PtRu alloy plating film and laminated structure having the same

Abstract

The present invention relates to a noble metal thin film composed of a PtRu alloy. The present invention is a plating film composed of a PtRu alloy composed of 2 mass% or more and 20 mass% or less of Ru, the balance of Pt, and inevitable impurities, and having a Vickers hardness of 450 Hv or more. A laminated structure formed of the PtRu alloy plating film is composed of an intermediate layer (11) composed of any one of pure metals of Ni, Cr, Mn, Fe, Co, Cu, Au, Ag, Pd, Pt, W or alloys of these metals and a noble metal layer (12) composed of the PtRu alloy plating film of the present invention on a substrate (10). The noble metal thin film of the present invention is useful as a protective layer of a connector or the like, is high in hardness, and is excellent in corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a plating film composed of a PtRu alloy. Specifically, it relates to a plating film composed of a PtRu alloy of a predetermined composition, which is high in hardness and excellent in corrosion resistance. In addition, the present application relates to a laminated structure provided with the PtRu alloy plating film. BACKGROUND

[0002] Various connectors and terminals are used in electronic / electrical equipment and semiconductor devices. These connectors need to have stable contact reliability while ensuring electrical conductivity, and most of them have a predetermined laminated structure. As a connector having a laminated structure, an intermediate layer of Ni or the like is formed on a substrate composed of Cu or a Cu alloy or the like, and further a noble metal layer is formed thereon. The noble metal layer is formed in order to protect the lower layer and the substrate and ensure stable conduction. In particular, since the connector is premised on repeated plugging and unplugging, friction occurs between the connector and the counterpart connector. In order to prevent the intermediate layer or the substrate from being exposed due to this friction, the noble metal layer is formed. In addition, the noble metal layer functions as an environmental barrier layer to suppress corrosion of the substrate or the like due to its chemical stability.

[0003] As the above-mentioned noble metal layer formed on the substrate of the connector and functioning as a protective layer or the like, an application example of an Au plating film has been used so far. Then, a plating film using Pt or RhRu alloy or the like is used instead of Au which is relatively soft.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Utility Model Registration No. 3211820

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-256163 SUMMARY

[0008] [PROBLEMS TO BE SOLVED BY THE INVENTION]

[0009] In recent years, with the widespread use of electronic equipment such as smartphones and tablet terminals and their miniaturization, there is an increasing demand for a noble metal layer for these connectors, which is high in hardness and excellent in corrosion resistance. In response to such a demand, the conventional plating film composed of a noble metal such as Pt or a noble metal alloy needs to be higher in hardness and also advantageous in terms of cost.

[0010] Therefore, the present application provides a plating film which is high in hardness and excellent in corrosion resistance, for a noble metal layer useful in connectors for electronic equipment and the like and other applications requiring a protective layer.

[0011] [MEANS FOR SOLVING THE PROBLEMS]

[0012] The present application that solves the above problems is a plating film composed of a PtRu alloy composed of 2 mass% or more and 20 mass% or less of Ru, the balance of Pt, and inevitable impurities, and having a Vickers hardness of 450 Hv or more.

[0013] The present inventors found the possibility of a plating film composed of a PtRu alloy as a noble metal plating film that can solve the above problems. Ru is one of noble metals and is a high-hardness metal relative to Pt, and thus high-hardening of the film formed by alloying with Pt can be expected. In addition, Ru also has chemical stability like Pt, and thus the weather resistance of the PtRu alloy plating film is expected to be excellent. Furthermore, since Ru is a noble metal that is less expensive than Pt and Rh, cost reduction by alloying with Ru can also be expected. Also, regarding plating films of Pt and Ru, the composition of the plating solution used to form each plating film is known, and thus it is believed that an alloy plating film can also be formed.

[0014] However, there are few reports of practical examples of PtRu alloy as a protective film, and there is little knowledge of the optimization of the specific composition of the alloy, etc. In addition, the optimization of the alloy plating solution and plating process for forming a PtRu alloy film by plating is also unclear. Thus, the present inventors have researched a suitable composition of a PtRu alloy plating film while developing a PtRu alloy plating solution, and thus conceived the above-described present application. Hereinafter, a PtRu alloy plating film according to the present application and a laminated structure formed thereby will be described.

[0015] As described above, the present application relates to a noble metal alloy plating film composed of a PtRu alloy. Pt is a noble metal whose usefulness as a protective film for connectors and the like is confirmed. Also, by alloying Ru with Pt, an effect of increasing the hardness relative to Pt can be expected.

