Method for manufacturing nanostem copper foil by femtosecond laser engraving

Abstract

This invention provides a method for manufacturing nanostructured copper foil using femtosecond laser engraving, comprising the following steps: S1. The surface of a cathode roller is subjected to mechanical and chemical grinding or other processes to make its surface smooth with a surface roughness Rz < 1.5µm, preferably Rz < 1.0µm, more preferably Rz < 0.5µm, and then cleaned and dried. S2. The pretreated cathode roller is fixed on the worktable of a femtosecond laser processing equipment, and the laser processing parameters are adjusted to uniformly engrave the surface of the cathode roller, forming a nanostructure on the surface of the cathode roller. The size of the nanostructure is 30–200 nm, and the density is 10⁹–10¹⁰ ions / cm². S3. The cathode roller with the nanostructure on its surface is installed on a foil-forming machine, and the foil-forming process is started. Copper ions are continuously deposited on the surface of the cathode roller, so that the nanostructure on the surface of the cathode roller is synchronously transferred to the smooth surface of the copper foil. The copper foil is rotated out of the liquid surface with the cathode roller, and after peeling, washing, drying, and winding, the nanostructured copper foil is obtained. The nano-grown copper foil then undergoes surface treatment processes such as anti-oxidation treatment, passivation treatment, and coating with silane coupling agent to obtain the final nano-grown copper foil. This invention effectively solves the technical problems of weak interfacial bonding between existing copper foil and special high-performance resin, high high-frequency signal transmission loss, cumbersome production process, high cost, and poor process stability.

Description

Technical Field

[0001] This invention relates to the field of copper foil manufacturing, and specifically to a method for manufacturing nanofiber copper foil using femtosecond laser engraving. Background Technology

[0002] Copper foil is a core material in the manufacture of electronic components, especially indispensable in PCB manufacturing. In the traditional copper foil production process, the foil production process is the core step: copper is continuously deposited on the surface of the cathode roller, and after rotating out of the liquid surface with the cathode roller, it undergoes peeling, washing, drying, and winding to obtain the raw foil. The side in contact with the cathode roller is called the smooth side, and its surface contour is almost completely consistent with the surface of the cathode roller, which is a replica of the surface morphology of the cathode roller.

[0003] Because the original copper foil has a smooth surface, its adhesion to substrates such as resin is insufficient, failing to meet the requirements of high-end electronic components. Therefore, in existing technologies, it is usually necessary to perform additional roughening treatment on the copper foil surface, forming a layer of nodular particles (copper nodules) on the copper foil surface through electrochemical methods to increase the surface roughness of the copper foil and improve its interfacial adhesion with the resin. At the same time, with the iteration of 5G communication and high-speed computing devices, high-frequency scenarios (above 10GHz) place higher demands on the signal transmission performance of copper foil. Conventional electrolytic copper foil, due to its high surface roughness, suffers from severe signal loss problems in high-frequency transmission, restricting the performance improvement of high-end devices.

[0004] Currently, the mainstream copper foil surface roughening technology in the industry is the electrochemical roughening process. This process requires additional steps such as coarse curing, where copper nodules are deposited on the copper foil surface through an electrolytic reaction to achieve surface roughening modification. In addition, although attempts have been made to reduce the surface roughness of copper foil to meet the low-loss requirements of high-frequency applications, this has resulted in a significant decrease in the interfacial adhesion between the copper foil and the resin substrate, making it difficult to simultaneously meet the dual requirements of low loss and high interfacial adhesion. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for manufacturing nano-grown copper foil using femtosecond laser engraving, which solves the technical problems of weak interfacial bonding between existing copper foil and special high-performance resin, high high-frequency signal transmission loss, cumbersome production process, high cost, and poor process stability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for fabricating nanofiber copper foil using femtosecond laser engraving includes the following steps:

[0008] S1. Grind the surface of the cathode roller to make it smooth, remove the surface oxide layer, oil and impurities, and then clean and dry it to ensure that there are no residual water stains or dirt on the surface of the cathode roller.

