- Differential pair signals
- External crystal signals
- Power and ground signals (particularly VBUS and Earth GND)
Important rules for the routing of these critical signals are:
- Run all critical signals on a signal plane adjacent to a solid ground plane layer, if possible.
- Never cross power and ground plane boundaries with critical signals, particularly at a 90° angle.
- Avoid 90° turns in traces, use 45° turns or use bevels instead.
- Keep digital signals away from the differential pairs and the crystal circuitry.
- See the following sections for more information on the routing of critical signals.