[0016] In the composition of the PtRu alloy plating film of the present application, the Ru concentration is set to 2 mass% or more and 20 mass% or less. When the Ru concentration is less than 2 mass%, the effect of increasing the hardness is insufficient. In addition, the effect of increasing the hardness by alloying Ru with Pt becomes greater as the Ru concentration increases, but when it exceeds 20 mass%, a large increase cannot be expected. Furthermore, the PtRu alloy plating film of the present application is formed by a plating method (electrolytic plating), and as described later, the Ru concentration of the PtRu alloy plating film can be adjusted by the ratio of the Pt concentration to the Ru concentration in the plating solution. When the Ru concentration in the plating solution is too high, the deposition efficiency of the entire alloy film tends to decrease. Thus, in the PtRu alloy plating film of the present application, the upper limit of the Ru concentration is set to 20 mass%.

[0017] The PtRu alloy plating film of the present application is essentially composed of Pt and Ru. The purity of the Pt and Ru is preferably 90 mass% or more, more preferably 99.0 mass% or more. However, the PtRu alloy plating film of the present application can contain inevitable impurities. As the inevitable impurities, Fe, Ni, Cr, Co, Mn, Cu, Au, Ag, Pd, W, Mg, Na, Rh, Ge, Zn, Sn, Re, and the like can be exemplified. These inevitable impurities are derived from the components in the PtRu alloy plating solution. Specifically, impurities in the metal salts (Pt salt and Ru salt) and the incorporation of additives from the plating solution can be considered. The content of the inevitable impurities is preferably 1000 ppm or less in total.

[0018] Note that the composition (Ru concentration) and the impurity content of the PtRu alloy plating film can be measured by electron beam microprobe analysis (EPMA), energy dispersive X-ray spectroscopy (EDX), fluorescent X-ray analysis (XRF), and the like on the surface or cross section of the film. In addition, for the solution after dissolving the PtRu alloy plating film, inductively coupled plasma emission spectroscopy (ICP) can be used to analyze the Ru concentration and the like.

[0019] Further, the PtRu alloy plating film of the present application having the above composition range has a Vickers hardness of 450 Hv or more. The hardness value of the PtRu alloy plating film increases with an increase in the Ru concentration. Further, the PtRu alloy plating film of the present application has a higher hardness than a Pt plating film as a related art, if the same substrate is used, and exhibits appropriate wear resistance as a protective layer for connectors and the like. The hardness of the PtRu alloy plating film is more preferably 500 Hv or more. Note that the hardness of the PtRu alloy plating film is somewhat affected by the type of the substrate / base material, but the PtRu alloy plating film of the present application is 450 Hv or more regardless of the material of the substrate. Note that the upper limit of the hardness value varies depending on the substrate and the like, but a hardness of 900 Hv can be exhibited within the above upper limit of the Ru concentration.

[0020] The thickness of the PtRu alloy plating film of the present application is preferably 0.1 μm or more and 5.0 μm or less. If the thickness is less than 0.1 μm, it is difficult to maintain the protective effect on the substrate for a long period of time. Further, for a PtRu alloy plating film exceeding 5.0 μm, defects such as cracks can be included in the film if the film is manufactured by a plating method.

[0021] Further, the PtRu alloy plating film of the present application is composed of fine and dense PtRu alloy crystallites, thereby ensuring the above hardness characteristics and corrosion resistance. The particle diameter of the PtRu alloy crystallites is preferably 50 nm or more and 200 nm or less, more preferably 60 nm or more and 150 nm or less, and even more preferably 70 nm or more and 100 nm or less, on average. The above More preferably, the following The above The following. Note that the measurement / calculation of the crystallite diameter of the PtRu alloy plating film can be based on the half-value width of the diffraction peak obtained by X-ray diffraction analysis (XRD) and calculated according to the Scherrer formula.

[0022] Here, the plating method of the manufacturing method of the PtRu alloy plating film related to the present application described above is described. The PtRu alloy plating film can be manufactured by electrolytic plating on a suitable substrate. When the plating film is manufactured using the electrolytic plating method, the substrate is immersed in a PtRu alloy plating solution necessary to contain a Pt salt and a Ru salt to perform electrolysis.

[0023] The PtRu alloy plating solution suitable in the present application is a PtRu alloy plating solution containing a 2-valent Pt salt and a Ru salt, sulfuric acid, and sulfamic acid as essential components.