[0009] S2. Fix the pretreated cathode roller on the worktable of the femtosecond laser processing equipment, adjust the laser processing parameters, and uniformly engrave the surface of the cathode roller to form a nanostructure with a size of 30–200 nm and a density of 10⁻⁶. 9 –10¹ 0 Items / cm², surface roughness Rz≤0.3μm.

[0010] The principle of nanotree formation: When a femtosecond laser acts on the surface of the cathode roller, it instantly and ultrafast heats the titanium surface, causing the titanium material to locally melt and vaporize, followed by rapid cooling and solidification. Due to the extremely rapid cooling rate, the molten titanium droplets do not have time to spread and directly shrink into spherical shapes, ultimately forming nanoscale nanotrees (nanoparticles / nanobuncle) on the surface of the cathode roller. These nanotrees are distributed among each other, forming a micro-nano composite multi-level rough structure. This processing method has the advantages of a small heat-affected zone and controllable structure, and the size and distribution density of the nanotrees can be precisely controlled.

[0011] S3. Install the cathode roller with the nanostructure on its surface onto the foil production line and start the foil production process. Copper ions are continuously deposited on the surface of the cathode roller, so that the nanostructure on the surface of the cathode roller is synchronously transferred to the smooth surface of the copper foil. The copper foil is rotated out of the liquid surface with the cathode roller and is obtained after peeling, washing, drying and winding.

[0012] The standard parameters for the copper foil production process can be used with existing production standards without additional adjustments, ensuring that the basic properties of the copper foil, such as thickness and purity, meet industry requirements. During the transfer process, the copper foil and the nanostructure on the cathode roller surface are closely bonded, ensuring accurate replication of the nanostructure. Ultimately, the size and spacing of the nanostructures on the copper foil surface are consistent with those on the cathode roller surface.

[0013] Furthermore, in step S1, the cathode roller is made of titanium, and the surface roughness Rz after grinding is ≤1.5µm. Titanium has good high temperature resistance and corrosion resistance, can withstand the instantaneous high temperature during femtosecond laser engraving, and its surface is easy to induce the formation of nanostructures, making it suitable as an engraving substrate.

[0014] Furthermore, in step S2, the laser processing parameters are: femtosecond laser pulse width 100–300 fs, laser frequency 100–500 kHz, energy density 0.3–1.0 J / cm², and the laser uses a surface scanning method with a scanning interval of 50 nm.

[0015] Furthermore, in step S2, the femtosecond laser processing equipment uses a Ti:sapphire femtosecond laser amplifier with an output wavelength of 800nm, laser pulse stability ≤±5%, and scanning accuracy ≤10nm.

[0016] Furthermore, it also includes step S4, post-treatment of the nano-grown copper foil, which involves one or more combinations of surface cleaning, anti-oxidation treatment, passivation treatment, and coating with silane coupling agent.

[0017] The process of this invention does not limit the thickness of the copper foil; various thicknesses can be produced using this method, typically 9-70µm. This process can be used to produce common high-frequency, high-speed copper foils, including but not limited to reverse-processed copper foil (RTF) and ultra-low profile copper foil (HVLP).

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] 1. Significantly Improved Interfacial Bonding: By transferring nanostructures onto the copper foil surface using femtosecond lasers, a micro-nano composite multi-level roughness structure is constructed, significantly increasing the specific surface area of ​​the copper foil. Simultaneously, the nanostructures exhibit high surface activity, readily forming chemical bonds with substrates such as resins. Combined with mechanical interlocking and anchoring effects, this transforms interfacial bonding from simple physical adhesion to chemical bonding, effectively solving the problem of weak interfacial bonding between ultra-low roughness copper foil and special high-performance resins such as hydrocarbons, LCP, and PPO. The interfacial bonding strength between copper foil and resin is increased by more than 30% compared to traditional copper foil, while avoiding the hidden dangers of copper nodule detachment and copper powder inclusion, thus improving product reliability.

