A method for surface activation of a very low profile copper foil by plasma-assisted processing and the resulting copper foil

Abstract

The application provides a surface activation method of a plasma-assisted processing ultra-low profile copper foil and a copper foil obtained by the method, and belongs to metal surface treatment. The surface activation method comprises the following steps: sequentially cleaning and drying the ultra-low profile copper foil to obtain a pretreated copper foil; and placing the pretreated copper foil in a plasma processing chamber to activate the surface of the copper foil, i.e. completing the surface activation. In the surface activation method, the plasma processing is a dry process, and no strong acid, strong base or organic solvent is needed, no waste liquid is discharged, the green manufacturing requirement is met, the processing is uniform and controllable, large-area continuous production can be realized, the parameters can be accurately regulated, the batch consistency is good, and the method is suitable for various specifications of ultra-low profile copper foils, including electrolytic copper foils and calendered copper foils.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to a plasma-assisted surface activation method for ultra-low profile copper foil and the resulting copper foil. Background Technology

[0002] With the development of fifth-generation mobile communication (5G), high-frequency and high-speed circuit boards, and fine-line technology, the performance requirements for copper foil in copper-clad laminates (CCLs) and printed circuit boards (PCBs) are increasingly stringent. Ultra-low profile copper foil, due to its extremely low surface roughness (R²), is particularly important. Z With a thickness of ≤1.0μm, it can effectively reduce the skin effect loss of high-frequency signals, making it the preferred material for high-frequency circuit boards.

[0003] However, the smooth surface and small specific surface area of ​​ultra-low profile copper foil result in poor adhesion to resin matrices (such as epoxy resin and polyimide). Traditional methods to improve adhesion involve chemical roughening, which involves etching the copper foil surface to create an uneven structure to increase mechanical interlocking. However, this method significantly increases surface roughness (R0). Z Typically increasing the thickness to over 2 μm, it disrupts the extremely low profile characteristics, thereby degrading high-frequency performance. Furthermore, the chemical roughening process uses large amounts of strong acids and strong oxidants, leading to environmental pollution and wastewater treatment problems.

[0004] In recent years, researchers have attempted to improve the bonding between copper foil and resin through chemical methods such as silane coupling agents and self-assembled monolayers. However, these methods often involve wet processes, which are cumbersome, and the coupling agent is unevenly distributed on smooth surfaces, resulting in limited improvement in bonding strength. Some literature reports the use of plasma treatment to remove contaminants or alter surface energy in copper foil, but existing techniques mostly focus on cleaning or reduction treatments and do not systematically introduce specific polar functional groups to enhance chemical bonding for extremely low-profile copper foil while maintaining low roughness.

[0005] Therefore, developing an activation method that can introduce highly reactive polar functional groups into the surface of extremely low profile copper foil without increasing surface roughness is of great significance for meeting the manufacturing requirements of high frequency circuit boards. Summary of the Invention

[0006] The purpose of this invention is to provide a surface activation method for ultra-low profile copper foil with plasma-assisted treatment and the resulting copper foil, thereby solving the problem of poor adhesion between ultra-low profile copper foil and resin in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a surface activation method for plasma-assisted ultra-low profile copper foil, the surface activation method comprising the following steps: 1) The very low profile copper foil is sequentially cleaned and dried to obtain pretreated copper foil; 2) Place the pretreated copper foil in a plasma treatment chamber to activate the surface of the copper foil, thus completing the surface activation. In the activation process, the working gas is an oxygen-containing gas, a nitrogen-containing gas, or a mixture thereof.

[0008] Preferably, the surface roughness R of the ultra-low profile copper foil is... Z The diameter is 0.1~0.8μm, and the thickness is 6~70μm.

[0009] Preferably, in step 1), the cleaning reagent is one or more of acetone, ethanol and deionized water, the cleaning is ultrasonic cleaning, the ultrasonic cleaning time is 5~20 min, and the ultrasonic cleaning power is 50~500W.

[0010] Preferably, in step 2), the processing chamber pressure is 1~1000Pa, the radio frequency power supply frequency is 13.56MHz, the processing power is 50~500W, and the processing time is 5~300s.

[0011] Preferably, in step 2), the working gas flow rate during the activation process is 10~500 sccm.

[0012] Preferably, the roughness of the copper foil after surface activation is 0~0.1μm different from that of the ultra-low profile copper foil; The surface of the activated copper foil has hydroxyl and / or carboxyl polar functional groups.

[0013] The present invention also provides a copper foil obtained by a surface activation method for ultra-low profile copper foil assisted by plasma treatment.

