In integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different layers. A via on an integrated circuit is often called a through-chip via. A via connecting the lowest layer of metal to diffusion or poly is typically called a "contact".
Different types of vias:
(1) Through hole.
(2) Blind via.
(3) Buried via.
The grey and green layers are non-conducting, while the thin orange layers and vias are conductive.
PCB Via current capacity chart showing 1mil Plating Via Current Capacity & Resistance vs Diameter on a 1.6mm PCB
In printed circuit board design, a via consists of two pads in corresponding positions on different layers of the board, that are electrically connected by a hole through the board. The hole is made conductive by electroplating, or is lined with a tube or a rivet. High-density multi-layer PCBs may have microvias: blind vias are exposed only on one side of the board, while buried vias connect internal layers without being exposed on either surface. Thermal vias carry heat away from power devices and are typically used in arrays of about a dozen.
A via consists of:
Barrel — conductive tube filling the drilled hole
Pad — connects each end of the barrel to the component, plane or trace
Antipad — clearance hole between barrel and metal layer to which it is not connected
A via may be at the edge of the board so that it is cut in half when the board is separated; this is known as a castellated hole and is used for a variety of reasons, including allowing one PCB to be soldered to another in a stack.