Process for forming a silver film

Abstract

A method for forming a silver film (F), comprising: Arranging an anode (11), a substrate (B) as a cathode, and a separator (13) such that the separator (13) is located between the anode (11) and the substrate (B) and the separator (13) is in contact with a surface of the substrate (B), wherein the separator (13) comprises an electrolyte solution (L) containing silver ions; and Applying a voltage between the anode (11) and the substrate (B) to form a silver film (F) on the substrate (B), wherein: the separator (13) is a porous membrane without a functional ion exchange group, the electrolyte solution (L) contains organic sulfonic acid ions, the electrolyte solution (L) is a silver methanesulfonate-potassium iodide bath, the electrolyte solution (L) further comprises N-(3-hydroxy-1-butylidene)-p-sulfanilic acid HBPSA, the content of silver methanesulfonate in the silver methanesulfonate-potassium iodide bath is 50 to 500 g / L, the content of potassium iodide in the silver methanesulfonate-potassium iodide bath is 200 to 800 g / L, the HBPSA content in the silver methanesulfonate-potassium iodide bath is 20 to 40 g / L, and the substrate (B) comprises a crystalline metal, and the silver film (F) is formed on the crystalline metal.

Description

Technical area

[0001] The present invention relates to a method for forming a silver film. State of the art

[0002] A metal film is formed on a surface of a substrate to form, for example, a metal circuit pattern of an electronic circuit board and the like. As a film formation technique of the metal film, a film formation method using solid electrolyte deposition (SED method) is known, for example, as disclosed in JP H05-148681A. Solid electrolyte deposition is a technique in which a separator (solid), such as a solid electrolyte membrane, is brought into contact with a substrate (solid) to form a film. This has the advantage that excess liquid (waste liquid) is small and environmental pollution can be reduced.

[0003] Specifically, JP H05-148681 A discloses a metal film forming apparatus comprising an anode, a cathode, a solid electrolyte disposed between the anode and the cathode, and a power supply unit that applies a voltage between the anode and the cathode. In the apparatus disclosed in JP H05-148681 A, the anode is formed of a metallic material forming a metal film, and the anode is partially ionized by applying the voltage to the anode and the cathode. In the apparatus disclosed in JP H05-148681 A, the metal ions generated by the ionization of the anodes pass through the solid electrolyte to be deposited on a substrate disposed in the cathode side, whereby the metal film is formed on the substrate surface.

[0004] JP 2016-169399 A discloses a metal film forming apparatus comprising at least 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. In the metal film forming apparatus, the voltage is applied between the anode and the substrate in a state where the solid electrolyte membrane is brought into contact with the substrate from the upper side, thereby reducing metal ions contained in the solid electrolyte membrane to form a metal film on a surface of the substrate. The film forming apparatus comprises a liquid housing portion between the anode and the solid electrolyte membrane. The liquid housing portion surroundsaccommodates an electrolyte solution containing the metal ions, so that the electrolyte solution contacts the anode and the solid electrolyte membrane. The film-forming device includes a vibrator that vibrates at least the anode in a state where the solid electrolyte membrane is brought into contact with the substrate.

[0005] Meanwhile, due to its high electrical conductivity, excellent corrosion resistance, and solderability, silver plating film is widely used industrially as a plating layer on electrical contacts. When an inverter is heated to high temperatures, a silver bond layer sintered with silver paste is used instead of a soldered bond layer, which has a low melting point. When the sintered silver bond layer is used, a silver plating layer is used as a buffer layer. While a cyanide bath is generally used as a silver plating bath for the silver plating layer, it has disadvantages in working conditions and wastewater treatment due to its high toxicity.Therefore, a non-cyanide bath without cyanogen was investigated, and for example, silver chloride-potassium iodide 1), silver chloride-sodium thiosulfate base 2), silver nitrate-tartaric acid base 3), silver chloride-potassium ferrocyanide base 4), and thiocyanic acid base bath 5) were reported.

[0006] Kondo, et al. (KONDO, Tetsuya [et al.]: Silver plating from silver methane sulfonate-potassium iodide baths. In: Journal of the Surface Finishing Society of Japan, Vol. 42, 1991, No. 2, pp. 241-245. ISSN 0915-1869. DOI: https: / / doi.org / 10.4139 / sfj.42.241) and Inoue, et al. (INOUE, Hiroyuki; YAMAKAWA, Koji; MASAKI, Seishi: Mechanisms of silver electrodeposition from potassium iodide bath. In: Journal of the Surface Finishing Society of Japan, Vol. 44, 1993, No. 1, pp. 55-59. ISSN 0915-1869. DOI: https: / / doi.org / 10.4139 / sfj.44.55) disclose processes for silver plating using silver methanesulfonate-potassium iodide baths.

[0007] Furthermore, EP 3 680 367 A2 discloses a film forming apparatus and a method for producing a metal film using this film forming apparatus according to the prior art. SUMMARY

[0008] As described above, since the solid electrolyte deposition is a technique in which a separator (solid) such as a solid electrolyte membrane is brought into contact with a substrate (solid) to form a film, there is an advantage that the waste liquid is reduced and the environmental load can be reduced.

[0009] However, it has been found that in an attempt to form a silver film by conventional solid electrolyte deposition, a portion where no film is formed is generated on the substrate of a formation target, thus failing to obtain a uniform film in some cases. Specifically, for example, it has been found that solid electrolyte deposition using a solid electrolyte membrane generates a silver dendrite in the solid electrolyte membrane, thus failing to form a silver film uniformly in some cases. Furthermore, it has been found that in some cases, due to various other factors, the silver film cannot be uniformly formed by conventional solid electrolyte deposition.

