Flexible PCB manufacturing

FPCB(FPC) is a flexible printed circuit board: it is a printed circuit board which is made of flexible base material, and is composed of an insulating substrate and a conductive layer, and a bonding agent is arranged between the insulating substrate and the conductive layer.

Because of its continuous and automatic production, high wiring density, light weight, small size, wiring error less flexible and elastic can change shape and other characteristics, are widely used in military, defense and consumer electronic products such as digital cameras, watches, notebook computer and other fields.

Flexible PCB Profile

The flexible circuit board, referred to as "soft" in the industry known as FPC, is the use of flexible insulation substrate (mainly polyimide or polyester film) made of printed circuit board, [1] has many hard printed circuit board does not have the advantages. For example, it can be free to bend, roll, fold. The use of FPC can greatly reduce the volume of electronic products, the application of electronic products to high density, small, high reliability direction of development needs. Therefore, FPC has been widely used in the fields of aerospace, military, mobile communication, portable computers, computer peripherals, PDA, digital cameras and other fields or products.

FPC also has the advantages of good heat dissipation, easy installation and low cost.

The flexible printed circuit board has the points of one side, two sides and a multilayer board. The substrate is mainly used in polyimide. The material has high heat resistance and good dimensional stability, and the covering film with mechanical protection and good electrical insulation performance is the final product. The surface layer and the inner conductor of the double-sided, multilayer printed circuit board are electrically connected with the inner and outer layer circuit through the metallization.

Flexible circuit board function can be divided into four kinds, respectively (Lead, Line) lead line printed circuit (Printed, Circuit) connector (Connector) and multi-function integration system (Integration of Function), the use of computer, computer peripheral covering system, consumer appliances and cars such as the scope of people's livelihood
 

Flexible PCB Categories


Single layer FPCB

One layer of protective film is covered by one side PI clad plate material, and a soft circuit board is formed.

double-sided FPCB

The double side PI board is used for the completion of the double side circuit, and the two sides are respectively coupled with a layer of protective film to become a circuit board with double layers of conductors.

Dual Access FPCB

Pure copper materials used in circuit fabrication, respectively in successively in both sides of each plus a layer of protective film, but only become a single conductor in double-sided circuit board has a circuit board exposed conductor.

Single  side double layers board

For pressing the adhesive layer two single-sided PI copper clad plate material in the middle with in the specific location of the window, as in the local area of pressure, double conductor circuit board two layer structure to achieve the separation of local circuit board has high flexural properties in the delamination area.
 

Advantages and disadvantages of FPCB

Advantages of FPCB:

  •  free bending, winding, folding, can be arbitrarily arranged in accordance with the requirements of the space layout, and any movement and expansion in three-dimensional space, so as to achieve the integration of components assembly and wire connection;
  • using FPC can greatly reduce the volume and weight of electronic products;
  • FPC also has good heat resistance and weldability, easy installation and low cost advantages, even integrated design, hardware and software combination also make up the flexible substrate in the element bearing the limitations slightly in a certain extent.

Disadvantages of FPCB

  • a one-time initial cost is high
The soft PCB is designed for special application, manufacturing, so the circuit design, start wiring and photographic plate by the cost of higher. Unless there is a special need to apply soft PCB, usually a small amount of application, it is best not to use.
  • change and repair of soft PCB is difficult
Soft PCB once made you want to change, must start from the map or the preparation of light painting program, so it is not easy to change. Its surface covered with a layer of protective film, to remove before repair, and to restore after the repair, it is more difficult to work.
  •  restricted by size
Soft PCB is not popular in the case, usually with the batch process manufacturing, and therefore limited by the size of the production equipment, can not be done very long, very wide.
  •  improper operation is easy to damage
Connected due to improper operation caused by damage to the flexible circuit, the soldering and rework operation requires trained personnel.

FPCB For SMT

The process requirements FPC surface SMT and conventional PCB and SMT solutions have many differences, SMT process to do FPC, the most important is the location. Because FPC board hardness is not enough, more soft, if you do not use a dedicated board, you can not complete the fixed and transmission, it can not complete the printing, patch, over the furnace and other basic SMT processes.

