Metal film and method for manufacturing the same

Abstract

To provide a method for producing a metal film in which a copper plated film having a three-dimensional structure is deformed according to a purpose, the three-dimensional structure having nano-precipitates composed of copper deposited or intersected with voids on a base material, and provide specifically a method for producing a metal film by which a metal film having a structure with improved mechanical strength as a whole film or a structure capable of exhibiting a better anchoring effect is simply realized with less load on the base material, and the metal film.SOLUTION: A method for producing a metal film according to the present invention includes a plating step of forming a copper plating film having a three-dimensional structure in which nano-precipitates composed of copper are deposited or intersected with voids on a base material by electroplating, and a low-temperature heat treatment step of heat-treating the copper plating film at a temperature below a melting point of copper.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a metal film and a method for manufacturing the metal film. [Background technology]

[0002] The present inventors have invented a copper plating film having a three-dimensional structure on a substrate (object to be plated) in which fine nano-precipitates made of copper are deposited or intertwined with voids (gaps) (this structure in which precipitates are deposited or intertwined with voids (gaps) is referred to as a "three-dimensional structure" in this application; however, not all precipitates necessarily have voids between them) (Patent Document 1: JP 2015-42776 A). This copper plating film can impart a fine three-dimensional structure to the surface of a substrate and has a variety of applications.

[0003] For example, this three-dimensional structure has an extremely large specific surface area and a complex, non-uniform morphology containing voids, providing excellent anchoring (bonding) properties. Therefore, if copper on which this copper plating film is formed is used as the negative electrode current collector for a lithium-ion battery, it is possible to fix large amounts of active materials such as tin and silicon and prevent their peeling. Furthermore, resin materials can be firmly bonded to this copper plating film (Patent Document 2: JP 2019-151090 A). Thus, this series of inventions related to this copper plating film has the potential to greatly advance Japan's industry. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-42776 [Patent Document 2] Japanese Patent Application Publication No. 2019-151090 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-106093 [Non-patent literature]

[0005] [Non-Patent Document 1] Yoichi Kamikoriyama, Hiroshi Imamura, Atsushi Muramatsu & Kiyoshi Kanie, “Ambient Aqueous-Phase Synthesis of Copper Nanoparticles and Nanopastes with Low-Temperature Sintering and Ultra-High Bonding Abilities”, SCIENTIFIC REPORTS, 29 January 2019, 9:899 Summary of the Invention [Problem to be solved by the invention]

[0006] Problems associated with conventional copper plating films include the insufficient mechanical strength of nanoprecipitates associated with three-dimensional structures, the small bonding area with the substrate, and weak adhesion to the substrate, resulting in insufficient mechanical strength for the entire film. In response to these problems, Patent Document 3 (JP 2017-106093 A) proposes that after nanoprecipitates are formed on a substrate, a reinforcing plating process is performed using a plating bath containing an additive that selectively deposits copper on the base side of the precipitates, thereby increasing the bonding area, strengthening adhesion, and improving the mechanical strength of the entire film. However, this process requires a second plating step using the additive, which is time-consuming and likely to increase costs. For these reasons, there has been a need for a method for more easily modifying the three-dimensional structures associated with conventional copper plating films with minimal stress on the substrate, thereby creating structures with improved or enhanced properties and functions, or structures that can be applied to solving new problems. [Means for solving the problem]

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a method for producing a metal film in which a copper plating film having a three-dimensional structure on a substrate in which copper nanoprecipitates are deposited or intertwined with voids is deformed according to the purpose, and a method for producing a metal film that can easily produce a metal film having a structure with improved mechanical strength as a whole or a structure that can exert a better anchoring effect, with little load on the substrate, and such a metal film.

[0008] The present invention solves the above problems by the solution means described below as one embodiment.