[0014] The beneficial effects of this invention are: The surface roughness R of copper foil before and after treatment by the method of the present invention Z The variation is no more than 0.1μm, fully preserving the ultra-low profile characteristics and meeting the requirements for low-loss transmission of high-frequency signals. After treatment, the percentage of oxygen atoms on the surface of the copper foil can reach 12-20%, indicating a high density and uniform distribution of polar functional groups such as hydroxyl and carboxyl groups. The peel strength of the activated ultra-low profile copper foil with common resins (such as epoxy resin and polyimide) is more than 30% higher than that of the untreated copper foil, and can be increased by up to 120%. In addition, plasma treatment is a dry process that does not require the use of strong acids, strong alkalis or organic solvents, and there is no waste liquid discharge, which meets the requirements of green manufacturing. Moreover, the treatment is uniform and controllable, enabling large-area continuous production with precise parameter control and good batch consistency. It is suitable for ultra-low profile copper foil of various specifications, including electrolytic copper foil and rolled copper foil. Detailed Implementation

[0015] This invention provides a surface activation method for plasma-assisted ultra-low profile copper foil, the surface activation method comprising the following steps: 1) The very low profile copper foil is sequentially cleaned and dried to obtain pretreated copper foil; 2) Place the pretreated copper foil in a plasma treatment chamber to activate the surface of the copper foil, thus completing the surface activation. In the activation process, the working gas is an oxygen-containing gas, a nitrogen-containing gas, or a mixture thereof.

[0016] This invention employs low-temperature plasma technology, utilizing active particles (oxygen atoms, hydroxyl radicals, nitrogen radicals, etc.) generated by the discharge of a working gas (such as O2, CO2, N2, or NH3) to react with copper atoms or cuprous oxide on the surface of copper foil. In oxygen plasma, the copper surface is oxidized, forming oxygen-containing functional groups, primarily hydroxyl (-OH) and carboxyl (-COOH) groups. In nitrogen or ammonia plasma, amino groups (-NH2) can be introduced, which can then be partially converted into oxygen-containing functional groups upon exposure to air. These polar functional groups can chemically react with epoxy, carboxyl, and hydroxyl groups in the resin, thereby forming a strong chemical bond between the copper foil and the resin. Unlike traditional mechanical roughening, plasma activation only involves chemical modification at a depth of a few nanometers to tens of nanometers on the surface, without altering the microstructure and roughness of the copper foil, thus fully preserving the excellent high-frequency characteristics of the extremely low profile copper foil.

[0017] In this invention, the surface roughness R of the ultra-low profile copper foil is... Z The preferred thickness is 0.1~0.8μm, more preferably 0.2~0.6μm, even more preferably 0.4~0.5μm, and the preferred thickness is 6~70μm, more preferably 20~60μm, even more preferably 30~50μm.

[0018] In this invention, in step 1), the cleaning reagent is preferably one or more of acetone, ethanol and deionized water, the cleaning is preferably ultrasonic cleaning, the ultrasonic cleaning time is preferably 5-20 min, more preferably 8-16 min, more preferably 10-12 min, and the ultrasonic cleaning power is preferably 50-500 W, more preferably 100-400 W, more preferably 200-300 W.

[0019] In this invention, the purpose of cleaning is to remove oil, dust, and natural oxide layer from the surface of the copper foil.

[0020] In this invention, the drying process is preferably performed by sequentially blowing and drying; The drying process is preferably carried out using an inert gas, preferably nitrogen or argon. The drying is preferably carried out under vacuum conditions, the drying temperature is preferably 45~55℃, more preferably 46~52℃, even more preferably 48~50℃, and the drying time is preferably 20~30min, more preferably 22~28min, even more preferably 25~26min.

[0021] In this invention, in step 2), the processing chamber pressure is preferably 1~1000Pa, more preferably 200~800Pa, and even more preferably 400~600Pa; the radio frequency power supply frequency is preferably 13.56MHz; the processing power is preferably 50~500W, more preferably 100~400W, and even more preferably 200~300W; and the processing time is preferably 5~300s, more preferably 60~240s, and even more preferably 120~180s.

[0022] In this invention, in step 2), the working gas flow rate during the activation process is preferably 10-500 sccm, more preferably 50-400 sccm, and even more preferably 200-300 sccm.

[0023] In this invention, the oxygen-containing gas is preferably oxygen, air, or carbon dioxide, and the nitrogen-containing gas is preferably nitrogen or ammonia.

[0024] In this invention, the roughness of the copper foil after surface activation is preferably 0~0.1μm and more preferably 0.02~0.08μm, and even more preferably 0.04~0.06μm. The surface of the activated copper foil preferably has hydroxyl and / or carboxyl polar functional groups.

