What is Flexible Printed Circuit?

Flexible printed circuit is a one PCB circuit board type, also known as “Flexible PCB”. Flexible PCB is made of flex circuit material such as polyimide or polyester film. It has the advantages of high wiring density, lightweight, thin thickness, bendable, high flexibility, etc. Withstands millions of dynamic bends without damaging the wire. According to the requirements of space layout, 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.

Types of Flexible Printed Circuit

Single Sided Flex PCB

Single sided flex PCB the simplest Flex board, it has only one copper layer. It is usually processed on the basis of two raw materials: “base material, glue and copper foil” and “coverlay and glue”. The base material used by flexible printed circuit is generally polyimide (PI), but not limited to, it can also be polyethylene terephthalate, aramid fiber ester and polyvinyl chloride.

2 Layer Flexible Printed Circuit

2 Layer flexible printed circuit contains top and bottom sides copper, it’s increased the wiring density per unit area. Generally, when the wiring of the circuit 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 board is added vias structure to connect two layers of copper foil (that is, 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, metallized through holes and electroplating, and form conductive paths between different layers. In this way, no complicated welding process is required. Compared with single side flex PCB and 2 Layer flexible circuit board, 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 board. However, there is also a compromise option, that is 4 layer Flex PCB.

Flexible Printed Circuit Products

Features of Flexible Printed Circuit

Flexible

Flexible printed circuit boards can be bent, wound and folded freely. Also it can be arranged arbitrarily according to the requirements of space layout, and can be moved and stretched in three-dimensional space arbitrarily, so as to achieve the integration of component assembly and wire connection

Smaller

The use of flexible printed circuit can greatly reduce the volume and weight of electronic products. Suitable for the development of electronic products in the direction of high density, miniaturization and high reliability.

Solderability

Flexible printed circuit also has good heat dissipation and solderability and is easy to assemble, low overall cost advantages. The design of the combination of FPC PCB and rigid PCB also makes up for the slight deficiency of the flexible substrate in the load-bearing capacity of the components to a certain extent.

Flex PCB Manufacturing Parameter

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.

Flexible PCB Adhesive

ADH is an adhesive, which is the most important part in the manufacturing process of flexible copper clad laminates. Many important performance indicators in the board are determined by the performance of the glue. 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 be able to withstand various process conditions and the erosion of chemicals used in the manufacture of flex printed circuit boards, without delamination or degradation.

Flexible PCB Polyimide&Polyester

Polyimide&Polyester contains PI base Flexible Printed Circuitmaterial, PI coverlay, PI stiffener material PI base material: Flexible PCB printed circuit board materials are divided into two types: those with glue and those without glue. Whether it is a material with glue or without glue, Polyimide is a must indispensable.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 Printed Circuit Application

Flexible Printed Circuit Application

Traditional Field

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

Mobile Electronics Market

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

5G, Wearable Devices

Driven by emerging markets such as 5G and wearable devices, Flexible printed circuit will also use in new growth space.

Other Devices

Flexible printed circuit widely use in Camcorder, CDRW cubic element patch,CD RW drive parts,PDP, Camera Module, Laser Printer Head drive parts, Mobile phone electromagnetic wave shielding.

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 work board 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 customer.

Dry Film Lamination

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

Exposure

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

The part of the dry film that is not exposed to light will be washed off by NaCO3, 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 process (ferric chloride and copper chloride) and alkaline etching process (ammonia). The acid method is used to etch the inner layers of flexible printed circuit board, it is accurate and cheap but time consuming. The alkaline method is used to etch the outer layer of the flexible PCB, which is fast and expensive.

Dry Film Stripping

Flexible printed circuit board dry film stripping removes 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, generally 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 networks of the flexible printed circuit board, 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 main components are glass fiber cloth and epoxy resin glue, which is the same as the FR4 material used in PCB.

Steel stiffener is 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.

PI stiffener is as same as the coverlay film, consisting of PI and adhesive release paper, but the PI layer is thicker, can be processed and produced from 0.05mm to 0.25mm, 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 the principle of screen printing, mainly printing the product model, production date code, and 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, which is equivalent to a cutting workstation. At present, the main equipment used in this workstation on the market is flex circuit punching machine and 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.

Inspection&Packing

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 packaging, micro-membrane packaging, tray packaging, etc.

Why choose us?

Quick Turn Flexible Printed Circuit Fabrication

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

Complex PCB Technologies

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

• Good Quality
• Reliable Material
• Lead time in Time

Quote Now