Terminal material and electrical connection terminal

Abstract

To provide a terminal material and an electrical connection terminal which have an Ag coating layer having improved wear resistance due to addition of an additive and in which corrosion is suppressed.SOLUTION: A terminal material 1 includes: a base material 11; a strike layer 13 that is configured from Ag or an Ag alloy, the strike layer covering a surface of the base material 11; an intermediate layer 14 that is configured from Ag or an Ag alloy, the intermediate layer being in contact with a surface of the strike layer 13 and covering the surface of the strike layer 13; and a surface layer 15 that contains Ag and at least one of a sulfur-containing organic compound and a carbon material, the surface layer being in contact with a surface of the intermediate layer 14 and covering the surface of the intermediate layer 14. The purity of Ag in each of the strike layer 13 and the intermediate layer 14 is higher than the purity of Ag in the surface layer 15, and the intermediate layer 14 is thicker than the strike layer 13. Also, an electrical connection terminal is constituted by including the terminal material 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a terminal material and an electrical connection terminal. [Background technology]

[0002] In automobiles, electrical connection terminals with a surface coating of Ag are often used for applications such as high current. While terminals with a surface coating of Ag have excellent heat resistance, corrosion resistance, and electrical conductivity, Ag is soft and prone to adhesion, making the surface susceptible to wear during sliding. Therefore, one method of utilizing Ag's excellent properties, such as heat resistance and electrical conductivity, while suppressing wear is to incorporate additive elements such as Se into the Ag coating layer to increase its hardness and create a hard silver layer.

[0003] However, converting the Ag coating layer on the terminal surface into a hard silver layer by adding an additive element such as Se may not sufficiently improve wear resistance. For example, as terminals become larger in current, a high contact load must be applied to the electrical contacts. However, when such a high contact load is applied to slide the electrical contacts, conventional hard silver layers may not be able to fully meet the required wear resistance. In such cases, applying an Ag coating layer with better wear resistance than conventional hard silver layers to the surface of the terminal is considered. For example, Patent Document 1 discloses the production of a silver-plated product by forming a silver surface layer on a base material using a silver plating solution containing benzothiazoles or their derivatives. This method is described as producing a silver-plated product with better wear resistance than conventional products. Furthermore, Patent Document 2 discloses a metal part having a substrate coated with an Ag-graphene composite plating film, in which the graphene dispersed in the Ag-graphene composite plating film has a specific size, content, and orientation. This method is described as achieving both improved conductivity and improved wear resistance for the silver plating film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-048977 [Patent Document 2] Japanese Patent Publication No. 2022-170877 Summary of the Invention [Problem to be solved by the invention]

[0005] As disclosed in Patent Documents 1 and 2, the wear resistance of an Ag coating layer on an electrical connection terminal can be improved by adding an additive made of an organic compound or a carbon material such as graphene to the Ag coating layer. However, corrosion of the terminal material can be a problem when using such an additive-added Ag coating layer. As corrosion of the terminal material progresses, the surface contact resistance increases, making it difficult to form and maintain a stable electrical connection at the electrical contacts of the electrical connection terminal. Corrosion of terminal materials with Ag coating layers can occur when the electrical connection terminal is exposed to high-temperature and high-humidity environments during transportation or use, or when it comes into contact with corrosive substances such as electrolyte solutions and corrosive gases. In addition to having high wear resistance, terminal materials with Ag coating layers are desired to have enhanced corrosion resistance so that they can maintain low contact resistance even when exposed to corrosion-prone environments such as high-temperature and high-humidity environments and contact with corrosive substances.

[0006] In view of the above, an object of the present invention is to provide a terminal material and an electrical connection terminal having an Ag coating layer with enhanced wear resistance due to the addition of an additive, and which are corrosion-resistant. [Means for solving the problem]

[0007] The terminal material of the present disclosure comprises a substrate, a strike layer made of Ag or an Ag alloy and covering the surface of the substrate, an intermediate layer made of Ag or an Ag alloy and in contact with the surface of the strike layer and covering the surface of the strike layer, and a surface layer containing Ag and at least one of a sulfur-containing organic compound and a carbon material and in contact with the surface of the intermediate layer and covering the surface of the intermediate layer, wherein the strike layer and the intermediate layer have a higher Ag purity than the surface layer, and the intermediate layer is thicker than the strike layer.

