JP2024046910A - METHOD AND APPARATUS FOR FORMING METAL PLATING FILM - Google Patents

Abstract

[Problem] To provide a method and an apparatus for forming a metal film that can stably coat an aluminum substrate with a metal film of uniform quality. [Solution] This method forms a metal film on an aluminum substrate having a zinc underlayer, and includes disposing a solid electrolyte membrane between the aluminum substrate as an anode and a cathode, disposing a solution containing metal ions of a metal to be plated on the aluminum substrate between the anode and the solid electrolyte membrane, and applying a voltage to the anode while contacting the solid electrolyte membrane with the aluminum substrate, pressurizing the solution and pressurizing the aluminum substrate through the solid electrolyte membrane in conjunction with the pressurization, thereby depositing the metal ions contained within the solid electrolyte membrane on the zinc underlayer of the aluminum substrate. [Selected Figure] Figure 1B

Description

The present invention relates to a method and apparatus for forming a metal plating film (also referred to simply as a "film" or "metal film" in this specification, etc.).

Conventionally, when manufacturing electronic circuit boards, etc., a metal film is formed on the surface of the board to form a metal circuit pattern. For example, as a deposition technique for such a metal film, a deposition technique has been proposed in which a metal film is formed on the surface of a semiconductor substrate such as Si by a plating process such as electroless plating, or a PVD method such as sputtering.

However, when plating processes such as electroless plating are performed, rinsing with water is required after plating, and the rinsing waste liquid must be treated. In addition, when a film is formed on the surface of a substrate using a PVD method such as sputtering, internal stress is generated in the coated metal film, so there are limitations on how thick the film can be. In particular, in the case of sputtering, film formation may only be possible under high vacuum conditions.

In view of this, a metal film forming device has been proposed that uses, for example, an anode, a cathode, a solid electrolyte placed between the anode and the cathode, and a power supply unit that applies a voltage between the anode and the cathode.

In this device, the anode is made of a metal material that forms the metal film, and by applying a voltage to the anode and cathode from a power supply, a portion of the anode is ionized, and the metal ions pass through the solid electrolyte and are deposited on the substrate placed on the cathode side, coating the surface of the substrate with a metal film.

Furthermore, as an example of a technique in which an insoluble anode can be used as the anode in such a technique, for example, Patent Document 1 discloses a method for forming a metal film, which comprises disposing a solid electrolyte membrane between an anode and a cathode, contacting the solid electrolyte membrane with a substrate, conducting the cathode with the substrate, applying a voltage between the anode and the cathode, and depositing metal ions contained inside the solid electrolyte membrane on the cathode side to form a metal film made of the metal of the metal ions on the surface of the substrate, and which is characterized in that a solution containing the metal ions is disposed between the anode and the solid electrolyte membrane, and when the solid electrolyte membrane is contacted with the substrate, the solution is pressurized, and the metal film is formed while pressurizing the substrate via the solid electrolyte membrane with the liquid pressure of the solution.

Patent Document 2 discloses a metal film forming apparatus that includes an anode, a solid electrolyte membrane disposed between the anode and a substrate serving as a cathode, and a power supply unit that applies a voltage between the anode and the substrate, and that forms a metal film made of the metal by contacting the solid electrolyte membrane with the surface of the substrate and applying a voltage between the anode and the substrate to cause metal ions contained inside the solid electrolyte membrane to precipitate on the surface of the substrate, and that includes a mounting table on which the substrate is placed, and a suction unit that sucks the solid electrolyte membrane from the substrate side so that the solid electrolyte membrane is in close contact with the surface of the substrate placed on the mounting table when forming the metal film.

Patent Document 3 discloses a method for forming a nickel film, which includes arranging an anode, a metal substrate functioning as a cathode, and a solid electrolyte membrane containing a solution containing nickel ions and chloride ions, so that the solid electrolyte membrane is located between the anode and the metal substrate and in contact with the surface of the metal substrate, and applying a voltage between the anode and the metal substrate to form a nickel film on the surface of the metal substrate in contact with the solid electrolyte membrane, in which the solution contains at least one nickel salt as a nickel source, a solvent, and optionally a pH buffer, the at least one nickel salt being selected from the group consisting of nickel chloride, nickel sulfate, and nickel acetate, and the concentration of the chloride ions is 0.002 to 0.1 mol/L.

JP 2014-051701 A International Publication No. 2015/072481 JP 2018-159120 A

In the solid-phase electrodeposition (SED) method, which coats the surface of a substrate with a metal film, if metallic aluminum is used as the substrate, an oxide film forms on the surface of the aluminum substrate, and plating does not adhere to this oxide film. Therefore, the surface of the aluminum substrate to be plated is usually plated in advance with zinc or the like.

