Introduction
Flexible circuit boards need the right copper to work well. Two common types are ED copper and RA copper. They may look similar, but they behave very differently when bent. This article explains how ED copper and RA copper compare and which one is best for flexible PCBs.
ED Copper in Flex Circuit Boards (Electrodeposited Copper)
Manufacturing Process
ED copper (electrodeposited copper) is made in a factory using electricity and a copper-salt liquid bath. In simple terms, copper is “grown” onto a spinning metal drum. As the drum turns, a very pure layer of copper deposits onto its surface, then the finished foil is peeled off and rolled into coils.
A key reason ED copper is popular is that this process is continuous and scalable. Factories can run long production lines and make large amounts of foil with the same thickness again and again. Thickness is controlled mainly by:
- the electric current (how fast copper deposits),
- the time the copper stays on the drum,
- and the bath chemistry.
After the foil is made, manufacturers often add surface treatments. These treatments help copper bond strongly to flexible insulating films (often polyimide). In real flex PCB production, good bonding matters because weak bonding can lead to peeling or cracking when the circuit bends or heats up. ED copper is known for having many surface treatment options, including different roughness “profiles” made to improve adhesion or electrical behavior.
Structure, Performance, and Thickness
ED copper has a microstructure that is often described as column-like grain growth (grains grow more “up and down”). This structure gives ED copper consistent electrical performance, but it can make the copper less forgiving under repeated bending, because cracks can start along grain boundaries when the foil is flexed many times.
What this means for flex PCBs:
- ED copper can work well when the flex circuit is bent once and then left in place (static flex).
- It is more likely to fail early in designs that bend again and again, especially at tight bend radii (dynamic flex).
Thickness benefits:
ED copper is widely used because it can be produced in very thin foils with good uniformity. Thin copper helps build:
- ultra-thin flexible circuits,
- lighter assemblies,
- and tighter packaging in compact electronics.
Electrical and surface notes:
- ED copper has strong conductivity like other copper foils.
- Standard ED copper can be rougher than RA copper, but modern ED foil families include low-profile options designed to reduce surface roughness for better high-speed behavior.
Applications and Cost
ED copper is commonly chosen for high-volume, cost-sensitive flexible PCBs. This is because electrodeposition can be scaled efficiently, making ED foil generally less expensive and easier to source than RA foil.
Where ED copper fits best (typical use cases):
- Static flexible PCBs (bent during assembly, then stays fixed)
- Consumer electronics interconnects (phones, laptops, camera modules)
- Flex tails and connector jumpers where long flex life is not required
ED Copper Applications
Cost reality:
When companies build millions of units, even small material savings matter. ED copper helps control cost without sacrificing basic electrical performance—so it often becomes the default choice unless the design requires heavy movement.
RA Copper in Flex Circuit Boards (Rolled Annealed Copper)
Manufacturing Process
RA copper (rolled annealed copper) is made by mechanically rolling copper thinner and thinner, then heating it (annealing) to remove stress and make it softer. This rolling + annealing cycle may be repeated several times until the foil reaches the target thickness.
A simple way to explain it:
- Rolling stretches and flattens the copper grains.
- Annealing relaxes the metal so it becomes less “springy” and more bend-friendly.
Because this method takes more steps and more energy than electrodeposition, RA copper is typically more expensive. But what you gain is mechanical durability, especially important for flexible circuits that move.
Structure, Performance, and Thickness
RA copper is known for its aligned, long grain structure (often described like fibers running in one direction). This structure is a major reason RA copper survives bending better: instead of cracks starting easily, the grain alignment helps the foil handle repeated stretching and compression during flexing.
Why RA copper performs better in dynamic flex:
In dynamic bending, copper is constantly pulled and squeezed at the bend line. Over time, this causes metal fatigue. Many flex PCB guides describe RA copper as having higher ductility and fatigue resistance, making it the safer choice for moving designs.
Thickness and design notes:
- RA copper is available in many thicknesses, but it’s often selected for reliability rather than extreme thinness.
- Designers also consider the rolling direction in RA foil. Some flex design guidance notes that trace direction relative to the copper’s grain direction can affect bend life, so manufacturers may recommend orienting critical dynamic traces thoughtfully.
