An electrolytic copper foil, its preparation method and application

Abstract

This invention discloses an electrolytic copper foil, its preparation method, and its applications. The preparation method of the electrolytic copper foil includes the following steps: sequentially subjecting raw foil to acid washing, grain structure optimization treatment, roughening treatment, plating of a functional layer, and silane coupling treatment, followed by drying and winding to obtain the electrolytic copper foil. The grain structure optimization treatment of the raw foil forms a copper layer with a special grain structure, and the surface roughness of the copper layer is optimized by precisely controlling the coarse curing conditions. This synergistically improves the high-frequency transmission and interface bonding performance of the electrolytic copper foil. The resulting electrolytic copper foil exhibits both lower signal transmission loss and high peel strength, as well as low warpage and excellent mechanical properties, meeting the requirements of ultra-high-speed communication for electromagnetic shielding layer materials with low transmission loss and high reliability bonding strength.

Description

Technical Field

[0001] This invention relates to the field of copper foil processing technology, specifically to an electrolytic copper foil, its preparation method, and its application. Background Technology

[0002] Electrolytic copper foil, etched into a grid pattern, can be used as a shielding layer and is widely applied in electromagnetic shielding. With the widespread adoption of 5G and the development of Advanced Driver Assistance Systems (ADAS), electronic devices are demanding increasingly higher frequencies for signal transmission, requiring the use of millimeter waves exceeding 3GHz or even 30GHz. In such high-frequency applications, the skin effect of signal transmission becomes more pronounced, meaning the current mainly flows on the surface of the conductor. This necessitates that electromagnetic shielding materials not only possess good bulk conductivity but also optimize surface properties to reduce signal transmission loss. Furthermore, to ensure the reliability of the shielding layer under complex operating conditions, the copper foil and the polymer substrate must have high peel strength. Generally, reducing surface roughness helps reduce high-frequency signal loss; however, moderate roughness is crucial for ensuring sufficient specific surface area to achieve high peel strength. This contradiction presents significant technical challenges in achieving high-frequency, high-speed electrolytic copper foil that balances low loss and high peel strength.

[0003] Chinese patent application CN112118672A discloses an advanced inversion electrolytic copper foil with a long island-like microstructure, comprising a micro-roughened surface having multiple non-uniformly distributed copper crystals; wherein different numbers of the copper crystals are stacked together to form individual copper whiskers, and different numbers of the copper whiskers are aggregated together to form individual copper crystal clusters; wherein, under scanning electron microscopy at a 35-degree tilt angle and 10000x magnification, the micro-roughened surface has at least ten first smooth regions with a length of 250 nm and a width of 250 nm, at least one second smooth region with a length of 500 nm and a width of 500 nm, and at least one long island-like microstructure with a length of more than 1500 nm. This electrolytic copper foil can reduce insertion loss and improve signal integrity without compromising peel strength. However, the test data shows that the signal transmission loss of the electrolytic copper foil in this scheme is still relatively high (the insertion loss at 8 GHz is still above -0.5 dB / in and the insertion loss at 16 GHz is above -0.9 dB / in), which is difficult to meet the stringent requirements of next-generation ultra-high-speed communication for extremely low transmission loss.

[0004] Chinese patent application CN120797102A discloses an electrolytic copper foil having at least one low-roughness surface; the copper nodules on the low-roughness surface are rod-shaped protrusions and / or granular protrusions, with a spacing of 10~650nm between two adjacent protrusions, a height of 300~800nm ​​for the rod-shaped protrusions, and a height of 80~250nm for the granular protrusions; and every 25μm of the low-roughness surface... 2 Within the area, the number of the rod-shaped copper nodules and / or the granular protrusions is 50-150. This electrolytic copper foil has a more uniform surface morphology with less unevenness, effectively reducing surface roughness, improving signal integrity of the copper foil substrate, and enhancing the peel strength between the copper foil and the substrate. However, test data shows that while this solution reduces signal transmission loss to some extent, its effect on improving peel strength is limited; the peel strength after lamination with the resin substrate is <1.0 N / mm, which may pose a risk in applications requiring high reliability.

