Audit a complete path

Choose a difficult net and trace its physical path from the component land to its destination. Record every microvia, intervening land, lateral connection, and reference transition. Repeat for power and ground paths that carry different loading or use different geometry.

This path audit can reveal a design that uses several approved individual features in an unapproved combination. Ask for confirmation of the entire structure, including what sits beneath a stacked connection and how each interface is formed.

Specify interfaces, not only outer appearance

A flat finished land cannot show all the interfaces inside a multilayer interconnect. The IPC microvia reliability warning describes weak-interface concerns that may become evident during thermal exposure. That is a reason to request relevant performance evidence, not to assume every stacked construction fails.

The evidence should represent the proposed materials and geometry closely enough to answer the product's risk questions. Identify meaningful differences between a qualification vehicle and the production layout instead of treating any attractive micrograph as universal proof.

Keep the build history attached to the design

For an illustrative wearable controller, suppose a material change is proposed after the prototype to improve sourcing. Even with unchanged copper artwork, the change can affect the assumptions behind drilling, lamination, and impedance. Reopen the affected reviews and retain the approval with the new build revision.

  • Track material designations and approved alternatives.
  • Preserve the accepted via-stack drawing and inspection locations.
  • Link changes to the engineering evidence that supports them.
  • Confirm that repeat orders reference the same accepted baseline.

Make supplier comparisons equivalent

Compare quotations using the same finished thickness, stack intent, via structures, electrical requirements, and acceptance plan. Separate tooling and qualification work from repeat production. A cheaper proposal may be a useful alternative, but only after its technical differences are visible and accepted by the design owner.

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

Does a passed prototype qualify all later builds?

No. Its value depends on the tested construction and conditions. Material, geometry, process, or assembly changes can require additional evidence.

Should all any-layer boards use the same coupon?

No. A useful coupon represents the relevant interconnect structures and agreed failure criteria of the actual design.

References & further reading

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