All You Need to Know About Copper Thickness Requirements for Flex Circuits

Marko Wang
May 19, 2023

Welcome to our article, where we explore the crucial role of copper thickness in flex PCB (Printed Circuit Boards). If you’re involved in the world of PCB design and manufacturing, you know that every aspect of the PCB plays a significant role in its performance and functionality. Copper thickness is no exception.

Table of Contents

Why Copper Thickness Matters in Flex PCBs

You might be wondering why is copper thickness such a big deal. Well, the thickness of the copper traces in a flex PCB affects its conductivity, power handling capabilities, and ability to withstand mechanical stress and bending.

Choosing the appropriate copper thickness is vital to ensure optimal signal integrity, reliability, and durability of your flex circuits.

Whether you’re a seasoned PCB designer or new to the field, this blog will provide valuable insights into copper thickness in flex PCBs. So, let’s get on with it. Let’s check why copper thickness in Flex PCB matters. Let’s answer the question, “How can it impact the performance of flexible circuits?”

Stay tuned for our in-depth exploration and the benefits of partnering with a reputable flex PCB manufacturer like us, MV Flex Circuit.

Electrical Requirements in Flex Circuits

Understanding the electrical requirements and considerations is crucial in all things electronics. To get the great performance and dependability, you have to delve into specific electrical aspects. These are things that matter in PCBs (flex, rigid, or rigid-flex):

Voltage Levels

Circuits can operate at various voltage levels, ranging from low-power to high-power applications. It’s important to determine the voltage requirements of your specific application to ensure proper design and insulation.

Signal Integrity

Maintaining signal integrity is vital for the accurate transmission of data and communication within the flex circuit. Factors such as controlled impedance, controlled crosstalk, and controlled skew significantly preserve signal quality.

Impedance Control

Especially so for flex circuits, it is required to control impedance. Why? To minimize signal reflections and ensure impedance matching with connected components. Precise impedance control helps prevent signal degradation and enables reliable data transfer.

Noise Reduction

Flex circuits can be susceptible to electromagnetic interference (EMI) and radio frequency interference (RFI). (We have a previous blog about this topic, click here.)

Proper grounding, shielding, and routing techniques are essential for minimizing noise and preserving signal integrity.

Now that all these important electrical issues are clear let’s move on. In the next section, we’ll examine the current carrying capabilities issue- the second concept you need to grasp aside from electrical requirements.

Current Carrying Capacity & Copper Thickness in Flex PCB

Understanding the relationship between current carrying capacity and copper thickness is essential. This lets you know that your PCB can handle the required electrical loads. Let’s explore this connection and learn how to select the appropriate copper thickness for various real-life applications:

Aerospace

Flex PCBs with higher current carrying capacity are often preferred in aerospace applications, where reliability and safety are paramount. Thicker copper layers are commonly utilized to accommodate the higher power demands of avionics systems and ensure efficient and uninterrupted operation.

Automotive Electronics

With the increasing complexity of automotive electronics, flex PCBs play a vital role in enabling advanced functionalities. Selecting the right copper thickness ensures optimal current carrying capacity for components like engine control units, infotainment systems, and advanced driver-assistance systems (ADAS).

Consumer Electronics & Household Goods

Consumer electronics and household goods encompass a wide range of products, such as smartphones, tablets, appliances, and wearable devices. Depending on the power requirements of these devices, the copper thickness in flex PCB can vary to ensure efficient power delivery and avoid potential overheating issues.

Industrial Automation

Flex PCBs are used extensively for controlling and monitoring equipment in industrial automation. Copper thickness selection is critical to support the high current loads associated with motors, sensors, and actuators, ensuring reliable operation in demanding industrial environments.

Smart Devices

Smart devices, including IoT devices and connected gadgets, rely on flex PCBs for compact designs and improved functionality. The appropriate copper thickness must be chosen to handle the power demands of these devices while maintaining space efficiency.

Telecommunication

The telecommunications industry relies heavily on flex PCBs for high-speed data transmission and networking equipment. Optimal copper thickness in flex PCB is crucial for achieving low signal losses and supporting high current flow in the transmission lines and power distribution circuits.

Wearable Devices & Medical Devices

Wearable devices, such as fitness trackers and medical devices, require flexible PCBs that are lightweight, flexible, and capable of handling the necessary current. Choosing the right copper thickness certifies adequate power supply and functionality in these compact, portable devices.

Selecting an appropriate copper thickness in flex PCB for your specific application requires careful consideration of the current carrying capacity requirements and the electrical constraints of the components involved.

Capabilities and Tolerances Most Flexible PCB Manufacturers Can Offer

A major PCB manufacturer should know how to use Copper Thickness in Flex PCB. At MV Flex Circuit, we offer a wide range of flexible PCB capabilities and tolerances to answer many customer-centric needs. Just like the industry leaders, our offerings include the following:

Layer Count

We can manufacture flexible circuits with various layer counts, ranging from single-sided to complex multilayer designs, providing flexibility for different application requirements.

Copper Thickness (Of Course!)

There are options for copper thicknesses, including 0.5 oz (17.5 µm), 1 oz (35 µm), and 2 oz (70 µm), and we can also customize copper thicknesses to meet specific current carrying capacity and electrical requirements.

