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As designs get denser and layer counts climb, through-hole vias start consuming routing space you can't afford to lose. Blind and buried vias solve that problem, and ASC Sunstone builds both.
STANDARD
Drilled all the way through the board, connecting all layers, Simple to fabricate, but consumes routing space on every layer it passes through
ADVANCED
Connects an outer layer to one or more inner layers, but not the opposite outer layer. Visible from one side only.
ADVANCED
Connects two or more inner layers without reaching either outer layer. Completely hidden inside the board.
Both blind and buried vias allow you to route signals without consuming the routing space, and pad real estate, that a full through-hole via would claim on every layer it passes through. The tradeoff is fabrication complexity and cost, which is why it's worth understanding exactly what you're gaining before specifying them.
A blind via is drilled from one outer layer to a target inner layer and stops there. Because it doesn't exit the other side of the board, it frees up routing space on every layer it doesn't reach particularly valuable on the opposite outer layer and any inner layers below the drill depth
Blind vias require controlled-depth drilling (laser or mechanical) and specialized plating to ensure the hole is fully copper-plated to the bottom of the blind cavity.
| Factor | Blind via | Buried via |
|---|---|---|
| Layers connected | Outer layer to inner layer(s) | Inner layer to inner layer(s) |
| Visible externally | One side only | Not visible |
| Outer layer space freed | One outer layer (opposite side) | Both outer layers |
| Fabrication | Controlled-depth drilling + | Sequential lamination |
| method | plating | |
| Relative cost | Higher than through-hole; lower than buried | Highest — sequential lamination adds process steps |
| Best signal path for | Surface-to-inner layer connections | Inner layer-to-inner layer connections |
| HDI / fine-pitch BGA | Strongly preferred | Useful in combination with blind vias |
Via depth-to-diameter ratio should generally not exceed 8.1 for reliable plating. Tighter aspect ratios improve plating
Decide which layers connect through blind or buried vias early, changing this late requires re-examining the entire stack-up and can impact cost.
Stacked vias can connect multiple layers with minimal space but increase complexity. Confirm with your manufacturer.
Blind and buried vias typically allow smaller diameters than through-hole vias. Confirm drill and pad sizes for your stack-up.
Ensure CAD rules are configured for blind/buried vias. Generic rules may miss controlled-depth or lamination issues.
Consult your fabrication partner early to avoid costly redesigns and ensure feasibility.
You need to connect surface-mount components to inner layers efficiently, you're working with fine-pitch BGAs where through-hole vias can't break out cleanly, or you need shorter via stubs to reduce inductance in high-speed or RF designs.
You need complex interconnections between inner layers that would otherwise require through-hole vias consuming outer layer space, or you're working on a high-layer-count design where both outer surfaces need to remain fully available for components and routing.
You're designing a high-density, high-layer-count board that needs maximum routing flexibility across all layers, HDI designs, advanced computing hardware, and mil/aero electronics often combine both types in a single stack-up.
Your routing density doesn't require the additional complexity, your schedule or budget doesn't accommodate the added fabrication steps, or your design is straightforward enough that standard vias achieve the routing goals without compromise.
It depends on the design, but the increase is real and worth planning for. Blind vias add cost primarily through controlled-depth drilling requirements and the more involved plating process needed to fill a cavity rather than a through-hole. Buried vias typically cost more than blind because sequential lamination adds a full additional fabrication cycle, the inner layers must be drilled, plated, inspected, and then laminated with the remaining layers before the outer layer processing begins. The total cost increase varies by layer count, via density, and which layers are involved, so it's worth discussing with our team early if cost is a constraint.
Through-hole vias have a stub, the unused portion of the via barrel below the signal layer. At high frequencies, that stub acts as a transmission line discontinuity and creates resonant reflections at specific frequencies, degrading signal integrity. Blind vias eliminate the stub entirely because the via ends exactly where the signal transitions layers. This reduces via inductance, improves impedance continuity, and is one of the primary reasons HDI and high-speed digital designs favor blind vias over through-hole alternatives.
Yes, and it's common. Most HDI designs use through-hole vias for non-critical connections, blind vias for BGA breakout and high-speed signal transitions, and sometimes buried vias for inner-layer routing where both outer surfaces need to stay clear. The key is planning layer pairings and the fabrication sequence carefully, since buried vias must be drilled and plated before final lamination. Your CAD tool's stack-up manager and your fab team both need to be aligned on the complete via structure before production.
A stacked via is a combination of via types placed directly on top of each other in the stackup, for example, a blind via on the top layer stacked over a buried via in the middle of the board, allowing a signal to traverse multiple layers in a tight footprint. They're useful in very dense designs where routing real estate is extremely constrained. The tradeoff is that stacked vias are more mechanically complex and require precise layer-to-layer registration. They should be used intentionally, not as a default, and are worth discussing with AS Sunstone engineering before finalizing.
Aspect ratio is the via depth divided by the via diameter. As this ratio increases, it becomes harder to plate copper uniformly all the way to the bottom of the hole, the chemistry has less time and flow to reach the deepest point before the top starts plating over. An 8:1 ratio is a widely accepted practical limit for reliable plating; designs that push beyond this risk thin or incomplete copper at the bottom of the via, which can cause opens or early field failures. Staying within this limit is especially important for blind vias where the plating must reach a closed bottom.
As early as possible, ideally before your layer stack-up is finalized. Once you've locked in layer count, materials, and which layers need to communicate, changing via strategy becomes expensive. ASC Sunstone's engineering team can review your via requirements, confirm which combinations are within our process capabilities, and flag any potential yield or cost concerns before you've committed to a design direction. A short conversation early saves a much longer one after the files are submitted.
Talk to one of our specialists before finalizing your stack-up, It's the best way to avoid surprises .