ED Copper Foil vs RA Copper: Which is Best for Your PCB?

Choosing the right copper foil for your PCB project isn’t just about checking a box on a spec sheet. After 15 years of designing flex circuits and rigid-flex boards, I’ve seen firsthand how picking ED copper when you needed RA copper (or vice versa) can turn a promising design into a reliability nightmare.

This guide breaks down everything you need to know about ED copper foil and RA copper—their manufacturing differences, performance characteristics, and exactly when to use each type. Whether you’re designing a static flex for LED lighting or a dynamic flex that needs to survive 100,000 bend cycles, you’ll find practical guidance here.

What is ED Copper Foil?

ED copper (electrodeposited copper) is the workhorse of the PCB industry. This type of copper foil is manufactured through an electrochemical process where copper ions are deposited onto a rotating titanium drum from a copper sulfate solution.

Here’s how the ED copper manufacturing process works:

The process starts with a copper sulfate electrolyte solution. A titanium drum rotates slowly through this solution while connected to a DC voltage source as the cathode. Copper ions in the solution are attracted to the drum surface, where they deposit as a thin, uniform layer of copper.

As the drum rotates, the newly formed ED copper foil is continuously peeled away and wound onto collection rolls. The thickness of the foil depends on the drum’s rotation speed—slower speeds produce thicker copper, while faster speeds yield thinner foils.

ED Copper Grain Structure

What makes ED copper unique is its grain structure. When you look at electrodeposited copper under a microscope, you’ll see a distinctive columnar or “pillar” crystal structure. The copper crystals grow perpendicular to the foil surface, creating long vertical grain boundaries.

This vertical grain orientation is the key factor that determines ED copper foil’s mechanical properties. The pillar-like structure makes the foil strong in compression but more susceptible to cracking when bent repeatedly. Think of it like a bundle of pencils standing upright—they’re strong when pushed down but break if you try to flex them sideways.

What is RA Copper Foil?

RA copper (rolled annealed copper) takes a completely different manufacturing approach. Instead of electrochemical deposition, RA copper starts as a thick copper ingot—typically around 20cm thick—that’s mechanically rolled and heat-treated until it reaches the desired thickness.

The rolling process works like this: Pure copper billets pass through a series of progressively tighter rollers, reducing thickness with each pass. Between rolling stages, the copper undergoes annealing (heat treatment) to relieve internal stresses and restore ductility. This roll-and-anneal cycle repeats until the foil reaches its final thickness, typically between 9μm and 105μm.

RA Copper Grain Structure

The mechanical rolling process creates a fundamentally different microstructure in RA copper. Under magnification, you’ll see flattened, elongated grains oriented parallel to the foil surface. This lamellar (layered) grain structure is what gives RA copper its superior flexibility.

When you bend RA copper foil, stress distributes evenly across the horizontal grain boundaries rather than concentrating at weak points. The result is dramatically better fatigue resistance—RA copper can extend 20% to 45% of its original length before failing, compared to just 4% to 11% for ED copper.

ED Copper vs RA Copper: Key Differences at a Glance

Understanding the fundamental differences between these two copper types will help you make better material decisions. Here’s a direct comparison:

Property	ED Copper Foil	RA Copper Foil
Manufacturing Method	Electrochemical deposition	Mechanical rolling + annealing
Grain Structure	Vertical/columnar (pillar-like)	Horizontal/lamellar (layered)
Surface Roughness (Smooth Side)	0.35-0.40 μm RMS	~0.35 μm RMS
Extensibility	4-11%	20-45%
Thickness Range	5-400 μm	9-105 μm
Relative Cost	Lower	Higher
Bend Cycle Resistance	Limited	Excellent
Signal Integrity (High-Freq)	Lower (rougher surface)	Higher (smoother surface)
Adhesion to Substrate	Strong (rough matte side)	Requires adhesive layer
Fine Line Etching	Better	Moderate

When to Choose ED Copper for Your PCB

ED copper foil isn’t just the budget option—it’s genuinely the better choice for many applications. Here’s when ED copper makes sense:

Static Flex Applications

If your flexible PCB won’t bend during normal operation, ED copper is often the right call. Static flex circuits are “bent once and stay bent”—they flex during installation but remain stationary afterward.

