Start from return paths and power delivery, then assign signal layers. The remaining copper count is not automatically usable routing capacity.
What to consider
Each high-speed route needs a reference through its complete path. A power plane may act as a reference only within a design that accounts for return-current transfer and decoupling. Splits, voids and crowded antipads can interrupt a nominally continuous plane. Plane allocation should be reviewed with the actual route corridors.
A practical review example
Mark the reference plane under a signal from driver pad to receiver pad, including each transition. If any segment crosses a split, change the route or stack allocation before tuning its length.
Checks before release
- Inspect plane continuity around dense via fields.
- Plan ground transfer at layer changes.
- Keep power-current and return-path requirements visible in the stackup drawing.
Connect this decision to fabrication
Use the stackup planner to organize the initial discussion. Keep proposed values separate from the approved drawing and document the effect of any change on the rest of the construction.
- Give every signal layer a defined return-path strategy.
- Review material and copper balance about the board center.
- Specify every via span and the factory-approved lamination sequence.
Technical references
HDI construction types and definitionsFabrication design guidelinesReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.