[0020] 2. Significantly Reduced High-Frequency Signal Transmission Loss: Nanostructured copper foil controls the surface roughness Rz to 0.1–1.5 μm (far lower than the 1–2.5 μm of traditional electrolytic copper foil), significantly shortening the high-frequency current transmission path, suppressing the skin effect, and reducing conductor loss by 15%–30%. Simultaneously, the tiny size and spacing of the nanostructures allow for nanoscale mechanical intercalation with the resin, reducing interfacial voids and local polarization. Combined with low-dielectric resin, the dielectric loss can be stabilized at 0.002–0.004, achieving the dual advantages of "low conductor loss and controllable dielectric loss," making it suitable for 10–112 Gbps high-speed PCBs and high-frequency millimeter-wave applications, filling the technological gap in high-end high-frequency copper foil. Furthermore, the nanoscale structure can excite weak plasmons at <100 GHz, further improving signal fidelity.

[0021] 3. Simplified production process and significantly reduced costs: This invention eliminates the need for additional electrochemical roughening and coarse curing processes found in traditional methods. By using a femtosecond laser to engrave the cathode roller and simultaneously transfer the engraving onto the copper foil surface, it integrates copper foil surface modification with the foil production process, simplifying the production flow and shortening the production cycle. Simultaneously, it reduces costs associated with electrolyte consumption and equipment maintenance. Furthermore, the process has a wide processing window and high stability, enabling stable mass production with high batch consistency, further reducing production costs and simplifying quality control. Calculations show that using this process can reduce overall copper foil production costs by more than 20%.

[0022] 4. High process controllability and wide adaptability: The femtosecond laser engraving parameters can be precisely controlled, and the size, spacing and density of nanoclusters can be adjusted according to actual application needs, thereby controlling the surface roughness, interfacial bonding force and high-frequency loss performance of copper foil, adapting to the usage needs of different high-end electronic components; at the same time, this process can be directly connected to existing raw foil production lines without the need for large-scale modification of existing equipment, making it easy to promote and apply industrially.

[0023] 5. Stable product performance and broad application prospects: The nanostructure of the nano-copper foil is formed through physical transfer, which is tightly bonded to the copper foil substrate and has stable performance. It is not prone to problems such as structural detachment and performance degradation during long-term use. Its low loss and high bonding strength characteristics are suitable for the development needs of high-end fields such as high-speed PCB and high-frequency millimeter-wave devices. With the rapid development of industries such as 5G and high-end manufacturing, its application prospects are very broad. Detailed Implementation

[0024] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Example 1

[0026] A method for fabricating nanofiber copper foil using femtosecond laser engraving includes the following steps:

[0027] S1. Cathode Roller Pretreatment

[0028] A titanium cathode roller (2700mm in diameter and 1380mm in width) was selected, and its surface was finely ground to ensure that the cathode roller surface was flat, clean, and had a surface roughness Rz ≤ 1.5µm.

[0029] S2. Femtosecond laser engraving

[0030] The pretreated titanium cathode roller was fixed on the worktable of the femtosecond laser processing equipment, and the laser processing parameters were adjusted as follows: pulse width 200 fs, frequency 300 kHz, energy density 0.6 J / cm². The laser processing equipment was started, and the cathode roller rotated uniformly at a speed of 5 r / min. The laser used a surface scanning method with a scanning interval of 50 nm to uniformly engrave the surface of the cathode roller. After engraving, a nanostructure was formed on the surface of the cathode roller, with a nanostructure size of 80–120 nm and a density of 5 × 10⁻⁶. 9 pcs / cm²

[0031] S3. Nanostructure Transfer and Copper Foil Preparation

[0032] A cathode roller with a nanostructure on its surface is installed on the foil production line to start the foil production process. Copper ions are continuously deposited on the surface of the cathode roller, simultaneously replicating the nanostructure on the surface of the cathode roller. Subsequently, the copper foil is rotated out of the liquid surface with the cathode roller, and after peeling, washing, drying and winding, nanostructured foil is obtained.

