A heat-resistant copper foil and a method for producing the same

Abstract

The present application relates to the technical field of electrolytic copper foil, and particularly relates to a heat-resistant copper foil and a preparation method thereof. A volume ratio of a (220) crystal plane texture in the heat-resistant copper foil is 70% to 100%, and 80% to 100% of grain boundaries are arranged along a [110] crystal direction. By forming a high-ratio (220) texture, a nearly single-orientation crystal structure is formed. The high-purity texture makes the grain boundaries highly ordered arranged along the [110] crystal direction. The synergistic effect of the sub-micron columnar crystal structure and the single (220) texture endows the copper foil with excellent thermal stability. After annealing, the grain size fluctuation is small, the (220) texture retention rate is greater than or equal to 70%, and the grain coarsening rate of the copper foil is more than 50% of the same kind of copper foil in the prior art. The combination of the atomic arrangement characteristics of the (220) crystal plane and the columnar crystal structure makes the copper foil have excellent ductility while maintaining high strength, which is conducive to improving the thermal stability, strength and ductility of the copper foil under complex thermal exchange conditions, and meets the performance requirements of the copper foil in high-end fields.

Description

Technical Field

[0001] This invention relates to the field of electrolytic copper foil technology, and in particular to a heat-resistant copper foil and its preparation method. Background Technology

[0002] In high-end fields such as semiconductor packaging and power batteries, copper foil, as a core conductive material, directly determines the signal integrity, heat dissipation efficiency, and long-term reliability of devices due to its thermomechanical stability. With the popularization of advanced packaging processes such as high-temperature resin lamination (150–250℃) and multilayer stacking, as well as fast-charging technology for power batteries, copper foil faces stress concentration and performance degradation problems caused by grain coarsening and grain boundary migration during high-frequency thermal cycling. Studies have shown that (220) crystal texture, due to its unique crystallographic properties, can significantly improve the mechanical strength and high-temperature structural stability of copper foil. Therefore, the precise control of crystal texture has become a key direction for overcoming technical bottlenecks.

[0003] However, there are many types of grain texture in the current copper foil, and the texture optimization process is complicated and cumbersome. The proportion of (220) texture in copper foil is generally low, and the performance degrades severely in high-frequency thermal cycling, which cannot meet the reliability requirements. Summary of the Invention

[0004] Therefore, it is necessary to provide a heat-resistant copper foil and its preparation method, which can effectively reduce the degree of grain coarsening at high temperatures and improve the reliability of copper foil under complex thermal cycling conditions.

[0005] The technical solution is as follows:

[0006] A heat-resistant copper foil, wherein the volume percentage of the (220) crystal plane texture in the heat-resistant copper foil is 70%~100%, and 80%~100% of the grain boundaries are arranged along the

[110] crystal direction.

[0007] In one embodiment, the proportion of Σ3 grain boundaries in the heat-resistant copper foil is greater than or equal to 40%, and the change rate of the proportion of Σ3 grain boundaries before and after annealing is less than or equal to 0.5%.

[0008] In one embodiment, the average grain size is 0.9~1.1 μm, and the average grain size change rate before and after annealing is less than or equal to 6%.

[0009] A method for preparing heat-resistant copper foil, the method comprising the following steps:

[0010] Cathode pretreatment: Pure titanium plate is used as cathode plate. The deposition surface of the cathode plate is polished. The deposition surface of the cathode plate is rinsed with deionized water, dilute sulfuric acid and anhydrous ethanol in sequence and then dried.

[0011] Electrolyte preparation: Add copper sulfate pentahydrate and sulfuric acid to deionized water, stir until dissolved, then add sodium chloride and gelatin to form the electrolyte;

[0012] Electrodeposition: A ruthenium-iridium-titanium anode plate and a pretreated cathode plate are placed parallel to each other in an electrolyte solution, and constant current deposition is performed to form a copper foil;

[0013] Post-processing: The broken crystal grains on the smooth surface of the copper foil are etched with an etchant to remove the surface broken crystals.

[0014] In one embodiment, the step of cathode pretreatment specifically includes: polishing the deposition surface of the cathode plate with 1500-grit sandpaper to make the roughness Ra of the deposition surface 0.5~2 μm.

