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[FAQ] Why it is desirable to route high-speed signals on the external layers of the printed circuit board?

Andrey Andrey
Prodigy 40 points

I watched TI precession lab about USB(https://training.ti.com/layout-basics-for-usb-designs?context=1139747-1138099-1139813-1138770). 

At 8 minutes it is said: "Routing priority should be given to the high-speed signal traces, placing them on the top layer".
Why?
This is due to stub? Or are there other reasons

  • 0
    TI__Guru* 93670 points

    Hi Andrey,

    You are correct. This is mainly suggested to eliminate stub effects. Other than this or if stub is less than quarter wavelength of the rise/fall time of the operating data rate, strip line actually can provide a better noise/cross talk immunity since you are shielding the trace between layers.

    Regards,, Nasser