A buried via connects internal layers and becomes enclosed by later board processing. It must be formed and plated while the relevant subassembly is accessible.
What to consider
A buried connection may span a central core or a smaller internal subassembly. Each arrangement affects the lamination sequence and available drilling/plating process. Filling can be required for planarity, stacked connections or process needs, but “buried” does not by itself mean “copper filled.”
A practical review example
For 1+6+1, an L2–L7 core connection becomes buried after the outer layers are added. Verify whether that connection is appropriate under the BGA and whether its land size blocks the intended escape.
Checks before release
- Show core and subassembly spans.
- Specify filling only where the process requires it.
- Review aspect ratio of the internal drilled structure.
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.