[0005] Chinese patent application CN115287714A discloses a method for preparing electrolytic copper foil with high peel strength and high elongation, comprising: preparing VLP green foil using a DC electrodeposition process; pretreating the VLP green foil with acid pickling; then introducing special additives into an electroplating thickening tank to thicken the copper layer, forming a mountain-shaped copper layer on the surface of the VLP green foil; and finally performing a blackening-ashing-passivation treatment to obtain the finished copper foil. By controlling the thickness of the VLP green foil and the thickened copper layer and combining special additives, the surface morphology, roughness, mechanical properties, and peel strength of the copper foil can be controlled, achieving a peel strength of 1.2-2 kg / cm². 2 This technology can significantly improve the elongation of copper foil. However, its focus is on optimizing mechanical properties and bonding strength, without addressing performance improvements in high-frequency signal transmission loss. Furthermore, increased surface undulations may exacerbate high-frequency losses.

[0006] Therefore, an effective solution is provided that can synergistically optimize the peel strength and high-frequency signal integrity of electrolytic copper foil, while taking into account low warpage and excellent mechanical properties, which is conducive to broadening the application of electrolytic copper foil in the field of electromagnetic shielding. Summary of the Invention

[0007] To overcome the shortcomings of the existing technology, the present invention aims to provide a method for preparing electrolytic copper foil, wherein the prepared electrolytic copper foil has the characteristics of low signal transmission loss, high peel strength, low warpage, and excellent mechanical properties.

[0008] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing electrolytic copper foil, comprising the following steps: sequentially performing acid washing, grain structure optimization treatment, roughening treatment, plating of functional layer, silane coupling treatment on raw foil, and then drying and winding to prepare electrolytic copper foil; The grain structure optimization process includes placing the acid-washed raw foil in an electrolyte for electroplating, depositing copper grains on both sides of the raw foil, and then baking it at 150-160℃ for 20-30 seconds to obtain a copper foil with optimized grain structure. The electrolyte contains 40-50 g / L copper ions, 80-100 g / L sulfuric acid, and 2-4 mg / L chloride ions. The electrolyte temperature is 37-43℃, and the electroplating current density is 10-16 A / dm³. 2 ; The roughening process includes placing the copper foil with optimized grain structure in a roughening solution for surface roughening via electrolysis, then placing it in a curing solution for surface curing via electrolysis, and finally washing it with water to obtain the roughened copper foil. The roughening solution contains copper ion concentrations of 9-11 g / L, sulfuric acid concentrations of 100-110 g / L, tungstate concentrations of 15-25 mg / L, and molybdate concentrations of 3-5 mg / L. The temperature of the roughening solution is 27-32°C, and the roughening current density is 16-18 A / dm³. 2 The copper ion concentration in the curing solution is 48-52 g / L, and the sulfuric acid concentration is 100-110 g / L; the temperature of the curing solution is 27-32℃; and the curing current density is 10-12 A / dm³. 2 .

[0009] Furthermore, the tungstate in the roughening solution is selected from sodium tungstate, and the molybdate is selected from sodium molybdate.

[0010] Furthermore, the present invention preferably uses a raw foil with a thickness of 12-15 μm.

[0011] Furthermore, the pickling step includes placing the raw foil in a pickling solution for surface treatment; wherein the pickling solution is a sulfuric acid solution with a concentration of 140-150 g / L; and the temperature of the pickling solution is 34-40°C. Pickling can remove surface impurities on both sides of the raw foil and increase the adhesion strength of the subsequent large-grain copper layer on the surface of the raw foil.

[0012] Furthermore, the step of plating the functional layer includes sequentially plating a barrier layer and an anti-oxidation layer onto the micro-roughened copper foil.