[0008] The electrical connection terminal of the present disclosure is constructed including the terminal material, and at least in the electrical contact portion that comes into contact with the opposing conductive member, the strike layer, the intermediate layer, and the surface layer are formed on the surface of the substrate. [Effects of the Invention]

[0009] The terminal material and electrical connection terminal of the present disclosure are terminal materials and electrical connection terminals having an Ag coating layer with enhanced wear resistance due to the addition of an additive, and are therefore corrosion-resistant. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating the configuration of a terminal material according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view showing the structure of an electrical connection terminal according to one embodiment of the present disclosure. [Figure 3] 3A and 3B are electron microscope images of a cross section of the terminal material. Fig. 3A is a low-magnification image, and Fig. 3B is a high-magnification image of the area near the intermediate layer in Fig. 3A. [Figure 4] Figures 4A and 4B show the relationship between the thickness of the intermediate layer and contact resistance in a corrosion test when a sulfur-containing organic compound is added to the surface layer. Figure 4A shows the case where a salt spray was used as the corrosion test, and Figure 4B shows the case where a four-component gas mixture was used. Each shows data before and after the corrosion test. [Figure 5]Figures 5A and 5B show the relationship between the thickness of the intermediate layer and contact resistance in a corrosion test when graphite is added to the surface layer. Figure 5A shows the case where a salt spray was used as the corrosion test, and Figure 5B shows the case where contact was made with a four-component gas mixture. Each shows data before and after the corrosion test. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Description of the embodiments of the present disclosure] First, an embodiment of the present disclosure will be described.

[0012] [1] The terminal material disclosed herein comprises a substrate, a strike layer made of Ag or an Ag alloy and covering the surface of the substrate, an intermediate layer made of Ag or an Ag alloy and in contact with the surface of the strike layer and covering the surface of the strike layer, and a surface layer containing Ag and at least one of a sulfur-containing organic compound and a carbon material and in contact with the surface of the intermediate layer and covering the surface of the intermediate layer, wherein the strike layer and the intermediate layer have a higher Ag purity than the surface layer, and the intermediate layer is thicker than the strike layer.

[0013] In the terminal material, the Ag-containing surface layer contains at least one of a sulfur-containing organic compound and a carbon material as an additive. This gives the surface layer high wear resistance. An intermediate layer with a high Ag purity and a thickness greater than the strike layer is formed between the surface layer and the strike layer. The presence of this intermediate layer makes the terminal material less susceptible to corrosion, even when placed in a corrosive environment.

[0014] [2] In the above aspect [1], the average grain size of the crystal grains constituting the intermediate layer may be greater than the thickness of the strike layer. In this case, the strike layer is formed thin enough to effectively enhance the adhesion of the intermediate layer and the surface layer to the substrate, and the intermediate layer is formed thick enough to easily provide a terminal material that is excellent in corrosion prevention.

[0015] [3] In the above-mentioned aspects [1] or [2], the average grain size of the crystal grains constituting the intermediate layer may be larger than the average grain size of the crystal grains constituting the strike layer. In this case, too, the strike layer is formed thin enough to effectively enhance the adhesion of the intermediate layer and the surface layer to the substrate, and the intermediate layer is formed thick enough to easily provide a terminal material that exhibits excellent corrosion suppression effects.

[0016] [4] In any one of the above aspects [1] to [3], the thickness of the intermediate layer may be 0.4 μm or more and 3.0 μm or less, in which case the intermediate layer is highly effective in suppressing corrosion of the terminal material against both liquid corrosive substances such as salt water and gaseous corrosive substances such as SO2, H2S, NO2, and Cl2.

[0017] [5] In any one of the above aspects [1] to [4], the substrate may be made of Cu or a Cu alloy, and the terminal material may further have a base layer made of Ni or a Ni alloy between the substrate and the strike layer. Materials in which a base layer of Ni or a Ni alloy is provided on the surface of a Cu or Cu substrate are widely used as base materials for terminal materials, but by forming a strike layer and an intermediate layer on the surface of the base material and then forming a surface layer, a terminal material can be obtained in which the layers have excellent adhesion to the base material and the surface layer is minimally affected by corrosion and other changes.

[0018] [6] The electrical connection terminal of the present disclosure is configured to include any one of the terminal materials [1] to [5] above, and at least in the electrical contact portion that comes into contact with the mating conductive member, the strike layer, the intermediate layer, and the surface layer are formed on the surface of the substrate. This electrical connection terminal is configured to include the terminal material having a surface layer with excellent wear resistance and in which corrosion is suppressed by the contribution of the intermediate layer, so that the electrical contact portion has high wear resistance and is less likely to corrode even when transported or used in a corrosive environment.

