Ultra HDI describes a move toward substantially finer interconnect geometries and more demanding fabrication control. Supplier definitions and production windows need to be compared explicitly.
What to consider
A finer line/space number cannot be evaluated independently from copper thickness, surface finish, solder mask registration and inspection resolution. Ask whether the published limit represents prototypes, qualified production or a development target. Packaging substrate processes and PCB processes may use similar vocabulary but different material and qualification systems.
A practical review example
When comparing two suppliers, request one table containing finished conductor size, copper thickness, laser-via geometry, minimum land and supported panel dimensions for the same construction.
Checks before release
- Ask for a demonstrated production window.
- Review inspection and electrical-test access.
- Avoid treating one advertised minimum as a complete capability.
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.