Basics - why is high speed routing different from low speed:

• Instead of thinking of traces as wires, they could be thought of as transmission lines meaning that uncontrolled trace geometry could introduce reflections, ringing, or EMI
• As a rule of thumb, if the propagation delay (travel time of signal) is greater than 1/6 of the rise time (time for signal to go from low to high state), we must use high speed routing rules.

Differential pairs (tx and rx):

• KiCad has a tool for this - route > differential pair
• Also should set up differential pair width and gap using File > Board Setup > Design Rules > Net Classes. Set this based off of the impedance calculator in KiCad.
• Need to travel side by side for the entire journey
• The P and N traces must be the same length. Use the length tuning tool to fix this. Meanders should be on the mismatched ends.
• Place capacitors side by side as well.
• Usb 3.0 - RX1 TX1 need to be matched (maybe!!)

Imepedance control:

• 90 ohms +- 10%. Traces are usually very wide and far apart. Check with a calculator

High-speed signals "return" through the ground plane directly underneath the trace.

• Never route a high-speed pair over a split or gap in the ground plane. This creates massive EMI (noise) and ruins signal integrity.
• If you must switch a pair from the Top layer to the Bottom layer, place GND Vias right next to your signal vias. This gives the return current a path to follow the signal to the other side.

Vias and bends: