It is divided into rigid circuit board, flexible circuit board and soft hard combination board. Generally, the PCB shown in the first figure below is called rigid pcb, and the Yellow connection line in the second figure is called flexible PCB. The intuitive difference between rigid pcb and flexible PCB is that flexible PCB can be bent. There are common PCB with thickness of 0.2mm, 0.2mm, 1.2mm, 0.2mm, 1.2mm, 0.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1.2mm, 1. The common thickness of flexible PCB is 0.2mm, and a thickened layer will be added at the back of the part to be welded. The thickness of the thickened layer varies from 0.2mm to 0.4mm. The purpose of understanding these is to provide a spatial reference for structural engineers when they design. Rigid pcb materials commonly include: phenolic paper laminate, epoxy paper laminate, polyester glass felt laminate, epoxy glass cloth laminate; flexible PCB materials commonly include: polyester film, polyimide film, fluorinated ethylene propylene film.