Start with a channel requirement
Record the interface, lane assignment, path length, target differential impedance, permitted mismatch, and required verification. Identify which limits come from the system specification and which remain proposals. Link this record to the impedance review. The phrase high speed is not specific enough to establish routing rules or an acceptance test.
Pair review boundaries
| Review item | Design question | Evidence or action |
|---|---|---|
| Routing | What width, spacing and reference are proposed? | Use a reviewed regional stackup |
| Termination | Do pin assignment and contact side preserve the pair? | Check connector and mating-board drawings |
| Length adjustment | Which system tolerance is being satisfied? | Keep the requirement source in the design record |
| Validation | Is impedance alone sufficient evidence? | Define the required channel measurements or analysis |
Review the pair in every region
Check trace width, spacing, reference copper, and dielectric arrangement across moving spans and supported terminals. Include connector pin assignments and polarity in the review. Use connector selection to resolve the real mating interface; matching nominal pitch alone says little about the electrical channel. Pay particular attention where the regional stack or reference changes.
Keep matching subordinate to the real geometry
Before adding length compensation, identify what electrical requirement it addresses and whether its placement creates a crowded or mechanically awkward region. Evaluate compensation with the complete route and reference environment. Exchange the reviewed geometry with the fabricator, and specify how critical results will be verified. A nominally matched CAD length does not prove channel compliance.
Before you release the design
- Mark each controlled pair by net name.
- Review every reference and construction transition.
- Check terminal polarity against the mating assembly.
- Recheck length and spacing after mechanical changes.
Watch points
- A connector's advertised interface support does not qualify the full flex channel.
Practical questions
Should differential traces always remain close together?
Their geometry should follow the reviewed channel design. Spacing, reference, impedance, crosstalk, and manufacturability interact; a general visual preference is not a substitute for those requirements.
Does equal physical length guarantee timing alignment?
It is one geometric input. The effective electrical paths also depend on their environments and transitions, so use the interface's actual verification criteria.
Technical references
References support the material or design context. Check the exact grade, part number, document revision and project conditions before release.Updated 27 September 2026 · Technical content policy · Engineering guidance supports project review; the agreed drawing defines the build.