[0009] The method for manufacturing a metal film according to the present invention is characterized by comprising a plating step of forming a copper plating film having a three-dimensional structure in which nano-precipitates made of copper are deposited or intertwined with voids on a substrate by an electroplating method, and a low-temperature heat treatment step of heat-treating the copper plating film at a temperature below the melting point of copper.

[0010] This method fuses and deforms the nano-precipitates in the copper plating film, allowing the production of a metal film with a new structure more suitable for bonding to resin materials, etc. The degree of fusion can be adjusted by the heat treatment temperature, allowing the production of multiple types of metal films. Furthermore, a low-temperature process below the melting point of copper reduces the high-temperature load on the substrate, and the use of no additives prevents chemical effects on the substrate, allowing the surface morphology to be formed into a desired shape. This allows the transformation of a fine three-dimensional structure into a shape more suitable for bonding to resin materials, etc., using an extremely simple method while reducing energy and material costs.

[0011] Specifically, in the low-temperature heat treatment step, the nanoprecipitates can be fused together by the heat treatment to form irregularly shaped precipitates, and the irregularly shaped precipitates can be mixed with or substituted for the nanoprecipitates to form a three-dimensional structure on the substrate in which the irregularly shaped precipitates are deposited or intertwined with voids. Alternatively, in the low-temperature heat treatment step, the nanoprecipitates can be fused together by the heat treatment to form a void-free copper film on the substrate.

[0012] Furthermore, in the plating step, the electrolytic plating method can be used to form a copper plating film having a three-dimensional structure in which nanoprecipitates of several tens of nanometers in size (10 nm or more but less than 100 nm) are deposited with voids or interlaced. Alternatively, in the plating step, the electrolytic plating method can be used to form a copper plating film having a three-dimensional structure in which particulate nanoprecipitates are deposited with voids or plate-like nanoprecipitates are interlaced with voids. These copper plating films can then be transformed into a desired shape in a low-temperature heat treatment step.

[0013] Specifically, in the low-temperature heat treatment step, the heat treatment can fuse the particulate nanoprecipitates or the plate-like nanoprecipitates to form irregular precipitates, and the irregular precipitates can be mixed with or substituted for the particulate nanoprecipitates and deposited on the substrate with voids, or can be mixed with or substituted for the plate-like nanoprecipitates to form a three-dimensional structure in which the irregular precipitates intersect with each other and with voids. Alternatively, in the low-temperature heat treatment step, the heat treatment can fuse the particulate nanoprecipitates or the plate-like nanoprecipitates to form a void-free copper film on the substrate.

[0014] In addition, polyacrylic acid can be added to the plating bath in the plating step. The substrate can be made of copper.

[0015] Furthermore, the metal film according to the present invention is a metal film that is a modified copper plating film having a three-dimensional structure in which nano-precipitates made of copper are deposited or intertwined with voids on a substrate, and is characterized in that irregular precipitates formed by the nano-precipitates fusing together on the substrate are mixed with or replace the nano-precipitates, forming a three-dimensional structure in which the nano-precipitates are deposited or intertwined with voids.

[0016] Another metal film according to the present invention is a metal film that is a modified copper plating film having a three-dimensional structure in which nano-precipitates made of copper are deposited or intertwined with voids, and is characterized in that the nano-precipitates are fused together to form a void-free copper film on the substrate.

[0017] The nanoprecipitates may be several tens of nanometers in size, 10 nm or more but less than 100 nm. That is, the metal film according to the present invention may be a modified copper plating film having a three-dimensional structure in which copper nanoprecipitates of 10 nm or more but less than 100 nm in size are deposited or intertwined on a substrate, with voids therebetween.

