A
printed circuit board (
PCB) mechanically supports and electrically connects
electronic components using
conductive tracks, pads and other features
etched from copper sheets
laminated onto a non-conductive
substrate. PCBs can be
single sided (one copper layer),
double sided (two copper layers) or
multi-layer (outer and inner layers). Multi-layer PCBs allow for much higher component density. Conductors on different layers are connected with plated-through holes called
vias. Advanced PCBs may contain components - capacitors, resistors or active devices - embedded in the substrate.