Printed circuit board construction

A printed circuit board (PCB) is a laminated sandwich structure of conductive and insulating layers.
A basic printed circuit consists of a flat sheet of insulating material FR4, Rogers or Polyamide for flexible circuits, and a layer of copper foil, laminated to the substrate. Chemical etching divides the copper into separate conductive lines called tracks or circuit paths, pads for connections, metallized holes (vias) for passing connections between layers of copper as solid conductive areas for electromagnetic shielding or other purposes.

Each of the conductive layers is designed with copper tracks (similar to wires on a flat surface) that provide electrical connections on that conductive layer. Another manufacturing process adds plated or metallized holes that allow interconnections between layers.

PCBs mechanically support electronic components using pads for bonding the component terminals and electrically connect them using traces of one or more layers of copper sheets laminated on and/or between layers of conductive substrate sheets.
A printed circuit board can have several layers of copper which are almost always arranged in pairs. The number of layers and the designed interconnection between them (vias, PTHs) gives a general estimate of the complexity of the board.

Using multiple layers allows for more routing options and better control of signal integrity.