Distinguish the design request from the build proposal

The designer may begin with target geometry, while the fabricator proposes a construction using its available material forms and processes. Preserve both views until differences are reconciled. Approval should identify the accepted build, not merely acknowledge receipt of an attractive stack diagram.

Altium's manufacturing documentation guidance uses a layer stack drawing or table to communicate layer and material information. Add the project specific information needed to resolve electrical and mechanical assumptions rather than relying on layer names alone.

Review the electrical consequences

For each controlled structure, compare signal and reference layers, dielectric dimensions, copper assumptions and material properties with the model used by the designer. Identify whether proposed trace width adjustments affect package escape, neckdowns or other constrained features.

Check all via spans against the new geometry. A change that preserves total board thickness may change a microvia's depth or a critical transmission line. Total thickness agreement is therefore only one check in the approval.

Define acceptable flexibility explicitly

Some requirements can be expressed as performance targets; others depend on a specific material or geometry. Identify the difference. If alternatives are allowed, require enough information to assess equivalence and document who can approve them. Avoid phrases such as equivalent material without an agreed comparison basis.

  • Match layer numbering to the copper and drill files.
  • State material identifiers and relevant construction details.
  • Separate nominal, finished and tolerance values.
  • Link impedance structures and coupon requirements to their layers.

Close the loop into CAD and purchasing

Update the design rules and fabrication drawing when the accepted construction changes their assumptions. Recheck affected routing rather than approving the supplier proposal only in an email. Store the approved stackup identifier in the order baseline and final archive.

For repeat orders, ask for confirmation that the approved construction remains the proposed build. If availability forces a substitution, use the documented change process. A previous successful order should not make future construction details invisible.

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

Can I approve only the total thickness?

That leaves important details unresolved. Review internal dielectric dimensions, copper, material identity, via spans and impedance assumptions as well as finished board thickness.

When should stackup approval happen?

Obtain feasibility feedback before detailed routing and final approval before manufacturing release. Revisit it whenever a design or supplier change affects its assumptions.

References & further reading

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