[0010] Therefore, the present invention provides a method which enables the uniform formation of a silver film by solid electrolyte deposition.

[0011] The following describes one aspect of the embodiment. (1) A method for forming a silver film, comprising: disposing an anode, a substrate as a cathode, and a separator such that the separator is located between the anode and the substrate, and the separator is in contact with a surface of the substrate, wherein the separator comprises an electrolytic solution containing silver ions; and applying a voltage between the anode and the substrate to form a silver film on the substrate. The separator is a porous membrane without ion-exchange functional groups. The electrolytic solution contains organic sulfonic acid ions. The electrolytic solution is a silver methanesulfonate-potassium iodide bath. The electrolytic solution further comprises N-(3-hydroxy-1-butylidene)-p-sulfanilic acid HBPSA. The content of silver methanesulfonate in the silver methanesulfonate-potassium iodide bath is 50 to 500 g / L. The content of potassium iodide in the silver methanesulfonate-potassium iodide bath is 200 to 800 g / L.The HBPSA content in the silver methanesulfonate-potassium iodide bath is 20 to 40 g / L. The substrate contains a crystalline metal, and the silver film is formed on the crystalline metal. (2) In the process according to (1), the porous membrane is a porous polyolefin resin membrane. (3) In the process according to (2), the porous polyolefin resin membrane is a porous polyethylene resin membrane. (4) In the method according to any one of (1) to (3), the crystalline metal is a nickel film. (5) In the process according to (4), the nickel film has a columnar crystalline shape.

[0012] This invention provides a method which enables the uniform formation of a silver film by solid electrolyte deposition. SHORT DESCRIPTION OF THE DRAWING Fig.1A is a schematic cross-sectional view illustrating an exemplary configuration of a film forming apparatus that can be used for a forming method according to the embodiment; and Fig. 1B is a schematic cross-sectional view showing a process for forming a silver film on a substrate using the film forming apparatus of Fig. 1A represents. DETAILED DESCRIPTION

[0013] This embodiment is a method for forming a silver film. The method includes: disposing an anode, a substrate as a cathode, and a separator such that the separator is located between the anode and the substrate and the separator is in contact with a surface of the substrate, wherein the separator comprises an electrolytic solution containing silver ions; and applying a voltage between the anode and the substrate to form a silver film on the substrate. The separator is a porous membrane without an ion-exchange functional group. The electrolytic solution contains organic sulfonic acid ions. The substrate contains a crystalline metal, and the silver film is formed on the crystalline metal.

[0014] This embodiment can provide a method that enables the uniform formation of the silver film by solid electrolyte deposition.

[0015] In this embodiment, a porous membrane without an ion-exchange functional group is used as the separator in the solid electrolyte deposition. Using the porous membrane without an ion-exchange functional group as the separator reduces the capture of silver ions in the separator, thereby making it possible to suppress the generation of silver dendrite in the separator. Meanwhile, when a solid electrolyte membrane is used in the solid electrolyte deposition, it is difficult to form a uniform silver film. This is believed to be caused by the following reasons. In the solid electrolyte membrane, a channel called an ion channel with a diameter of a few nm is deposited. Ion-exchange functional groups including sulfonic acid groups are present in a wall surface (surface) of the solid electrolyte membrane that defines the ion channel.When a voltage is applied between the anode and cathode, metal ions move from the anode to the cathode in the ion channel. However, when the metal ions are silver ions, the silver ions easily migrate to the solid electrolyte membrane due to water adhesion and the application of voltage. Therefore, it is assumed that silver dendrite is easily generated in the solid electrolyte membrane.

[0016] In this embodiment, an electrolytic solution containing organic sulfonic acid ions is used for the electrolytic solution. The organic sulfonic acid ions are close to the silver ions in the electrolytic solution. In a silver film formation reaction, a decomposition reaction of water in the electrolytic solution occurs in addition to the reduction of the silver ions, thereby generating hydrogen gas. When the electrolytic solution contains the organic sulfonic acid ions, since the organic sulfonic acid ions are close to the silver ions, the decomposition reaction of water in the electrolytic solution can be suppressed, and thus the generation of hydrogen gas can be suppressed.

[0017] Furthermore, in this embodiment, the silver film is formed on a crystalline metal. The surface of the crystalline metal has fine unevenness. As described above, in the silver film formation reaction, the decomposition reaction of water in the electrolytic solution occurs in addition to the reduction of silver ions, thereby generating hydrogen gas. While the generated hydrogen gas can be diffused in the electrolytic solution by stirring and the like in a plating method using an electrolyzer, the hydrogen gas easily remains between the separator and the substrate surface, and the remaining hydrogen gas hinders the reaction, possibly generating a portion where no film is formed in the case of solid electrolyte deposition.However, in this embodiment, the film formation on the crystalline metal causes the generated hydrogen gas to easily diffuse due to the fine unevenness on the surface of the crystalline metal, and consequently the hydrogen gas is easily emitted from between the separator and the substrate surface.

[0018] For the reasons described above, it is believed that the forming method according to this embodiment enables the uniform formation of the silver film.

[0019] The following describes the method for forming the silver film according to this embodiment in detail with reference to the drawing.

[0020] Fig. 1A and Fig. 1B illustrates an exemplary film forming apparatus to which the forming method according to this embodiment is applied.