[0024] As the 2-valent Pt salt, an inorganic acid salt containing at least one of a sulfuric acid group (SO4) or a sulfonic group (SO3), a nitro group (NO2), a nitric acid group (NO3), an amine (NH3), an acetic acid group (AcO) (H2O), a hydroxyl group (OH) is preferably used. As specific examples, there can be listed: sulfuric acid Pt (PtSO4), dinitrosulfuric acid Pt (Pt(SO4)(NO3)2), nitric acid Pt (Pt(NO3)2), dinitro diamine Pt (Pt((NH3)2(NO3)2), diamine dichloro Pt (Pt(NH3)2Cl2), trichloroamine Pt acid (HPtCl3(NH3)) or a salt thereof, tetranitro Pt acid (H2PtCl4) or a salt thereof, tetrasulfonic Pt acid (H6Pt(SO3)4) or a salt thereof, tetraamine Pt phosphoric acid (H2Pt(NH3)4) or a salt thereof, and the like. On the other hand, as the Ru salt, there can be applied sulfuric acid Ru (RuSO4) or nitric acid Ru (Ru(NO3)2), chlorinated Ru (RuCl3).

[0025] As to the content of each component in the PtRu alloy plating solution related to the present application, it is preferable that the Pt concentration is set to 1 g / L or more and 15 g / L or less, the Ru concentration is set to 0.1 g / L or more and 10 g / L or less, the total sulfuric acid concentration is set to 10 g / L or more and 200 g / L or less, and the sulfamic acid concentration is set to 0.1 g / L or more and 20 g / L or less. In addition, as to the PtRu alloy plating film related to the present application, the Ru concentration is 2 mass% or more and 20 mass% or less, but the composition of the alloy film can be adjusted by the ratio of the Pt concentration to the Ru concentration of the alloy plating solution. According to the research of the present inventors, it is preferable that 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 set to 0.1 or more and 0.8 or less.

[0026] Note that, in order to suppress the deposition efficiency of the PtRu alloy and the generation of cracks in the alloy film, the chlorine concentration in the above-described PtRu alloy plating solution is preferably 500 mg / L or less. In the case where the chlorine concentration is set to the above-described range, it is preferable that, for the Pt salt and the Ru salt, no metal salt having chlorine as a constituent element is used, or even if used, the chlorine concentration is not more than the above-described range at the time of the bath preparation.

[0027] In addition, the PtRu alloy plating solution has the above-described Pt and Ru salts, sulfuric acid, and sulfamic acid as essential components, but an additive can be appropriately added. For example, an anionic surfactant, an alkali metal or an alkaline earth metal, or the like can promote the deposition of Pt and Ru and contribute to the formation of a high-quality PtRu alloy film. In addition, a well-known additive such as a pH buffer, a complexing agent, a stabilizer, or the like can be used.

[0028] As the conditions for plating using the above-described plating solution, the pH of the PtRu alloy plating solution is preferably 1 or less, and the temperature is preferably 45°C or higher and 65°C or lower, and the current density is preferably 2.0 A / dm 2 or higher and 10 A / dm 2 or lower.

[0029] Then, a laminated structure is formed by forming the PtRu alloy plating film according to the present application as a noble metal layer on a suitable substrate. The material, shape / dimensions of the substrate are not limited. As the material of the substrate, Cu or a Cu alloy (phosphor bronze, brass, beryllium copper, white copper, Cossen copper), Fe or an Fe alloy (Fe-Ni alloy, Fe-Ni-Co alloy, stainless steel), or the like can be listed. In addition, even if the substrate is other than the above-described materials, it is acceptable if a conductive pattern of Cu, Ag, or the like can be formed. The shape of the substrate is not particularly limited to a sheet shape, a tape shape, or the like.

[0030] The noble metal layer composed of the PtRu alloy plating film can be directly formed on the substrate. However, in applications to various uses such as connectors, a laminated structure in which an intermediate layer having various purposes is formed between the substrate and the noble metal layer is often adopted. The laminated structure is a laminated structure including a substrate, at least one intermediate layer formed on at least a part of the surface of the substrate, and a noble metal layer formed on the intermediate layer, and is a laminated structure in which the above-described PtRu alloy plating film is formed as the noble metal layer.

[0031] Figure 1 A manner of using the laminated structure of the PtRu alloy plating film according to the present application is exemplified. As described above, the noble metal layer 12 of the PtRu alloy plating film can be directly formed on the surface of the substrate 10 Figure 1 (a). In addition, an intermediate layer 11 can be provided between the noble metal layer 12 and the substrate 10 (Figure 1 (b)). And, as Figure 1 As in example (c), the intermediate layer 11 can also be composed of multiple layers, including the first intermediate layer 11a and the second intermediate layer 11b.