[0015] In one embodiment, the step of cathode pretreatment specifically includes:

[0016] After the deposition surface of the cathode plate is polished, it is rinsed with deionized water for 5 min, ultrasonically cleaned with 5% dilute sulfuric acid for 2-4 min, and ultrasonically cleaned with anhydrous ethanol for 1-3 min before being dried.

[0017] In one embodiment, in the step of electrolyte preparation, the concentration of copper ions in the electrolyte is 50-80 g / L, the concentration of sulfuric acid is 80-100 g / L, the concentration of chloride ions is 5-10 mg / L, and the concentration of gelatin is 1-3 mg / L.

[0018] In one embodiment, in the electrolyte preparation step, the purity of copper sulfate pentahydrate is not less than 99%, the purity of sulfuric acid is not less than 98%, the purity of sodium chloride is not less than 99%, and the gelatin is animal gelatin.

[0019] In one embodiment, the steps are as follows: during electrodeposition, the electrolyte temperature is 10~50℃, the current density is 10~60A / dm², and the electrodeposition rotation speed is 1000~1200 rpm.

[0020] In one embodiment, the post-treatment step includes: 30 g / L copper chloride dihydrate, 15 ml / L hydrochloric acid, and 15 g / L sodium chloride.

[0021] In one embodiment, in the post-processing step, the etching time is 4-6 minutes.

[0022] Beneficial effects:

[0023] The aforementioned heat-resistant copper foil, by forming a high proportion of (220) texture, forms a nearly single-orientation crystal structure. This high-purity texture ensures that the grain boundaries are highly ordered along the

[110] crystal direction. The synergistic effect of the submicron columnar crystal structure and the single (220) texture endows the copper foil with excellent thermal stability. Furthermore, after annealing, the grain size fluctuation is small, and the (220) texture retention rate is ≥70%, which can achieve a grain coarsening rate that is more than 50% better than that of similar copper foils in the prior art. The atomic arrangement characteristics of the (220) crystal plane combined with the columnar crystal structure enable the copper foil to maintain high strength while possessing excellent ductility, which is beneficial to improving the thermal stability, strength and ductility of the copper foil under complex thermal exchange conditions, and meeting the performance requirements of copper foil in high-end fields.

[0024] The above-mentioned method for preparing heat-resistant copper foil involves grinding the deposition surface of the cathode plate to form a micron-level roughness, which promotes the heterogeneous nucleation of copper ions during electrolysis. By grinding and pre-cleaning the pure titanium cathode plate, a suitable surface is provided for the orderly deposition of copper ions. By controlling the concentration of copper sulfate pentahydrate, sulfuric acid, sodium chloride and gelatin in the electrolyte, a chemical environment is created for the preferential growth of the (220) crystal plane. Combined with constant current electrodeposition under specific conditions and targeted post-etching treatment, surface fragments can be removed. The copper foil obtained can form a high proportion of (220) texture. While ensuring the preset thickness of the copper foil, it is beneficial to improve the thermal stability, strength and ductility of the copper foil under complex thermal exchange conditions, thus meeting the performance requirements of copper foil in high-end fields. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of a method for preparing heat-resistant copper foil according to an embodiment of the present invention;

[0028] Figure 2 The XRD patterns of deposited and annealed copper foils obtained in one embodiment of the present invention are shown below.

[0029] Figure 3 This is a comparison chart of the texture retention rate of copper foil (220) under different annealing times in one embodiment of the present invention;

[0030] Figure 4 This is an orientation imaging image of the copper foil described in one embodiment of the present invention, obtained from EBSD analysis.

