Double-Sided Boards of both sides have wiring. However, to use the wire on both sides, and both sides must be in the room with appropriate electrical connections for the job. Such a circuit between the "bridge" is called the guide hole (via). Guide hole in the PCB, metal filled or coated with holes, which can be connected to the conductors on both sides. Because dual-panel area than single-panel twice as big, and because the wiring can be interleaved with each other (you can go around the other side), it is more suitable for use in more complex than single-panel circuit.