What are the different types of copper used in PCBs? What is Electro Deposited (ED) Copper and how is it different from Rolled Annealed (RA) copper?
Editorial Team - PCB Directory
Jul 17, 2022
Copper is an essential material that is used as the conducting layer in Printed Circuit Boards. Layers of copper are added to a PCB and traces are etched on them to form parts through which electrical signals can flow. The two most common types of copper used in PCBs are Electro Deposited (ED) copper and Rolled Annealed (RA) copper.
What is Electro Deposited (ED) Copper?
Electro Deposited (ED) copper is a lightweight material used in most low-cost PCBs where flexibility is not an essential parameter. They are the primary choice of copper material for manufacturing rigid printed circuit boards. ED copper is manufactured by depositing copper foil using the electrolysis method. Electricity is passed through solutions containing copper compounds through cathode and anode. The copper from the anode gets oxidized and pure copper metal gets collected on the cathode. This pure copper from the cathode is then placed onto a rolling cylindrical metallic rod to form a thin layer of copper foil. This Thin layer of copper is brittle and has a rough surface which makes it rigid. Moreover, the rough surface of ED copper also causes a relatively high insertion loss when compared with RA copper, irrespective, this type of copper is optimal enough to be used in low frequency/ small scale applications. ED copper is most often used in rigid PCB boards. However, ED Copper foil can extend from 4% to 11%, making it useful for small scale Flexible PCB applications such as wearable displays, car taillights, and phototherapy.
What is Rolled Annealed (RA) Copper?
Rolled Annealed (RA) copper foil is made by subjecting a copper strip through a rolling mill until it reaches its desired thickness. RA copper has a smoother surface which makes them ideal for use in flexible circuitry. The smoothness of the surface will cause low insertion loss of high-frequency signals. Insertion loss is kept to a minimum, to obtain the best performance.
RA Copper or Rolled Annealed copper is a popular choice for rigid-flex PCBs, flex circuit manufacturing, and bendable boards. RA Copper foil has excellent extensibility/flexibility up to 20% to 45% making it ideal for flexible PCBs. However, they are considerably more expensive than ED Copper.
Image Source: Best Technology
As seen in the figure above, an ED copper foil has a vertical grain structure and the RA Copper foil has a horizontal grain structure. When subjected to high temperatures, the ED copper foil continues to have a rough surface while a smoother surface can be observed for RA Copper foil.
ED Copper vs RA Copper
RA Copper is a popular choice for rigid-flex PCBs, flex circuit manufacturing, and bendable boards. They are primarily used for more complex heavier applications that require high current and flexibility like flip phones, radar systems, and medical electronic devices.
ED copper is a lightweight material used in the manufacture of low-cost PCBs where flexibility is not an essential parameter. They are the primary choice of copper material for manufacturing cell phones and digital cameras.
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