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RA Copper VS ED Copper: Which Copper Foil for Flex PCB Substrate?

PCBONLINE Team

Wed, Jul 13, 2022

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Flexible PCB materials include copper, adhesive, and polyimide (PI) or pester (PET). For copper used for flexible PCBs (FPC), both rolled & annealed copper (RA copper) and electro deposit copper (ED copper) can be used as the substrate material.

The copper foil is used as the flexible PCB substrate and circuit layers. The copper type decides the flexibility of the FPC and is an important factor affecting the PCB price. Which copper do you choose as the substrate material of your flexible PCB?

flex PCB copper foil

Part 1. RA Copper for Flexible PCB

RA copper is used for flexible PCBs that bend repeatedly in use. The flex section of rigid-flex PCBs must use RA copper.

RA copper foil

The applications of flexible PCBs using rolled copper include slider phone boards, foldable phone boards, artificial satellites, new-energy cars, radar systems, medical electronic devices, aerospace industrial controllers, etc.

Rolled & annealed copper (RA copper) is made from a copper ingot with a thickness of about 20cm. The copper ingot is rolled and annealed repeatedly until its reaches the copper thickness that the flexible PCB wants.

Under a 1000x microscope, you can find the cross-section of RA copper foil has a layered crystal structure.

RA copper lattice structure

RA copper foil has excellent extensibility. It can extend 20% to 45% of its original length. However, RA copper has a rough surface, which makes circuit etching not very fine.

Price of RA copper foil for flexible PCBs: high (if the copper thickness is smaller than 0.5oz, such as 1/3oz, the thinner, the more expensive)

Part 2. ED Copper for Flexible PCB

ED copper is used for flexible PCBs that work in a static state.

ED copper foil

The applications of flexible PCBs using ED copper include lighting, wearable devices, displays, car taillights, advertising logos, phototherapy and beauty, and lighting filling.

Electro deposit copper (ED copper) foil is made by electroplating acid copper plating solution on stainless steel to precipitate a uniform copper film. By continuous peeling and winding, we get ED copper foil.

Under a 1000x microscope, you can find the cross-section of ED copper foil has a pillar crystal structure.

ED copper luttice structure

The extensibility of ED copper foil is 3 times less than that of RA copper foil. Shortly, ED copper foil can extend 4% to 11% of its original length. But ED copper foil has a fine surface, which is very helpful to etch fine circuit traces. Besides, the PCB pads after surface finishes are flat.

Now the manufacturing technology for ED copper is getting more advanced. ED copper foil can have better extensibility by thermal treatments. Though its lattice structure is still pillars, the ED copper has a layered copper atomic arrangement.

Price of ED copper foil for flexible PCBs: regular (the thicker, the more expensive)

Part 3. RA Copper vs ED Copper

After PCB assembly, we will connect the PCB assembly with a computer and transfer the program to the IC.

Now you've learned RA copper and ED copper for flexible PCB substrate. Which type of copper foil do you choose for flexible PCB fabrication? Please check the differences between RA copper and ED copper below.

RA copper
ED copper
Crystallization

RA copper sketch

ED copper

Bending endurance
High
Low
Etching
Need special treatment
Easy
FPC application
Flex PCBs that need frequent bending, including rigid-flex PCBs
Flex PCBs that work in a static state
Lattice structure
Pillar
Layered
Price
Three times higher than ED copper
Middle

The copper foil is just part of the flexible PCB price. And you should choose the copper type according to your application and fabrication requirements. It's suggested that in the PCB design stage, you fully communicate with your PCB fabricator to settle down all the details, including copper specs.

Part 4. One-Stop Flexible Laminate and PCB Manufacturer

So which flexible PCB fabricator do you choose? PCBONLINE is a one-stop flexible PCB manufacturer that fabricates the FPC laminates, finished flex PCBs, and FPC assemblies. You can custom order flexible PCBs using RA copper or ED copper without a quantity limit.

From the video below, you can check how we fabricate flexible PCB laminates and finished circuit boards from RA copper/ED copper, adhesive, and PI.

Here are reasons to have flexible PCB manufactured from PCBONLINE:

  • PCBONLINE provides one-stop flexible PCB manufacturing, and you can save time and budget with our one-stop services.
  • Strong fabrication capabilities to meet your custom requirements: laminates with or without adhesive, FPC using transparent PET, minimum finished FPC width 2.36mm, minimum trace width/space 0.1mm/0.1mm...
  • Free flexible PCB design assistance and professional one-on-one engineering support throughout your project.
  • Fabricate flexible PCBs using RA copper, ED copper, and high-extensibility ED copper.

If you are in the flexible PCB design stage or looking for a flex PCB/PCBA fabricator, you can send your Gerber and contact PCBONLINE by email at info@pcbonline.com to communicate with us about your project.


Frequently asked questions about RA copper and ED copper

Question 1
What is the copper thickness of flexible PCBs from PCBONLINE?

Answer 1: From PCBONLINE, the thicknesses of RA and ED copper can be 12μm, 18μm, 35μm, and 70μm.

Question 2
Do you fabricate RA and ED copper foil?

Answer 2: No, we don't fabricate copper foil but we can use copper foil, adhesive, and PI/PET to fabricate custom laminates of flexible PCBs. If you need RA/ED copper foil, we can provide it from our stock.

Question 3
What is the trend of RA and ED copper foil?

Answer 3: As flexible electronic products get smaller and require higher reliability, now new RA and ED copper types emerge: high-flexibility RA copper (with 7 times the flexibility of regular RA copper), 9μm ultra-thin ED copper for ultra-fine circuits, and RA alloy copper (better thermal stability and mechanical performance than regular RA copper).


© This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.

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