The most basic type of PCB is the original single-layer board which, as the name suggests, involves mounting one layer of copper on a substrate. Later developments led to double-layer and multi-layer PCBs, which saw multiple copper layers applied to two or more substrate layers. This made it possible to add a much higher density of components to the PCB and use them to create more powerful devices. While multi-layer boards did make maintenance more difficult, they soon became so cheap to make that it is now often more cost-effective to replace an entire board than to repair it.
Today, the most common substrate is FR-4 glass epoxy, though new materials have emerged as the popularity of PCBs has grown. Examples of PCB configurations include rigid PCBs, flexible PCBs, rigid-flex PCBs, and high-frequency PCBs. The different configurations often use different substrates. And there are many different types of PCB such as Flexible PCB, Rigid-Flex PCB, HDI PCB Board, High Frequency PCB, Aluminum PCB, Ceramic PCB, Multilayer PCB, etc.
http://www.betonpcb.com/pcb-assembly/