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Rules and requirements for PCB wiring


Rules and requirements for PCB wiring

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1. The routing direction of adjacent planes forms an orthogonal structure.

Avoid walking different signal lines in the same direction in adjacent layers, so as to reduce unnecessary inter layer interference; When it is difficult to avoid this situation due to the limitation of board structure (such as some backplanes), especially when the signal rate is high, it should be considered to use the ground plane to isolate each wiring layer and the ground signal line to isolate each signal line.

2. The wiring of small discrete devices must be symmetrical

SMT pad leads with dense spacing shall be connected from the outside of the pad, and direct connection in the middle of the pad is not allowed.

3. Loop minimum rule

The ring area formed by the signal line and its loop shall be as small as possible. The smaller the ring area is, the less the external radiation is and the less the external interference is received.

4. Stub does not appear

Stub is not allowed in routing.

5. Same network wiring width

The wiring width of the same network shall be consistent. The change of linewidth will cause uneven line characteristic impedance and reflection when the transmission speed is high. Under some conditions, such as connector outgoing line and BGA package outgoing line with similar structure, the change of line width may not be avoided due to the small spacing, so the effective length of the inconsistent part in the middle should be minimized.

6. Prevent signal lines from forming self loops between different layers

Such problems are easy to occur in the design of multi-layer plates, and the self ring will cause radiation interference.

7. Avoid acute angles and right angles

In PCB design, acute angles and right angles should be avoided to produce unnecessary radiation. At the same time, the production process performance of PCB is not good.