Introduction to the development of FPC board materials

The basic characteristics of FPC flexible boards depend on the properties of the substrate material. Therefore, to improve the technical performance of FPC flexible circuit boards, the performance of the substrate must first be improved. Then, Xiaobian introduces the development of soft board materials for everyone!




    1. Comparison of properties of common film substrates
    The function of the film substrate is to provide a carrier for the conductor and an insulating medium between the wires while bending and crimping. The FPC soft board substrate is commonly used as a PI polyimide film and a PET polyester film. Flexible copper clad laminates have the same halogen-free environmental requirements as rigid copper clad laminates, and green materials are an inevitable trend. Polyester (PET) resin can be mechanically and electrically versatile, and the biggest disadvantage is poor heat resistance, which is not suitable for direct welding assembly. The binder is a combination of a copper foil and a substrate film, and commonly used are a PI resin, a PET resin, a modified epoxy resin, and an acrylic resin.

     2. Two-layer structure of PI substrate
    Flexible copper clad laminates (FCCL) typically have a three-layer structure, namely polyimide, adhesive and copper foil. Since the adhesive affects the performance of the flexible board, especially electrical properties and dimensional stability, a two-layer flexible copper clad laminate without adhesive is developed. At present, there are many methods for depositing a plated metal layer on a polyimide film, and a high-performance flexible plate tends to use a two-layer structure copper clad laminate.

    3. LCP substrate
    Liquid crystal polymer (LCP) copper clad laminate, which is continuously hot pressed by a thermoplastic liquid crystal polymer film through a covered copper foil to obtain a single-sided or double-sided copper clad laminate having a water absorption rate of only 0.04 % and a dielectric constant of 2.85 at 1 GHz, which is suitable for a high frequency plate. Requirements. The polymer is in a liquid crystal state, and is melted by heat to be "TLCP hot melt liquid crystal polymer". The advantages of TLCP can be injection molded, can be extruded into a film to become a substrate for PCB and FPC, and can be processed twice to achieve recycling. The low moisture absorption, high frequency suitability, and thermal dimensional stability of the TLCP film make the TLCP film enter the application on the FPC-COF multilayer substrate.

    4. Halogen-free flexible substrate that meets environmental requirements
    Halogen-free (bromine) substrates have been developed for use in both rigid and flexible boards, including flexible substrates including FCCL, cover films, bonding sheets, and solder resists, as well as reinforcing sheets that are both flame retardant and halogen-free.

    5. New copper foil
    The conductive material of FPC soft board is mainly copper-copper foil, and some alloys such as aluminum, nickel, gold and silver are used. The conductor layer is basically required to be resistant to bending in addition to electrical conduction. Copper foils are produced according to different methods, such as electrolytic copper foil and rolled copper foil. The difference between RA and ED copper foil is that the crystal shape is different. RA copper foil is columnar, uniform, flat, easy to rough or etched; ED copper foil is a fish scale-like sheet stack, smooth and toughness of rolled copper foil Ok, and roughening or etching becomes difficult.

    6. Conductive silver paste
    In the manufacture of FPC soft board, conductive ink is printed on the insulating film to form a wire or a shielding layer. Most of the conductive ink is a silver paste conductive paste, and the conductive layer formed by printing is required to have low electrical resistance, strong bonding, flexibility, and printing operation. It is easy to cure. Using conductive ink to make graphics is also an environmentally friendly, low-cost technology