ED Copper vs. RA Copper in Flex PCBs

In the development of flexible printed circuit boards, the selection of copper foil type ED or RA is a fundamental technical decision. It directly affects mechanical performance, reliability, manufacturability, and cost. This article helps procurement professionals and design engineers understand the essential differences between these copper types to guide optimal material selection.

What is ED Copper?

Electro-deposited (ED) copper is produced through an electrochemical plating process. Copper ions in an electrolyte solution are deposited onto a rotating drum, forming a thin foil that is later stripped and treated. The process yields a columnar, directional grain structure with relatively low ductility. ED copper is widely used due to its low cost and high-volume production efficiency.

What is RA Copper?

Rolled Annealed (RA) copper is created by mechanically rolling a copper ingot into thin foil and then heat-treating it (annealing) to increase ductility. The result is a smooth-surfaced foil with an equiaxed (uniform) grain structure and excellent mechanical flexibility. RA copper is well-suited to applications requiring repeated bending or dynamic flexing.

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Manufacturing Process

The manufacturing processes for ED and RA copper result in significantly different material properties:

ED Copper: Formed by electroplating copper onto a drum. The grain structure is vertical (columnar), and the foil tends to be stiffer and more brittle. Surface treatments can improve adhesion to dielectrics but do not overcome mechanical limitations. For example, standard ED copper foil typically withstands fewer than 1,000 flex cycles at a bend radius of 5 mm before cracking, making it suitable mainly for static applications.

RA Copper: Produced through rolling and thermal annealing, which compresses the grains and enhances flexibility. The annealing step is critical in reducing internal stress and achieving a ductile microstructure capable of withstanding mechanical deformation. In contrast, RA copper can survive over 1,000,000 flex cycles at the same 5 mm bend radius, due to its ductile grain structure and higher elongation, making it ideal for dynamic flex applications.

RA Copper Vs. ED Copper

Below is a side-by-side comparison of key attributes:

Aspect	ED Copper	RA Copper
Manufacturing Method	Electroplated on drum	Rolled and thermally annealed
Grain Structure	Columnar, anisotropic	Fine-grained, equiaxed
Flexibility	Low, prone to cracking	High, excellent bend endurance
Fatigue Resistance	Limited (static bend only)	High (dynamic flex capable)
Surface Texture	Rougher, often treated for adhesion	Smoother, naturally ductile
Cost	Lower	Higher
Use Cases	Static flex, cost-sensitive designs	Dynamic flex, mission-critical systems
Electrical Conductivity	~5.8×10⁷ S/m	~5.8×10⁷ S/m

While both offer similar electrical performance, mechanical reliability is the key differentiator. RA copper’s elongation can reach 20–30%, while ED copper typically achieves only 10–15%.

Cost Considerations

Cost is a major factor in large-scale flex PCB production. ED copper benefits from:

• Simpler, scalable manufacturing

• Lower raw material and energy costs

• Widespread availability

RA copper, although more expensive, offers value in applications where failures from cracking or fatigue could lead to higher downstream costs, such as repairs, returns, or safety issues. When reliability outweighs cost, RA copper is the better investment.

Typical Application Scenarios

Application	Preferred Copper Type	Rationale
Static flex cables and connectors	ED Copper	Limited mechanical motion; cost is a priority
Foldable smartphones and displays	RA Copper	High dynamic flex reliability
Wearable electronics	RA Copper	Continuous movement and user contact
Automotive sensors and ECUs	RA Copper	Vibration resistance and thermal cycling required
Consumer electronics (low motion)	ED Copper	Budget-focused designs with minimal flexing
Medical catheters and implants	RA Copper	Reliability and bio-compatibility critical

For hybrid applications, some multilayer flex PCB designs may strategically use both copper types—RA copper in outer dynamic layers, and ED copper in inner, static layers—to balance cost and performance.

Conclusion

The choice between ED Copper vs RA Copper in flex PCB design is more than a cost-versus-performance decision—it’s a matter of application suitability. ED copper is a strong candidate for static, cost-driven designs. In contrast, RA copper’s superior mechanical resilience makes it the go-to solution for dynamic flexing and reliability-critical systems.

By aligning copper selection with the mechanical demands of the end application and involving PCB fabricators early in the design process, engineering and procurement teams can reduce risk, extend product life, and ensure both performance and cost objectives are met.