PCB circuit board is the basic electronic component of all electronic circuit design. As the main support, it carries all the devices that make up the circuit. The function of PCB is not only to combine scattered components, but also to ensure the regularity of circuit design and avoid the confusion and errors caused by manual wiring.
In this paper, the five key points of PCB design in power supply design are introduced in detail.
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 trend shall be linear (or separated) and shall not blend with each other. The purpose is to prevent mutual interference. The best trend is straight, but it is generally difficult to achieve. The most unfavorable trend is circular. Fortunately, isolation can be set to bring improvement. For DC, small signal and low voltage PCB design, the requirements can be lower. So “reasonable” is relative.
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, it is required to be grounded at the same point, for example, multiple ground wires of the forward amplifier shall be connected with the main line ground after merging, etc. In reality, due to various restrictions, it is difficult to do it completely, but we should try our best to follow it. This problem is quite flexible in practice. Everyone has his own set of solutions. It is easy to understand if it can be explained for specific circuit boards.
3. Reasonably arrange power filter / decoupling capacitor
Generally, 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 to these components as possible. If they are too far away, they will have no effect. Interestingly, when the layout of power filter / decoupling capacitor is reasonable, the problem of grounding point is not so obvious.
4. If the line diameter is required, the size of buried hole and through hole shall be appropriate
If it is possible to make a wide line, never make it thin; High voltage and high frequency lines shall be round and smooth without sharp chamfer, and right angles shall not be used for turning. The ground wire should be as wide as possible, and it is best to use large-area copper coating, which greatly improves the problem of docking location. The size of the pad or via hole is too small, or the pad size does not match the drilling size properly. The former is unfavorable to manual drilling and the latter is unfavorable to NC drilling. It is easy to drill the pad into “C” shape, or drill off the pad. The conductor is too thin, and there is no copper coating in a large area of non wiring area, which is easy to cause uneven corrosion. That is, after the non wiring area is corroded, the thin wire is likely to be corroded too much, or seems to be broken, or completely broken. Therefore, the function of copper coating is not only to increase the area of ground wire and anti-interference.
5. Number of vias, solder joints and linear density
Some problems are not easy to be found in the early stage of circuit production. They often emerge in the later stage. For example, there are too many wire holes, and the slight carelessness of copper sinking process will bury hidden dangers. Therefore, through-line holes should be minimized in the design. The density of parallel lines in the same direction is too large, so it is easy to connect together during welding. Therefore, the linear density should be determined according to the level of welding process. The distance between welding points is too small, which is not conducive to manual welding. The welding quality can only be solved by reducing work efficiency. Otherwise, it will leave hidden dangers. Therefore, the determination of the minimum distance of the welding joint should comprehensively consider the quality and work efficiency of the welding personnel.
If we can fully understand and master the above precautions for PCB design, we can greatly improve the design efficiency and product quality. Correcting existing errors in production will save a lot of time and cost, rework time and material investment.
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