Two build-up layers per side provide another escape depth and introduce another set of interconnect and process choices.
What to consider
Microvias can be offset between adjacent layers or stacked at a shared location, subject to process qualification. Staggering uses lateral space; stacking concentrates connections and demands particular attention to interfaces and thermal performance. Draw the structure rather than assuming the build-up label defines it.
A practical review example
An eight-layer 2+4+2 construction can route through L1–L2 and L2–L3 transitions, with the mirrored structure at the bottom. The four-layer core still needs its own connection plan.
Checks before release
- Specify stacked versus staggered transitions.
- Confirm fill and cap requirements.
- Request evidence for the actual via stack.
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.