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PCB layout experience sharing
374 0 Jun 15.2022, 16:02:22

In design, layout is an important part. The quality of the layout result will directly affect the effect of the wiring, so it can be considered that a reasonable layout is the first step to a successful PCB design.

There are two layout methods, one is interactive layout and the other is automatic layout.

Generally, it is adjusted by interactive layout on the basis of automatic layout. During layout, the gate circuit can also be redistributed according to the wiring situation, and the two gate circuits can be exchanged to make it the best layout for easy wiring.

After the layout is completed, the design files and related information can also be returned and marked on the schematic diagram, so that the relevant information in the PCB board is consistent with the schematic diagram, so that the future filing and design changes can be synchronized. The information is updated to enable board-level verification of the electrical performance and functionality of the circuit.

Common rules for wiring

The direction control rules of the trace:

That is, the wiring directions of adjacent layers form an orthogonal structure. Avoid running different signal lines in the same direction on adjacent layers to reduce unnecessary interlayer interference; when it is difficult to avoid this situation due to board structure limitations (such as some backplanes), especially when the signal rate is high, It should be considered to isolate each wiring layer with a ground plane, and isolate each signal line with a ground signal line.
Open-loop inspection rules for traces:

Generally, wiring with one end floating is not allowed, mainly to avoid "antenna effect" and reduce unnecessary interference radiation and reception, otherwise it may bring unpredictable results.

Trace length control rules:

That is, the short-line rule, the wiring length should be kept as short as possible in the design to reduce the interference problem caused by the long wiring, especially some important signal lines. In the case of driving multiple devices, the network topology to be used should be decided on a case-by-case basis.

Impedance matching check rules:

The wiring width of the same network should be kept the same. The change of the line width will cause the uneven characteristic impedance of the line. When the transmission speed is high, reflection will occur. This situation should be avoided as much as possible in the design.

Device decoupling rules:

Add necessary decoupling capacitors on the printing plate to filter out the interference signal on the power supply and stabilize the power supply signal. In a multi-layer board, the position of the decoupling capacitor is generally not too high, but for a double-layer board, the layout of the decoupling capacitor and the wiring method of the power supply will directly affect the stability of the entire system, and sometimes even affect the design. success or failure. In high-speed circuit design, the correct use of decoupling capacitors is related to the stability of the entire board.

Chamfering Rules:

Sharp and right angles should be avoided in PCB design, resulting in unnecessary radiation and poor process performance

Ground return rules:

The minimum loop rule is that the area of the loop formed by the signal line and its loop should be as small as possible. The smaller the loop area, the less external radiation and the less external interference it receives.

Integrity rules for power and ground planes:

For areas with dense via holes, care should be taken to avoid the holes being connected to each other in the hollow area of the power supply and the ground layer, forming a division of the plane layer, thereby destroying the integrity of the plane layer, and thus causing the loop area of the signal line in the ground layer to increase. .
layout check
Does the printed board size match the processing drawing size? Can it meet the PCB manufacturing process requirements? Are there any positioning marks?

Are there any conflicts between components in two-dimensional and three-dimensional spaces?
Is the layout of components dense and orderly? Is it all finished?
Can the components that need to be replaced frequently be easily replaced? Is the plug-in board easy to plug into the device?

Whether there is an appropriate distance between the thermal element and the heating element

Is there a radiator installed where heat dissipation is required? Is the air clear?

The layout should consider the overall aesthetics. Whether a product is successful or not, one should pay attention to the internal quality, and the other is to take into account the overall aesthetics. Only when both are perfect can the product be considered a success. On a PCB board, the layout of components should be balanced, dense and orderly, and should not be top-heavy or heavy.
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