[0018] The nanoprecipitates may be particulate or plate-like nanoprecipitates. That is, the metal film according to the present invention may be a modified copper plating film having a three-dimensional structure in which particulate copper nanoprecipitates are deposited on a substrate with voids, or in which plate-like nanoprecipitates intersect with voids. In this case, the metal film according to the present invention may be a metal film formed on the substrate in which irregular precipitates formed by the fusion of particulate nanoparticles or plate-like nanoparticles intersect with voids, intermixed with or replacing the particulate nanoprecipitates and deposited with voids, or intermixed with or replacing the plate-like nanoprecipitates and formed with voids and intersect with voids. Another metal film according to the present invention may be a metal film formed on the substrate in which the particulate nanoprecipitates or plate-like nanoprecipitates are fused with each other, forming a void-free copper film.

[0019] The substrate may be made of copper. [Effects of the Invention]

[0020] According to the present invention, a copper plating film having a three-dimensional structure in which copper nanoprecipitates are deposited or intertwined with voids can be easily deformed into a desired shape with little load on the substrate, thereby obtaining a metal film having a structure with improved mechanical strength as a whole and a structure that can exert a better anchoring effect. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is an explanatory diagram illustrating the mechanism of three-dimensional structuring of precipitates. [Figure 2] FIG. 2 is an SEM photograph of the surface and cross section of a copper plating film according to an embodiment of the present invention. [Figure 3] FIG. 3 shows SEM photographs of the surface and cross section of a copper plating film before and after heat treatment according to an example of the present invention. [Figure 4] Figure 4 is an enlarged photograph of Figure 3(c)(d). [Figure 5] Figure 5 is an enlarged photograph of Figure 3(e)(f). DETAILED DESCRIPTION OF THE INVENTION

[0022] (Metal Film Manufacturing Method) Hereinafter, a method for manufacturing a metal film according to an embodiment of the present invention will be described with reference to the drawings. In this application, the copper plating film after heat treatment is generally referred to as a "metal film," but for convenience of explanation, it may also be referred to simply as a "copper plating film after heat treatment." The method for manufacturing a metal film according to this embodiment is characterized by including a plating step S1 in which a copper plating film having a three-dimensional structure in which copper nanoprecipitates are deposited or intertwined with voids is formed on a substrate by electroplating, and a low-temperature heat treatment step S2 in which the copper plating film is heat-treated at a temperature below the melting point of copper. A detailed description will be given below.

[0023] The present invention provides a metal film having a new structure that is a deformation of a copper plating film having a three-dimensional structure in which copper nanoprecipitates are deposited or intersecting with voids. Therefore, first, a plating step S1 is performed to form a copper plating film having such a fine three-dimensional structure on a substrate. This step S1 uses an electroplating method, and specifically, it may be performed by a known method described in Patent Document 1, etc.

[0024] Electrolytic plating is a method in which a substrate is immersed in a plating bath made of an electrolytic solution and metal ions in the electrolytic solution are deposited on the substrate by passing electricity through it. Therefore, the substrate is limited to a conductor, but the type of conductor is not limited. For example, various metals such as copper and steel can be used. Furthermore, the shape and size of the substrate are not limited. Furthermore, strike plating may be applied to the substrate as appropriate. The term "substrate" as used herein includes substrates on which such a strike-plated film is formed.

[0025] In step S1, a copper electroplating process is performed by immersing a substrate in a plating bath containing copper and passing an electric current through it to form a copper plating film on the substrate. Adding a predetermined amount of polyacrylic acid, a polyacrylic acid derivative, or a salt of either of these to the plating bath can form a fine three-dimensional structure consisting of plate-like nanoprecipitates (see Patent Document 1). As shown in Figure 1, the addition of polyacrylic acid preferentially adsorbs to specific crystal faces of the substrate (a copper plate in Figure 1), suppressing copper deposition from these faces (Figure 1(a)). Copper is deposited only on crystal faces not adsorbed by polyacrylic acid (Figure 1(b)). Furthermore, polyacrylic acid preferentially adsorbs to specific crystal faces of the deposited copper (Figure 1(c)). As a result, the copper plating (copper precipitate) grows in a specific direction (Fig. 1(d)), and a fine three-dimensional structure (Fig. 2(a)(b)) can be formed on the substrate, in which non-uniform thin copper nano-precipitates about tens of nanometers thick intersect and overlap with voids.