However, the zinc coating (zinc undercoat layer) formed on the aluminum substrate is an amphoteric element that dissolves in acids and bases, and can easily be corroded by contact with a solution that contains dissolved metals such as copper and nickel, which are to be further formed on the aluminum substrate.

The present invention was made in consideration of these points, and its purpose is to provide a metal film deposition method and deposition device that can stably coat an aluminum substrate with a metal film of uniform quality.

The inventors have investigated various means for solving the above problems, and as a result, have found that a method for forming a metal coating made of the metal by disposing a solid electrolyte membrane between an aluminum substrate having a zinc underlayer as an anode and a cathode, disposing a solution containing metal ions of the metal to be plated on the aluminum substrate between the anode and the solid electrolyte membrane, and pressurizing the aluminum substrate through the solid electrolyte membrane with the liquid pressure of the solution when the solid electrolyte membrane is brought into contact with the zinc underlayer of the aluminum substrate, thereby depositing the metal ions contained inside the solid electrolyte membrane on the aluminum substrate, is capable of forming a metal coating of uniform quality on the zinc underlayer of the aluminum substrate. This invention has been completed.

That is, the gist of the present invention is as follows.
(1) A method for forming a metal coating on an aluminum substrate having a zinc undercoat, comprising the steps of:
A solid electrolyte membrane is disposed between an anode and the aluminum substrate as a cathode;
a solution containing metal ions of a metal to be plated on the aluminum base material is placed between the anode and the solid electrolyte membrane;
While applying a voltage to the anode, the solid electrolyte membrane is brought into contact with the aluminum base material, and the solution is pressurized and the aluminum base material is pressurized via the solid electrolyte membrane in association with the pressurization, thereby precipitating the metal ions contained inside the solid electrolyte membrane onto a zinc underlayer of the aluminum base material.
(2) The method according to (1), wherein the solution is a solution containing nickel ions.
(3) A metal film forming apparatus comprising: an anode; a spare anode connected in parallel to the anode; a cathode which is an aluminum substrate having a zinc underlayer; a solution storage section which stores a solution containing metal ions and is disposed between the anode and the cathode; a pressurizing section which pressurizes the solution in the solution storage section; a solid electrolyte membrane provided in the solution storage section which is pressurized together with a surface of the cathode when the pressurizing section pressurizes the solution; and a power supply section which applies a voltage between the anode and/or the spare anode and the cathode,
the spare anode is disposed at a position in the solution storage section such that the spare anode can be electrically connected to the power supply section, the solution, the solid electrolyte membrane, and the cathode immediately after the solution is introduced into the solution storage section,
The film forming apparatus introduces the solution while applying a voltage to the spare anode, thereby causing conduction between the power supply unit, the spare anode, the solid electrolyte membrane, the solution, and the cathode, and simultaneously causing current to flow between the power supply unit, the spare anode, the solid electrolyte membrane, the solution, and the cathode, thereby forming a metal film of the metal ions on the cathode.
The film forming apparatus.
(4) The film forming apparatus according to (3), wherein the spare anode is disposed immediately above the solid electrolyte membrane below the solution storage section.
(5) The film forming apparatus according to (3) or (4), wherein the solution contains nickel ions.

The present invention provides a method and apparatus for forming a metal film that can stably coat an aluminum substrate with a metal film of uniform quality.

FIG. 2 is a schematic cross-sectional view of a film forming apparatus 1A. 1B is a diagram illustrating a process of forming a metal coating F on a surface (zinc underlayer) Ba of an aluminum substrate B using the film forming apparatus 1A of FIG. 1A. Example I-1. This is a digital microscope image showing the state of the zinc underlayer of the aluminum substrate when a solution containing nickel ions is dropped onto the zinc underlayer of the aluminum substrate in a corrosion experiment of the zinc underlayer. 4 is a graph showing the relationship between voltage application time and inter-electrode potential in Example 1. 13 is a graph showing the relationship between voltage application time and inter-electrode potential in Comparative Example 1. 1 is a digital microscope image (N=3) showing the state of a nickel coating plated on a zinc undercoat layer of an aluminum substrate in Example 1. 1 is a digital microscope image (N=3) showing the state of a nickel coating plated on a zinc undercoat layer of an aluminum substrate in Comparative Example 1. 1 is a digital microscope image (N=2) showing the state of a nickel coating plated on a zinc undercoat layer of an aluminum substrate in Comparative Example 2. FIG. 1 is a diagram comparing a conventional method for forming a metal film with a method for forming a metal film of the present invention.

