What Are the Materials Used in Flexible Circuit Boards

Introduction to Flexible Circuit Boards (FPC)

What is a Flexible Circuit Board?

FPC (Flexible Printed Circuit) is a board made of a flexible insulating substrate. Flexible circuit boards can provide good electrical performance and have the characteristics of high assembly density, lightweight, and minimal thickness. These properties make them ideal for compact electronic applications. They are mainly used in mobile phones, notebook computers, PAD, digital cameras, LCM, and aerospace products. The flexibility of these circuits allows them to bend and conform to complex shapes, making them indispensable in modern electronics design.

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Classification of FPC - What are the types of flexible electronics?

According to the combination of base material and copper foil, FPC can be divided into:

1. Adhesive Flexible Circuit Board: It means that the copper foil and the substrate are glued together by glue, which is also a standard flexible printed circuit board we use.

2. Non-adhesive Flexible Circuit Board: The combination method differs between adhesive and non-adhesive flexible boards. In non-adhesives flex PCB boards, hot press the copper foil and the substrate together. In comparison, its flexibility, The bonding strength of copper foil and substrate, the flatness of the pad, and other parameters are better than the flexible PCB with glue.

According to the structure, FPC can be divided into:

· Single-layer flexible circuit board: This is the simple structure of a flexible PCB. Usually, its raw materials include a substrate, transparent glue, copper foil, protective film(Cover lay), etc.

· Double-sided Flexible Circuit Board: There are pads on both sides of the double-sided flexible circuit board, mainly used for connection with other circuit boards.

· Double-layer Flexible Circuit Board: When the circuit is too complicateda double-layer or even multilayer circuit board is needed.

· Multilayer Flexible Circuit Board: The most typical difference between a multilayer PCB and a single-layer PCB is the addition of a via structure to connect each layer of copper foil.

Features of FPC Products - What are the advantages of flexible circuits?

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1) It can be bent freely, folded, and wounded and can be moved and stretched freely in a three-dimensional space. This makes them suitable for dynamic applications like wearable devices or foldable displays.

2) It has good heat dissipation performance, and FPC can be used to reduce the product volume. This characteristic enhances reliability by preventing overheating in compact devices.

3) Offers lightweight, miniaturization, and thinness. For component devices, it is integrated with wires and plays a pivotal role in electronic products.

Manufacturing materials for flexible circuit boards - How to make a flexible PCB?

The construction of flexible circuit boards relies on several key materials:

Copper Foil

Copper foil is a conductive layer that covers and adheres to an insulating substrate and forms conductive lines through subsequent selective etching. There are two types:

· Rolled copper foil is made by repeatedly rolling a copper plateThe elongation rate of rolled copper foil is 20% — 45%

· The electrolytic copper foil is continuously produced on the circular cathode drumits elongation rate is 4% — 40%.

The standard thickness of the copper foil is 0.5oz (18um), 1.0oz (35um), and 2.0oz (70um).

Insulating Substrate

The insulating substrate for flexible PCB is a flexible insulating filmAt present, insulating materials for flexible electronics manufacturing are divided into PI(Polyimide) Film, PET(Polyester) Film

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PI (Polyimide): PI has high-temperature resistance characteristicsIt is the most commonly used material for FPC manufacturing

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PET (Polyester): If used under conditions that do not require high-temperature resistancethe polyester film has moisture absorption and dimensional stability better than PI.

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PTFE: PTFE has excellent comprehensive propertiesIt is mainly used in the manufacture of flexible copper clad laminates to use its excellent dielectric properties.

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Adhesives

The role of adhesive is to bond film and metal foilUsually, adhesives have two types: Acrylic and Epoxy

· Acrylic: Excellent heat resistance but relatively lower electrical performance.

· Epoxy: Balanced properties but requires stricter pressing conditions.

Cover Lay (Protective Film)

The cover layer is an insulating protective layer covering the surface of the flexible circuit board It enhances mechanical strength while protecting conductors from environmental damage.

There are dry film types using polyimide as well as photosensitive development types suitable for fine-pitch assemblies.

Reinforcing Materials (Stiffeners)

Reinforcing material is a hard material added to a local areato strengthen component area and facilitate installation. These include:

· FR4: Glass-reinforced epoxy laminate.

· PI/PET: Polyimide or polyester films.

· Aluminum/Steel Sheets: Provide additional mechanical support or heat dissipation.

Flexible circuit boards that need reflow during assembly need to use PI/FR4/Aluminum/Stainless steel

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For businesses looking to integrate reliable yet sophisticated electronics into their products quickly and efficiently, PCBAStore offers comprehensive solutions. From prototyping to mass production runs involving complex multilayer FPCs or high-density interconnects (HDIs), PCBAStore delivers precision-engineered results tailored to your specifications.

As the most popular PCB manufacturing and assembly company based in China ,we have been offering full spec electronic manufacturing solutions for 16 . From PCB design, layout to PCB prototyping, mass fabrication and then to
PCB assembly, electronics box-build assembly services, our Printed circuit boards are widely built into robotics, medical, automobile, communication, industry and consumer electronics.We deal in the followings: Flex PCB, custom PCB, prototype PCB, turnkey PCB assembly, electronic PCB assembly, low volume PCB assembly etc.

Request your quote today at PCBAStore for custom-designed flexible circuit boards built with industry-leading materials that meet stringent quality standards.

FAQ:

1. What are the primary base materials for FPCBs?

Polyimide (PI): Offers excellent flexibility, thermal stability, and electrical insulation. Commonly used in high-performance applications.

Polyester (PET): Provides good flexibility and is cost-effective, suitable for less demanding applications.

2. What metals are used for conductive traces?

Copper (Cu): Most commonly used due to its excellent electrical conductivity.

Gold (Au): Used in high-reliability applications for its corrosion resistance.

Silver (Ag): Offers high conductivity but is less commonly used due to cost and oxidation concerns.

3. What are coverlay materials?

Polyimide-based coverlays: Provide insulation and protection for the conductive traces.

4. Are there any advanced materials used in FPCBs?

Carbon Nanotube (CNT) composites: Enhance thermal conductivity and mechanical strength.

Anisotropic Conductive Films (ACF): Used for connecting components in displays and other applications.