[0021] Fig.Figure 1A is a schematic cross-sectional view of a film forming apparatus 1A. The film forming apparatus 1A includes an anode 11, a substrate B as a cathode, a porous membrane 13, and a power supply unit 16. The porous membrane 13 is disposed between the anode 11 and the substrate B, serves as a separator, and has no ion-exchange functional groups. The power supply unit 16 applies a voltage between the anode 11 and the substrate B.

[0022] The film-forming apparatus 1A further includes a housing 20. The housing 20 includes a chamber 21 that houses a silver-containing solution L such that the silver-containing solution L is disposed between the anode 11 and the porous membrane 13. The silver-containing solution L housed in the chamber 21 is in contact with the porous membrane 13 and the anode 11.

[0023] The chamber 21 is provided with an opening 22 larger than a surface area of the substrate B. The opening 22 is covered with the porous membrane 13, and the silver-containing solution L is fluidly sealed in the chamber 21. The film forming apparatus 1A further includes a placement table 40 on which the substrate B is placed. The film forming apparatus 1A further includes a pressing section 30 at the upper portion of the housing 20.

[0024] Fig. Fig. 1B is a drawing for describing a process for forming a silver film F on the surface of the substrate B using the film forming apparatus 1A of the Fig. 1A.

[0025] As in Fig.1B, in a state where the substrate B is placed on the placement table 40, the placement table 40 and the casing 20 are relatively moved to sandwich the substrate B between the porous membrane 13 and the placement table 40, thereby disposing the silver-containing solution L on the surface of the substrate B via the porous membrane 13.

[0026] Next, the power supply unit 16 applies the voltage between the anode 11 and the substrate B, and silver ions contained in the porous membrane 13 are reduced at the surface of the substrate B to deposit silver on the surface, thereby forming the silver film F.

[0027] In this embodiment, a porous membrane without ion-exchange functional groups is used as the separator. Using the porous membrane without ion-exchange functional groups as the separator reduces the trapped silver ions in the separator, thereby enabling the suppression of silver dendrite generation in the separator.

[0028] While the porous membrane without an ion-exchange functional group is not particularly limited, for example, a porous polyolefin resin membrane containing a polyolefin resin can be used. The polyolefin resin includes, for example, polyethylene, polypropylene, polybutylene, or a mixture thereof. The porous polyolefin resin membrane, in some embodiments, is a porous polyethylene resin membrane containing a polyethylene resin. The porous membrane, in some embodiments, has a mesh structure with a three-dimensional and irregularly connected network structure. The porous membrane may have a single-layer structure or may have a multi-layer structure. One polyolefin resin may be used alone, or two or more polyolefin resins may be used together or in combination.

[0029] The polyolefin resin comprises polyethylene in some embodiments, and polyethylene includes ultra-high molecular weight polyethylene, high-density polyethylene having a density of 0.942 or more, medium-density polyethylene having a density of 0.925 or more and less than 0.942, low-density polyethylene having a density of less than 0.925, and the like. The polyethylene need not be an ethylene homopolymer, but may also be a copolymer comprising a small amount of another α-olefin. As the α-olefin other than ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth)acrylic acid, (meth)acrylic acid ester, styrene, or the like can be used.

[0030] The polyethylene may comprise one polyethylene, or may comprise two or more polyethylenes. As a polyethylene blend, a blend of two or more ultra-high molecular weight polyethylenes differing in Mw, a blend of two or more high-density polyethylenes differing in Mw, a blend of two or more medium-density polyethylenes differing in Mw, or a blend of two or more low-density polyethylenes differing in Mw may be used. Or a blend of two or more polyethylenes selected from the group consisting of ultra-high molecular weight polyethylene, high-density polyethylene, medium-density polyethylene, and low-density polyethylene may be used.

[0031] While the method for producing a porous membrane using a polyolefin resin as a raw material is not particularly limited, it can be exemplified as follows. For example, a resin is melted with a plasticizer such as liquid paraffin, extruded from a T-die to form a sheet shape, the resulting sheet is stretched, and then the plasticizer contained in the sheet is extracted.

[0032] The method for producing the porous membrane mainly includes a dry method (stretching pore-forming process) and a wet method (phase separation method). The dry method is a method in which a membrane made of a polymer and having a uniform composition is annealed to form a lamellar structure, and then this membrane is uniaxially stretched to cleave an interface in the lamellar structure, thereby forming holes. In the porous membrane formed by the dry method, the holes penetrate linearly in a thickness direction of the porous membrane. Meanwhile, the wet method isWet method: A process in which a membrane of microphase-separated polymer and solvent is prepared, and a solvent phase is extracted and separated from this membrane, thereby forming holes. The membrane may be stretched before extraction and removal of the solvent, or may be stretched after extraction and removal of the solvent. The wet method enables the production of porous membranes with various hole structures by selecting the combination of polymer and solvent, the stretching condition, and the like. Since the holes formed by the wet method form a three-dimensional irregular and uniform network structure, the porous membrane obtained by the wet method has high mechanical strength.As the porous membrane used in this embodiment, a porous membrane manufactured by the wet process (wet separator) is used in some embodiments. Since the wet separator has a relatively high number of unevennesses on its surface, hydrogen gas is easily released or emitted to the outside or to the environment.

