Blind via PCB · Buried vias
Blind Via PCB & Buried Via Fabrication
Blind and buried vias connect only the layers that need connecting. They free routing channels and cut stub length without adding layers, using sequential lamination.
- Blind via aspect ratio
- 1:1
- Min. laser drill
- 75 µm
- Max. lamination
- 7-step
- Min. mechanical drill
- 0.10 mm
What are blind and buried vias
Blind and buried vias, explained.
A blind via connects an outer layer to one or more inner layers without passing through the board. A buried via connects inner layers only and is invisible from both surfaces. Both are made by drilling and plating sub-stacks before final lamination.
They recover routing space that through-holes waste on every layer, shorten via stubs on high-speed nets and allow denser BGA breakout, often avoiding a layer-count increase.
Types
Blind, buried and through vias compared.
| Via type | Connects | Made by |
|---|---|---|
| Through via | Top to bottom | Single drill after lamination |
| Blind via (mechanical) | Outer to inner layer(s) | Controlled-depth drill or sub-lamination |
| Blind microvia (laser) | Outer to adjacent layer | Laser drill per build-up — see microvia |
| Buried via | Inner to inner layer | Drill + plate core sub-stack before lamination |
Choosing a via
Blind vs buried via vs through via: which to use?
Start with a through via; it is the cheapest structure and needs one drill after lamination. Move to a blind via when an outer-layer pad must reach only the next one or two layers, for example to escape a fine-pitch BGA without blocking routing on every layer below. Use a buried via when two inner layers need a connection and the outer layers must stay free for components. Laser-drilled microvias are the smallest blind vias and are covered on the laser drilling page; we treat blind, buried and microvia spans as one via plan, reviewed together with the stack-up.
Specifications
Blind & buried via specifications.
| Parameter | Capability |
|---|---|
| Mechanical blind via aspect ratio | Up to 1:1; minimum mechanical drill 0.10 mm |
| Laser blind microvia | 75 µm minimum laser drill, 1:1 |
| Sequential lamination | Up to 7 build-up cycles |
| Registration | ±3 mil standard; ±2 mil for HDI |
| Fill options | Epoxy-filled, copper-filled (stacked), capped |
Cost
What blind and buried vias cost.
Each blind or buried layer pair needs its own drill and plating cycle before lamination, adding roughly 15–30% per extra sequential step. A 1+N+1 structure typically costs 30–50% more than a through-hole-only design. That premium is often recovered by saving layers or board area.
Complex builds
Blind and buried vias in complex builds.
Blind and buried vias are reviewed together with the HDI step count and lamination sequence. Their value is in solving a specific routing or layer-transition problem while keeping the build sequence realistic. Every distinct via span is another drill-and-plate cycle, so we look for the fewest spans that route the board.
- Show start and stop layers for every via type
- Tie the via schedule to the stack-up and lamination plan
- Call out impedance-sensitive transitions
Signal integrity
Signal-integrity benefits.
Through-holes leave stubs on layers the signal does not use, and those stubs resonate at multi-GHz rates. Blind and buried vias, or back-drilled through-holes, remove the stub. They also free routing channels on layers the via does not need to cross, which can save a layer pair. See high speed PCB.
Example structures
Example blind and buried via structures.
| Structure | Description | Laminations |
|---|---|---|
| Through-hole only | All vias top-to-bottom | 1 |
| Buried core via | Inner core drilled and plated, then laminated | 2 |
| 1+N+1 | Blind microvias from each outer layer to the next | 2 |
| 2+N+2 | Two build-up layers per side, stacked or staggered | 3 |
| Mechanical blind | Controlled-depth drill from one side | 1 (depth-controlled) |
RFQ
What to include in your RFQ.
- Fabrication data and stack-up intent
- Via schedule with spans
- Lamination plan if known
- Impedance and reliability requirements
- Quantities and schedule
Design
Design tips.
- List start and stop layers for every via span in the drill table
- Minimize the number of distinct spans — each adds a lamination cycle
- Keep blind via aspect ratio ≤ 1:1
- Use staggered rather than stacked vias where density allows
- Combine with via in pad for BGA breakout
FAQ
Common questions.
What is a blind via in a PCB?
A plated via that runs from an outer layer to one or more inner layers but not through the whole board.
What is a buried via?
A via connecting inner layers only, not visible from either outer surface.
Do blind and buried vias increase PCB cost?
Yes, about 15–30% per extra lamination cycle; a 1+N+1 design is typically 30–50% more than through-hole only.
Blind via vs microvia: what is the difference?
A microvia is a laser-drilled blind via (from 75 µm) spanning one layer. Mechanical blind vias can span several layers.
Are blind and buried vias HDI?
They are core HDI techniques; see HDI PCB.
Can blind vias be mechanically drilled?
Yes, with controlled-depth drilling for shallow spans, or by drilling sub-laminates before final lamination.
Ready when your files are
Send your design for a capability check.
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