Due to the increase in the package density of integrated circuits, the interconnection is highly concentrated, which makes the use of multi-substrate necessary. In the layout of printed circuits, unforeseen design problems arise, such as noise, stray capacitance, crosstalk, etc. Therefore, the printed circuit board design must be committed to minimizing the length of the signal line and avoiding parallel routes.

　　Obviously, in a single panel, or even a dual panel, none of these needs can be satisfactorily answered due to the limited number of intersections that can be achieved. In the case of a large number of interconnect and cross requirements, the board must be expanded to more than two layers in order to achieve a satisfactory performance, thus the emergence of multi-layer circuit boards.

　　Therefore, the original intention of manufacturing multilayer circuit boards is to provide more freedom to choose the appropriate routing path for complex and/or noise-sensitive electronic circuits. The multilayer circuit board has at least three conductive layers, two of which are on the outer surface, while the remaining layer is synthesized within the insulating board. The electrical connection between them is usually achieved by plating through holes on the cross-section of the circuit board. Unless otherwise noted, multilayer printed circuit boards, like dual panels, are generally plated through holes.

　　A multi-substrate is made by stacking two or more layers of circuits on top of each other with reliable pre-set interconnections between them. Since drilling and plating are done before all the layers are rolled together, this technique violates the traditional fabrication process from the start. The innermost two layers are made up of traditional double panels, while the outer layers are different, they are made up of separate single panels. Before rolling, the inner substrate will be drilled, electroplated through holes, pattern transfer, development, and etched. The outer layer to be drilled is the signal layer, which is plated in such a way as to form a balanced copper ring at the inner edge of the through hole. The layers are then rolled together to form a multi-substrate, which can be connected (between components) using wave soldering.