[0033] A functional group is an atom or group of atoms that causes a characteristic or characteristic reactivity of an organic compound and is also referred to as a functional atom group or a functional or functional group. An ion-exchange functional group includes both a cation-exchange functional group and an anion-exchange functional group. A cation-exchange functional group includes a sulfonic acid group, a sulfonimide group, a sulfonmethide group, a phosphonic acid group, a carboxylic acid group, or the like. An anion-exchange functional group includes a quaternary ammonium group, a quaternary pyridinium group, primary to tertiary amino groups, a pyridyl group, an imidazolyl group, or the like.Note that a group (group without ion-exchange property) other than the ion-exchange functional group includes an alkyl group, an olefin group, an acetylene group, an aromatic group, or the like. "Without an ion-exchange functional group" means that the ion-exchange functional groups are not included at all (that is, only groups other than the ion-exchange functional groups are included), or that the ion-exchange functional groups are not substantially included. "The ion-exchange functional groups are not substantially included" means that even if the ion-exchange functional groups are included, the amount is an amount that does not substantially impart the ion-exchange function to the porous membrane.In particular, this is included in the case where the porous membrane does not contain any of the ion exchange functional groups, when a ratio of the atomic number between oxygen and carbon in the porous membrane obtained by X-ray photoelectron spectroscopy is 0.1 or less, or 0.02 or less in some embodiments.

[0034] The presence or absence of ion-exchange functional groups can be determined by various qualitative and quantitative analysis methods. For the qualitative analysis method, a suitable method can be selected depending on the functional group. For example, the presence or absence of the sulfonic acid group can be determined by an alkali fusion test or an iron hydroxamic acid (iron hydroxamate) test. The presence or absence of the carboxylic acid group can be determined by an iron hydroxamate test, a pH test, or the like. Quantitative analysis methods include ultraviolet spectroscopy, infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, mass spectrometry, and X-ray photoelectron spectroscopy using chemical modification, X-ray diffraction, or the like.

[0035] An arithmetic-average roughness (Ra) of the porous membrane is 28 to 60 nm in some embodiments, and 32 to 50 nm in some embodiments. In this specification, the arithmetic-average roughness (Ra) is the arithmetic-average roughness defined in Japanese Industrial Standard R 1683 (2007). The arithmetic-average roughness (Ra) in the surface of the separator can be measured using an atomic force microscope (Nano Scope II, manufactured by Digital Instruments).

[0036] A pore diameter of the porous membrane is, for example, 20 to 1000 nm, and in some embodiments, 25 to 500 nm. The pore diameter in the above-described range enables improvement in current efficiency. Here, the pore diameter means a volume-average pore diameter distribution. The pore diameter distribution can be obtained by a mercury porosimetry method ("method of mercury penetration") according to Japanese Industrial Standard R 1655: 2003. The mercury porosimetry method is a method in which pressure is applied or applied.is applied to cause mercury to penetrate into open pores, a relationship between a volume of mercury penetrating the open pores and a pressure value applied at that time is obtained, and a diameter of the open pore is calculated by the Washburn formula which is based on the consequence that the open pore is assumed to have a columnar shape.

[0037] A porosity of the porous membrane is 20 to 80% in some embodiments. The porosity of the porous membrane of 20% or more enables the achievement of a satisfactory permeability of the electrolyte solution. The porosity of the porous membrane of 80% or less enables the provision of a satisfactory mechanical strength of the membrane. The porosity is 25 to 65%, and in some embodiments 30 to 55%. The porosity is a proportion (volume %) of a pore section in the porous membrane, and can be obtained from a result obtained by measuring a sample volume (cm 3 ) and the mass (g) obtained using the formula below. Porosity(%)=(1−Mass / (Resin Density×Sample Volume))×100

[0038] An air permeability of the porous membrane is, for example, 5 to 500 s / 100cm 3 , and in some embodiments 10 to 260 s / 100cm 3. When the air permeability is within the range described above, power efficiency can be improved. The air permeability is measured according to Japanese Industrial Standard L 1096-6-27-1A or ASTM-D737.

[0039] A thickness of the porous membrane is, for example, 5 to 175 µm, and in some embodiments, 12 to 150 µm. When the thickness is within the above-described range, the current efficiency can be improved.

[0040] A commercially available battery separator can be used as the porous membrane. This commercially available separator is inexpensive compared to a conventional solid electrolyte membrane with ion exchange functional groups, and further cost reduction is expected.

[0041] In this embodiment, the electrolytic solution contains at least one silver ion source and contains organic sulfonic acid ions. The electrolytic solution containing organic sulfonic acid ions enables the suppression of the decomposition reaction of water in the electrolytic solution, and thus the generation of hydrogen gas can be suppressed.

[0042] As the silver ion source, silver methanesulfonate is used as the organic silver sulfonate in the present invention. The use of organic silver sulfonate enables the presence of silver ions and organic sulfonic acid ions, which are used in this embodiment, in the electrolytic solution. The organic silver sulfonate includes silver alkanesulfonate, silver arylsulfonate, or the like. The silver alkanesulfonate includes, for example, (C1 to C6) silver alkanesulfonate. The silver alkanesulfonate includes silver methanesulfonate, silver ethanesulfonate, silver propanesulfonate, or the like. The silver arylsulfonate includes silver benzenesulfonate, silver p-toluenesulfonate, or the like. One silver ion source can be used alone, or two or more silver ion sources can be used together. The electrolytic solution does not contain cyanide in some embodiments.The content of the silver ion source in the electrolyte solution is, for example, 50 to 500 g / L, in some embodiments 100 to 450 g / L, and in some embodiments 150 to 400 g / L.

