Multilayer PCB is one of the most complex types in printed circuit board which consists of three or more conductive layers, and these layers are pressed together to form a multilayer PCB. The price of a multilayer PCB is relatively high than custom one because of its complicated PCB manufacturing process, low yield rate and difficult to rework.
It is necessary and more popular to use multilayer PCB as the packaging density is constantly increasing in integrated circuit which will lead to interconnect highly concentrated. In a PCB layout, designers found it is common that sometimes unexpected design problem will appear, such as noise, stray capacitance, etc. Therefore, when design printed circuit board, it must be committed to make the length of signal wire as short as possible and avoid parallel circuits, etc. Obviously, it is hard to get satisfied solution from single-sided PCB or even double-sided PCB, due to the cross circuit number is limited. In the demand of mass interconnection and inter-digitation, if printed circuit board wants to achieve a satisfactory performance, it must be extend to more than two layers, thus the multilayer PCB appeared.
Multilayer PCB at least has three conductive layers, two layers on surface side, and the rest of the layers are synthesized inside the insulation part. The electrical connection between each layer is usually realized by plated through hole. Unless special instructions, both multilayer PCB and double-sided PCB are plated through hole printed circuit boards.