Preferred embodiments of the present invention will now be described in detail.
In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity, and the actual dimensions and shapes are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. The metal plating film forming method and film forming apparatus of the present invention are not limited to the following embodiments, and can be embodied in various forms with modifications and improvements that can be made by those skilled in the art, without departing from the gist of the present invention.

The present invention relates to a method for forming a metal film on an aluminum substrate having a zinc underlayer, which comprises disposing a solid electrolyte membrane between an anode and the aluminum substrate as a cathode, disposing a solution containing metal ions of a metal to be plated on the aluminum substrate between the anode and the solid electrolyte membrane, and applying a voltage to the anode while contacting the solid electrolyte membrane with the aluminum substrate, pressurizing the solution and pressurizing the aluminum substrate through the solid electrolyte membrane in association with the pressurization, thereby depositing the metal ions contained within the solid electrolyte membrane on the zinc underlayer of the aluminum substrate.

According to the present invention, when forming the film, a solution containing metal ions is placed between the anode and the solid electrolyte membrane, and a voltage is applied to the anode by a power supply unit placed between the anode and an aluminum substrate having a zinc underlayer. Then, the solid electrolyte membrane is brought into contact with the aluminum substrate, and the power supply unit, anode, solution, solid electrolyte membrane, and aluminum substrate are electrically connected, and electricity is passed at the same time. This allows the metal ions contained in the solution to move from the anode side to the cathode side and become contained inside the solid electrolyte membrane, and further these metal ions can be precipitated on the cathode side of the solid electrolyte membrane, i.e., on the zinc underlayer of the aluminum substrate.

A solution containing metal ions is often acidic or alkaline in order to dissolve the metal. When such a solution comes into contact with a zinc underlayer on the surface of an aluminum substrate, it oxidizes zinc and dissolves it in the solution as zinc ions based on an oxidation-reduction reaction, and may also generate hydrogen gas. Furthermore, in this reaction, electrons present in the substrate may also affect the dissolution of zinc and the generation of hydrogen gas (corrosion). In the present invention, by passing electricity simultaneously with conduction, it is possible to provide a deposition potential for reducing metal ions to metal, i.e., for forming a metal film on the zinc underlayer, before the oxidation-reduction reaction occurs, and the electrons present in the substrate can also be used for forming a metal film, rather than for corroding zinc. Therefore, according to the present invention, it is possible to suppress the corrosion of the zinc underlayer on the surface of an aluminum substrate by the solution, specifically, the partial dissolution of zinc and the generation of hydrogen gas based on the oxidation-reduction reaction due to contact between the solution (particularly, an acidic solution) and zinc.

In addition, in the present invention, when the solid electrolyte membrane is brought into contact with the aluminum substrate, a solution containing metal ions is pressurized, and the liquid pressure of this solution pressurizes the aluminum substrate via the solid electrolyte membrane, while forming a metal coating. As a result, according to Pascal's principle, the solid electrolyte membrane can apply uniform pressure to the surface of the aluminum substrate by the liquid pressure of the pressurized solution.

Here, the thickness of the metal film increases as it is formed. If the thickness of the film to be formed is thin and the solid electrolyte film is flexible, the distance between the solid electrolyte film and the aluminum substrate may be constant. However, in a more preferred embodiment, the distance between the solid electrolyte film and the aluminum substrate is increased according to the increase in the thickness of the metal film during formation of the metal film. According to this embodiment, the distance between the solid electrolyte film and the aluminum substrate is increased according to the increase in the thickness of the metal film to be formed, so that the solid electrolyte film hardly bends (deforms) due to the increase in the thickness of the metal film, and a metal film with excellent uniformity can be formed.

In an even more preferred embodiment, the solution is placed in an enclosed space, the solution in the enclosed space is pressurized, and a metal film is formed while the solution is maintained in a pressurized state, and the increase in thickness of the metal film is estimated by measuring the liquid pressure of the solution.

According to this embodiment, as the film thickness increases, the pressurized solution in the sealed space is further pressurized through the solid electrolyte film, so the film thickness of the metal film itself can be managed based on the increase in the liquid pressure of the solution. Here, by using this estimated increase in the film thickness of the metal film, the distance between the solid electrolyte film and the aluminum base material can be easily increased according to the increase in the film thickness, as in the above-mentioned embodiment.