[0031] Figure 5 This is the inverse pole figure of the EBSD analysis results of the copper foil described in one embodiment of the present invention;

[0032] Figure 6 This is a grain boundary distribution map from the EBSD analysis results of the copper foil described in one embodiment of the present invention;

[0033] Figure 7 This is a grain size distribution diagram from the EBSD analysis results of the copper foil described in one embodiment of the present invention;

[0034] Figure 8 This is an orientation imaging image from the EBSD analysis results of the annealed copper foil in one embodiment of the present invention;

[0035] Figure 9 This is the inverse pole figure in the EBSD analysis results of the annealed copper foil in one embodiment of the present invention;

[0036] Figure 10 This is a grain boundary distribution diagram from the EBSD analysis results of the annealed copper foil in one embodiment of the present invention;

[0037] Figure 11 This is a grain size distribution diagram from the EBSD analysis results of the annealed copper foil in one embodiment of the present invention;

[0038] Figure 12 This is a stress-strain curve of the copper foil described in one embodiment of the present invention. Detailed Implementation

[0039] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0040] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0042] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0044] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0045] An embodiment of the present invention provides a heat-resistant copper foil in which, within the observation area, the volume ratio of the (220) crystal plane texture in the heat-resistant copper foil is 70-100%, and more than 80% of the grain boundaries are arranged along the

[110] crystal direction.

[0046] The aforementioned heat-resistant copper foil, by forming a high proportion of (220) texture, forms a nearly single-orientation crystal structure. This high-purity texture ensures that the grain boundaries are highly ordered along the

[110] crystal direction. The synergistic effect of the submicron columnar crystal structure and the single (220) texture endows the copper foil with excellent thermal stability. Furthermore, after annealing, the grain size fluctuation is small, and the (220) texture retention rate is more than 70%, which can achieve a grain coarsening rate that is more than 50% better than that of similar copper foils in the prior art. The atomic arrangement characteristics of the (220) crystal plane combined with the columnar crystal structure enable the copper foil to maintain high strength while possessing excellent ductility, which is beneficial to improving the thermal stability, strength and ductility of the copper foil under complex thermal exchange conditions, and meeting the performance requirements of copper foil in high-end fields.

[0047] Optionally, the volume percentage of the (220) crystal plane texture in the heat-resistant copper foil can be 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any other value within the range. It should also be noted that the percentage of grain boundaries arranged along the

[110] crystal direction, which is the proportion of grain boundaries under EBSD analysis, can be 81%, 84%, 90%, 93%, 95%, 100%, or any other value within the range, and is not specifically limited here.

[0048] In one embodiment, within the observation area, the proportion of Σ3 grain boundaries in the heat-resistant copper foil is greater than or equal to 40%, and the change rate of the proportion of Σ3 grain boundaries before and after annealing is less than 0.5%. Specifically, ordinary large-angle grain boundaries have high energy and disordered atomic arrangement, easily becoming channels for grain migration at high temperatures, leading to rapid grain coarsening and a sharp decline in the mechanical and electrical properties of the copper foil. In contrast, Σ3 grain boundaries, due to their highly ordered structure and high atomic matching degree, have only 1 / 3 to 1 / 2 the energy of ordinary large-angle grain boundaries, resulting in greater resistance to grain migration. This significantly inhibits the grain growth rate at high temperatures, maintaining the fine-grained structure and stable performance of the copper foil. The small change rate before and after annealing reflects the thermal stability of Σ3 grain boundaries. In the actual thermal cycling environment of use, Σ3 grain boundaries are not easily transformed into high-energy ordinary large-angle grain boundaries, nor are they easily eliminated due to grain growth. This stability prevents grain boundary degradation in copper foil during long-term thermal cycling: if the proportion of Σ3 grain boundaries decreases significantly with annealing, their ability to inhibit grain coarsening and resist cracking will rapidly diminish, leading to a degradation in the heat resistance of the copper foil; however, a change rate of ≤0.5% means that the advantages of Σ3 grain boundaries persist during thermal cycling, ensuring the long-term stability of the copper foil's performance. A high proportion of Σ3 grain boundaries ≥40%, through their low energy and low diffusivity, directly enhances the copper foil's resistance to grain coarsening and thermal fatigue. A change rate of ≤0.5% before and after annealing ensures the long-term maintenance of this advantage under high-temperature conditions. Together, these factors improve the heat resistance reliability of this heat-resistant copper foil under high-frequency thermal cycling and help reduce problems such as fracture and decreased conductivity caused by grain boundary failure.

[0049] The annealing conditions are as follows: annealing temperature is 150°C~200°C, annealing time is 5~24 h, atmosphere is nitrogen, argon, hydrogen, etc., and heating rate is 5~10°C / min.

