Why Most PCBs are Multilayer Boards?
Single-side board is the most basic printed circuit board with all components fabricated on one side and all lines on the other side. Unlike single-side board, lines on double-side board can be fabricated on both side, and is more suitable for the complicated PCB board. Take radio for example, use single-side board or double-side board is enough.
With the rapid development of microelectric technology, the requirement for the printed circuit board has become more and more complicated. Both single-side board and double-side board are not suitable, because electromagnet interference here is difficult to deal with. That’s why multilayer board appears, and the layer of board means independent routing layer, the number of which is always even number.
The advantage of multilayer board are as follows：high-density mounting, tiny size, short spacing between components, fast signal transmission speed, low resistance, good shielding performance and more. However, the more layers of your PCB board, the more expensive and the longer processing period. 4-layer or 6-layer board is always used in our daily PC.
Actually, multilayer board is laminated by etched several single boards or double boards.