Allegro PCB Design Tutorial

If you are designing a high speed PCB, you will be required to keep the traces within a tight range of impedace for high speed signals. The impedance depend most importantly the trace width ( and also the thickness of the dielectric). You should calculate the thickness beforehead since once the dense traces are routed, it may be tough to change the trace thickness.

You can find the trace impedabce in Allegro by going to setup => Cross Section. The two things that you need to focus are Width ( of trace) and Thickness ( of Dielectric)

Check "single impedance" and it will calculate and display the the impedance

Increasing trace width reduces Impedance

Increasing the thickness of Dielectric increases impedance

By playing with these two parameters you can set desired impedance.

Here is the youtube showing this.