In the design of flexible printed circuit boards (FPCs), substrate thickness is always a key constraint - it determines the lower limit of bending radius, the upper limit of wiring density, and the utilization efficiency of internal space of the device. When the PI substrate was thinned from the traditional 25 μ m and 12.5 μ m to 7 μ m, a critical engineering boundary was breached.

What is the concept of 7 μ m? As a reference, the thickness of a standard A4 paper is about 70-100 μ m, and a 7 μ m PI substrate is only about one tenth the thickness of the paper. At this scale, the flexibility of PI film has reached a new height - the bending radius can be as small as sub millimeter level, providing unprecedented design freedom for extreme space limited scenarios such as wiring in the hinge area of foldable screen phones and soft board connections for micro camera modules.

2、 PI: "Performance not reduced" logic on 7 μ m substrate

Thinning polyimide film to 7 μ m is not simply about "thinning" the material. The reason why PI can still maintain its engineering value at this extreme thickness is due to its inherent material properties:

• Extreme temperature resistance:PI film can be used stably within a temperature range of -200 ° C to 300 ° C (or even wider). After copper plating, this characteristic is preserved, allowing the 7 μ m PI copper plated film to withstand high temperature processes such as reflow soldering without performance degradation.
• High mechanical strength:The PI film itself has high tensile strength and wear resistance, and can withstand large mechanical stresses without easily breaking. Even if thinned to 7 μ m, its tensile strength can still meet the processing and usage requirements of flexible circuits.
• Excellent electrical insulation:The volume resistivity and surface resistivity of PI film are both at extremely high levels, which can effectively prevent current leakage. After copper plating, the PI layer still provides reliable insulation isolation.
• Chemical stability:PI film has the ability to resist corrosion and chemical erosion. The PI copper plated film from Advanced Institute Technology exhibits excellent alcohol resistance - after being wiped with alcohol, there is no peeling or powder loss.

It is precisely these intrinsic properties that are preserved at a thickness of 7 μ m that make ultra-thin PI copper plated films the substrate choice for high reliability flexible circuits.

3、 Vacuum Sputtering Copper Plating: "Growing" Precision 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 highly vacuum environment (usually below 1 × 10 ⁻ ³ Pa), high-purity oxygen free copper targets are bombarded with high-energy ions to sputter copper atoms, which are accurately deposited on the surface of PI thin films under the action of electric and magnetic fields, gradually forming a uniform and dense copper film.

Vacuum sputtering copper plating on 7 μ m ultra-thin substrates faces a series of unique technical challenges:

4、 Copper layer thickness: fine control 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. Advanced Institute Technology's copper layer thickness covers 0.5-50 μ m and supports customization.

5、 Key performance: Technical confidence of 7 μ m specification

6、 Core application layout of 7 μ m PI copper plated film from FPC to COF

7、 Selection considerations: from copper layer thickness to application scenarios

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 "thinning" - at the 7 μ m scale, the thermal management, tension control, coating uniformity, and adhesion of materials are facing new engineering boundaries. It is precisely these boundary conditions that have been overcome one by one - achieving copper layer purity of over 99.99%, film thickness deviation within ± 2%, and 5B level adhesion through vacuum sputtering technology - 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.