The insulation film forms the basic layer of the circuit, and the adhesive bonded the copper foil to the insulating layer. In multi -layer design, it is bonded with the inner layer. They are also used as protective coverage to separate circuits from dust and humidity, and can reduce the stress during the deflection, and copper foil forms a conductive layer.

　　In some flexible circuits, rigid components formed by aluminum or stainless steel are used. They can provide the stability of the size, providing physical support for the resettlement of components and wires, and release of stress. Adhesives bond the rigid components and flexible circuits together. In addition, there is also a material that is sometimes used in a flexible circuit. It is a bonding layer. It is formed formed by coating on both sides of the insulating film. The bonding layer provides environmental protection and electronic insulation functions, and can eliminate a layer of film, as well as multi -layer capabilities with less bonding layer.

　　There are many types of insulating film materials, but the most commonly used is polyanine and polyester materials. Nearly 80%of all flexible circuit manufacturers in the United States use polypelide film materials, and about 20%of the polyester film materials are used. Polybamine material has non -flammable, geometric size is stable, has a high resistance strength, and has the ability to withstand welding temperature. Polyester, also known as polyethylnetephthalate for short ), Its physical properties are similar to polyamide, have a lower dielectric constant, and the absorption of humidity is small, but it is not resistant to high temperature. The melting point of polyester is 250 ° C, and the glass conversion temperature (TG) is 80 ° C. This limits the use of them in applications that require a large number of end welding. In low temperature applications, they are rigid. Nevertheless, they are suitable for products such as calls such as telephones and other products that are not exposed in harsh environments. Polybamine insulation film is usually combined with polylide or acrylic adhesion. Polyester insulation material is generally combined with polyester adhesion. The advantages of combining the same characteristics of materials can have size stability after dry welding, or after multiple layer pressure circulation operations. Other important features in the adhesive are lower dielectric constants, higher insulation resistance values, high glass conversion temperature and low moisture absorption rate.