HDI microvias can reduce unused interconnect length, but core through vias may still create stubs. Analyze the complete signal path.
What to consider
A stub is the conductive via segment beyond the used connection. Whether it materially affects a channel depends on its geometry and the signal spectrum. Backdrilling can remove part of a mechanical via stub, subject to depth tolerance and clearance. It is a separate process choice rather than an automatic part of HDI.
A practical review example
For a connector transition into an inner layer, model the remaining plated barrel below the connection. Compare the modeled channel against an approved backdrill option and an alternative routing layer.
Checks before release
- Specify backdrill side, stop depth and residual stub requirement.
- Include registration and depth tolerances.
- Keep planes and unrelated traces clear of the backdrill envelope.
Connect this decision to fabrication
Use the design checklist to organize the initial discussion. Keep proposed values separate from the approved drawing and document the effect of any change on the rest of the construction.
- Record depth and diameter using the same units and measurement convention.
- Check capture lands, target lands and registration together.
- Match the test coupon to the actual interconnect construction.
Technical references
Fabrication design guidelinesHistorical IPC microvia reliability warning (2019)References checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.