[0019] [Details of the embodiments of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0020] <Terminal material> A terminal material according to an embodiment of the present disclosure will be described below. A cross section of a terminal material 1 according to an embodiment of the present disclosure is shown schematically in FIG.

[0021] (Outline of terminal material composition) The terminal material 1 has a substrate 11 and a plurality of metal coating layers that coat the surface of the substrate 11. The coating layers include, from the substrate 11 side, an underlayer 12, a strike layer 13, an intermediate layer 14, and a surface layer 15. Of these, the underlayer 12 is provided optionally. The strike layer 13, the intermediate layer 14, and the surface layer 15 are each composed of a layer whose main component is Ag (a layer containing 50% or more by mass of Ag).

[0022] The substrate 11 is formed as a metal plate. The type of metal forming the substrate 11 is not particularly limited, and various metal materials generally applicable as substrates for electrical connection members such as terminals can be used. Preferably, the substrate 11 is formed of Cu or a Cu alloy, which is commonly used as a substrate for terminals.

[0023] The underlayer 12 is an optional layer. However, when the substrate 11 is made of Cu or a Cu alloy, it is preferable to provide the underlayer 12 made of Ni or a Ni alloy between the substrate 11 and the strike layer 13, in contact with the surface of the substrate 11. The underlayer 12 enhances the adhesion of the strike layer 13, intermediate layer 14, and surface layer 15 to the substrate 11 and also serves to prevent the diffusion of constituent elements of the substrate 11, such as Cu, into the strike layer 13, intermediate layer 14, and surface layer 15. If the constituent elements of the substrate 11 diffuse into these upper layers and reach the surface of the surface layer 15, they may be oxidized, potentially increasing the contact resistance of the surface layer 15. However, the provision of the underlayer 12, in addition to the corrosion-inhibiting effect of the intermediate layer 14 (described later), effectively prevents deterioration of the surface layer 15. The thickness of the underlayer 12 can be, for example, in the range of 0.5 μm to 10 μm.

[0024] The strike layer 13 is a layer that covers the surface of the substrate 11 via the underlayer 12. The strike layer 13 is composed of Ag or an Ag alloy and has a higher Ag purity than the surface layer 15. Preferably, the strike layer 13 has an Ag purity of 99.0% by mass or more, and even 99.5% by mass or more. The strike layer 13 may contain only Ag and unavoidable impurities, or may contain, in addition to Ag and unavoidable impurities, an additive element that acts to harden the Ag layer. Examples of such additive elements include Se, Sb, C, N, and S.

[0025] The thickness of the strike layer 13 is smaller than the thickness of the intermediate layer 14. The specific thickness of the strike layer 13 is not particularly limited, but a range of 0.01 μm or more and 0.1 μm or less can be exemplified as a suitable thickness. The strike layer 13 serves to enhance the adhesion of the intermediate layer 14 and the surface layer 15 to the substrate 11 and the underlayer 12. In particular, when the strike layer 13 is provided on the surface of the underlayer 12 made of Ni or a Ni alloy, the strike layer 13 is formed in close contact with the surface of the underlayer 12 while reducing Ni oxide on the surface of the underlayer 12.

[0026] The intermediate layer 14 is a layer that contacts the surface of the strike layer 13 and covers the surface of the strike layer 13. The intermediate layer 14 is composed of Ag or an Ag alloy and has a higher Ag purity than the surface layer 15. Like the strike layer 13, the intermediate layer 14 also preferably has an Ag purity of 99.0% by mass or more, and even 99.5% by mass or more. The intermediate layer 14 may contain only Ag and unavoidable impurities, but may also contain an additive element that hardens the Ag layer in addition to Ag and unavoidable impurities. Examples of such additive elements include Se, Sb, C, N, and S.

[0027] The thickness of the intermediate layer 14 is greater than the thickness of the strike layer 13. The specific thickness of the intermediate layer 14 is not particularly limited, but a range of 0.2 μm or more and 3.0 μm or less can be exemplified as a suitable example. As will be explained in detail later, providing the intermediate layer 14 can suppress corrosion of the terminal material 1 and improve the corrosion resistance of the terminal material 1.

