Selection of FPC material for flexible circuit

- Aug 19, 2016-

    With the continuous development of science and technology, is closely related to the modern society and electronic technology, ultra small mobile phones, portable computers, memory, hard disk drives, optical disk drives, automotive electronics products are the product miniaturization, light the demanding requirements. To achieve this goal, it must be in the production process, components, materials and other aspects of the in-depth discussion. In order to meet the challenge, a flexible circuit which can be used for three-dimensional electronic assembly can be bent into a myriad of shapes. In recent years, the use of flexible circuits has been extended to 3 radio communications, computer and automotive electronics applications outside the field. Have been used as a lead beam special substrate and flexible circuit has mature into the replacement rigidity and module circuit board applications. In these applications tend to have a book or 3D electronic assembly requirements, also in order to meet at the same time with the application of flexible and rigid requirements, rigid - flexible technology fusion with rigid circuit board flexible circuit, now many flexible and rigid - flexible laminated structure is applied in all kinds of electronic products. This paper focuses on the selection of materials in flexible circuits.

    The material used in the flexible circuit is an insulating film, an adhesive, and a conductor (see Figure 1). Forming an insulating film base layer circuit, adhesive bonded to the insulating layer on the copper foil. In the multi-layer design, it is then bonded to the inner layer. They are also used as protective cover, in order to make the circuit and dust and damp separated by vast, and the ability to decrease during the flexural stress, copper foil to form a conductive layer.

    In some flexible circuit, the rigid links formed by aluminum or stainless steel, they can provide the dimensional stability, the placement of components and wires provides physical support, and stress release. The adhesive bonded the rigid member and the flexible circuit together. In addition, there is also a kind of material is sometimes used in flexible circuit, it is the bonding layer, it is in the two side of the insulation film coated with adhesive and formed. The adhesive layer provides an environment protection and electronic insulation function, and can eliminate a layer of thin film, and has the ability to have a small number of bonding layers.

    There are many kinds of insulating film materials, but the most commonly used are poly (cool) polyimide and polyester materials. At present, nearly 80% of all flexible circuit manufacturers in the United States use polyimide film materials, and about 20% of the use of polyester film materials. Polyimide is non flammable, dimension stability, high tear strength, and has the ability to withstand the welding temperature, polyester, also known as polyethylene double stupid dicarboxylic acid salt (polyethylene terephthalate (PET), its physical properties similar to poly imide, with a lower dielectric constant, absorption of moisture is very small, but not high temperature.

    The melting point of the polyester is 250 degrees C and the glass transition temperature (Tg) is 80, which limits the use of a large number of end to end welding applications. In low temperature applications, they are rigid. Still, they are suitable for use in products such as telephones and other products that do not need to be exposed to harsh environments.

    A flexible circuit technology developed in the United States Cranston Roly-Flex circuits. It don't in the conventional method, it does not use copper conductors and adhesive to form a circuit, only mining with a penetration of silver conductive ink agent, by printing attached to polyester insulating film base material. A conductive epoxy resin, called Poly-Solder, can be used to attach a surface mount device (SMD) to the flexible circuit.

    Through in the first layer on the conductive layer covered with a layer of polymer based insulating layer, and then add on the second conductive layer way to form a multi-layer flexible circuit, electrically conductive vias provide interconnections between the layers.

    The conventional flexible circuit alternative way, suitable for 40 DEG C to 85 DEG C temperature range of use, has been widely used in radio communication, keyboard, temperature automatic regulator, electronic game machine, display and electronic medical instrument.

    With the requirement of "smaller, faster, cheaper" assembly, flexible circuit "flexible" features, to achieve the miniaturization of the electronic products, updates to the notebook computer, mobile phone, this kind of portable products replacement has a important significance.

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