The so-called "no rules, no square circle", PCB design is the same. When engineers carry out PCB layout, some "rules" must be followed by everyone.
1. Understand the manufacturer's manufacturing specifications – trace width, trace spacing, via hole requirements and layer requirements.
2. Limit values of vias, trace width and safe spacing should be avoided.
3. Rule priority: if there are rules, signal traces with rule requirements shall be arranged first, and then non key signal lines shall be arranged.
4. Priority of key signal line: power supply, simulation signal, high-speed signal, clock signal, differential signal and synchronous signal are arranged in priority.
5. Density first: start wiring from the devices with the most complex connection relationship on the board, and start wiring from the area with the most dense wiring on the board.
6. In general, the distance from the line to the edge of the board should be more than or equal to 2mm. If the conditions cannot be met, it should be at least no less than 20MIL.
7. In addition to the short interconnects and fanout wires on the surface, the signal wires are arranged in the inner layer as far as possible.
8. Under the metal shell device, there is no via hole and surface wiring.
9. As far as possible for clock signal, high-frequency signal, sensitive signal and other key signals to provide special wiring layer, and ensure its minimum loop area. The signal quality is ensured by shielding and increasing the safe distance.
10. The direction control rule of routing, that is, the routing direction of adjacent layers is orthogonal structure. Different signal lines should be avoided to go in the same direction in the adjacent layers to reduce unnecessary inter layer interference; when this situation is difficult to avoid due to board structure constraints (such as some back boards), especially when the signal rate is high, it should be considered to isolate the wiring layers with the ground plane and isolate the signal wires with the land signal wires.
11. All signal wires must be chamfered with an angle of 45 degrees, except for special cases.
12. The ring area formed by the signal wire and its loop should be as small as possible. The smaller the ring area is, the less the external radiation is and the smaller the interference received from the outside.
13. In PCB layout, it is necessary to avoid sharp angle and right angle to produce unnecessary radiation, and at the same time, the process performance is not good.
14.In order to reduce the crosstalk between lines, it is necessary to ensure that the line spacing is large enough. When the line center spacing is not less than 3 times the line width, 70% of the electric field can not interfere with each other, which is called 3W rule. To achieve 98% of the electric field without mutual interference, a 10 W spacing can be used.
15. When the analog power supply and the analog power supply can't work reliably, it is possible to reduce the interference of analog power supply to analog power supply. Therefore, the filter capacitor of the chip should be placed close to the chip, the digital circuit and the analog circuit should be separated, and the analog part can not take digital signal.
16. The pin of power supply and ground should be placed near the via. The shorter the lead between the via and the pin is, the better. At the same time, the lead of power supply and ground should be as thick as possible to reduce the impedance.The so-called "no rules, no square circle", PCB design is the same. When engineers carry out PCB layout, some "rules" must be followed by everyone.
