Multi-Layer Circuit boards. In order to increase the area that can be wired, the multilayer board uses more single or double-sided wiring boards. Using a double-sided inner layer and two single-sided outer layers, the printed circuit board which is alternately arranged by the positioning system and the insulating bonding material and the conductive pattern is interconnected according to design requirements becomes four layers, similiar stack up for 6 layer, 8 layers etc. The layers are more than two called multiple layers printed circuit board. The number of layers of the board does not mean that there are several layers of independent wiring layers. In special cases, empty layers are added to control the thickness of the board. Usually the number of layers is even and the outermost two layers are included.