FPC flexible circuit board is a kind of printed circuit board with high wiring density, light weight and thin thickness, which is made of polyimide or polyester film. It is mainly used in mobile phones, tablet computers, medical devices, LED, automotive electronics, smart wear and other products. The types of FPC can be divided into single-sided FPC, double-sided FPC, multi-layer FPC and combination of software and hardware FPC.
The single-sided FPC has a layer of chemically etched conductive patterns, and the conductive pattern layer is a calendered copper foil. The insulating substrate can be polyimide, polyethylene terephthalate, aramid fiber ester and polyvinyl chloride. Single sided FPC can be divided into the following four sub categories:
- Single side connection without covering layer
The wire pattern is on the insulating substrate, and there is no covering layer on the wire surface. Its interconnection is realized by tin welding, fusion welding or pressure welding.
- Single side connection with covering layer
Compared with the single side connection without covering layer, only a layer of covering layer is added on the wire surface. The pad shall be exposed when covering, and it can be simply not covered in the end area.
- Double sided connection without covering layer
The connection panel interface can be connected on the front and back of the wire. A passage hole can be opened on the insulating substrate at the bonding pad. This passage hole can be punched, etched or made by other mechanical methods on the required position of the insulating substrate.
- Double sided connection with covering layer
Different from the two-sided connection without the covering layer, there is a covering layer on the surface, and the covering layer has access holes, allowing both sides to be terminated, and still maintaining the covering layer, which is made of two layers of insulating materials and a layer of metal conductor.
The double-sided FPC has a conductive pattern made of etching on both sides of the insulating base film, which increases the wiring density per unit area. The metallized hole connects the figures on both sides of the insulating material to form a conductive path to meet the design and use functions of flexibility. The covering film can protect the single and double sided wires and indicate the location of the components.
Multilayer FPC refers to laminating three or more layers of single-sided or double-sided flexible circuits together, forming metallized holes through drilling and electroplating, and forming conductive paths between different layers. In this way, complex welding processes are not required. Its advantages are light weight of the substrate film and excellent electrical properties. Multilayer FPC can be further divided into the following types:
- Finished flexible insulating substrate
The finished products made on flexible insulating substrate are specified as flexible. This structure usually bonds the two ends of many single-sided or double-sided microstrip flexible FPCs together, but their center parts are not bonded together, so that they are highly flexible.
- Finished soft insulating substrate
If it is made on a flexible insulating substrate, the finished product can not be flexed as specified.
The combination of soft and hard FPC is a PCB with FPC characteristics and PCB characteristics formed by combining flexible PCB and hard PCB according to relevant process requirements after pressing and other processes. The soft and hard combination board has the characteristics of FPC and PCB at the same time. It can be used in some products with special requirements, including a certain flexible area and a certain rigid area. It is very helpful to save the internal space of the product, reduce the volume of the finished product, and improve the performance of the product.