Heat-resistant copper foil and preparation method thereof

Abstract

The invention relates to the technical field of electrolytic copper foils, in particular to a heat-resistant copper foil and a preparation method thereof, the volume ratio of (220) crystal face texture in the heat-resistant copper foil is 70%-100%, and 80%-100% of crystal boundaries are arranged along the [110] crystal orientation. By forming a high-proportion (220) texture, an approximately single-oriented crystal structure is further formed, and the high-purity texture enables crystal boundaries to be highly and orderly arranged along the [110] crystal orientation; through the synergistic effect of the submicron columnar crystal structure and the single (220) texture, the copper foil is endowed with excellent thermal stability. Moreover, 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 which is more than 50% superior to that of similar copper foils in the prior art can be realized; the atomic arrangement characteristic of the (220) crystal face is combined with the columnar crystal structure, so that the copper foil has excellent ductility while keeping high strength, the heat stability, strength and ductility of the copper foil under the complex heat exchange condition are improved, and the requirements of the high-end field for the performance of the copper foil are met.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytic copper foil, in particular to a heat-resistant copper foil and a preparation method thereof. Background Art

[0002] In high-end fields such as semiconductor packaging and power batteries, copper foil is a core conductive material, and its thermomechanical stability directly determines the signal integrity, heat dissipation efficiency, and long-term reliability of the device. With the popularization of advanced packaging processes such as high-temperature resin pressing (150–250°C) and multi-layer stacking, as well as power battery fast charging technology, copper foil faces problems such as grain coarsening and grain boundary migration, which lead to stress concentration and performance degradation during high-frequency thermal cycles. Studies have shown that the (220) crystal plane texture can significantly improve the mechanical strength and high-temperature structural stability of copper foil due to its unique crystallographic properties. Therefore, the precise control of crystal texture has become a key direction to break through the technical bottleneck.

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

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

[0005] The technical solution is as follows:

[0006] A heat-resistant copper foil, wherein the volume proportion of the (220) crystal plane texture in the heat-resistant copper foil is 70% to 100%, and 80% to 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 a heat-resistant copper foil, comprising the following steps:

[0010] Cathode pretreatment: Use pure titanium plate as cathode plate, polish the deposition surface of cathode plate, rinse the deposition surface of cathode plate with deionized water, dilute sulfuric acid and anhydrous ethanol in sequence and then blow dry;

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

[0012] Electrodeposition: Place the ruthenium-iridium-titanium anode plate and the pre-treated cathode plate in parallel in the electrolyte and perform constant current deposition to form copper foil;

[0013] Post-processing: Use etching liquid to corrode the broken crystal grains on the smooth surface of the copper foil to remove the surface broken crystals.

[0014] In one embodiment, step: cathode pretreatment specifically includes: using 1500-grit sandpaper to polish the deposition surface of the cathode plate so that the roughness Ra of the deposition surface is 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 minutes, ultrasonically cleaned with 5% dilute sulfuric acid for 2-4 minutes, and ultrasonically cleaned with anhydrous ethanol for 1-3 minutes, and then blown dry.

[0017] In one embodiment, step: in the preparation of the 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.

[0018] In one embodiment, step: 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.

[0019] In one embodiment, in the step: during the electrodeposition, the electrolyte temperature is 10-50°C, the current density is 10-60A / dm², and the electrodeposition speed is 1000-1200 rpm.

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

[0021] In one embodiment, in step: post-processing, the corrosion treatment time is 4 to 6 minutes.

