Electrical contact pair and terminal pair

Abstract

Provided is an electrical contact pair comprising a set of a convex electrical contact and a flat electrical contact, the electrical contacts each having, on the surface thereof, a coating layer comprising Ag. Also provided is a terminal pair comprising the electrical contact pair. The surface of the flat electrical contact has improved wear resistance.　A electrical contact pair (1) comprises: a convex electrical contact (2) that protrudes outward; and a flat electrical contact (3) that has a lower curvature than that of the convex electrical contact (2) and is capable of electrically contacting the convex electrical contact (2) at the surface of the flat electrical contact (3). The convex electrical contact (2) has, on the surface thereof, a lower-purity Ag coating layer (24) comprising Ag and a sulfur-containing organic compound and having an Ag content of 97.0-99.5 mass%. The flat electrical contact (3) has, on the surface thereof, a high-purity Ag coating layer (34) comprising Ag and having an Ag content of 99.9 mass% or more.

Description

Electrical contact pair and terminal pair

[0001] The present disclosure relates to an electrical contact pair and a terminal pair.

[0002] In automobiles, terminals with an Ag coating layer on the surface may be used as electrical connection terminals for high currents. Terminals with an Ag coating layer on the surface are excellent in heat resistance, corrosion resistance, and conductivity. However, due to the property that Ag is soft and prone to adhesion, when subjected to sliding, the surface is likely to wear. Therefore, as one means of suppressing wear while utilizing the excellent properties of Ag such as heat resistance and conductivity, a method may be adopted in which an additive element such as Se is contained in the Ag coating layer to increase the hardness of the Ag coating layer and form a hard silver layer.

[0003] However, making the Ag coating layer on the terminal surface a hard silver layer by containing an additive element such as Se may not sufficiently improve the wear resistance. For example, as the current of the terminal increases, it becomes necessary to apply a high contact load to the electrical contact. When sliding the electrical contact with such a high contact load applied, a conventional general hard silver layer may not sufficiently meet the required wear resistance. In such a case, it is conceivable to apply an Ag coating layer having better wear resistance than a conventional general hard silver layer as the Ag coating layer provided on the surface of the electrical contact of the terminal. For example, Patent Document 1 discloses manufacturing a silver plating material by forming a surface layer made of silver on a material using a silver plating solution containing benzothiazoles or their derivatives. It is said that a silver plating material with better wear resistance than before can be obtained thereby.

[0004] Japanese Unexamined Patent Application Publication No. 2022 - 048977

[0005] A combination of an embossed, protruding electrical contact and a flat electrical contact is often used as an electrical contact pair in a terminal pair consisting of a pair of terminals. For example, in the mating type terminal pair 4 shown in Figure 3, the female terminal 5 is provided with a protruding electrical contact 2, and the male terminal 6 is provided with a flat electrical contact 3. When mating and connecting a terminal pair having a protruding electrical contact and a flat electrical contact in this way, the protruding electrical contact slides and moves along the surface of the flat electrical contact. Therefore, the area of ​​the region involved in sliding (sliding part) on the terminal surface tends to be larger for the flat electrical contact than for the protruding electrical contact. In the example shown in Figure 3, the sliding portion of the female terminal 5 is, as shown by the solid ellipse, only the top of the bulging electrical contact 2, or in addition to that, only the front and rear ends of the internal opposing contact surface 52 that faces the bulging electrical contact 2 with the male terminal 6 in between. In contrast, the sliding portion of the male terminal 6 is, as shown by the dotted ellipse, the entire range of movement when the male terminal 6 is fitted with the female terminal 5, and is involved in the sliding between terminals 5 and 6.

[0006] To suppress wear on the sliding surfaces of terminal pairs, it is effective to form a highly wear-resistant coating layer on the surfaces of these sliding parts. If wear of the coating layer can be suppressed on the surface of the sliding parts of electrical contacts, the effect of wear suppression will be enhanced. In particular, if wear can be suppressed on the surface of flat electrical contacts, where the sliding surface area tends to be large, the effect will be especially high. Furthermore, by suppressing wear on the surface of electrical contacts, it becomes unnecessary to form a thick coating layer in anticipation of wear, and the material cost required for forming the coating layer can be reduced. This effect is also higher in flat electrical contacts, where the sliding surface area tends to be large. As described above, in terminals equipped with an Ag coating layer, wear resistance can be improved by making the Ag coating layer a hard silver layer or by adding additives consisting of organic compounds to the Ag coating layer. However, the inventors' investigation revealed that, in a terminal pair equipped with a bulging electrical contact and a flat electrical contact, simply forming an Ag coating layer on the surfaces of both electrical contacts in any combination, which is said to be effective in improving their wear resistance, is insufficient to effectively suppress wear on both electrical contacts, particularly the flat electrical contact. It is necessary to carefully consider the configuration of the Ag coating layer formed on the surface of each of the electrical contacts.

[0007] In view of the above, the objective is to provide an electrical contact pair and a terminal pair comprising a bulging electrical contact and a flat electrical contact, each having a coating layer containing Ag on their surfaces, which can improve the wear resistance of the surface of the flat electrical contact.

[0008] The electrical contact pair of the present disclosure includes a bulging electrical contact that bulges toward the surface and a flat electrical contact that has a smaller curvature than the bulging electrical contact and is capable of electrically contacting the bulging electrical contact on its surface, wherein the bulging electrical contact has a low-purity Ag coating layer on its surface containing Ag and a sulfur-containing organic compound, with an Ag content of 97.0% by mass or more and 99.5% by mass or less, while the flat electrical contact has a high-purity Ag coating layer on its surface containing Ag, with an Ag content of 99.9% by mass or more.

[0009] The terminal pair of the present disclosure includes a first terminal having a first contact portion and a second terminal having a second contact portion, wherein the set of the first contact portion and the second contact portion constitutes the electrical contact pair and is electrically contactable with respect to each other.

[0010] The electrical contact pair and terminal pair of this disclosure are an electrical contact pair comprising a set of a bulging electrical contact and a flat electrical contact, each having a coating layer containing Ag on its surface, and a terminal pair having such an electrical contact pair, which can improve the wear resistance of the surface of the flat electrical contact.