[0050] It should be noted that the observation area is the observation angle of the heat-resistant copper foil cross section under arbitrary conditions through EBSD (electron backscatter diffraction) analysis, and the detection and data collection statistics are carried out.

[0051] In one embodiment, the average grain size is 0.9–1.1 μm, and the rate of change of the average grain size before and after annealing is less than or equal to 6%. Specifically, when the grain size is in the range of 0.9–1.1 μm, the grain boundary density of the copper foil is significantly increased. This can hinder long-range atomic diffusion and overall grain boundary slip through the interaction between grain boundaries, thereby reducing the thermal deformation of the copper foil at high temperatures. In addition, the grains on both sides of the grain boundary of the fine grains can disperse local stress through slight orientation adjustments, avoiding stress concentration at the interface of a few coarse grains, thereby reducing the risk of cracking caused by thermal cycling. Furthermore, a change rate of less than 6% before and after annealing can avoid performance degradation caused by grain coarsening, which helps to ensure that the microstructure of the copper foil remains close to its initial state after high-temperature aging, thus ensuring its heat resistance reliability. Furthermore, all grain sizes range from 0.9 to 1.1 μm, which is fine-grained but not ultra-fine or submicron-sized. This balances grain size enhancement with high-temperature stability: if the grain size is <0.9 μm, the grain boundary energy is too high, making it easier for grain boundary coalescence to lead to rapid coarsening at high temperatures; if the grain size is >1.1 μm, the grain boundary density is insufficient, making it difficult to effectively hinder atomic movement and stress transmission at high temperatures. Therefore, a grain size of 0.9–1.1 μm retains the advantages of fine grains in resisting thermal deformation while reducing the coarsening driving force through a moderate grain size. Combined with a low rate of change, this further improves the high-temperature structural stability of the heat-resistant copper foil.

[0052] In one embodiment, within the observation region, columnar crystals with an aspect ratio greater than or equal to 5 account for ≥80% of the area of ​​all grains in the heat-resistant copper foil. Furthermore, the angle between the growth direction of the columnar crystals and the thickness direction of the heat-resistant copper foil is ≤20%. The heat resistance of the copper foil is directly related to the stability of its microstructure. The aspect ratio is the ratio of the length to the width of the columnar crystal grains. Compared to equiaxed crystals, columnar crystals exhibit superior structural stability at high temperatures due to their preferential growth along a specific direction. Heat-resistant copper foil with columnar crystals having an aspect ratio ≥5 and an area ratio ≥80% exhibits high grain boundary density and orderly arrangement along a preferred direction. This high proportion of slender columnar crystals hinders high-temperature atomic diffusion through dense grain boundaries, suppresses grain coarsening, maintains the fine-grain strengthening effect, and enhances resistance to thermal deformation. Their consistent orientation makes thermal expansion anisotropy more coordinated, reducing stress concentration caused by expansion differences during thermal cycling and lowering the risk of cracking. Numerous slender grain boundaries form a physical barrier, delaying grain boundary slip and void formation, improving thermal fatigue resistance. At the same time, the orderly arrangement reduces electron scattering to maintain high conductivity. The low surface roughness of the uniform fine grains facilitates tight bonding with electrode materials to reduce interfacial impedance. Furthermore, the excellent structural stability at high temperatures ensures the consistency of mechanical and electrical properties during long-term service, meeting the requirements of high-frequency thermal cycling scenarios.

[0053] Furthermore, before and after annealing, the change rate of the number of columnar crystals with an aspect ratio greater than or equal to 5 is less than or equal to 10%. This helps maintain its high grain boundary density and orientation consistency, continuously hinders atomic diffusion to suppress grain coarsening, reduces stress concentration caused by structural abrupt changes during thermal cycling, stabilizes conductivity and mechanical properties, and ensures that the performance of this heat-resistant copper foil degrades slowly during long-term thermal cycling, thus meeting the reliability requirements of high-temperature service scenarios.

