If a single panel or a double panel is used, the circuit volume will be large, which will bring great difficulties to the wiring. In addition, the electromagnetic interference between the lines is not easy to handle, so a multi-layer board appears (the number of layers represents several layers of independent wiring layers, usually even numbers).
Why do PCBs have to be multi-layered?
Advantages of multi-layer boards:
The assembly density is high and the volume is small; the connection between the electronic components is shortened, the signal transmission speed is increased; the wiring is convenient; for the high-frequency circuit, the ground layer is added, so that the signal line forms a constant low impedance to the ground; the shielding effect is good. However, the higher the number of layers, the higher the cost, the longer the processing cycle, and the more troublesome quality inspection.
Our common computer boards usually use four-layer or six-layer boards, but now there are more than 100 layers of practical printed circuit boards. The difference between the six-layer board and the four-layer board is that there are two internal signal layers between the ground layer and the power layer, which is thicker than the four-layer board.
Multilayer boards are actually laminated and bonded by etched several single or double panels. The double panel is easy to distinguish. Looking at the light, except for the two sides of the line, the other places are transparent. For four-layer and six-layer boards, because the layers in the PCB are very tightly coupled, there is no good way to distinguish if there is a corresponding mark on the board.