Three build-up layers per side can resolve deeper package escape, with more process steps and a stronger need for early factory involvement.
What to consider
The design should demonstrate why two build-ups are insufficient. Review the route from each package region through the build-up to the core and ensure plane access is not sacrificed to routing density. Discuss the cumulative thermal history and qualification of each stacked or offset transition.
A practical review example
A twelve-layer 3+6+3 structure allocates six layers to the core and six to the outer build-ups. Compare it to a fourteen-layer 2+10+2 alternative before judging cost from layer count alone.
Checks before release
- Document the routing reason for the third build-up.
- Compare a larger-core lower-order alternative.
- Agree fabrication and assembly thermal exposure.
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.