Identify the construction being evaluated

Draw the actual microvia spans and their relation to other vias, lands and buildup layers. Distinguish stacked and staggered arrangements and list any variants used on the board. Ask which coupon features represent each variant and why they are considered relevant.

IPC's 2019 industry warning reported microvia failures that were not identified by traditional acceptance methods alone. This supports a construction specific discussion of evidence; it does not mean every microvia structure fails or that one universal test proves every design.

Specify a test question before a test name

Decide whether the work is screening a production lot, qualifying a construction, comparing alternatives or investigating a failure. These purposes can require different sample plans and interpretation. Write the question in plain language so purchasing and engineering agree on what the report is meant to establish.

IPC-TM-650 2.6.27 addresses convection reflow assembly simulation. If such a method is selected, use its applicable revision and the project's agreed procedure; do not invent a thermal profile from a generic website checklist.

Make the evidence package explicit

Agree on specimen identity, monitored features, measurement records and how the coupon maps to the manufactured board lot. Define who reviews anomalous results and whether additional investigation is needed. A test request without an agreed disposition process can leave production waiting on an avoidable argument.

  • Document via stack geometry and the represented construction.
  • Identify method, revision, conditions and acceptance agreement.
  • Define sample selection and manufacturing lot traceability.
  • Request raw or summary records appropriate to the engineering question.

Carry the evidence through design changes

Retain the material, process and assembly assumptions associated with the test. A result from a different geometry or exposure should not be treated as direct proof of the new construction without an engineering assessment. Compare the differences explicitly when using previous evidence.

For repeat production, determine which results are routine acceptance records and which belong to a broader qualification program. Keep both retrievable, while recognizing that they serve different purposes and may cover different populations of boards.

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 visual inspection enough to establish microvia reliability?

It provides useful structural evidence but may not reveal every failure mechanism. Select a verification approach appropriate to the construction, assembly exposure and product requirements.

Can a supplier's generic coupon report qualify my design?

Review whether its geometry, material system, manufacturing history and test conditions represent your construction. Document any differences before relying on the result.

References & further reading

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