[0054] In one embodiment, within the observation area, along the thickness direction of the heat-resistant copper foil, the columnar crystals, accounting for more than 75% of the total number, constitute ≥90% of the total thickness of the heat-resistant copper foil. This ≥75% columnar crystal length along the thickness direction, exceeding 90% of the total thickness, signifies strong columnar crystal penetration and highly consistent orientation. This reduces disordered grain boundaries perpendicular to the thickness direction, lowers stress concentration due to expansion differences during thermal cycling, and significantly reduces the risk of cracking. The penetrating grain boundaries form a continuous barrier, hindering atomic diffusion and grain coarsening at high temperatures, maintaining a fine-grained strengthening effect, and significantly enhancing resistance to thermal deformation. Simultaneously, the ordered arrangement of long columnar crystals reduces electron scattering, ensuring stable conductivity, and provides more uniform bonding with adjacent material interfaces, improving interlayer adhesion. This allows the copper foil to maintain mechanical strength and dimensional stability over long periods during high-frequency thermal cycling, meeting the requirements of high-temperature service scenarios.

[0055] Furthermore, before and after annealing, the change rate of the number of columnar crystals with a length accounting for ≥90% of the total thickness of the heat-resistant copper foil is less than or equal to 8%. This helps to reduce disordered grain boundaries perpendicular to the thickness direction, continuously suppress stress concentration caused by grain boundary differences during thermal cycling, hinder atomic diffusion and grain coarsening, maintain resistance to thermal deformation and cracking, ensure stable conductivity and mechanical properties, guarantee that the performance of this heat-resistant copper foil degrades slowly during long-term high-temperature service, and improve heat resistance reliability.

[0056] An embodiment of the present invention provides a method for preparing heat-resistant copper foil, the method comprising the following steps:

[0057] S10. Cathode pretreatment: Pure titanium plate is used as cathode plate. The deposition surface of the cathode plate is polished. The deposition surface of the cathode plate is rinsed with deionized water, dilute sulfuric acid and anhydrous ethanol in sequence and then dried.

[0058] S20. Electrolyte preparation: Add copper sulfate pentahydrate and sulfuric acid to deionized water, stir until dissolved, then add sodium chloride and gelatin to form an electrolyte.

[0059] S30, Electrodeposition: The ruthenium-iridium-titanium anode plate and the pretreated cathode plate are placed parallel to each other in the electrolyte, and constant current deposition is performed to form copper foil;

[0060] S40. Post-treatment: Use an etching solution to etch the broken crystal grains on the smooth surface of the copper foil to remove the surface broken crystals.

[0061] The above-mentioned method for preparing heat-resistant copper foil, in the process of implementation, forms a micron-level roughness by polishing the deposition surface of the cathode plate, which can promote the heterogeneous nucleation of copper ions during electrolysis. By polishing and pre-cleaning the pure titanium cathode plate in multiple steps, a suitable surface is provided for the orderly deposition of copper ions. By controlling the concentration of copper sulfate pentahydrate, sulfuric acid, sodium chloride and gelatin in the electrolyte, a chemical environment is created for the preferential growth of the (220) crystal plane. Combined with constant current electrodeposition under specific conditions and targeted post-etching treatment, surface fragments can be removed. The copper foil obtained can form a high proportion of (220) texture. While ensuring the preset thickness of the copper foil, it is beneficial to improve the thermal stability, strength and ductility of the copper foil under complex thermal exchange conditions, and meet the needs of high-end fields for copper foil performance.

[0062] Among them, the pure titanium cathode plate has a high surface smoothness and resistance to electrolyte corrosion, which can reduce the adhesion between the copper foil and the substrate, improve the peeling efficiency, and the stability of titanium can ensure a uniform electric field at the cathode interface, which is conducive to the uniform deposition of copper ions and reduces defects such as pinholes and nodules in the copper foil. Furthermore, the ruthenium-iridium titanium anode plate has excellent corrosion resistance and electrocatalytic activity, long life in acidic electrolytes, and can stably release oxygen, avoiding anode dissolution and electrolyte contamination, and maintaining a stable copper ion concentration. At the same time, this electrode combination has good conductivity and low cell voltage, which can reduce electrolysis energy consumption, and the titanium material can be recycled and reused, meeting the requirements of energy conservation and environmental protection. Ultimately, it can improve the thickness uniformity, mechanical properties and surface quality of copper foil, making it suitable for high-precision electronic applications.

[0063] In one embodiment, step S10, cathode pretreatment, specifically includes: polishing the deposition surface of the cathode plate with 1500-grit sandpaper to make the roughness Ra of the deposition surface 0.5~2 μm.

