As a flexible printed circuit board, FPC plays a crucial role in the performance, functionality, and reliability of the entire circuit board through its four major structural layers – substrate, copper coating, covering film, and adhesive layer.
The substrate is the most basic structural layer of FPC, which is usually made of polyimide (PI) or polyester (PET) materials. Polyimide has high heat resistance and insulation properties, and is commonly used in applications that require high heat resistance; Polyester has lower cost, better flexibility and processability, but relatively poor heat resistance, and is mostly used in general consumer electronics products. The substrate not only provides support for the circuit, but also ensures its stability in high temperature and humid environments. Its thickness is usually between 0.0125mm and 0.1mm.
The copper-clad layer is the conductive layer of FPC, usually made of electrolytic copper foil or rolled copper foil, with a thickness generally between 12 μ m and 35 μ m. The copper foil layer directly determines the conductivity and durability of FPC, and it adheres to the substrate to form circuit patterns. Electrolytic copper foil has a lower cost and is suitable for applications that do not require high flexibility; And rolled copper foil has good ductility, suitable for scenarios that require high flexibility and high-frequency bending. The copper foil layer is precisely engraved with conductive lines on the copper foil through fine circuit manufacturing processes, such as dry film lithography, ensuring high density and accuracy of the circuit.
Cover film, also known as protective film, is a thin film that covers the surface of copper foil circuits to protect them from external environmental damage such as moisture, dust, mechanical damage, etc. The covering film is usually made of the same material as the substrate, such as polyimide or polyester, with a thickness between 0.0125mm and 0.05mm. The covering film not only improves the durability of the circuit, but also allows for the installation of windows on it for soldering and electrical connections, making FPC assembly and maintenance more convenient.
Adhesive layers are used to bond materials from different layers together, increasing the stability of the structure. Common adhesive materials are acrylic and epoxy resins, which exhibit excellent heat resistance, chemical resistance, and flexibility. The thickness of the adhesive layer is generally 0.01mm to 0.05mm, and the design takes into account the firmness and flexibility of the bonding to ensure that the circuit board will not delaminate or break during bending and folding processes.
These four structural layers, through complex manufacturing processes and precise material selection, collectively endow FPC with characteristics such as lightweight, strong flexibility, and high temperature resistance. The flexibility and bendability of FPC enable it to meet the design requirements of devices of different shapes and sizes, providing a better user experience. At the same time, its high-density wiring capability and lightweight characteristics greatly reduce the volume and weight of equipment, making it an indispensable component of modern electronic products.