Generally speaking, PCB circuit boards have upper and lower layers, located on the upper and lower surfaces of the substrate. The circuits on the upper and lower layers are different. This is due to the needs of circuit design and safety considerations. For example, the lines and grounding parts of the power supply part are generally on a non-connected layer. Sometimes, it may not be possible to arrange all the lines on one layer, or the lines arranged on one layer cannot control the circuit. At this time, a multi-layer PCB is needed. Multi-layer PCBs stack single-layer PCBs together so that different circuits can be saperated to meet the needs of complex circuits. Generally, the number of layers of PCB is divided into 2 layers and 4 layers, 6 floors, 8 floors, 10 floors, etc.
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