[0011] Figure 1 is a schematic cross-sectional view showing an electrical contact pair according to one embodiment of the present disclosure. Figures 2A and 2B are schematic cross-sectional views showing the layer structure of the metal material constituting the electrical contact pair, where Figure 2A shows the metal material constituting the bulging electrical contact and Figure 2B shows the metal material constituting the flat electrical contact. Figure 3 is a cross-sectional view showing an example of the structure of a terminal pair according to one embodiment of the present disclosure. Figure 4 shows in table format the results of measuring the wear depth, friction coefficient, and contact resistance by sliding the two electrical contacts together for several samples with different types of Ag coating layers provided on the surfaces of the bulging electrical contact and the flat electrical contact.

[0012] [Description of Embodiments of the Disclosure] First, embodiments of the disclosure will be described.

[0013] [1] The electrical contact pair of the present disclosure includes a bulging electrical contact that bulges toward the surface and a flat electrical contact that has a smaller curvature than the bulging electrical contact and is capable of electrically contacting the bulging electrical contact on its surface, wherein the bulging electrical contact has a low-purity Ag coating layer on its surface containing Ag and a sulfur-containing organic compound, with an Ag content of 97.0% by mass or more and 99.5% by mass or less, while the flat electrical contact has a high-purity Ag coating layer on its surface containing Ag, with an Ag content of 99.9% by mass or more.

[0014] The above-described electrical contact pair, by having a coating layer containing Ag on both the surface of the bulging electrical contact and the flat electrical contact, utilizes the properties of Ag, such as heat resistance, corrosion resistance, and high conductivity, to achieve good electrical contact characteristics and durability. Furthermore, as will be demonstrated in later embodiments, by providing a low-purity Ag coating layer containing a sulfur-containing organic compound with an Ag content of 97.0% to 99.5% by mass on the surface of the bulging electrical contact, and a high-purity Ag coating layer with an Ag content of 99.9% or more by mass on the surface of the flat electrical contact, high wear resistance can be obtained for both types of electrical contacts. In particular, a significant improvement in wear resistance can be obtained on the surface of the flat electrical contact.

[0015] [2] In the embodiment of [1] above, it is preferable that the content of the sulfur-containing organic compound in the low-purity Ag coating layer is 0.5% by mass or more and 3.0% by mass or less. In this case, a high effect of improving wear resistance by the sulfur-containing organic compound can be obtained in the electrical contact pair, and the contact resistance between the electrical contacts can be kept low.

[0016] [3] In the embodiment of [1] or [2] above, the high-purity Ag coating layer may be configured as a hard silver layer. This provides a high wear suppression effect and excellent durability in the flat electrical contact.

[0017] [4] In any one embodiment of [1] to [3] above, in the bulging electrical contact and the flat electrical contact, a base layer made of Ni or a Ni alloy is formed by coating the surface of a substrate made of Cu or a Cu alloy, and the low-purity Ag coating layer and the high-purity Ag coating layer are formed by coating the surface of the base layer, respectively. The base layer made of Ni or a Ni alloy plays a role in improving the adhesion of the Ag coating layer to the substrate made of Cu or a Cu alloy, and in suppressing the diffusion of the substrate metal into the Ag coating layer.

[0018] [5] In the embodiment of [4] above, it is preferable that an intermediate layer with a higher Ag purity than the low-purity Ag coating layer is formed between the base layer and the low-purity Ag coating layer in the bulging electrical contact. The intermediate layer, which is composed of a high-purity Ag layer, plays a role in suppressing corrosion of the substrate and base layer due to the influence of sulfur-containing organic compounds contained in the low-purity Ag coating layer.

[0019] [6] The terminal pair of the present disclosure includes a first terminal having a first contact portion and a second terminal having a second contact portion, wherein the set of the first contact portion and the second contact portion is composed of one of the electrical contact pairs described in [1] to [5] above and is electrically contactable with each other. This terminal pair has improved wear resistance because it has the above-mentioned electrical contact pair as a set of contact portions that are electrically contactable with each other. In particular, a high wear resistance improvement effect can be obtained in the terminal having the flat electrical contact.

[0020] [7] In the embodiment of [6] above, the first terminal is configured as a mating type female terminal having the bulging electrical contact, and the second terminal is configured as a male terminal having the flat electrical contact and mating with the first terminal. In a mating type terminal pair consisting of a female terminal and a male terminal, the female terminal is generally provided with an embossed, bulging electrical contact as the contact portion, and the male terminal is generally provided with a tab-shaped flat electrical contact as the contact portion. However, by providing the bulging electrical contact and the flat electrical contact that constitute the above electrical contact pair as their respective contact portions, high wear resistance can be obtained at the electrical contact portion between the two electrical contacts. In particular, a high effect can be obtained in improving wear resistance at the flat electrical contact of the male terminal, where the area of ​​the sliding portion with the mating electrical contact is large.

[0021] [8] In the embodiment described in [7] above, it is preferable that the area of ​​the high-purity Ag coating layer provided on the second terminal is larger than the area of ​​the low-purity Ag coating layer provided on the first terminal. In the male terminal (second terminal) having a flat electrical contact, the area of ​​the sliding part involved in sliding with the mating electrical contact is larger than in the female terminal (first terminal) having a bulging electrical contact. Therefore, by providing a larger area of ​​Ag coating on the male terminal than on the female terminal, the effect of improving the wear resistance of the electrical contact pair by providing Ag coating layers in a predetermined combination is enhanced. Furthermore, by taking advantage of the increased wear resistance of the flat electrical contact of the male terminal and forming a thin Ag coating layer, a significant effect of suppressing material costs can be obtained.

[0022] [Details of Embodiments of the Disclosure] The electrical contact pairs and terminal pairs according to embodiments of the disclosure will be described in detail below with reference to the drawings. Unless otherwise specified, the values ​​indicating various characteristics are those obtained at room temperature and in air.

[0023] <Electrical Contacts> Figure 1 schematically shows an electrical contact pair 1 according to one embodiment of the present disclosure in a cross-sectional view. The electrical contact pair 1 according to one embodiment of the present disclosure includes a bulging electrical contact 2 and a flat electrical contact 3. The bulging electrical contact 2 and the flat electrical contact 3 can make electrical contact with each other on their respective surfaces.

