A multilayer circuit board is a circuit board made up of two or more conductive layers (copper layers) superimposed on each other. The copper layers are bonded together by a resin layer (prepreg). Drilling and plating have been completed. Multi-substrates are manufactured by stacking two or more circuits together with reliable preset interconnections between them. This technique violated the conservative production process from the beginning. The two innermost layers consist of traditional double-layer panels, while the outer layers are different. Before rolling, the internal substrate will be drilled, plated through holes, transferred, developed and etched. The outer layer drilled is the signal layer, which is electroplated by forming a balanced copper ring on the inner edge of the through hole, and then these layers are rolled together to form a multilayer circuit board that can be connected to each other by wave soldering.

The multi-layer circuit board is relatively expensive, the manufacturing process is complicated, the output is low, and it is difficult to rework.

Due to the increase in the packaging density of integrated circuits, the interconnection lines are highly concentrated. This necessitates the use of multiple substrates. Unforeseen design issues such as noise, stray capacitance, and crosstalk can occur in printed circuit layouts. Therefore, the design must focus on minimizing the length of the signal line and avoiding parallel traces. Obviously, in a single panel, or even in a double panel, these requirements are not satisfactory due to the limited number of crossovers that can be achieved. In the case of a large number of interconnection and crossover requirements, in order to achieve satisfactory performance, the circuit board must be expanded to more than two layers, thereby presenting a multilayer circuit board. Therefore, the original intention of manufacturing multi-layer circuit boards is to provide more freedom in choosing appropriate wiring paths for complex or noise-sensitive electronic circuits.

Two of them are on the outer surface, and the multilayer wiring board has at least three conductive layers, and the remaining layers are synthesized in the insulating board. The electrical connection between them is usually achieved through plated through holes in the cross section of the circuit board. Unless otherwise specified, multilayer printed circuit boards, like double-sided boards, are usually plated through holes.