Common static flex applications using ED copper include:

• LED lighting strips and modules
• Battery pack connections
• Display interconnects
• Automotive tail lights
• Advertising signage
• Consumer electronics (cameras, keypads)

For these applications, ED copper’s lower cost and excellent etching characteristics outweigh its flexibility limitations.

Rigid PCBs and Multilayer Boards

The vast majority of rigid PCBs use ED copper foil, and for good reason. When the board isn’t going to flex, the columnar grain structure isn’t a liability. ED copper bonds exceptionally well to FR-4 and other rigid substrates without requiring additional adhesive layers.

For multilayer PCBs, ED copper’s consistent thickness and predictable etching behavior make it the standard choice. The rougher matte side creates strong mechanical bonds with prepreg during lamination.

Fine-Pitch and HDI Designs

Here’s something that surprises some engineers: ED copper actually etches more predictably than RA copper. The vertical grain structure allows for cleaner, more consistent trace edges when etching fine-pitch circuits.

If you’re working on HDI (High Density Interconnect) boards with tight trace/space requirements, ED copper’s etching behavior gives you tighter process control.

Cost-Sensitive Projects

Let’s be honest—budget matters. ED copper foil typically costs 20-30% less than equivalent RA copper. For high-volume production of static applications, those savings add up quickly.

Thick Copper Applications (Above 2oz)

For heavy copper applications requiring current-carrying capacity above 2oz (70μm), ED copper is often the only practical choice. The electrodeposition process can produce much thicker foils than rolling, and the adhesive-free construction keeps overall stack-up thickness manageable.

When to Choose RA Copper for Your PCB

RA copper costs more for a reason—when you need dynamic flexibility, nothing else will do. Here’s when RA copper is worth the premium:

Dynamic Flex Circuits

If your flex PCB needs to bend repeatedly during operation, RA copper is non-negotiable. The horizontal grain structure distributes bending stress across the material rather than concentrating it at grain boundaries.

Dynamic flex applications requiring RA copper include:

• Laptop hinges and display connections
• Smartphone fold mechanisms
• Wearable device straps
• Robotic arm joints
• Medical devices with moving components
• Printer head assemblies
• Automotive steering column connections

For applications requiring thousands or millions of bend cycles, RA copper prevents the fatigue cracking that would quickly destroy an ED copper circuit.

Rigid-Flex PCB Designs

In rigid-flex boards, the flexible sections must use RA copper—no exceptions. These transition zones experience repeated stress during handling and operation. Using ED copper in a rigid-flex design is a common mistake that leads to field failures.

The rigid sections can use either copper type, so some designers spec RA copper throughout for simplicity. Others use ED copper in rigid sections to save cost, accepting the added complexity of mixed material handling during fabrication.

High-Frequency and RF Applications

This is where things get technically interesting. Copper surface roughness directly impacts signal loss at high frequencies. At microwave and millimeter-wave frequencies (above 10 GHz), even small differences in surface roughness translate to measurable insertion loss.

RA copper’s smoother surface provides 10-20% lower signal degradation compared to standard ED copper at frequencies above 10 GHz. For 5G infrastructure, radar systems, and high-speed digital applications, this performance gap matters.

If you’re designing for high-frequency applications but need to use ED copper for other reasons, look into low-profile ED copper variants (sometimes called VLP or HVLP copper) that undergo additional surface treatment to reduce roughness.

Thermal Cycling Environments

Here’s a less obvious application: RA copper handles thermal shock better than ED copper. During rapid temperature changes, the horizontal grain structure accommodates thermal expansion stress more evenly.