In a further preferred embodiment, the metal coating is formed using an anode having a shape corresponding to the deposition area on the surface of the aluminum base material where the metal coating is to be formed. According to this embodiment, by using an anode having a shape corresponding to the deposition area, the electric field lines from the anode to the aluminum base material can be made uniform. This allows a metal coating with excellent uniformity to be formed in the desired deposition area.

The present invention further discloses a metal film forming apparatus more suitable for carrying out the above-mentioned metal film forming method. The metal film forming apparatus according to the present invention includes an anode, a spare anode, a cathode, a solution storage unit, a pressurizing unit, a solid electrolyte membrane, and a power supply unit. The cathode is an aluminum substrate having a zinc underlayer. The solution storage unit is for storing a solution containing metal ions arranged between the anode and the cathode. The pressurizing unit is for pressurizing the solution in the solution storage unit. The power supply unit is for applying a voltage between the anode and/or the spare anode and the cathode. The solid electrolyte membrane is arranged in a position such that the solid electrolyte membrane is pressurized by the liquid pressure of the solution pressurized by the pressurizing unit in the solution storage unit arranged between the anode and the cathode, and the surface of the cathode is pressurized by the pressurized solid electrolyte membrane. The spare anode is arranged in the solution storage section at a position where the power supply unit, the solution, the solid electrolyte membrane, and the cathode can be electrically connected to each other immediately after the solution is introduced into the solution storage section, for example, below the solution storage section, i.e., directly above the solid electrolyte membrane, so as to be connected in parallel to the anode. In the metal film forming device of the present invention, the solution is introduced while applying a voltage to the spare anode, and electricity is passed between the power supply unit, the spare anode, the solid electrolyte membrane, the solution contained inside the solid electrolyte membrane, and the cathode at the same time, and a metal film made of the metal of the metal ion is formed on the cathode.

According to the film forming apparatus of the present invention, during film formation, the anode, the solution storage section for storing a solution containing metal ions, the solid electrolyte membrane, and the aluminum substrate having a zinc underlayer as the cathode are arranged, and the power supply section arranged between the anode and the aluminum substrate starts applying voltage to the spare anode connected in parallel to the anode. Then, as soon as the solution containing metal ions is introduced into the solution storage section, the power supply section, the spare anode, the solution, the solid electrolyte membrane, and the aluminum substrate are electrically connected, and electricity is passed. As a result, the metal ions contained in the solution move from the spare anode side toward the cathode side and are contained inside the solid electrolyte membrane, and the metal ions can be precipitated on the cathode side of the solid electrolyte membrane, i.e., on the zinc underlayer of the aluminum substrate.

A solution containing metal ions is often acidic or alkaline in order to dissolve the metal. When such a solution comes into contact with a zinc underlayer on the surface of an aluminum substrate, it oxidizes zinc and dissolves it in the solution as zinc ions based on an oxidation-reduction reaction, and may further generate hydrogen gas. Furthermore, in this reaction, electrons present in the substrate may also affect the dissolution of zinc and the generation of hydrogen gas (corrosion). In the present invention, by passing electricity simultaneously with conduction, it is possible to provide a deposition potential for reducing metal ions to metal, i.e., for forming a metal film on the zinc underlayer, before the oxidation-reduction reaction occurs, and the electrons present in the substrate can also be used for forming a metal film, rather than for corroding zinc. Therefore, according to the present invention, particularly in large-scale film formation where it may take time to fill the solution storage section with the solution, it is possible to suppress corrosion of the zinc underlayer on the surface of the aluminum substrate by the solution, specifically, partial dissolution of zinc and generation of hydrogen gas based on an oxidation-reduction reaction due to contact between the solution (particularly an acidic solution) and zinc. After the solution storage section is filled to the extent that the solution contacts the anode, the application of voltage can be switched from the reserve anode to the anode.

Furthermore, in the present invention, when the solid electrolyte membrane is brought into contact with the aluminum substrate, the solution in the solution storage unit is pressurized by the pressurizing unit, so that the aluminum substrate is pressurized via the solid electrolyte membrane by the liquid pressure of the solution, thereby forming a metal coating. As a result, according to Pascal's principle, the solid electrolyte membrane in the solution storage unit can uniformly pressurize the surface of the aluminum substrate by the liquid pressure of the pressurized solution.

Here, the thickness of the metal film increases as it is formed. Here, if the thickness of the film to be formed is thin and the solid electrolyte film is flexible, the distance between the solid electrolyte film and the aluminum base material may be constant. However, in a more preferred embodiment, the distance between the solid electrolyte film and the aluminum base material is increased according to the increase in the thickness of the metal film during formation of the metal film. According to this embodiment, the distance between the solid electrolyte film and the aluminum base material is increased according to the increase in the thickness of the metal film to be formed, so that the solid electrolyte film hardly bends (deforms) due to the increase in the metal film thickness, and a metal film with excellent uniformity can be formed.

