Through-Via vs Blind Via vs Buried Via
PCB vias come in three types: through-vias drill completely through the board, blind vias connect an outer layer to one or more inner layers, and buried vias connect only inner layers without touching the outer surfaces. The choice affects PCB density, cost, and high-frequency performance.
Through-Via (Through-Hole Via)
A through-via is drilled through the entire PCB stackup from top to bottom. It connects any combination of layers and is the simplest and cheapest via type to manufacture. The unused portion of the barrel (via stub) can cause resonances at high frequencies.
Advantages
- Lowest manufacturing cost — standard PCB process
- Available on all layer counts — 2-layer through 20+ layer
- Reliable and well-characterized
- Simple to design and verify
Disadvantages
- Via stub creates parasitic resonance at high frequencies
- Occupies routing space on all layers, even unused ones
- Back-drilling required above ~10 GHz to remove stub
- Not suitable for high-density component placement
When to use
Use through-vias for most designs, power/ground connections, and any application below 5–10 GHz where stub resonance is not a concern.
Blind and Buried Via
Blind vias start at an outer layer and terminate at an inner layer without exiting the other side. Buried vias connect only inner layers with no connection to the outer surfaces. Both require sequential lamination — a more complex and expensive process.
Advantages
- Higher routing density — vias only use the layers they need
- No via stub — better high-frequency performance
- Enables HDI (High-Density Interconnect) designs for BGA and fine-pitch ICs
- Buried vias leave outer layers free for other routing
Disadvantages
- Significantly higher cost — requires sequential lamination and additional drill passes
- Harder to inspect and rework
- Design rules more complex — layer transition constraints
- Longer PCB lead times
When to use
Use blind/buried vias for high-density BGAs (0.5 mm pitch and below), HDI designs, multi-layer RF PCBs above 10 GHz, and when routing density cannot be achieved with through-vias.
Key Differences
- ▸Through-via: cheapest, available on all layers; blind/buried: costly, needs sequential lamination
- ▸Via stub in through-vias causes resonance at high frequencies; blind/buried have no stub
- ▸Blind/buried vias dramatically increase routing density for fine-pitch BGAs
- ▸Through-via back-drilling is an alternative to blind vias for removing stubs above 10 GHz
- ▸HDI PCBs (smartphones, laptops) use stacked micro-vias (blind) extensively
Summary
Use through-vias for most PCB designs — they are cheap, reliable, and sufficient for most applications. Use blind/buried vias when routing density demands it (fine-pitch BGAs, HDI) or when RF performance above 10 GHz requires stub-free transitions. The cost premium is significant; validate whether through-vias + back-drilling can achieve your requirements first.
Frequently Asked Questions
What is a micro-via?
A micro-via is a blind via with diameter ≤ 0.15 mm (150 µm), typically drilled by laser. Used in HDI designs to connect BGA pads to inner layers without occupying much PCB real estate. Standard in smartphones and laptops.
What is back-drilling?
Back-drilling (controlled-depth drilling) removes the unused via stub from through-vias by drilling from the back of the board to the last connected layer. This eliminates the stub resonance that limits high-frequency performance, achieving results similar to blind vias at lower cost for high-layer-count boards.
How much inductance does a typical via add?
A 0.3 mm drill, 0.6 mm pad via through a 1.6 mm board adds approximately 1–2 nH of inductance. At 1 GHz this is 6–12 Ω — often negligible. At 10 GHz it is 60–120 Ω — significant enough to cause reflections on a 50 Ω line. Use via pads sized for the impedance needed.
Do I need anti-pads around vias?
Anti-pads (clearance holes in ground/power planes) are required to prevent short circuits to adjacent planes. For RF signals, the anti-pad diameter also affects the characteristic impedance of the via transition. Larger anti-pads reduce parasitic capacitance but increase inductance.