PCBs in automotive under-hood applications, industrial equipment, and aerospace systems benefit from RA copper’s thermal cycling resilience. ED copper in narrow traces can develop thermal stress cracks under repeated heating/cooling cycles.

ED Copper Foil Applications Beyond PCBs

It’s worth noting that ED copper foil has become critically important outside the traditional PCB industry. The lithium-ion battery market now consumes enormous quantities of ED copper as the current collector for battery anodes.

ED copper’s characteristics make it ideal for battery applications:

• High purity (99.8%+) ensures consistent electrochemical performance
• Uniform thickness from the electrodeposition process
• Can be manufactured extremely thin (down to 4-6μm) for high energy density cells
• Lower cost than RA copper for high-volume battery production

With electric vehicle production ramping up globally, ED copper foil demand from the battery industry now rivals demand from PCB manufacturing. This has occasionally created supply chain tensions that PCB designers should keep in mind for long-term projects.

ED Copper Foil Thickness Options and Specifications

Understanding available thickness options helps you optimize your design. ED copper foil offers the widest thickness range of any copper type, from ultra-thin battery-grade foils to heavy copper for power applications.

Standard ED Copper Thickness Chart

Copper Weight	Thickness (μm)	Thickness (mils)	Typical Application
1/4 oz	8.5	0.33	Ultra-fine pitch, HDI
3/8 oz	12	0.47	High-density digital
1/2 oz	18	0.71	Standard digital circuits
1 oz	35	1.38	General purpose, most common
2 oz	70	2.76	Power circuits, thermal management
3 oz	105	4.13	High current, heavy copper
4+ oz	140+	5.5+	Extreme power, bus bars

For flexible PCBs, common ED copper thicknesses are 12μm, 15μm, 25μm, and 35μm. Thinner copper provides better flexibility even with ED copper’s inherent brittleness, but limits current-carrying capacity.

RA Copper Thickness Limitations

RA copper’s rolling process limits its practical thickness range to approximately 9μm to 105μm. Achieving thinner foils becomes increasingly difficult and expensive due to the mechanical rolling constraints. For ultra-thin applications below 9μm, ED copper is typically the only option.

Cost Comparison: ED Copper vs RA Copper Economics

Let’s talk real numbers. Material cost significantly impacts total PCB pricing, especially for flexible circuits where copper represents a larger percentage of material cost.

Relative Pricing Factors

ED copper foil costs roughly 20-35% less than equivalent RA copper, though exact pricing varies by:

• Foil thickness (thinner = more expensive per unit area)
• Volume purchased
• Surface treatment grade
• Market conditions (copper commodity pricing)

For a typical 1oz flexible circuit, the copper material cost difference between ED and RA might be $0.50-$2.00 per square foot. On a large production run, this adds up quickly.

Total Cost Considerations

However, material cost isn’t the whole story. Consider these factors:

Assembly and handling: RA copper’s flexibility can make it easier to handle during assembly, potentially reducing labor costs and defects.

Yield rates: Using ED copper in an inappropriate dynamic flex application leads to field failures and warranty costs that dwarf any material savings.

Reliability testing: If you’re uncertain about copper selection, reliability testing (bend testing, thermal cycling) adds development cost but prevents expensive failures.

Adhesive requirements: RA copper flexible circuits typically require adhesive bonding to the substrate, adding both material cost and processing steps. ED copper can bond directly to many substrates.

The lowest-cost copper isn’t always the most economical choice when you factor in total lifecycle costs.

Surface Roughness and Its Impact on Performance

Surface roughness deserves deeper discussion because it affects multiple aspects of PCB performance.

The Roughness Trade-Off

The matte (rough) side of ED copper foil typically has higher surface roughness than RA copper. This roughness serves a purpose—it creates mechanical interlocking with the dielectric substrate, improving peel strength.

However, roughness increases conductor loss in two ways:

1. Skin effect: At high frequencies, current flows primarily on the conductor surface. A rougher surface means electrons travel a longer path, increasing resistance.
2. Dielectric loss: Surface roughness affects the copper-dielectric interface, potentially increasing dielectric loss.