[0033] S4. Post-treatment of nanofiber copper foil

[0034] The rolled-up nanofiber copper foil is subjected to conventional surface treatments, including anti-oxidation treatment, passivation treatment, and coating with silane coupling agent.

[0035] The final obtained nanofiber copper foil, after testing, showed that the surface nanofiber size was 80–120 nm and the density was 5 × 10⁻⁶. 9 The surface roughness Rz is ≤1.5 μm, and the interfacial bonding strength with LCP resin is 35% higher than that of traditional electrolytic copper foil. At 10 GHz, the conductor loss is 10% lower than that of traditional electrolytic copper foil, which meets the application requirements of 10–112Gbps high-speed PCBs.

[0036] The nano-grown copper foil prepared by this invention is mainly used in the following fields:

[0037] (1) High-speed PCB field: Adapted to the manufacturing of 10–112Gbps high-speed PCBs, especially high-frequency signal transmission lines. The low conductor loss and controllable dielectric loss characteristics of nano-grown copper foil can effectively reduce energy loss in the high-frequency signal transmission process, improve signal transmission rate and fidelity, and solve the problem of excessive loss of traditional copper foil in high-speed PCBs. At the same time, its high interface bonding force can ensure that the copper foil is tightly bonded to high-frequency resin substrates such as LCP and PPO, avoiding faults such as line detachment and short circuits, and improving the reliability of PCBs.

[0038] (2) High-frequency millimeter-wave device field: For high-frequency millimeter-wave devices (such as antennas, filters, etc.) used in 5G and next-generation communication equipment, the nanoscale topology of the nano-grown copper foil can suppress the skin effect and dielectric loss, adapting to the signal transmission requirements of the millimeter-wave band (28GHz and above). At the same time, its high surface activity can improve the assembly stability of the device and extend the service life of the device. According to tests, the millimeter-wave device using the nano-grown copper foil of this invention has a total loss of more than 18% in the 28GHz band compared with the traditional copper foil device.

[0039] (3) Other high-end electronic components: used in high-end electronic components that require low loss and high reliability, such as aerospace electronic components and precision instruments. The excellent performance of nano-grown copper foil can meet the needs of use under extreme working conditions, while simplifying the production process of components and reducing production costs.

[0040] I. Effects of different process parameters on the properties of nanofiber copper foil

[0041] Using the same process steps as in Example 1, only the core processing parameters of the femtosecond laser were adjusted to prepare nanostructured copper foils with different properties. The specific parameters and performance test results are shown in the table below:

[0042] Implementation number Femtosecond laser pulse width (fs) Laser frequency (kHz) Energy density (J / cm²) Nanoparticle size (nm) Nanoparticle density (cells / cm²) Surface roughness Rz (μm) Conductor loss reduction rate (%) 1 100 100 0.3 30–60 <![CDATA[1×10¹ 0 ]]> 0.1 30 2 200 300 0.6 80–120 <![CDATA[5×10 9 ]]> 0.2 22 3 300 500 1.0 150–200 <![CDATA[1×10 9 ]]> 0.3 15

[0043] As shown in the table above, within the process window defined by this invention (pulse width 100–300 fs, frequency 100–500 kHz, energy density 0.3–1.0 J / cm²), nanostructured copper foil with surface roughness Rz≤1.5μm and conductor loss reduction of 15%–30% can be stably prepared. With the increase of laser pulse width, frequency, and energy density, the nanostructure size increases and the density decreases, the surface roughness increases slightly, and the conductor loss reduction rate decreases slightly, but all meet the performance requirements of this invention, indicating that this process is highly controllable and the parameters can be adjusted according to actual needs.