Applications and Cost
RA copper is the go-to choice for dynamic flexible PCBs, where the circuit bends repeatedly during normal use. Examples include wearables, folding parts, and hinged products.
Common RA copper applications:
- Wearables (bands, sensors, health devices)
- Foldable or hinged electronics
- Robotics and moving cable assemblies
- Rigid-flex “bend zones” (the flexible section between rigid boards)
Cost and value:
RA copper costs more up front, but it can reduce expensive problems later, like:
- cracked traces,
- product returns,
- repairs,
- or failures in safety-critical devices.
So, a simple rule many engineers follow is:
- If the flex PCB moves often, RA copper is usually worth the extra cost.
ED Copper vs RA Copper: Key Differences
Thickness & Build Options
ED copper is easier to make in very thin layers. This helps create ultra-thin flexible PCBs. RA copper is usually thicker and stronger. Thicker copper makes the board harder to bend, but it can carry more current and last longer in moving designs.
Flexibility and Bending Endurance
RA copper is much better for bending many times. It can flex again and again without cracking. ED copper can crack faster if bent often. Because of this, RA copper is the better choice for moving or folding flexible PCBs.
Etching Capability
ED copper is easier to etch during PCB manufacturing. This makes it good for fine circuit patterns. RA copper can be etched too, but it may need more careful processing. This can slightly increase production difficulty and cost.
FPC Application Scenarios
ED copper is best for static flexible PCBs, where bending happens only once. RA copper is best for dynamic flexible PCBs, where bending happens many times. Choosing the right copper depends on how the PCB will be used.
Lattice Structure Comparison
ED copper has a straight, vertical grain structure. This makes it less flexible. RA copper has long, flat grains that run in one direction. These grains help stop cracks from forming during bending, which increases the PCB’s life.
Cost and Availability
ED copper is cheaper and easier to buy. It is widely used in mass production. RA copper costs more and may have longer lead times. However, its longer life makes it worth the cost in high-flex applications.
Choose MV Flex Circuit – Your Professional Flexible & Rigid-Flex PCB Manufacturer
With over 20 years of hands-on manufacturing experience, MV Flex Circuit focuses on fabricating flexible PCBs, rigid-flex PCBs, and rigid PCBs, committing to providing globally reliable Flex & Flex-rigid PCB solutions.
We maintain stock of ED and RA copper foils for immediate production deployment, efficiently meeting your rapid manufacturing needs.
Our production capabilities are suited for high-end flexible and rigid-flex PCB demands:
we can manufacture up to 8-layer flexible PCBs and 20-layer rigid-flex PCBs, with rich and proven successful project experience in wearable devices, foldable mobile phones, medical equipment, aerospace and other high-precision, high-reliability fields.
Quality is our core priority. All production processes strictly follow IPC Class 2/3 industry standards, and our factory holds complete certifications including ISO, UL, REACH, and ROHS, ensuring all products comply with global market access requirements.
Every PCB undergoes comprehensive testing. Including 100% E-test, AOI, X-ray, ICT, flying probe testing, and custom test fixture verification to rigorously control product quality and eliminate defective deliveries.
Ready to start your flexible/rigid-flex PCB project with optimized ED/RA copper foil selection?
Send your Gerber files to sales@flexiblepcbboard.com, and we will provide a free DFM check for your project evaluation, along with a detailed, transparent quotation.
FAQs About RA Copper and ED Copper
What copper thicknesses are available for flexible PCBs?
Flexible PCBs use many copper thicknesses. Common options are very thin copper for light, flexible designs and thicker copper for stronger circuits. Thinner copper bends more easily, while thicker copper can carry more electricity but is harder to bend.
Do manufacturers fabricate RA and ED copper foil?
Yes, most PCBs manufacturers have the ability to deal with RA copper, as well as ED copper. ED copper is more common and easier to source. RA copper is also widely available, but it may cost more and take longer to get.
What are the recent developments in the field of RA and ED copper foil?
New ED copper types are being made more flexible than before. These improved versions last longer during bending. At the same time, RA copper is being refined to be thinner and smoother for modern flexible and high-speed electronics.
Conclusion
Flexible PCBs are used with ED copper and RA copper though they are used in different applications. ED copper is low cost and good for static bending. RA copper is stronger and best for repeated bending. Choosing the right copper helps flexible PCBs last longer and work better.
