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FPC, also known as FPCB, stands for Flex Printed Circuit Board. It refers to a printed circuit board made from flexible insulating materials and is a type of PCB (Printed Circuit Board).
Compared to rigid printed circuit boards, FPCs are flexible and bendable, smaller in size, and lighter in weight. They play a crucial role in electronic devices by
providing electrical connectivity and serving as a bridge, thereby enhancing product performance and reducing size.
There is no absolute superiority or inferiority in performance between FPC and rigid printed circuit boards; the difference lies only in their form factor and flexibility.
Due to their thinness and flexibility, FPCs are primarily used in compact applications and scenarios requiring flexible connections, such as micro-miniature electronic devices,
flip phones, and the data connection components between the body and screen of foldable products like laptops.
1. Applications of FPCs
Rigid boards impose some limitations on product design because they cannot be installed in confined spaces. Circuit boards in products frequently subjected to mechanical shock
require vibration resistance. Flexible PCBs are more suitable for this purpose because they can be bent and wrapped as needed.
They can survive harsh temperatures ranging from -200 to 400 degrees Celsius. These features make flexible PCBs more reliable and durable than traditional circuit boards.
Computers and Accessories
Flexible PCBs are very robust against signal and atmospheric conditions. Hard drives in computers contain flex PCBs because these PCBs provide high data transfer rates
on physically small circuit boards. Other electronic devices such as printers, calculators, and laptop LCDs are often designed with flex PCBs.
Aircraft
Aircraft electronic systems are often packed with cables and must be lightweight. A typical Airbus contains nearly 100 kilometers of cables, while a helicopter contains
approximately 12 kilometers. When it comes to the reliability and performance of aircraft systems, there can be no compromise. Flex PCBs reduce weight and
significantly improve performance even under mechanical shock, making them an ideal choice for aircraft.
Automobiles
Automotive products are becoming increasingly compact over time. Flexible PCBs add compactness to designs because, regardless of their shape, they can be placed in limited spaces
and still function efficiently. Flex PCBs enable designers to create lightweight products while maintaining performance.
Flex PCBs are commonly used in engine management computers, airbag controllers, and other electronic components in automotive products.
Because cars are often exposed to high temperatures, which are tolerable for flexible PCBs, these boards are a staple in modern automotive products.
Mobile Phones
Mobile phones are small yet packed with features. Ever wonder how to design dense circuitry in such a compact housing?
Flexible PCBs enable the synchronization of multiple components while minimizing space requirements.
Using wiring harnesses or rigid boards to synchronize components is disadvantageous due to the limited size and shape of mobile phones. Furthermore, mobile phones heat up,
and traditional circuit boards cannot withstand these high temperatures. Flex PCBs also add waterproofing to their designs.
Currently, mobile phones and digital books are developing flexible PCBs, a major technological breakthrough. As technology advances, flexible PCBs are also evolving, and hopefully,
in the near future, we will be able to bend our phones like a page.
Medical Electronics
Medical electronics require a high degree of precision and durability. Wearable devices currently under development are often developed using flexible PCBs,
whose flexibility makes them suitable for host devices.
2. FPC Main Raw Materials
The main raw materials include: base material, cover film, reinforcement, and other auxiliary materials.
Base Material
Adhesive Base Material
Adhesive base material mainly consists of three parts: copper foil, adhesive, and PI. It is divided into single-sided and double-sided base materials.
Materials with copper foil on only one side are single-sided base materials, while materials with copper foil on both sides are double-sided base materials.
Adhesive-Free Base Material
Adhesive-free base material is a base material without an adhesive layer. Compared to conventional adhesive base materials, it lacks the intermediate adhesive layer and
consists only of copper foil and PI. Compared to adhesive base materials, it has advantages such as thinner thickness, better dimensional stability, higher heat resistance,
higher bending resistance, and better chemical resistance. It is now widely used.
Copper Foil
Currently, the following copper foil thicknesses are commonly used: 1oz, 1/2oz, and 1/3oz. A thinner 1/4oz copper foil is now available. This material is already used in China for
ultra-fine circuit products (line width and spacing of 0.05mm and below). As customer requirements become increasingly demanding, this type of material will be widely used in the future.
Coversheet
Main components: release paper, adhesive, and PI. Ultimately, only the adhesive and PI remain on the product. The release paper is removed during the production process and
no longer used (it protects the adhesive from foreign matter).
Reinforcement
This material is specifically designed for FPCs and is applied to specific areas of the product to increase support strength and compensate for the "soft" nature of FPCs. Currently,
the following reinforcement materials are commonly used:
a. FR4 reinforcement: Mainly composed of fiberglass cloth and epoxy resin adhesive, the same FR4 material used in PCBs;
b. Steel sheet reinforcement: Made of steel, it offers greater hardness and support strength;
c. PI reinforcement: Similar to the coversheet, it consists of PI and adhesive release paper, but the PI layer is thicker and can be produced in thicknesses ranging from 2 mils to 9 mils.
Other Auxiliary Materials
a. Pure Adhesive: This adhesive film is a heat-curing acrylic adhesive consisting of a protective paper/release film and a layer of adhesive. It is primarily used for bonding laminates,
rigid-flex boards, and FR-4/steel reinforced boards.
b. Electromagnetic Protection Film: This film is applied to the board surface for shielding.
c. Pure Copper Foil: This film consists solely of copper foil and is primarily used in the production of hollow boards.
With the increasing popularity of the Internet of Things, 5G, driver assistance systems (ADAS), and generative artificial intelligence (Gen-AI),
the amount of information continues to increase, and data communication requires high-speed and high-frequency transmission. FPC will play a key role in the electronics industry.