[0022] Beneficial effects:

[0023] The heat-resistant copper foil forms a nearly single-oriented crystal structure by forming a high proportion of (220) texture. This high-purity texture allows the grain boundaries to be highly ordered along the

[110] crystal direction. The synergistic effect of the submicron columnar crystal structure and the single (220) texture gives the copper foil excellent thermal stability. Moreover, 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 existing technology. The atomic arrangement characteristics of the (220) crystal plane combined with the columnar crystal structure enable the copper foil to maintain high strength while having excellent ductility, which is conducive 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 preparation method of the heat-resistant copper foil is implemented by grinding the cathode plate deposition surface to form micron-level roughness, which can promote the heterogeneous nucleation of copper ions during the electrolysis process. The pure titanium cathode plate is polished and pre-treated with multiple cleaning steps to provide a suitable surface for the orderly deposition of copper ions. By regulating the concentrations 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-corrosion treatment, the surface broken crystals can be removed. The copper foil finally obtained can form a high-ratio (220) texture, and 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, meeting the performance requirements of copper foil in high-end fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 Flowchart of a method for preparing heat-resistant copper foil according to one embodiment of the present invention;

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

[0029] Figure 3 A comparison diagram of the texture retention rate of the copper foil (220) at different annealing times according to an embodiment of the present invention;

[0030] Figure 4 This is an orientation imaging diagram of the EBSD analysis results of the copper foil described in one embodiment of the present invention;

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

[0032] Figure 6 This is a grain boundary distribution diagram of the EBSD analysis results of the copper foil according to one embodiment of the present invention;

[0033] Figure 7 is a grain size distribution diagram of the EBSD analysis results of the copper foil according to one embodiment of the present invention;

[0034] Figure 8 This is an orientation imaging diagram of the EBSD analysis results of the annealed copper foil according to one embodiment of the present invention;

[0035] Figure 9 is an inverse pole figure in the EBSD analysis result of the annealed copper foil according to one embodiment of the present invention;

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

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

[0038] Figure 12 FIG. 4 is a stress-strain curve diagram of the copper foil according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0040] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present 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 the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0042] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0043] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0044] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate 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 implementation methods.

[0045] An embodiment of the present invention provides a heat-resistant copper foil. In an observation area, the volume proportion 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 heat-resistant copper foil described above forms a nearly single-oriented crystal structure by forming a high proportion of (220) texture. This high-purity texture allows the grain boundaries to be highly ordered along the

[110] crystal direction. The synergistic effect of the submicron columnar crystal structure and the single (220) texture gives the copper foil excellent thermal stability. Moreover, after annealing, the grain size fluctuation is small, and the (220) texture retention rate is over 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 having excellent ductility, which is conducive 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 fraction of the (220) crystal plane texture in the heat-resistant copper foil may be 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any other value within the range. It should also be noted that the number fraction of grain boundaries arranged along the

[110] crystal direction under EBSD analysis may 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 high-angle grain boundaries have high energy and disordered atomic arrangement, and are easily converted into channels for grain migration at high temperatures, resulting in rapid grain coarsening and a sharp decline in the mechanical and electrical properties of the copper foil. However, due to the highly ordered structure and high atomic matching of the Σ3 grain boundaries, their energy is only 1 / 3 to 1 / 2 of that of ordinary high-angle grain boundaries, and their resistance to grain boundary migration is large. This can significantly inhibit the grain growth rate at high temperatures and maintain the fine-grained structure and stable performance of the copper foil. The small change rate before and after annealing reflects the thermal stability of the Σ3 grain boundaries. In the thermal cycling environment of actual use, the Σ3 grain boundaries are not easily converted into high-energy ordinary high-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 effects on inhibiting grain coarsening and resisting cracking will rapidly diminish, leading to degradation of the copper foil's heat resistance. A change rate of ≤0.5% means that the advantages of the 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% directly enhances the copper foil's resistance to grain coarsening and thermal fatigue through its low-energy and low-diffusivity properties. A change rate of ≤0.5% before and after annealing ensures that this advantage is maintained over the long term in high-temperature environments. The combined effect of these two factors improves the heat-resistant reliability of this heat-resistant copper foil under high-frequency thermal cycling, helping to 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 cross section of the heat-resistant copper foil through EBSD (electron backscatter diffraction) analysis under arbitrary conditions, 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 average grain size change rate before and after annealing is less than or equal to 6%. Specifically, when the grain size is in the grain range of 0.9~1.1 μm, the grain boundary density of the copper foil is significantly improved, which can hinder the long-range diffusion of atoms and the overall slip of grain boundaries 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 rate of change before and after annealing of less than 6% can avoid performance degradation caused by grain coarsening, which is beneficial to ensure that the microstructure of the copper foil remains close to its initial state after high-temperature aging, thereby ensuring its heat-resistant reliability. Furthermore, all grains range from 0.9 to 1.1 μm, which is fine but not at the ultrafine submicron level. This balances fine grain strengthening with high-temperature stability. If the grains are smaller than 0.9 μm, their grain boundary energy is too high, making it more susceptible to rapid coarsening through grain boundary merging at high temperatures. If the grains are larger than 1.1 μm, the grain boundary density is insufficient, making it difficult to effectively hinder atomic motion and stress transfer at high temperatures. Therefore, a grain size of 0.9 to 1.1 μm retains the thermal deformation resistance of fine grains while reducing the driving force for coarsening through a moderate grain size. Combined with a low rate of change, this further enhances the high-temperature structural stability of the heat-resistant copper foil.

