The vehicle architecture is currently in a critical period of transformation. With the rise of electric vehicles, there is a significant breakthrough in architecture design, which represents an excellent opportunity to rethink electrical and electronic architecture design. Meanwhile, due to the large amount of existing content still present in hybrid and internal combustion engine vehicles, adopting innovative methods has become equally important. The trend of transitioning from 12V to 48V spans across all vehicle models, providing an opportunity to re-examine the wires and connectors used throughout the entire process.
In this context, flat cables have become a key choice for power and signal connections in specific situations. Flexible flat cables and flexible printed circuits are the two main types, which exhibit unique advantages in size, weight, heat dissipation, and automation. To fully utilize these advantages, new manufacturing technologies, components, and connection systems are needed, and developing them will open up new horizons of design flexibility.
When examining the internal structure of today's battery electric vehicles, the flattened feature of their construction can be clearly observed, mainly due to the battery pack modules being tightly arranged under the cockpit floor in a tile like manner. At the same time, the interconnection of various components through a large number of power lines, signal lines, and data lines is particularly prominent.
Combining the above two factors, it is not difficult to understand why car manufacturers are increasingly focusing on the strategy of using flat cables in electrical/electronic architecture design.
The application of flat cable technology in the automotive industry is not a new phenomenon. Since the 1960s, this technology has been used for in car connectivity, aiming to reduce space occupation. However, with the popularity of fine gauge wires and terminals, original equipment manufacturers (OEMs) tend to use circular wires to meet most of their needs.
At present, in order to support vehicles with rich functions and electrification, the density requirements for wiring and connections in the industry have reached unprecedented heights. In this context, flat cables demonstrate their unique advantages, including reducing weight, shrinking volume, improving heat dissipation efficiency, and supporting higher levels of automation.
Classification and Characteristics of Flat Cables
Flat cables are mainly divided into two categories: flexible flat cables (FFCs) and flexible printed circuit boards (FPCs), each with different advantages and limitations.
Flexible flat cable
Flexible flat cables (FFCs) are composed of several parallel arranged straight copper or aluminum conductors, which are insulated by extruding thermoplastic insulation materials such as polyurethane or laminating with covering materials such as polyethylene terephthalate. Subsequently, laser technology is used to cut the laminated material to expose the contact points on the conductor. Given the linear nature of FFCs, they are often folded to form the desired shape.
The continuous production process of FFCs allows for arbitrary customization of their length. The thickness of the conductor can reach over 1mm, but thicker conductors will make the FFCs more rigid. The width of a single conductor generally does not exceed 16mm, while the maximum width of FFCs depends on the production process. The production of FFCs is the fastest and most cost-effective method for making flat cables.
Flexible printed circuit board
FPCs are made of flexible copper-clad laminates. According to the desired pattern, copper is removed through masking and chemical etching, followed by applying a cover material with a cut to expose the conductor contact area.
FPCs can not only replace traditional wires, but also replace traditional rigid printed circuit boards. They support multi-layer conductors and can integrate electronic components with surface mount devices, fuses, and intersections. Compared to FFCs, FPCs are more durable and support a maximum width of 600mm.
FPCs are typically limited to a thickness of 2 ounces of copper and a length of 1.2 meters, and the chemical etching process generates significant material waste. In addition to FFCs and FPCs, other flat cable technologies are being developed for potential automotive applications, and innovation in this field is expected to accelerate.
Compared with traditional wiring harnesses, using flat cables has several significant advantages.
Size and weight: Flat cable technology enables the use of thinner conductors while maintaining mechanical strength and durability, typically resulting in a weight reduction of up to 40% and a volume reduction of up to 35% for the overall wiring harness system. This includes a comprehensive consideration of all related components such as connectors, fixtures, and straps.
The unique structural design of flat cables is the key to achieving these significant reductions. For traditional circular wires, any reduction in size is constrained by the fact that a single cable and its terminals must be able to withstand any stress or deformation experienced by the connection points and wiring harnesses. In contrast, flat cables are composed of multiple layers, which not only provide stress relief but also ensure the firmness of terminal connections - enabling the use of finer conductors in many application scenarios.
Heat dissipation performance: Compared to circular wires, flat cables exhibit excellent thermal performance. Specifically, flat cables have a larger surface area under equal volume conditions, effectively promoting heat dissipation and enabling conductors of the same volume to carry higher currents.
Flexibility in design: Flat cables have multiple significant advantages. They are particularly suitable for applications with planar structures, such as being built into battery modules. Its high flexibility makes it an ideal choice for adapting to sports or small bending radius environments, such as in steering wheel airbags. Flat cables can be fixed with adhesives without the need for mechanical fixtures and without the need for additional straps or protective layers, which are typically necessary to protect traditional wiring harnesses.
