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Structure and material properties of flexible circuit boards and selection methods

Industry News|2022-03-12| admin

  Flexible printed circuit board (Flexible Printed Circuit) can be freely bent, rolled, and folded. Flexible circuit board is made of polyimide film as the base material. It is also called soft board or FPC in the industry. According to the number of layers, its process flow is divided into double-sided flexible circuit board process flow and multi-layer flexible circuit board process flow. The FPC flexible board can withstand millions of times of dynamic bending without damaging the wires. It can be arbitrarily arranged according to the spatial layout requirements, and can be moved and stretched arbitrarily in the three-dimensional space, so as to achieve the integration of component assembly and wire connection. Flexible circuit boards can greatly reduce the volume and weight of electronic products, and are suitable for the development of electronic products in the direction of high density, miniaturization and high reliability.

  Structure of flexible board: According to the number of layers of conductive copper foil, it is divided into single-layer board, double-layer board, multi-layer board, double-sided board, etc.

  Material properties and selection methods

  (1) Base material: The material is polyimide (POLYMIDE), which is a high temperature resistant and high strength polymer material. It can withstand a temperature of 400 degrees Celsius for 10 seconds and has a tensile strength of 15,000-30,000PSI. The 25μm thick substrate is the cheapest and most widely used. If the circuit board needs to be harder, a 50μm substrate should be used. Conversely, if the circuit board needs to be softer, a 13μm substrate is used.

  (2) The transparent glue of the substrate: divided into epoxy resin and polyethylene, both of which are thermosetting glue. The strength of polyethylene is relatively low. If you want the circuit board to be softer, choose polyethylene. The thicker the substrate and the clear glue on it, the stiffer the board. If the circuit board has a relatively large bending area, a thinner substrate and transparent adhesive should be used to reduce the stress on the surface of the copper foil, so that the chance of micro-cracks in the copper foil is relatively small. Of course, for such areas, single-layer boards should be used wherever possible.

  (3) Copper foil: divided into rolled copper and electrolytic copper. Rolled copper has high strength and is resistant to bending, but it is more expensive. Electrolytic copper is much cheaper, but has poor strength and is easy to break. It is generally used in occasions where it is rarely bent. The choice of copper foil thickness depends on the minimum lead width and minimum spacing. The thinner the copper foil, the smaller the minimum width and spacing that can be achieved. When choosing rolled copper, pay attention to the rolling direction of the copper foil. The rolling direction of the copper foil should be consistent with the main bending direction of the circuit board.

  (4) Protective film and its transparent adhesive: 25μm protective film will make the circuit board harder, but the price is relatively cheap. For circuit boards with relatively large bending, it is best to use a 13μm protective film. Transparent glue is also divided into epoxy resin and polyethylene. The circuit board using epoxy resin is relatively hard. When the hot pressing is completed, some transparent glue will be extruded from the edge of the protective film. If the size of the pad is larger than the size of the opening of the protective film, the extruded glue will reduce the size of the pad and cause its edges to be irregular. At this time, the transparent glue with a thickness of 13 μm should be used as much as possible.

  (5) Pad coating: For circuit boards with relatively large bending and some exposed pads, electroplating nickel + chemical gold plating layer should be used, and the nickel layer should be as thin as possible: 0.5-2μm, chemical gold layer 0.05-0.1 μm.

  Established in 2010, Shenzhen Yingtong Hengyi Technology Co., Ltd. is a high-tech enterprise integrating R&D, production, sales and service. The factory area of ??the company is more than 9,000 square meters, and there are more than 360 employees, including more than 30 engineers and technicians. The company has an FPC automatic production line, as well as SMT placement technology and equipment, and has gathered a group of high-quality R&D personnel and production technicians. For more than ten years, the company has been deeply involved in the field of electronic circuit boards and has developed into a brand enterprise in the FPC industry. , the products cover circuit board proofing, LED display soft board, flexible circuit board, soft-rigid combination board, PCB circuit board, FPC circuit board, FPC cable, FPC soft board, industrial control FPC button, automotive circuit board, graphics card BGA, FPCA, etc. , the annual production capacity is about 100,000 square meters or more. Products are widely used in communication mobile phones, computers and network equipment, consumer electronics, automotive electronics, industrial control and other fields. The products sell well in Shenzhen, Guangzhou, Dongguan, Chongqing, Wuhan, Shanghai, Jiangsu, Zhejiang and other parts of the country, and the products radiate to Asia and Europe. And many other countries and regions, it can meet the needs of electronic brand customers for various circuit board products.


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