[0064] Among them, polishing with 1500-grit sandpaper forms a cathode plate deposition surface with a roughness Ra of 0.5~2 μm, which further improves the suitability of the cathode plate surface. This not only provides sufficient heterogeneous nucleation sites for copper ions, but also avoids grain orientation disorder caused by an excessively rough surface. This polishing method is conducive to precisely controlling the surface roughness so that the copper foil nucleation is uniform, reducing the generation of disordered grains, and helping to increase the proportion of (220) texture in the copper foil to more than 95%.

[0065] Specifically, in step S10, the cathode pretreatment, after the deposition surface of the cathode plate is polished, it is sequentially rinsed with deionized water for 5 min, ultrasonically cleaned with 5% dilute sulfuric acid for 2-4 min, and ultrasonically cleaned with anhydrous ethanol for 1-3 min before being dried. In this way, rinsing with deionized water can remove mechanical impurities from the surface; ultrasonic cleaning with 5% dilute sulfuric acid can dissolve the oxide layer on the surface of the titanium plate, exposing a fresh metal surface and improving the cathode activity; ultrasonic cleaning with anhydrous ethanol further degreases and quickly evaporates to dry, avoiding the dilution of the electrolyte by residual water. The three steps work together to ensure that the cathode surface is clean, free of oxidation and impurities, which is conducive to thoroughly removing surface contaminants and oxide layers, reducing impurity-induced defects during copper ion deposition, improving the uniformity of copper foil grain orientation, and thus improving the (220) texture retention rate of the grains; at the same time, it enhances the initial bonding force between the copper foil and the substrate and reduces the breakage rate during peeling.

[0066] In one embodiment, in step S20, electrolyte preparation, the concentration of copper ions in the electrolyte is 50-80 g / L, the concentration of sulfuric acid is 80-100 g / L, the concentration of chloride ions is 5-10 mg / L, and the concentration of gelatin is 1-3 mg / L. The concentrations of copper ions and sulfuric acid provide sufficient raw materials and a conductive environment for electrodeposition; the synergistic effect of gelatin and chloride ions mainly selectively inhibits the growth of high-energy crystal planes such as (111) and (200), indirectly promoting the formation of preferred orientation texture of the (220) crystal plane, forming a columnar crystal structure. By using this combination of electrolyte concentrations, the proportion of (220) texture can be increased and stabilized at over 90%, and the columnar crystals are more neatly arranged; the low concentration of gelatin avoids brittleness caused by excessive inhibition, taking into account both strength and ductility, and improving reliability under thermal cycling conditions.

[0067] Furthermore, in step S20, the preparation of the electrolyte, the purity of copper sulfate pentahydrate is not less than 99%, the purity of sulfuric acid is not less than 98%, the purity of sodium chloride is not less than 99%, and the gelatin is animal gelatin. High-purity raw materials reduce the introduction of impurity ions such as Fe and Pb, and avoid texture disorder caused by impurity segregation at grain boundaries. Optionally, the gelatin can be bovine bone gelatin, fish skin gelatin, etc.

[0068] In one embodiment, in step S30, electrodeposition, the electrolyte temperature is 10~50℃, the current density is 10~60 A / dm², and the electrodeposition rotation speed is 1000~1200 rpm. Specifically, the temperature range of 10~50℃ is beneficial for balancing the ion diffusion rate and the adsorption stability of the additives; the current density of 10~60 A / dm² controls the copper ion reduction rate, avoiding excessively high rates that lead to coarse grains; the high-speed stirring at 1000~1200 rpm enhances electrolyte convection, reduces copper ion concentration polarization near the cathode, and ensures uniform growth of columnar crystals along the vertical direction. These process parameters help improve the uniformity of copper foil thickness, increase the aspect ratio of columnar crystals, reduce the grain coarsening rate after annealing, and further improve the thermal stability of the copper foil.