[0052] In one embodiment, within the observed area of ​​the heat-resistant copper foil, columnar crystals with an aspect ratio of 5 or greater account for 80% or more of the total area of ​​all grains. 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 preferentially grow in a specific direction, resulting in greater structural stability at high temperatures. Heat-resistant copper foil with a columnar crystal area of ​​≥80% with an aspect ratio of ≥5 has a high grain boundary density and is arranged in an orderly manner along the preferred direction. The dense grain boundaries can hinder the diffusion of high-temperature atoms, inhibit grain coarsening to maintain the fine grain strengthening effect, and enhance resistance to thermal deformation. Its consistent orientation makes the thermal expansion anisotropy more coordinated, reduces the stress concentration caused by expansion differences during thermal cycles, and reduces the risk of cracking. A large number of slender grain boundaries form a physical barrier, delaying grain boundary sliding and void formation, and improving thermal fatigue resistance. At the same time, the orderly arrangement reduces electron scattering to maintain high conductivity. The surface roughness of the uniform fine crystals is low, which is conducive to close bonding with the electrode material to reduce interface impedance. It also has excellent structural stability at high temperatures, ensuring the consistency of mechanical and electrical properties in long-term service and meeting the needs of high-frequency thermal cycle scenarios.

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

[0054] In one embodiment, in the observation area, along the thickness direction of the heat-resistant copper foil, the length of the columnar crystals that accounts for more than 75% of the total thickness of the heat-resistant copper foil is ≥90%. Along the thickness direction, the length of the columnar crystals that accounts for more than 75% of the total thickness is more than 90%, which means that the columnar crystals have strong penetration and highly consistent orientation: they reduce the disordered grain boundaries perpendicular to the thickness direction, reduce the stress concentration caused by expansion differences during thermal cycles, and greatly reduce the risk of cracking. The penetrating grain boundaries form a continuous barrier, hindering atomic diffusion and grain coarsening at high temperatures, maintaining the fine grain strengthening effect, and significantly enhancing the ability to resist thermal deformation. At the same time, the orderly arranged long columnar crystals reduce electron scattering, ensure stable conductivity, and more uniformly bond with the interface of adjacent materials, improve interlayer adhesion, and can maintain mechanical strength and dimensional stability for a long time in high-frequency thermal cycles, adapting to the needs of high-temperature service scenarios.

[0055] Furthermore, before and after annealing, the change in the number of columnar crystals whose length accounts for 90% or more of the total thickness of the heat-resistant copper foil is less than or equal to 8%. This helps reduce disordered grain boundaries perpendicular to the thickness, continuously suppresses stress concentration caused by grain boundary differences during thermal cycling, hinders atomic diffusion and grain coarsening, maintains resistance to thermal deformation and cracking, ensures stable electrical conductivity and mechanical properties, and ensures that the performance of the heat-resistant copper foil degrades slowly during long-term high-temperature service, thereby improving heat resistance and reliability.