[0043] Organic sulfonic acid can also be used as the organic sulfonic acid ion source. Organic sulfonic acid includes alkanesulfonic acid, arylsulfonic acid, or the like. Alkanesulfonic acid includes methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, methylbutanesulfonic acid, hexanesulfonic acid, or the like. Arylsulfonic acid includes toluenesulfonic acid, phenylsulfonic acid, phenolsulfonic acid, or the like. One organic sulfonic acid ion source can be used alone, or two or more sulfonic acid ion sources can be used together.

[0044] The electrolyte solution may comprise various electrolytes, represented by acids and bases, together with the silver ion source and / or the organic sulfonic acid ion source. Without particular limitation, the electrolyte includes hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid, succinimide, boric acid, sulfamic acid, or the like. Salts of acids and bases may also be used as the electrolyte. It may contain alkali metal chloride salts or alkali metal nitrate salts, for example, a conductive salt such as potassium chloride or potassium nitrate. One electrolyte may be used alone, or two or more electrolytes may be used together. For example, the electrolyte may contain a mixture of acids, a mixture of bases, or a mixture of one or more acids and one or more bases. The electrolyte content in the electrolyte solution is, for example, 1 to 100 g / L.

[0045] The electrolyte solution may contain a buffer. While the buffer is not particularly limited, it includes a borate buffer, a phosphate buffer, a citrate buffer, a carbonate buffer, a sulfamate buffer, or the like.

[0046] For example, a pH or pH value of the electrolyte solution is 3.0 to 10.0, and 4.5 to 7.0 in some embodiments.

[0047] In some cases, the electrolyte solution may contain an additive. While the additive is not limited, it may include a corrosion inhibitor, a stabilizer, or similar.

[0048] In the present invention, the electrolyte solution is a silver methanesulfonate-potassium iodide bath. The silver methanesulfonate-potassium iodide bath is an aqueous solution containing at least silver methanesulfonate and potassium iodide. Silver methanesulfonate is included as a silver ion source, and potassium iodide is included as a complexing agent. The silver methanesulfonate-potassium iodide bath may contain various electrolytes, typified by acids and bases, buffers, and the like, in addition to the silver methanesulfonate and potassium iodide. The acid to be added includes methanesulfonic acid in some embodiments. When the silver methanesulfonate-potassium iodide bath is used as the electrolyte solution, at least two ligands are present for the silver ions, methanesulfonic acid ions, and iodide ions.The presence of methanesulfonic acid ions and iodide ions as ligands causes the ligands to easily dissociate from the silver ions, thereby causing the silver ions to easily deposit on the substrate. In other words, the presence of the two ligands, methanesulfonic acid ions and iodide ions, causes an interaction between the ligands, causing the silver ions to easily dissociate.

[0049] The electrolyte solution is a silver methanesulfonate-potassium iodide bath to which N-(3-hydroxy-1-butylidene)-p-sulfanilic acid (HBPSA) is added. By using the silver methanesulfonate-potassium iodide bath to which HBPSA is added as the electrolyte solution, a fine silver film can be produced.

[0050] A content of the silver methanesulfonate in the silver methanesulfonate-potassium iodide bath is 50 to 500 g / L, in some embodiments 100 to 450 g / L, in some embodiments 130 to 400 g / L, in some embodiments 150 to 350 g / L, and in some embodiments 160 to 300 g / L. A content of the potassium iodide in the silver methanesulfonate-potassium iodide bath is 200 to 800 g / L, and in some embodiments 300 to 700 g / L, and in some embodiments 400 to 600 g / L. A content of the HBPSA in the silver methanesulfonate-potassium iodide bath is 20 to 40 g / L.

[0051] In this embodiment, the substrate may be a substrate used as the cathode and containing a crystalline metal. In this embodiment, the silver film is formed on the crystalline metal. The film formation on the crystalline metal causes the generated hydrogen gas to easily diffuse due to the fine unevenness on the surface of the crystalline metal, and thus the hydrogen gas is easily emitted from between the separator and the substrate surface.

[0052] The material of the substrate includes gold, copper, aluminum, nickel, manganese, cobalt, zinc, an alloy thereof, or the like. The substrate may be formed of only a crystalline metal, or may contain another metal, such as an amorphous metal. The substrate may have a configuration, for example, in which a crystalline metal film is formed on an amorphous metal film. The crystalline metal film and / or the amorphous metal film may be formed by a single layer or may be formed by a plurality of layers. The substrate may be deposited on a substrate body such as a resin, a silicon plate, or ceramic. The crystalline metal film may be formed, for example, by solid electrolyte deposition using the solid electrolyte membrane.An exemplary usable film forming apparatus includes an apparatus having the configuration using the solid electrolyte membrane as the separator in the film forming apparatus 1A shown in FIG. Fig. 1A and Fig. 1B, used.

[0053] The crystalline metal on which the silver film is formed is a nickel film in some embodiments, and is a columnar crystalline nickel film in some embodiments. In one embodiment, the substrate comprises the columnar crystalline nickel film, and the silver film is formed on the columnar crystalline nickel film in some embodiments. For example, the substrate may be formed by a single layer of the columnar crystalline nickel film, or may have a configuration in which a columnar crystalline nickel film is formed on a metal film other than the columnar crystalline nickel. Forming the silver film on the columnar crystalline nickel makes it easy to remove air involved in bringing the separator and the substrate into contact and hydrogen generated in the plating process.Electrodeposition processes allow the formation of a more uniform silver film at the interface between the separator and the substrate. Without particular limitation, the film thickness of the columnar crystalline nickel film is, for example, 0.1 to 50 µm, and in some embodiments, 3 to 45 µm.

