Application of FPC Flexible Circuit Board in Automotive Circuits

There are many types of PCB, which can be divided into rigid board (R-PCB), flexible board (FPC) and rigid-flexible board according to the softness of the substrate. According to the layers of the conductive pattern, it can be divided into single panel, double panel and multi-layer panel. In addition, there are special product categories, such as high-speed high-frequency board, high-density connecting board (HDI), packaging substrate, etc. The production process of PCB can be roughly divided into two parts, one is to produce the circuit layer, the other is to combine, press and reprocess the circuit layer with other layers, and finally form FPC. When the signal transmission lines are distributed at the outermost layer of FPC, in order to avoid signal distortion caused by electromagnetic interference in the signal transmission process, FPC will be laminated with a layer of electromagnetic shielding film after laminating the covering film, which plays a role in shielding external electromagnetic interference, thus ensuring the normal operation of FPC circuit.

As far as the main downstream application structure of FPC is concerned in 2019, smartphones, PCs, other consumer electronics, automobiles, tablets, servers/data centers accounted for 44.9%, 18.5%, 14.2%, 6.6%, 4.8% and 4% respectively. Smartphones have always been the main source of downstream demand growth for FPC. With the saturation of major markets since 2018, the industry continues to be weak, and the shipment of 5G replacement will pick up slightly in 2021, while the continuous growth of shipments of wearable devices will bring continuous increment to FPC products. At present, the demand for FPC products in the wearable device market still has a large room for development. It is expected that with the further expansion of the wearable device market, the FPC market size will also be further expanded. In the field of automobiles, the current market size of automotive FPC is less than 10 billion yuan. Compared with the traditional Wiring Harness, FPC integration has high production efficiency and high dimensional accuracy, and is suitable for large-scale mass production. At the same time, in terms of technology, FPC wire harness scheme has many advantages, such as high integration, automatic assembly, assembly accuracy, ultra-thin thickness, super softness, light weight and so on. Take lithium iron phosphate battery as an example, the battery needs to be filled with multiple cells, and FPC is used for collection between cells. The improved 590 module contains 16 cells, and two FPCs are used in total. In the long module based on double-row cells, the number of cells can reach 32, and the number of FPCs used will double.

Automotive wiring loom is the main network of automobile circuit. It is a component of connecting circuit, which is mainly composed of wires, terminals, connectors, sheaths, etc. after the contact terminals (connectors) made of copper are pressed with wires and cables, and the insulators or metal shells are pressed by plastic. Automotive wiring harness products are customized products, and different vehicle manufacturers and their different models have different design schemes and quality standards. FPC is a printed circuit board made of flexible insulating substrate. Compared with hard boards, it has many advantages, such as high wiring density, thinness, free bending and three-dimensional assembly. Therefore, it has obvious advantages in product modeling design and reliability design, and is suitable for miniaturized and lightweight electronic products. It conforms to the development trend of intelligent and portable electronic products in downstream industries, and is widely used in consumer electronics fields such as smart phones, tablets, wearable devices, automotive electronics, communications and other fields.

The automobile manufacturing industry witnessed the highest deployment of robot automation. Welding, assembly, machine maintenance, material removal and parts transfer are the most suitable assembly operations for robot automation. However, for tasks that need judgment and decision-making, there is still room for improvement in robot performance. Wire Harness is the nervous system of automobile, which is composed of wires and Connector assemblies of various sizes and shapes. The harness transmits various control and power signals between the main control unit, the battery and various parts of the automobile. Assembling such cables with connectors requires a high technical level and takes the most time. It involves pairing cables with appropriate connectors, and fixing complex wiring structures inside the car. Traditionally, it is difficult for robots to install wire harnesses on the car body. Therefore, in order to simplify the complex problems related to wiring harness, various methods are being adopted to simplify the wiring harness architecture and improve the functions of robots. The goal of simplifying wiring harness manufacturing needs to persistently promote automation and wiring harness automation; Lightweight is the nervous system of its development. As an important part of the whole vehicle in automotive wiring harness, it accounts for 2% of the total weight of the whole vehicle, and it continues to expand with the increase of automotive electronic equipment. Lightweight harness is becoming more and more important to reduce the energy consumption of single vehicle. The weight of automotive wiring harness copper wire accounts for 75%, which is the main lightweight direction.

With the reshaping of industry with technology as the core, the influx of new generations and the emergence of new thoughts, the extension of automobile industry and automobile as consumer goods are undergoing great and profound changes. Facing the rapid development of automobile electrification, intelligence and networking, the design strategy of automotive wiring harness system is low-carbon, energy-saving, lightweight and intelligent integration. FPC flexible flat wiring harness has the characteristics of small volume, light weight and soft structure, and is suitable for wiring harness in narrow spaces, such as automobile ceiling and network. A trolley selects FPC flexible flat wiring harness instead of traditional wiring harness, which reduces the overall weight of wiring harness by about 50% and the volume by about 60%. In addition, the integration of electronic module, switch and FPC harness can reduce the use of connectors and accessories and reduce the cost. Therefore, the application of FPC wiring harness can better optimize the space, reduce energy consumption and realize the green travel of the whole vehicle. At present, FPC is widely used in new energy vehicles to replace the traditional battery sampling line.

The global market in automotive wiring harness is expected to reach the value of USD 91.53 billion by 2025. Due to the market-oriented trend, everyone wants a piece of it. All wire harness manufacturers, like Kable-X, are studying to replace the existing copper materials with other materials, so as to achieve the goal of lightening the whole vehicle. Lightweight requirement is also an increasing challenge in aerospace. Several early manufacturers of wiring harness used aluminum or aluminum alloy instead of copper as conductive and signal transmission materials, and also put forward some feasible and operational schemes. (Some of these technical articles are open, some are confidential, and you can get them if you want to. ) Because using aluminum will lose weight by 20%-40% compared with copper, and it has advantages in cost. At the same time, using this corrosion-resistant material in areas that may be affected by water does not require separate corrosion-resistant treatment. Of course, there are other alternative options, and the ultimate goal is to replace the heavy copper cable. However, various related schemes are not popular in application at present. "Over the years, people have predicted the inherent decline of copper many times, but the combination of advanced chip technology and improvement in signal integrity design has enabled engineers to find ways to expand the actual bandwidth of copper." Including the wiring harness technology (IHT) of flexible printed circuit boards developed in Britain, which is helpful to manufacture flexible printed circuits of any length. The company manufactured the world's first and longest 26-meter FPC, which can support the control and transmission of power and communication signals without additional wiring harness. Because of its lightweight advantages, this technology has been used in spacecraft and can be used in automobiles to achieve the same advantages. However, the industry believes that the future wiring harness will be designed for system optimization and manufacturability, hoping that it will be simpler, smaller and lighter. Lightweight of automotive wiring harness market is still the main tone of future development, but there is a long way to go, and Rome was not built in a day. The intelligent development of electric vehicles is a trend of automobile technology development in the future. The wide application of electric vehicles has created more new technology applications related to automobiles, thus giving automobiles more sociality. At present, the solution of turning on FPC power battery represented by Tesla has been completely recognized by the market, because it can greatly reduce weight, realize light weight and improve space utilization. It can also realize the advantages of automatic assembly, adding fuse current protection design to improve safety, etc. With the widespread adoption of PC scheme in mainstream models of electric vehicles, FPC scheme has been pushed into the mainstream scheme of power battery signal transmission.