[0024] The bulging electrical contact 2 has a shape that bulges outwards on the surface (embossed shape). The specific bulging shape of the bulging electrical contact 2 is not particularly limited, but it is preferable that it has a shape that approximates a semi-ellipsoid or a partial ellipsoid (ellipsoidal crown; a shape obtained by cutting out a part of an ellipsoid with a plane; ellipsoids include perfect spheres). More preferably, it has a shape that approximates a hemisphere or a partial sphere (spherical crown; a shape obtained by cutting out a part of a sphere with a plane). In this specification, "approximating a certain shape" generally refers to a shape in which the dimensional deviation from that shape is within 10%.

[0025] The flat electrical contact 3 has a planar structure with a smaller curvature (larger radius of curvature) than the bulging electrical contact 2. The specific shape of the flat electrical contact 3 is not particularly limited, and it may have a curved shape that is gentler than the bulging shape of the bulging electrical contact 2, but it is preferable that it has a flat shape that is planar or approximates a planar shape. The bulging electrical contact 2 and the flat electrical contact 3 make electrical contact with each other on their respective surfaces, thereby forming an electrical connection between the metal material 20 constituting the bulging electrical contact 2 and the metal material 30 constituting the flat electrical contact 3. When forming electrical contact between the two electrical contacts 2 and 3, as shown in the figure, the bulging electrical contact 2 comes into contact with the surface of the flat electrical contact 3 at its top.

[0026] The combination of a partially ellipsoidal bulging electrical contact 2 and a planar flat electrical contact 3 is often used in male-female mating terminal pairs, as will be explained later with reference to Figure 3. By inserting and removing a terminal (male terminal 6) having a flat electrical contact 3 from a terminal (female terminal 5) having a bulging electrical contact 2, the bulging electrical contact 2 and the flat electrical contact 3 are slid relative to each other within the plane of the flat electrical contact 3 (for example, in the lateral direction in the figure), thereby reversibly forming and dissolving electrical contact between the two electrical contacts 2 and 3.

[0027] Figures 2A and 2B schematically show the layer structure of the metal materials 20 and 30 constituting the bulging electrical contact 2 and the flat electrical contact 3, respectively, in cross-sectional views. As shown in Figure 2A, the bulging electrical contact 2 is made of a metal material 20 having a low-purity Ag coating layer 24 on its surface. As shown in Figure 2B, the flat electrical contact 3 is made of a metal material 30 having a high-purity Ag coating layer 34 on its surface. The bulging electrical contact 2 and the flat electrical contact 3 are in contact with each other at the surfaces of their respective low-purity Ag coating layers 24 and high-purity Ag coating layers 34. Both the low-purity Ag coating layer 24 and the high-purity Ag coating layer 34 are made of metal layers with Ag as the main component, but their component compositions are different from each other. The details of the structure of the bulging electrical contact 2 and the flat electrical contact 3 will be explained below in order.

[0028] (Structure of bulging electrical contact) As shown in Figure 2A, the bulging electrical contact 2 is composed of a metal material 20 having a base material 21 and a low-purity Ag coating layer 24 that covers the surface of the base material 21. The type of base material 21 is not particularly limited, and various metal materials that are generally applicable as base materials for electrical connection members, including terminals, can be used. Preferably, the base material 21 is composed of Cu or a Cu alloy, which is commonly used as a base material for terminals.

[0029] The low-purity Ag coating layer 24 is the layer exposed on the outermost surface of the metal material 20. The low-purity Ag coating layer 24 contains Ag and a sulfur-containing organic compound. In the low-purity Ag coating layer 24, the Ag content is in the range of 97.0% by mass or more and 99.5% by mass or less.

[0030] The type of sulfur-containing organic compound contained in the low-purity Ag coating layer 24 is not particularly limited, but preferred examples include sulfur-containing polymers such as benzothiazoles, thiols, sulfides, disulfides, and sulfonated anionic polymers such as naphthalene sulfonic acid polymers, and their derivatives. The sulfur-containing organic compound may be used alone or in combination of two or more. In particular, mercaptobenzothiazole and its derivatives, and thiodiethanol are preferred. The type of derivative is not particularly limited, but examples include metal salts such as sodium salts.

[0031] In the low-purity Ag coating layer 24, the sulfur-containing organic compound plays a role in improving wear resistance. Specifically, when the bulging electrical contact 2 is brought into contact with the flat electrical contact 3 and slid, it suppresses adhesion between the low-purity Ag coating layer 24 and the high-purity Ag coating layer 34, contributing to keeping the coefficient of friction between the two electrical contacts 2 and 3 low. In particular, the benzothiazoles and their derivatives mentioned above show a high effect in improving the hardness of the low-purity Ag coating layer 24 and, as a result, improving wear resistance by refining the Ag crystals. In this specification, the sulfur-containing organic compound contained in the low-purity Ag coating layer 24 includes all components derived from sulfur-containing organic molecules, including forms in which the shape of the sulfur atom-containing organic molecule is maintained, forms in which at least a part of such molecules undergo intramolecular bond cleavage or rearrangement, and forms in which at least a part of the constituent atoms, including sulfur atoms, form bonds with external atoms such as Ag. The content of the sulfur-containing organic compound also refers to the total amount of all these components.

[0032] By containing Ag at a concentration of 97.0% by mass or higher, the low-purity Ag coating layer 24 can fully utilize the properties exhibited by Ag, such as heat resistance, corrosion resistance, and conductivity, as properties of the low-purity Ag coating layer 24. In particular, by ensuring high conductivity in the low-purity Ag coating layer 24, the contact resistance on the surface of the bulging electrical contact 2 is reduced, and a good electrical connection can be formed between it and the mating flat electrical contact 3. Furthermore, the high conductivity of the low-purity Ag coating layer 24 can suppress heat generation when a large current flows through the metal material 20, making it easier to apply the bulging electrical contact 2 to applications where large currents are applied, such as high-current terminals. Furthermore, when manufacturing electrical connection members such as terminals having bulging electrical contacts 2, a load is applied to the metal material 20 by machining, such as press molding, to form the terminal shape. However, since the low-purity Ag coating layer 24 contains Ag with a purity of 97.0% by mass or more, the ductility of Ag can be utilized to suppress damage to the low-purity Ag coating layer 24 caused by machining of the metal material 20. From the viewpoint of further enhancing these effects, it is more preferable that the Ag concentration in the low-purity Ag coating layer 24 be 98.0% by mass or more, and even more preferably 99.0% by mass or more.

