As the name implies, a multi-layer circuit board is a circuit board with more than two layers that can be called multi-layer, such as four-layer, six-layer, eight-layer and so on. Of course, some designs are three-layer or five-layer circuits, also called multi-layer PCB circuit boards. For conductive traces larger than two-layer boards, there are insulating substrates between layers to separate them. After each layer of circuit is printed, the circuit of each layer is overlapped by pressing, and then drilled, and the conduction between the circuits of each layer is realized by via holes. The advantage of the multi-layer circuit board is that the circuit can be distributed in the multi-layer wiring, so that more precise products can be designed, or the smaller products can be realized by the multi-layer board, such as mobile phone circuit boards, micro projectors, and recording Pen etc. In addition, multiple layers can increase design flexibility, better control of differential impedance and single-ended impedance, and better output of certain signal frequencies.

Multilayer circuit boards are an inevitable product of the development of electronic technology in the direction of 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 very large-scale integrated circuits, the development of high-density, high-precision and high-level digitization has led to the emergence of fine lines, small aperture penetrations, and blind hole burying. Technology such as hole height, plate thickness and aperture ratio to meet market demand. Due to the demand for high-speed circuits in the computer and aerospace industries, it is required to further increase the packaging density, coupled with the shrinking of the size of separate components and the rapid development of microelectronics, electronic equipment is also developing in the direction of reducing the size and quality. Single and double-sided printed boards are available due to

Space constraints make it impossible to achieve a further increase in assembly density. Therefore, it is necessary to consider the use of printed circuits with more layers than double-sided circuit boards, which creates conditions for the emergence of multilayer circuit boards.