FPC flexible printed circuit board overview
Printed circuit boards are basic products in the electronics industry and are widely used in electronic products such as communication equipment, computers, automotive electronics, industrial equipment, and various household appliances. Their main function is to support circuit components and interconnect circuit components. FPC flexible printed circuit boards are a large category of printed circuit boards, as shown in Figures. According to the structure of FPC flexible printed circuit boards, they can be divided into single-sided boards, double-sided boards, and multi-layer boards according to the number of conductor layers.
Main raw materials for manufacturing FPC flexible printed circuit boards
(1) Flexible copper clad laminate (FCCL): According to the difference between one side covered with copper foil or both sides covered with copper foil, it is called single-sided copper clad laminate and double-sided copper clad laminate; according to the difference between the presence or absence of adhesive between the copper foil and the substrate film, it is called adhesive copper clad laminate and non-adhesive copper clad laminate. The structure of the flexible copper clad laminate is shown in Figure 3. The commonly used substrate films of flexible copper clad laminates include polymer films such as polyimide (PI), polyester (PET), polyethylene 2,6-naphthalate (PEN:), and liquid crystal polymer (LCP). Copper clad laminates are mainly responsible for the three functions of conductivity, insulation, and support in the entire printed circuit board. The performance, quality, processability during the manufacturing process, manufacturing cost, and manufacturing level of the printed circuit board depend to a large extent on the performance of the copper clad laminate.
(2) Cover film: It is composed of an organic film and an adhesive, as shown in Figure 4. The function of the cover film is to protect the completed flexible circuit conductor part. Adhesive films have different types of substrate films and adhesives and thickness specifications. Some FPC flexible printed circuit boards do not use cover films on their surfaces, but instead use solder mask coating to reduce costs.
(3) Adhesive film: It is formed by pouring adhesive on both sides or one side of a substrate film. There are also adhesive films with a pure adhesive layer without a substrate, as shown in Figure 5. Adhesive films have different types of adhesives and thickness specifications. Adhesive films are used for bonding and insulation between multilayer boards.
(4) Copper foil: There are electrolytic copper foil and rolled copper foil, as well as different copper foil thickness specifications. Copper foil is used for two surface conductor layers when producing multilayer printed circuit boards.
In addition, some FPC flexible printed circuit boards use stiffener materials, such as metal sheets, plastic sheets, resin films and epoxy glass substrates. The function of the stiffener is to reinforce the part of the flexible circuit board for support and fixation, as shown in Figure 6. Because it is not used by all FPC flexible printed circuit boards, it is not included in the unit consumption standard.
FPC flexible printed circuit board processing process
Sheet by sheet processing: similar to the intermittent step-by-step processing of rigid boards.
FPC flexible printed circuit board processing uses the same process and similar equipment conditions as rigid boards. In terms of processing form, there are sheet by sheet processing: Sheet by Sheet, similar to the intermittent step-by-step processing of rigid boards, or roll to roll processing, which is a roll of substrate continuous processing.
(1) Flexible single-sided printed circuit board manufacturing process
(2) Flexible double-sided printed circuit board manufacturing process
(3) Flexible multi-layer printed circuit board manufacturing process
Conclusion
FPC flexible printed circuit boards are divided into single-sided, double-sided and multilayer types. Raw materials include FCCL, cover film, etc. Processing includes sheet-by-sheet and roll-to-roll methods.