[0033] On the other hand, by keeping the concentration of Ag in the low-purity Ag coating layer 24 below 99.5% by mass, the wear resistance of the low-purity Ag coating layer 24 can be effectively improved. This is because, in the low-purity Ag coating layer 24, the concentration of Ag is kept low, and components other than Ag, such as sulfur-containing organic molecules, are included at a certain concentration, which improves the hardness of the low-purity Ag coating layer 24. Furthermore, the probability of contact between Ag atoms decreases, making Ag adhesion less likely, and thus reducing the coefficient of friction on the surface of the low-purity Ag coating layer 24. From the viewpoint of further enhancing these effects, it is more preferable that the concentration of Ag in the low-purity Ag coating layer 24 be below 99.4% by mass.

[0034] In the low-purity Ag coating layer 24, if the Ag content is in the range of 97.0% by mass or more and 99.5% by mass or less, the low-purity Ag coating layer 24 may contain other components in addition to Ag and sulfur-containing organic compounds. However, from the viewpoint of minimizing the influence on properties imparted by sulfur-containing organic compounds, it is preferable that the low-purity Ag coating layer 24 is composed only of Ag and sulfur-containing organic compounds, excluding unavoidable impurities. In particular, it is preferable that additive elements such as Se, which are suitably added to the high-purity Ag coating layer 34 described later and have the effect of hardening the Ag layer, are not contained in the low-purity Ag coating layer 24, excluding unavoidable impurities and atoms such as C, S, and N derived from the added sulfur-containing organic compounds. Furthermore, it is preferable that the content of sulfur-containing organic compounds in the low-purity Ag coating layer 24 is 0.5% by mass or more and 3.0% by mass or less. As a result, a significant improvement in wear resistance can be obtained by adding sulfur-containing organic compounds, while minimizing the decrease in conductivity of the low-purity Ag coating layer 24 due to the addition of a large amount of sulfur-containing organic compounds.

[0035] As described above, in the low-purity Ag coating layer 24, sulfur-containing organic compounds, including benzothiazoles, have the effect of refining the Ag crystals. For example, it is preferable that the particle size of the Ag crystal grains in the low-purity Ag coating layer 24 is 5 nm or more and 20 nm or less. Refinement of the Ag crystal grains contributes to an increase in the hardness of the low-purity Ag coating layer 24, and it is preferable that the hardness of the low-purity Ag coating layer 24 is 90 HV or more and 150 HV or less on a Vickers hardness scale.

[0036] The thickness of the low-purity Ag coating layer 24 is not particularly limited. For example, a thickness of 0.5 μm or more, or 5 μm or less, can be exemplified. The low-purity Ag coating layer 24 can sufficiently exhibit the effect of improving wear resistance even if it is not formed to a thick thickness, so its thickness may be 2 μm or less.

[0037] In the metal material 20 constituting the bulging electrical contact 2, the low-purity Ag coating layer 24 may be directly formed on the surface of the base material 21. Alternatively, another type of metal layer may be formed between the base material 21 and the low-purity Ag coating layer 24. An example of such another type of metal layer is a base layer 22 made of Ni or a Ni alloy. The base layer 22 made of Ni or a Ni alloy suppresses the diffusion of constituent elements of the base material 21, such as Cu, into the low-purity Ag coating layer 24, and also plays a role in improving the adhesion of the low-purity Ag coating layer 24 to the base material 21. The thickness of the base layer 22 can be exemplified as being in the range of 0.5 μm or more and 10 μm or less.

[0038] Furthermore, an intermediate layer 23a may be provided directly beneath the low-purity Ag coating layer 24, that is, between the base layer 22 and the low-purity Ag coating layer 24, consisting of a layer with a higher Ag purity than the low-purity Ag coating layer 24 (and the high-purity Ag coating layer 34 described later). The intermediate layer 23a plays a role in suppressing corrosion of the substrate 21 and the base layer 22 due to the influence of sulfur-containing organic compounds contained in the low-purity Ag coating layer 24. Furthermore, a strike layer 23b may be provided below the intermediate layer 23a, that is, between the base layer 22 and the intermediate layer 23a. The strike layer 23b is provided as a layer with a higher Ag purity than the low-purity Ag coating layer 24 (and the high-purity Ag coating layer 34 described later) and is thinner than the intermediate layer 23a. Preferably, the strike layer 23b is composed of crystal grains smaller than those of the intermediate layer 23a. The strike layer 23b plays a role in improving the adhesion between the low-purity Ag coating layer 24 and the intermediate layer 23a to the base layer 22. Alternatively, the intermediate layer 23a may be omitted, and only the strike layer 23b may be provided. In the metal material 20, at the interfaces of mutually adjacent layers, some of the metal atoms constituting the layers on both sides may form an alloy. Furthermore, while it is preferable that the low-purity Ag coating layer 24 is exposed on the outermost surface of the metal material 20, a coating made of organic material or the like may be formed on the surface of the low-purity Ag coating layer 24, as long as it does not significantly impair the properties of the low-purity Ag coating layer 24. However, since the sulfur-containing organic compound contained in the low-purity Ag coating layer 24 can act as a discoloration inhibitor, it is not necessary to provide a separate layer of discoloration inhibitor on the surface of the low-purity Ag coating layer 24.

[0039] The preferred configuration of the low-purity Ag coating layer 24 is as described above, but for example, the Ag plating layer disclosed in Patent Document 1 can be suitably applied as the low-purity Ag coating layer 24. The low-purity Ag coating layer 24 can be formed by any method, such as plating or vapor deposition. Using a plating method is particularly preferable from the viewpoint of simplicity, etc. For example, electroplating can be performed using an Ag plating solution containing a sulfur-containing organic compound. A bulging electrical contact 2 can be manufactured by forming metal layers such as an appropriate underlayer 22, strike layer 23b, and intermediate layer 23a on the surface of the substrate 21, then forming the low-purity Ag coating layer 24 to form a flat metal material 20, and then press-working the metal material 20 to form a bulging shape.

[0040] (Configuration of flat electrical contacts) As shown in Figure 2B, the flat electrical contact 3 is composed of a metal material 30 having a base material 31 and a high-purity Ag coating layer 34 that covers the surface of the base material 31. Similar to the base material 21 of the metal material 20 that constitutes the bulging electrical contact 2, the base material 31 of the metal material 30 that constitutes the flat electrical contact 3 is not particularly limited in terms of metal type, but it is preferable that it be composed of Cu or a Cu alloy.