Roughness Specifications

ED copper foil comes in several roughness grades:

ED Copper Type	Typical Roughness (Rz)	Best For
Standard ED	4-8 μm	General purpose, good adhesion
RTF (Reverse Treated Foil)	2-4 μm	Balance of adhesion and signal integrity
VLP (Very Low Profile)	1-2 μm	High-frequency applications
HVLP (Hyper Very Low Profile)	0.5-1 μm	Millimeter-wave, highest performance

For most applications below 5 GHz, standard ED copper works fine. Above 10 GHz, consider VLP or HVLP variants to minimize insertion loss.

Making the Right Choice: A Decision Framework

After all this detail, here’s a practical decision framework:

Choose ED Copper Foil when:

• The flex circuit won’t bend during operation (static flex)
• You’re designing rigid PCBs
• Cost is a primary concern
• You need copper thicker than 2oz
• Fine-pitch etching is critical
• Operating frequency is below 5 GHz

Choose RA Copper when:

• The circuit must survive repeated bending (dynamic flex)
• You’re designing rigid-flex boards (for flex sections)
• High-frequency performance above 10 GHz is required
• Thermal cycling reliability is critical
• Maximum bend cycle life is needed

Consider low-profile ED copper (VLP/HVLP) when:

• You need ED copper’s cost and etching advantages
• But also need improved high-frequency performance
• Standard ED roughness would compromise signal integrity

Common Mistakes to Avoid

Based on real-world failures I’ve investigated, here are mistakes to avoid:

1. Using ED copper in dynamic flex sections: This is the most common and most costly mistake. Even a few thousand bend cycles will crack ED copper traces.
2. Specifying RA copper when ED would work fine: Unnecessary cost increase. If your flex is truly static, save the budget for other improvements.
3. Ignoring copper type in rigid-flex transitions: The flex zones in rigid-flex boards need RA copper regardless of what you use in the rigid sections.
4. Overlooking roughness for high-frequency designs: Standard ED copper above 10 GHz leaves performance on the table.
5. Not communicating copper type to your fabricator: Make your copper spec explicit. “Flexible PCB” doesn’t automatically mean RA copper to every fab house.

Testing and Qualification for Copper Foil Selection

Before committing to production, validate your copper selection through appropriate testing. Here’s what to consider:

Bend Testing for Flexible Circuits

IPC-TM-650 provides standard test methods for flex circuit reliability. Key tests include:

MIT Fold Endurance Test: Measures how many 180° fold cycles a flex circuit can withstand before conductor failure. RA copper typically survives 10-100x more cycles than ED copper in this test.

Mandrel Bend Test: Wraps the flex circuit around cylinders of decreasing diameter to determine minimum bend radius before damage occurs.

For dynamic flex applications, require your supplier to provide bend test data or conduct your own qualification testing before production release.

Thermal Cycling Qualification

For applications exposed to temperature extremes, thermal shock testing reveals copper type suitability:

• Standard test: -40°C to +125°C, 1000 cycles minimum
• Automotive qualification: -55°C to +150°C per AEC-Q100 or similar
• Aerospace: Per MIL-STD requirements

RA copper’s horizontal grain structure generally provides better thermal cycling performance, particularly for narrow traces susceptible to stress concentration.

Peel Strength Testing

Verify that your copper adheres adequately to the substrate material. IPC standards specify minimum peel strength requirements (typically 1.0-1.5 lb/inch for flexible circuits). ED copper’s rougher matte side generally provides higher initial peel strength, but RA copper with appropriate adhesive systems also meets requirements.

Industry Trends Affecting ED Copper and RA Copper

The copper foil market is evolving rapidly. Understanding these trends helps you make forward-looking material decisions:

Electric Vehicle Impact

EV battery production has dramatically increased ED copper demand. Battery-grade ED copper foils (4-8μm thickness) now represent a significant portion of global ED copper production. This has occasionally created supply constraints for PCB-grade foils, so consider supply chain resilience for long-term projects.