In a preferred embodiment, the anode and/or spare anode have a shape that corresponds to the deposition area on the surface of the aluminum base material where the metal coating is to be deposited. According to this embodiment, by using an anode and/or spare anode shaped according to the deposition area, the electric field lines from the anode and/or spare anode to the aluminum base material can be made uniform. This allows a metal coating with excellent uniformity to be deposited in the desired deposition area.

The following describes a deposition device that can suitably implement the metal coating deposition method according to an embodiment of the present invention.

Figure 1A is a schematic cross-sectional view of the film forming apparatus 1A. The film forming apparatus 1A includes an anode 11, an aluminum substrate B having a zinc underlayer on its surface Ba as a cathode, a solid electrolyte membrane 13 disposed between the anode 11 and the aluminum substrate B, and a power supply unit 16 that applies a voltage between the anode 11 and/or spare anode 12 and the aluminum substrate B.

The film forming apparatus 1A further includes a housing 20. The housing 20 is formed with a solution storage section 21 that stores a solution L containing metal ions so that the solution L containing metal ions can be placed between the anode 11 and the solid electrolyte membrane 13.

The solution storage section 21 has an opening 22 formed therein that is larger than the surface (zinc underlayer) Ba of the aluminum substrate B. The opening 22 is covered with a solid electrolyte membrane 13. The solution L containing metal ions is stored in a tank T in a state in which it can flow into the solution storage section 21, i.e., in a state in which it can be introduced and/or discharged by a pump P and, if necessary, an on-off valve (not shown). Note that, although the introduction and/or discharge of the solution L containing metal ions is performed in one tank T in FIG. 1A, the introduction and/or discharge may be performed in two or more separate tanks.

Furthermore, a spare anode 12 is provided below the solution storage section 21 of the housing 20, i.e., directly above the solid electrolyte membrane 13.

The film forming apparatus 1A further includes a mounting table 40 on which the substrate B is placed.

The film forming apparatus 1A further includes a pressure applying section 30A on the upper portion of the housing 20.

Figure 1B illustrates the process of forming a metal coating F on the surface Ba of an aluminum substrate B using the film forming apparatus 1A in Figure 1A.

As shown in FIG. 1B, while a voltage is applied to the spare anode 12 by the power supply unit 16, the aluminum base material B is placed on the mounting table 40 so that the zinc underlayer Ba and the solid electrolyte membrane 13 are in contact with each other, and the mounting table 40 and the housing 20 are moved relative to each other to sandwich the aluminum base material B between the solid electrolyte membrane 13 and the mounting table 40. Then, the solution L containing metal ions is introduced into the solution storage unit 21, so that the solution L containing metal ions is placed on the surface Ba of the aluminum base material B via the solid electrolyte membrane 13.

By using the arrangement shown in FIG. 1B, a voltage has been applied to the spare anode 12 in advance, so that the power supply unit 16, the spare anode 12, the solution L containing metal ions, the solid electrolyte membrane 13, and the aluminum substrate B are electrically connected, and electricity flows at the same time, reducing the metal ions contained in the solid electrolyte membrane 13 on the surface Ba of the aluminum substrate B, causing the metal to precipitate on the surface Ba, and forming a metal coating F.

The film forming apparatus is equipped with a moving section (pressure applying section) that moves the solid electrolyte film and the aluminum substrate relatively so as to increase the distance between them according to the increase in the thickness of the metal film during the formation of the metal film. According to the present invention, the moving section can increase the distance between the solid electrolyte film and the aluminum substrate according to the increase in the thickness of the metal film being formed, so there is almost no deformation of the solid electrolyte film due to the increase in the thickness of the metal film, and a metal film with excellent uniformity can be formed.

The film forming apparatus may also be equipped with a pressure gauge (liquid pressure measuring unit) (not shown) that measures the liquid pressure of the solution L containing metal ions contained in the sealed space of the housing 20.

The film forming apparatus may further include a control device (control unit) (not shown) that estimates the increase in thickness of the metal film during film formation based on the hydraulic pressure of the solution measured by the hydraulic pressure measuring unit, and controls the relative movement of the solid electrolyte film and the aluminum substrate by the moving unit based on the estimated increase in thickness of the metal film.