[0041] The high-purity Ag coating layer 34 is the layer exposed on the outermost surface of the metal material 30. The high-purity Ag coating layer 34 contains Ag, with an Ag content of 99.9% by mass or more. Preferably, the high-purity Ag coating layer 34 is composed of a hard silver layer. Here, a hard silver layer is a layer of Ag or an Ag alloy whose surface hardness is approximately 90 HV or higher, preferably 110 HV or higher, on a Vickers hardness scale. Furthermore, it is preferable that the surface hardness of the high-purity Ag coating layer 34 is higher than the surface hardness of the low-purity Ag coating layer 24 of the bulging electrical contact 2.

[0042] The high-purity Ag coating layer 34 may contain only Ag and inevitable impurities, but in addition to Ag and inevitable impurities, it preferably contains an additive element having an effect of hardening the Ag layer. Examples of such additive elements include Se, Sb, C, N, S, etc. In particular, it is preferable to use Se as the additive element. The addition amount of these additive elements is suppressed to a range of 0.1% by mass or less in the entire high-purity Ag coating layer 34.

[0043] Since the high-purity Ag coating layer 34 has a high Ag purity of 99.9% by mass or more, the properties exhibited by Ag, such as heat resistance, corrosion resistance, conductivity, etc., can be effectively utilized as the properties of the high-purity Ag coating layer 34. The upper limit of the Ag concentration in the high-purity Ag coating layer 34 is not particularly defined, but it is preferable to suppress it to a concentration at which an additive element for hardening the Ag layer, such as Se, can be added.

[0044] The thickness of the high-purity Ag coating layer 34 is not particularly limited. For example, from the viewpoint of sufficiently exhibiting the properties possessed by the high-purity Ag coating layer 34, 1 μm or more is preferable, and 3 μm or more is more preferable. On the other hand, from the viewpoint of ensuring the workability of the metal material 30, etc., 10 μm or less is preferable. As will be described later, due to the effect of the combination of forming the low-purity Ag coating layer 24 on the surface of the bulged electrical contact 2 and forming the high-purity Ag coating layer 34 on the surface of the flat electrical contact 3, during the sliding between the two electrical contacts 2 and 3, particularly the wear of the high-purity Ag coating layer 34 on the surface of the flat electrical contact 3 is suppressed. Therefore, there is less need to form the high-purity Ag coating layer 34 thick considering wear. Thus, the thickness of the high-purity Ag coating layer 34 can be made smaller, and it can also be made smaller than the thickness of the Ag layers (24, 23a, 23b) provided on the surface of the metal material of the bulged electrical contact 2. [[ID=⑦]] [[ID=⑧]]

[0045] The metal material 30 constituting the flat electrical contact 3 may also have other metal layers, such as an underlayer 32, between the high-purity Ag coating layer 34 and the base material 31, similar to the metal material 20 having the bulging electrical contact 2. Furthermore, a coating made of organic material or the like may be present on the surface of the high-purity Ag coating layer 34. The applicable configurations for these underlayer 32 and coatings are the same as those described above for the metal material 20 constituting the bulging electrical contact 2. The same also applies to the fact that there is no need to provide a layer of discoloration inhibitor on the surface. In the metal material 30 constituting the flat electrical contact 3, similar to the metal material 20 having the bulging electrical contact 2, an intermediate layer and / or strike layer made of high-purity Ag may be provided. If provided, the configuration should be the same as that described above for the metal material 20. However, in the case of the metal material 30, the need to provide an intermediate layer or strike layer is low, given that the high-purity Ag coating layer 34 is provided on the surface.

[0046] The high-purity Ag coating layer 34 can be formed by any method, such as plating or vapor deposition. Using a plating method is particularly preferable from the viewpoint of simplicity. For example, electroplating can be performed using an Ag plating solution containing additive elements such as Se that have the effect of hardening the Ag layer. A metal layer such as an underlayer 32 can be formed on the surface of the substrate 21 as appropriate, and then the high-purity Ag coating layer 34 can be formed to create a metal material 30, and a flat plate-shaped electrical contact 3 can be formed from this metal material 30.

[0047] (Characteristics of the electrical contact pair) As described above, the electrical contact pair 1 according to this embodiment includes a bulging electrical contact 2 having a low-purity Ag coating layer 24 on its surface and a flat electrical contact 3 having a high-purity Ag coating layer 34 on its surface, and both electrical contacts 2 and 3 are able to electrically contact each other on the surfaces of both Ag coating layers 24 and 34. The low-purity Ag coating layer 24 contains a sulfur-containing organic compound in addition to Ag, and the concentration of Ag is 99.5% by mass or more and 97.0% by mass or less. On the other hand, the high-purity Ag coating layer 34 contains Ag at a concentration of 99.9% by mass or more.

[0048] Since the surfaces of both the bulged electrical contact 2 and the flat electrical contact 3 are coated with a metal layer mainly composed of Ag, which is a metal excellent in properties such as heat resistance, corrosion resistance, and conductivity, the electrical contact pair 1 has excellent electrical contact characteristics and durability. Further, by providing a low-purity Ag coating layer 24 containing a sulfur-containing organic compound and having the Ag concentration suppressed within a predetermined range on the surface of the bulged electrical contact 2, the occurrence of adhesion is suppressed between the flat electrical contact 3 and the bulged electrical contact 2, and the friction coefficient during sliding is kept low. As a result, the electrical contact pair 1 has high wear resistance.

[0049] As shown in the subsequent examples, by providing a low-purity Ag coating layer on at least one of the surfaces of the bulged electrical contact ② and the flat electrical contact ③, a higher effect in reducing the friction coefficient and improving the wear resistance can be obtained than in the case where high-purity Ag coating layers are provided on the surfaces of both the electrical contacts ② and ③. In particular, by providing the low-purity Ag coating layer 24 on the bulged electrical contact 2 and the high-purity Ag coating layer 34 on the flat electrical contact 3, a very high effect can be obtained in improving the wear resistance on the surface of the flat electrical contact 3. By suppressing the wear on the surfaces of both the electrical contacts ② and ③, even if sliding is repeated between the electrical contacts ② and ③, the state in which the electrical contacts ② and ③ are coated with the Ag coating layers 24 and 34 is maintained over a long period, and the properties originally possessed by the Ag coating layers 24 and 34, such as heat resistance, corrosion resistance, and high conductivity, are exhibited over a long period. In particular, when sliding is performed between the electrical contacts ② and ③, the sliding portion (indicated by a dotted ellipse in FIG. 3) on the flat electrical contact 3 is more likely to have a larger area than the sliding portion (indicated by a solid ellipse in FIG. 3) on the bulged electrical contact 2. Therefore, by effectively improving the wear resistance on the surface of the flat electrical contact 3, a large effect of improving the wear resistance can be obtained in the sliding portion. Further, by improving the wear resistance, it is not necessary to form the high-purity Ag coating layer 34 thick in advance in anticipation of wear, and it becomes easier to suppress the material cost of the flat electrical contact 3 and the terminal including the same.