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

[0057] S10, cathode pretreatment: using pure titanium plate as cathode plate, polishing the deposition surface of cathode plate, and washing the deposition surface of cathode plate with deionized water, dilute sulfuric acid and anhydrous ethanol in sequence, and then drying;

[0058] S20, preparing an electrolyte: adding copper sulfate pentahydrate and sulfuric acid to deionized water, stirring until dissolved, and then adding sodium chloride and gelatin to form an electrolyte;

[0059] S30, electrodeposition: placing a ruthenium-iridium-titanium anode plate and a pretreated cathode plate in parallel in an electrolyte, performing constant current deposition to form a copper foil;

[0060] S40, post-processing: using a corrosive solution to corrode the broken crystal grains on the smooth surface of the copper foil to remove the surface broken crystals.

[0061] The above-mentioned heat-resistant copper foil preparation method, during the implementation process, forms micron-level roughness by grinding the deposition surface of the cathode plate, which can promote the heterogeneous nucleation of copper ions during the electrolysis process, and provides a suitable surface for the orderly deposition of copper ions by grinding and multi-step cleaning pretreatment of the pure titanium cathode plate; by regulating the concentrations 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-corrosion treatment, the surface broken crystals can be removed, and the copper foil finally obtained can form a high-ratio (220) texture, and 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, meeting the performance requirements of copper foil in high-end fields.

[0062] Among them, the pure titanium cathode plate has a high surface finish and is resistant to electrolyte corrosion. It can reduce the adhesion between the copper foil and the substrate and improve the stripping efficiency. The stability of titanium can ensure the uniformity of the cathode interface electric field, 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, a long life in acidic electrolytes, can stably release oxygen, avoid anode dissolution and contamination of the electrolyte, and maintain 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, which meets the needs of energy conservation and environmental protection. It can ultimately improve the thickness uniformity, mechanical properties and surface quality of the copper foil, making it suitable for applications in high-precision electronics.

[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, 1500-grit sandpaper is used to polish the cathode plate deposition surface to a roughness Ra of 0.5-2 μm, further improving the suitability of the cathode plate surface. It can provide sufficient heterogeneous nucleation sites for copper ions and avoid the disordered grain orientation caused by the over-rough surface. This polishing method is conducive to precisely controlling the surface roughness to ensure uniform nucleation of the copper foil, reduce the generation of disordered grains, and help increase the proportion of (220) texture in the copper foil to more than 95%.

[0065] Specifically, in step S10, cathode pretreatment, after the deposition surface of the cathode plate is polished, it is sequentially rinsed with deionized water for 5 minutes, ultrasonically cleaned with 5% dilute sulfuric acid for 2-4 minutes, and ultrasonically cleaned with anhydrous ethanol for 1-3 minutes before being blown dry. In this way, the deionized water rinse can remove surface mechanical impurities; the 5% dilute sulfuric acid ultrasonic cleaning can dissolve the surface oxide layer of the titanium plate, expose the fresh metal surface, and improve the cathode activity; the anhydrous ethanol ultrasonic cleaning further degreases and quickly evaporates and dries to avoid 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 completely removing surface pollutants and oxide layers, reducing impurity-induced defects during copper ion deposition, improving the consistency of copper foil grain orientation, and thereby improving the (220) texture retention rate of the grains; at the same time, it enhances the initial bonding strength between the copper foil and the substrate, and reduces the breakage rate during peeling.

[0066] In one embodiment, in step S20, during the preparation of the 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. 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), and indirectly promotes the formation of a preferred orientation texture of the (220) crystal plane, forming a columnar crystal structure. By using this electrolyte concentration combination, the proportion of the (220) texture can be increased and stabilized at more than 90%, and the columnar crystals are arranged more neatly; low-concentration gelatin avoids brittleness caused by excessive inhibition, takes into account both strength and ductility, and improves reliability under thermal cycling conditions.

