PCB design glossary
Via
AKA: vias
A plated hole that electrically connects a net between two or more layers of a PCB.
A via is a small plated-through hole that connects copper from one PCB layer to another. Through-hole vias span the whole board; blind vias connect an outer layer to an inner one; buried vias connect two inner layers and aren't visible from outside.
Vias add inductance and take up routing space, so good layout minimizes them — especially on high-speed signals. They're also a budget item: blind and buried vias cost extra at fabrication.
Types of via
Blind, buried and filled vias add process steps, so they raise the price noticeably. Most boards use only through-hole vias.
- Through-hole via: drilled through the whole board. The cheapest and most common.
- Blind via: connects an outer layer to one or more inner layers without going all the way through.
- Buried via: connects inner layers only and cannot be seen from outside.
- Microvia: a tiny laser-drilled via, usually one layer deep, used on high-density (HDI) boards.
- Via-in-pad: a via placed inside a component pad, filled and capped so solder does not wick into it. Used under BGAs and fine-pitch parts.
Typical via sizes
A common, low-cost via is a 0.3 mm drill with a 0.6 mm pad, which leaves a 0.15 mm annular ring. Many fabs can go smaller at extra cost. The limit is the board's aspect ratio: the thicker the board, the larger the smallest hole the fab can plate reliably.
Vias and current
A via's current capacity depends on its drill size and plating thickness. For power nets, use several vias in parallel rather than one, which also lowers resistance and inductance. Stitching vias, placed along the edge of a plane or next to signal vias, tie ground layers together and give return currents a short path between layers.
- Tented vias are covered by soldermask, which protects them and stops solder bridging to nearby pads.
- Avoid vias in SMD pads unless they are filled, or solder will wick away during reflow.
- Each via on a high-speed trace adds a small discontinuity; keep them few.
Work it out with a free tool
Will one via carry the current, or do you need several?
The via current calculator uses IPC-2152 to estimate what a single plated hole carries for your drill size and plating, so you know when to add a second via.
Check via current