PCB Design Scheme

When designing a PCB scheme, you should pay attention to the following 5 points:
1. There should be a reasonable direction: such as input/output, AC/DC, strong/weak signal, high frequency/low frequency, high voltage/low voltage, etc., their direction should be linear (or separated), and must not be mutually blend. Its purpose is to prevent mutual interference. The best direction is in a straight line, but it is generally not easy to achieve, and the most unfavorable direction is a circular one. Fortunately, isolation can be set to bring improvement. For DC, small signal, low voltage PCB design requirements can be lower. So "reasonable" is relative.

2. Choose a good grounding point: I don’t know how many engineers and technicians have discussed the small grounding point, which shows its importance. Under normal circumstances, it is required to have a common ground, such as: multiple ground wires of the forward amplifier should be merged and then connected to the trunk ground, etc. . . . In reality, it is difficult to do it completely due to various restrictions, but it should be followed as best as possible. This question is quite flexible in practice. Everyone has their own set of solutions. It is easy to understand if it can be explained for a specific circuit board.

3. Reasonable arrangement of power supply filter/decoupling capacitors: Generally, only a few power supply filter/decoupling capacitors are drawn in the schematic diagram, but it is not indicated where they should be connected. In fact, these capacitors are set up for switching devices (gate circuits) or other components that need filtering/decoupling. These capacitors should be arranged as close to these components as possible, and they will be useless if they are too far away. Interestingly, when the power supply filtering/decoupling capacitor placement is reasonable, the ground point problem becomes less obvious.

4. The lines are exquisite: the lines that can be made wide should not be made thin; the high-voltage and high-frequency lines should be smooth, and there should be no sharp chamfers, and no right angles should be used for corners. The ground wire should be as wide as possible, and it is best to use a large area of ​​copper, which greatly improves the connection point problem.

5. Although some problems occur in the post-production, they are brought about by the PCB design. They are:

A. There are too many wire holes, and the copper sinking process will bury hidden dangers if it is not careful. Therefore, the design should minimize the via holes.

B. The density of parallel lines in the same direction is too large, and it is easy to connect into one piece during welding. Therefore, the linear density should be determined according to the level of the welding process.

C. The distance between the solder joints is too small, which is not conducive to manual welding, and the welding quality can only be solved by reducing the work efficiency. Otherwise, there will be hidden dangers. Therefore, the determination of the minimum distance of the welding point should comprehensively consider the quality and ergonomics of the welding personnel.

D. The size of the pad or via is too small, or the pad size does not match the size of the drill hole. The former is not good for manual drilling, and the latter is not good for CNC drilling. It's easy to drill the pads into a "c" shape, and drill off the pads for heavier ones.

E. The wire is too thin, and there is no copper coating in the large unwiring area, which is easy to cause uneven corrosion. That is, when the unwiring area is corroded, the thin wires are likely to corrode too much, or seem to be broken, or completely broken. Therefore, the role of setting copper plating is not only to increase the ground wire area and anti-interference.