Why are there serpentine traces on the PCB board?

Why are there serpentine traces on the PCB board?

Any trace on the PCB will cause a time delay to the signal when it passes the high-frequency signal. The main role of the serpentine trace is to compensate the smaller delay portion of the "same set of related" signal lines. These portions Usually there is no or less additional logic processing than other signals; the most typical is the clock line, usually it does not need any other logic processing, so its delay will be less than other related signals.

The isoline length of the high-speed digital PCB board is to keep the delay difference of each signal within a range, to ensure the validity of the data read by the system in the same cycle (when the delay difference exceeds one clock cycle, the next cycle will be misread Data), generally requires that the delay difference does not exceed 1/4 clock cycle, and the line delay difference per unit length is also fixed. The delay is related to the line width, line length, copper thickness, and layer structure, but too long a line will increase the distributed capacitance. And distributed inductance to make the signal quality, so the clock IC pin is generally connected to RC termination, but the serpentine trace does not play the role of inductance, on the contrary, the inductance will cause higher harmonic phase shift in the rising element in the signal As a result, the signal quality is deteriorated. Therefore, it is required that the distance between the serpentine lines is at least twice the line width. The smaller the rise time of the signal, the more susceptible to the influence of distributed capacitance and distributed inductance.

Because different applications have different functions, if the serpentine trace appears in the computer board, it mainly plays the role of a filtering inductor to improve the anti-interference ability of the circuit, and the serpentine trace in the computer motherboard.

Is mainly used in some clock signals, such as CIClk, AGPClk, and its role has two points:

1, impedance matching.

2, filter inductor.

For some important signals, such as HUBLink in INTEL HUB architecture. There are 13 roots running at 233MHz. The requirements must be exactly the same length to eliminate the hidden danger caused by time delay. Winding is the only solution. In general, the line spacing of the serpentine trace is> = 2 times the line width. The meandering line on the PCI board is to meet the line length requirements of the PCI 33MHz Clock. If it is a general-purpose PCB board with a distributed parameter LC filter, it can also be used as the inductor coil of a radio antenna, and short and narrow serpentine wires can be used as fuses and so on.