[0054] The columnar crystalline nickel is nickel with a columnar crystal structure, and the columnar crystal is an aggregate of dendrite-shaped (or cellular) crystals that have the same growth direction. In this specification, it is an aggregate of crystals that have columnar structures approximately perpendicular to the surface of the substrate. One skilled in the art can roughly select the material, conditions, and the like for forming the columnar crystalline nickel film. As a nickel-containing solution used for forming the columnar crystalline nickel film, a nickel chloride-nickel acetate plating bath is used in some embodiments. The columnar crystalline nickel film can be formed, for example, by solid electrolyte deposition using the solid electrolyte membrane.An exemplary film forming apparatus includes a film forming apparatus having the configuration using the solid electrolyte membrane as the separator in the film forming apparatus 1A shown in FIG. Fig. 1A and Fig. 1B. A nickel chloride-nickel acetate plating bath can be used as the nickel-containing solution. The current density during the formation process of the columnar crystalline nickel film is, for example, 0.5 to 15 A / dm 2 , and in some embodiments 5 to 10 A / dm 2In one embodiment, the columnar crystalline nickel film is formed on a copper substrate. Forming the columnar crystalline nickel film on the copper substrate enables suppression of the dissolution of copper ions from the copper substrate during the formation of the silver film. The material of the solid electrolyte membrane may include a fluorine-based resin such as Nafion (registered trademark) manufactured by DuPont de Nemours, Inc., a hydrocarbon resin, a polyamide acid resin, a resin having an ion-exchange function such as Selemion (CMV, CMD, and CMF series) manufactured by AGC Inc., and the like. A thickness of the solid electrolyte membrane is, for example, 50 to 400 µm, or 100 to 200 µm.

[0055] The anode may be a soluble anode or an insoluble anode. The soluble anode may comprise a silver plate, a silver sphere, a silver madreporite, a silver mesh, or the like. An insoluble anode may comprise, for example, a porous metal body formed from a material with a low oxygen overvoltage, such as platinum or iridium oxide, or an insoluble anode in which a porous metal body having high corrosion resistance, such as titanium, is coated with platinum, ruthenium oxide, iridium oxide, or the like.

[0056] According to the embodiment described above, the silver film can be formed uniformly by the solid electrolyte deposition. [Examples]

[0057] While the following describes the present invention specifically with examples and comparative examples, the embodiment is not limited thereto. (Example 1)

[0058] In Example 1, a silver film was formed as a separator on a nickel film (columnar crystalline nickel) on a sputtered copper substrate by solid electrolyte deposition using a porous polyethylene resin membrane. As a film-forming device, a device was used which complies with the Fig. 1A shown configuration. <substrat>

[0059] As a substrate, the nickel film (nickel film / sputtered copper substrate) formed on the sputtered copper substrate was prepared by the following process.

[0060] First, a polyimide tape (Kapton tape: 650R#25, manufactured by Teraoka Seisakusho Co., Ltd.) provided with an opening of 10 × 20 mm was placed on the sputtered copper substrate, thereby defining a nickel film formation area. Subsequently, a nickel film (targeted film thickness: 5 µm) was formed on the sputtered copper substrate by solid electrolyte deposition using a solid electrolyte membrane (product name: Nafion, manufactured by DuPont de Nemours, Inc.). As the film formation apparatus, one having the configuration in which a solid electrolyte membrane was used as a separator in the film formation apparatus 1A shown in Fig. 1A and Fig. 1B. Other nickel film formation conditions are as follows. Nickel plating bath: 1 M nickel chloride-nickel acetate bath (pH 4.0) Anode: Foamed or expanded nickel (NI-318201, manufactured by Nilaco Corporation) Pressure: 1.0 kN Temperature: 60 °C Current value: 150 mA Film formation time (application or application time): 200 seconds

[0061] The obtained nickel film was crystalline nickel (specifically, columnar crystalline nickel). <Poröse Membran ohne funktionelle Ionenaustauschgruppe>

[0062] A porous polyethylene resin membrane without an ion-exchange functional group was fabricated as the separator. A commercially available lithium-ion battery separator (product name: SETELA, manufactured by Toray Industries, Inc., average film thickness: 12 µm) was used as the porous polyethylene resin membrane. The oxygen-to-carbon ratio of the porous membrane, measured by an X-ray electron spectroscopy measuring device (PHI-5800, manufactured by ULVAC-PHI), was 0.01 to 0.02, and it was confirmed that the porous membrane did not contain any ion-exchange functional groups. <Silber-Ionen enthaltende elektrolytische Lösung bzw. Elektrolytlösung>

[0063] As the electrolytic solution, a silver methanesulfonate-potassium iodide bath having the following composition was prepared.

[0064] Composition of the silver methanesulfonate-potassium iodide bath (pH 7): Silver methanesulfonate: 200 g / L Potassium iodide: 500 g / L HBPSA: 25 g / L *Water was used as the solvent. *pH was adjusted to 7.0 with a potassium hydroxide solution. <silberfilm-bildung>

[0065] First, a degreasing treatment, a water cleaning treatment, a pickling treatment (immersion in a 10% sulfuric acid aqueous solution at room temperature for 30 seconds), and a water cleaning treatment were performed on the nickel film formed on the sputtered copper substrate in this order. An oxide film present on the nickel film surface is removed by the aqueous sulfuric acid solution.

