Draw the signal path through the via
List the entry and exit routing layers and draw the barrel between them. Mark any conductive portion above or below those connections. TI's high-speed layout guidance includes via discontinuities among the structures requiring attention. In an HDI board, review every constituent via in a transition, including buried or through-hole segments. A route that begins with a microvia can still encounter a stub farther into the interconnect path.
Prioritize by electrical relevance
Create a table of critical nets, via structures, unused spans, and intended analysis bandwidth. A short low-speed control route and a demanding serial channel do not need identical treatment. Use a transmission-line or electromagnetic model appropriate to the geometry to determine whether a stub is material to the channel margin. Avoid inventing a universal maximum length from the data rate alone. Packages, antipads, dielectric environment, and the remaining channel affect the decision.
Compare alternatives before the escape is fixed
The first option may be to route on a different layer so more of the barrel is used. Backdrilling may remove unwanted copper without changing the basic through-hole construction. Blind or microvia structures may avoid creating the unused span. Each choice changes other constraints: reference transitions, pad clearance, build sequence, or routing access. Compare the complete escape and transition, not just the resulting stub length. A local improvement can create a worse route elsewhere.
Specify and verify what remains
If backdrilling is chosen, define the entry side, protected connection layer, drill clearance, and acceptable residual structure with the fabricator. If blind vias are chosen, verify the permitted layer spans and connection geometry in the released drill data. Review the final CAM interpretation against the intended path. A design-rule pass is helpful only when the via usage, layer stack, and manufacturing operations in the tool match those that will be produced.
A continuous reference keeps the return path close
Dielectric · geometry + material
Core or build-up dielectric
Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.
Common questions
Does every via need backdrilling?
No. Apply it where the electrical assessment and chosen construction justify it. Many vias do not have a consequential unused span.
Do microvias guarantee a stub-free channel?
No. They can avoid long unused barrels locally, but the entire transition may also contain buried or through-hole structures that need review.
References & further reading
Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.