[0032] The intermediate layer is formed to ensure the adhesion (bonding strength) between the noble metal layer (PtRu alloy coating) and the substrate, to impart corrosion resistance to the substrate, to act as a barrier layer, to reduce contact resistance, and to prevent diffusion. In the above-described laminated structure, at least one intermediate layer is formed. That is, multiple intermediate layers can be formed beneath the noble metal layer. The material of the intermediate layer is any one of pure metals such as Ni, Cr, Mn, Fe, Co, Cu, Au, Ag, Pd, Pt, and W, or alloys of these metals.

[0033] As a specific component of the intermediate layer and the stacked structure formed therefrom, in order to ensure the tightness of the precious metal layer, an intermediate layer composed of pure metals such as Au, Ag, Pd, and Pt or their alloys is formed directly below the precious metal layer.

[0034] In addition, in order to prevent the dissolution of the substrate or other base material and to act as a barrier layer, Ni or Ni alloy (NiW, NiMo, CoW, CoMo) is formed below the noble metal layer or the aforementioned intermediate layer such as Au.

[0035] In addition, sometimes an intermediate layer composed of NiP, NiPW, or CoP is formed on the surface of the substrate. The NiP coating is a dense and hard metal layer that imparts corrosion resistance and wear resistance to the substrate. It should be noted that the intermediate layer composed of NiP, NiPW, or CoP can have a crystalline or amorphous structure.

[0036] As described above, various functions can be appropriately configured for the intermediate layer between the substrate and the noble metal layer (PtRu alloy coating). There is no limitation on the number of intermediate layers. Furthermore, the noble 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 provided on a portion of the substrate, and the intermediate layer and the noble metal layer can be formed at that electrical contact portion. Furthermore, there are no limitations on the method for forming the intermediate layer. Plating methods (electrolytic plating and electroless plating), sputtering methods, chemical vapor deposition (CVD, ALD), vacuum vapor deposition, etc., are all applicable as methods for forming the intermediate layer. Furthermore, there are no particular limitations on the thickness of the intermediate layer; it is set according to each configuration / function.

[0037] Furthermore, the PtRu alloy coating and laminate structure of this invention can be suitably applied to connectors and terminals in electronic / electrical equipment, semiconductor devices, etc. For connectors, it can be applied to both male and female (plug / socket) connectors.

[0038] [The effects of the invention]

[0039] As described above, the present application proposes a plating film composed of a PtRu alloy of a predetermined Ru concentration as a plating film which can function as a protective layer. The PtRu alloy plating film exhibits high hardness and appropriate wear resistance, and also has good corrosion resistance. In addition, it has a uniform metallic luster and is also good in appearance. According to these advantages, the PtRu alloy plating film according to the present application is useful for a protective layer of a connector or a terminal of a smartphone or the like, and has durability against repeated plugging and unplugging. In addition, it is also useful as a plating film of a jewelry or the like. BRIEF DESCRIPTION OF DRAWINGS

[0040] [ Figure 1 ] is a drawing illustrating a manner of forming a noble metal layer composed of the PtRu alloy plating film according to the present application and a laminated structure. DETAILED DESCRIPTION

[0041] Hereinafter, an embodiment of the present application will be described. In the present embodiment, a PtRu alloy plating solution is prepared from a divalent Pt salt and a Ru salt, and a PtRu alloy plating film is formed by electrolytic plating. In the present embodiment, five kinds of PtRu alloy plating solutions in which the Ru concentration in the plating solution is changed are prepared, PtRu alloy plating films having different Ru concentrations are formed, and their hardness is evaluated.

[0042] Preparation of PtRu alloy plating solution

[0043] A basic bath was prepared by adding sulfuric acid and sulfamic acid to dinitro sulfated Pt (Pt(SO4)(NO3)2) and Ru sulfate (RuSO4) so as to have a Pt concentration of 10 g / L, a Ru concentration of 1 to 5 g / L, and a total sulfuric acid concentration of 80 g / L. Then, 100 mg / L of sodium dodecyl sulfate (manufactured by Kao Corporation, EMAL (registered trademark)) as an anionic surfactant and 4 g / L of Mg sulfate as an alkaline earth salt in terms of Mg concentration were added, and finally the pH was adjusted to 1, whereby the plating solution was prepared. Note that the chlorine concentration of the PtRu alloy plating solution was 0.5 mg / L.

