A multi-layer circuit board, as the name suggests, can only be called a multi-layer circuit board if it has two or more layers, such as four layers, six layers, eight layers, and so on. Of course, some designs have three or five layers of circuitry, also known as multi-layer PCB circuit boards.

For conductive wiring diagrams larger than two-layer boards, there is an insulating substrate separating the layers. After each layer of the circuit is printed, it is then pressed together to overlap each layer of the circuit. Afterwards, drill holes to achieve conductivity between each layer of circuits through vias. The advantage of multi-layer PCB circuit boards is that the circuits can be distributed and wired within multiple layers, allowing for the design of more precise products. Alternatively, smaller products can be realized through multi-layer boards. For example, products with larger volumes such as mobile phone circuit boards, miniature projectors, and recording pens. In addition, multiple layers can increase design flexibility, better control differential impedance and single ended impedance, as well as better output of some signal frequencies.

Multilayer circuit boards are an inevitable product of the development of electronic technology towards high speed, multifunctionality, large capacity, and small volume. With the continuous development of electronic technology, especially the widespread and in-depth application of large-scale and ultra large scale integrated circuits, multi-layer printed circuits are rapidly developing towards high-density, high-precision, and high-level digitization. Technologies such as micro lines, small aperture penetrations, blind hole buried holes, and high plate thickness to aperture ratios are being developed to meet market needs. Due to the demand for high-speed circuits in the computer and aerospace industries, there is a need to further increase packaging density. In addition, with the reduction in the size of separated components and the rapid development of microelectronics, electronic devices are moving towards a smaller size and lighter weight; Due to the limited available space, it is no longer possible to further improve the assembly density of single and double-sided printed boards. Therefore, it is necessary to consider using printed circuits with more layers than double-sided boards. This has created conditions for the emergence of multi-layer circuit boards.