Single-layer PCBs and double-layer PCBs are two basic types of boards that have only one or two layers of conductive materials over the substrate. When more routing space or signal integrity is required, multi-layer PCBs are suited to meet these demands. Unlike single-layer and double-layer PCBs, multilayer PCBs stack multiple layers of conductive and insulating materials to create a complex network of connections. The stack-up typically includes copper layers, cores, substrates, and prepreg.