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If you need a manufacturer who can manufacture flexible PCBs for you, you should make it clear that this PCB Manufacturer should have a mature and current process flow for manufacturing flexible circuit boards. Considering factors such as manufacturing cost, we suggest that you choose a Chinese FLEX PCB manufacturer. Because, at present, the PCB Manufacturing industry is basically concentrated in China. It is not only because China’s manufacturing industry is very developed, but also because it has a very mature production process and can effectively reduce the cost of manufacturing products for you. To visit our factory, please click here.

Everything You Must Know About Flexible PCB

What Are Flexible Circuit Boards ?

Flexible PCB Definition, and For a new product to be better applied, we need to understand exactly what it means and everything about it.

Flexible PCB, also known as flexible electronics, flexible circuit board, Flex PCB, Flexi board, flex circuits.

Flexible Circuit Boards, as the name suggests, are special types of circuits that can bend and adjust to the shape of the device and product in which they are installed. They are made of a flexible substrate and have the capability to adapt according to the shape.

Physically, you can consider flexible printed circuit (FPC) boards just like a PCB with components, but the only difference is that the substrate can be bent. The same components can be mounted on an FPC, and the same functionality can be obtained just like a normal rigid PCB.

There are special plastic substrates used to make a flexible circuit board. It could be Polyimide or polyester film. Sometimes, you will see a polyester sheet and silver conductive lines on it; We will introduce in detail later on Which material is used in flexible PCB.

These circuits are used in special projects when you care more about the compactness and minimalist design of the product. It has greatly revolutionized the electronics industry and has played a significant role in reducing the size of the products or devices.

What are Advantages of Flexible PCB ?

Custom flexible PCBs are becoming more and more popular, we need to understand the benefits of using Flexi circuits.

Flexible PCBs have many advantages, and that is why they are used in many places. In some cases, it is necessary to use FPCs. Let’s have a look at some of the most important advantages of FPCs.

FPCs can easily bend and take the available space; therefore, they save a lot of space and help in making the final product more and more compact. In contrast, you need a dedicated space for rigid PCBs, and they cannot bend at all. Even a flexible board can be installed in multiple levels and can be connected through flexible circuits. 

The circuit or conductive lines on the board are quite thin, and the same goes with the insulating material or dielectric. These things make the circuit much lighter in weight. 

FPCs are more reliable as there are fewer joints and wire connectors on the board. Usually, there is no need for a wire connector as flexible circuits are more than enough. It makes the PCB more stable and reliable. Moreover, the PCB can bear vibrations and shock because it has the ability to bend, so it is more reliable, and there are fewer chances of failure. It offers excellent durability, high density, high heat dissipation, and long-term performance.

Flexible circuits are compatible with almost all types of components and connectors and can be used in almost all types of applications and devices. Therefore, it is the most compatible type of circuit. 

Its performance is also commendable. It can bear extreme temperatures up to 400ᵒC. Moreover, it also prevents reactions with air, acids, and chemicals in the area.

Flexible circuits help you to have cost control because they are more reliable and stable. There are fewer chances of errors, and the cost of component replacement and re-working is saved. Moreover, it can easily fit in any available area, which reduces the overall assembly cost.

These benefits make flex PCBs ideally fit for a wide range of applications in industries such as Military, Transportation, Medical, Consumer Electronics, Automotive, Aerospace, Communications and Industrial.

The benefits of flexible circuit boards

The benefits of flexible circuit boards

What Are Flexible PCBs Used For?

Flexible PCBs are used for hundreds of applications where you need to take care of flexibility, compactness, and reliability. It is capable of adopting any available space, and it has advantages that other types of PCBs don’t have, so it is used in many applications.

What Are Flexible PCBs Used For
  • Interconnectors

    The most important use of flexible PCBs is as interconnectors. These circuits can bend, so they can be used to connect circuits, such as two or more rigid circuits. It plays a significant role and eliminates the use of connecting wires and other unreliable solutions. 

  • Automotive

    In the automotive industry, flexible circuits are widely used. It is because when automobiles run on the road, the PCB has to suffer from shocks and vibrations. In this case, a rigid PCB cannot last for a long-time. Therefore, flexible circuits are preferred. 

