Definition

A multilayer PCB has three or more copper layers laminated together with insulating dielectric material. The innermost layers are etched cores; outer layers start as copper foil. Connections between layers are made with plated through-holes, blind vias, and buried vias. Multilayer construction enables complex routing, dedicated power/ground planes, and controlled impedance. Layer stackup design balances signal integrity, manufacturability, and cost. Most complex electronics use 4-16 layer boards; extreme applications may use 30-50+ layers.