1、 PCB design requirements
1. Right
This is the most basic and important requirement of PCB design. It can accurately realize the connection relationship of electrical schematic diagram and avoid interference
Avoid "short circuit" and "open circuit" these two simple and fatal mistakes. This basic requirement is in manual design
It is not easy to design PCB with simple CAD software. Generally, products have to go through more than two rounds of trial
The CAD software with strong function has the inspection function, which can ensure the correctness of electrical connection.
2. Reliable
This is a higher level requirement in PCB design. Connecting the right circuit board is not necessarily reliable, for example
Unreasonable plate selection, incorrect plate thickness and installation, improper layout and wiring of components may lead to
PCB can not work reliably, early failure or even not work correctly. Another example is multi-layer board and single, double-sided
Compared with the board, it is much easier to design, but it is not as reliable as the single or double-sided board. From the perspective of reliability
In other words, the simpler the structure is, the smaller the use area is, the fewer the layers of the board are, and the higher the reliability is.
3. Reasonable
This is a deeper and more difficult requirement in PCB design. A printed board assembly from the printed board
The manufacturing, inspection, assembly and debugging of PCB, the assembly and debugging of the whole machine, and the use and maintenance of PCB, are all related to PCB
For example, the shape of the board is not well selected, the processing is difficult, the lead hole is too small, and the assembly is difficult,
It is difficult to keep the pilot height, improper selection of external connection and maintenance. Every difficulty can lead to success
The cost of the project is increased and the working hours are extended. And every reason for the difficulty comes from the fault of the designer. There is no absolute agreement
Rational design, only the process of continuous rationalization. It requires a sense of responsibility and rigorous style of the designer, as well as
In practice, we summarize and improve the experience.
4. Economy
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This is a goal that is not difficult to achieve and difficult to achieve, but must be achieved. It's not difficult to say
Low price, board size as small as possible, connection with direct welding wire, surface coating with the cheapest, choose the lowest price
The price of PCB manufacturing will drop. But don't forget, these cheap options may be
As a result, the manufacturability and reliability become worse, the manufacturing cost and maintenance cost rise, and the overall economy is not necessarily divided
So it's not easy“ "Must" is the principle of market competition. Competition is ruthless, a principle
Advanced, high-tech products may die prematurely due to economic reasons.
experience:
1. There should be a reasonable trend: input / output, AC / DC, strong / weak signal, high frequency / low frequency,
High pressure / low pressure, etc. their trend should be linear (or separated) and should not blend with each other. Its purpose is to
Prevent mutual interference. The best direction is straight line, but it is not easy to realize. The most unfavorable direction is ring,
Fortunately, isolation can bring improvement. For DC, small signal, low voltage PCB design requirements can be adjusted
Lower it. So "reasonable" is relative.
2. Choose a good grounding point: I don't know how many engineers and technicians have discussed it
It shows its importance. In general, common ground is required, for example, multiple ground wires of forward amplifier should be combined
And then connected with the main line and so on. In reality, due to various restrictions, it is difficult to complete it, but we should try our best to follow it.
This problem is quite flexible in practice. Everyone has their own set of solutions. If you can target at
It's easy to understand the circuit board of the body.
3. Reasonable layout of power filter / decoupling capacitor: generally, only a few power filter / decoupling capacitors are drawn in the schematic diagram
Coupling capacitors, but it is not indicated where they should be connected. In fact, these capacitors are switching devices (gate circuits)
These capacitors should be placed as close to these components as possible,
It doesn't work if you're too far away. Interestingly, when the power filter / decoupling capacitor arrangement is reasonable, grounding is not necessary
The problem of point is not so obvious.
4. The line has the fastidious: has the condition to make the wide line never to make the thin line; The high voltage and high frequency lines shall be smooth and free from noise
Sharp chamfers and corners shall not be right angles. The ground wire should be as wide as possible, and it is better to use large area copper coating
There has been a considerable improvement in the problem of grounding points.
5. Although some problems occur in post production, they are brought about by PCB design
If there are too many holes in the wire, the hidden danger will be buried if the copper deposition process is not careful. Therefore, the number of through holes should be reduced as much as possible in the design.
The density of parallel lines in the same direction is too large, so it is easy to connect them into one piece during welding. Therefore, the linear density should depend on the welding process
To determine the level. The distance of solder joint is too small, which is not conducive to manual welding, and can only be solved by reducing the work efficiency
Welding quality. Otherwise, hidden dangers will be left. Therefore, the determination of the minimum distance of solder joint should consider the welding personnel
The quality and efficiency of the students. The size of pad or through hole is too small, or the size of pad and drilling hole are not matched properly. the former
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It is not good for manual drilling, and the latter is not good for NC drilling. It is easy to drill the pad into a "C" shape, and it is more difficult to drill out the pad
The dish. The conductor is too thin, and there is no copper deposit in the large area without wiring, which is easy to cause uneven corrosion. Namely
When the non wiring area is corroded, the thin wire may be corroded too much, or it seems to be broken, or completely broken. So,
The function of copper coating is not only to increase the area of ground wire and anti-interference.