[0066] Subsequently, a silver film (targeted film thickness: 2 µm) was formed using the film forming apparatus described above, which was Fig. 1A and Fig. 1B. While the substrate, porous membrane, and electrolyte solution used were as described above, the other conditions were set as follows. Anode: Silver plate (AG-403518, manufactured by Nilaco Corporation) Temperature: 40 °C Pressure: 1.0 kN Film formation time (application or application time): 376 seconds Current value: 10 mA

[0067] The current value 10 mA corresponds to the current density 5 mA / cm 2 .

[0068] In particular, as in Fig. As shown in Figure 1B, the porous polyethylene resin membrane was pressed against the substrate at a pressure of 1.0 MPa by the pressing section of the film-forming device. Subsequently, a voltage was applied between the anode and the substrate (for 376 seconds) by the power supply unit 16 to maintain a current value of 10 mA, while maintaining the substrate temperature at 40°C by a temperature controller, thereby forming a silver film (target film thickness: approximately 2 µm). Accordingly, silver was deposited on the substrate, and the silver film was formed. As a post-treatment, the substrate was immersed in a 15% potassium pyrophosphate (K4P2O7) solution at room temperature for 30 seconds, followed by water cleaning and drying. A silver film E1 was obtained by the above-described process. <auswertung>[Appearance]

[0069] Regarding the obtained silver film E1, the appearance was observed with a microscope (VH-8000, KEYENCE CORPORATION). Consequently, it was confirmed that a uniform silver film was formed without any portion where no film was formed. [Electricity efficiency]

[0070] Regarding the resulting silver film E1, the weight of the silver film deposited on the substrate was measured. A relationship between this measured value and a theoretical precipitation amount calculated using Faraday's law was obtained, thereby calculating the current efficiency of the silver film. The current efficiency was 100%. (Example 2)

[0071] A silver film E2 was formed by a method similar to that of Example 1, except that the current value was set to 20 mA and the film-forming time was set to 188 seconds during silver film formation. The appearance and current efficiency were evaluated by a method similar to that of Example 1. The current value of 20 mA corresponds to a current density of 10 mA / cm 2 .

[0072] It was confirmed that a uniform silver film without a portion where no film was formed was formed in Example 2. The current efficiency was 100%. (Example 3)

[0073] A silver film E3 was formed by a method similar to that of Example 1, except that the current value was set to 30 mA and the film-forming time was set to 126 seconds during silver film formation. The appearance and current efficiency were evaluated by a method similar to that of Example 1. The current value of 30 mA corresponds to a current density of 15 mA / cm. 2 .

[0074] It was confirmed that a uniform silver film without a film-deposited portion was formed in Example 3. The current efficiency was 98%. (Comparison example 1)

[0075] A silver film C1 was formed by a method similar to that of Example 1, except that a solid electrolyte membrane (product name: Nafion, manufactured by DuPont de Nemours, Inc.) was used as the separator in place of the porous polyethylene resin membrane during silver film formation. The appearance and current efficiency were evaluated by a method similar to that of Example 1.

[0076] In Comparative Example 1, the silver film C1 included a portion where no film was formed and was not formed uniformly. The current efficiency was 4%. (Comparison example 2)

[0077] A silver film C2 was formed by a method similar to that of Example 1, except that a silver nitrate bath was used as the electrolyte solution below. The appearance and current efficiency were evaluated by a method similar to that of Example 1.

[0078] Composition of the silver nitrate bath (pH = 9): Silver nitrate: 40 g / L Sodium pyrophosphate: 20 g / L Ammonium sulfate: 120 g / L 25% ammonia solution: 40 mL / L *Water was used as the solvent. *pH was adjusted to 9.0 with an ammonia solution.

[0079] In Comparative Example 2, the silver film C2 included a portion where no film was formed and was not formed uniformly. The current efficiency was 7%. (Comparison example 3)

[0080] A silver film C3 was formed by a method similar to that of Example 1, except that an amorphous nickel film containing a nickel-phosphorus alloy was formed on the sputtered copper substrate, and a silver film was formed on the amorphous nickel film. The appearance and current efficiency were evaluated by a method similar to that of Example 1. The amorphous nickel film was formed by an electroless plating method using an electroless nickel bath containing phosphinate as a reducing agent.

[0081] In Comparative Example 3, the silver film C3 included a portion where no film was formed and was not formed uniformly. The current efficiency was 13%. (Discussion)

[0082] As described above, while the uniform silver film was obtained in Examples 1 to 3, the portion in which no film was formed was generated and the uniform silver film was not obtained in Comparative Examples 1 to 3.

[0083] Specifically, in Comparative Example 1, a silver dendrite was formed in the solid electrolyte membrane. It is believed that the silver dendrite interfered with the movement of silver ions, thus creating the portion where no film was formed. Meanwhile, the porous polyethylene resin membrane used in the examples lacked ion-exchange functional groups for capturing silver ions. Therefore, it is believed that the silver ions were efficiently transported from the anode to the cathode, enabling the formation of a uniform silver film.

