1. PI, as a special engineering material, has been widely used in fields such as aviation, aerospace, microelectronics, nanomaterials, liquid crystals, separation membranes, lasers, etc. It has flame retardancy, high and low temperature resistance, and can be used at temperatures ranging from -200 ℃ to 426 ℃ for a long time. In the production of FPC, the main PI used are PI protective films and PI reinforcement sheets. PI protective film is used for circuit insulation, and PI reinforcement board is used in the area on the back of the FPC gold finger. The thickness of PI reinforcement film mainly depends on the design drawings and usage environment, and different thicknesses of PI reinforcement are selected for pressing.

2. FR4 itself, as a fire-resistant material, has higher mechanical properties, dimensional stability, impact resistance, and moisture resistance than paper substrates. It has excellent electrical performance, high working temperature, and its performance is less affected by the environment. In terms of processing technology, it has great advantages over other resin based fiberglass cloth boards. In FPC production, it is mainly used as a reinforcement plate, and mainly used as the back of the FPC welding area to strengthen the hardness of the welding area, protect the electronic components in this area from being damaged due to the continuous bending and extension of the FPC, and also because its wear resistance is not as good as PI, it generally does not need to be reinforced with gold fingers.

3. Steel sheet reinforcement mainly refers to the reinforcement of 303 stainless steel. 303 stainless steel is a austenitic stainless steel with sulfur and selenium content, which is easy to cut, rust resistant, and wear-resistant. It is used in situations where easy cutting and high surface finish are required. FPC reinforcement often has different shapes, while stainless steel 303 is easy to etch. Therefore, in FPC products that require high stability, this type of steel sheet reinforcement is often used. As the steel sheet reinforcement cannot be drilled using CNC, nor can it be cut using FPC lasers, it is mainly made using the method of chemical etching, and its cost is relatively high.