A through via is the default. It is drilled after lamination, plated in one pass, and inspected like every other hole. Blind, buried and microvias break that simplicity: they require sequential lamination, extra drilling passes and tighter registration, and they change how the board fails.
The cost difference is easy to quote and hard to justify without understanding the reliability trade-off. This article covers the four via types, where the cost comes from, and what to check before choosing one.
The four via types
- Through via: drilled through the whole board after final lamination. The cheapest and most inspectable.
- Blind via: connects an outer layer to an inner layer, without going through the board.
- Buried via: connects inner layers only, and is completed before the outer layers are laminated.
- Microvia: a laser-drilled via, typically 0.1 mm or smaller, connecting one build-up layer to the next.
Blind and buried vias require the board to be laminated in stages. A microvia requires laser drilling and, in most HDI builds, sequential lamination as well.
Where the cost comes from
| Via type | How it is formed | Cost index | Main cost driver |
|---|---|---|---|
| Through | Mechanical drill after lamination | 1.0 | Hole count, aspect ratio |
| Blind | Sequential lamination + drill | 1.4–1.8 | Extra lamination cycle |
| Buried | Sequential lamination + drill before outer layers | 1.6–2.2 | Extra cycles, registration |
| Microvia | Laser drill + build-up lamination | 1.5–2.5 | Laser passes, via fill |
The index is relative and depends on layer count and via fill. The important point is that the cost is driven by cycles and passes, not by the via itself.
Each additional lamination cycle adds handling, registration error and yield loss. A board with buried vias has at least one extra cycle before the outer layers go on. A microvia build adds a cycle for every build-up layer pair.
Reliability: what changes
A through via has a long barrel and a high aspect ratio. Under thermal cycling, the barrel expands and the copper fatigue life depends on plating thickness and hole wall quality.
A blind or buried via has a shorter barrel, which can improve fatigue life, but it introduces a via bottom and a dielectric interface that must be clean and well plated. A poorly plated blind via can fail at the bottom, where inspection is hardest.
A microvia has a small capture pad and a thin dielectric. Its reliability depends on:
- Laser drill quality and desmear.
- Plating coverage at the via bottom.
- Via fill and planarization for via-in-pad.
- Registration between the microvia and the target pad.
Stacked microvias concentrate stress layer to layer. Staggered microvias distribute it, at the cost of routing area.
DFM rules that matter
- Keep the capture pad large enough for registration tolerance, not just for the drill.
- Define the via type per layer on the drawing, not only "HDI".
- Avoid stacking more than three microvias without a reliability review.
- Specify via fill and cap for via-in-pad; unfilled microvias trap flux.
- Check the aspect ratio of blind vias; a deep blind via plates poorly at the bottom.
- Keep buried vias away from the board edge and from high-stress corners.
- Require a cross-section at the worst-case via in the first article.
How to choose
Use a through via unless the routing or the component pitch forces otherwise. Move to blind or buried vias when the through via blocks too many routing channels, or when the aspect ratio becomes unmanufacturable.
Use microvias when the component pitch requires escape routing on the outer layers. Then decide stacked or staggered based on routing density and reliability, not only on cost.
A common mistake is to specify an HDI build for a board that could be routed with through vias at a larger layer count. The HDI build may be smaller, but it is not always cheaper or more reliable.
FAQ
Are blind vias more reliable than through vias?
Not automatically. A shorter barrel can help fatigue life, but the via bottom and the plating quality become critical. The process matters more than the type.
Can a buried via be inspected?
Only by cross-section or X-ray before the outer layers are added. That is why buried via quality depends on in-process control, not final inspection.
Do microvias always need via fill?
Only when they are in a pad or under a component. For non-functional or covered microvias, fill may not be required, but the surface must still be planar for the next lamination.
Is a higher layer count cheaper than HDI?
Sometimes. If the design can be routed with through vias on more layers, the extra laminate may cost less than two build-up cycles. Run both stackups before deciding.
What to send for a via review
- Stackup with via types per layer
- Component pitch and escape requirements
- Via-in-pad and fill requirements
- Aspect ratio and drill sizes
- Reliability or thermal cycling requirement
- Acceptance class
Send your stackup for a via review, or review our HDI capability and multilayer capability.
Reviewed by the Benchuang process engineering team.