[0013] The step of plating the barrier layer includes placing the roughened copper foil in a blackening solution for blackening treatment, followed by water washing to obtain blackened copper foil; wherein the concentration of copper ions in the blackening solution is 1.5-2.0 g / L, the concentration of nickel is 2.2-2.8 g / L, the concentration of cobalt is 1.5-2.2 g / L, the concentration of sodium citrate is 52-70 g / L, and the concentration of boric acid is 40-58 g / L; the pH of the blackening solution is 2.2-3.2, the temperature is 28-32℃, and the current density of the blackening treatment is 2.6-3.0 A / dm³. 2 .

[0014] The step of plating the anti-oxidation layer includes placing the blackened copper foil in a passivation solution for passivation treatment, washing it with water, and obtaining the passivated copper foil; wherein, the passivation solution contains CrO4 2- The concentration of K₄P₂O₇ was 2.0-2.5 g / L, and the concentration of K₄P₂O₇ was 90-100 g / L; the pH of the passivation solution was 11-12, and the temperature was 30-40℃; the current density for passivation treatment was 2.0-2.6 A / dm³. 2 .

[0015] Further, the silane coupling treatment step includes coating the surface of the copper foil after the functional layer has been plated with an organosilane coupling agent solution to obtain a silane-coupled copper foil; the concentration of the organosilane coupling agent solution is 1.0-1.5 g / L, the pH is 9-12, and the temperature is 25-35℃. The organosilane coupling agent is selected from at least one of KH550, KH560, and KH570.

[0016] In a preferred embodiment, the organosilane coupling agent is selected from KH560, and the concentration of the organosilane coupling agent solution is 1.5 g / L, the pH is 12, and the temperature is 35°C.

[0017] The water washing step described in this invention involves washing with ultrapure water at a temperature of 25-35°C and a pH of 6.8-7.2.

[0018] Furthermore, the drying temperature is 130-140℃, and the drying time is 5-10 seconds.

[0019] Furthermore, the winding speed is 4-6 m / min.

[0020] Secondly, the present invention provides an electrolytic copper foil, which is prepared by the preparation method described in the present invention.

[0021] In the preparation method of the present invention, a large-grain copper layer is plated on both sides of the copper foil after grain structure optimization treatment; preferably, the average maximum diameter of the large-grain copper layer is 3-5 μm, and the thickness of the large-grain copper layer on one side is 1.5-3.0 μm; the total thickness of the electrolytic copper foil is 15-18 μm.

[0022] Thirdly, this invention provides the application of the aforementioned electrolytic copper foil in the preparation of electromagnetic shielding layers. Specifically, this includes, but is not limited to, electromagnetic shielding layers for plasma displays and PCBs for electromagnetic shielding.

[0023] The present invention has the following beneficial effects: The preparation method of this invention optimizes the grain structure of the green foil to form a copper layer with a special grain structure, and optimizes the rough structure of the copper layer surface by precisely controlling the coarse curing conditions. This synergistically improves the high-frequency transmission and interface bonding performance of the electrolytic copper foil. The resulting electrolytic copper foil can achieve both lower signal transmission loss and high peel strength, and has low warpage and excellent mechanical properties. It can meet the requirements of ultra-high-speed communication for electromagnetic shielding layer materials with low transmission loss and high reliability bonding strength. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation process of an electrolytic copper foil according to the present invention. Detailed Implementation

[0025] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0026] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0027] The raw foil used in the embodiments and comparative examples of this invention is a commercially available standard foil with a thickness of 12 μm; tensile strength ≥350 MPa, elongation ≥3%, warpage ≤10 mm, and surface roughness Rz≤1.0 μm and Ra≤0.15 μm for smooth and rough surfaces.

