PtRu alloy plating film and laminated structure including the PtRu alloy plating film

Abstract

To provide a plating film with excellent high hardness and anticorrosiveness, and a laminated structure of metal layers using the film in relation to a useful noble metal layer as a protective layer of connectors etc.SOLUTION: The present invention relates to a noble metal thin film made of a PtRu alloy. The present invention relates to a plating film comprising a PtRu alloy. The PtRu alloy includes Ru of between 2 mass% and 20 mass%, and a remainder Pt and inevitable impurities. The PtRu alloy plating film has a Vickers hardness value of 450 Hv or more. A laminated structure of the PtRu alloy plating films comprises: an interlayer 11 whose base material 10 is made of either a pure metal of Ni, Cr, Mn, Fe, Co, Cu, Au, Ag, Pd, Pt, or W, or a metal alloy of one of them; and a noble metal layer 12 made of the PtRu alloy plating film of the present invention.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a plating film made of a PtRu alloy. More specifically, the present invention relates to a plating film made of a PtRu alloy of a predetermined composition that has high hardness and excellent corrosion resistance. The present invention also relates to a laminate structure including this PtRu alloy plating film. [Background technology]

[0002] Various connectors and terminals are used in electronic and semiconductor devices. These connectors require both electrical conductivity and stable contact reliability, and many have a specific laminated structure. Connectors with a laminated structure have a substrate made of Cu or Cu alloy, on which an intermediate layer of Ni or other material is formed, and then a precious metal layer is formed on top of that. The precious metal layer is formed to protect the underlying layer and substrate and ensure stable electrical conductivity. Connectors, in particular, are designed to be used while repeatedly inserting and removing connectors, which creates friction between them and the mating connector. The precious metal layer is formed to prevent the intermediate layer and substrate from being exposed due to this friction. Furthermore, due to its chemical stability, the precious metal layer acts as an environmental barrier to inhibit corrosion of the substrate.

[0003] Until now, gold plating films have been widely used as the precious metal layers formed on the substrates of connectors to act as protective layers, etc. However, since then, plating films of platinum and RhRu alloys have come to be used instead of the relatively soft gold. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Utility Model Registration No. 3211820 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-256163 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the dramatic spread and miniaturization of electronic devices such as smartphones and tablet devices, there has been an increasing demand for precious metal layers with high hardness and excellent corrosion resistance for use in connectors for these devices. In response to these demands, there is a need for plating films made of conventional precious metals such as Pt or precious metal alloys that are harder and more cost-effective.

[0006] Therefore, the present invention provides a plating film with high hardness and excellent corrosion resistance for a precious metal layer that is useful in connectors for electronic devices and other applications requiring a protective layer. [Means for solving the problem]

[0007] The present invention, which solves the above-mentioned problems, provides a plating film made of a PtRu alloy, the PtRu alloy containing 2% by mass or more and 20% by mass or less of Ru, the remainder being Pt and unavoidable impurities, and having a Vickers hardness of 450 Hv or more.

[0008] The present inventors have found that a plating film made of a PtRu alloy can solve the above-mentioned problems. Ru is a type of precious metal and is harder than Pt, so alloying it with Pt is expected to increase the hardness of the coating. Furthermore, because Ru is chemically stable like Pt, PtRu alloy plating films are expected to have excellent weather resistance. Furthermore, because Ru is a less expensive precious metal than Pt or Rh, alloying with Ru is also expected to reduce costs. Furthermore, the compositions of plating solutions for forming Pt and Ru plating films are publicly known, and it is believed that alloy plating films can also be formed.

[0009] However, there are few reports of practical applications of PtRu alloys as protective films, and little knowledge exists regarding the optimization of specific configurations such as alloy composition. Furthermore, the optimization of alloy plating solutions and plating processes for forming PtRu alloy films by plating is also unclear. Therefore, the present inventors have been developing PtRu alloy plating solutions while also studying PtRu alloy plating films with suitable configurations, leading to the invention described above. The PtRu alloy plating film and the resulting laminate structure according to the present invention are described below.

[0010] As described above, the present invention relates to a precious metal alloy plating film made of a PtRu alloy. Pt is a precious metal whose usefulness as a protective film for connectors and the like has been confirmed. Furthermore, alloying Pt with Ru is expected to increase the hardness of Pt.

