Introduction
Flexible circuit boards (FPC) are employed in a number of movable devices. For example, cars, smartphones, and so on. FPC is known to save space as well as the weight of the devices. The role of FPC materials is very important. The right materials support easy bending and functionality. Low-quality materials usually affect the performance of the board and result in cracking. Here is an introduction to FPC materials to help you learn well-known.
What Is an FPC?
FPC full form flexible printed circuit board. These are also known as flexible circuits. It is a type of printed circuit board that is thin and can easily bend and twist. FPCs use a flexible film as a base, making them different from traditional boards. This film made the board bend and fit into the small spaces.
The substrate of an FPC is usually polyimide (PI) or polyester (PET). That way, FPC supports the manufacturing of compact and wearable devices. Many industries use these types of flexible circuits.
For example, these circuits are applied in smartphones to connect small parts. Movable medical tools also use it because it is light and thin.
How is FPC Different from Rigid PCB?
A hard base material is utilized in a rigid PCB. Most of the time, that base is FR4. It is not easy to flex a rigid circuit board.
On the other hand, an FPC uses a soft base and protective film. Due to this film, it is easy to bend, roll, or curve when required. Rigid boards are used in fixed designs. FPC fits moving or tight designs. So, the main difference is flexibility.
Structure of an FPC
An FPC has a simple layered structure, with each layer performing a particular job.
- Base film like PI or PET
- Copper foil layer
- Adhesive layer in some designs
- Coverlay film
- Stiffener in specific areas
For the base layer, manufacturers usually use polyimide or polyester. On top of this layer, a copper foil is laminated to create traces.
Based on the JIS C5017 standards, single sided and double sided boards use copper foil on PET or PI substrate. In single sided boards, traces are only used on one side. While in double sided boards, you will see copper traces on both sides.
In some cases, manufacturers use the FPC On Board process. Using SMT reflow soldering in FOB, soft and hard boards are bonded together.
Types of FPC Materials Used
Core Base Materials Used in FPC
The base material forms the main body of an FPC. It provides the board with its flexibility and shape. Most FPC boards use two base films. These are Polyimide and Polyester.
Polyimide, or PI, is the most used base film. PI provides good heat resistance and also keeps a stable electrical performance. They are also easily bendable without being damaged.
Polyester, or PET, costs less than PI. It works well in simple designs. It fits products that do not face high heat. However, PET does not resist heat like PI. So, manufacturers usually use PET in low-temperature applications.
Conductive Materials in FPC
FPC conductive layer is made up of copper foil. It transmits electrical signals. The copper is laminated on the base film by the manufacturers in order to form circuit lines.
FPC uses two main copper types, rolled annealed copper and electrodeposited copper.
Rolled annealed copper is easy to bend. It handles repeated bending well. Thus, it is suitable for moving or flexing areas.
Electrodeposited copper costs less. It is effective when not much bending is needed. However, it does not handle repeated bending like rolled annealed copper does.
Adhesive and Non Adhesive Materials
Some flexible circuit boards utilize adhesive layers. Bonding copper is done on these layers to the base film. Thus, the layers remain intact. In order to form a bond, adhesive is applied between the base film and the copper layers.
Additionally, there are some non-adhesive flexible circuits. In this type of board, copper is bonded with the base film. In between, no layer of adhesive is included. This makes the board thinner and more thermally-stable, although it may be expensive.
Dielectric and Insulation Materials
Good dielectric materials can withstand heat and maintain stable electrical performance. Flexible boards often use dielectric materials like polyimide for insulation. Some designs can also utilize polyester. They act as a protective layer and prevent the board from short circuits. Also, they stop unwanted electrical flows.
Coverlay and Protective Materials
A protective film that is laminated over copper traces is called Coverlay. It insulates the surface of the circuit against dust and moisture. Normally, polyimide film with adhesive is applied by many manufacturers. This type of coverlay material retains its flexibility and guards the circuit.
Stiffeners and Reinforcement Materials
In flexible PCBs connector and component areas need support. So, manufacturers add stiffeners. Moreover, stiffeners are usually placed under connectors and components.
Common stiffener materials include:
- Polyimide
- FR4
- Stainless steel
Each one adds support to the board.
Factors to Consider When Choosing FPC Materials
When choosing materials for your flexible PCBs, consider these factors.
- Bending abilities. Rolled annealed copper supports repeated bending.
- Heat tolerance. Polyimide tolerates heat more.
- Signal stability. Choose a good dielectric material for stable signal transfer.
- Thickness. Go adhesiveless if a thin board is needed.
- Cost. Prefer reliability but consider budget as well.
Our Professional FPC Manufacturing Services
As a professional FPC & rigid-flex PCB manufacturer with over 20 years of practical production experience, MV Flex Circuit specialize in delivering high-quality flexible circuits built for performance and reliability.
We support up to 8 layers for flexible PCBs and 20 layers for rigid-flex PCBs, with full stiffener capabilities to handle even your most complex circuit designs.
We stock a wide range of premium FPC materials, including PI, PET, rolled annealed copper, and specialized laminates, helping you lower material costs and speed up production lead times.
All our products are manufactured in strict compliance with IPC Class 2 & Class 3 standards, and our factory holds ISO, UL, REACH, and RoHS certifications to meet global market access requirements.
Every board undergoes rigorous quality testing, including 100% E-test, AOI, X-ray inspection, ICT, flying probe test, and dedicated test fixture verification to ensure the quality.
If you have an FPC project, send your Gerber files and BOM to us today. Our expert engineering team will provide a free DFM check and deliver a detailed, competitive quote for your project.
Conclusion
The performance of a flexible circuit is determined by the FPC materials. Smart material choice results in improved performance and improves the lifespan of products. Flexibility is offered by the base film, which is usually of PI or PET. Copper over the base carries signals while adhesive bonds layers. For copper roll, annealed is preferred as it can be bent repeatedly. Also, stiffeners are used to add support to components.
