In short: Blind vias connect an outer layer to one or more inner layers without passing fully through the board, and buried vias connect only inner layers; both are built with sequential lamination to squeeze more routing into HDI boards, at a real cost premium over a simple through-hole via.
Why a plain through-hole via eventually runs out of room
A standard plated through-hole (PTH) via drills from the top copper layer all the way to the bottom, even if the net it carries only needs to hop between layer 2 and layer 3. On a two- or four-layer board that waste is harmless. On a modern 12-layer smartphone or server board carrying a 0.4 mm-pitch BGA, it is fatal: every PTH punches a keep-out hole through all layers, blocking routing channels on planes it never touches and consuming precious escape space under the package.
This is the problem HDI (High Density Interconnect) design solves with structured vias. Instead of one drill that spans the whole stack, the fabricator builds the stack in stages and places vias that span only the layer pair that actually needs them. The two workhorses are the blind via and the buried via. If you want the full taxonomy of microvias, stacked, staggered and skip vias, see our companion piece on via types in PCB.
Precise definitions
- Blind via: starts on an external layer (top or bottom) and terminates on an internal layer without emerging on the far side. Example: an L1→L2 microvia under a BGA ball.
- Buried via: connects two or more internal layers only; it is invisible from either surface because the outer layers are laminated over it later. Example: an L3→L4 via inside the core.
- Through via: the reference case — spans L1 to Ln.
Rule of thumb: if you can see the via opening on a finished board's surface it is blind (or through); if you cannot see it at all, it is buried.
Sequential lamination — how they are actually built
Blind and buried vias are not drilled into a finished board. They exist because the board is built up in laminated sub-stacks. A typical 1+N+1 or 2+N+2 HDI build goes like this:
- Start with the inner core (say L3–L4). Drill and plate the buried vias here, then fill and planarize them.
- Laminate prepreg and copper foil onto both faces, adding L2 and L5.
- Laser-drill the blind microvias from the new outer foil down one layer, plate them.
- Repeat the build-up for L1 and L6, add the final blind layer-pair microvias, then solder mask and finish.
Each added layer-pair is one more lamination cycle, and each cycle means another full press, bake, drill (mechanical or UV laser), desmear and plate pass. Fabricators quote complexity in lamination cycles precisely because that is the dominant cost and yield driver. A board needing three sequential laminations costs far more than a single-press through-hole board of the same layer count.
Cost: what you actually pay for
The cost premium is not the drilling itself — it is the extra process cycles and the yield hit. A broad industry rule is that each sequential lamination adds roughly 15–30% to bare-board fabrication cost, and laser-drilled stacked microvias add more. Numbers vary by fabricator and volume, but the ranking is stable.
| Via strategy | Lamination cycles | Relative fab cost | Typical use |
|---|---|---|---|
| Through-hole only | 1 | 1.0× (baseline) | 4–8 layer, low density |
| Through + buried (1 core drill) | 1–2 | ~1.3× | Backplanes, dense cores |
| 1+N+1 blind microvia | 2 | ~1.6× | Single BGA fan-out |
| 2+N+2 stacked HDI | 3+ | 2–3× | Smartphones, 0.4mm BGA |
Design takeaway: only buy the lamination cycles you need. Many boards escape a tight BGA with a single blind layer-pair and finish the rest on through vias — a 1+N+1 build rather than a full any-layer HDI.
Design and tooling considerations
Via spans must be legal for your fabricator's build. EDA tools enforce this through a layer-pair / via-span definition in the stackup editor — Cadence Allegro and Sigrity, Siemens Xpedition and PADS, and Synopsys/Ansys signal-integrity flows all let you declare which blind and buried spans exist and then DRC-check that every via uses a defined span. Getting this wrong produces a board the fab simply cannot build.
- Aspect ratio: laser-drilled blind microvias are typically limited to about 0.8:1 to 1:1 (depth:diameter), e.g. a 100 µm via into a 100 µm dielectric. Mechanically drilled buried vias allow much higher ratios.
- Via-in-pad: blind microvias under BGA pads must usually be filled and capped (copper-filled, planarized) so solder does not wick away — an added plating step.
- Registration: every lamination cycle stacks tolerance. Any-layer HDI demands tight layer-to-layer registration, which is itself a yield cost.
Teams building these stackups for the first time often lean on a design partner; firms like Avecas design services handle HDI stackup planning and DFM so the lamination plan matches what the chosen fab can yield.
When to reach for each
Use a buried via when a signal lives entirely inside the stack — inner-layer bus routing, power distribution between planes — and you want the surface layers clear. Use a blind via to escape fine-pitch components on the surface, especially BGAs where through vias would blow up the fan-out. Combine them in stacked or staggered arrangements for any-layer HDI when nothing else fits. For a structured walk through every option including skip and stacked microvias, our via types guide and the HDI stackup design article go deeper.
Want to design a real HDI stackup end-to-end — layer-pair planning, microvia DFM and signal integrity? Our CourseTron PCB design courses walk you through sequential lamination on live boards with Allegro and Xpedition.
Frequently asked questions
Can a blind via and a buried via be stacked on top of each other?
Yes. In any-layer HDI, a blind microvia on the outer layer-pair is routinely stacked directly over a buried via in the core (a copper-filled stacked via). This needs filled, planarized vias and tight registration, and it is one of the more expensive constructions.
Why are blind vias usually laser-drilled while buried vias are mechanically drilled?
Blind microvias are small and shallow (one dielectric deep), so a UV/CO2 laser gives the precision and aspect ratio needed. Buried vias span thicker inner cores where mechanical drilling is cheaper and handles the higher depth-to-diameter ratio.
Do blind and buried vias improve signal integrity?
Often, yes. Shorter via spans mean less stub, lower parasitic capacitance and smaller keep-outs, which helps high-speed nets. But stacked microvias introduce reliability concerns (thermo-mechanical fatigue), so IPC reliability testing matters for critical designs.
Are blind/buried vias always worth the cost?
No. If a 6- or 8-layer through-hole board routes cleanly, through vias are cheaper and more reliable. Only move to blind/buried when density (fine-pitch BGAs, high layer count) genuinely forces it.