PCB News - What are the advantages of the serpentine line

Snake line is a type of routing method often used in Layout. Its main purpose is to adjust the delay to meet the system timing design requirements. The designer must first have this understanding: the serpentine line will destroy the signal quality, change the transmission delay, and try to avoid using it when wiring. However, in actual design, in order to ensure that the signal has sufficient hold time, or to reduce the time offset between the same group of signals, it is often necessary to deliberately wind the wire.

So, what effect does the serpentine line have on signal transmission? What should I pay attention to when wiring? The two most critical parameters are the parallel coupling length (Lp) and the coupling distance (S), as shown in Figure 1-8-21. Obviously, when the signal is transmitted on the serpentine trace, the parallel line segments will be coupled in a differential mode. The smaller the S and the larger the Lp, the greater the degree of coupling. It may cause the transmission delay to be reduced, and the signal quality is greatly reduced due to crosstalk. The mechanism can refer to the analysis of common mode and differential mode crosstalk in Chapter 3.


The following are some suggestions for Layout engineers when dealing with 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 approaches 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 high-speed signal lines and those with strict timing requirements, try not to use serpentine lines, especially in small areas.
5. You can often use serpentine traces at any angle, such as the C structure in Figure 1-8-20, 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 you can consider spiral routing for winding. Simulation shows that its effect is better than normal serpentine routing.

The above is an introduction about the advantages of the serpentine line. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.