A blind via connects an outer copper layer to an internal layer without passing through the full board. A buried via connects internal layers and is not exposed at either finished surface. These terms describe layer access. They do not, by themselves, specify drilling method, hole size, filling or the manufacturing sequence.
Choose the span that solves the routing problem
Start by marking the layers each net actually needs. A through via may reserve space on layers it does not use; a shorter connection can recover some of that routing area. The benefit must be compared with the added process steps and the supplier's ability to reproduce the construction.
A blind connection can be a laser microvia or another approved construction. Avoid using “blind via” and “microvia” as interchangeable terms in the drawing. Give the supplier both the layer span and the physical feature requirements.
Compare access and process timing
| Via type | Access in the finished board | Planning consequence |
|---|---|---|
| Through via | Both outer surfaces | Check unused barrel length and inner-layer clearance |
| Blind via | One outer surface | Define the termination layer and how the feature is formed |
| Buried via | Neither outer surface | Form and evaluate the inner structure before it becomes enclosed |
Watch the interface between structures
An HDI design may combine blind microvias with buried vias. Show whether a surface-to-inner path lands directly over a buried structure or reaches it through a trace. That arrangement affects available area and the manufacturing discussion. Do not let the CAM team guess from coincident coordinates.
Review copper distribution and reference planes around the complete path. Moving a connection away from a through-hole structure can improve access in one region while creating an interruption elsewhere. The routing comparison should include antipads, planes and assembly pads, not just drill symbols.
Prepare a clear via schedule
Give each allowed via type a unique identifier. List start and stop layers, finished dimensions, pad requirements, fill or cap requirements and any prohibited combinations. Keep the drill data and design rules consistent with that schedule.
During quotation, ask the supplier to mark which features drive extra processing and which alternatives preserve the electrical intent. Evaluate a suggested alternative in the layout before accepting it. If it changes the sequence or interconnect arrangement, update the construction record and validation plan. The result should be an approved, reproducible route through the board rather than a generic promise to manufacture blind and buried vias.
Continue the engineering review
- PCB microvia design fundamentals
- Sequential lamination in HDI fabrication
- HDI PCB stackup selection
- HDI PCB engineering hub
Review your HDI requirements
Share the board revision, proposed stackup, quantity and open questions. Include the requirements discussed in this guide so the project review starts with the same assumptions.