It is preferable that the pressure gauge is electrically connected to the control unit so that the pressure value of the solution L containing metal ions measured by the pressure gauge is input as a signal to the control unit for controlling the pressurizing unit 30A, the piping, the pump P, etc. According to this embodiment, the solution L containing metal ions is contained in an enclosed space, the solution in the enclosed space is pressurized by the pressurizing unit 30A, and the metal film is formed while maintaining the solution in a pressurized state, so that the liquid pressure of the solution also increases according to the increase in the metal film. This makes it possible to estimate the increase in the thickness of the metal film by measuring the liquid pressure of the solution and manage the thickness of the metal film. The control unit can control the distance between the solid electrolyte film and the aluminum substrate based on the estimated increase in the thickness of the metal film, and as a result, a metal film with excellent uniformity can be automatically formed.

In the present invention, the anode may be, but is not limited to, a metal coated on an aluminum substrate, such as nickel, oxygen-free copper, or a metal that is more noble than the metal of the metal ion that is not dissolved in a solution containing the metal ion, such as gold. Thus, the anode may be either a soluble anode or an insoluble anode.

The spare anode may have the same structure as the anode described above, i.e., may be, for example, a metal coated on an aluminum substrate, such as nickel, oxygen-free copper, or a metal that is more noble than the metal of the metal ion that is not dissolved in the solution containing the metal ion, such as gold, but is not limited to the following. The spare anode may be a soluble spare anode or an insoluble spare anode.

In the present invention, a zinc underlayer is formed on the surface of the aluminum substrate (cathode). The zinc underlayer on the surface of the aluminum substrate may be present on the surface of the aluminum substrate to be plated. The zinc underlayer may be formed by a method known in the art, for example, by a double zincate method. The aluminum substrate on which the zinc underlayer is formed may be a substrate made of a metal material such as aluminum, or a substrate on which aluminum metal is formed as an underlayer on the treatment surface of a resin or silicon substrate.

In the present invention, the solid electrolyte membrane is not limited as long as it can be impregnated with metal ions by contacting it with a solution containing metal ions, and can precipitate metal derived from the metal ions on the zinc underlayer on the surface of the aluminum substrate when an electric current is applied. Examples of materials for the solid electrolyte membrane include fluorine-based resins such as Nafion (registered trademark) manufactured by DuPont, hydrocarbon-based resins, polyamic acid resins, and resins with ion exchange functions such as Selemion (CMV, CMD, CMF series) manufactured by Asahi Glass Co., Ltd.

In the present invention, the thickness of the solid electrolyte membrane is, for example, usually 1 μm to 400 μm, preferably 3 μm to 100 μm.

In the present invention, examples of the metal coating to be applied on the zinc undercoat of the aluminum substrate include nickel, copper, and gold coatings. When preparing a solution containing metal ions, examples of the metal compounds to be added and dissolved include halogen compounds such as chlorides and bromides, inorganic salts such as sulfates, sulfamates, and nitrates, and organic acid salts such as acetates and citrates. Specifically, examples of nickel compounds include nickel chloride, nickel sulfate, nickel sulfamates, nickel nitrates, and nickel acetate. Examples of copper compounds include copper chloride, copper sulfate, and copper acetate. These compounds can be used alone or in combination of two or more. The concentration of the metal ions is not limited to the following, but is, for example, 0.1 mol/L to 2.0 mol/L, more preferably 0.8 mol/L to 1.2 mol/L. As the solution containing metal ions, a solution containing nickel ions is preferable.

In the present invention, the pH of the solution containing metal ions is not limited. In the present invention, the power supply unit, the anode (spare anode), the solution, the solid electrolyte membrane, and the aluminum substrate are electrically connected, and electricity is passed at the same time, so that corrosion of the zinc underlayer due to the pH of the solution is suppressed. Therefore, the pH of the solution containing metal ions may be particularly acidic, for example, pH 1 to 4, or basic, for example, pH 8 to 11. The pH of the solution containing metal ions is preferably 2.0 to 5.0, and more preferably 2.5 to 4.5. By setting the pH in this way, the metal deposition current efficiency can be improved, and the metal film can be easily formed at high speed. The film formation speed of the metal film can be adjusted by conditions other than pH, such as metal ions in the solution, current value, anode material, anode area, and temperature.

In the present invention, the solution containing metal ions may contain any other components in addition to the metal ions. The solution containing metal ions may contain, for example, a solvent and a pH buffer. Examples of the solvent include water or ethanol. Examples of the pH buffer include an acetate buffer or a succinate buffer.

The present invention will be described in more detail below using examples and comparative examples, but the technical scope of the present invention is not limited to these.