[0028] The surface layer 15 is a layer that contacts the surface of the intermediate layer 14 and coats the surface of the intermediate layer 14. The surface layer 15 contains Ag and an additive. The additive contains at least one of a sulfur-containing organic compound and a carbon material. The type of sulfur-containing organic compound is not particularly limited, but suitable examples include sulfur-containing polymers such as benzothiazoles, thiols, sulfides, disulfides, and sulfonated anionic polymers, as well as derivatives thereof. The sulfur-containing organic compound may be used alone or in combination of two or more. The type of carbon material is also not particularly limited, and graphite, graphene, carbon fiber, fullerene, carbon nanotubes, etc. can be used. Graphite is particularly preferred. The carbon material may also be used alone or in combination of two or more. The surface layer 15 is preferably composed only of Ag and the additive, excluding unavoidable impurities, but may also contain metal elements other than Ag as long as their amount is less than that of Ag.

[0029] In the terminal material 1 according to this embodiment, a strike layer 13, an intermediate layer 14, and a surface layer 15 are formed in this order on the surface of a substrate 11. As long as the strike layer 13 and the intermediate layer 14, and the intermediate layer 14 and the surface layer 15, are in direct contact with each other, other layers may be included, including an underlayer 12. The surface layer 15 is preferably exposed on the outermost surface of the terminal material 1, but a thin film such as an organic layer (not shown) may be provided on the surface of the surface layer 15 as long as it does not significantly affect the properties of the surface layer 15.

[0030] (Surface details) In the surface layer 15, the sulfur-containing organic compound and the carbon material serve to improve the wear resistance of the surface layer 15. That is, when an electrical contact made of the terminal material 1 according to this embodiment is brought into contact with another electrical contact (including one made of the terminal material 1) and the electrical contacts are caused to slide against each other, the sulfur-containing organic compound and the carbon material suppress adhesion between the two electrical contacts. The surface layer 15 also contributes to maintaining a low coefficient of friction between the two electrical contacts. The effects of improving the wear resistance and reducing the coefficient of friction are mainly achieved by increasing the hardness of the surface layer 15 due to the refinement of Ag crystals and by reducing the Ag concentration in the surface layer 15. The sulfur-containing organic compound and the carbon material can be contained in the surface layer 15 by adding them to a plating solution used when forming the surface layer 15 by plating. The sulfur-containing organic compound and carbon material contained in the surface layer 15 in this manner often maintain the molecular structure of the sulfur-containing organic compound and the skeletal structure of the carbon material even within the surface layer 15. However, even when at least a part of the molecular structure of the sulfur-containing organic compound or the skeletal structure of the carbon material has changed or disappeared, the sulfur-containing organic compound and the carbon material are still considered to be contained in the surface layer 15.

[0031] The content of the additive in the surface layer 15 is not particularly limited, but the purity of Ag in the surface layer 15 is preferably 99.5% by mass or less, and more preferably 99.4% by mass or less. Furthermore, when the additive is a sulfur-containing organic compound, the purity of Ag is preferably 99.0% by mass or less, and even more preferably 98.5% by mass or less. In this way, by containing a sufficient amount of additive in the surface layer 15, the effects of improving wear resistance and reducing the friction coefficient can be significantly achieved. On the other hand, the purity of Ag in the surface layer 15 is preferably 97.0% by mass or more, and even more preferably 98.0% by mass or more. Furthermore, when the additive is made of a carbon material, the purity of Ag is preferably 99.0% by mass or more. In this way, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and electrical conductivity, can be fully utilized as properties of the surface layer 15.

[0032] The thickness of the surface layer 15 is not particularly limited, but may be, for example, 0.5 μm or more and 10 μm or less. Forming the surface layer 15 to a thickness of 0.5 μm or more can enhance the effect of improving wear resistance. It is more preferable that the thickness of the surface layer 15 be 1.0 μm or more. On the other hand, by limiting the thickness of the surface layer 15 to 10 μm or less, the corrosion inhibition effect of the intermediate layer 14, which will be described next, can be enhanced. It is more preferable that the thickness of the surface layer 15 be 5.0 μm or less.