FPCB Structure

In accordance with the conductive copper foil layer is divided, divided into single plate and double plates, multilayer board, double sided board etc.. The structure of the single layer plate: the structure of the flexible plate is the most simple structure of the flexible plate. Usually the substrate + transparent glue + copper foil is a set of purchased raw materials, protective film + transparent glue is another kind of raw materials purchased. First of all, to process copper foil etching to the circuit protective film to expose the pad corresponding to drilling. After the cleaning and rolling method to combine the two. And then exposed to the welding plate part of the electric plating or tin, etc.. This plate is done. Generally have to punch into the appropriate shape of the small circuit board. There is no direct protective film on the copper foil printed solder layer, so the cost will be lower, but the mechanical strength of circuit board will become worse. Unless the strength is not high but the price needs to be as low as possible, it is best to apply the method of the protective film. The structure of double plate: when the circuit is too complex, not single plate wiring or the needs of copper to ground shield, you need to use the double plate and multilayer board. The difference between the typical multilayer board with the single plane is increased via structure to connect each layer of copper foil. The first process base + transparent glue + copper foil is made a hole. The first hole in the substrate and copper foil, copper plating on a certain thickness after cleaning, hole well. After the production process and the same as the single-layer plate. The structure of the double plate: both sides of the double board are provided with pads, which are mainly used for connecting with other circuit boards. Although it is similar to the structure of the monolayer, but the production process is very different. It is the raw material of copper foil, protective film + transparent adhesive. According to the first pad position requires drilling on the protective film, then the copper foil paste, corrosion pad and the wire and then affixed another drill hole protection film.

Flexible PCB Cost

The price of flexible assembly is declining and becoming closer to the traditional rigid circuit. The main reason is the introduction of the updated materials, improved the production process and the change of the structure. Now the structure makes the product more thermal stability, there is very little material does not match. Some of the newer materials can make more precise lines because of the thinner copper layer, which makes the assembly more lightweight and more suitable for smaller spaces.

In the past, the rolling process of copper foil with adhesive in the coating adhesion to the medium, now can not use directly generated on the medium copper foil adhesive. These techniques can get a few microns thick copper layers to get 3m.1 and even narrower precision lines. Remove the flexible circuit after some adhesives with flame retardant properties. This can not only accelerate the uL certification process can further reduce costs. Flexible printed circuit board solder mask and other surface coatings to reduce the cost of flexible assembly. In the next few years, the smaller, more complex and more assembled flexible circuits will require more innovative methods of assembly, and the need to increase the hybrid flexible circuit. The challenge for flexible circuit industry is to use its technological advantages to keep in sync with the computer, telecommunications, consumer demand and active market. In addition, the flexible circuit will play an important role in lead free operation.

FPCB Prospect

Flexible circuit industry is in a small but rapid development. Polymer thick film method is a kind of high efficiency and low cost production technology. The process is on the cheap flexible substrate, and the conductive polymer ink is printed on the selective network. Its representative flexible substrate is PET. Polymer thick film conductor comprises a metal screen method or toner filler filler. Polymer thick film itself is very clean, the use of lead-free SMT adhesive, without etching. Because of the low cost, the polymer thick film method circuit is the 1/10 of the price of the copper polyimide film circuit, and the price of the rigid circuit board is 1/2 ~ 1/3. Polymer thick film method especially suitable for equipment control panel. In mobile phones and other portable products, polymer thick film method is suitable for the conversion of components, switches and lighting devices on printed circuit boards into polymer thick film circuit. Both to save costs, but also to reduce energy consumption.

In the next few years, the smaller, more complex and more assembled flexible circuits will require more innovative methods of assembly, and the need to increase the hybrid flexible circuit. The challenge for flexible circuit industry is to use its technological advantages to keep in sync with the computer, telecommunications, consumer demand and active market. In addition, the flexible circuit will play an important role in lead free operation.
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