Terminal material and electrical connection terminal

Abstract

Provided are a terminal material and an electrical connection terminal, both of which have an Ag coating layer with enhanced wear resistance through the addition of additives, and for which corrosion is suppressed.　A terminal material 1 comprises: a base material 11; a strike layer 13 which is composed of Ag or an Ag alloy and covers a surface of the base material 11; an intermediate layer 14 which is composed of Ag or an Ag alloy, contacts a surface of the strike layer 13, and covers such surface of the strike layer 13; and a surface layer 15 which includes Ag and at least one of a sulfur-containing organic compound and a carbon material, contacts a surface of the intermediate layer 14, and covers such surface of the intermediate layer 14. The strike layer 13 and the intermediate layer 14 have a higher purity of Ag than the surface layer 15, and the intermediate layer 14 is thicker than the strike layer 13. Also, the electric connection terminal is constituted by including the terminal material 1.

Description

Terminal materials and electrical connection terminals

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

[0002] In automobiles, electrical connection terminals with an Ag coating layer on the surface are sometimes used as electrical connection terminals for applications such as high current. Terminals with an Ag coating layer on the surface have excellent heat resistance, corrosion resistance, and conductivity. However, due to the soft nature of Ag and its tendency to adhere, the surface is prone to wear when subjected to sliding. Therefore, as one means of suppressing wear while utilizing the excellent properties of Ag, such as heat resistance and conductivity, a method of increasing the hardness of the Ag coating layer by adding an additive element such as Se to the Ag coating layer and forming a hard silver layer may be used.

[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, it is possible to apply an Ag coating layer with better wear resistance than conventional hard silver layers to the surface of the terminal. For example, Patent Document 1 discloses the production of a silver-plated product by forming a surface layer of silver on a base material using a silver plating solution containing benzothiazoles or their derivatives. This method is described as providing a silver-plated product with superior wear resistance compared to conventional methods. 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.

[0004] JP 2022-048977 A JP 2022-170877 A

[0005] As disclosed in Patent Documents 1 and 2, the wear resistance of 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, terminal materials having such additives and an Ag coating layer can sometimes suffer from corrosion. 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 having an Ag coating layer can occur when the electrical connection terminal is exposed to high temperature and humidity during transportation or use, or when the terminal comes into contact with corrosive substances such as electrolyte solutions or corrosive gases. In addition to having high wear resistance, terminal materials having an Ag coating layer 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 humidity or 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 that have an Ag coating layer with enhanced wear resistance due to the addition of an additive, and that are corrosion-resistant.

[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.

[0009] The terminal material and electrical connection terminal of the present disclosure have an Ag coating layer with increased wear resistance due to the addition of additives, and are therefore less susceptible to corrosion.

[0010] FIG. 1 is a cross-sectional view schematically illustrating the configuration of a terminal material according to an embodiment of the present disclosure. FIG. 2 is a perspective view illustrating the structure of an electrical connection terminal according to an embodiment of the present disclosure. FIGS. 3A and 3B are electron microscope images of a cross section of a terminal material. FIG. 3A is a low-magnification image, and FIG. 3B is a high-magnification image of the intermediate layer and its vicinity in FIG. 3A . FIGS. 4A and 4B are graphs illustrating the relationship between the thickness of the intermediate layer and the contact resistance in a corrosion test when a sulfur-containing organic compound is added to the surface layer. As corrosion tests, FIG. 4A shows the case where salt spray was performed, and FIG. 4B shows the case where contact with a four-type mixed gas was performed. Data before and after the corrosion test are shown, respectively. FIGS. 5A and 5B are graphs illustrating the relationship between the thickness of the intermediate layer and the contact resistance in a corrosion test when graphite is added to the surface layer. As corrosion tests, FIG. 5A shows the case where salt spray was performed, and FIG. 5B shows the case where contact with a four-type mixed gas was performed. Data before and after the corrosion test are shown, respectively.

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

[0012] [1] A terminal material according to 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.

[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 to be sufficiently thin, which is highly effective in increasing the adhesion of the intermediate layer and the surface layer to the substrate, and the intermediate layer is formed to be sufficiently thick, which tends to result in a terminal material that is excellent in inhibiting corrosion.

[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 to be sufficiently thin, which is highly effective in increasing the adhesion of the intermediate layer and the surface layer to the substrate, and the intermediate layer is formed to be sufficiently thick, which tends to result in a terminal material that is excellent in inhibiting corrosion.

