Board systems classified into the following three:

Single-sided circuit board

Single-Sided Boards

We have just mentioned, so we call this PCB is called single panel (Single-sided). Because there are many single-panel strict limitations in the design of the line (because only one side, and between the wiring alone can not pay * path must around), so only early before the use of such a circuit board.

Double panel

Double-Sided Boards

This has both surfaces of a wiring board. However, to use on both sides of the wire must be between the two sides have the proper electrical connection down. This circuit between the "bridge" called the pilot hole (via). Pilot hole in the PCB, full of holes or painted metal, it can be connected to the wire on both sides. Because the double-sided single panel area than twice as big, and because the wiring can be interleaved with each other (you can go around the other side), it is more suitable than a single panel

More complex circuits.

(Source: The main classification board)