Keep the fabrication sequence visible. Evaluate 2+14+2 or 3+12+3 as candidate notation, then verify the actual escape and plane allocation.
What to consider
Eighteen-layer HDI requires a clear distinction between the central multilayer construction and the outer high-density additions. More core layers can increase mechanical-via aspect ratio without changing microvia depth.
Conceptual layer allocation
Compare 2+14+2 or 3+12+3. This illustration assigns copper functions only; it does not define dielectric thickness, impedance or an approved via structure.
| Build-up per side | Core copper layers | Total copper layers |
|---|---|---|
| 1 | 16 | 18 |
| 2 | 14 | 18 |
| 3 | 12 | 18 |
A practical review example
If board thickness grows while mechanical drill diameter stays fixed, review plating capability separately from the short laser microvias. They are different aspect-ratio problems.
Checks before release
- Allocate signal, ground and power copper before counting routing capacity.
- Agree pressed dielectric values and finished thickness.
- Define every laser and mechanical via span.
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.