Manufacturing Process of Flexible Printed Circuit

Flexible Printed Circuits are integral to modern electronics, and their production demands precision, scalability, and strict quality control. Factories specializing in FPC manufacturing must balance advanced technology with efficient workflows to meet high-volume demands while ensuring reliability.

The flexible printed circuit manufacturing process is a highly precise and multi-step procedure that transforms raw materials into flexible, lightweight, and high-performance circuit boards.

FPC Fabrication Steps (Etching Production Process)

1. Material Cutting

First, we cut the entire roll of copper foil substrate (usually PI + copper foil) into the required size for subsequent processing.

2. Surface Cleaning

Next, the surface of the cut copper foil is cleaned to remove dust and oil, ensuring that the photosensitive film applied later adheres securely.

3. Applying Photoresist Dry Film

A photosensitive film (dry film photoresist) is applied to the surface of the copper foil, which acts as a "protective cover."

4. Exposure and Development

Using a mask (film) to expose the traces we want to retain. After development, the trace pattern is revealed on the copper foil.

5. Etching the Copper Foil

A chemical solution is used to etch away the areas not protected by the photoresist, leaving only the desired copper traces.

6. Stripping

Removing the photoresist dry film that protects the traces, the complete copper foil circuit is formed.

7. Coverlay

A layer of PI coverlay is applied to the circuit surface and securely bonded using heat pressing. Openings are only made for the pads and functional areas.

8. Drilling and Plating

Laser or mechanical drilling is used where through-holes are required. Copper deposition and plating are then performed to provide interconnection between circuits on different layers.

9. Surface Treatment

To prevent copper oxidation and improve solderability, the pad surface is treated with treatments such as immersion gold, immersion silver, and OSP.

10. Forming

In the final step, the board is punched or laser cut into the customer's desired shape, completing a complete flexible circuit board.

Single-sided and double-sided are the two main types of flexible circuit board, and each type has a different manufacturing process. Flex Plus will help you understand their differences.

Single-sided FPC Manufacturing Process

Most single-sided flexible circuits are typically manufactured by bonding copper foil to a layer of polyimide dielectric film. This bonding process typically uses a layer of adhesive to ensure a strong bond between the copper foil and the polyimide. Another manufacturing method is to bond the copper directly to the dielectric without the use of an adhesive, and this composite material is called an adhesiveless substrate.

The formation of a copper circuit is achieved through photolithography imaging, development, and etching.

• One method is to pre-punch holes in the polyimide material. The pre-punched PI material is laminated to the substrate on which the copper circuit has been formed to form a covering layer to protect the circuit.

• Another method is to use optical imaging technology to accurately cover the solder mask layer in specific areas of the circuit to protect the circuit and prevent short circuits during soldering (the solder mask layer, as a selective dielectric, only covers the parts that need protection and does not affect other parts of the circuit).

Single-sided Flex PCB

A single-sided flexible circuit is the simplest form of flex PCB, characterized by a circuit pattern on only one side of the substrate. The flexible printed circuit manufacturing process includes the following steps:

Material cutting → CNC drilling → Dry film laminate → alignment → exposure → developing → etching → decoating → surface treatment → pasting covering film → pressing → curing → surface treatment → immersion nickel gold → printing characters → shearing → electrical measurement → punching → final inspection → packaging → shipping

Double-sided Flexible Printed Circuit Manufacturing Process

A double-sided flexible circuit is a type of FPC that has conductive copper layers on both sides of a flexible dielectric substrate. Double-sided circuit boards begin with two copper layers separated by an insulating film. Similar to single-sided designs, the bonding between the substrate film and the copper conductors can use adhesive or be adhesiveless. 

Double-sided Flex PCB

 Double-sided flexible circuits have circuits on both side of the substrate, allowing for more complex designs and greater functionality. The manufacturing process for the double-sided circuit is more intricate than the single-sided circuits, involving the following steps:

Material cutting → CNC drilling → PTH → copper plating → pretreatment  → Dry film laminate → aligning → exposure → developing → graphic plating → decoating → pretreatment → Dry film laminate → alignment exposure → developing → etching → decoating → surface treatment → pasting covering film → pressing → curing → immersion nickel gold→ printing characters → shearing → electrometering → punching → final inspection → packaging → shipping

The flex PCB material usage and cost of single and double-sided PCBs are different. A double-sided circuit requires more materials and involves more complex manufacturing steps, resulting in higher costs. We provide more cost-effective solutions by optimizing its manufacturing processes.

Summary

Flex Plus is a flexible PCB manufacturer that focuses on various circuit boards and provides customized solutions to meet the needs of different customers. Our flex PCB products are widely used in medical and health, new energy vehicles, communication products, precision modules for mobile phones, industrial control, hearing aids, and other technological fields. Flex Plus has established good cooperative relationships with many well-known customers in North America, Europe, Japan, Southeast Asia, and mainland China.