[0050] As described above, in the electrical contact pair 1 according to this embodiment, by adopting a combination in which a low-purity Ag coating layer 24 is provided on the bulging electrical contact 2 and a high-purity Ag coating layer 34 is provided on the flat electrical contact 3 (high purity on the flat side), a high wear resistance improvement effect and friction reduction effect can be obtained on both electrical contacts 2 and 3, especially on the flat electrical contact 3. However, as shown in later embodiments, even if the high-purity Ag coating layer is provided on the bulging electrical contact 2 and a low-purity Ag coating layer is provided on the flat electrical contact 3 (high purity on the bulging side), a certain degree of wear resistance improvement and friction reduction effect can be obtained on both electrical contacts 2 and 3. However, in the case of the high-purity on the bulging side combination, even if a high wear resistance improvement effect is obtained on the surface of the bulging electrical contact, the wear resistance improvement effect on the surface of the flat electrical contact is not so high.

[0051] However, since both the combination of high purity on the flat side and the combination of high purity on the bulging side have their own characteristics, one should choose either combination after considering these characteristics. For example, as simulated in the sliding test of the later embodiment, in situations where both electrical contacts 2 and 3 are in contact with each other by mating terminal pairs and subjected to slight sliding due to vibration or thermal cycles, the combination of high purity on the flat side exhibits a very high effect in improving wear resistance. On the other hand, in situations where both electrical contacts 2 and 3 are slid over long distances, such as during the insertion and removal of terminal pairs, the combination of high purity on the bulging side may show a high effect in improving wear resistance. Furthermore, in low-purity Ag coating layers, the inclusion of sulfur-containing organic compounds may make the metal structure brittle, and in the combination of high purity on the flat side, processing the metal material into a bulging shape to create the bulging electrical contact 2 may lead to damage such as cracks. Damage to the coating layer may also lead to a decrease in wear resistance. Considering these factors, for example, if the priority is to improve the wear resistance of the flat electrical contact 3, or if there is a particular need to suppress wear due to fine sliding such as vibration and thermal cycles, or if the processing applied to the bulging electrical contact 2 is not so severe, then a combination of high purity for the flat side may be adopted. On the other hand, if the priority is to improve the wear resistance of the bulging electrical contact 2, or if there is a particular need to suppress wear due to long-distance sliding such as terminal insertion and removal, or if the processing applied to the bulging electrical contact 2 is severe, then a combination of high purity for the bulging side may be adopted.

[0052] The electrical contact pair 1 according to this embodiment can be applied as a component of the electrical contact portion of various electrical connection members. The type of electrical connection member is not particularly limited, but it is preferable that the formation / dissolution of the electrical connection involves sliding between the electrical contacts 2 and 3. As will be described below, the electrical contact pair 1 according to this embodiment can be suitably applied as a contact pair for an electrical connection terminal.

[0053] <Terminal Pair> The terminal pair according to the embodiment of the present disclosure includes the electrical contact pair 1 according to the embodiment of the present disclosure described above. That is, in a terminal pair including a first terminal having a first contact portion and a second terminal having a second contact portion, the set of the first contact portion and the second contact portion is made of the electrical contact pair 1 according to the embodiment of the present disclosure and is made electrically contactable with each other.

[0054] The specific type and shape of the terminal pair are not particularly limited, but a configuration consisting of a mating type terminal pair, as shown in terminal pair 4 in Figure 3, is preferred. Terminal pair 4 is configured as a set of a female terminal 5 and a male terminal 6 that can be mated with the female terminal 5. The female terminal 5 is a first terminal having a bulging electrical contact 2 as the first contact portion, and the male terminal 6 is a second terminal having a flat electrical contact 3 as the second contact portion. A low-purity Ag coating layer 24 is provided on the surface of the contact portion of the female terminal 5, and a high-purity Ag coating layer 34 is provided on the surface of the contact portion of the male terminal 6.

[0055] The female terminal 5 and male terminal 6 have shapes similar to known mating-type female and male terminals. The female terminal 5 has a clamping portion 53. The clamping portion 53 is formed in a rectangular tubular shape with an open front, and has an elastic contact piece 51 on the inside of the bottom surface of the clamping portion 53 that is folded inward towards the rear. On the other hand, the male terminal 6 has a tab portion 61 formed in a flat plate shape at its front. When the tab portion 61 of the male terminal 6 is inserted into the clamping portion 53 of the female terminal 5, the elastic contact piece 51 of the female terminal 5 contacts the tab portion 61 of the male terminal 6 at the embossed portion 51a that bulges inward towards the inside of the clamping portion 53, applying an upward force to the tab portion 61. The surface of the ceiling portion of the clamping portion 53 facing the elastic contact piece 51 is designated as the internal opposing contact surface 52, and the tab portion 61 of the male terminal 6 is pressed against the internal opposing contact surface 52 by the elastic contact piece 51, thereby clamping and holding the tab portion 61 within the clamping portion 53. As a result, an electrical contact is formed and maintained between the embossed portion 51a of the female terminal 5, which is a bulging electrical contact 2, and the surface of the tab portion 61 of the male terminal 6, which is a flat electrical contact 3.

