Regarding Rigid FR4 PCB, it could be categorised in three types according the layer counts.
Firstly it is single-sided PCB, normally component parts on one side, circuits are lay out on the other side. Because circuits only appear on one side, so this kind of PCB board is called single- sided PCB. Single-sided PCB is usually manufactured with simple technology and low cost, but the disadvantages is that single-sided PCB cannot be applied to complex products.
Secondly it is double-sided PCB, which is an extension of the single-sided PCB, Double-sided PCB will replace single side PCB when single-sided PCB cannot satisfy the needs of electronic products. Double side PCB both sides cover with copper and circuits, which can be conducted by making plated through holes.
Thirdly it is multilayer PCB, which contains more than three layer circuits. Insulating materials such as prepreg are used among layers to adhibit and insulate each layer. Multilayer circuit board
is the direction of electronic products with high speed, multi-functional, large capacity and high power.