1、 Design requirements of printed boards
1. Right
This is the most basic and important requirement of PCB design. It can realize the connection relationship of electrical schematic diagram accurately, and avoid it
Avoid the two simple and fatal errors of "short circuit" and "open circuit". This basic requirement is in manual design
And PCB designed with simple CAD software is not easy to do, and general products are subject to more than two rounds of test
The CAD software with strong function has the inspection function, which can ensure the correctness of electrical connection.
2. Reliable
This is the higher level requirement in PCB design. Connecting the correct circuit board may not be reliable, for example
Unreasonable plate selection, plate thickness, incorrect installation and fixing, improper layout and wiring of components may result in
PCB can not work reliably, and it fails to work correctly in early stage. And then, it is multi-layer board and single and double-sided plate
Compared with the board, it is much easier to design, but it is not as reliable as single or double-sided board. From the perspective of reliability.
In other words, the simpler the structure, the smaller the use surface, the less the number of layers of the board, the higher the reliability.
3. Reasonable
This is a deeper and less easy requirement in PCB design. A printed board assembly, from printing
The board manufacturing, inspection, assembly, debugging to the whole machine assembly and commissioning, until the use and maintenance, is no exception with the printed board
The rationality of the plate is closely related to the selection of the shape of the plate, the difficulty of processing, and the difficulty of assembling the lead hole too small,
It is difficult to leave the pilot height, improper maintenance of the connection outside the board, etc. Every difficulty can lead to success
This increase, the work hours are extended. And every reason for the difficulty is due to the designer's mistakes. There is no absolute combination
The design of the theory is only a process of continuous rationalization. It requires the responsibility and rigorous style of the designer, and
In practice, the experience of summary and improvement is broken.
4. Economy
This is a goal that is not difficult to achieve and not easy to achieve, but must be achieved. Say "no difficulty", plate selection.
Low price, minimum board size, direct welding conductor for connection, cheapest surface coating, lowest price selection.
The price of PCB manufacturing will drop. But don't forget that these cheap options may
The overall economy is not necessarily divided into two parts: the process and reliability are poor, and the manufacturing and maintenance costs are increased
So it's not easy“ Must be the principle of market competition. Competition is ruthless, one principle
Advanced, high-tech products may die due to economic reasons.
experience:
1. Reasonable direction: such as input / output, AC / DC, strong / weak signal, high frequency / low frequency,
High / low pressure, etc., their direction should be linear (or separated) and should not blend with each other. Its purpose is to
Prevent interference with each other. The best direction is to be straight, but it is not easy to realize generally, and the most unfavorable direction is ring,
Fortunately, isolation can be set to improve. For DC, small signal, low voltage PCB design requirements can
Lower it. So "reasonable" is relative.
2. Choose a good grounding point: I don't know how many engineering technicians have done to it
It is important. In general, it is required to point the ground, such as: multiple ground wires of forward amplifier shall be combined
Then connect with the trunk line, etc. In reality, it is difficult to complete it because of various restrictions, but we should try to follow it.
This problem is quite flexible in practice. Everyone has a solution of their own. If it can be targeted
The circuit board of the body is easy to understand.
3. Arrange the power filter / decoupling capacitor reasonably: generally, only a few power filter / decoupling are drawn in the schematic diagram.
Coupling capacitors, but not indicating where they should be connected. Actually, these capacitors are switches (gate circuits)
Or other components that need filtering / decoupling, the capacitor shall be arranged as close as possible to these components,
It doesn't work too far away. Interestingly, when the power filter / decoupling capacitor arrangement is reasonable, the ground
The point is not so obvious.
4. Lines have to pay attention to: the line with conditions to do width will never be fine; High voltage and high frequency lines shall be circular sliding, and no
Sharp chamfering, bending shall not be right angle. The ground wire should be as wide as possible, and it is better to use large area copper coating. This pair
The grounding point problem has been greatly improved.
5. Some problems occurred in the post production, but they were brought about in PCB design. They are:
Too many passing holes, copper sinking process will be buried a little bit of hidden danger. Therefore, the over-line hole should be minimized in the design.
The density of the parallel lines is too high, so it is easy to join into a piece when welding. Therefore, the line density should be based on the welding process
The level of is determined. The distance between welding points is too small, which is not conducive to manual welding, and can only be solved by reducing the working efficiency.
Welding quality. Otherwise, there will be hidden dangers. Therefore, the minimum distance of welding joints should be determined by considering welding personnel comprehensively
Quality and work efficiency. The size of the pad or the over-line hole is too small, or the size of the pad is not matched with the drilling hole size. the former
It is not good for manual drilling, while the latter is bad for NC drilling. Easy to drill the pad into "C" shape, and drill off the welding if heavy
The dish. The wires are too thin, and there is no copper coating in the large area of the ungraded area, which is easy to cause uneven corrosion. Namely
When the corrosion of the non wiring area is completed, it is likely that the fine conductor will be excessively corroded, or it may not be broken or completely broken. So,
The effect of copper coating is not only to increase the area of ground wire and anti-interference.
