Rigid-Flex PCB What is the typical copper thickness in Rigid-Flex PCB?

Rigid-flex PCBs are highly versatile and essential in many modern electronics, from consumer gadgets to complex industrial systems. These boards combine the characteristics of both rigid and flexible circuits, allowing them to be compact, durable, and adaptable to various environments. The copper thickness is one of the most critical factors in determining a Rigid-Flex PCB’s performance, reliability, and overall functionality. The copper layer plays a crucial role in signal transmission, power distribution, and the overall robustness of the board. In this blog post, we will explore the typical copper thicknesses used in Rigid-Flex PCBs, why these choices matter, and how they affect the performance and longevity of the devices they power.

Importance of Copper Thickness for Signal Integrity

When designing a Rigid-Flex PCB, engineers must perform a delicate balancing act. They must consider mechanical flexibility, electrical conductivity, heat dissipation, and the device’s physical constraints. The copper thickness, a fundamental parameter, directly influences these factors, underscoring their complexity and importance in ensuring the board’s optimal performance.

Typically, the copper thickness for Rigid-Flex PCBs ranges from 0.5 oz/ft² to 2 oz/ft² (oz means ounce per square foot), with some specialised designs using thicker copper for high-power applications. The copper thickness is often selected based on the device’s required electrical and thermal performance. For example, a higher copper thickness is frequently used in power distribution circuits, where more current needs to flow through the PCB. Conversely, thinner copper is typically used for signal lines or other low-power applications.

Choosing the right copper thickness ensures that the Rigid-Flex PCB will have the appropriate electrical conductivity to handle the required current without overheating or causing excessive voltage drops. Additionally, a well-chosen copper thickness allows the PCB to maintain signal integrity, which is particularly crucial in high-frequency or high-speed applications.

Typical Copper Thickness Options

In most Rigid-Flex PCB applications, the copper thickness is typically chosen from standard options. These standard thicknesses are designed to meet the needs of most common applications, ensuring optimal performance while maintaining cost-effectiveness and manufacturability.

Rigid-Flex PCBs’ most common copper thicknesses are 1 oz/ft², 1.5 oz/ft², and 2 oz/ft². Engineers use 1 oz/ft² copper for low-power applications, such as signal routing, where the current requirements are minimal. 1.5 oz/ft² is a middle-ground choice, providing more power capacity for moderately high-power applications like LED circuits or small power converters. Engineers use 2 oz/ft² copper for higher-power circuits that need to handle larger currents, such as motor control systems, automotive electronics, or medical devices.

Beyond these standard thicknesses, some applications require custom copper thicknesses, especially when the circuit needs to handle extreme currents or when the board needs to be very thin yet still robust. For instance, high-current power supply circuits may use 3 oz/ft² or even 5 oz/ft² copper to ensure the board can handle the necessary power without excessive heat buildup.

How Copper Thickness Affects Electrical Performance in Rigid-Flex PCBs

Copper thickness directly impacts the electrical performance of a Rigid-Flex PCB, particularly in signal integrity and current carrying capacity. A thicker copper layer can reduce the overall resistance of the circuit, which is beneficial in applications with high currents, such as power supplies or motor drives. In contrast, designers often use thinner copper in signal lines, where high resistance may not pose a problem but could introduce signal attenuation, especially in high-frequency applications.

In high-speed circuits, it is critical to ensure that the copper thickness is not so thick that it causes signal distortion or impedance mismatch. Engineers must select the copper thickness in conjunction with the PCB’s design parameters to maintain a consistent impedance profile, which is essential for high-speed data transmission. Thicker copper also helps minimise the voltage drop, which is especially important in power-sensitive applications like handheld devices or wearables.

In addition to reducing resistance, a thicker copper layer can help distribute heat more effectively, preventing hotspots that might otherwise damage the board or components. This is especially crucial in high-power applications, where heat dissipation is a significant concern.

Copper Thickness and Flexibility: Finding the Right Balance

Rigid-flex PCBs combine traditional PCB rigidity with flexible circuit flexibility. However, increasing the thickness of the copper can affect the board’s flexibility. This trade-off is crucial when selecting the copper thickness for a Rigid-Flex PCB.

Thicker copper layers make the PCB stiffer and more rigid, potentially limiting the overall bending capabilities of the circuit’s flexible parts. For highly flexible areas of a Rigid-Flex PCB, it is crucial to use thinner copper to ensure the circuit retains its ability to bend and conform to the desired shape. Manufacturers often consider this when designing a Rigid-Flex PCB and optimise the copper thickness for electrical performance and mechanical flexibility.

Effect of Copper Thickness on Thermal Management

Thermal management is another critical factor influencing copper thickness selection in Rigid-Flex PCBs. Heat dissipation becomes a growing concern as electronic devices become smaller and more powerful. Copper thickness plays a vital role in the PCB’s heat dissipation capabilities. A thicker copper layer can help spread the heat more effectively, preventing hotspots and maintaining the components’ reliability.

In high-power applications, such as power electronics or automotive applications, engineers use a thicker copper layer to help dissipate heat across the PCB, reducing the risk of thermal damage. However, it is also essential to consider the overall design of the PCB, including the layout of the copper layers, heat sinks, and other thermal management techniques. For example, copper planes (large uninterrupted copper areas) often provide a low-resistance path for heat dissipation.

Thinner copper may be sufficient for low-power applications where heat is less of a concern. However, even in these cases, ensuring adequate copper distribution throughout the PCB can help maintain the device’s overall stability.

Selecting the Right Copper Thickness Based on Application Needs

When selecting the right copper thickness for a Rigid-Flex PCB, it is crucial to consider the application’s specific needs. Different types of electronic devices have varying power, signal, and mechanical requirements, which should guide the copper thickness decision.

For instance, consumer electronics like smartphones, wearables, and tablets often require a balance between thin copper for flexibility and sufficient thickness for power handling. On the other hand, medical devices may demand more precise control over signal integrity and power distribution, necessitating thicker copper in specific areas of the Rigid-Flex PCB. Similarly, automotive electronics and industrial control systems often require thicker copper to handle high currents and provide better thermal management.

Copper Thickness as a Key Factor in Rigid-Flex PCB Design

In this article, we have explored the typical copper thickness options in Rigid-Flex PCBs, how copper thickness affects electrical performance, flexibility, and thermal management, and how to select the right copper thickness based on the application’s specific needs. With this knowledge, users and manufacturers can make more informed decisions when designing or purchasing Rigid-Flex PCBs, ensuring the end product performs reliably and efficiently in real-world conditions.