Multilayer pcb is due to increased packing density of integrated circuits, leading to interconnect highly concentrated, which makes use of multiple substrates become necessary. In the printed circuit layout, the emergence of unforeseen design problems, such as noise, stray capacitance, crosstalk, etc. Therefore, the printed circuit board design must work towards making the minimum length of signal lines and to avoid parallel routes. Clearly, in a single panel, or even double-sided, due to the limited number of cross can be achieved, these requirements can not get a satisfactory answer. Needs a large number of interconnections and cross-case, the circuit board to achieve a satisfactory performance, it must be extended to two or more board layers, resulting in a multi-layer circuit board. Therefore, the original intention of manufacturing multi-layer circuit board is complex and / or noise-sensitive electronic circuitry to select the appropriate routing paths to provide more degrees of freedom.
　　Multilayer pcb at least three conductive layers, two outer surface, while the remaining layer of insulation board to be synthesized in. The electrical connection between them is usually on the cross-section through the circuit board through-hole plating to achieve. Unless otherwise noted, multi-layer printed circuit boards and double-sided, as is generally plated through-well plates.