[0044] In addition, in the present embodiment, a Pt plating film was also formed using a Pt plating solution for comparison. The Pt plating solution contains 10 g / L of the same Pt salt as described above, does not contain a Ru salt, and has the same composition as the present embodiment except for this.

[0045] Then, PtRu alloy plating films and Pt plating films were formed using the above PtRu alloy plating solution and Pt plating solution. In this embodiment, as substrates, a Cu plate (20 mm x 40 mm x 0.1 mm) and a multilayer substrate (Cu / Ni / Au) on which Ni (thickness 3.0 μm) / Au (thickness 0.1 μm) were plated were prepared, and plating films were formed for each of them. The plating conditions were set to be: bath temperature 60°C, current density 4.0 A / dm2, and plating time 30 minutes to 60 minutes. 2 The plating time was adjusted to be 30 minutes to 60 minutes with a target film thickness of 5 μm.

[0046] After the plating treatment, the composition of the formed PtRu alloy plating film was analyzed (Ru concentration measurement) using EDX. Then, the hardness of each plating film was measured. For the hardness measurement, Vickers hardness (Hv) was measured using a Vickers hardness tester with a load of 10 g.

[0047] In addition, in order to confirm the corrosion resistance of the formed PtRu alloy plating film, electrolytic cycle tests were performed on the samples after the film formation. The conditions of the electrolytic cycle test were that each sample was applied with a voltage of 5 V for 30 seconds in a 5 mass% sodium chloride solution (temperature: room temperature), and this was repeated as one cycle. Then, the corrosion resistance was evaluated in terms of the number of cycles until the substrate was exposed, and the maximum was counted to be 200 cycles. These evaluation results are shown in Table 1.

[0048]

[0049] It was confirmed from Table 1 that the Ru ratio of the PtRu alloy plating film (No. 1 to No. 5) formed in this embodiment increased as the Ru concentration of the plating solution increased, and was composed of a PtRu alloy of 3 mass% to 12.3 mass%. The hardness of the PtRu alloy plating film was 450 Hv or more on any substrate. Also, it was confirmed that the PtRu alloy plating film (No. 1 to 5) formed in this embodiment had a high hardness compared to the Pt plating film (No. 6) in which Ru was not alloyed.

[0050] In addition, the hardness of the PtRu alloy plating film substantially increased as the Ru concentration increased. Also, a Vickers hardness of 760 Hv or more was exhibited in the multilayer substrate. In addition, none of the PtRu alloy plating films had cracks, and the corrosion resistance was good. Furthermore, a uniform metallic luster was exhibited, and the appearance was also good.

[0051] Note that, for the PtRu alloy plating film formed in this embodiment, XRD analysis was performed after the film formation to measure the average crystallite diameter (Scherrer constant: 0.94). The average crystallite diameter of the PtRu alloy film of No. 1 to No. 5 of this embodiment was 50 nm or more. within the range of 0.1 to 0.5.

[0052] [Industrial Applicability]

[0053] As described above, the PtRu alloy plating film according to the present application is composed of a PtRu alloy having high hardness, and is also excellent in corrosion resistance. The present application is useful not only for a protective plating layer of electronic devices such as connectors and terminals of smartphones, tablet terminals, and the like, but also for forming a plating film on jewelry and the like.

[0054] [Explanation of Symbols]

[0055] 10 substrate

[0056] 11 intermediate layer

[0057] 11a first intermediate layer

[0058] 11b second intermediate layer

[0059] 12 noble metal layer

Claims

1. A PtRu alloy plating film, which is produced by electroplating using a PtRu alloy plating solution, and is composed of a PtRu alloy, wherein the PtRu alloy is composed of 2 mass% or more and 20 mass% or less of Ru, the balance of Pt, and inevitable impurities, and the Vickers hardness is 450 Hv or more and less than 750 Hv.

2. A laminated structure comprising: a base material, at least one intermediate layer formed on at least a part of the surface of the base material, and a noble metal layer formed on the intermediate layer, the noble metal layer being composed of the PtRu alloy plating film according to claim 1. The average crystallite diameter of the PtRu alloy is The above In the following, 3. The laminated structure according to claim 2, wherein the intermediate layer is composed of any one of a pure metal or an alloy of Ni, Cr, Mn, Fe, Co, Cu, Au, Ag, Pd, Pt, and W.

4. The laminated structure according to claim 2, wherein the base material is composed of any one of Cu or a Cu alloy, and Fe or an Fe alloy.

5. A connector or a terminal having the laminated structure according to claim 2. ​ ​ ​ ​ ​ ​ ​

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