[0011] The composition of the PtRu alloy plating film of the present invention has a Ru concentration of 2% by mass or more and 20% by mass or less. A Ru concentration of less than 2% by mass results in little effect in increasing hardness. Furthermore, the hardness increase effect of alloying Pt with Ru increases with increasing Ru concentration, but when the Ru concentration exceeds 20% by mass, not much increase is expected. Furthermore, the PtRu alloy plating film of the present invention is formed by a plating method (electroplating). As described below, the Ru concentration of the PtRu alloy plating film can be adjusted by adjusting the ratio of the Pt concentration to the Ru concentration in the plating solution. If the Ru concentration in this plating solution is excessively high, the deposition efficiency of the entire alloy film tends to decrease. Therefore, the upper limit of the Ru concentration in the PtRu alloy plating film of the present invention is set to 20% by mass.

[0012] The PtRu alloy plating film of the present invention is essentially composed of Pt and Ru. The purity of Pt and Ru is preferably 90% by mass or more, and more preferably 99.0% by mass or more. However, the PtRu alloy plating film of the present invention is permitted to contain unavoidable impurities. Examples of such unavoidable impurities include Fe, Ni, Cr, Co, Mn, Cu, Au, Ag, Pd, W, Mg, Na, Rh, Ge, Zn, Sn, and Re. These unavoidable impurities originate from the components of the PtRu alloy plating solution. Specifically, impurities in the metal salts (Pt salts and Ru salts) and contamination from additives to the plating solution are considered. The total content of the unavoidable impurities is preferably 1000 ppm or less.

[0013] The composition (Ru concentration) and impurity content of the PtRu alloy plating film can be measured by subjecting the surface or cross section of the film to electron microprobe analysis (EPMA), energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence analysis (XRF), etc. Also, the Ru concentration, etc., of a solution in which the PtRu alloy plating film is dissolved can be analyzed by inductively coupled plasma optical emission spectroscopy (ICP).

[0014] The PtRu alloy plating film of the present invention within the above composition range has a Vickers hardness of 450 Hv or more. The hardness of the PtRu alloy plating film increases with increasing Ru concentration. The PtRu alloy plating film of the present invention has a higher hardness than conventional Pt plating films on the same substrate, and exhibits suitable wear resistance as a protective layer for connectors and the like. The hardness of this PtRu alloy plating film is more preferably 500 Hv or more. While the hardness of a PtRu alloy plating film is somewhat affected by the type of substrate and substrate, the PtRu alloy plating film of the present invention must be 450 Hv or more regardless of the substrate material. The upper limit of the hardness value varies depending on the substrate, but at the upper limit of the Ru concentration mentioned above, a hardness of 900 Hv can be exhibited.

[0015] The thickness of the PtRu alloy plating film of the present invention is preferably 0.1 μm or more and 5.0 μm or less. If the thickness is 0.1 μm or less, it becomes difficult to maintain the protective effect on the substrate for a long period of time. Furthermore, if the PtRu alloy plating film is more than 5.0 μm thick, defects such as cracks may be present in the film when it is produced by a plating method.

[0016] Furthermore, the PtRu alloy plating film of the present invention is composed of fine and dense PtRu alloy crystallites, thereby ensuring the above-mentioned hardness characteristics and corrosion resistance. The average particle size of the PtRu alloy crystallites is preferably 1 Å or more and 100 Å or less, and more preferably 1 Å or more and 10 Å or less. The crystallite size of the PtRu alloy plating film can be measured and calculated using the Scherrer formula based on the half-width of the diffraction peak obtained by X-ray diffraction analysis (XRD).

[0017] Here, we will explain the plating method for producing the PtRu alloy plating film according to the present invention. The PtRu alloy plating film can be produced by electrolytic plating of a suitable substrate. In producing the plating film by electrolytic plating, the substrate is immersed in a PtRu alloy plating solution essentially containing Pt salt and Ru salt to perform electrolysis.

[0018] A PtRu alloy plating solution suitable for the present invention is a PtRu alloy plating solution containing, as essential components, a divalent Pt salt, a Ru salt, sulfuric acid, and sulfamic acid.