[0026] The mechanism by which a three-dimensional structure consisting of particulate nanoprecipitates is formed instead of plate-shaped nanoprecipitates by adjusting the polyacrylic acid concentration, for example, is basically the same, and as described above, a characteristic three-dimensional structure consisting of non-uniform nanoprecipitates, such as plate-shaped and particulate nanoprecipitates, is formed by the selective growth of the precipitate (copper) due to the selective adsorption of polyacrylic acid. As used herein, "nanoprecipitates" refers to precipitates with a size of about several tens of nanometers, that is, 10 nm or more but less than 100 nm, with plate-shaped precipitates having a thickness of about several tens of nanometers and particulate precipitates having a diameter of about several tens of nanometers.

[0027] As an example, Figures 2(a) to 2(d) show SEM images of copper plating films produced in step S1. The inset photographs in each figure show the corresponding enlarged photographs. The copper plating film was produced by adding a predetermined amount of polyacrylic acid (molecular weight approximately 5000) to a plating bath containing copper sulfate pentahydrate (CuSO4 5H2O) and sulfuric acid (H2SO4), and depositing copper on the steel sheet substrate (on the strike-plated film) under predetermined electrodeposition conditions using a phosphorus-containing copper sheet as the anode and a steel sheet with a copper strike-plated film formed on it as the cathode.

[0028] Figure 2(a) shows the polyacrylic acid 3×10 -4 The surface of the copper plating film formed in the plating bath containing M, Figure 2(b) shows a cross section, and on the substrate, a three-dimensional structure is formed in which non-uniform plate-like nano-precipitates of about 30 to 40 nm in thickness intersect with each other, including voids, i.e., a three-dimensional structure in which plate-like precipitates are crowded together. On the other hand, Figure 2(c) shows the surface of the copper plating film formed in the plating bath containing M, and -4The surface of a copper plating film formed using an M-containing plating bath (Figure 2(d)) shows a cross-section of the surface. This film exhibits a three-dimensional structure on the substrate, consisting of uneven, tens of nanometer-sized nanoprecipitates with voids, i.e., a cluster of rod-shaped structures formed by the deposition of nanoprecipitates with specific orientations. The copper plating films shown in Figures 2(a) and 2(b) exhibit a fine, complex, interwoven structure with voids, while the copper plating films shown in Figures 2(c) and 2(d) exhibit a fine, complex, uneven structure with voids, providing excellent anchoring (bonding) properties to resin materials and other materials. Furthermore, because these roughened films have an extremely large specific surface area, the interface distance is long when joined to resin materials and moisture penetration is limited. This results in excellent corrosion resistance at the interface and excellent adhesion durability.

[0029] In this way, the shape of the deposit can be adjusted by adjusting the polyacrylic acid concentration. Furthermore, the thickness of the three-dimensional structure, as well as the shape, size, and density of the deposit (the size and degree of voids) can be adjusted by adjusting the plating bath composition, such as the copper ion concentration (here, the concentration of copper sulfate pentahydrate), and electrodeposition conditions, such as the current density and bath temperature. Therefore, the shape of the nanoprecipitates in the copper plating film formed in step S1 is not limited. Alternatively, as shown in Figures 2(c) and 2(d), the three-dimensional structure may be relatively thin, forming a densely packed underlayer of deposits.

[0030] Next, the copper plating film formed in step S1 is subjected to a low-temperature heat treatment step S2 at a temperature below the melting point of copper (1083°C). This process fuses and deforms the nano-precipitates in the copper plating film, producing a metal film with a new structure more suitable for bonding with resin materials, etc. The degree of fusion can be adjusted by adjusting the heat treatment temperature, allowing for the production of multiple types of metal films. This step S2, performed at a low temperature below the melting point of copper (300°C in the example), reduces the high-temperature load on the substrate, and by not using additives, the desired surface morphology can be formed without chemically affecting the substrate. Therefore, even materials that are sensitive to heat or chemically sensitive can be used for the substrate. This method reduces the load on the substrate, reduces energy and material costs, and allows for the extremely simple transformation of a fine three-dimensional structure into a shape more suitable for bonding with resin materials, etc.