[0084] In Comparative Example 2, while the silver film was being formed using the silver nitrate bath, air bubbles of the hydrogen gas interfered with the silver film formation, thereby generating the portion where no film was formed. Meanwhile, in Examples 1 to 3, using the silver methanesulfonate-potassium iodide bath, it was possible to form the silver film uniformly. Organic sulfonic acid ions, such as methanesulfonic acid ions, are ligands that have a high stability constant with respect to silver ions and are present close to the silver ions in the electrolytic solution. Therefore, it is believed that in Examples 1 to 3, it was possible to suppress the decomposition reaction of water and, consequently, to suppress the generation of hydrogen gas.

[0085] In Comparative Example 3, while the silver film was being formed on the amorphous nickel film, air bubbles of hydrogen gas interfered with the silver film formation, creating a portion where no film was formed. This is believed to be because the surface of the amorphous nickel film is flatter than the surface of the crystalline nickel film, and the generated hydrogen gas was trapped between the amorphous nickel film and the separator. Meanwhile, the crystalline nickel film used in the examples has fine unevenness on its surface, and the presence of unevenness causes the generated hydrogen gas to move easily.Therefore, it is considered that in Examples 1 to 3, it is difficult for the hydrogen gas as air bubbles to stay between the nickel film and the separator, thereby enabling the suppression of the generation of the portion in which no film is formed due to the air bubbles. (Examples 4 to 11)

[0086] Silver films E3 were formed by the method similar to that of Example 1, except that silver methanesulfonate-potassium iodide baths having the following compositions were used as the electrolyte solutions and the current density was set to 5 mA / cm 2 , 10 mA / cm 2 , or 15 mA / cm 2 The appearance and power efficiency were evaluated by a method similar to that of Example 1. Table 1 shows the results. [Table 1] Silver methanesulfonate content (g / L) Potassium iodide content (g / L) HBPSA content (g / L) Appearance Current efficiency at 5 mA / cm 2 (%) Current efficiency at 10 mA / cm 2 (%) Current efficiency at 15 mA / cm 2 (%) Example 4 134 500 25 Evenly 90 68 44 Example 5 168 500 25 Evenly 100 86 62 Example 6 200 500 25 Evenly 100 95 71 Example 7 268 500 25 Evenly 100 100 91 Example 8 200 400 25 Evenly 100 90 53 Example 9 200 600 25 Evenly 100 98 73 Example 10 200 500 20 Evenly 100 94 71 Example 11 200 500 40 Evenly 100 86 51 (Discussion)

[0087] It was confirmed that the current efficiency varies depending on the current value and bath composition in solid electroplating using a silver methanesulfonate-potassium iodide bath. The film formation rate has a positive correlation with the current density. As the film formation rate increases, the number of film formations per unit time decreases. Accordingly, if uniform film formation is enabled at a high current density, the manufacturing cost can be reduced. Here, with reference to Japanese Industrial Standard H8618 (Industrial Silver Plating), a "uniform" rating was given to a case where a non-film-formed portion with a diameter of 10 µm or more was absent on the silver film, and Ra was in a range of 0.1 to 0.6 µm and Rz was in a range of 1.0 to 5.0 µm for the surface roughness of the silver film.

[0088] Upper limits and / or lower limits of the respective numerical ranges in this description may be suitably combined to describe an intended range. For example, upper limits and lower limits of the numerical ranges may be suitably combined to describe an intended range, upper limits of the numerical ranges may be suitably combined to describe an intended range, and lower limits of the numerical ranges may be suitably combined to describe an intended range.

[0089] It should be understood that throughout this specification, the expression "ein," "eine," "eines," "der," "die," and "das" should be understood as including the term "das," unless otherwise indicated.

[0090] While the embodiment has been described in detail, the specific configuration is not limited to the embodiment. DESCRIPTION OF REFERENCE SYMBOLS 1A Film forming device 11 Anode 13 Separator (porous membrane without functional ion exchange group) 16 Power supply unit 20 housings 21 Chamber 22 Opening 30 pressing section 40 side table L Electrolyte solution B Substrate (cathode) F Silver film< / auswertung> < / substrat>

Claims

[1] A method for forming a silver film (F), comprising: Arranging an anode (11), a substrate (B) as a cathode, and a separator (13) such that the separator (13) is located between the anode (11) and the substrate (B) and the separator (13) is in contact with a surface of the substrate (B), wherein the separator (13) comprises an electrolyte solution (L) containing silver ions; and Applying a voltage between the anode (11) and the substrate (B) to form a silver film (F) on the substrate (B), wherein: the separator (13) is a porous membrane without a functional ion exchange group, the electrolyte solution (L) contains organic sulfonic acid ions, the electrolyte solution (L) is a silver methanesulfonate-potassium iodide bath, the electrolyte solution (L) further comprises N-(3-hydroxy-1-butylidene)-p-sulfanilic acid HBPSA, the content of silver methanesulfonate in the silver methanesulfonate-potassium iodide bath is 50 to 500 g / L, the content of potassium iodide in the silver methanesulfonate-potassium iodide bath is 200 to 800 g / L, the HBPSA content in the silver methanesulfonate-potassium iodide bath is 20 to 40 g / L, and the substrate (B) comprises a crystalline metal, and the silver film (F) is formed on the crystalline metal. [2] The method according to claim 1, wherein the porous membrane is a porous polyolefin resin membrane. [3] The method according to claim 2, wherein the porous polyolefin resin membrane is a porous polyethylene resin membrane. [4] A method according to any one of claims 1 to 3, wherein the crystalline metal is a nickel film. [5] The method according to claim 4, wherein the nickel film has a columnar crystalline shape.

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