Serpentine traces are a relatively unique routing pattern encountered in PCB design (as shown in the figure). Many people don't understand their significance. Below is a brief introduction to their significance.

Serpentine traces have different functions depending on their application:

1. Computer motherboards:

If serpentine traces appear on a computer board, they primarily serve as a filter inductor and impedance matching, improving the circuit's interference resistance. Serpentine traces on computer motherboards are primarily used for clock signals, such as PCI-Clk, AGPCIk, IDE, and DIMM signal lines.

2. Radio antenna inductors:

If used on ordinary PCBs, in addition to serving as filter inductors, they can also serve as radio antenna inductors. For example, they are used as inductors in 2.4G walkie-talkies.

3. Strictly maintaining equal lengths for signal routing eliminates potential risks caused by time skew.

Some signal traces must be strictly equal in length. The purpose of equal trace lengths on high-speed digital PCBs is to keep signal delays within a certain range, ensuring the validity of data read by the system within the same cycle. (Delay differences exceeding one clock cycle will result in erroneous readings of the next cycle's data.) For example, the HUBLink in the Intel Hub architecture has 13 traces, operating at a frequency of 233MHz. These traces must be strictly equal in length to eliminate potential skew risks, and routing is the only solution. Generally, the delay difference is required to be no more than 1/4 of a clock cycle, and the delay difference per unit length of trace is also fixed. The delay depends on trace width, length, copper thickness, and board layer structure. However, excessive trace length increases distributed capacitance and inductance, degrading signal quality. Therefore, clock IC pins are typically terminated with RC terminations. However, serpentine traces do not act as inductors. On the contrary, inductance can cause phase shifts in higher harmonics on the rising edge of the signal, degrading signal quality. Therefore, the spacing between serpentine traces must be at least twice the trace width. The slower the signal rise time, the more susceptible it is to distributed capacitance and inductance.

4. Distributed parameter LC filter

The serpentine trace plays the role of a distributed parameter LC filter in some special circuits.