Ultra-HDI terminology is not a complete manufacturing specification. Define the actual feature sizes, construction and performance that the design needs, then ask a qualified supplier to review them. This guide is a project-planning framework, not a claim that a particular feature size or process is available for every order.
Translate the density goal into geometry
Identify the component pitch, escape channels, conductor dimensions, via spans and registration needs. Determine which features are essential and which can be relaxed. A board containing a small fine-feature region may have different production options from a board requiring the same geometry everywhere.
Ask for process-specific design rules
Have the supplier describe the proposed patterning, copper build-up and interconnect approach and provide the applicable design rules. Do not reuse conventional etch assumptions without review. Record finished conductor shape, spacing and surface requirements when they matter to impedance or assembly.
Use a representative qualification vehicle
Include the difficult geometry, via transitions, pad fields and relevant electrical structures in the evaluation. Define the inspections and measurements before fabrication. A demonstration with easier geometry does not establish capability for the actual product.
Plan verification and supply continuity
Agree how defects, dimensions and interconnect performance will be evaluated. Ask about lot records, change notification and repeat-order control. Consider whether an alternate source can reproduce the construction or whether the product will depend on a tightly controlled single process.
Example: a dense interposer region
List the fine-line region separately from ordinary routing, then identify how it connects to the rest of the stack. Review the transition as carefully as the smallest feature. A successful local pattern is not sufficient if registration, via connection or assembly access fails at the boundary.
Design review checklist
- Specify dimensions instead of relying on a technology label.
- Use supplier-approved rules for the proposed process.
- Validate representative structures and acceptance methods.
- Record process changes and repeat-order dependencies.