[0031] The heat treatment in step S2 involves holding the substrate on which the copper plating film has been formed at a predetermined temperature below the melting point of copper for about one hour. It is more preferable to perform the heat treatment in an inert atmosphere (vacuum, argon gas atmosphere, nitrogen gas atmosphere, etc.) or a reducing atmosphere (hydrogen gas atmosphere, etc.) against oxidation. The following describes the form (structure) of the metal film that can be produced by the method according to this embodiment and its industrial applicability, using examples. [Example]

[0032] (Metal film morphology) In accordance with step S1 according to this embodiment, a copper plating film was formed on a copper plate, which was a substrate, under the following conditions.

[0033] (1) Plating bath composition Copper sulfate pentahydrate (CuSO4 5H2O) 0.85M Sulfuric acid (H2SO4) 0.55M Polyacrylic acid (molecular weight approximately 5000) 3 x 10 -4 M (2) Electrodeposition conditions (electrodeposition is performed by the current control method) Anode: Phosphorous copper plate Cathode (base material): copper plate Current density: 1.0Adm -2 Current consumption: 27C Bath temperature: 25℃

[0034] The polyacrylic acid used was "Polyacrylic Acid 5,000" manufactured by Fujifilm Wako Pure Chemical Industries. The copper plate used as the substrate was 10 cm 2 The parts were insulated by masking with masking tape except for the above part, and as a pretreatment, they were ultrasonically cleaned for 5 minutes, then degreased with a commercially available degreaser (60°C) for 5 minutes, and then pickled with 10% sulfuric acid (60°C) for 1 minute.

[0035] Next, the copper plating film formed on the copper plate was heat-treated at 300°C, 500°C, 700°C, and 900°C, respectively. For the heat treatment, a tabletop lamp heating device manufactured by ULVAC, product name: "MILA-3000," was used. The copper plate was placed inside the device and heated to the set temperature, held for 1 hour for heat treatment, then naturally cooled to near room temperature, and the copper plate was removed from the device. The atmosphere mode inside the device during the heat treatment was set to "vacuum."

[0036] Figure 3 shows SEM photographs of the surface and cross section of the copper plating film before and after heat treatment. Figure 3(a) shows the surface before heat treatment, and Figure 3(b) shows its cross section, showing the copper plating film formed by step S1 according to this embodiment. A fine three-dimensional structure was confirmed in which non-uniform plate-like copper nano-precipitates with a thickness of approximately 30 to 40 nm intersected with voids.

[0037] Furthermore, Figure 3(c) shows the surface at a heat treatment temperature of 300°C, and Figure 3(d) shows its cross section. Figure 3(e) shows the surface at a heat treatment temperature of 500°C, and Figure 3(f) shows its cross section. Figure 3(g) shows the surface at a heat treatment temperature of 700°C, and Figure 3(h) shows its cross section. Figure 3(i) shows the surface at a heat treatment temperature of 900°C, and Figure 3(j) shows its cross section.

[0038] In all copper plating films heat-treated at temperatures between 300 and 900°C, structural changes due to the fusion of plate-like nanoprecipitates were confirmed compared to before heat treatment (Fig. 3(c)-(j)). In the copper plating film heat-treated at 300°C, irregularly shaped precipitates formed by the fusion of plate-like nanoprecipitates were observed to intermingle with the nanoprecipitates, forming a new three-dimensional structure in which they intersect and overlap with voids (Fig. 3(c)(d) and Fig. 4). In addition, in the copper plating film heat-treated at 500°C, irregularly shaped precipitates formed by the fusion of plate-like nanoprecipitates were observed to replace the nanoprecipitates, forming a new three-dimensional structure in which they intersect and overlap with voids (Fig. 3(e)(f) and Fig. 5). The newly formed irregular precipitates increased in thickness and width as the fine size of the nanoprecipitates relaxed, their straight plate-like shape transformed into a curved shape, and their sharp corners or edges became rounded or bulged, transforming into rounded block shapes. As a whole, they had a sponge-like shape, and the thickness and width of each part were irregularly shaped and not uniform.