[0033] (Details of the middle layer) In the terminal material 1 according to this embodiment, the intermediate layer 14 is provided between the strike layer 13 and the surface layer 15, thereby enhancing the corrosion resistance of the terminal material 1. The surface layer 15 contains an additive composed of at least one of a sulfur-containing organic compound and a carbon material, thereby providing high abrasion resistance. However, the presence of these additives and a low Ag purity make the terminal material 1 more susceptible to corrosion than a material without these additives. However, the provision of the intermediate layer 14 below the surface layer 15 reduces corrosion of the terminal material 1. This is believed to be because the dense crystals of the intermediate layer 14 make it less permeable to corrosive substances, particularly liquid corrosive substances, thereby preventing contact between the substrate 11 and the underlayer 12 and the corrosive substances, thereby preventing the formation of corrosive products in the substrate 11 and the underlayer 12. Electrical connection terminals formed from the terminal material 1 may be placed in environments prone to corrosion, such as high temperature, high humidity, or contact with corrosive substances, during transportation or use. However, the presence of the intermediate layer 14 prevents corrosion of the terminal material 1 even in such environments. By suppressing corrosion of the terminal material 1, the contact resistance on the surface of the surface layer 15 is maintained low, making it possible to form a good electrical connection on the surface of the surface layer 15 and further maintain that electrical connection stably.

[0034] In particular, a thickness of 0.2 μm or greater for the intermediate layer 14 can effectively suppress corrosion of the terminal material 1 caused by liquid corrosive substances, such as electrolyte solutions including salt water, and the resulting increase in contact resistance. This is believed to be because a thicker intermediate layer 14 can effectively suppress contact between the substrate 11 and the underlayer 12 and the corrosive substances. A thickness of 0.4 μm or greater, such as 1.0 μm or greater, or even 2.0 μm or greater is more preferable. On the other hand, a thickness of 3.0 μm or less for the intermediate layer 14 can effectively suppress corrosion of the terminal material 1 caused by gaseous corrosive substances, such as sulfur dioxide (SO2), hydrogen sulfide (HS), nitrogen dioxide (NO2), and chlorine (Cl2), which constitute the four-component gas mixture used in the examples, and the resulting increase in contact resistance. This is thought to be because, by not making the intermediate layer 14 too thick, gaseous corrosive substances can easily penetrate to the base layer 12 and substrate 11 without remaining in the surface layer 15 or intermediate layer 14, effectively suppressing the formation of a corrosion film on the surface layer 15. Setting the thickness of the intermediate layer 14 to 0.2 μm or more and 3.0 μm or less effectively suppresses the increase in contact resistance of the terminal material 1 due to corrosion by both liquid and gaseous corrosive substances. For example, the contact resistance values ​​after the salt spray test and gas contact test under the conditions shown in the examples can be suppressed to 0.2 mΩ or less. Furthermore, forming the intermediate layer 14 to a thickness of 0.2 μm or more, particularly 0.4 μm or more, significantly improves the wear resistance of the surface of the surface layer 15 and reduces the friction coefficient.

[0035] As shown in the examples below, the effect of inhibiting corrosion of the terminal material 1 by a liquid corrosive substance is sufficiently high when the thickness of the intermediate layer 14 is 0.4 μm, and the effect is not significantly improved even if the thickness of the intermediate layer 14 is made thicker. Therefore, from the viewpoint of reducing the material cost required for the intermediate layer 14 and improving the processability of the terminal material 1, it is preferable to keep the thickness of the intermediate layer 14 within a small range, not less than 0.4 μm and not more than 3.0 μm. For example, it is preferable to set the thickness of the intermediate layer 14 to be not less than 0.4 μm and not more than 1.0 μm.

[0036] Both the intermediate layer 14 and the strike layer 13 are composed of Ag or Ag alloy layers with a higher Ag purity than the surface layer 15. The intermediate layer 14 and the strike layer 13 may have the same composition. However, the intermediate layer 14 and the strike layer 13 are formed independently through separate plating processes. That is, the strike layer 13 is formed first, and then the intermediate layer 14 is formed on the surface of the strike layer 13. Therefore, as shown in FIG. 3B, in many cases, a clear interface can be confirmed at the boundary between the strike layer 13 and the intermediate layer 14 through electron microscope observation. The strike layer 13 is a thin layer formed to improve adhesion between the lower and upper layers. To enhance its functionality, it is formed at a low speed using a plating solution with a low Ag concentration. In contrast, the intermediate layer 14 is suitably formed at a relatively high speed to ensure a certain thickness. Differences in the plating conditions often result in differences in the structure of the strike layer 13 and the intermediate layer 14.