[0028] Example 1 This embodiment provides an electrolytic copper foil, the preparation process of which is as follows: Figure 1 As shown, the specific preparation steps are as follows: S1. Pickling: 12μm raw foil is continuously passed through the pickling tank at a speed of 5m / min for surface treatment to remove surface impurities on both sides of the raw foil; the tank contains a sulfuric acid aqueous solution with a concentration of 145g / L and the temperature is controlled at 37℃; S2. Grain Structure Optimization Treatment: The pickled green foil is introduced into a special electroplating tank for electroplating, depositing copper grains on both sides of the green foil surface; the concentration of copper ions in the electrolyte is 40 g / L, the concentration of sulfuric acid is 80 g / L, and the concentration of chloride ions is 2 mg / L; a titanium anode is used, the distance between the cathode and the anode is 5 cm, and the electroplating is carried out at a constant temperature of 37℃ with an application rate of 10 A / dm². 2 The current density was controlled, and the electroplating time was controlled at 50s. After electroplating, the copper foil was baked in a baking zone at 150℃ for 20s to obtain a copper foil with optimized grain structure; the average maximum diameter of the formed copper layer grains was 4.9μm, and the thickness of the large grain copper layer on one side was 3μm. S3. Roughening Treatment: The copper foil with optimized grain structure is introduced into a roughening tank for surface roughening through electrolysis at 30℃ and 16A / dm². 2 The surface was roughened for 50 seconds under the following conditions: copper ion concentration of 10 g / L, sulfuric acid concentration of 110 g / L, sodium tungstate concentration of 20 mg / L, and sodium molybdate concentration of 4 mg / L in the roughening solution. After roughening, the surface was cured by electrolysis in a curing tank at 30℃ and 10 A / dm². 2 The copper ion concentration in the curing solution was 48 g / L and the sulfuric acid concentration was 110 g / L under the curing conditions for 50 seconds. After curing, the copper foil was thoroughly washed with ultrapure water at 30°C to obtain roughened copper foil. S4. Plating Functional Layer: Micro-roughened copper foil is introduced into a blackening bath and plated at 30℃ and 3.0 A / dm². 2 Under the following conditions, the blackening treatment lasted for 50 seconds. The concentrations of copper ions, nickel, cobalt, sodium citrate, and boric acid in the blackening solution were 1.8 g / L, 2.5 g / L, 1.8 g / L, 60 g / L, and 45 g / L, with a pH of 2.8. After blackening, the solution was transferred to a passivation tank at 30°C and 2.6 A / dm³. 2 Passivation treatment under certain conditions for 50 seconds, CrO4 in the passivation solution in the tank 2- The concentration of K4P2O7 was 2.3 g / L, the concentration of K4P2O7 was 95 g / L, and the pH was 12. After passivation, the copper foil was thoroughly washed with ultrapure water at 30°C to obtain passivated copper foil. S5. Silane coupling treatment: A KH560 silane coupling agent solution with a concentration of 1.2 g / L (pH=10, temperature 30℃) is uniformly coated on the surface of the passivated copper foil by spraying to obtain silane-coupled copper foil; S6. Drying and winding: The silane-coupled copper foil is dried at 135℃ for 8s and then wound at a speed of 5m / min to prepare an electrolytic copper foil with a total thickness of 18μm (the thickness of the electrolytic copper foil is tested according to standard GB / T 29847-2013).

