For the most basic PCB, the components are concentrated on one side and the wires are concentrated on the other side. Because it can only be routed on one side, this kind of PCB is called a single-sided board, and both sides of a double-sided board can be wired, so the wiring area is more than a single side. The panel is doubled and is suitable for more complex circuits.

For simple circuits such as radios, single and double panels are usually used. However, electronic products are updated and the complexity of the circuit is greatly increased, and higher requirements are placed on the electrical performance of the PCB. If single and double panels are also used, Then the volume will be large, the wiring will be very difficult, and the interference between the lines will not be easy to deal with. So the multilayer board came into being.

The assembly density of PCB multi-layer boards is high. Small size; the connection between electronic components is shortened, which speeds up the transmission speed; it is convenient for wiring; for high-frequency circuits, a ground layer is added to make the signal line form a constant low impedance to the ground, and the shielding effect is better.