[0037] As shown in Figures 3A and 3B, the intermediate layer 14 is composed of a structure containing relatively large crystal grains, while the strike layer 13 is less likely to have such large crystal grains. Therefore, the average grain size of the crystal grains constituting the intermediate layer 14 tends to be larger than the average grain size of the crystal grains constituting the strike layer 13. This also includes cases where the strike layer 13 does not have crystal grains large enough to be recognized by an electron microscope. Furthermore, the average grain size of the crystal grains in the intermediate layer 14 tends to be larger than the thickness of the strike layer 13. The average grain size of the crystal grains in the intermediate layer 14 is not particularly limited, but can be in the range of 0.1 µm or more and 0.5 µm or less. The average grain size of the crystal grains in the strike layer 13 can be, for example, 0.1 µm or less.

[0038] <Electrical connection terminal> An electrical connection terminal according to one embodiment of the present disclosure includes the terminal material 1 according to the embodiment of the present disclosure described above. In the electrical connection terminal, the laminated structure of the strike layer 13, intermediate layer 14, and surface layer 15 is formed at least in the electrical contact portion that comes into contact with a mating conductive member, such as a mating electrical connection terminal. The strike layer 13, intermediate layer 14, and surface layer 15 (and base layer 12) may be formed over the entire surface of the electrical connection terminal or only in a partial region including the electrical contact portion, as long as they are formed at least in the electrical contact portion.

[0039] While the specific type and shape of the electrical connection terminal are not particularly limited, FIG. 2 illustrates an example in which the electrical connection terminal is a mating-type male terminal 2. The male terminal 2 has a shape similar to that of a known mating-type male terminal. That is, the male terminal 2 has a terminal connection portion 21 at the front and a wire connection portion 22 at the rear. The terminal connection portion 21 is the portion electrically connected to the mating female terminal and has a flat tab-like structure. The terminal connection portion 21 of the male terminal 2 is inserted from the tip side into the box-shaped interior of a female terminal having a box-shaped terminal connection portion, thereby mating and connecting the male terminal 2 and the female terminal. In the male terminal 2, an electric wire is electrically and physically connected to the wire connection portion 22. In the male terminal 2, a strike layer 13, an intermediate layer 14, and a surface layer 15 are formed on at least the surface of the terminal connection portion 21, together with an appropriate base layer 12. Preferably, the entire male terminal 2 is made of the terminal material 1 having these coating layers.

[0040] In this structure, the surface layer 15 is exposed on the outermost surface of the terminal connection portion 21 of the male terminal 2. As a result, when the terminal connection portion 21 of the male terminal 2 is inserted into the box-shaped terminal connection portion of the female terminal with sliding to form an electrical connection, the surface layer 15 improves the wear resistance at the contact point between the male terminal 2 and the female terminal, resulting in high wear resistance. The coefficient of friction during sliding is also kept low. Furthermore, the presence of the intermediate layer 14 maintains low contact resistance of the terminal material 1 even in a corrosive environment, thereby forming and maintaining a good electrical connection between the male terminal 2 and the female terminal. Note that the mating female terminal may be made of the terminal material 1 according to an embodiment of the present disclosure having the above-mentioned coating layers, as with the male terminal 2, or may be made of another metal material. An example of another metal material is a material formed by exposing a high-purity Ag layer on the outermost surface, as with the intermediate layer 14. [Example]

[0041] Examples are shown below. However, the present invention is not limited to these examples. Here, the corrosion inhibition effect of the intermediate layer in the terminal material was verified. Unless otherwise specified, the preparation and evaluation of samples were carried out at room temperature in the atmosphere.

[0042] <Sample preparation> A 1.0 μm thick Ni layer was formed as an underlayer on the surface of a clean Cu alloy substrate by electroplating. Next, an Ag strike layer was formed on the surface of the Ni layer by electroplating. The Ag strike layer had a thickness of 0.1 μm or less and an Ag purity of 99.9 mass%. Furthermore, an Ag intermediate layer was formed on the surface of the Ag strike layer by electroplating. In Samples 1 to 5 and 7, the thickness of the intermediate layer was as shown in Table 1 below. In Sample 6, no intermediate layer was formed.

