Multi-Layer Boards In order to increase the area that can be wired, multi-layer boards use more single- or double-sided wiring boards. Using a double-sided as the inner layer, two single-sided as the outer layer or two double-sided as the inner layer, two single-sided as the outer layer of the printed circuit board, through the positioning system and insulation bonding material alternately together and the conductive pattern according to the design requirements of the interconnection of the printed circuit board will become a four-layer, six-layer printed circuit boards, also known as multilayer printed circuit boards.
The number of layers of the board does not mean that there are several separate wiring layers, in special cases will add empty layers to control the thickness of the board, usually the number of layers are even, and includes the outermost two layers. Most mainframe boards are 4 to 8-layer structure, although technically it is possible to do nearly 100 layers of PCBs in theory.
Most large supercomputers use quite a few layers of motherboards, although because such computers can already be replaced by many clusters of ordinary computers, ultra-layer boards have gradually fallen out of use. Because the layers in the PCB are tightly integrated, it is generally less easy to see the actual number, but if you look closely at the motherboard, you can still see.