Flexible Board Thickness

Flex Board Thickness

Our flexible PCBs are available in different thicknesses, typically ranging from 0.1 mm (4 mils) to 0.3 mm (12 mils) or more, ensuring the desired mechanical flexibility and durability.

Minimum Trace/Spacing

Fine trace and spacing dimensions? Yes, we can make it as low as 0.1 mm (4 mils) or even smaller, enabling high-density circuit designs and accommodating densely packed components.

Minimum Hole Size

Our capabilities allow us to achieve small hole sizes, typically ranging from 0.15 mm (6 mils) to 0.2 mm (8 mils), meeting the requirements of intricate designs.

Surface Finish

We offer a range of surface finish options, including HASL, ENIG, OSP, immersion tin, or silver, ensuring excellent solderability, corrosion resistance, and compatibility with various assembly processes.

Tolerances

High precision is achievable. We have tolerances of ±10% for impedance control, ±0.05 mm (±2 mils) for hole size, and ±0.1 mm (±4 mils) for trace width and spacing. We are also capable of meeting tighter tolerances based on specific project requirements.

Also, we understand that every flex PCB project is unique, and we can provide solutions tailored to you and you alone. Our team is ready to collaborate openly with you, delivering flexible PCBs that meet your rigorous requirements.

In the next section, we’ll jump into the mechanical flexibility considerations and design guidelines for flex PCBs. Keep reading as we expound on the most important points.

Mechanical Flexibility & Copper Thickness in Flex PCBs

Why does thickness matter, and how do you balance copper thickness and circuit flexibility?

Striking a Balance Between Copper Thickness and Circuit Flexibility

The copper layer’s thickness directly affects the flex PCB’s overall flexibility. Thicker copper layers provide higher current carrying capacity but can also reduce the circuit’s flexibility. On the other hand, thinner copper layers offer increased flexibility but may have limitations regarding current handling capabilities. Achieving the desired mechanical flexibility while meeting the electrical requirements is a delicate balancing act.

Design Considerations

The choice of copper thickness depends on the intended application and the specific mechanical requirements. For applications where the flex PCB needs to bend, twist, or conform to complex shapes, thinner copper layers are preferred to maintain flexibility without compromising performance. Design consideration covers three things, to be exact. They are:

Bend Radius

The bend radius refers to the minimum radius that a flex PCB can safely bend without causing damage to the circuit or compromising its performance.
A larger bend radius allows for more flexibility and reduces the risk of stress-induced failures in the flex circuit.
This requirement depends on the specific application and the mechanical constraints of the system in which the flex PCB will be integrated.

Trace Layout

The layout of the traces on the flex PCB should be carefully designed to accommodate the required flexibility.
Wide and straight traces are generally more flexible than narrow and tightly curved ones.
Curved traces with gradual turns are preferred over sharp angles, as they distribute stress more evenly and minimize the risk of cracking or breaking.

Component Placement

The placement of components on the flex PCB should consider the mechanical stress that the circuit may experience during bending or flexing.
All components should be positioned in areas with lower mechanical stress, avoiding high-stress regions such as tight bends or areas prone to repeated flexing.
The risk of mechanical failures or damage to the circuit can be minimized by strategic placement.

Copper Weight Distribution

Copper weight distribution on the flex PCB maximizes circuit flexibility. The second component of creating a balance is this. Deliberately place thicker copper traces in areas that require higher current carrying capacity and use thinner copper in more flexible sections.

Reinforcement Techniques

In some cases, additional reinforcement techniques can be employed to enhance the flex PCB’s overall rigidity and mechanical stability. This can include using stiffeners or selective plating to reinforce specific areas while maintaining flexibility in other regions.

Material Selection

Choosing the right substrate materials also influences the circuit’s mechanical properties. Flexible materials with good dimensional stability, such as polyimide or polyester, can complement the desired mechanical flexibility of the circuit while providing the necessary electrical insulation. For this third element of striking your balance, we have some additional pointers:

The choice of materials for the flex PCB is critical. Consider the best you can buy for your budget. Flexible substrates such as polyimide or polyester are commonly used due to their excellent flexibility and dimensional stability. These materials can withstand repeated bending and twisting without causing damage to the circuit or affecting its electrical performance.

Testing and Validation

Before finalizing the design, thorough testing and validation are needed. Warrant that the chosen copper thickness and overall circuit construction meet electrical and mechanical requirements. Rigorous testing can identify potential issues and allow adjustments to optimize the flex PCB’s performance.

Here’s a video to illustrate how PCB testing is done in real life:

So far, we’ve discussed two issues: electrical requirements, current carrying capacity, and mechanical flexibility issues vis a vis copper thickness in flex PCB.

In the next section, we’ll take a look at the guidelines, and essential factors, when working with Copper Thickness in Flex PCB products. Stay with us as we generate more tips for the circuit designs you need!

Best Guidelines for Copper Thickness in Flex PCB

By considering key factors such as current carrying capacity, impedance control, and mechanical flexibility, you can select an appropriate copper thickness for your flex PCB.