[0019] Suitable divalent platinum salts include inorganic acid salts containing at least one of sulfate (SO), sulfo (SO), nitro (NO), nitrate (NO), amine (NH), aquo (HO), and hydroxyl (OH). Specific examples include platinum sulfate (PtSO), platinum dinitrosulfide (Pt(SO)(NO), platinum nitrate (Pt(NO), dinitrodiammine platinum (Pt(NH)(NO), diaminedichloro platinum (Pt(NH)Cl), trichloroamine platinum acid (HPtCl(NH)) or its salt, tetranitro platinum acid (HPtCl) or its salt, tetrasulfo platinum acid (HPt(SO)) or its salt, and tetraammine platinum phosphate (HPt(NH)). On the other hand, for Ru salts, Ru sulfate (RuSO4), Ru nitrate (Ru(NO3)2), and Ru chloride (RuCl3) can be applied.

[0020] The contents of each component in the PtRu alloy plating solution according to the present invention are preferably as follows: Pt concentration is 1 g / L to 15 g / L, Ru concentration is 0.1 g / L to 10 g / L, total sulfuric acid concentration is 10 g / L to 200 g / L, and sulfamic acid concentration is 0.1 g / L to 20 g / L. The PtRu alloy plating film according to the present invention has a Ru concentration of 2 mass% to 20 mass%, and the composition of this alloy film can be adjusted by the ratio of the Pt concentration to the Ru concentration in the alloy plating solution. According to the studies of the present inventors, the ratio of the Pt concentration to the Ru concentration (Ru concentration (g / L) / Pt concentration (g / L)) in the PtRu alloy plating solution is preferably 0.1 to 0.8.

[0021] In order to improve the deposition efficiency of the PtRu alloy and to suppress the formation of cracks in the alloy film, the PtRu alloy plating solution described above preferably has a chlorine concentration of 500 mg / L or less. When the chlorine concentration is within the above range, it is preferable not to use metal salts containing chlorine as a constituent element for the Pt salt and Ru salt, or, even if they are used, to ensure that the chlorine concentration does not exceed the above range when the plating solution is prepared.

[0022] The PtRu alloy plating solution essentially contains the Pt and Ru salts, sulfuric acid, and sulfamic acid described above, but additives may also be added as needed. For example, anionic surfactants, alkali metals, or alkaline earth metals can promote the deposition of Pt and Ru while contributing to the formation of a high-quality PtRu alloy film. Well-known additives, such as pH buffers, complexing agents, and stabilizers, can also be used.

[0023] The conditions for electrolytic plating using the above plating solution are preferably a pH of 1 or less for the PtRu alloy plating solution, a temperature of 45°C to 65°C, and a current density of 2.0 A / dm 2 More than 10A / dm 2 It is preferable to have the following:

[0024] The PtRu alloy plating film according to the present invention is formed as a precious metal layer on a suitable substrate to form a laminate structure. There are no limitations on the material, shape, or dimensions of the substrate. Examples of substrate materials include Cu or Cu alloys (phosphor bronze, brass, beryllium copper, nickel silver, Corson copper), Fe or Fe alloys (Fe-Ni alloy, Fe-Ni-Co alloy, stainless steel), etc. Substrates made of materials other than those mentioned above may also be used, provided that they have a conductive pattern of Cu, Ag, etc. formed on them. The substrate shape is not particularly limited and may be in the form of a chip, tape, or the like.

[0025] The precious metal layer made of PtRu alloy plating film may be formed directly on the substrate. However, when applied to various applications such as connectors, a laminate structure is often adopted in which an intermediate layer having various purposes is formed between the substrate and the precious metal laminate. This laminate structure includes a substrate, at least one intermediate layer formed on at least a portion of the surface of the substrate, and a precious metal layer formed on the intermediate layer, with the PtRu alloy plating film formed as the precious metal layer.

[0026] FIG. 1 illustrates an embodiment of a laminate structure using a PtRu alloy plating film according to the present invention. As described above, a precious metal layer 12, which is a PtRu alloy plating film, may be formed directly on the surface of a substrate 10 (FIG. 1(a)). Alternatively, an intermediate layer 11 may be provided between the precious metal layer 12 and the substrate 10 (FIG. 1(b)). As illustrated in FIG. 1(c), the intermediate layer 11 may be composed of multiple layers, including a first intermediate layer 11a and a second intermediate layer 11b.