[0043] Next, a surface layer was formed by electroplating on the surface of the intermediate layer for Samples 1 to 5 and 7, and on the surface of the strike layer for Sample 6. For Samples 1 to 5, DuPont's "SILVERON GT-210 Durability Silver," a plating solution containing a sulfur-containing organic compound, was used. For Samples 6 and 7, Umicore's "ARGUNA C-100," a plating solution containing graphite, was used. The thickness of the surface layer was as shown in Table 1 below. "SILVERON" and "ARGUNA" are registered trademarks.

[0044] Additionally, samples 1a to 1c were prepared with intermediate layer thicknesses between those of Sample 1 (0.2 μm) and Sample 3 (1.0 μm). The intermediate layer thickness was 0.4 μm for Sample 1a, 0.6 μm for Sample 1b, and 0.8 μm for Sample 1c. For Samples 1a to 1c, the conditions other than the intermediate layer thickness, such as the raw materials used and manufacturing method, were the same as those for Samples 1 and 3 to 5, including the surface layer thickness (1.0 μm).

[0045] <Evaluation method> (1) Confirmation of the laminated structure The cross-sectional state of Samples 1 to 6 was observed using a scanning electron microscope (SEM), and it was confirmed that a laminated structure consisting of an underlayer, a strike layer, an intermediate layer (except for Sample 6), and a surface layer was formed.

[0046] (2) Confirmation of the composition of the intermediate and surface layers The component compositions of the intermediate layer and surface layer were confirmed for Samples 1 to 6. Specifically, the element contents in the intermediate layer and surface layer were analyzed using a glow discharge optical emission spectrometer (GD-OES). Confirmation of the surface layer of Sample 2 was omitted.

[0047] (3) Evaluation of corrosion behavior The corrosion behavior of samples 1 to 6 and samples 1a to 1c was evaluated using the contact resistance on the surface of the surface layer as an index. Contact resistance was measured by bringing an embossed contact point with a radius of 3.0 mm formed on each sample into contact with each flat plate-shaped sample. For the measurement, the embossed contact point was brought into contact with the surface of the surface layer of each sample plate at its top, and contact resistance was measured using the four-terminal method while applying a contact load of 30 N. The open-circuit voltage was 20 mV and the applied current was 10 mA.

[0048] The above contact resistance measurements were performed on each sample in its initial state before the corrosion test and in its state after the corrosion test. The corrosion tests included a salt spray test and a gas contact test. The salt spray test was performed in accordance with JIS Z 2371, as specified in JASO D616:2021 6.28. Specifically, each sample was sprayed with neutral salt water at 35°C for 96 hours. After the salt spray test, the samples were then left in a thermostatic chamber at 85°C and 95% RH for 96 hours. The gas contact test was performed in accordance with "Test Method 4" specified in JIS C 5402-11-7. Specifically, a gas flow of a four-component mixed gas, in which 0.2 ppm SO2, 0.01 ppm H2S, 0.2 ppm NO2, and 0.01 ppm Cl2 were added to air, was circulated through a test tank containing each sample for 96 hours at a temperature of 25°C and a humidity of 75% RH.

[0049] <Test Results> Table 1 below shows the types of additives added to the surface layer, the thicknesses of the surface layer and intermediate layer, and the analysis results of the component compositions of the surface layer and intermediate layer for Samples 1 to 7.

[0050] [Table 1]

[0051] According to Table 1, it is confirmed that the intermediate layer has a high Ag purity of 99.9 mass% in all samples. On the other hand, regarding the surface layer, a coating layer with low Ag purity containing C and S is formed in samples 1 to 5, reflecting the addition of sulfur-containing organic compounds. Furthermore, in samples 6 and 7, a coating layer with low Ag purity containing C is formed, reflecting the addition of graphite.

[0052] Figures 3A and 3B show representative SEM images of the cross section of sample 3. Figure 3A is a low-magnification image, and Figure 3B is a high-magnification image of the vicinity of the intermediate layer (14) in Figure 3A. As shown in Figure 3A, the underlayer (12), intermediate layer (14), and surface layer (15) are layered on the surface of the substrate (11). Furthermore, Figure 3B confirms that a thin strike layer (13) is formed between the underlayer (12) and intermediate layer (14). A clear interface exists between the intermediate layer (14) and the surface layer (15). The strike layer (13) and intermediate layer (14) are also observed as layers with different structures, and a clear interface can be seen between the two layers. The strike layer does not contain crystal grains large enough to be seen with an SEM and is observed to be light gray overall, whereas the intermediate layer contains crystal grains ranging in size from several hundred nanometers to several micrometers. In each sample, including sample 3, the average grain size of the crystal grains making up the intermediate layer was 0.14 μm or more and 0.32 μm or less. As no clear crystal grains were observed in the SEM images of the strike layer, it was determined that the average grain size was 0.1 μm or less.

