There are normal three basic types of printed circuits boards(PCB) are available.
We have just mentioned, the basic PCB, components concentrated in one side, circuits are concentrated on the other side. Because the circuits only in one side, so we call this is single-sided PCB. Now only use this kind in the early stage.
The circuits on the both side in this kind board. But with the circuit on both sides, the sides must have the appropriate electrical connections, the circuit between a “bridge” is called the plated through hole (via). PTH is in the PCB, the holes filled or coated with metal, it can be connected to the circuits with both sides. This kind more suitable for use in more complex products than the single-sided PCB.
3. The multilayer PCB
In order to increase the area for routing, multilayer spend more single-sided or double-sided circuit board. The number of multilayer PCB using more double-sided PCB, and use the insulation between each layer to stick firmly. Board are several layers to represent the separate circuit layers, usually layers are even, and includes the outerside two layers. Most of the boards are 4 to 8 layer structure.