[0039] Therefore, the newly formed metal film can bond resin materials and the like with higher strength and stability than the copper plating film before heat treatment, making it possible to more effectively form bonded bodies with resin materials and bonded bodies between a substrate and a resin material via the metal film. Specifically, the irregular precipitates allow the resin injected by injection molding or the like to efficiently penetrate the appropriately widened voids and flow into the rounded curved interior, allowing the resin to be completely injected into the voids in the metal film. Furthermore, the bulges at the edges act as fasteners to lock the solidified resin. Furthermore, the metal film increases in thickness and width as the multiple nanoprecipitates fuse together, increasing the bonding area with the substrate and improving adhesion to the substrate, significantly improving the mechanical strength of the film as a whole. Therefore, the three-dimensional structure is not deformed or collapsed by the impact of resin injection by injection molding or the like, and provides an excellent anchoring effect for the injected resin material, thereby enabling higher-strength and more stable bonding of the resin material.

[0040] The copper plating film heat-treated at 500°C has a certain degree of thickness thinner than before the heat treatment (see the arrows in Figures 3(b)(f)), and it can be confirmed that the interface with the copper plate substrate has disappeared and part of the film has become integrated with the copper plate. This also clearly shows that the bonding area with the substrate has increased and the adhesion to the substrate has improved, making it possible to form a stronger bond between the substrate and resin material, etc., via the metal film.

[0041] On the other hand, in the copper plating films heat-treated at temperatures of 700°C and 900°C, the plate-like nanoprecipitates fused together, the three-dimensional structure disappeared, and a film consisting of copper containing no voids was formed, with the entire film being integrated with the copper substrate (Fig. 3(g)-(j)). This means that copper was joined in a low-temperature process below the melting point of copper, demonstrating that the newly formed metal film can function as a bonding material capable of joining copper and copper at low temperatures below the melting point.

[0042] Low-temperature sintering by nanoparticle formation of metals has been known, and Non-Patent Document 1 describes an example of successful joining of two copper plates via copper nanopaste in a nitrogen atmosphere at 200°C. However, in this case, the nanoparticles must be stabilized and coated with a protective layer to prevent oxidation, and the joining of the copper plates must also be carried out in an inert atmosphere.

[0043] In contrast, the copper plating film of this example was already oxidized, with an oxide film formed on the film surface. However, despite this, the metal film formed by heat treatment below the melting point was integrated and bonded entirely to the copper substrate. This is thought to be due to the fine three-dimensional structure of nanoprecipitates. This copper plating film was shown to have a very distinctive structure in which, even when the film surface was oxidized to a certain degree, the nanoprecipitates fused and deformed by low-temperature heat treatment below the melting point, allowing the entire film to be completely bonded and integrated with the copper metal. Furthermore, while it is certainly preferable to perform the low-temperature heat treatment in an inert or reducing atmosphere, it is not necessarily necessary to perform it in these atmospheres for copper plating films that have already been oxidized.

[0044] According to the above examples, by heat-treating a copper plating film having a three-dimensional structure in which fine copper nanoprecipitates are deposited or intertwined with voids (gaps) at a temperature of about 600°C or less, preferably 300°C to 500°C, and more preferably 400°C to 500°C, irregular precipitates with high mechanical strength and excellent anchoring effect can be introduced into the copper plating film while maintaining the three-dimensional structure, thereby forming a metal film that can bond resin materials and the like with higher strength and stability compared to the copper plating film before heat treatment. In this example, the heat treatment was performed on a copper plating film having a three-dimensional structure in which non-uniform plate-like nanoprecipitates are intertwined with voids. However, for example, heat treatment may also be performed on a copper plating film having a three-dimensional structure in which non-uniform particulate nanoprecipitates are deposited with voids. In this case, a metal film can be formed in which irregular precipitates in which nanoprecipitates are fused together are introduced into the copper plating film while maintaining the three-dimensional structure.

