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Flexible PCB

What is Flexible PCB-flex PCB-flexible Printed Circuit-flexible pcb design

What is Flexible Printed Circuit?

Flexible printed circuit is a one PCB circuit board type, also called "Flexible PCB."

Flexible PCBs are made of flex circuit materials such as polyimide or polyester film.

It has the advantages of high wiring density, lightweight, thin thickness, bendable, high flexibility, etc. It withstands millions of dynamic bends without damaging the wire.

According to the space layout requirements, it can be moved and stretched arbitrarily. Realize three-dimensional assembly and achieve the effect of integration of component assembly and wire connection. It has advantages that other types of circuit boards cannot match.

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Types of Flexible Printed Circuit

Single Sided Flex PCB

Single-sided flex PCB is the simplest Flex board and has only one copper layer. It is usually processed based on two raw materials: "base material, glue, and copper foil" and "overlay and glue." The base material used by flexible printed circuits is generally polyimide (PI), but it can also be polyethylene terephthalate, aramid fiber ester, and polyvinyl chloride.

2 Layer Flexible Printed Circuit

The 2-layer flexible printed circuit contains copper top and bottom sides, increasing the wiring density per unit area. Generally, when the circuit wiring is more complicated, and the single-sided flex PCB cannot meet the wiring requirements, the 2-layer flexible circuit board will be selected. Compared with single-sided Flex PCB, the biggest difference between 2-layer flexible circuit boards is the added vias structure connecting two layers of copper foil (two layers of conductive patterns) to form a conductive path.

4 Layer Flexible Printed Circuit

4 Layer flexible printed circuit is to press single-sided and 2 Layer flex PCB together, metalized through holes and electroplating, and form conductive paths between different layers. In this way, no complicated welding process is required. Compared with single-sided flex PCB and 2-layer flexible circuit boards, 4-layer flexible PCB has higher reliability, better thermal conductivity, and more convenient assembly. But it loses the excellent flexibility of single and 2-layer flexible circuit boards. However, there is also a compromise option, which is 4 4-layer Flex PCB.

Benefits of Flexible Printed Circuit

Benefits of Flexible Printed Circuit-Flexible


Flexible printed circuit boards can be bent, wound, and folded freely. It can be arranged freely to fit the space and moved and stretched in any direction.

Benefits of Flexible Printed Circuit-Lightweight


Flexible PCBs are very thin and light, which helps save space and weight in electronic devices. This technology is good for making small, reliable electronic products with many features.

Benefits of Flexible Printed Circuit-Durability


Designers create Flex PCBs to withstand a broad range of temperatures. And the flexibility of flexible printed circuit boards contributes to their durability. These devices are strong and can handle vibrations, shocks, and movement without damage.

Flex PCB Manufacturing Parameter

Item Technical Parameters Specification
Min Flex PCB PCB Line Width/Space 2/3 mil Finished Copper Thickness H oz
Min Flex PCB Pad Ring of Via 3 mil Distance between hole edge to ring outskirt
 Min Flex PCB Pad Ring of PTH 5 mil Distance between hole edge to ring outskirt
 Min Flex PCB Via Size 4 mil
 Min Flex PCB Thickness of Double sided 0.1 mm Final Board Thickness
Min Flex PCB Thickness of Multilayer 0.2 mm Final Board Thickness
Max Flex PCB Thickness 0.35 mm Final Board Thickness
 Max Flex PCB Dimension 260×620 mm Single and Double Sided  PCB
 Space Between Line to Board Edge 8 mil Milling of Outline
 Max Flex PCB Layers 8 Layer
Flex PCB Solder Mask Color Yellow,Black,White
Flex PCB Silkscreen Color White,Black
FPC PCB Surface Finishing ENIG,ENEPIG,ImAg,ImTin,OSP, Gold Plating
Max Finishing Copper Thickness 3 oz
Dielectric Thickness 2.5 mil
Flex PCB Material ShenYi Stand Polyimide, Halogen Free Polyimide, Adhesive and Stiffener
Flex Stiffener Material FR4 Stiffener, Polyimide Stiffener, Steel Stiffener

Flexible PCB Material

The three elements of flexible PCB material: Copper Foil, Adhesive, Polyimide&Polyester.

