PCB design is complicated, and various unexpected factors frequently affect the overall scheme. How can we tame the scattered parts with different personalities? How to draw a neat, efficient and reliable PCB? Let’s take stock today.
PCB design seems to be complex, not only to consider the direction of various signals, but also to consider the transmission of energy, the distress caused by interference and heating is always accompanied. But in fact, the summary is very clear. We can start from two aspects
To put it bluntly, “how to put it” and “how to connect it.”.
Does that sound very easy? Let’s sort out “how to place” first
1. According to the layout principle of “big before small, difficult before easy”, that is, important unit circuits and core components should be given priority. This is the same as eating a buffet: if the appetite of the buffet is limited, choose what you like first, and if the PCB space is limited, choose what’s important first.
2. The layout should refer to the principle block diagram and arrange the main components according to the main signal flow direction of the single board. The layout shall meet the following requirements as far as possible: the total connection line shall be as short as possible, and the key signal line shall be the shortest; the layout of decoupling capacitor shall be close to the power pin of IC as far as possible, and the circuit formed between it and power supply and ground shall be the shortest; the wrong way of signal running shall be reduced, and accidents on the road shall be prevented.
Big before small, difficult before easy
3. The arrangement of components should be convenient for debugging and maintenance, that is, large components cannot be placed around small components, and there should be enough space around the components to be debugged, which often makes the situation very embarrassing.
4. For the same circuit structure, the “symmetrical” standard layout should be adopted as far as possible, and the layout should be optimized according to the standard of uniform distribution, balanced center of gravity and beautiful layout.
Uniform distribution and balanced center of gravity
5. The same type of plug-in components should be placed in one direction in X or Y direction. For the same type of polarized discrete components, it is also necessary to strive to keep consistent in X or Y direction, so as to facilitate production and inspection.
Uniform polarity layout
6. The heating elements should be evenly distributed to facilitate the heat dissipation of the single board and the whole machine, and the temperature sensitive elements other than the temperature detection elements should be far away from the components with large heat.
Uniform distribution of heating components
7. High voltage and large current signals should be completely separated from low current and low voltage weak signals; analog signals should be separated from digital signals; high frequency signals should be separated from low frequency signals; high frequency components should be fully separated. In the layout of components, it should be considered that the components using the same power supply should be put together as far as possible to facilitate the separation of power supply in the future.
The above is about “how to put” that is, the main considerations of layout. On the other hand, how to connect is more complicated
Key signal line priority: Simulation of small signal, high-speed signal, clock signal and synchronization signal and other key signal priority wiring;
The principle of density priority: start with the most complex devices on the board. Starting from the most densely connected area on the board.
PCB layout example