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 Copper Conductors in Flexible Circuits: Enhancing Performance and Flexibility

Copper Conductors in Flexible Circuits: Enhancing Performance and Flexibility


In modern electronics, the flexibility and efficiency of FPCs depend on their conductive layers. Choosing the right copper conductor for your flexible circuit. that is crucial for achieving optimal performance and reliability. This article delves into copper conductor for flexible circuit and the critical differences between rolled copper (RA) and electrolytic copper (ED) foils. highlighting their unique properties and suitable applications. Whether you’re designing for high flexibility, durability, or cost-effectiveness. Understanding these copper conductors will empower you. to make informed decisions that elevate your circuit designs. Join us as we explore how to select the best copper conductor for your flexible circuit


The Role of Conductive Layers in Flexible Circuits

Flexible Printed Circuits (FPCs) play a crucial role in display panels. and modules like Chip On Film (COF) technology. These circuits feature a thin copper layer. applied using rolled copper (RA) or electrolytic copper (ED) processes. The conductive layer, made from rolled or electrolytic copper foil. offers excellent electrical conductivity and ductility. Common copper thicknesses range 9µm、12µm、18µm、24µm、35µm、70µm to 105µm. catering to various flexible circuit applications, from lightweight designs to more robust requirements.

Copper foil thickness and conductivity significantly impact the quality and performance of FPCs. Typically, FPC copper thickness ranges from 17µm to 70µm. each offering unique conductive and processing properties. Additionally, the surface treatment and cleanliness of copper foil are crucial for the overall quality of FPCs. Understanding the differences between rolled and electrolytic copper. and choosing the right one ensures optimal performance for your flexible circuits.

What is Rolled Copper?

Rolled copper foil (RA copper) refers to an extremely thin copper product. much like a sheet of paper, with thicknesses ranging from 5µm to 135µm. The term “rolled” signifies the process of compressing and elongating the copper to achieve this thinness. Producing thinner and wider copper foil becomes increasingly challenging.

Characteristics of Rolled Copper Foil

Rolled copper foil boasts low surface oxygen levels, allowing it to adhere to various substrates. including metals and insulating materials. It operates effectively across a wide temperature range. Primarily used for electromagnetic shielding and anti-static applications. it combines conductive copper foil with a metal substrate. to offer excellent conductivity and electromagnetic shielding. Variants include self-adhesive copper foil, double-sided copper foil, and single-sided copper foil.

As a fundamental material in the electronics industry. electronic-grade copper foil (with purity above 99.7% and thickness between 5µm and 105µm) sees increasing demand. It finds extensive applications in industrial calculators. communication devices, QA equipment, lithium-ion batteries. consumer electronics like TVs, VCRs, CD players, copiers, telephones. HVAC systems, automotive electronics, and gaming consoles. The market demand for high-performance electronic-grade copper foil continues to rise globally.

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What is Electrolytic Copper?

Electrolytic copper (ED copper) production involves using crude copper (with a copper content of 99%). formed into thick plates as the anode, while pure copper forms the cathode. The process uses a mixed solution of sulfuric acid (H2SO4) and copper sulfate (CuSO4) as the electrolyte. When electricity is applied, copper dissolves from the anode into copper ions (Cu2+). and moves toward the cathode. Upon reaching the cathode, these ions gain electrons and deposit as pure copper, known as electrolytic copper.

Impurities in the crude copper, such as iron and zinc, also dissolve into ions (Zn2+ and Fe2+). These ions, however, do not easily deposit on the cathode compared to copper ions. By adjusting the voltage, these impurities remain in the solution. while less reactive impurities like gold and silver settle at the bottom of the electrolysis tank. This process yields highly pure electrolytic copper, essential for various high-purity applications.

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Differences in Manufacturing Processes of RA and ED

Comparison ContentRolled Copper FoilElectrolytic Copper Foil
Manufacturing ProcessCopper billet, copper strips undergo repeated rolling, surface treatmentCopper sulfate solution electrolytic deposition, surface treatment
Process FlowComplex process, long cycleSimple process, short cycle
Equipment RequirementsHighRelatively high
Production CostHighLow
Main Production and Consumption RegionsChina, Japan, South Korea, USAJapan, China, South Korea
PriceRelatively expensiveRelatively cheap
Purity≥99% Cu≥98% Cu
StrengthHighRelatively low
Anti-Tensile PerformanceGood (can bend 2-3 times the diameter of the copper foil pipe)Relatively poor
FlexibilityHighRelatively poor
CompactnessHighRelatively high
Crystal StructureFibrous structureMicroscopic crystalline structure
ThicknessUltra-thin thickness uniformAchievable
WidthSubject to rolling mill (generally ≤600mm)Adjustable
SurfaceBrightRelatively bright
UniformityGoodRelatively good

Manufacturing Process of Rolled Copper (RA Copper):

Rolled copper involves compressing high-purity copper (greater than 99.98%) to adhere it onto the FPC. The copper foil has a lamellar crystal structure. providing excellent adhesion and high operating temperatures. It can withstand soldering at 260°C without blistering.

This method results in copper foil with good flexibility. although its conductivity is slightly lower than electrolytic copper.

Manufacturing Process of Electrolytic Copper (ED Copper):

Electrolytic copper is produced using specialized electrolysis machines. continuously depositing copper ions from a copper sulfate solution onto a rotating drum.

This process forms a columnar crystal structure after undergoing oxidation and roughening treatments.

ED copper typically offers higher conductivity but less flexibility compared to rolled copper.

Thickness and Flexibility:

  • Rolled copper is generally thinner and more flexible.
  • Electrolytic copper tends to be thicker and less flexible.

Surface Uniformity and Smoothness:

  • Rolled copper has better surface uniformity and smoothness.
  • Electrolytic copper may not match the surface quality of rolled copper but usually has higher purity.

Electrical Conductivity:

  • Rolled copper shows higher resistance with decreasing thickness.
  • Electrolytic copper generally provides better conductivity than rolled copper.


  • Rolled copper tends to be more expensive to produce.
  • Electrolytic copper is usually more cost-effective.
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How to Choose the Copper Layer for Flexible Circuits ?

When selecting the conductive layer for FPC substrates. you should decide between Rolled Annealed (RA) Copper. and Electrolytic (ED) Copper based on specific application scenarios. Consider the material’s physical properties, conductivity, and cost. If there are special performance requirements. such as high demands for conductivity, mechanical strength, or flexibility. choose the material that meets these technical specifications. Generally, if the FPC needs to undergo dynamic bending, opt for RA Copper. For FPCs that only require 3-5 bends (assembly bending), choose ED Copper.

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