In the design of flexible printed circuit boards (FPCs) and high-density interconnect (HDI) boards, engineers face a continuously tightening constraint: devices are becoming thinner, leaving less space for flexible circuits. The hinge area of mobile phone foldable screens, the inner cavity of wearable devices, and the soft board connection of micro cameras - these scenarios are changing the requirement for FPC substrate thickness from "as thin as possible" to "must be thin".

The traditional copper-clad laminate (FCCL) consists of three layers: PI substrate, adhesive layer, and copper foil. The adhesive layer usually accounts for a considerable proportion of the total thickness, becoming the main obstacle to thinning. A more thorough solution is becoming an industry consensus:Non adhesive copper plated film——Directly depositing copper layer on the surface of PI film by vacuum sputtering, eliminating the adhesive layer, and reducing the total thickness of the material to its limit.

2、 Why PI: Material Logic of 7 μ m Substrate

The reason why polyimide (PI) has become the preferred substrate for flexible circuits is due to its series of irreplaceable comprehensive properties:

Key conclusion:When the thickness of the PI substrate is reduced to 7 μ m, the above properties are not significantly compromised due to thinning - this is precisely the core value of PI as a high-performance engineering plastic.

3、 Vacuum Sputtering Copper Plating: "Growing" Copper Layer on 7 μ m Substrate

The copper layer of the 7 μ m PI copper plated film was prepared using roll to roll (R2R) vacuum magnetron sputtering process. In a vacuum environment, high-speed particles bombard copper targets with extremely high energy, causing copper atoms or molecules to sputter from the surface of the target and accurately deposit on the surface of the PI film under the action of electric and magnetic fields, gradually forming a uniform and dense copper film.

4、 Copper layer thickness: Performance range from 0.1 μ m to 1 μ m

Based on a 7 μ m PI substrate, copper plated film products with different copper layer thicknesses can be prepared by precisely controlling the sputtering process parameters. The thickness of the copper layer varies from 0.1 μ m to 1 μ m, and different thicknesses correspond to different performance focuses:

Note: The thickness of the copper layer is the nominal reference value, and the specific performance is subject to the actual product specifications.

5、 The engineering value of 7 μ m: not just 'thinner'

In FPC manufacturing, the product advantages of PI copper plated film include high heat resistance, good flexibility, good peel strength, good uniformity of copper layer, and excellent dimensional stability. The PI copper plating film of Advanced Institute Technology has no cracks on the surface of the copper film after ten cycles of bending operation.

6、 Application scenario: Diversified layout from FPC to COF

7、 Selection considerations: Engineering decisions from substrate to copper layer

8、 Conclusion

The essence of 7 μ m PI copper plating film is an engineering product that combines the extreme thinning of PI thin film with precision copper plating process. It is not simply a "thinner" iteration - at the 7 μ m scale, material thermal management, tension control, coating uniformity, and adhesion all face new engineering boundaries. It is precisely these boundary conditions that have been overcome one by one that enable the 7 μ m PI copper plated film to move from the laboratory to mass production, becoming a reliable material option for high-density FPC, COF substrates, and flexible electronic devices.

For FPC design engineers, understanding the process constraints and performance opportunities behind the thickness of 7 μ m - why it is 7 μ m instead of thinner, and how to choose the thickness of the copper layer - is more valuable than simply remembering a specification.