Requirements for PCB Design

2019/1/15 18:42:29

1. Correct

This is the most basic and important requirement of PCB design, to accurately realize the connection relationship of electrical schematic diagram, and to avoid the two simple and fatal errors of "short circuit" and "open circuit". This basic requirement is not easy to achieve in manual design and PCB design with simple CAD software. Generally, products have to go through more than two rounds of trial production and modification, while CAD software with strong functions has inspection function to ensure the correctness of electrical connection.


2. Reliable


This is a higher level of PCB design requirements. Correctly connected circuit boards may not be reliable, such as unreasonable plate selection, plate thickness and improper installation and fixation, improper layout and wiring of components may lead to PCB can not work reliably, early failure or even correct work. If again much layer board and sheet, double face plate are compared, when the design wants much easier, but as far as reliable character is inferior however sheet, double face plate. From the perspective of reliability, the more simple the structure, the smaller the surface, the fewer the number of sub-layers, the higher the reliability.




3. Reasonable


This is a deeper level of PCB design, more difficult to achieve the requirements. A PCB components, from PCB fabrication, inspection, assembly, debugging to whole machine assembly and debugging, until the use of maintenance, all without exception is reasonable or not is closely related with the printed circuit board, such as the board shape well processing difficulties, pin hole is too small assembly difficulty, was left pilot highly difficult, outside the plate connected to incorrect maintenance difficulties, and so on. Every difficulty can result in higher costs and longer hours. And every cause of difficulty is due to the designer's mistakes. There is no absolutely reasonable design, only continuous rationalization of the process. It requires the designer's sense of responsibility and rigorous style of work, as well as the practice of summary, improve the experience.


4. Economic


This is a goal that is not difficult to achieve, is not easy to achieve, but must be achieved. Say "not difficult", plank chooses low price, plank dimension is as far as possible small, join with direct welding lead, surface coating USES the cheapest, choose the processing plant with lowest price to wait a moment, the price of printed board manufacturing can drop. But do not forget, these cheap choice may cause craft sex, reliability to become poor, make manufacturing cost, maintenance cost rises, overall economy is not certain cent is handled, because this says "not easy". "Must" is the principle of market competition. Competition is relentless, a principle of advanced, high-tech new products may die because of economic reasons.


To have a reasonable trend: such as input/output, ac/dc, strong/weak signal, high/low frequency, high/low frequency, high/low pressure/low pressure, etc., their trend should be linear (or separation), not blend with each other. The purpose is to prevent mutual interference. The best trend is to press straight line, but implement not easily commonly, the most unfavorable trend is annular, fortunately, can set segregation to bring improvement. For dc, small signal, low voltage PCB design requirements can be lower. So "reasonable" is relative.




Choose a good site: a small site on the number of engineers and technicians do not know how much it has been discussed, it shows its importance. Common ground is generally required, such as: a number of ground lines of the forward amplifier should be combined and then connected to the main ground and so on. In reality, it is difficult to do this because of various restrictions, but you should try to follow them. The problem is quite flexible in practice. Everyone has their own solution. It is easy to understand if it can be explained according to the specific circuit board.


Reasonable arrangement of power filter/decoupling capacitors: generally, only a few power filter/decoupling capacitors are drawn in the schematic diagram, but it is not pointed out where they should be connected. These capacitors are actually set up for switching devices (gate circuits) or other components that require filtering/decoupling, and the placement of these capacitors should be as close to these components as possible, so that they will not work if they are too far away. Interestingly, when the power filter/decoupling capacitance is properly aligned, the connection point problem is less obvious.


Line pay attention to: conditional to do wide line never do fine; High voltage and high frequency line should be round slippery, do not have sharp chamfer, turn a corner also must not use right Angle. Ground wire should be as wide as possible, had better use large area to deposit copper, this butt point problem has considerable improvement.




Although some problems occur in post-production, they are brought about by PCB design. They are: there are too many wire holes, and even a slight mistake in copper precipitation process may cause hidden trouble. Therefore, the design should be as far as possible to reduce the thread hole. Parallel lines are too dense to be soldered together. Therefore, the linear density should be determined according to the level of the welding process. The distance between solder joints is too small, which is not conducive to manual welding.


Otherwise it will leave a hidden danger. Therefore, the determination of the minimum distance of welding joints should take into account the quality and efficiency of welding personnel. The size of welding disc or thread hole is too small, or the size of welding disc and drilling hole are not matched properly. The former is unfavorable to manual drilling, while the latter is unfavorable to numerical control drilling. Easy to drill into the "c" shape of the welding disc, heavy drill off the welding disc. The wire is too thin, and the large area of unwired area is not set copper coating, easy to cause uneven corrosion. That is, when the wiring area is not finished corrosion, the thin wire is likely to be too much corrosion, or seems to be broken, or completely broken. Therefore, the role of copper coating is not only to increase the ground area and anti-interference.

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