[0027] The intermediate layer is formed for purposes such as ensuring adhesion (bonding strength) between the precious metal layer (PtRu alloy plating film) and the substrate, imparting corrosion resistance to the substrate, acting as a barrier layer, reducing contact resistance, and preventing diffusion. In the above-described laminated structure, at least one intermediate layer is formed. That is, multiple intermediate layers can be formed under the precious metal layer. The material of the intermediate layer is composed of a pure metal such as Ni, Cr, Mn, Fe, Co, Cu, Au, Ag, Pd, Pt, or W, or an alloy of these metals.

[0028] As a specific configuration of the intermediate layer and the resulting laminated structure, an intermediate layer made of a pure metal such as Au, Ag, Pd, or Pt or an alloy thereof is formed directly below the precious metal layer to ensure adhesion of the precious metal layer.

[0029] Furthermore, Ni or Ni alloys (NiW, NiMo, CoW, CoMo) are formed under the noble metal layer or the intermediate layer of Au or the like to prevent dissolution of the base material or to form a barrier layer.

[0030] Furthermore, an intermediate layer made of NiP, NiPW, or CoP may be formed on the surface of the substrate. NiP plating is a dense and hard metal layer that provides corrosion resistance and wear resistance to the substrate. The intermediate layer made of NiP, NiPW, or CoP has a crystalline or amorphous structure.

[0031] As described above, various functional intermediate layers can be appropriately arranged between the substrate and the precious metal layer (PtRu alloy plating film). There is no limit to the number of intermediate layers. Furthermore, the precious metal layer is formed on the intermediate layer, but the intermediate layer only needs to be formed on at least a portion of the substrate. For example, an electrical contact portion can be set on a portion of the substrate, and the intermediate layer and precious metal layer can be formed on this electrical contact portion. There is no limit to the method for forming the intermediate layer. Any of plating methods (electrolytic plating and electroless plating), sputtering, chemical vapor deposition (CVD, ALD), vacuum deposition, etc. can be used to form the intermediate layer. There is also no particular limit to the thickness of the intermediate layer, and it can be set depending on the respective configurations and functions.

[0032] The PtRu alloy plating film and laminate structure according to the present invention can be suitably applied to connectors and terminals in electronic and electrical equipment, semiconductor devices, etc. As for connectors, they can be applied to both male and female (plug and receptacle) connectors. [Effects of the Invention]

[0033] As described above, the present invention provides a plating film made of a PtRu alloy with a predetermined Ru concentration that can function as a protective layer. This PtRu alloy plating film has high hardness, favorable wear resistance, and good corrosion resistance. It also has a uniform metallic luster and a good appearance. Due to these advantages, the PtRu alloy plating film of the present invention is useful as a protective layer for connectors and terminals of smartphones and other devices, and is durable against repeated insertion and removal. It is also useful as a plating film for jewelry and other items. [Brief explanation of the drawings]

[0034] [Figure 1] 1A and 1B are diagrams illustrating the form and laminate structure of a precious metal layer made of a PtRu alloy plating film according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, an embodiment of the present invention will be described. In this embodiment, a PtRu alloy plating solution was prepared from a divalent Pt salt and a Ru salt, and a PtRu alloy plating film was formed by electrolytic plating. In this embodiment, five types of PtRu alloy plating solutions were prepared with different Ru concentrations in the plating solution, and PtRu alloy plating films with different Ru concentrations were formed and their hardness was evaluated.

[0036] Preparation of PtRu alloy plating solution A basic bath with a Pt concentration of 10 g / L, a Ru concentration of 1-5 g / L, and a total sulfuric acid concentration of 80 g / L was prepared by adding Pt dinitrosulfide (Pt(SO4)(NO3)2) and Ru sulfate (RuSO4) with sulfuric acid and sulfamic acid. Then, 100 mg / L of sodium lauryl sulfate (Emal®, manufactured by Kao Corporation) was added as an anionic surfactant, and 4 g / L of magnesium sulfate as an alkaline earth salt was added. Finally, the pH was adjusted to 1 to prepare the plating bath. The chlorine concentration of this PtRu alloy plating solution was 0.5 mg / L.

