Plan interfaces before placement. A useful interface matrix connects each connector or device port to its electrical standard, component requirements and physical route. Treat single-ended buses, differential links, analog inputs and power connections according to their own constraints instead of forcing them into one generic high-speed rule.
Document each interface as a small system
For every link, record the transmitter, receiver, voltage domains, topology, cable or connector, and expected operating modes. Identify the governing specification and device application note. Include reset, startup and unpowered-device conditions when they affect the interface behavior.
Separate timing from signal quality
Propagation delay and skew affect timing; reflection, crosstalk and loss affect the received waveform. A layout can satisfy a length rule while violating an eye or noise-margin requirement. Define the corresponding validation method for each requirement so a single CAD report is not used as proof of everything.
Place protection at the relevant boundary
Interfaces that leave the enclosure can bring ESD and other disturbances into the circuit. Review the path through the connector, protective components and return connection. The useful placement depends on the disturbance and protection design; a device symbol in the schematic is not evidence of effective board-level protection.
Reserve access for bring-up
Decide how firmware loading, protocol observation and fault isolation will work. Test pads and headers should not create unacceptable loading or long stubs on sensitive channels. Where a direct probe is unsuitable, plan an alternate observation method before the board is released.
Create an interface review row
Use columns for interface name, endpoint part numbers, topology, electrical constraints, reference layers, protection, test method and owner. For a serial link, record the lane mapping and polarity explicitly. For an open-drain bus, record pull-up ownership and the expected bus loading. Unknown fields become review actions.
Design review checklist
- Map signals across every connector and cable.
- Confirm voltage-domain and power-sequencing compatibility.
- Attach device-specific routing and test requirements.
- Name an owner for every unresolved interface question.