A printed circuit board (PCB) is the board substrate used to electrically connect and mechanically support the electronic components. It is made up of an insulating material called a substrate, a layer of conductive material, which is then covered with a thin layer of dielectric material. The PCB is used to connect the components together and provide power and signal paths between them. This is achieved by connecting each component to the PCB and linking them with copper tracks, traces, or foil patterns. PCB design requires knowledge of components, engineering, and electrical engineering to ensure that boards are optimized for their intended application. PCBs come in various sizes and shapes and are often custom-designed to fit the application they are meant to be used in.