[0069] In one embodiment, in step S40, the post-treatment, the etching solution includes: 30 g / L copper chloride dihydrate, 15 ml / L hydrochloric acid, and 15 g / L sodium chloride. This etching solution, through the coordination of chloride ions with copper, achieves a significantly higher etching rate for disordered fragmented grains (low orientation consistency) than for (220) textured columnar grains, enabling selective removal and obtaining a completely columnar crystal structure. This is beneficial for reducing the surface roughness of the copper foil, increasing the fragmented grain removal rate, reducing surface defects, alleviating stress concentration at high temperatures, and improving thermal cycling reliability.

[0070] In one embodiment, in step S40, the etching time is 4-6 min. The etching time of 4-6 min can fully dissolve the surface fragments while avoiding excessive etching damage to the columnar crystal structure (220), balancing surface quality and thickness accuracy. Under the premise of ensuring the removal of fragments, it is beneficial to reduce the copper foil thickness loss rate; the surface flatness is improved, and the bonding force with the resin is enhanced.

[0071] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0072] Example 1:

[0073] A method for preparing copper foil, the specific steps of which are as follows:

[0074] (1) Cathode pretreatment

[0075] Pure titanium plates were used as cathode plates, and the deposition surface was polished with 1500-grit sandpaper.

[0076] After polishing, rinse with deionized water for 5 minutes.

[0077] After rinsing, ultrasonically clean with 5% dilute sulfuric acid for 3 minutes;

[0078] After cleaning, ultrasonically clean with anhydrous ethanol for 2 minutes. After cleaning, blow dry the cathode plate for later use.

[0079] (2) Electrolyte preparation

[0080] Add copper sulfate pentahydrate (80 g / L) and sulfuric acid (100 g / L) to deionized water and stir until completely dissolved. Then add sodium chloride (10 mg / L) and gelatin (2 mg / L) and control the electrolyte temperature at 30℃.

[0081] (3) Electrodeposition process

[0082] The pretreated cathode plate and the ruthenium-iridium-titanium anode plate were placed parallel to each other in the electrolyte, and constant current deposition was performed at a current density of 30 A / dm². The electrolyte rotation speed was controlled at 1200 rpm, and the deposition time was 15 min, resulting in a heat-resistant copper foil with a thickness of 35 μm.

[0083] (4) Post-processing

[0084] A etching solution consisting of 30 g / L copper chloride dihydrate (CuCl2・2H2O), 15 ml / L hydrochloric acid (HCl), and 15 g / L sodium chloride (NaCl) was used to etch the broken crystal grains on the smooth surface (cathode surface) of the copper foil for 5 minutes to remove surface broken crystals.

[0085] To evaluate the high-temperature structural stability of the aforementioned heat-resistant copper foil, the samples were placed in a tube furnace under an argon protective atmosphere and heated to 180°C at a heating rate of 10 °C / min. Isothermal annealing was then performed for 5 h, 12 h, and 24 h, followed by slow cooling to room temperature in the furnace. The grain orientation of the pristine and annealed copper foils was measured using a SmartLab 9KW X-ray diffractometer (XRD).

[0086] See test results Figure 2 The results showed that the heat-resistant copper foil prepared by the above method had a significantly higher diffraction peak intensity on the (220) crystal plane than other crystal planes. The texture coefficient of the original copper foil (220) crystal plane reached 98% based on texture coefficient calculations. (See also...) Figure 3 The texture retention rate of copper foil (220) with different annealing times was ≥98%.

[0087] Specifically, the texture factor of the crystal planes in the copper foil is calculated according to the following formula:

[0088]

[0089] Wherein, TC (hkl) I is the texture coefficient of the (hkl) crystal plane of the copper foil under test. (hkl) I represents the diffraction degree of the copper foil (hkl) crystal plane. 0(hkl) The diffraction degree of the standard copper powder (hkl) crystal plane is denoted by n, where n is the number of diffraction peaks.

[0090] Further, please refer to Figures 4 to 7 , Figures 4 to 7 The orientation imaging diagram, inverse pole diagram, grain boundary distribution diagram, and grain size distribution diagram of the copper foil described in one embodiment of the present invention are shown respectively. Figures 8 to 11 The orientation imaging diagram, inverse pole diagram, grain boundary distribution diagram, and grain size distribution diagram of the annealed copper foil in one embodiment of the present invention are shown respectively. EBSD test samples of the original state and the sample annealed at 180℃ for 24 h were prepared using a cross-sectional ion polishing device. Field emission scanning electron microscopes equipped with electron backscattering probes (EBSD, NordlysMax3) were used to detect and collect information on the microstructure of the copper foil cross-section, including grain size and grain orientation. The test results show that the deposited copper foil exhibits a (220) preferred orientation columnar crystal structure with an average grain size of 1 μm. After annealing for 24 h, the grain size increased to 1.04 μm, fluctuating by 4%. The columnar crystal morphology did not significantly coarsen, the twin ratio remained at approximately 46%, and the grain orientation was still predominantly (220).

