Flexible Printed Circuit (FPC), with its notable advantages such as lightweight, thinness, and the ability to bend and fold freely, has been widely applied in the electronics industry. The technology of FPC originated in the 1970s, initially developed by the United States to advance rocket technology for space exploration. This technology uses polyester film or polyimide as the substrate, offering high reliability and excellent flexibility. By embedding circuit designs on flexible plastic substrates, FPC can integrate a large number of precision components within limited space, forming a flexible circuit. This type of circuit can be bent and folded at will, featuring light weight, small volume, good heat dissipation, and easy installation, thereby breaking the limitations of traditional interconnection technologies. The structure of FPC mainly includes insulating film, conductor, and adhesive. As a key solution to meet the miniaturization and mobility demands of electronic products, FPC significantly reduces the volume and weight of electronic devices, aligning with the development trends of high density, miniaturization, and high reliability.

Material Composition of FPC    

1.Insulating Film

The insulating film forms the base layer of the circuit, and the adhesive is used to fix the conductor layer onto the insulating layer. In multi-layer designs, the insulating film also serves as an internal adhesive and can act as a protective layer, preventing the circuit from dust and moisture while reducing stress during bending. The conductor layer is typically made of copper foil, which is used to achieve the conductive function of the circuit.

2. Conductor

Copper foil is the most commonly used conductor material in FPC, which can be produced through electro-deposition (ED) or electroplating processes. Electro-deposited copper foil has a shiny side and a matte side, with special treatment to enhance its adhesive properties. Forged copper foil combines flexibility and rigidity, making it suitable for applications requiring dynamic deflection.

3. Adhesive

The adhesive is not only used to bond the insulating film with the conductor material but can also serve as a cover layer or protective coating. The cover layer is formed by screen printing the adhesive onto the insulating film, creating a laminated structure. Not all laminated structures contain adhesive; adhesive-free laminated structures enable thinner circuit designs and higher flexibility while improving thermal conductivity. Since the adhesive-free structure eliminates thermal resistance, its thermal conductivity is superior to that of adhesive-based laminated structures, making it suitable for high-temperature working environments.

FPC Manufacturing Process

FPC comes in various types, including single-sided FPC, double-sided FPC, and multi-layer FPC. The manufacturing processes differ depending on the type.

Process Flow for Double-Sided and Multi-Layer FPC

Cutting → Drilling → PTH (Plated Through Hole) → Electroplating → Pre-treatment → Dry Film Lamination → Alignment → Exposure → Development → Pattern Plating → Stripping → Pre-treatment → Dry Film Lamination → Alignment → Exposure → Development → Etching → Stripping → Surface Treatment → Cover Film Lamination → Lamination → Curing → Nickel Gold Plating → Printing Text → Cutting → Electrical Testing → Punching → Final Inspection → Packaging → Shipment

Process Flow for Single-Sided FPC

Cutting → Drilling → Dry Film Lamination → Alignment → Exposure → Development → Etching → Cover Film Lamination → Lamination → Curing → Surface Treatment → Nickel Gold Plating → Printing Text → Cutting → Electrical Testing → Punching → Final Inspection → Packaging

(Note: The above process flows can be adjusted and optimized according to actual production requirements.)

Analysis of FPC Advantages and Disadvantages

Advantages of FPC

Flexible Printed Circuit is made of flexible insulating substrates and offers numerous advantages that rigid printed circuits cannot match:

l High Flexibility: FPC can bend, wind, and fold freely, allowing for three-dimensional arrangement according to space layout requirements, achieving integrated design of component assembly and circuit connection.

l Lightweight and Miniaturization: FPC significantly reduces the volume and weight of electronic products, aligning with the design trends of high density, miniaturization, and high reliability. Therefore, FPC is widely used in aerospace, military, mobile communications, laptops, computer peripherals, PDAs, digital cameras, and other fields.

l Excellent Heat Dissipation and Soldering Performance: FPC has good heat dissipation and solderability, facilitating assembly and reducing overall costs. The combination of flexible and rigid designs partially compensates for the insufficient component load-bearing capacity of flexible substrates.

Disadvantages of FPC

l High Initial Costs: Since FPC is custom-designed and manufactured for specific applications, the initial costs of circuit design, wiring, and photolithography are relatively high. Unless there are special requirements, FPC is not recommended for small-batch applications.

l Difficult Maintenance and Replacement: Once FPC is manufactured, if design modifications are needed, it must start from the original blueprint or programming data, making the process complex. Additionally, the surface of FPC is usually covered with a protective film, and repairs require removing the protective film, fixing the issue, and then reapplying the film, increasing the difficulty of maintenance.

l Prone to Damage: During installation and connection, improper handling can easily damage FPC. Soldering and rework require personnel with professional training, raising the operational threshold.