What is a via in a PCB?
A via is a small plated hole in a PCB that electrically connects copper on two or more layers. Vias carry signals, power and ground between layers and can also conduct heat. The main types are through-hole vias, blind vias, buried vias and microvias, which differ in how many layers they span and how they are made.
PCB vias explained
A via starts as a drilled hole. After drilling, the hole walls are made conductive with a thin chemical copper layer and then electroplated to build up copper thickness. The plated barrel connects to pads on each layer it passes through. On layers where the via should not connect, a clearance, or anti-pad, isolates it from surrounding copper.
The simplest type is the through-hole via, which passes through the whole board and is mechanically drilled after all layers are laminated. It is the cheapest and most common via.
Blind vias connect an outer layer to one or more inner layers without passing through the whole board. Buried vias connect inner layers only and are not visible from the outside. Both require drilling at intermediate stages of the build, or depth-controlled drilling, which adds process steps.
Microvias are very small vias, usually laser-drilled, that connect adjacent layers in HDI designs. They can be stacked on top of each other or staggered between layers.
Vias can also be treated after plating. Tenting covers the via with solder mask. Plugging fills the via partly or fully, and filling with resin or conductive material followed by copper capping allows via-in-pad, where a via sits directly in a component pad. Filled and capped vias are common under BGAs and thermal pads.
Via design affects reliability: the aspect ratio of board thickness to drill diameter influences how well the barrel can be plated, and the annular ring around the hole must survive drilling tolerances.
When via choice matters
Via choice matters as soon as routing density, BGA fan-out, signal integrity or thermal management become important. Through-hole vias are the default, but they consume space on every layer, which can block routing under dense packages.
Blind, buried and microvias free up space and shorten signal paths but add lamination or drilling cycles, increasing cost and complexity. Via-in-pad requires filling and capping; an unfilled via in a pad can wick solder away from the joint during reflow.
Typical reliability risks include insufficient plating in high-aspect-ratio holes, cracks in the barrel under thermal cycling, annular ring breakout and stacked microvias that separate under stress. For high-speed signals, the unused section of a through-hole via, the stub, can cause signal reflections; back-drilling or blind vias reduce this. For thermal vias under power components, the number, size and filling of the vias affect heat transfer and solderability.
Through-hole vs blind vs buried vias vs microvias
Through-hole vias are simple and robust and suit most designs. Blind and buried vias save routing space on dense multilayer boards. Microvias enable HDI designs with fine-pitch BGAs, but add process steps and design rules for stacking and filling.
Vias in your quote request
In your quote request, state which via types the design uses and include separate drill files for each blind, buried or microvia span. Note any tenting, plugging, filling or via-in-pad requirements in the fabrication notes, as well as any back-drilling. If you use filled vias under BGAs or thermal pads, say so explicitly. Our free DFM check flags vias with small annular rings, high aspect ratios or untreated vias in pads.
Need boards built? Upload your Gerber files for a free quote and DFM check from the right manufacturer in our network.
PCB manufacturing →FAQ about PCB vias
What is a via on a PCB?
A via is a plated hole that electrically connects copper on different layers of a PCB. It allows signals, power and ground to move between layers and can also carry heat away from components. Vias come in several types, including through-hole, blind, buried and microvias, depending on which layers they connect.
How are vias made in PCBs?
Vias are made by drilling a hole, mechanically or with a laser, and then plating its walls. A thin layer of chemical copper makes the hole conductive, and electroplating builds up copper thickness to form the barrel. Blind and buried vias are drilled at intermediate stages of the build, and vias may then be tented, plugged or filled.
What is the difference between blind and buried vias?
A blind via connects an outer layer to one or more inner layers and is visible from one side of the board only. A buried via connects inner layers only and cannot be seen from either side. Both save routing space compared with through-hole vias, but require additional drilling and lamination steps.
Related terms
- Microvia
A microvia is a small laser-drilled blind via, typically 150 µm or less in diameter (per IPC-T-50M definition), used to connect adjacent layers in HDI boards. Microvias enable routing for high pin-count BGAs and densely packed components that conventional mechanical vias cannot support.
- HDI
HDI (High Density Interconnect) describes PCBs with significantly higher routing density than conventional boards, achieved through microvias, thinner traces, and sequential lamination. HDI is essential for high pin-count BGAs, compact electronics, and applications in smartphones, medical devices, automotive ECUs, and aerospace systems.
- Annular ring
An annular ring is the ring of copper that surrounds a drilled and plated hole on a PCB pad. It is measured from the edge of the hole to the outer edge of the pad. A sufficient annular ring ensures a reliable connection between the hole and the trace, even when the drill is slightly off-centre.
- Multilayer PCB
A multilayer PCB is a printed circuit board with three or more copper layers, separated by insulating dielectric and laminated together under heat and pressure. Inner layers carry signals or form solid power and ground planes, and plated vias connect the layers. Most multilayer boards use an even number of layers, such as four, six or eight.
- Plating
Plating refers to the electroplating or electroless deposition of metal onto a PCB, primarily copper plating inside drilled holes to make them conductive, and final surface finish plating (ENIG, immersion silver, etc.) on exposed pads. Plating thickness affects current capacity, reliability, and IPC class compliance.
- Stack-up
A PCB stack-up is the cross-sectional arrangement of copper layers, cores and prepreg that make up a multilayer board. It defines the layer order, dielectric thicknesses, copper weights and material properties. The stack-up is critical for controlled impedance, signal integrity, EMC performance and manufacturability, and it should be agreed with the manufacturer before layout is finalised.