[0056] Here, on the surface of the metal material 20 constituting the female terminal 5, as shown by the solid ellipse, the embossed portion 51a of the elastic contact piece 51 and the front and rear corners of the internal opposing contact surface 52 are sliding portions that are subjected to sliding when inserting and removing the male terminal 6. At least on the surface of these sliding portions, a low-purity Ag coating layer 24 is formed together with other metal layers such as the base layer 22, strike layer 23b, and intermediate layer 23a as appropriate (figure not shown). Then, on the metal material 30 forming the male terminal 6, as shown by the dotted ellipse, the area on the upper and lower surfaces of the tab portion 61 that can come into contact with the embossed portion 51a and the internal opposing contact surface 52 of the female terminal 5 within the distance of terminal insertion and removal is a sliding portion. At least on the surface of these sliding portions, a high-purity Ag coating layer 34 is formed together with other metal layers such as the base layer 32 as appropriate (figure not shown). Up to a maximum, a low-purity Ag coating layer 24 may be formed on the entire surface of the female terminal 5, and a high-purity Ag coating layer 34 may be formed on the entire surface of the male terminal 6. However, from the viewpoint of reducing material costs, it is preferable to form each Ag coating layer 24, 34 on the smallest possible area, including the surface of the sliding parts of each terminal 5, 6.

[0057] In this way, a low-purity Ag coating layer 24 is formed on the surface of the embossed portion 51a of the elastic contact piece 51 of the female terminal 5, which becomes a bulging electrical contact 2, and on the surface of the sliding portion of the internal opposing contact surface 52, and a high-purity Ag coating layer 34 is formed on the surface of the sliding portion of the tab portion 61 of the male terminal 6, which becomes a flat electrical contact 3. As a result, high wear resistance can be obtained at the electrical contact portion between the female terminal 5 and the male terminal 6. Because the electrical contact portion has high wear resistance, even if sliding occurs between the female terminal 5 and the male terminal 6, a state with a low coefficient of friction is stably maintained. For example, even if the terminal pair 4 is used in an environment that is frequently subjected to slight sliding due to vibration or thermal cycles, the properties of the Ag coating layers 24 and 34, such as heat resistance, corrosion resistance, and high conductivity, can be maintained at the contact portion for a long period of time. In particular, in the male terminal 6, where the sliding surface is formed over a large area, the wear resistance is effectively improved, so that even after sliding due to insertion and removal of the terminal pair 4, the high-purity Ag coating layer 34, which has an excellent wear resistance improvement effect, is retained on the surface of the sliding surface of the male terminal 6 for a long period of time. Furthermore, since it is no longer necessary to form the high-purity Ag coating layer 34 of the male terminal 6 thickly in anticipation of wear, material costs can be reduced by forming the high-purity Ag coating layer 34 thinly. In particular, the material cost reduction effect is greater when the area of ​​the high-purity Ag coating layer 34 on the male terminal 6 is larger than the area of ​​the low-purity Ag coating layer 24 on the female terminal 5.

[0058] Examples are shown below. However, the present invention is not limited to these examples. Here, the relationship between the composition of the Ag coating layer of the bulging and flat electrical contacts constituting the electrical contact pair and the characteristics of the electrical contact pair was investigated. Unless otherwise specified, the samples were prepared and evaluated at room temperature in air.

[0059] <Sample Preparation> First, two types of metal materials were prepared: a low-purity Ag coating material and a high-purity Ag coating material. Specifically, the following layers were sequentially formed on the surface of a clean Cu alloy substrate with a thickness of 0.25 mm by electroplating, to form the low-purity Ag coating material and the high-purity Ag coating material. The layered configurations are shown in Figures 2A and 2B, respectively. The Ag concentration in each Ag layer was evaluated using a glow discharge emission spectrometer (GD-OES). • Low-purity Ag coating material - Ni underlayer (thickness 1.0 μm), Ag strike layer (thickness 0.1 μm or less, Ag purity 99.9% by mass or higher), Ag intermediate layer (thickness 1.0 μm, Ag purity 99.9% by mass or higher), low-purity Ag coating layer (thickness 1.0 μm, Ag purity 98.0% by mass). The low-purity Ag coating layer was prepared using DuPont's "SILVERON GT-210 Durability Silver," a plating solution containing sulfur-containing organic compounds. • High-purity Ag coating material - Ni underlayer (thickness 1.0 μm), high-purity Ag coating layer (thickness 5.0 μm, Ag purity 99.9% by mass or higher, Se added).

[0060] Using the fabricated metal material, a set of bulging and flat specimens was created as a model of an electrical contact pair, as shown in Figure 1. For the bulging specimen, a hemispherical bulge with a radius of R3 mm was formed by press working the metal material. For the flat specimen, a flat metal material was used as the flat electrical contact. In each sample, the metal material constituting the bulging and flat specimens had Ag coatings in the combinations shown in the table in Figure 4.

[0061] <Evaluation Method> A sliding test was performed on each sample, consisting of a set of bulging and flat test pieces, by repeatedly sliding them against each other. After the sliding test was completed, the wear depth was measured on the surfaces of the bulging electrical contacts of the bulging test piece and the flat electrical contacts of the flat test piece. In addition, the coefficient of friction and contact resistance were measured during the sliding test. The specific methods for each test are as follows.

[0062] - For each electrical contact pair of the sliding test specimen, the bulging electrical contact of the bulging test piece was brought into contact with the flat electrical contact of the flat test piece at its top, and the bulging test piece was slid along the surface of the flat test piece. The contact load was set to 2N (maximum surface pressure 420MPa). The sliding motion involved reciprocating 1000 times over a distance of 0.02 mm at a sliding speed of 1 Hz. This sliding test simulates micro-sliding caused by vibration and thermal cycles in terminal pairs.

[0063] - For measuring the wear depth, the film thickness was measured using an X-ray fluorescence film thickness gauge at the electrical contacts of each test piece after sliding. The X-ray irradiation diameter at the measurement point was set to 0.03 mmφ, and the pitch of the measurement points was set to 0.03 mm. The distribution of the Ag coating film thickness on the surface of each electrical contact was measured. In the obtained film thickness distribution, the wear depth was recorded by subtracting the film thickness value of the thinnest point from the average film thickness of the non-sliding area.

[0064] - Friction coefficient: The friction coefficient was measured during the sliding test. Specifically, the kinetic friction force acting between electrical contacts was measured using a load cell during sliding. The value obtained by dividing the kinetic friction force by the load was defined as the (kinetic) friction coefficient.

[0065] • Contact resistance was measured during the contact resistance sliding test. The measurement was performed using the four-terminal method. The open-circuit voltage was 20 mV and the current was 10 mA.

[0066] <Test Results> Figure 4 summarizes the type of coating layer at each electrical contact and the results of each evaluation for samples 1 to 4.