    Moreover, flexible circuits can adopt the design of the vehicle and adjust according to the needs. It does not create any hindrance in the design of the vehicle, and the designer has a free hand. It is also a compact option as the flexible circuits save a lot of space. Thus, these circuits are commonly used in automotive electronics, mainly in ABS, dashboards, and EMUs.

  • Medical Equipment and Devices

    Flexible circuits have brought a revolution to the medical field. With the help of circuits, we can design almost anything that can go with the human body, such as prosthetic limbs or arms. These arms are flexible, and they need a flexible circuit to operate. Similarly, other devices that are mounted over or inside the human body can have flexible circuits of compact nature. We can take the example of a hearing aid. It requires a flexible circuit. 

    Medical equipment, especially that requires movement, also uses flexible circuits. Thus, these circuits are widely used for medical purposes.

  • Industrial Electronics

    Industrial equipment and electronics also use flexible circuits. Industrial machinery uses these circuits because of extreme temperature, flexible design, and space-saving. 

  • Gadgets and Phones

    Flexible circuits have played a major role in the miniaturization of mobile phones and gadgets. We have small, slim, and minimalist smartphones. Nowadays, almost all mobile phones and gadgets use flexible circuits. It is because these circuits do not take much space and can bend easily. We know that wearable devices, such as smartwatches, are quite compact, and there is minimal space in them. Thus, a flexible circuit is necessary. 

  • Aerospace

    Flexible PCBs also contribute to the aerospace industry. Satellites, space robots, machinery in the space station, and other similar things need flexible PCBs. The shape of these objects is not as regular as things we use on earth. Aerospace objects are different in shape, and reliability is a major factor in selecting a PCB. Thus, flexible circuits play a significant role in aerospace projects.

  • Consumer Electronics

    Things that we use every day, such as calculators, home appliances, music players, printers, televisions, and many others, use flexible circuits. These circuits make the devices more compact, reliable, and better in performance.

Types of Flexible PCB Boards

Flexible PCB boards are divided into various types. These boards are differentiated on the basis of layers and properties.

Single Sided Flexible PCB

Single sided Flexible PCB

This is the simplest type of flexible PCB that has only one conductive layer. A thin flexible dielectric film, such as Polyimide, is used. There is only one conductive layer on the board.

Multilayer Flexible PCB

Multilayer Flexible PCB

In a multilayer flexible PCB, there are multiple conductive layers of copper. It has at least three copper/conductive layers or more. There is a thin layer of Polyimide between two conductive layers. These layers are interconnected with the help of vias. There are different types of vias used to connect layers, and you can also create holes to attach components with leads. You can call a multilayer PCB the combination of single-layer and double-layer circuits. The surface ones are just like the single-layer circuit, and the layers beneath the surface are just like double-layer circuits.

Double Sided Flexible PCB

Double sided Flexible PCB

Double-sided flexible PCBs have two conductive layers, one on each surface. You have components or conductive lines on both sides. The dielectric film is sandwiched between the copper layers. These flexible circuits are more economical compared to single-sided flexible PCBs because you have a high circuit density as components can be placed on both sides.

Rigid-flexible PCB

Rigid-flex PCB

A rigid-flex PCB is the combination of rigid PCBs and flexible PCBs. There can be multiple rigid and flexible parts to create one circuit. Most of the time, we cannot go with a rigid or flexible PCB, and in these cases, we need to use a rigid-flex PCB. The flexible part can bend easily, and the rigid part takes its required space. Usually, the rigid parts are connected via flexible circuits. Due to the versatility of these PCBs, they are used in many applications. They are used in aerospace, automobiles, communication, medical equipment, and consumer electronics.

Double access or back bared Flexible PCB

Double access or back bared Flexible PCB

Dual access or back bare flexible PCB is a special type of single-sided flexible circuit. There is only one layer of copper, but it is arranged in a special manner to be accessed from both sides. This is the specialty of a dual-access flexible circuit. A pre-punched dielectric film is applied over a single copper layer. The copper is etched in a way there are openings or access points in the dielectric film.