[0025] In this invention, under the influence of high-energy electrons, ions, and free radicals in plasma, copper atoms on the surface of the copper foil react with active species in the plasma to generate polar functional groups such as hydroxyl (-OH) and / or carboxyl (-COOH). These functional groups are chemically bonded to the copper surface, forming a stable activation layer.

[0026] The present invention also provides a copper foil obtained by a surface activation method for ultra-low profile copper foil assisted by plasma treatment.

[0027] In this invention, the activated copper foil is preferably stored in a sealed or inert atmosphere, and the storage time is recommended not to exceed 72 hours, so as to avoid contamination or deactivation of the surface polar functional groups.

[0028] This invention introduces polar functional groups such as hydroxyl and carboxyl groups onto the surface of copper foil through plasma technology without increasing the surface roughness of the copper foil, thereby enhancing the chemical bonding between the copper foil and the resin, while maintaining excellent high-frequency signal transmission performance.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1

[0031] A thickness of 18 μm and an initial surface roughness R are selected. Z The ultra-low profile electrolytic copper foil with a diameter of 0.45 μm was cut into 10 cm × 10 cm samples. Cleaned sequentially with acetone, anhydrous ethanol, and deionized water using ultrasonication (ultrasonic power 320W) for 5 minutes each, then dried with high-purity nitrogen and placed in a vacuum drying oven at 50°C for 30 minutes. A low-pressure radio frequency plasma treatment device was used. The copper foil was placed in the treatment chamber, and the vacuum was evacuated to 10 Pa. The working gas was introduced: oxygen (O2) at a flow rate of 50 sccm. The radio frequency power supply (13.56 MHz) was turned on at a power of 200 W, the treatment pressure was stabilized at 20 Pa, and the treatment time was 60 s. After treatment, the copper foil was removed, thus completing the surface activation.

[0032] Example 2

[0033] A thickness of 12 μm and an initial surface roughness R are selected. Z The ultra-low profile electrolytic copper foil with a diameter of 0.28 μm was cut into 10 cm × 10 cm samples. Cleaned sequentially with acetone, anhydrous ethanol, and deionized water using ultrasonication (ultrasonic power 320W) for 5 minutes each, then dried with high-purity nitrogen and placed in a vacuum drying oven at 50°C for 30 minutes. A low-pressure radio frequency plasma treatment device was used. The copper foil was placed in the treatment chamber, and the vacuum was evacuated to 10 Pa. The working gas was carbon dioxide (CO2) at a flow rate of 50 sccm. The radio frequency power supply was turned on (13.56 MHz) at a power of 200 W, the treatment pressure was stabilized at 20 Pa, and the treatment time was 100 s. After treatment, the copper foil was removed, thus completing the surface activation.

[0034] Example 3

[0035] A thickness of 35 μm and an initial surface roughness R are selected. Z The ultra-low profile electrolytic copper foil with a diameter of 0.62 μm was cut into 10 cm × 10 cm samples. Cleaned sequentially with acetone, anhydrous ethanol, and deionized water using ultrasonication (ultrasonic power 320W) for 5 minutes each, then dried with high-purity nitrogen and placed in a vacuum drying oven at 50°C for 30 minutes. A low-pressure radio frequency plasma treatment device was used. The copper foil was placed in the treatment chamber, and the vacuum was evacuated to 10 Pa. The working gas was air, with a flow rate of 50 sccm. The radio frequency power supply (13.56 MHz) was turned on, with a power of 200 W. The treatment pressure was stabilized at 20 Pa, and the treatment time was 90 s. After treatment, the copper foil was removed, thus completing the surface activation.

[0036] Comparative Example 1

[0037] A thickness of 18 μm and an initial surface roughness R are selected. Z The ultra-low profile electrolytic copper foil with a diameter of 0.45 μm was cut into 10 cm × 10 cm samples. The copper foil was cleaned sequentially with acetone, anhydrous ethanol, and deionized water using ultrasonic cleaning (ultrasonic power of 320W) for 5 minutes each, then dried with high-purity nitrogen gas, and placed in a vacuum drying oven at 50°C for 30 minutes to obtain the treated copper foil.

[0038] Comparative Example 2

[0039] The same ultra-low profile electrolytic copper foil as in Example 1 was selected, with a thickness of 18 μm and an initial surface roughness R. Z =0.45μm.

[0040] The copper foil was ultrasonically cleaned for 5 minutes each with acetone, anhydrous ethanol and deionized water, and then dried with high-purity nitrogen. Preparation of micro-etching solution: Mix sodium persulfate, sulfuric acid and water, wherein the concentration of sodium persulfate is 80 g / L and the concentration of sulfuric acid is 50 mL / L (mass fraction of about 5%), and control the solution temperature at 30℃; The cleaned and dried copper foil was completely immersed in the micro-etching solution and soaked for 60 seconds, during which it was gently stirred to ensure uniform roughening. Remove the copper foil and immediately rinse it thoroughly with plenty of deionized water to remove any residual micro-etching solution from the surface. Then, dry it with high-purity nitrogen to obtain the treated copper foil.