[0067] Furthermore, in step S20, during the preparation of the electrolyte, the purity of copper sulfate pentahydrate is no less than 99%, the purity of sulfuric acid is no less than 98%, and the purity of sodium chloride is no less than 99%. The gelatin is animal-derived gelatin. High-purity raw materials reduce the introduction of impurity ions such as Fe and Pb, and prevent impurities from segregating at grain boundaries and causing textural disturbances. Optionally, the gelatin can be bovine bone gelatin, fish skin gelatin, or the like.

[0068] In one embodiment, in step S30, during electrodeposition, the electrolyte temperature is 10-50°C, the current density is 10-60 A / dm², and the electrodeposition speed is 1000-1200 rpm. Specifically, the temperature range of 10-50°C can help balance the ion diffusion rate and the additive adsorption stability; the current density of 10-60 A / dm² controls the copper ion reduction rate to avoid coarse grains caused by excessively high rates; and the high-speed stirring of 1000-1200 rpm enhances electrolyte convection, reduces the polarization of copper ion concentration near the cathode, and ensures uniform growth of columnar crystals in the vertical direction. The above process parameters are conducive to improving the thickness uniformity of the copper foil, increasing the aspect ratio of the columnar crystals, reducing the grain coarsening rate after annealing, and further improving the thermal stability of the copper foil.

[0069] In one embodiment, in step S40, post-processing, 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 effect of chloride ions and copper, has a significantly higher etching rate on the surface disordered broken crystal grains (low orientation consistency) than on the (220) texture columnar crystals, achieving selective removal and obtaining a complete columnar crystal structure, which is beneficial for reducing the surface roughness of the copper foil, improving the broken crystal removal rate, reducing surface defects, alleviating stress concentration at high temperatures, and improving thermal cycling reliability.

[0070] In one embodiment, in step S40, post-processing, the etching treatment time is 4 to 6 minutes. The etching time of 4 to 6 minutes can fully dissolve the surface broken crystals while avoiding excessive corrosion damage to the main structure of the (220) columnar crystals, balancing the surface quality and thickness accuracy. Under the premise of ensuring the removal of broken crystals, it is beneficial to reduce the thickness loss rate of the copper foil; improve the surface flatness and enhance the bonding strength with the resin.

[0071] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0072] Example 1:

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

[0074] (1) Cathode pretreatment

[0075] A pure titanium plate was used as the cathode plate, and the deposition surface was polished with 1500-grit sandpaper;

[0076] After polishing, rinse with deionized water for 5 min;

[0077] After rinsing, ultrasonic cleaning was performed using 5% dilute sulfuric acid for 3 min;

[0078] After cleaning, ultrasonically clean the plate with anhydrous ethanol for 2 minutes. After cleaning, blow dry the cathode plate and set it aside.

[0079] (2) Preparation of electrolyte

[0080] Copper sulfate pentahydrate (80 g / L) and sulfuric acid (100 g / L) were added to deionized water and stirred until completely dissolved. Then, sodium chloride (10 mg / L) and gelatin (2 mg / L) were added. The electrolyte temperature was controlled at 30°C.

[0081] (3) Electrodeposition process

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

[0083] (4) Post-processing

[0084] The copper foil's smooth surface (cathode side) was etched for 5 minutes using an 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) to remove the surface crystals.

[0085] To evaluate the high-temperature structural stability of the heat-resistant copper foil, samples were placed in an argon-protected tube furnace and heated to 180°C at a rate of 10°C / min. They were then isothermally annealed for 5, 12, and 24 hours, respectively, and then slowly cooled to room temperature. The grain orientation of the original and annealed copper foils was measured using a SmartLab9KW X-ray diffractometer (XRD).