[0053] Next, Figures 4A to 5B show the results of evaluating the corrosion behavior of terminal materials using contact resistance as an index. Figures 4A and 4B show the results for Samples 1 to 5 and Samples 1a to 1c, which have a sulfur-containing organic compound added to the surface layer, and Figures 5A and 5B show the results for Samples 6 and 7, which have a graphite added to the surface layer. Figures 4A and 5A show the results for a salt spray corrosion test, and Figures 4B and 5B show the results for a gas contact corrosion test. Each figure shows the relationship between the thickness of the intermediate layer and the contact resistance value. The gray shapes show the measurement results before the corrosion test, and the black shapes show the measurement results after the corrosion test. In Figures 4A and 4B, the circles indicate the case where the surface layer thickness is 1.0 μm, and the squares indicate the case where the surface layer thickness is 5.0 μm.

[0054] First, let's examine the results of adding graphite to the surface layer in Figures 5A and 5B. Compared to when no intermediate layer was provided (thickness 0 μm), when an intermediate layer was provided (thickness 1.0 μm), the contact resistance before the corrosion test was slightly higher, but the contact resistance after the corrosion test was significantly lower. In both the salt spray test in Figure 5A and the gas contact test in Figure 5B, the provision of an intermediate layer reduced the contact resistance after the corrosion test to less than one-third. These results confirm that the provision of an intermediate layer can suppress the increase in contact resistance due to corrosion in terminal materials.

[0055] Next, we examine the effect of intermediate layer thickness based on the data for the case in which a sulfur-containing organic compound was added to the surface layer (Figures 4A and 4B). The salt spray test results (Figure 4A) show that contact resistance after the corrosion test is particularly low, below 0.2 mΩ, when the intermediate layer thickness is 0.4 μm or greater. On the other hand, the gas contact test results (Figure 4B) show that contact resistance after the corrosion test is particularly low, below 0.2 mΩ, when the intermediate layer thickness is 3.0 μm or less. This indicates that an intermediate layer thickness of 0.4 μm to 3.0 μm can effectively suppress the increase in contact resistance due to corrosion of the terminal material against both liquid and gaseous corrosive substances. For both liquid and gaseous corrosive substances, no significant change in contact resistance was observed when the intermediate layer thickness was between 0.4 μm and 3.0 μm. Furthermore, particularly in gas contact tests, it was confirmed that the intermediate layer was highly effective in suppressing corrosion of the terminal material and the resulting increase in contact resistance, even when the thickness of the surface layer increased from 1.0 μm to 5.0 μm.

[0056] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0057] 1 Terminal material 11 Base material 12 Base layer 13 Strike Level 14 Middle Class 15 Surface layer 2 Male terminals (electrical connection terminals) 21 Terminal connection part 22 Wire connection

Claims

1. A substrate; a strike layer made of Ag or an Ag alloy and covering the surface of the substrate; an intermediate layer made of Ag or an Ag alloy and in contact with and covering the surface of the strike layer; a surface layer that contains Ag and at least one of a sulfur-containing organic compound and a carbon material, and that is in contact with the surface of the intermediate layer and covers the surface of the intermediate layer; the strike layer and the intermediate layer have a higher Ag purity than the surface layer; The intermediate layer is thicker than the strike layer.

2. The terminal material according to claim 1 , wherein the average grain size of the crystal grains constituting the intermediate layer is larger than the thickness of the strike layer.

3. The terminal material according to claim 1 , wherein the average grain size of the crystal grains constituting the intermediate layer is larger than the average grain size of the crystal grains constituting the strike layer.

4. The terminal material according to claim 1 , wherein the intermediate layer has a thickness of 0.4 μm or more and 3.0 μm or less.

5. the substrate is made of Cu or a Cu alloy; The terminal material according to claim 1 , further comprising an underlayer made of Ni or a Ni alloy between the substrate and the strike layer.

6. 6. An electrical connection terminal comprising the terminal material according to claim 1, wherein the strike layer, the intermediate layer, and the surface layer are formed on the surface of the substrate at least in an electrical contact portion that comes into contact with a mating conductive member.

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