Definition

High Density Interconnect (HDI) PCBs use laser-drilled micro-vias (typically ≤150 µm diameter), fine lines/spaces (≤100 µm), and build-up layer construction to achieve higher wiring density than conventional PCBs. HDI enables routing escape from fine-pitch BGAs and CSPs. Common structures include 1+N+1 (one build-up layer each side), 2+N+2, and any-layer (all vias are micro-vias). HDI reduces layer count, board size, and improves signal integrity through shorter via stubs.