The multi-layer circuit board is called multi-layer circuit board only if it is two layers or more. Before, we have analyzed what is double-sided circuit board, so many layers of boards are more than two layers, such as four layers, six layers, eight layers, etc. Of course, some designs are three or five layer circuits, also called Multilayer PCB circuit board. The conductive wiring diagram of the board larger than the second floor is separated by insulating substrate between the layers. After each layer of circuit is printed, the lines of each layer are overlapped together by pressing. Then drill holes to realize the continuity between each layer of lines by passing through holes. The advantage of Multilayer PCB circuit board is that the circuit can be distributed in multi-layer wiring, so that more precise products can be designed. Or smaller products can be achieved by multi-layer board. For example: mobile phone circuit board, micro projector, recording pen and other volume products. In addition, the multi-layer can increase the flexibility of design, better control differential impedance and single end impedance, and some signal frequency better output.

Multilayer circuit board is the inevitable product of electronic technology developing to high speed, multi-function, large capacity and small volume. With the continuous development of electronic technology, especially the extensive and in-depth application of large-scale and large-scale integrated circuits, multi-layer printed circuits are rapidly developing to the direction of high density, high precision and high-level digital, which brings up the technology of micro line, small aperture penetration, blind hole embedded hole high plate thickness aperture ratio, etc. to meet the needs of the market. Due to the need of computer and aerospace industry for high-speed circuits, it is required to further improve the packaging density, coupled with the reduction of the size of separation elements and the rapid development of microelectronics, the electronic equipment is developing in the direction of volume reduction and quality reduction; Due to the limitation of available space, it is impossible to further improve the assembly density of single and double-sided printed boards. Therefore, it is necessary to consider the use of more printed circuits than double-sided boards. This creates the condition for the appearance of multilayer circuit board.