Polymer thick film flexible PCB

Polymer Thick Film Flexible PCB

PCB stands for Printed Circuit Board, but we all know that there is no printing involved. The word “Printed” is just a way to describe the circuit according to its physical appearance. However, Polymer Thick Film (PTF) flexible circuits are the real printed circuits. Several types of conductive inks are used to print the circuit on the base. Most of the time, the ink is applied with the help of stencils. These PCBs are commonly used as single-layer or double-layer circuits; however, multilayer circuits are also possible. They are commonly used for low-voltage applications because they are not suitable for high-voltages.

Sculptured Flexible PCB

Sculptured Flexible PCB

Sculptured Flexible PCBs are the special PCBs that have connectors or solder cup terminations. These can be used as a connection between two circuits or for connecting a circuit to another via the female connector. It eliminates the use of connectors and wires in circuitry and makes it more reliable. These are quite flexible and can offer excellent performance.

Flexible PCB Design - Typical Flex PCB Structure Diagram and stackup

I hope that the schematic diagram of the flex electronics structure we have listed can help you with your flexible circuit design.

Singler Layer FPC

The single-layer flexible PCB has the simplest stackup. At the bottom, there is the base layer of Polyimide or any other flexible material. Then we have adhesive and, after that, the copper layer. This is the simplest stackup. The copper layer is not left alone; a protective film called flex coverlay is applied. This protective film is made of Polyimide along with an adhesive. 

Double access or back bared Flexible PCB

The stack-up is just like the single-layer PCB, but there is a laser opening from the base of the PCB to access the circuitry.

Double-layer FPC

The middle layer is made of flexible insulating material, which is the base. Then, there are copper layers on both sides, along with an adhesive. Finally, the copper on both sides has a coverlay.

Multilayer FPC

Multilayer FPCs are the combination of single and double-sided FPCs. In the middle, we have double-layer FPCs, just like a polyimide layer sandwiched between copper layers. The surface layers have one copper layer, and there is a protective coverlay at the top and bottom.

How To Make Flexible PCB?

FPC is divided into four types: single-layer flexible PCB, double-sided flex PCB, multi-layer Flexi PCB, and rigid-flexible PCB board. It is mainly made of polyimide or polyester film as the basic material. Other components include insulating film, conductor, and adhesive.

Learn more about our Flexible PCB Manufacture Capability and Knowledge of Flexible Printed Circuit Board Processing Technology

Single-sided Flexible PCB Manufacturing Process

Cutting → Drilling → Dry Film Lamination → Position and Exposure → Develop → Etching → Remove Dry Film → Surface Finish → Coverlay Lamination →Lamination → Curing → Surface Finish → Immersion Gold → Silkscreen → V-cutting/scoring → Electrical Test → Punching → FQC → Packaging → Shipment

Single-sided Flexible PCB Manufacturing Process flow chart

Double-sided Flexible PCB Manufacturing Process

Cutting → Drilling → PTH → Electroless Plating → Pretreating → Dry Film Lamination → Position → Exposure → Develop → Pattern Plating → Remove Dry Film → Pretreating → Dry Film Lamination → Position and Exposure → Develop → Etching → Remove Dry Film → Surface Finish → Coverlay Lamination → Lamination → Curing → Immersion Gold → Silkscreen → V-cutting/scoring → Electrical Test → Punching → FQC → Packaging → Shipment

Double-sided Flexible PCB Manufacturing Process

Download the single-layer flexible PCB manufacturing process and double-sided Flex PCB manufacturing process ppt and PDF.

Flex Circuit Coverlay - A Special Process For Flexible PCB Fabrication

Flex Circuit Coverlay is a protective film, also known as coverfilm, to protect the external circuit. The internal circuit is safe, and it does not need protection, but the external circuit is prone to oxidation and reactions. Thus, there is a need for a cover, and it is provided by Flex Circuit Coverlay.

The Coverlay works just like a solder mask that is used in a rigid PCB. It protects the circuit from various chemical reactions. But it is different from solder masks in one aspect, and that is flexibility. 

A solder mask will tear and break if you try to bend it, so it can never be applied on a flexible circuit. But Flex Circuit Coverlay is flexible, and it works perfectly well on the flex circuit. 

Flex Circuit Coverlay is actually made of Polyimide along with an adhesive. After placing the coverlay on the circuit, it is pressed through heat and pressure. Therefore, it sticks to the board and works as a protective film. 