I-1. Corrosion experiment of zinc underlayer (1) A zinc underlayer was plated on the surface of an aluminum substrate by the double zincate method.
(2) The aluminum substrate having the zinc underlayer prepared in (1) was heated to 60° C. on a hot plate.
(3) On the zinc undercoat layer of the aluminum substrate heated to 60° C. in (2), several drops of a solution containing nickel ions (Top Sedona BN (nickel sulfamate), manufactured by Okuno Chemical Industries Co., Ltd., pH 4) were dropped.
(4) (3) The state of the zinc underlayer on the surface of the aluminum substrate onto which the solution was dropped was observed immediately after dropping the solution (0 seconds), 10 seconds, 20 seconds, 30 seconds, and 3 minutes later, using a digital microscope (VHX-1000, manufactured by Keyence Corporation).

I-2. Results The results are shown in Figure 2. It was found from Figure 2 that the zinc undercoat layer on the aluminum substrate surface started to corrode (dissolve and generate hydrogen gas) and form uneven corrosion about 10 to 20 seconds after the solution containing nickel ions was dropped onto it.

II-1. Experimental study on plating of aluminum substrate [Example 1]
(1) In a housing, a nickel anode as an anode, a solution storage section for filling with a solution containing metal ions of a metal to be plated and arranged so as to be in contact with the anode, and a solid electrolyte membrane (Nafion NRE212, manufactured by DuPont) arranged so as to cover the opening of the solution storage section were prepared, and an anode section including the anode, the solution storage section, and the solid electrolyte membrane was assembled.
(2) The solution container of the anode part prepared in (1) was filled with a solution containing nickel ions (Top Sedona BN (nickel sulfamate), manufactured by Okuno Chemical Industries Co., Ltd., pH 4).
(3) A voltage was applied to the anode of the anode part filled with the solution containing nickel ions in (2) by using a power source connected to the anode.
(4) While applying a voltage to the anode in (3), the solid electrolyte membrane was brought into contact with an aluminum substrate (aluminum plate (A1050), 50 mm x 50 mm x 2 mm) having a zinc underlayer formed by a double zincate method as a cathode, thereby conducting electricity among the power source, anode, solution, solid electrolyte membrane, and aluminum substrate, and passing a current at a temperature of 55°C and a current density of 48.8 mA/ ^cm2 . The aluminum substrate was masked with PI tape to leave an opening of 20 mm x 10 mm, and a film was formed only on the opening.
(5) In the circuit energized in (4), pressurization of the solution was started, and the liquid pressure of the solution pressurized the solid electrolyte membrane and further the aluminum substrate through the solid electrolyte membrane.
(6) In (5), a nickel coating was deposited on the zinc undercoat layer of the aluminum substrate by applying a pressure of 1 MPa for 300 seconds.

[Comparative Example 1]
(1) In a housing, a nickel anode as an anode, a solution storage section for filling with a solution containing metal ions of a metal to be plated and arranged so as to be in contact with the anode, and a solid electrolyte membrane (Nafion NRE212, manufactured by DuPont) arranged so as to cover the opening of the solution storage section were prepared, and an anode section including the anode, the solution storage section, and the solid electrolyte membrane was assembled.
(2) The solution container of the anode part prepared in (1) was filled with a solution containing nickel ions (Top Sedona BN (nickel sulfamate), manufactured by Okuno Chemical Industries Co., Ltd., pH 4).
(3) The solid electrolyte membrane in the anode part filled with the solution in (2) was brought into contact with an aluminum substrate (aluminum plate (A1050), 50 mm x 50 mm x 2 mm) having a zinc underlayer formed by a double zincate method as a cathode. The aluminum substrate was masked with PI tape to leave an opening of 20 mm x 10 mm, and the film was formed only on the opening.
(4) In the state where the anode part and the cathode were in contact with each other in (3), the solution was started to be pressurized, and the liquid pressure of the solution applied pressure to the solid electrolyte membrane and further to the aluminum substrate via the solid electrolyte membrane, stabilizing the pressure between the solid electrolyte membrane and the zinc underlayer on the surface of the aluminum substrate. Note that the pressurization was carried out for the purpose of improving the conformability of the solid electrolyte membrane in the anode part to the substrate (including minute irregularities on the surface) and bringing the substrate and the solid electrolyte membrane into uniform contact.
(5) After stabilization for about 30 seconds to about 1 minute in (4), a voltage was applied to the anode using a power source, and the power source, anode, solution, solid electrolyte membrane, and aluminum substrate were electrically connected to each other, and electricity was passed at a temperature of 55° C. and a current density of 48.8 mA/ ^cm2 .
(6) In (5), a nickel coating was deposited on the zinc undercoat layer of the aluminum substrate by applying a pressure of 1 MPa for 300 seconds.