5G and High-Frequency Applications

The rollout of 5G infrastructure has accelerated demand for low-profile copper foils. More PCB designs now require VLP or HVLP copper to meet signal integrity requirements at millimeter-wave frequencies. Expect copper roughness specifications to become standard design parameters rather than afterthoughts.

Miniaturization Trends

As devices shrink and trace widths narrow, copper selection becomes more critical. Fine-pitch designs under 50μm trace/space are more sensitive to copper grain structure effects. The industry is developing modified ED coppers with improved characteristics for ultra-fine-line applications.

Useful Resources for PCB Copper Foil Selection

Here are some valuable resources for deeper technical information:

Technical Specifications and Standards:

• IPC-4562: Metal Foil for Printed Wiring Applications (industry standard for copper foil specifications)
• IPC-2223: Sectional Design Standard for Flexible Printed Boards

Manufacturer Technical Resources:

• Rogers Corporation: Copper Foils for High Frequency Materials (whitepaper) — Available at rogerscorp.com
• Isola Group: High-Speed Digital and RF Material Selection Guides
• DuPont: Pyralux Flexible Circuit Materials Data Sheets

Industry Organizations:

• IPC (Association Connecting Electronics Industries): ipc.org
• FPC Consortium: Resources for flexible circuit design

Online Calculators:

• Saturn PCB Design Toolkit: Trace width, impedance, and thermal calculations
• JLCPCB Impedance Calculator: Quick online impedance modeling

Frequently Asked Questions About ED Copper and RA Copper

Can I use ED copper for any flexible PCB?

You can use ED copper for static flex applications where the circuit bends during installation but stays fixed during operation. However, for dynamic flex applications requiring repeated bending, RA copper is essential. Using ED copper in a dynamic flex application will result in trace cracking and premature failure.

Why is RA copper more expensive than ED copper?

RA copper costs more due to its complex manufacturing process. Creating thin foil by repeatedly rolling and annealing a copper ingot requires more equipment, energy, and processing time than electrodeposition. The material waste is also higher in rolling processes. Expect RA copper to cost 20-40% more than equivalent ED copper.

What copper type should I use for rigid-flex PCBs?

For rigid-flex boards, use RA copper in all flexible sections without exception. The rigid sections can use either ED or RA copper. Many designers standardize on RA throughout for simplicity, while others use ED copper in rigid areas to reduce cost. Always communicate your requirements clearly to your PCB fabricator.

Does copper type affect impedance control?

Yes, copper surface roughness impacts impedance, particularly at high frequencies. Rougher copper (standard ED) increases effective conductor loss and can affect impedance consistency. For controlled impedance applications above 5 GHz, consider low-profile ED copper (VLP/HVLP) or RA copper to improve predictability.

How do I specify copper type on my PCB fabrication drawing?

Include the copper type in your fabrication notes and stackup documentation. Specify “ED copper” or “RA copper” for each layer explicitly. For flexible sections, note whether the application is static or dynamic flex. If you need specific roughness grades (STD, RTF, VLP, HVLP), include those specifications as well.

Conclusion: Matching Copper to Your Application

The ED copper vs RA copper decision ultimately comes down to understanding your application’s mechanical and electrical requirements. ED copper foil offers lower cost, excellent adhesion, and predictable etching—making it ideal for rigid boards and static flex circuits. RA copper delivers superior flexibility and high-frequency performance for dynamic flex applications and demanding RF designs.

Don’t default to one type out of habit. Evaluate each project individually, considering bend requirements, frequency range, thermal environment, and budget constraints. The right copper choice prevents field failures and optimizes both performance and cost.

When in doubt, consult with your PCB fabricator early in the design process. Experienced flex circuit manufacturers can provide application-specific guidance and help you avoid costly material mismatches.