[0029] Example 2 This embodiment provides an electrolytic copper foil, the preparation process of which is as follows: Figure 1 As shown, the specific preparation steps are as follows: S1. Pickling: 12μm raw foil is continuously passed through the pickling tank at a speed of 5m / min for surface treatment to remove surface impurities on both sides of the raw foil; the tank contains a sulfuric acid aqueous solution with a concentration of 145g / L and the temperature is controlled at 37℃; S2. Grain Structure Optimization Treatment: The pickled green foil is introduced into a special electroplating tank for electroplating, depositing copper grains on both sides of the green foil surface; the electrolyte concentration is 50 g / L for copper ions, 100 g / L for sulfuric acid, and 4 mg / L for chloride ions; a titanium anode is used, the distance between the cathode and anode is 5 cm, and the electroplating is carried out at a constant temperature of 43℃ with an application rate of 16 A / dm². 2 The current density was controlled, and the electroplating time was controlled at 35s. After electroplating, the copper foil was baked at 160℃ for 30s in a baking zone to obtain a copper foil with optimized grain structure; the average diameter of the formed copper layer grains was 3μm, and the thickness of the copper layer on one side was 1.5μm. S3. Roughening treatment: The copper foil with optimized grain structure is introduced into a roughening tank for surface roughening through electrolysis at 30℃ and 18A / dm². 2 The surface was roughened for 35 seconds under the following conditions: copper ion concentration of 10 g / L, sulfuric acid concentration of 110 g / L, sodium tungstate concentration of 15 mg / L, and sodium molybdate concentration of 5 mg / L in the roughening solution. After roughening, the surface was cured by electrolysis in a curing tank at 30℃ and 12 A / dm². 2 The copper ion concentration in the curing solution was 52 g / L and the sulfuric acid concentration was 110 g / L under the curing conditions for 35 seconds. After curing, the copper foil was thoroughly washed with ultrapure water at 30°C to obtain roughened copper foil. S4. Plating Functional Layer: Micro-roughened copper foil is introduced into a blackening bath and plated at 30℃ and 3.0 A / dm². 2 Under the following conditions, the blackening treatment lasted for 35 seconds. The concentrations of copper ions, nickel, cobalt, sodium citrate, and boric acid in the blackening solution were 1.8 g / L, 2.5 g / L, 1.8 g / L, 60 g / L, and 45 g / L, with a pH of 2.8. After blackening, the solution was transferred to a passivation tank at 30°C and 2.6 A / dm³. 2 Passivation treatment under certain conditions for 35 seconds, CrO4 in the passivation solution in the tank 2- The concentration of K4P2O7 was 2.3 g / L, the concentration of K4P2O7 was 95 g / L, and the pH was 12. After passivation, the copper foil was thoroughly washed with ultrapure water at 30°C to obtain passivated copper foil. S5. Silane coupling treatment: A KH560 silane coupling agent solution with a concentration of 1.2 g / L (pH=10, temperature 30℃) is uniformly coated on the surface of the passivated copper foil by spraying to obtain silane-coupled copper foil; S6. Drying and winding: The silane-coupled copper foil is dried at 135℃ for 8s and then wound at a speed of 5m / min to prepare an electrolytic copper foil with a total thickness of 15μm (the thickness of the electrolytic copper foil is tested according to standard GB / T 29847-2013).

[0030] Comparative Example 1 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the concentration of copper ions in the electrolyte in step S2 is 90 g / L, the concentration of sulfuric acid is 120 g / L, and the concentration of chloride ions is 3 mg / L. The remaining steps and conditions are the same as those in Example 1.

[0031] Comparative Example 2 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the electroplating current density in step S2 is 60 A / dm². 2 The remaining steps and conditions are the same as in Example 1.

[0032] Comparative Example 3 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the baking temperature in step S2 is 120°C, while the remaining steps and conditions are the same as those in Example 1.

[0033] Comparative Example 4 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the baking temperature in step S2 is 200°C, while the remaining steps and conditions are the same as those in Example 1.

[0034] Comparative Example 5 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the baking time in step S2 is 60s, while the remaining steps and conditions are the same as those of Example 1.

[0035] Comparative Example 6 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the copper foil after electroplating in step S2 is not baked, while the remaining steps and conditions are the same as those in Example 1.

[0036] Comparative Example 7 This comparative example provides an electrolytic copper foil whose preparation steps differ from those of Example 1 in that sodium tungstate and sodium molybdate are not added to the roughening solution in step S3, while the remaining steps and conditions are the same as those in Example 1.

[0037] Comparative Example 8 This comparative example provides an electrolytic copper foil, the preparation steps of which differ from those of Example 1 in that the current density for the roughening treatment in step S3 is 30 A / dm. 2The remaining steps and conditions are the same as in Example 1.

[0038] Relevant performance tests: (1) Measurement of copper layer thickness and grain diameter: The prepared copper foil sample was placed in an argon ion polisher for cross-sectional polishing. Then, the polished copper foil sample was pasted onto the sample stage. The copper foil was characterized in the scanning electron microscope EBSD system, and the average value of the large grain copper layer thickness and the maximum diameter of the large grain copper layer of the copper foil sample was calculated.

