A microvia is a laser-drilled hole, usually 75 to 150 micrometres in diameter, connecting adjacent layers through a thin dielectric, with an aspect ratio of no more than about 1 to 1. Microvias can be staggered from layer to layer or stacked directly on top of each other, copper-filled, to reach deeper layers. They define HDI boards and are needed to escape fine-pitch BGAs, and stacked microvias are watched closely for separation at the target pad after thermal cycling.
Stack two microvias from L1 to L3 under the pad, copper filled, and stagger them below that.
Also heard as
- laser via
- uvia
- micro-via
Related terms
HDI
High-density interconnect: boards built with microvias, fine lines and sequential lamination for dense parts.
Via-in-pad
Via placed directly in a component pad, filled and plated over so solder cannot drain down it.
Blind via
Via that starts on an outer layer and ends at an inner layer without passing through the whole board.
Aspect ratio
Ratio of a board's thickness to the diameter of a drilled hole, which limits how well the hole can be plated.