[0016] [4] In any one of the above aspects [1] to [3], the thickness of the intermediate layer is preferably 0.4 μm or more and 3.0 μm or less. In this case, the intermediate layer is resistant to liquid corrosive substances such as salt water and SO ２ , H ２ S, NO ２ , Cl ２ It is highly effective in inhibiting corrosion of the terminal material against any of the gaseous corrosive substances such as ammonium nitrate, ...

[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 an electrical contact portion that comes into contact with a 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, thereby achieving high wear resistance in the electrical contact portion and being less susceptible to corrosion even when transported or used in a corrosive environment.

[0019] [Details of 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 the Configuration of the Terminal Material) 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, a base layer 12, a strike layer 13, an intermediate layer 14, and a surface layer 15. Of these, the base layer 12 is provided optionally. The strike layer 13, the intermediate layer 14, and the surface layer 15 are each configured as layers whose main component is Ag (layers containing 50% or more by mass of Ag).

[0022] The substrate 11 is formed as a metal plate. The type of metal constituting 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 a 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 inhibit 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 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, providing the underlayer 12, in addition to the corrosion-inhibiting effect of the intermediate layer 14 described below, effectively inhibits 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 hardens 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 oxides 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, or may contain, in addition to Ag and unavoidable impurities, an additive element that hardens the Ag layer. 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 described 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. may 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 content 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, and other layers may be included, including an underlayer 12, 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. The surface layer 15 is preferably exposed on the outermost surface of the terminal material 1, but a thin film (not shown), such as an organic layer, 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] (Details of the Surface Layer) 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 and slid against another electrical contact (including a case where the electrical contact is made of the terminal material 1 according to this embodiment), adhesion between the two electrical contacts is suppressed. 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 friction coefficient 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. In many cases, the sulfur-containing organic compound and the carbon material contained in the surface layer 15 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 it is preferable that the purity of Ag in the surface layer 15 be 99.5% by mass or less, and even 99.4% by mass or less. Furthermore, when the additive is a sulfur-containing organic compound, it is preferable that the purity of Ag be 99.0% by mass or less, and even 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 highly obtained. On the other hand, it is preferable that the purity of Ag in the surface layer 15 be 97.0% by mass or more, and even 98.0% by mass or more. Furthermore, when the additive is made of a carbon material, it is preferable that the purity of Ag be 99.0% by mass or more. In this way, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and 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 Intermediate 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 lower 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 thought to be because the crystals of the intermediate layer 14 tend to be dense, making them less permeable to corrosive substances, particularly liquid corrosive substances, thereby reducing contact between the substrate 11 and the underlayer 12 and the corrosive substances, thereby suppressing the generation of corrosive products in the substrate 11 and the underlayer 12. An electrical connection terminal formed from the terminal material 1 may be placed in an environment prone to corrosion, such as high temperature, high humidity, or contact with corrosive substances, during transportation or use, but the presence of the intermediate layer 14 can suppress corrosion of the terminal material 1 even in such an environment. By suppressing corrosion of the terminal material 1, the contact resistance of the surface of the surface layer 15 is maintained low, and a good electrical connection is formed on the surface of the surface layer 15, making it possible to stably maintain that good electrical connection.

[0034] In particular, if the thickness of the intermediate layer 14 is 0.2 μm or more, corrosion of the terminal material 1 caused by liquid corrosive substances such as electrolyte solutions including salt water, and an increase in contact resistance due to such corrosion, can be effectively suppressed. This is thought to be because thickening the intermediate layer 14 can effectively suppress contact between the substrate 11 and the underlayer 12 and the corrosive substances. More preferably, the thickness of the intermediate layer 14 is 0.4 μm or more, further 1.0 μm or more, or 2.0 μm or more. On the other hand, if the thickness of the intermediate layer 14 is 3.0 μm or less, the SO that constitutes the four-component mixed gas used in the examples can be effectively suppressed. ２ (sulfur dioxide), H ２ S (hydrogen sulfide), NO ２ (nitrogen dioxide), Cl ２Corrosion of the terminal material 1 caused by gaseous corrosive substances such as chlorine and an increase in contact resistance due to such corrosion can be effectively suppressed. This is thought to be because, by not making the intermediate layer 14 too thick, gaseous corrosive substances can easily permeate to the base layer 12 and the substrate 11 without remaining in the surface layer 15 or intermediate layer 14, thereby effectively suppressing the formation of a corrosion film on the surface layer 15. By setting the thickness of the intermediate layer 14 to 0.2 μm or more and 3.0 μm or less, an increase in contact resistance due to corrosion of the terminal material 1 caused by both liquid and gaseous corrosive substances can be effectively suppressed. 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, can effectively improve the wear resistance of the surface of the surface layer 15 and reduce the friction coefficient.