[0045] In another example, a copper substrate was used. Heat treatment of a copper plating film having a three-dimensional structure in which fine copper nanoprecipitates are deposited or intertwined with voids (gaps) at a temperature exceeding approximately 600°C, preferably 700°C or higher, eliminated the three-dimensional structure, and the entire void-free film was completely bonded to the copper substrate, forming an integrated bonded body. In this example, heat treatment was performed on a copper plating film having a three-dimensional structure in which non-uniform plate-like nanoprecipitates are intertwined with voids. However, heat treatment may also be performed on a copper plating film having a three-dimensional structure in which non-uniform particulate nanoprecipitates are deposited with voids. Other substrates may also be used. In this case, the nanoprecipitates are fused together to form a metal film in which a void-free copper film is formed on the substrate.

Claims

1. A copper-plated metal film having a three-dimensional structure in which plate-shaped copper particles having a size of 10 nm or more but less than 100 nm are deposited or intersected on a substrate, The copper-plated metal film has a three-dimensional structure in which the plate-shaped copper and irregularly shaped copper are mixed and intertwined with each other, leaving gaps between them, or the plate-shaped copper is replaced with the irregularly shaped copper, and the irregularly shaped copper is intertwined with each other, leaving gaps between them, leaving a three-dimensional structure in which the irregularly shaped copper is intertwined with each other, leaving gaps between them, The irregular copper is a block-shaped piece with rounded corners or bulges at the corners or edges, and has an irregular configuration in which the thickness or width of the part is not uniform. A metal film characterized by:

2. The substrate is made of copper. The metal film according to claim 1,

3. A plating process for forming a copper plating film having a three-dimensional structure in which nano-precipitates made of copper are deposited or intertwined with voids on a substrate by an electrolytic plating method; a low-temperature heat treatment step of heat-treating the copper plating film at a temperature equal to or lower than the melting point of copper, In the low-temperature heat treatment step, the nanoprecipitates are fused together by the heat treatment to form irregularly shaped precipitates, On the substrate, the irregular precipitates are mixed with or replace the nanoprecipitates to form a three-dimensional structure in which the irregular precipitates are stacked or intertwined and contain voids. A method for manufacturing a metal film, characterized by:

4. A plating process for forming a copper plating film having a three-dimensional structure in which nano-precipitates made of copper are deposited or intertwined with voids on a substrate by an electrolytic plating method; a low-temperature heat treatment step of heat-treating the copper plating film at a temperature equal to or lower than the melting point of copper, In the low-temperature heat treatment step, the nanoprecipitates are fused together by the heat treatment, forming a void-free copper film on the substrate; A method for manufacturing a metal film, characterized by:

5. In the plating step, a copper plating film having a three-dimensional structure in which nano-precipitates of 10 nm or more and less than 100 nm are deposited or intersected with voids is formed by the electrolytic plating method.

5. The method for producing a metal film according to claim 3 or 4, wherein:

6. In the plating step, a copper plating film having a three-dimensional structure in which particulate nanoprecipitates are deposited with voids or plate-like nanoprecipitates are intertwined with voids is formed by the electrolytic plating method. The method for producing a metal film according to any one of claims 3 to 5, characterized in that

7. In the plating step, polyacrylic acid is added to the plating bath. The method for producing a metal film according to any one of claims 3 to 6, characterized in that:

8. The substrate is made of copper. The method for producing a metal film according to any one of claims 3 to 7, characterized in that

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