Fabrication
Microvia
In plain English
A tiny laser-drilled tunnel that links two stacked layers of the board so wiring can pass between them — like a small elevator between two floors of a building.
The technical version
A microvia is a laser-drilled via, typically 0.075-0.15 mm in diameter, spanning a single dielectric layer in HDI boards. Microvias can be stacked or staggered to build high-density interconnect for fine-pitch BGAs. Their short span avoids the high aspect ratios that limit plating in through-hole vias.