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 should not blend with each other. The purpose is to prevent mutual interference. The best direction is to follow a straight line, but it is not easy to achieve. The most unfavorable trend is circular. Fortunately, isolation can be set to bring improvement. For DC, small signal, low voltage PCB design requirements can be lower. So “reasonable” is relative.

Analysis of five basic principles of PCB design

2. Choose a good grounding point: grounding point is often the most important

I don’t know how many engineers and technicians have discussed the small grounding point, which shows its importance. In general, common ground is required, such as: multiple ground wires of forward amplifier should be combined and then connected with main line ground, etc. In reality, due to various restrictions, it is difficult to completely do it, but we should try our best to follow it. This problem is quite flexible in practice. Everyone has his own set of solutions, which is easy to understand if it can be explained for specific circuit boards.

3. Reasonable arrangement of power filter / decoupling capacitor

In general, only a few power filter / decoupling capacitors are drawn in the schematic diagram, but where they should be connected is not indicated. In fact, these capacitors are set for switching devices (gate circuits) or other components that need filtering / decoupling. These capacitors should be arranged as close as possible to these components. If they are too far away, they will not work. Interestingly, when the power filter / decoupling capacitor arrangement is reasonable, the grounding problem is not so obvious.

4. If the line diameter is required, the size of buried hole is appropriate

If it is possible to make wide wires, never make them thin; high voltage and high frequency lines should be smooth without sharp chamfering and right angles for turning. The ground wire should be as wide as possible. It is better to use a large area of copper coating. This docking point problem has been greatly improved. The size of pad or wire hole is too small, or the size of pad and hole is not matched properly. The former is disadvantageous to manual drilling and the latter to numerical control drilling. It is easy to drill the pad into “C” shape, and drill out the pad if it is heavy. The wire is too thin, and there is no copper coating in the large area of non wiring area, which is easy to cause uneven corrosion. That is to say, when the non wiring area is corroded, the thin wire is likely to be over corroded, or it seems to be broken or completely broken. Therefore, the role of copper coating is not only to increase the area of ground wire and anti-interference.

5. Through hole number, solder joint and linear density

Some problems are not easy to find in the early stage of circuit production, they often emerge in the later stage, for example, too many wire holes, a little careless copper deposition process will bury hidden dangers. Therefore, the wire holes should be minimized in the design. The density of parallel lines in the same direction is too high, so it is easy to connect into a piece when welding. Therefore, the linear density should be determined according to the level of welding process. The distance between solder joints is too small, which is not conducive to manual welding, so 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 solder joint should consider the quality and efficiency of welding personnel.

If we can fully understand and master the above PCB design considerations, we can greatly improve the design efficiency and product quality. Correct the errors in the production, will save a lot of time and cost, save rework time and material investment.

Source: 21IC

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