[0039] (2) Peel strength test: The test was conducted in accordance with the standard GB / T 29847-2013.

[0040] (3) Copper powder shedding test: Place the rough side of the filter paper in contact with the coarsely cured surface of the copper foil, place a 200g weight on the other side of the filter paper, and drag the filter paper evenly for 50cm. Observe the copper powder on the rough surface of the filter paper and determine the grade. (Evaluation criteria for powder shedding grade: Grade 0: No copper powder shedding, Grade 1: Small amount of copper powder shedding, Grade 2: Obvious copper powder shedding) (4) Electrical performance loss test: The sample for electrical performance loss measurement was prepared using the same copper-clad laminate manufacturing method as the peel strength sample. The copper foil and PPO prepreg were laminated and then hot-pressed at a temperature of 250°C and a pressing pressure of 25-30 kg / m. 2 The hot-pressing time was 90 min. In the evaluation of electrical performance loss, transmission loss was measured using a 16 GHz bandwidth. The microstrip structure had the following characteristics: electrolyte thickness 50 μm, conductor length 1.0 mm, conductor thickness equal to the copper foil thickness, and conductor circuit width 100 μm.

[0041] (5) Warpage: Tested in accordance with standard GB / T 5230-2020.

[0042] (6) Mechanical property test: The room temperature tensile strength and room temperature elongation of electrolytic copper foil were tested in accordance with the standard GB / T 29847-2013.

[0043] Table 1 Performance test results of Examples 1-2 and Comparative Examples 1-8

[0044] As can be seen from the above results, the preparation method of the present invention optimizes the grain structure of the green foil to form a copper layer with a special grain structure, and optimizes the rough structure of the copper layer surface by precisely controlling the coarse curing conditions. This synergistically improves the high-frequency transmission and interface bonding performance of the electrolytic copper foil. The prepared electrolytic copper foil can achieve both lower signal transmission loss (16GHz electrical signal transmission loss is less than -0.72dB / in) and high peel strength (rough surface peel strength ≥1.35N / mm), with warpage ≤3mm, tensile strength ≥420MPa, and elongation ≥4.0%. This meets the requirements of ultra-high-speed communication for electromagnetic shielding layer materials with low transmission loss and high reliability bonding strength.

[0045] Compared with Example 1, Comparative Example 1 / 2 shows that the ion concentration in the electrolyte in step S2 is not within the required range or the current density of electroplating is too high. Although the resulting electrolytic copper foil has high peel strength, its electrical signal transmission loss is large, the warpage reaches more than 10 mm, and the elongation is low, which cannot meet the requirements for the use of electromagnetic shielding layer materials.

[0046] Compared with Example 1, Comparative Examples 3 / 4 / 5 / 6 show that in Comparative Example 3, the baking temperature in step S2 was too low, resulting in electrolytic copper foil with high peel strength but increased electrical signal transmission loss and a warpage of 11 mm. In Comparative Examples 4 / 5, the baking temperature or baking time in step S2 was too high, which did not significantly improve peel strength but instead increased electrical signal transmission loss and warpage, and significantly reduced tensile strength and elongation. In Comparative Example 6, no baking treatment was performed in step S2, resulting in electrolytic copper foil with low peel strength and high warpage. This indicates that the specific baking process in the preparation method of the present invention is beneficial for improving the peel strength and reducing warpage of electrolytic copper foil, while ensuring low electrical signal transmission loss and excellent mechanical properties.

[0047] Compared with Example 1, Comparative Example 7 did not add sodium tungstate and sodium molybdate to the roughening solution in step S3. The resulting electrolytic copper foil had low peel strength, high electrical signal transmission loss, and high warpage, which could not meet the requirements for electromagnetic shielding layer materials.

[0048] Compared with Example 1, Comparative Example 8 shows that the current density of the roughening treatment in step S3 is too high, resulting in low peel strength and high electrical signal transmission loss of the electrolytic copper foil.

