vias

Vias are conductive passages that connect copper layers in multilayer printed circuit boards (PCBs). They provide electrical connections for signals, power, and ground between different layers, enabling complex routing in compact layouts. In PCB terminology, a via is any drilled and copper-plated hole that forms an interlayer electrical path.

Common types include through vias, which span the full board thickness and connect all layers; blind vias, which connect an outer layer to a single internal layer without passing through the entire board; buried vias, which connect only internal layers; and microvias, which have very small diameters and are used in high-density interconnects. Some designs use via-in-pad to improve fan-out from components, often requiring filling and/or plugging to prevent solder wicking during assembly.

Manufacturing typically starts with drilling or laser drilling to create the void, followed by copper electroplating to form a conductive wall on the hole surfaces and along the exposed copper pads. The via may be left open or can be filled with conductive or non-conductive material for planarization or reliability purposes. Microvias are usually created with laser drilling and may be filled or capped. The via’s size and aspect ratio influence manufacturability, mechanical strength, and quality control.

Design considerations include ensuring adequate annular rings around vias, controlling hole diameters and tolerances, and accounting for impedance and signal integrity in high-speed designs. Thermal and mechanical stresses are important, as vias can contribute to reliability issues such as cracking or delamination under thermal cycling. Techniques such as via plugging, via filling, or backdrilling are used to mitigate these concerns, particularly in high-density or high-reliability applications.

In general usage, via is a Latin-derived term meaning “by way of,” but in electronics, vias specifically refer to these interlayer connections that enable multi-layer PCB functionality.