A printed circuit board (PCB) that comprises several alternating layers of metal and insulating medium, usually a glass-fibre weave. This enables complex circuits to be created in a small area by allowing several interconnection layers between the components. Metal layers can also be configured as ‘ground planes’ to provide shielding between different signal pathways; for example one metal level could be used for analogue signals, another for digital signals, with a ground plane between them.