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PCB factory’s recommendations for designing and handling serpentine lines and wiring should follow principles
2021-10-13
View:15
Author:Kavie

1. Some suggestions from PCB factory when designing and handling serpentine lines
1. Try to increase the distance (S) of parallel line segments, at least greater than 3H, H refers to the distance from the signal trace to the reference plane. In layman's terms, it is to go around a big bend. As long as S is large enough, the mutual coupling effect can be almost completely avoided.

2. Reduce the coupling length Lp. When the double Lp delay is close to or exceeds the signal rise time, the crosstalk generated will reach saturation.

3. The signal transmission delay caused by the serpentine line of the Strip-Line or Embedded Micro-strip is less than that of the Micro-strip. In theory, the stripline will not affect the transmission rate due to differential mode crosstalk.

4. For signal lines with high-speed and strict timing requirements, try not to use serpentine lines, especially in small areas.

5. You can often use snake-shaped traces at any angle, which can effectively reduce mutual coupling.

6. In high-speed PCB design, the serpentine line has no so-called filtering or anti-interference ability, and can only reduce the signal quality, so it is only used for timing matching and has no other purpose.

7. Sometimes the spiral routing can be considered for winding. Simulation shows that its effect is better than normal serpentine routing.
What principles should be followed in PCB circuit board layout design
The PCB circuit board is the support of the circuit components and devices in the electronic product. Even if the circuit schematic is designed correctly and the printed circuit board is not properly designed, it will adversely affect the reliability of electronic products. When designing a printed circuit board, you should pay attention to adopting the correct method, abide by the general principles of PCB design, and meet the requirements of anti-interference design.

2. Principles to be followed in PCB circuit board layout design:

First, consider the PCB size. When the PCB size is too large, the printed lines will be long, the impedance will increase, the anti-noise ability will decrease, and the cost will also increase; if the PCB size is too small, the heat dissipation will not be good, and adjacent lines will be easily disturbed. After determining the size of the printed circuit board, determine the location of the special components. Finally, according to the functional units of the circuit, all the components of the circuit are laid out.

The following principles should be observed when determining the location of special components:

1. Shorten the wiring between high-frequency components as much as possible, try to reduce their distribution parameters and mutual electromagnetic interference. Components that are susceptible to interference should not be too close to each other, and input and output components should be kept as far away as possible.

2. There may be a high potential difference between some components or wires. The distance between them should be increased to avoid accidental short circuits caused by discharge. The components with high voltage should be arranged as far as possible in places that are not easily reachable by hands during debugging.

3. Components weighing more than 15g should be fixed with brackets and then welded. Those components that are large, heavy, and generate a lot of heat should not be installed on the printed circuit board, but should be installed on the chassis bottom plate of the whole machine, and the heat dissipation problem should be considered. Thermal components should be far away from heating components.

4. For the layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, micro switches, etc., the structural requirements of the whole machine should be considered. If it is adjusted inside the machine, it should be placed on the printed circuit board where it is convenient for adjustment; if it is adjusted outside the machine, its position should match the position of the adjustment knob on the chassis panel.

5. The position occupied by the positioning hole of the printed board and the fixed bracket should be reserved.

When PCB layout of circuit components, it must meet the requirements of anti-interference design:

1. Arrange the position of each functional circuit unit according to the circuit flow, so that the layout is convenient for signal circulation, and the signal is kept in the same direction as possible.

2. Take the core component of each functional circuit as the center and lay out around it. The components should be evenly, neatly and compactly arranged on the PCB. Minimize and shorten the leads and connections between components.

3. For circuits operating at high frequencies, the distribution parameters between components must be considered. Generally, the circuit should be arranged in parallel as much as possible. In this way, it is not only beautiful, but also easy to install and weld, and easy to mass produce.

4. The components located on the edge of the PCB circuit board are generally not less than 2mm away from the edge of the circuit board. The best shape of the circuit board is rectangular. The length and width pairs are 3:2 or 4:3. When the size of the circuit board is larger than 200×150mm, the mechanical strength of the circuit board should be considered.