[0035] As shown in the examples below, the effect of suppressing 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 higher even if the thickness of the intermediate layer 14 is made thicker than that. Therefore, from the perspective 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, and 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 by separate plating processes, etc. 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 by 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, whereas 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 structural state 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 contain 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 examples of the average grain size include a 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 0.1 µm or less.

[0038] <Electrical Connection Terminal> An electrical connection terminal according to one embodiment of the present disclosure is configured to include 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 the 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 a portion electrically connected to a mating female terminal and has a flat tab-shaped 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. The mating female terminal may be made of the terminal material 1 according to an embodiment of the present disclosure having the above-described 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.

[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% by 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, a plating solution containing a sulfur-containing organic compound, "SILVERON GT-210 Durability Silver" manufactured by DuPont, was used. For Samples 6 and 7, a plating solution containing graphite, "ARGUNA C-100" manufactured by Umicore, was used. The thickness of the surface layer was as shown in Table 1 below. "SILVERON" and "ARGUNA" are registered trademarks.

[0044] In addition, 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. In Samples 1a to 1c, the conditions other than the thickness of the intermediate layer, such as the raw materials used and manufacturing method, were the same as those of Samples 1 and 3 to 5, including the thickness of the surface layer (1.0 μm).

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

[0046] (2) Confirmation of the composition of the intermediate layer and the surface layer The composition of the intermediate layer and the surface layer was confirmed for Samples 1 to 6. Specifically, the element contents in the intermediate layer and the 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. The contact resistance was measured by contacting each flat plate-shaped sample with an embossed contact point with a radius of 3.0 mm formed on each 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 the 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 current was 10 mA.

[0048] The above-mentioned contact resistance measurements were performed for 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 sample was left in a thermostatic chamber at a temperature of 85°C and a humidity of 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, the SO ２ : 0.2 ppm, H ２ S: 0.01ppm, NO ２ :0.2ppm, Cl ２ A gas flow of a four-type mixed gas, to which 0.01 ppm of CI 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 45, 46, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 6

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

[0050]

[0051] Table 1 confirms that the intermediate layer has a high Ag purity of 99.9 mass% in all samples. On the other hand, the surface layer of samples 1 to 5 has a coating layer with low Ag purity containing C and S, reflecting the addition of a sulfur-containing organic compound. Furthermore, samples 6 and 7 have a coating layer with low Ag purity containing C, 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 visible under SEM and is generally observed as a light gray, 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 constituting the intermediate layer was 0.14 μm or more and 0.32 μm or less. Since no clear crystal grains were observed in the SEM images of the strike layer, it can be seen 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, circles indicate the results for a surface layer thickness of 1.0 μm, and squares indicate the results for a surface layer thickness of 5.0 μm.

[0054] First, let us examine the results of adding graphite to the surface layer in Figures 5A and 5B. Compared to the case without an intermediate layer (thickness 0 μm), the presence of an intermediate layer (thickness 1.0 μm) slightly increases the contact resistance before the corrosion test, but significantly reduces the contact resistance after the corrosion test. In both the salt spray test in Figure 5A and the gas contact test in Figure 5B, the presence of an intermediate layer reduces the contact resistance after the corrosion test to less than one-third. These results confirm that the presence 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 in Figures 4A and 4B. The results of the salt spray test in Figure 4A show that the 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 results of the gas contact test in Figure 4B show that the 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 or greater and 3.0 μm or less 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 changed within the range of 0.4 μm or greater and 3.0 μm or less. 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.

[0057] REFERENCE SIGNS LIST 1 Terminal material 11 Base material 12 Underlayer 13 Strike layer 14 Intermediate layer 15 Surface layer 2 Male terminal (electrical connection terminal) 21 Terminal connection portion 22 Electric wire connection portion

Claims

1. A terminal material comprising: 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; and a surface layer containing Ag and at least one of a sulfur-containing organic compound and a carbon material and in contact with 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.

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 thickness of the intermediate layer is 0.4 μm or more and 3.0 μm or less.

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

6. An electrical connection terminal comprising the terminal material according to any one of claims 1 to 5, wherein the strike layer, intermediate layer, and surface layer are formed on the surface of the substrate at least in the electrical contact portion that comes into contact with the mating conductive member.

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