[0086] Test results refer to Figure 2 The results show that the heat-resistant copper foil prepared by the above copper foil preparation method has a significantly higher diffraction peak intensity on the (220) crystal plane than on other crystal planes. The texture coefficient calculation shows that the texture coefficient of the (220) crystal plane of the original copper foil reaches 98%; see Figure 3 The texture retention rate of copper foil (220) with different annealing times is ≥98%.

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

[0088]

[0089] Among them, TC (hkl) is the texture coefficient of the (hkl) crystal plane of the copper foil to be tested, I (hkl) is the diffraction degree of the copper foil (hkl) crystal plane, I 0(hkl) is the diffraction degree of the standard copper powder (hkl) crystal plane, and n is the number of diffraction peaks.

[0090] Further, see Figures 4 to 7 , Figures 4 to 7 The EBSD analysis results of the copper foil in one embodiment of the present invention respectively show the orientation image, inverse pole figure, grain boundary distribution map and grain size distribution map; Figures 8 to 11 The orientation image, inverse pole figure, grain boundary distribution and grain size distribution of the EBSD analysis results of the annealed copper foil described in one embodiment of the present invention are shown respectively. EBSD test specimens of the original state and the sample annealed at 180°C for 24 h were prepared by a cross-sectional ion polishing device. A field emission scanning electron microscope equipped with an electron backscatter probe (EBSD, NordlysMax3) was used to detect and collect microstructural information such as grain size and grain orientation of the copper foil cross section. The test results showed that the deposited copper foil had a columnar crystal structure with a (220) preferred orientation and 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 undergo significant coarsening, the twin ratio remained at about 46%, and the grain orientation was still mainly (220).

[0091] The stress-strain curve of copper foil was measured by tensile test, such as Figure 12 As shown, its tensile strength is 435 MPa and the elongation is 5.6%, indicating that the heat-resistant copper foil prepared by 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 arbitrarily. To make the description concise, 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 implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A heat-resistant copper foil, characterized in that The volume proportion of the (220) crystal plane texture in the heat-resistant copper foil is 70% to 100%, and 80% to 100% of the grain boundaries are arranged along the [110] crystal direction.

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

4. A method for preparing a heat-resistant copper foil, for preparing 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 comprises the following steps: Cathode pretreatment: Use pure titanium plate as cathode plate, polish the deposition surface of cathode plate, rinse the deposition surface of cathode plate with deionized water, dilute sulfuric acid and anhydrous ethanol in sequence and then blow dry; Preparation of electrolyte: Add copper sulfate pentahydrate and sulfuric acid to deionized water, stir until dissolved, then add sodium chloride and gelatin to form an electrolyte; Electrodeposition: Place the ruthenium-iridium-titanium anode plate and the pre-treated cathode plate in parallel in the electrolyte and perform constant current deposition to form copper foil; Post-processing: Use etching liquid to corrode the broken crystal grains on the smooth surface of the copper foil to remove the surface broken crystals.

5. The method for preparing the heat-resistant copper foil according to claim 4, wherein: Step: The cathode pretreatment specifically includes: using 1500-grit sandpaper to polish the deposition surface of the cathode plate to make the roughness Ra of the deposition surface 0.5-2 μm.

6. The method for preparing the heat-resistant copper foil according to claim 4, wherein: Steps: Cathode pretreatment specifically includes: After the deposition surface of the cathode plate was polished, it was 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, and then blown dry.

7. The method for preparing the heat-resistant copper foil according to claim 4, wherein: Steps: In the preparation of the 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; 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.

8. The method for preparing the heat-resistant copper foil according to claim 4, wherein: Steps: During electrodeposition, the electrolyte temperature is 10~50℃, the current density is 10~60 A / dm², and the electrodeposition speed is 1000~1200 rpm.

9. The method for preparing a heat-resistant copper foil according to any one of claims 4 to 8, wherein: Step: In the post-treatment, the etching solution includes: 30 g / L copper chloride dihydrate, 15 ml / L hydrochloric acid and 15 g / L sodium chloride; the etching treatment time is 4 to 6 minutes.

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