A blocked BGA escape, a fixed outline or an unacceptable interconnect stub can justify HDI. A small package pitch is a useful warning, not a complete decision rule.
What to consider
Start with the hardest package and the signals that leave it. Power/ground assignments, depopulated balls, pad size and required trace clearance all affect escape capacity. Try placement improvements and a conventional construction before adding build-up stages. Check that the proposed solution leaves continuous reference copper under critical routes.
A practical review example
Two packages with the same pitch can require different constructions if one has many signal rows and the other has a large ground region. Compare the actual pin maps before applying a pitch-based rule.
Checks before release
- Document the routing bottleneck.
- Test at least one simpler construction.
- Include enclosure thickness and connector requirements.
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.
- Prove the package escape on a small routing study.
- Compare complete constructions using the same reliability requirements.
- Resolve the fabrication process before locking the layout.
Technical references
HDI construction types and definitionsHDI design and manufacturing overviewReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.