Describe the structure precisely

Record whether the connection is single-level, staggered, stacked, or combined with another via type. Include the number of interfaces, relevant dimensions, target structure, dielectric construction, and final surface use. Two drawings with the same start and end layer can impose different manufacturing demands.

Keep the intended assembly history visible, including planned reflow operations and permitted rework. Add the service conditions that matter to the product. Reliability cannot be reduced to a single via diameter or material glass-transition temperature.

Understand why ordinary checks have limits

IPC has reported microvia failures that occur during thermal exposure and may be latent at room temperature. This is a specific reason to consider suitable performance-based evaluation where risk warrants it. It is not evidence that every stacked microvia is defective or that one alternative geometry is universally safe.

Use structural inspection to understand the sampled feature and performance testing to examine behavior during defined exposure. Assign each method a question rather than treating either as a complete substitute for the other.

Make the test vehicle representative

An illustrative qualification coupon containing only isolated single microvias would not directly establish the behavior of a deeper stacked production connection. List the differences, assess which can affect the result, and modify the vehicle or the conclusion accordingly.

  • Represent the most relevant via combinations and interfaces.
  • Identify material and process differences from production.
  • Define measurement resolution and failure criteria before testing.
  • Retain resistance records, sample identity, and exposure details.

Manage evidence when the design changes

IPC-TM-650 Method 2.6.27 addresses convection-reflow assembly simulation. Its use should be tied to agreed conditions and acceptance requirements. When a stack, material, via geometry, or assembly process changes, review which prior conclusions still apply and what additional evidence is needed to close the remaining gap.

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

Are staggered microvias always reliable?

No geometry provides an unconditional guarantee. Staggering changes the structure and routing tradeoff, but quality still depends on the process, materials, and exposures.

Can a room-temperature pass exclude thermal intermittents?

No. It establishes performance at the measured conditions. Use an appropriate stress and monitoring plan for thermally dependent concerns.

References & further reading

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