For components feature openings, it is necessary to create a hole using a drill or create a cut using a laser. The bad thing is that only large openings can be made in rectangles. Even if you drill a hole, the area around the hole becomes unprotected as there is no film for the protection.

Flex circuit with coverlay
Flex circuit coverlay adhesive squeeze out

Image and part of the quoted content courtesy of Allflexinc.com.

Flexible PCB materials - Materials for Quick Turn Flex Circuits Fabrication

Flexible PCB requires three materials to be ready for operations. The three materials are the base, adhesive, and metal foil.

Base material

The base material of any PCB is the most important one because it makes the PCB what it is. The flexible circuit is flexible because of the base material.

The base material acts as the dielectric or insulator. The conductive layers are created around it. It is basically the whole foundation of the PCB on which the components and conductive layers lie.

FPCs are usually made of Polyimide, and it is the most used base. Then, there is a polyester film which can also do wonders. However, we have more materials to be used as the base of a flexible circuit, and they are polyetherimide (PEI), polyethylene naphthalate (PEN), and various fluropolymers (FEP) and copolymers.

Nowadays, most flexible circuits are made of Polyimide because it has good flame resistance.

Bonding adhesive

We have an insulating layer, which is the base. Over it, there is a conductive base made of copper. These two are joined with the help of a bonding adhesive.

We have also discussed flex circuit coverlay and learned that adhesive also plays an important role in it.

There are two types of adhesives commonly used in the flexible circuit, and they are Acrylic and Epoxy. Acrylic adhesives have excellent heat resistance properties, but they have poor electrical properties. Moreover, they do not have good binding strength. On the other hand, Epoxy is a little lower in heat resistance, but its electric performance and bonding capabilities are good. The storage time of Acrylic is more than Epoxy. It can last for a longer time. In contrast, Epoxy keeps reacting, so it can’t be stored for a long time.

While selecting a good bonding adhesive, there are a few things the manufacturers consider, and they are flexibility, adhesion, electrical properties, and chemical inertness.

Metal foil

Metal foil is the one that conducts the electricity and creates the whole circuit. It is applied on the base using an adhesive, and after that, it is etched to get the circuit pattern. Usually, copper is used for this purpose because it is inexpensive and has excellent electric properties. There are different grades and types of copper foils available, and manufacturers use them according to their needs.

The thickness of copper is selected by the buyer. We can divide copper foil into two main categories: Rolled Copper Foil and Electrodeposited Copper Foil. For flexible PCBs, Rolled Copper Foil is used. Copper foil is made according to the needs. It is treated to enhance its peeling strength, oxidation resistance, and roughness.

Copper foil: divided into two types: electrolytic copper and rolled copper. The standard thicknesses are 1oz 1/2oz and 1/3 oz.

Substrate film: There are two standard thicknesses: 1mil and 1/2mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Cover Film: for surface insulation. Typical thicknesses are 1mil and 1/2mil.

Stiffener Film (PI Stiffener Film): Reinforce the mechanical strength of FPC to facilitate surface mounting operations. The typical thickness is 3mil to 9mil.

EMI: Electromagnetic shielding film protects the circuit board’s circuit from outside interference (strong electromagnetic area or susceptible to interference area).

In certain non standard cases, the circuit manufacturer may be called upon to create a specialty laminate by using a specified alternative metal foil, such as a special copper alloy or other metal foil in the construction. This is accomplished by laminating the foil to a base film with or without an adhesive depending on the nature and properties of the base film.

Advanced Learning

Is the cost of manufacturing flexible PCBs high?

Flexible PCBs are widely used due to their excellent physical and electrical properties. However, flexible PCBs’ manufacturing cost and price are still several times that of rigid PCBs. Many factors affect the price of FPC flexible circuit boards, such as material, manufacturing process, number of layers, quality, surface finish, copper foil thickness, size, delivery time, quantity, etc. Here we have listed 16 factors that affect the price of flexible PCBs.

IPC standards for flexible circuit board manufacturing

No.IPC Standards Serial NumberNameDescription
1IPC-4203Cover and Bonding Material for Flexible Printed Circuitry

This standard is for the cover and bonding material, as the name states. The cover refers to the base material, and bonding is the adhesive used to bind the metal foil and the base.

The standard does the classification of the dielectric films along with an adhesive. It also discusses the quality requirements and qualifications.