[0041] The copper foils obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests, and the results are shown in Table 1.

[0042] Surface roughness: Tested according to national standard GB / T 29847-2025 "Test Method for Copper Foil for Printed Circuit Boards"; Oxygen element atomic percentage: According to the national standard GB / T 19500-2025 "General Rules for X-ray Photoelectron Spectroscopy Analysis of Surface Chemical Analysis"; Peel strength between copper foil and resin: The copper foils obtained in Examples 1-3 and Comparative Examples 1-2 were pressed with epoxy resin prepregs at 180°C and 2.5MPa for 60 minutes to form copper-clad laminates with dimensions of 100mm×100mm×0.15mm. Test method: Using a universal testing machine, a strip sample with a width of 12.7 mm was obtained by direct cutting on the copper-clad laminate. The copper foil end was peeled off by about 25 mm and fixed on the fixture. Peeling was carried out in a direction perpendicular to the laminate at a tensile speed of 100 mm / min. The peeling force (unit: N / mm) during the stable phase of the peeling process was recorded.

[0043] Table 1 Performance test results of copper foils obtained in Examples 1-3 and Comparative Examples 1-2

[0044] As can be seen from Table 1, in terms of roughness retention, R in Examples 1-3... Z The changes were all 0.01 μm (far superior to +1.40 μm in Comparative Example 2), for example, R in Example 1. Z The value only increased from 0.45 μm to 0.46 μm, completely preserving the extremely low profile characteristics. Regarding the introduction of functional groups, XPS analysis confirmed that the oxygen content of Example 1 increased from the initial approximately 4% to 18.6%, Example 2 reached 15.2%, and Example 3 was 12.5%, all within the target range of 12-20%. Moreover, the high-resolution C1s spectrum showed characteristic peaks of C-OH and O=C-OH at ~286.0 eV and ~288.5 eV, respectively, indicating that hydroxyl and carboxyl groups were successfully introduced into the copper foil surface. In terms of adhesion, the peel strength of Example 1 reached 0.71 N / mm, an improvement of 121.9% compared to Comparative Example 1, far exceeding the target (≥30%). Example 3 reached 0.55 N / mm (an improvement of 71.9%), both meeting the requirements for adhesion of high-frequency copper clad laminates (typical value ≥0.53 N / mm). Although the peel strength of Comparative Example 2 was slightly lower, it was at the cost of sacrificing roughness.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for surface activation of ultra-low profile copper foil with plasma assistance, characterized in that, The surface activation method includes the following steps: 1) The very low profile copper foil is sequentially cleaned and dried to obtain pretreated copper foil; 2) Place the pretreated copper foil in a plasma treatment chamber to activate the surface of the copper foil, thus completing the surface activation. In the activation process, the working gas is an oxygen-containing gas, a nitrogen-containing gas, or a mixture thereof.

2. The surface activation method for ultra-low profile copper foil with plasma assistance according to claim 1, characterized in that, The surface roughness R of the ultra-low profile copper foil Z The diameter is 0.1~0.8μm, and the thickness is 6~70μm.

3. The surface activation method for ultra-low profile copper foil with plasma assistance according to claim 2, characterized in that, In step 1), the cleaning reagent is one or more of acetone, ethanol and deionized water, the cleaning is ultrasonic cleaning, the ultrasonic cleaning time is 5~20min, and the ultrasonic cleaning power is 50~500W.

4. The surface activation method for ultra-low profile copper foil with plasma assistance according to claim 1, characterized in that, In step 2), the processing chamber pressure is 1~1000Pa, the radio frequency power supply frequency is 13.56MHz, the processing power is 50~500W, and the processing time is 5~300s.

5. A surface activation method for ultra-low profile copper foil with plasma assistance according to claim 1 or 4, characterized in that, In step 2), during the activation process, the working gas flow rate is 10~500 sccm.

6. The surface activation method for ultra-low profile copper foil with plasma assistance according to claim 5, characterized in that, The difference between the surface roughness Rz of the activated copper foil and that before the treatment is no more than 0.1 μm.

7. The surface activation method for ultra-low profile copper foil with plasma assistance according to claim 6, characterized in that, The activated copper foil surface has hydroxyl and / or carboxyl polar functional groups.

8. The copper foil obtained by the surface activation method of plasma-assisted ultra-low profile copper foil according to any one of claims 1 to 7.

Images