PCB Classification By Number Of Layers
According to the number of circuit layers, PCB can be divided into single panel, double panel and multi-layer 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:
1: Single-Sided Boards: On the most basic PCB, the components are concentrated on one side, and the wires are concentrated on the other side (When there is a chip component, it is on the same side as the wire, and the plug-in device is on the other side). Because the wires only appear on one side, this PCB is called a single-sided board. Because the single panel has many strict restrictions on the circuit design (wirings cannot cross and must follow their own path), so only early circuits used this type of board.
2. Double-Sided Boards: This circuit board has wirings on both sides.
If you want to use the wires on both sides of the double-sided board, you must have a proper circuit connection between the two sides. This "bridge" between circuits is called via hole. The via hole is a small hole filled or coated with metal on the PCB, which can be connected to the wires on both sides. Because the area of the double-sided board is twice as large as that of the single-sided board, the double-sided board solves the difficulty of interleaving wiring in the single-sided board (which can be connected to the other side through the hole), and it is more suitable for more complicated circuits than the single-sided board.
3. Multi-Layer Boards: They use more single-sided or double-sided wiring boards. The printed circuit boards that using one double-sided board as inner layer with two single-sided boards as outer layer, or two double-sided boards as inner layer with two single-sided boards as outer layer, being alternated together through the positioning system and insulating bonding material, and whose conductive patterns are interconnected according to the design requirements will become four-layer and six-layer printed circuit boards, also known as multi-layer printed circuit boards. The number of board layers does not mean there are how many several independent wiring layers. In special cases, an empty layer will be added to control the thickness of the board. Usually, the number of layers is even, and includes the outermost two layers. Most of the motherboards are 4 to 8 layers structure, but technically can achieve nearly 100 layers PCB. Most large-scale supercomputers use quite multiple layers of motherboards, but because such computers can be replaced by clusters of many ordinary computers, ultra-multilayer boards have gradually been discontinued. Because the various layers in the PCB are tightly combined, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.