Note: It only discusses the flexible circuits covers and adhesives.

2IPC-4204Flexible Metal-CladDielectrics for Use in Fabrication of Flexible Printed Circuitry

This standard classifies the flexible metal-clad dielectric materials and discusses the quality requirements. These are the materials used for the fabrication of flexible printed boards.

3IPC-6013Qualification and Performance Specification for Flexible/Rigid-Flexible Printed Boards

This is a special specification for the qualification and performance of FPCs that are designed according to IPC-2221 and IPC-2223.

4IPC-FC-231CFlexible Base Dielectrics for Use in Flexible Printed WiringRevision C, April 1992.
5IPC-FC-241Flexible Metal-Clad Dielectrics for Use in Fabrication of Flexible Printed Wiring

We have discussed metal-clad dielectrics. This standard discusses these dielectrics for flexible printed wiring.

6IPC-2223Sectional Design Standard for Flexible/Rigid-Flexible Printed Boards

This standard is all about the design of the flexible and rigid-flex PCB. It highlights the specific requirements and discusses component mounting forms and interconnecting structures.

7IPC-ML-990Performance Specification for Flexible Multilayer Wiring1972 Edition, September 1972.
8IPC-FC-250ASpecification for Single- and Double-Sided Flexible Printed Wiring

This is a specification of flexible printed wiring. The wiring has the conductor patterns on a flexible base. There can be stiffeners and interfacial connections.

9IPC-RF-245Performance Specification for Rigid-Flex Printed BoardsIPC-RF-245, 1987 Edition, April 1987.

JHYPCB: A Leading Flexible PCB Manufacturer from China

JHYPCB is a leading PCB manufacturer that can manufacture almost every type of PCB, including flexible PCB. We can handle low to high volume orders and offer a fast turnaround. Our strict quality management system ensures optimal performance and safety. We are RoHS, ISO, and UL certified, and we take care of the international standards.

We can offer almost all PCB services, including flexible circuit prototypes and complete assemblies. Our reasonable prices, fast turnaround, and expert guidance are perfect for startups and small businesses. We offer a complete PCB solution under one roof.

For more information and details, feel free to contact our customer support team.

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FAQ

Most frequent questions and answers

Yes, we make single, double, and multi-layer Flex and Rigid-Flex PCBs.

We make different types of Flex and Rigid-Flex PCBs, depending on the structure, base material, adhesive, appearance, insulation base film, and metal conductor foil. Please consult our technical team for details suitable for your application.

Yes, we provide black PI stiffeners, yellow PI cover films, transparent polyimide films, white overlay, and brown PI copper clad laminates.

Yes. We have four manufacturing methods for adhesive-free copper foil base materials. We use spray plating, curtain coating, electroless deposition/electrolytic plating, and laminating.

Minimum thickness is 2 µm and the maximum is 200 µm. We ensure high chemical durability and processing compatibility for flexible printed circuits and do not sacrifice its original electrical property, heat-resistant property, and mechanical property.

IPC Standards for Rigid and Flexible PCBs

The list of IPC standards below applies to rigid PCBs and flex circuits. Take note that this list is not exhaustive, and additional IPC standards may need to be considered. You should consult the ipc.org website for a full list of available IPC standards.

  • IPC-2221A, Generic Standard on Printed Board Design
  • IPC-2223, Sectional Design Standard for Flexible Printed Boards
  • IPC-4101, Specification for Base Materials for Rigid and Multilayer Printed Boards
  • IPC-4202, Flexible Base Dielectrics for Use in Flexible Printed Circuitry
  • IPC-4203, Adhesive Coated Dielectric Films for Use as Cover Sheets for Flexible Printed Circuitry and Flexible Adhesive Bonding Films
  • IPC-4204, Flexible Metal-Clad Dielectrics for Use in Fabrication of Flexible Printed CircuitryIPC-6013, Qualification and Performance Specification for Flexible Printed Wiring

The functions of flexible circuit boards can be divided into four types: Lead Line, Printed Circuit, Connector, and Integration of Function. The use covers computers and computer peripherals—auxiliary systems, consumer electrical appliances, automobiles, etc. After the circuit is completed with single-sided PI copper-clad material, it is covered with a protective film to form a flexible circuit board with only a single-layer conductor.

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