[0037] For comparison, a Pt plating film was also formed using a Pt plating solution, which had the same composition as in the present embodiment except that it contained 10 g / L of the same Pt ​​salt as above but did not contain any Ru salt.

[0038] Then, a PtRu alloy plating film and a Pt plating film were formed using the PtRu alloy plating solution and the Pt plating solution. In this embodiment, two types of substrates were prepared: a Cu plate (20 mm x 40 mm x 0.1 mm) and a multilayer substrate (Cu / Ni / Au) in which the Cu plate was plated with Ni (thickness 3.0 μm) / Au (thickness 0.1 μm). A plating film was formed on each of them. The plating conditions were a bath temperature of 60°C and a current density of 4.0 A / dm 2 The plating time was adjusted to 30 to 60 minutes, aiming for a film thickness of 5 μm.

[0039] After plating, the PtRu alloy plating film was subjected to composition analysis (Ru concentration measurement) using EDX.Then, the hardness of each plating film was measured.The Vickers hardness (Hv) was measured using a Vickers hardness tester with a load of 10 g.

[0040] Furthermore, to confirm the corrosion resistance of the formed PtRu alloy plating film, an electrolysis cycle test was performed on the formed samples. The electrolysis cycle test was performed by applying a voltage of 5 V for 30 seconds to each sample in a 5% by mass sodium chloride solution (temperature: room temperature), and repeating this cycle. The corrosion resistance was evaluated based on the number of cycles required until the base was exposed, up to a maximum of 200 cycles. The evaluation results are shown in Table 1.

[0041] [Table 1]

[0042] Table 2 confirms that the Ru ratio of the PtRu alloy plating films (No. 1 to No. 5) formed in this embodiment increases with the Ru concentration in the plating solution, and that the films are composed of 3 mass % to 12.3 mass % PtRu alloy. The hardness of the PtRu alloy plating films is 450 Hv or higher on all substrates. It is clear that the PtRu alloy plating films (No. 1 to No. 5) formed in this embodiment have a higher hardness than the Pt plating film (No. 6) in which Ru is not alloyed.

[0043] Furthermore, the hardness of the PtRu alloy plating film generally increases with increasing Ru concentration. The multilayer substrate exhibited a maximum Vickers hardness of 760 Hv. Furthermore, no cracks were observed in any of the PtRu alloy plating films, and corrosion resistance was excellent. Furthermore, the films exhibited a uniform metallic luster, giving them a good appearance.

[0044] The PtRu alloy plating films formed in this embodiment were subjected to XRD analysis after film formation to measure their average crystallite diameters (the Scherrer constant was set to 0.94). The average crystallite diameters of the PtRu alloy films No. 1 to No. 5 of this embodiment were in the range of 1.5 Å to 2.0 Å. [Industrial Applicability]

[0045] As described above, the PtRu alloy plating film according to the present invention is composed of a high-hardness PtRu alloy and has good corrosion resistance. The present invention is useful for forming protective plating layers on electronic devices such as connectors and terminals of smartphones and tablet devices, as well as plating films on jewelry and other items. [Explanation of symbols]

[0046] 10 Base material 11 Middle Class 11a The first middle class 11b The second middle class 12 Precious metal layer

Claims

1. A plating film made of a PtRu alloy, The PtRu alloy contains 2% by mass or more and 20% by mass or less of Ru, the remainder being Pt and unavoidable impurities, The PtRu alloy has an average crystallite diameter of 1 Å or more and 100 Å or less, and a Vickers hardness of 450 Hv or more and 760 Hv or less.

2. A substrate; At least one intermediate layer formed on at least a portion of the surface of the substrate; a precious metal layer formed on the intermediate layer, 2. The laminated structure according to claim 1, wherein the precious metal layer is made of a PtRu alloy plating film.

3. 3. The laminated structure according to claim 2, wherein the intermediate layer is made of any one of a pure metal selected from the group consisting of Ni, Cr, Mn, Fe, Co, Cu, Au, Ag, Pd, Pt, and W, or an alloy of these metals.

4. 4. The laminated structure according to claim 2, wherein the substrate is made of either Cu or a Cu alloy, or Fe or an Fe alloy.

5. A connector or terminal having a laminated structure described in any one of claims 2 to 4.

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