In circuit design, the size of the current often leads to increased temperature, which can trigger a series of electrical performance issues. To address this challenge, designers typically prefer rigid PCB for high current applications. However, in some advanced projects or miniaturized circuits, even high current applications often require the unique advantages of flexible PCB. This shift may raise new issues, such as material availability, circuit bendability, and the impact on standard signal lines.
To help you better address these challenges, we have compiled this High Current Flexible PCB Guide, designed to provide you with practical insights and advice to aid in the successful design of your projects. Let’s explore this important topic together!
Perfect Combination of High Current and Flexible Circuits
In some electronic devices, the concept of high current design plays a crucial role, especially in applications requiring high power transmission. High current effectively drives components such as motors, transformers, and high-power LEDs, ensuring their normal operation and maximizing performance.
Flexible circuits, with their lightweight, bendable, and foldable characteristics, are widely used in various high-tech products, enabling complex connections and wiring in confined spaces to meet the shape and size requirements of different devices.
The combination of high current flexible PCB enables an innovative design that balances high power with miniaturization. This combination not only meets high current demands but also maintains the lightweight and flexible characteristics, making it suitable for various complex applications. Here are a few typical examples:
- Electric Vehicle Charging Systems: In electric vehicles, flexible circuits are used to connect the battery and charging systems, handling high currents while maintaining a compact system design.
- Wearable Devices: In high-performance wearable devices like heart rate monitors and fitness trackers, flexible circuits are used to connect sensors and processors, supporting significant current output.
- Medical Equipment: In some medical devices, circuits need to withstand high currents for power-intensive treatments such as laser or ultrasound therapies, while also being flexible enough to conform to the shape of the patient’s body.
Thickness, Current Carrying, and Flexibility
In high current circuit board design, there is a close relationship between thickness, current carrying, and flexibility. Typically, the standard copper thickness provided by manufacturers is 2 ounces (oz), but the current carrying of a PCB is directly related to the thickness of the internal copper foil layer. To meet high current demands, it is often necessary to increase the copper foil thickness, which in turn increases the overall thickness of the flexible PCB, affecting its flexibility.
To address the compatibility between these three factors, the following options can be considered:
- Special Materials: Using materials without adhesive structures, though this may significantly increase costs and manufacturing complexity, can effectively reduce overall bending thickness.
- Adding Surface Plating: By adding extra copper layers on top of the base copper, it is possible to achieve a finished copper thickness of up to 3 ounces. However, it should be noted that the added plating is usually done by electroplating, which may reduce overall flexibility.
- In-House Production: An improvement to the surface plating method is to separately purchase copper sheets of the required thickness and laminate them to polyimide using flexible adhesives. While this method addresses the lack of flexibility in electroplating, challenges may arise in high-layer, high-current flexible PCB since each copper layer requires an adhesive layer.
Coverlay
To prevent oxidation or wear of the flexible PCB’s surface circuits, a coverlay layer is typically added for protection. This protective layer bonds to the circuit surface via adhesive. For each 1 ounce of copper thickness, at least 0.001 inches of adhesive is required to ensure void-free lamination during the lamination process. While the adhesive thickness is crucial for circuit integrity and reliability, it also limits the PCB’s bending ability.
It is important to note that the initial adhesive thickness for the coverlay should not be considered the final thickness. During the lamination process, the adhesive thickness is significantly reduced as it flows to encapsulate the underlying circuit pattern. The extent of this reduction depends on the ratio of line widths to spacing in a given area. In designs with larger spacings between lines, the lamination process will experience a more significant thickness reduction. In contrast, high-density designs tend to see less reduction in adhesive thickness.
Combination of High Current and Low Level Signals
In modern PCB design, combining high current with standard level signal transmission requires consideration of several special factors, with the relationship between line width and copper thickness being particularly important. Typically, the thicker the copper, the wider the required line width. For instance, with 2-ounce base copper, the minimum line width and spacing must be 0.007 inches; this requirement increases with copper thickness.
Wider traces can carry more current, so in high current applications, designs must use wider traces and thicker copper layers to ensure stable signal transmission and enhance the overall performance of the circuit.
For high current flexible PCB, the requirement for controlled impedance also increases the core material thickness. To achieve specific impedance values, thicker core materials must be used, but this can reduce the flexibility of the board.
In such designs, engineers must carefully balance line width, copper thickness, and core material selection to meet the complex requirements of both high current and standard-level signal transmission.
Ending
In high current flexible PCB design, engineers must find a balance between multiple design factors to overcome the challenges of current transmission and signal integrity. From choosing copper thickness and line width to selecting flexible PCB materials and lamination techniques, every detail directly impacts the performance and reliability of the circuit. As current demands increase, designers must not only focus on the current-carrying capacity of the traces but also address the inherent bendability and load-bearing capacity issues of flexible PCB. Especially in high-tech fields like electric vehicles, wearable devices, and medical equipment, effectively utilizing the lightweight and deformable characteristics of flexible PCB while maintaining stable high current transmission is key to achieving innovative designs.
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