Classification according to the number of circuit layers: Divided into single panel, double panel and multilayer board. Common multi-layer boards are generally 4-layer boards or 6-layer boards, and complex multi-layer boards can reach dozens of layers. There are three main types of PCB boards:

Single-Sided PCB Circuits Board On the most basic PCB, parts are concentrated on one side and wires are concentrated on the other side. Because the wires only appear on one side, this PCB is called Single-sided. Because the single-sided board has many strict restrictions on the design circuit, this type of board is only used in early circuits.

Double-Sided PCB Circuits Board This type of circuit board has wiring on both sides, but to use the wires on both sides, you must have a proper circuit connection between the two sides. The "bridge" between such circuits is called via. A via is a small hole filled or coated with metal on the PCB. It can be connected to the wires on both sides. Because the area of the double-sided board is double that of the single-sided board, the double-sided board solves the difficulty of wiring interleaving in the single-sided board, and it is more suitable for use on more complicated circuits than the single-sided board.

Multi-Layer Boards In order to increase the area that can be routed, multi-layer boards use more single- or double-sided wiring boards. A printed circuit board with one double side as the inner layer, two single sides as the outer layer, or two double sides as the inner layer, and two single sides as the outer layer. The conductive pattern is alternately brought together by a positioning system and an insulating bonding material. The printed circuit boards that are interconnected according to design requirements become four-layer and six-layer printed circuit boards, also known as multilayer printed circuit boards. The number of layers of the board does not mean that there are several independent wiring layers. In special cases, an empty layer is added to control the thickness of the board. Usually, the number of layers is even and includes the two outermost layers. Most motherboards have a structure of 4 to 8 layers, but technically it can achieve nearly 100 layers of PCB boards. Most large supercomputers use fairly multilayer motherboards, but because such computers can already be replaced by clusters of many ordinary computers, supermultilayer boards have gradually been discontinued. Because the layers in the PCB are tightly coupled, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.

Classified by soft and hard:

Divided into Rigid PCB and flexible circuit boards, soft and hard board. The yellow connection line is called Flexible PCB. The intuitive difference between rigid PCB and flexible PCB is that flexible PCB can be bent. Common thicknesses of rigid PCBs are 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm, etc. The common thickness of a flexible PCB is 0.2mm. Where parts are to be soldered, a thick layer is added behind it. The thickness of the thick layer ranges from 0.2mm to 0.4mm. The purpose of understanding these is to provide them with a spatial reference when designing. Common materials for rigid PCBs include: phenolic paper laminates, epoxy paper laminates, polyester glass mat laminates, epoxy glass cloth laminates. Flexible PCB materials commonly include: polyester film, polyimide Amine film, fluorinated ethylene propylene film.