[0067] First, looking at the measurement results of wear depth, in sample 2, where a high-purity Ag coating layer was formed on the surface of both electrical contacts, the wear depth of both electrical contacts was large, at approximately 5 μm. In contrast, in samples 1, 3, and 4, where a low-purity Ag coating layer was formed on the surface of at least one electrical contact, the wear depth at both electrical contacts was kept to 0.5 μm or less, indicating a significant improvement in wear resistance. In particular, in sample 1, where a low-purity Ag coating layer was formed on the surface of the bulging electrical contact and a high-purity Ag coating layer was formed on the surface of the flat electrical contact, the wear depth on the surface of the flat electrical contact was kept to 0.06 μm. This is a small value, less than 1 / 4, compared to all other samples and all electrical contacts. The wear depth on the surface of the bulging electrical contact was kept to a small level, similar to samples 3 and 4. Thus, by forming a low-purity Ag coating layer on the surface of the bulging electrical contact and a high-purity Ag coating layer on the surface of the flat electrical contact, the wear resistance of both electrical contacts is improved, and it has been confirmed that a particularly high wear resistance improvement effect is obtained in the flat electrical contact.

[0068] Corresponding to the suppression of wear on the Ag coating layer, samples 1, 3, and 4, which have a low-purity Ag coating layer formed on the surface of at least one electrical contact, including sample 1, show a significantly reduced coefficient of friction throughout the entire sliding test period compared to sample 2, which has a high-purity Ag coating layer formed on the surfaces of both electrical contacts. Regarding contact resistance, sample 2 shows the lowest, but samples 1, 3, and 4 also consistently show sufficiently low contact resistance throughout the entire sliding period.

[0069] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0070] The above describes an embodiment in which a low-purity Ag coating layer is provided on the surface of a bulging electrical contact and a high-purity Ag coating layer is provided on the surface of a flat electrical contact. However, as confirmed in sample 3 of the embodiment in which a high-purity Ag coating layer is provided on the surface of a bulging electrical contact and a low-purity Ag coating layer is provided on the surface of a flat electrical contact, a certain degree of wear resistance improvement effect is obtained on the surfaces of both electrical contacts. Therefore, regardless of the shape of the electrical contacts, even when an electrical contact pair consisting of a first electrical contact and a second electrical contact is provided with a low-purity Ag coating layer on the surface of the first electrical contact and a high-purity Ag coating layer on the surface of the second electrical contact, the wear resistance improvement effect can be enjoyed. In other words, with the aim of providing an electrical contact pair and a terminal pair having such an electrical contact pair, each consisting of an electrical contact pair having an Ag-containing coating layer on its surface, the following configurations can be used to provide an electrical contact pair and a terminal pair.

[0071] - An electrical contact pair comprising a first electrical contact and a second electrical contact that is electrically contactable to the first electrical contact on its surface, wherein the first electrical contact has a low-purity Ag coating layer on its surface containing Ag and a sulfur-containing organic compound, with an Ag content of 97.0% by mass or more and 99.5% by mass or less, while the second electrical contact has a high-purity Ag coating layer on its surface containing Ag, with an Ag content of 99.9% by mass or more. - A terminal pair comprising a first terminal having a first contact portion and a second terminal having a second contact portion, wherein the set of the first contact portion and the second contact portion is composed of the electrical contact pair and is electrically contactable to each other.

[0072] In these cases, the same configurations as described above can be applied to the configurations of the low-purity Ag coating layer and the high-purity Ag coating layer, as well as to the electrical contact pairs and terminal pairs. The shapes of the first and second electrical contacts are not particularly limited, and any shape can be applied. However, in addition to the configuration described above in which the first electrical contact is a bulging electrical contact and the second electrical contact is a flat electrical contact, examples include the configuration in which the first electrical contact is a flat electrical contact and the second electrical contact is a bulging electrical contact, the configuration in which both electrical contacts are flat electrical contacts having a flat surface, and the configuration in which both electrical contacts are bulging electrical contacts having a bulging surface.

[0073] 1 Electrical contact pair 2 Bulging electrical contact 3 Flat electrical contact 20, 30 Metal material 21, 31 Base material 22, 32 Underlayer 23a Intermediate layer 23b Strike layer 24 Low-purity Ag coating layer 34 High-purity Ag coating layer 4 Terminal pair 5 Female terminal 51 Elastic contact piece 51a Embossed portion 52 Internal opposing contact surface 53 Clamping portion 6 Male terminal 61 Tab portion

Claims

1. An electrical contact pair comprising: a bulging electrical contact that bulges toward the surface; and a flat electrical contact that has a smaller curvature than the bulging electrical contact and is capable of making electrical contact with the bulging electrical contact at its surface, wherein the bulging electrical contact has a low-purity Ag coating layer on its surface containing Ag and a sulfur-containing organic compound, with an Ag content of 97.0% by mass or more and 99.5% by mass or less; and the flat electrical contact has a high-purity Ag coating layer on its surface containing Ag, with an Ag content of 99.9% by mass or more.

2. The electrical contact pair according to claim 1, wherein the content of the sulfur-containing organic compound in the low-purity Ag coating layer is 0.5% by mass or more and 3.0% by mass or less.

3. The electrical contact pair according to claim 1, wherein the high-purity Ag coating layer is configured as a hard silver layer.

4. The pair of electrical contacts according to claim 1, wherein in the bulging electrical contact and the flat electrical contact, a base layer made of Ni or a Ni alloy is formed by coating the surface of a substrate made of Cu or a Cu alloy, and the low-purity Ag coating layer and the high-purity Ag coating layer are formed by coating the surface of the base layer, respectively.

5. The electrical contact pair according to claim 4, wherein in the bulging electrical contact, an intermediate layer with a higher Ag purity than the low-purity Ag coating layer is formed between the base layer and the low-purity Ag coating layer.

6. A terminal pair comprising a first terminal having a first contact portion and a second terminal having a second contact portion, wherein the set of the first contact portion and the second contact portion is composed of an electrical contact pair according to any one of claims 1 to 5 and is electrically contactable with respect to each other.

7. The terminal pair according to claim 6, wherein the first terminal is configured as a mating type female terminal having the bulging electrical contact, and the second terminal is configured as a male terminal having the flat electrical contact and mating with the first terminal.

8. The terminal pair according to claim 7, wherein the area of ​​the high-purity Ag coating layer provided on the second terminal is larger than the area of ​​the low-purity Ag coating layer provided on the first terminal.

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