[0049] The above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing electrolytic copper foil, characterized in that, Includes the following steps: The raw foil is sequentially subjected to pickling, grain structure optimization treatment, roughening treatment, functional layer plating, and silane coupling treatment, and then dried and wound to prepare electrolytic copper foil. The grain structure optimization process includes placing the acid-washed raw foil in an electrolyte for electroplating, depositing copper grains on both sides of the raw foil, and then baking it at 150-160℃ for 20-30 seconds to obtain a copper foil with optimized grain structure. The electrolyte contains 40-50 g / L copper ions, 80-100 g / L sulfuric acid, and 2-4 mg / L chloride ions. The electrolyte temperature is 37-43℃, and the electroplating current density is 10-16 A / dm³. 2 ; The roughening process includes placing the copper foil with optimized grain structure in a roughening solution for surface roughening via electrolysis, then placing it in a curing solution for surface curing via electrolysis, and finally washing it with water to obtain the roughened copper foil. The roughening solution contains copper ion concentrations of 9-11 g / L, sulfuric acid concentrations of 100-110 g / L, tungstate concentrations of 15-25 mg / L, and molybdate concentrations of 3-5 mg / L. The temperature of the roughening solution is 27-32°C, and the roughening current density is 16-18 A / dm³. 2 The copper ion concentration in the curing solution is 48-52 g / L, and the sulfuric acid concentration is 100-110 g / L; the temperature of the curing solution is 27-32℃; and the curing current density is 10-12 A / dm³. 2 The tungstate in the roughening solution is sodium tungstate, and the molybdate is sodium molybdate.

2. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The pickling step includes placing the raw foil in a pickling solution for surface treatment; the pickling solution is an aqueous sulfuric acid solution with a concentration of 140-150 g / L; the temperature of the pickling solution is 34-40℃.

3. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The steps of plating the functional layer include sequentially plating a barrier layer and an anti-oxidation layer onto the roughened copper foil.

4. The method for preparing electrolytic copper foil according to claim 3, characterized in that, The step of plating the barrier layer includes placing the roughened copper foil in a blackening solution for blackening treatment, followed by water washing to obtain blackened copper foil; the concentration of copper ions in the blackening solution is 1.5-2.0 g / L, the concentration of nickel is 2.2-2.8 g / L, the concentration of cobalt is 1.5-2.2 g / L, the concentration of sodium citrate is 52-70 g / L, and the concentration of boric acid is 40-58 g / L; the pH of the blackening solution is 2.2-3.2, the temperature is 28-32℃, and the current density of the blackening treatment is 2.6-3.0 A / dm³. 2 ; The step of plating the anti-oxidation layer includes placing the blackened copper foil in a passivation solution for passivation treatment, washing it with water, and obtaining the passivated copper foil; the passivation solution contains CrO4 2- The concentration of K₄P₂O₇ was 2.0-2.5 g / L, and the concentration of K₄P₂O₇ was 90-100 g / L; the pH of the passivation solution was 11-12, and the temperature was 30-40℃; the current density for passivation treatment was 2.0-2.6 A / dm³. 2 .

5. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The silane coupling treatment step includes coating the surface of the copper foil after the functional layer has been plated with an organosilane coupling agent solution to obtain a silane-coupled copper foil; the concentration of the organosilane coupling agent solution is 1.0-1.5 g / L, the pH is 9-12, and the temperature is 25-35℃; the organosilane coupling agent is selected from at least one of KH550, KH560, and KH570.

6. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The drying temperature is 130-140℃, and the drying time is 5-10s; the winding speed is 4-6m / min.

7. An electrolytic copper foil, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The electrolytic copper foil according to claim 7, characterized in that, The electrolytic copper foil contains a large-grain copper layer; the average maximum diameter of the large-grain copper layer is 3-5 μm, and the thickness of the large-grain copper layer on one side is 1.5-3.0 μm.

9. The application of the electrolytic copper foil according to claim 7 in the preparation of an electromagnetic shielding layer.

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