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What is a FPC Flexible Printed Circuit Boards?

What is a FPC Flexible Printed Circuit Boards?

FPC Flexible Printed Circuit Boards, also known as Flex PCBs or Flexible PCBs, get their name from their ability to allow circuitry to be designed according to the shape of the electronic device or product.Flex boards feature a unique patterned printed circuitry and component arrangement.The malleable base material is a distinguishing characteristic of Flex PCBs.

Flexible printed circuit board technology offers a multitude of possibilities for different types of products and designs. It can help to reduce the size and weight of products, improve electronic packaging, withstand high temperature and etc. However, the flexible PCBs are easily damaged by improper personnel operation.

Influence factors

Damage to flexible printed circuit boards can be related to two factors: the environment and human factor.

  • Environment

Storage in unsuitable environments will affect flexible printed circuit boards. The common environment factors are as follows:

  • Humidity

A humid environment will let moisture in the flexible circuit board. It is well known that water conducts electricity. If there is water on the circuit board, it may connect the 2 circuits which should not be connected and cause a fault. Besides, the humid environment is suitable for the growth of microorganisms, which will also affect the quality of the flexible circuit board.

  • Staticelectricity

As same as rigid printed circuit boards, flexible circuit boards suffer from static electricity. The static charge will affect the etching on the PCB.

  • Dust

Dust is the insulator. If there is dust on the flexible PCB, it will reduce the heat dissipation capacity, and resulting in the failure of the PCB caused by high temperature.

  • Extreme cold or heat

The temperature is too cold or too hot will damage flexible PCB. The substrate expands by heat and contracts by cold. The extreme temperature deforms the substrate of flexible PCB, thus disconnecting the circuit and impeding the flow of current.

  • Chemicalcorrosion

Chemicals can corrode both the surface and circuit of flexible PCB. It is important to note that chemical smog also carries risks. If the chemical reagents are stored in the warehouses and other storage areas with flexible PCB, the chemical fumes from the reagents will corrode the flexible PCB after long contact.

  • Animal bite

If the factory does not do a good job of pest control, the emergence of insects and rats is at great risk. They bite all sorts of things, including flexible circuit boards, and if they do, the flexible PCB will become completely unusable.

Human factor

The design and manufacture of flexible circuit boards is a very complex task. There are many risks of accidental damage.

  • Design and manufacture errors

Flexible PCB needs to work properly when bent. So it's much more stringent in terms of design and production than rigid PCB. Unreasonable circuit layout design, improper material selection and mistakes in the manufacturing process will affect the bending degree of the flexible PCB.

  • Impact of external forces

Although the flexible PCB can be bent, if it is folded at 180°, there will still be undesirable wire breakage. Falling from a height, extruding and other external forces may damage the components on the flexible PCB, thus causing the whole PCB to fail. Scratch from hard object can damage the circuit, and frequently plug and unplug the flexible PCB can even cause tear in the flexible PCB in severe cases.

  • Components’ malfunction

Faulty PCB components may damage the circuit board by not working correctly. In some cases, these components cannot protect the PCB from overheating.

How to avoid damage?

  • Design

The design process of flexible PCB must consider the number of layers, the product's features, the circuit structure and the material. The designer must also consider how often the circuit bends and how the bending is formed, including how tight the bending is and how much it is bent. Designers can take full advantage of the technology's potential to work with flexible PCBs. These include identifying unique requirements for the flex PCB, while carefully defining the application and design priorities.

It is generally recommended to keep the flexible circuit's copper circuit bent in a vertical direction. If this is not possible, try to reduce the bending amplitude and frequency, or use conical bending according to the mechanical design.

Do not suddenly change the width of the wire, when the wire is connected to the pad, especially the flexible circuit terminal, will form a weak spot, with the time pass by, the copper sheet is very easy to burn-in. The tapering method is recommended.

  • PCB material

It is very important to choose the right material to accommodate the bending and to distribute the bending force evenly.

  • Notes for bending FPC Flexible Printed Circuit Boards

Do not bend directly on the through-holes of flexible circuit board; the golden finger plucking area, although there are reinforcement design, but still not suitable for bending this area; silkscreen, marking and other soldermask areas are strictly prohibited from bending more than 90° during assembly.

  • Flexible PCB assembly

The substrate material used by FPC has the characteristics of moisture absorption. - Before assembly, high temperature or SMT process may require customers to bake and dehumidify the PCB to prevent undesirable appearance of bubbles, stratification or blasting holes.

It is recommend that to move and take turn to solder the adjacent pins, to avoid local overheating.

  • Environment

Moisture protection measures must be taken for the storage places and packaging of flexible PCBs.The factory should be kept clean and undergo regular pest control maintenance.Strict anti-static work procedures must be carried out in the factory.Operators must wear anti-static clothing and wristband.

  • Usage

If the user needs to unplug the flexible PCB, he/she should hold the area of the connector, do not pull the FPC Flexible Printed Circuit Boards directly.

If the FPC Flexible Printed Circuit Boards does not work, how to repair it?

FPC not working may be due to soldering, components and circuit problems. - To check for any burn marks on FPC Flexible Printed Circuit Boards by careful observation.
Check the presence of copper fractures carefully.
Smell the circuit board for any peculiar smells.
Inspect the soldering for any poor quality.
Check the golden finger interface for mildew or blackened signs.

  • Components

It is necessary to test all components on the board until identifying the defective ones.
The elimination method should involve replacing the components on board with new ones to ensure all components are working correctly.

  • Soldering

Checking the soldering condition carefully and repair if there is bad soldering.

  • Circuit problem

Excluding components and soldering failure, circuit problems are the most complex.

The designer should modify the design and reproduce the PCB.

Although many factors can cause damage to FPC Flexible Printed Circuit Boards, paying attention to its design, manufacturing, storage, and usage can prevent such damage.