General principles of PCB cabling

Transferred from Zhang Fei actual combat electronic public number

General principles of PCB cabling

Shortest path and reduced interference

The overall process of PCB cabling is as follows:

1 understand the manufacturing specifications of manufacturers-line width, line spacing, over-hole requirements and layer requirements;

2 Determine the number of layers and define the functions of each layer;

3 Design Cabling rules-line width, line spacing, over-hole size, etc.

4 Define the line width of different net;

5 key signal lines-power, clock, audio, differential, sensitive analog signals, etc.;

6 Other signal line walking line;

7 Paving or paving the power supply (if there are different ground or power, but also to split the power and ground);

8 DRC inspection;

9 Control schematic on the connection highlight check;

Adjustment and inspection for all screen printing.

PCB Layer Selection Considerations

1 Plan the number of layers according to the circuit characteristics:

① high and low speed, analog and digital, and the impedance required to match;

Encapsulation of ② devices and core devices that need to be dispersed;

③ anti-jamming and reliability requirements;

④ in order to cut expenditure, to the cost of a good control.

2 Define the function of each layer according to the current trend and meaning of each layer

3 turn off unused layers to facilitate layout and cabling

PCB Cabling Rules Setting precautions

1 line width-Different net can be defined separately

2 selection of vias and determination of aperture

3 text font and font size for silk screen printing

4 Safe spacing:

① between the line and the walk;

② between the line and aperture;

③ between aperture and aperture;

④ line, between aperture and card edge

5 The level of the line and determining the direction of the route, etc.

PCB set the selection of the hole, there are a few things to note

1 Choose a reasonable size from the perspective of cost and signal quality.

2 PCB board signal traces as far as possible on the same layer, try not to use unnecessary vias, layout planning good traces

3 High-speed digital signal line to avoid cross-layer alignment, reduce the over-hole to signal reflection and interference.

4 The pin of the power supply and the ground should be placed near the hole, the shorter the lead between the hole and the pin, the better the power supply and the ground lead as thick as possible to reduce the impedance.

5 Place some grounded vias near the vias of the signal-changing layer to provide the nearest loop for the signal.

6 using Vias for heat conduction

Precautions when PCB traces are in line

1 direction of Route determination

2 The conductors at the input and output sides should avoid adjacent parallel

3 The direction of the adjacent layer is orthogonal structure.

4 Avoid unnecessary inter-layer crosstalk by eliminating the need to move different signal lines in the same direction on adjacent layers

5 When the PCB wiring is difficult to avoid the structure of parallel wiring, especially at high signal rate, should consider the ground plane to isolate the wiring layer, using ground to isolate the signal lines.

6 The alignment between the device and the device is as short and straight as possible.

7 power supply and critical signal line use wide line, power cord to calculate the required width according to the current size

8 Ensure that the analog, digital lines are separated from each other and do not route the digital signal line and the analog signal line in parallel, to avoid laying the digital signal line below the ADC package.

9 The same property of a group of buses, should be as far as possible to walk the line, so as long as possible. The grounding point of the same level circuit should be as close as possible, and the power filter capacitance of this stage circuit is also bell at this level of place.

General principles of PCB cabling