Flexible PCB Copper Foil

Copper foil can generally be divided into electrolytic copper foil and rolled copper foil.

Electrolytic copper is formed by separating copper ions in copper sulfate solution by electric current, and then it is completed after anti-oxidation and roughening treatment. Its characteristic is strong electrical conductivity, but relatively weak bending resistance.

Rolled copper foil is made by rolling the copper plate repeatedly, and its crystallization is a lamellar structure. It has good flexibility.

Applications of Flex PCBs

In mobile electronic devices such as smartphones and tablets, There are flexible printed circuits in the camera module, capacitive screen connection part, button part, optical drive induction head, receiving antenna, and other parts of the PC.

Traditional Field

Flexible Printed Circuits are used in many high-tech electronic fields. These include communications, computers, instruments, automobiles, medical care, industrial control, home appliances, CNC machine tools, camera modules, and intelligent battery management modules.

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Mobile Electronics Market

Mobile electronic devices like smartphones and tablets have flexible printed circuits. These circuits are in the camera module, capacitive screen, button, optical drive, antenna, and other PC parts.

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Wearable Devices

Flexible PCBs, like smartwatches and smart glasses, are key to wearable technology. Its lightness and flexibility make it suitable for body-wearable product design.

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Other Devices

Flexible printed circuits are used in various devices, such as camcorders, CD RW drives, cameras, and mobile phones, to shield against electromagnetic waves.

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Flexible PCB Adhesive

ADH is an adhesive, the most important part of the manufacturing process of flexible copper-clad laminates. The performance of the glue determines many important performance indicators on the board.

For example, peel strength between dielectric substrate and metal foil, flexural resistance, chemical properties, moisture resistance, adhesive layer flow properties, etc.

The adhesive used in flexible copper-clad laminates must withstand various process conditions and the erosion of chemicals used to manufacture flex-printed circuit boards without delamination or degradation.

Flexible PCB Polyimide&Polyester

Polyimide&Polyester contains PI base Flexible Printed material, PI coverlay, PI stiffener material, and PI base material.

Flexible PCB printed circuit board materials are divided into two types: those with and without. Polyimide is indispensable whether it is a material with glue or without glue.

PI coverlay: Its main function is for circuit insulation.PI stiffener material: It is often used in the area on the back of the whole finger of FPC PCB, and the PI ribs are used to increase the complexity and hardness of the fingers, making it easy to insert and remove.

Flexible PCB Fabrication

Material Cutting/Shearing

The flexible printed circuit board material is generally a roll of 250mm wide, 50M, or 100M long PI base material covered with a certain thickness of copper on one or both sides of the copper foil. Therefore, we need to cut the large roll into a workboard according to the size of the manufacturer's instructions.

CNC Drilling of Flexible PCB

Drilling is the second stop in the Flexible printed circuit board manufacturing process, and the quality of drilling is directly related to the function and accuracy of the product.

Along with the continuous development of high-density flexible PCB, Traditional mechanical drilling technology can no longer meet the market demand for small hole diameter, high precision, and high efficiency. Laser drilling has become the mainstream processing technology for flexible PCB microvias.

Plating Through Hole

VCP electroplating line using Faraday's theorem (the thickness of the coating is proportional to the current density and plating time) to plat the hole wall of the flexible printed circuit board to copper thickness following IPC standard or required by the customer.

Dry Film Lamination

Composed of PE, photoresist and PET, paste dry film on the flexible printed circuit board, to achieve the function of image transfer, and protect the circuit during the etching process.


According to the film exposure corresponding to the work job, the image of the flexible printed circuit graphic film is transferred to the dry film (completed in the 10,000-level dust-free workshop), and the main equipment is an automatic exposure machine.

Develop Image

NaCO3 will wash off the part of the dry film not exposed to light, and the dry film on the trace and copper will not be washed off. Useful wiring and copper of flexible printed circuit board are preserved

Pattern Etching

Flexible printed circuit board etching is the process of removing unwanted copper from a circuit board.

Etching has acid etching processes (ferric chloride and copper chloride) and alkaline etching processes (ammonia). The acid method is used to etch the inner layers of the flexible printed circuit board; it is accurate and cheap but time-consuming. The alkaline method, which is fast and expensive, is used to etch the outer layer of the flexible PCB.

