, and the amount of data in the field is too large. This will inevitably have higher requirements for the storage space of the device, and also the computing speed of the computer-based electronic products. Great influence. 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. So there must be a reasonable grid system to support the wiring. The distance between the legs of standard components is 0.1 inch/2.54mm, so the basis of the grid system is generally set at 0.1 inch or an integral multiple of less than 0.1 inch, such as: 0.05 inch, 0.025 inch, 0.02 inch, etc.

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 power supply and ground wire should be taken seriously, and the noise interference generated by the power supply and ground wire 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 the noise between the power supply and the ground wire. Lotus capacitor.

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 finest 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 for use. The ground of the analog circuit cannot be used in this way. A large area of copper layer is used as the ground wire, which is not used on the printed board. Connected to the ground as a ground wire in all places. Or it can be made into a multilayer board, and the power supply and ground wires occupy one layer each.

Design rule check

After the PCB wiring design is completed, it is necessary to carefully check whether the wiring design conforms to the rules set by the designer, and at the same time, it is necessary to confirm whether the rules made meet the requirements of the printed board production process. The general inspection has the following aspects: line and line, Whether the distance between the line and the component pad, the line and the through hole, the component pad and the through hole, and the distance between the through hole and the through hole is reasonable, and whether it meets the production requirements. Whether the width of the power line and the ground line are appropriate. Whether the power supply and the ground wire are tightly coupled.