# Trace Length in PCB

- Trace on a PCB
- True transmission line
- It has both significant inductance and capacitance per unit length.
- Lumped inductance and capacitance are proportion to the length.

- Contributing Parameters for Delay
- Trace length. Usually, the rest of the parameters are preset.
- Trace width, thickness, shape
- Distance of trace from its reference plane
- Dielectric constant of the board material and/or coating

- Trace Length Effect on Rise/Fall Time
- Impedance looking into the trace
- Characteristic impedance Z0 (for an infinitely long trace)
- Load of receiver (for an infinitesimally short trace), usually much larger than the Z0

- For a finite length trace, the load that the driver sees will be somewhere between those two.
- The amount of driver loading will affect the rise/fall time.

- Impedance looking into the trace