Dry Film Stripping

The flexible printed circuit board and dry film stripping remove the protective dry film layer on the FPC circuit board through a chemical reaction. This process is usually done using chemical solutions, which can decompose the chemical substances in the film layer and expose the flex-printed circuit board.

The development and etching film removal equipment is a horizontal DES line.

Stack up Flex PCB Coverlay

Flexible printed circuit board coverlay film, also called protective film, protects the circuit from oxidation and covers it for subsequent surface treatment if the area that does not need gold plating is covered with coverlay. In the subsequent SMT soldering, the role of prevent welding.

Hot Press Lamination

Through high temperature and high pressure pressing, followed by high heat baking, the thermosetting glue between the cover film and the board is cured to achieve the purpose of the two tightly combined. The curing working parameters are temperature 150 ° C, 1H. The main equipment is Fast presses and ovens;

Flexible Printed Circuit Board Surface Finish

Flexible printed circuit board surface treatment is mainly done by immersion gold or ENEPIG. According to customer requirements, metals such as nickel and gold are deposited on the exposed pads of Flexible PCB by using chemical or electroplating principles to protect the pads and maintain their solderability. The main equipment is gold-plated line and gold-plated line.

Flexible Circuit Open/Short Test

Check whether there are open and short circuits between different flexible printed circuit board networks, four-wire failure, etc., through test fixtures or equipment. The main equipment is an electric test machine and a flying probe test machine;

Flexible PCB Stiffener Assembly

The purpose of bonding Flex PCB stiffener is to strengthen the mechanical strength of the flexible printed circuit board and facilitate the mounting of parts on the surface of the PCB.

FPC stiffener materials are common polyimide stiffener, FR4 stiffener and steel stiffener.

FR4 stiffener's main components are glass fiber cloth and epoxy resin glue, which is the same as the FR4 material used in PCB.

Steel stiffeners are made of steel, which has strong hardness and support strength. Manual assembly is required, the process is more complicated, and the cost will be higher.

The PI stiffener is as same as the coverlay film, consisting of PI and adhesive release paper. Still, the PI layer is thicker, can be processed and produced from 0.05mm to 0.25mm, and the tolerance can be controlled at +/- 0.03mm, and the precision is high, high-temperature resistance (100°C-280°C).

Silkscreen Printing

Print the text ink on the flexible printed circuit board through screen printing, mainly printing the product model, production date code, various component identifications required by customers, etc. The main equipment includes screen printing machines, ovens, text inkjet printers, etc.;

Flexible PCB Punching

Flexible printed circuit board punching is a link in the FPC process, equivalent to a cutting workstation. At present, the main equipment used in this workstation on the market is a flex circuit punching machine and an FPC UV laser cutting machine.

The flexible PCB punching machine principle is to apply pressure through the cylinder to push the knife mold in the carrier and realize the flex circuit cutting at one time.

The principle of the flexible printed circuit board laser cutting machine is to irradiate the surface of the FPC with a high-energy and high-density laser beam and scan it back and forth through the vibrating mirror to form a cutting layer of glass material.


Through manual visual inspection, CCD, equipment to fully inspect the appearance and surface condition of the flexible printed circuit board, separate good products from defective products, and conduct reliability testing on the product to confirm whether it meets customer requirements.

Packaging and shipping flex circuits are carried out according to customer requirements. The main packaging methods include vacuum, micro-membrane, tray, etc.

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Quick Turn Flexible Printed Circuit Fabrication

King Sun is a Flex PCB manufacturer with high quality and advanced flexible PCB. We make flex PCB prototypes with quick turn lead time. Below is our quick turn flex circuits list:

Layer Count Standard Lead Time Quick Turn Around
1-2 Layer 4-5 DAY 24 Hours
4 Layer 5-6 DAY 48 Hours
 6 Layer 7-8 DAY 96 Hours
 8 Layer 9-10 DAY 140 Hours

Complex PCB Technologies

We make very complex and special Flexible Printed Circuit like below:

  • Good Quality
  • Reliable Material
  • Lead time in Time