[0091] The stress-strain curve of the copper foil was obtained by tensile testing, as follows: Figure 12 As shown, its tensile strength is 435 MPa and its elongation is 5.6%, indicating that the heat-resistant copper foil prepared using the preparation method of the present invention has both high strength and good ductility, and is suitable for service scenarios in long-term high-temperature environments.

[0092] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A heat-resistant copper foil, characterized by, The volume percentage of the (220) crystal plane texture in the heat-resistant copper foil is 70%~100%, and 80%~100% of the grain boundaries are arranged along the [110] crystal direction. The heat-resistant copper foil also includes submicron columnar crystals. The area percentage of columnar crystals with an aspect ratio greater than or equal to 5 in all grains is ≥80%. Before and after annealing, the change rate of the number of columnar crystals with an aspect ratio greater than or equal to 5 is less than or equal to 10%.

2. The heat-resistant copper foil according to claim 1, characterized by The proportion of Σ3 grain boundaries in the heat-resistant copper foil is greater than or equal to 40%, and the change rate of the proportion of Σ3 grain boundaries before and after annealing is less than or equal to 0.5%.

3. The heat-resistant copper foil according to claim 1, wherein The average grain size is 0.9~1.1 μm, and the change rate of the average grain size before and after annealing is less than or equal to 6%.

4. A method for preparing heat-resistant copper foil, used to prepare the heat-resistant copper foil according to any one of claims 1 to 3, characterized in that, The method for preparing the heat-resistant copper foil includes the following steps: Cathode pretreatment: Pure titanium plate is used as cathode plate. The deposition surface of the cathode plate is polished. The deposition surface of the cathode plate is rinsed with deionized water, dilute sulfuric acid and anhydrous ethanol in sequence and then dried. Electrolyte preparation: Add copper sulfate pentahydrate and sulfuric acid to deionized water, stir until dissolved, then add sodium chloride and gelatin to form an electrolyte. The concentration of copper ions in the electrolyte is 50-80 g / L, the concentration of sulfuric acid is 80-100 g / L, the concentration of chloride ions is 5-10 mg / L, and the concentration of gelatin is 1-3 mg / L. Electrodeposition: The ruthenium-iridium-titanium anode plate and the pretreated cathode plate are placed parallel to each other in the electrolyte and constant current deposition is performed to form copper foil. The electrolyte temperature is 10~50℃, the current density is 10~60 A / dm², and the electrodeposition speed is 1000~1200 rpm. Post-treatment: The copper foil surface is etched with an etchant to remove surface debris. The etchant consists of 30 g / L copper chloride dihydrate, 15 ml / L hydrochloric acid, and 15 g / L sodium chloride. The etching time is 4-6 minutes.

5. The method for preparing heat-resistant copper foil according to claim 4, characterized in that, Steps: In the cathode pretreatment, the specific steps include: polishing the deposition surface of the cathode plate with 1500-grit sandpaper to make the roughness Ra of the deposition surface 0.5~2 μm.

6. The method for preparing heat-resistant copper foil according to claim 4, characterized in that, Steps: The cathode pretreatment specifically includes: After the deposition surface of the cathode plate is polished, it is rinsed with deionized water for 5 min, ultrasonically cleaned with 5% dilute sulfuric acid for 2-4 min, and ultrasonically cleaned with anhydrous ethanol for 1-3 min before being dried.

7. The method for preparing heat-resistant copper foil according to claim 4, characterized in that, Steps: In the preparation of the electrolyte, the purity of copper sulfate pentahydrate is not less than 99%, the purity of sulfuric acid is not less than 98%, the purity of sodium chloride is not less than 99%, and the gelatin is animal gelatin.

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