Freeze one consistent review package

Provide the current copper data, drill definitions, stackup, fabrication drawing, netlist where applicable, and assembly information needed for dense features. Give all files a common revision identity. Altium's stack documentation separates material layers, via types, impedance profiles, and backdrill definitions; those categories are useful regardless of the CAD system. Check that the exported data agrees with the drawing. A correct drill file paired with an obsolete stackup can still produce the wrong interpretation.

Review the build sequence in cross-section

Mark every microvia and buried-via span, filling requirement, stacked or staggered arrangement, and sequential lamination step. Ask the fabricator to return the proposed construction with unresolved items highlighted. Compare the finished dielectric thicknesses with the geometry used in routing. Review any backdrilling, cavities, or special pad features in the same cross-section. The goal is to eliminate assumptions about what gets drilled, plated, filled, or laminated at each stage.

Close local constraints and electrical requirements

Inspect the densest BGA escapes, narrow copper corridors, mask webs, via-in-pad lands, and plane continuity. Confirm that required impedance adjustments can occur without breaking spacing rules. Check power access and decoupling placement before approving a route-saving change. Where a fabricator proposes an exception, capture the exact location and revised geometry. A blanket acceptance of DFM modifications makes later troubleshooting harder because the design team may not know which constraints changed.

  • Record each open item, responsible owner, and closure evidence.
  • Separate nominal CAD dimensions from agreed finished dimensions.
  • Verify assembly-sensitive changes with the assembly team.

Make acceptance measurable

Agree which inspections, coupons, electrical tests, and reliability evidence are required for this build. Define what the report must contain and which revision it represents. Do not add a test name without understanding the acceptance criterion or represented structure. Resolve all build-blocking items before release, then preserve the approved stackup and change log. This creates a usable baseline for repeat orders and gives future material or process substitutions a clear review path.

DESIGN NOTE / SCHEMATIC

Adjacent-layer access, one connection at a time

Signal copper

Dielectric · geometry + material

Reference copper

Core or build-up dielectric

Signal copper

Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.

Common questions

Is a zero-error CAD DRC enough to release HDI?

No. It checks encoded rules. Process sequence, material compatibility, tolerances, assembly treatment, and evidence requirements also need explicit review.

When should the fabricator first see the design?

Share the intended stackup and constrained escape geometry early, while changes remain practical. Follow with a final review of the actual release package.

References & further reading

Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.