[Comparative Example 2]
A nickel coating was deposited in the same manner as in Comparative Example 1, except that the pressure stabilization time in steps (4) and (5) was changed to about 5 seconds to about 10 seconds.

II-2. Results Figure 3 shows the relationship between the voltage application time and the inter-electrode potential in Example 1. Figure 4 shows the relationship between the voltage application time and the inter-electrode potential in Comparative Example 1. Figures 3 and 4 show that in Comparative Example 1, a potential difference occurs due to zinc corrosion before the voltage is applied to the anode.

Figure 5 shows images (N=3) of the nickel coating plated on the zinc underlayer of the aluminum substrate in Example 1, observed by a digital microscope. Figure 6 shows images (N=3) of the nickel coating plated on the zinc underlayer of the aluminum substrate in Comparative Example 1, observed by a digital microscope. Figure 7 shows images (N=2) of the nickel coating plated on the zinc underlayer of the aluminum substrate in Comparative Example 2, observed by a digital microscope. From Figures 5 to 7, it was found that a nickel coating of uniform quality can be stably coated on the aluminum substrate by applying a voltage to the anode before contacting the solid electrolyte membrane with the aluminum substrate having the zinc underlayer as the cathode. It was also found from Figures 6 and 7 that even if a voltage is applied to the anode within 10 seconds of contacting the solid electrolyte membrane with the aluminum substrate having the zinc underlayer as the cathode, corrosion occurs in the zinc underlayer on the aluminum substrate surface, resulting in uneven deposition in the nickel coating that is formed.

The above-described experiments have demonstrated that by changing the conventional process in which a solution containing metal ions is delivered and then an electric current is applied to form a film, as shown in Figure 8, to the process of the present invention in which a solution containing metal ions is delivered after a voltage is applied to the anode, and an electric current is applied and a film is formed at the same time as the solution is delivered, it is possible to stably form a metal coating of uniform quality on the zinc undercoat layer of an aluminum substrate.

REFERENCE SIGNS LIST 1A Film forming apparatus 11 Anode 12 Spare anode 13 Solid electrolyte membrane 16 Power supply unit 20 Housing 21 Solution storage unit 22 Opening 30A Pressurizing unit 40 Placement table L Solution containing metal ions T Tank P Pump B Aluminum substrate (cathode)
Ba: Surface of aluminum substrate (zinc undercoat layer)
F Metal Film

Claims (5)

1. A method for depositing a metallic coating on an aluminum substrate having a zinc undercoat, comprising the steps of:
A solid electrolyte membrane is disposed between an anode and the aluminum substrate as a cathode;
a solution containing metal ions of a metal to be plated on the aluminum base material is placed between the anode and the solid electrolyte membrane;
While applying a voltage to the anode, the solid electrolyte membrane is brought into contact with the aluminum base material, and the solution is pressurized and the aluminum base material is pressurized via the solid electrolyte membrane in association with the pressurization, thereby precipitating the metal ions contained inside the solid electrolyte membrane onto a zinc underlayer of the aluminum base material. The method of claim 1, wherein the solution is a solution containing nickel ions. 1. An apparatus for forming a metal film comprising: an anode; a spare anode connected in parallel to the anode; a cathode which is an aluminum substrate having a zinc underlayer; a solution storage section which stores a solution containing metal ions and is disposed between the anode and the cathode; a pressurizing section which pressurizes the solution in the solution storage section; a solid electrolyte membrane provided in the solution storage section which is pressurized together with a surface of the cathode when the pressurizing section pressurizes the solution; and a power supply section which applies a voltage between the anode and/or the spare anode and the cathode,
the spare anode is disposed at a position in the solution storage section such that the spare anode can be electrically connected to the power supply section, the solution, the solid electrolyte membrane, and the cathode immediately after the solution is introduced into the solution storage section,
The film forming apparatus introduces the solution while applying a voltage to the spare anode, thereby causing conduction between the power supply unit, the spare anode, the solid electrolyte membrane, the solution, and the cathode, and simultaneously causing current to flow between the power supply unit, the spare anode, the solid electrolyte membrane, the solution, and the cathode, thereby forming a metal film of the metal ions on the cathode.
The film forming apparatus. The film forming apparatus according to claim 3, wherein the spare anode is disposed directly above the solid electrolyte membrane below the solution storage section. The film forming apparatus according to claim 3 , wherein the solution contains nickel ions.

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