[0044] II. Application Testing of Nanoparticle-Based Copper Foil

[0045] The nanogrown copper foil prepared in Example 1 was applied to the manufacture of a 28GHz millimeter-wave PCB, and its performance was compared with that of a PCB using conventional electrolytic copper foil. The test results are as follows:

[0046] (1) Interface bonding performance: The peel strength of nano-grown copper foil and LCP resin is 1.8 N / mm, while the peel strength of traditional electrolytic copper foil and LCP resin is 1.3 N / mm. The interface bonding strength of nano-grown copper foil is increased by 38.5%, and there is no copper powder shedding phenomenon.

[0047] (2) High-frequency loss performance: In the 28GHz band, the conductor loss of the nano-grown copper foil PCB is 0.45dB / mm, while the conductor loss of the traditional electrolytic copper foil PCB is 0.62dB / mm, representing a 27.4% reduction in conductor loss;

[0048] (3) Signal transmission performance: When transmitting 112Gbps signals, the signal fidelity of the nano-grown copper foil PCB is 98.2%, while that of the traditional electrolytic copper foil PCB is 92.5%, which greatly improves the signal transmission performance.

[0049] Test results show that the nano-grown copper foil prepared by this invention is fully adapted to the application requirements of high-frequency millimeter-wave PCBs, and its performance is superior to that of traditional electrolytic copper foil, with significant application advantages.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating nanofiber copper foil using femtosecond laser engraving, characterized in that, Includes the following steps: S1. Perform mechanical and chemical grinding or other processes on the surface of the cathode roller to make it flat with a surface roughness Rz < 1.5µm, preferably Rz < 1.0µm, more preferably Rz < 0.5µm, and then clean and dry it. S2. Fix the pretreated cathode roller on the worktable of the femtosecond laser processing equipment, adjust the laser processing parameters, and uniformly engrave the surface of the cathode roller to form a nanostructure with a size of 30–200 nm and a density of 10⁻⁶. 9 –10¹ 0 pcs / cm²; S3. Install the cathode roller with the nanostructure on its surface onto the foil production line and start the foil production process. Copper ions are continuously deposited on the surface of the cathode roller, so that the nanostructure on the surface of the cathode roller is synchronously transferred to the smooth surface of the copper foil. The copper foil is rotated out of the liquid surface with the cathode roller and is obtained after peeling, washing, drying and winding. S4. The above-mentioned nanofiber-grown raw foil is subjected to surface treatment according to conventional procedures, namely, anti-oxidation treatment, passivation treatment, and coating with silane coupling agent. Finally, nanofiber-grown copper foil is obtained.

2. The method for manufacturing nanofiber copper foil by femtosecond laser engraving according to claim 1, characterized in that: In step S1, the cathode roller is made of titanium, and the surface roughness after grinding is Rz < 1.5µm, preferably Rz < 1.0µm, and more preferably Rz < 0.5µm.

3. The method for manufacturing nanofiber copper foil by femtosecond laser engraving according to claim 2, characterized in that: In step S2, the laser processing parameters are: femtosecond laser pulse width 100–300 fs, laser frequency 100–500 kHz, energy density 0.3–1.0 J / cm², and the laser uses a surface scanning method with a scanning interval of 50 nm.

4. The method for manufacturing nanofiber copper foil by femtosecond laser engraving according to claim 3, characterized in that: In step S2, the femtosecond laser processing equipment uses a Ti:sapphire femtosecond laser amplifier with an output wavelength of 800nm, laser pulse stability ≤±5%, and scanning accuracy ≤10nm.

5. The method for manufacturing nanostructured copper foil using femtosecond laser engraving according to any one of claims 1-4, characterized in that: It also includes step S4, post-treatment of the nano-grown copper foil, which involves one or more of the following processes: surface cleaning, anti-oxidation treatment, passivation treatment, and coating with silane coupling agent.