PCB design specification essentials

PCB design is complicated, and various unexpected factors frequently affect the realization of the overall plan. How can we tame scattered components with different personalities? How can I draw a neat, efficient and reliable PCB diagram? Let us take stock today.

PCB design seems complicated. It is necessary to consider the direction of various signals as well as the transmission of energy. The distress caused by interference and heat is always on the go. But in fact, the summary is very clear, and you can start from two aspects:

To put it bluntly, it is: "how to put it" and "how to connect".

Does it sound very easy? Let us first sort out the "how to put":

1. Follow the layout principle of "big first, then small, difficult first, easy first", that is, important unit circuits and core components should be laid out first. This is the same as eating a buffet: buffets have a limited appetite and pick the ones you like first, and when PCB space is limited, pick the important ones first.

2. The principle block diagram should be referred to in the layout, and the main components should be arranged according to the main signal flow of the board. The layout should meet the following requirements as far as possible: the total wiring should be as short as possible, and the key signal line should be the shortest; the layout of the decoupling capacitor should be as close as possible to the power supply pin of the IC, and the loop formed between it and the power supply and ground should be the shortest; reduce the signal Run unjustly to prevent accidents on the road.

Big first and then small, first difficult and then 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 must be enough space around components that need to be debugged. It will often become very embarrassing if it is too crowded.

4. For the circuit parts of the same structure, use the "symmetrical" standard layout as much as possible; optimize the layout according to the standards of uniform distribution, balanced center of gravity, and beautiful layout.

Evenly distributed, balanced center of gravity

5. The same type of plug-in components should be placed in one direction in the X or Y direction. The same type of polarized discrete components should also strive to be consistent in the X or Y direction to facilitate production and inspection.

Uniform Polarity Layout

6. The heating elements should generally be evenly distributed to facilitate the heat dissipation of the veneer and the whole machine. Temperature sensitive devices other than the temperature detection element should be kept away from the components with a large amount of heat.

Heating components are evenly distributed

7. High voltage and large current signals are completely separated from small current and low voltage weak signals; analog signals are separated from digital signals; high-frequency signals are separated from low-frequency signals; the spacing of high-frequency components should be sufficient. In the component layout, appropriate consideration should be given to placing the devices using the same power supply as close together as possible to facilitate future power supply separation.

The above are the main considerations about "how to put" or layout. The "how to connect" is relatively more complicated, generally speaking:

Key signal line priority: Prioritize routing of key signals such as analog small signals, high-speed signals, clock signals, and synchronization signals;

Density priority principle: Start wiring from the most complicated devices on the board. Start routing from the most densely wired area on the board.