# high speed signals in PCB

#### senmeis

Hi,

is it correct that high speed signals propagate in PCB as waves in dielectric materials such as FR4 according to microstrip principle?

Senmeis

#### stenzer

##### Full Member level 5
Hi,

it basically depends on your frequencies as well as on the length of your traces.
As a rule of thumb, if the trace length is shorter than a tenth of the wavelengt of the highest frequencies (${l}_{trace,max}$ < $\frac{{\lambda}_{max}}{10}$), wave propagation effects are negligible.

BR

#### volker@muehlhaus

For time domain guys, we need to care about controlled impedance when the line propagation delay becomes significant compared to pulse rise/fall time.

#### wwfeldman

@stenzer
does the measure of 1/10 wavelength mean only 1/10 wavelength or does it mean integer number of wavelengths + 1/10 wavelength?

#### FvM

##### Super Moderator
Staff member
is it correct that high speed signals propagate in PCB as waves in dielectric materials such as FR4 according to microstrip principle?
The PCB structures have to be analysed as planar transmission lines, line type according to the geometry e.g. micro strip, embedded stripline, coplanar strips with or w/o ground, coplanar waveguide.

#### stenzer

##### Full Member level 5
@wwfeldman
It means smaller than a tenth. So if the length of your trace is shorter than $\frac{\lambda}{ 10}$ (e.g. ${l}_{trace,max}$ = $\frac{\lambda}{12.3456789}$) wave propagation effects can be neglected, see The RF and Microwave Handbook.

BR