Electrical contact pairs and terminal pairs

Abstract

The present invention provides an electrical contact pair comprising 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 effectively suppress wear on the surface of the bulging electrical contact. [Solution] An electrical contact pair 1 comprising a bulging electrical contact 2 and a flat electrical contact 3, wherein the electrical contacts 2 and 3 each have Ag coating layers 2A and 3A on their surfaces, the Ag coating layer having Ag as the main component, the Ag coating layer on at least one surface has a modified Ag coating layer containing Ag and a sulfur-containing organic compound, the Ag coating layer on at least one surface has a modified Ag surface layer as the outermost layer, the modified Ag surface layer is a thinner layer than the contained Ag coating layer, and has a higher Ag concentration and a lower concentration of the sulfur-containing organic compound compared to the contained Ag coating layer.

Description

Technical Field

[0001] The present disclosure relates to electrical contact pairs and terminal pairs.

Background Art

[0002] In automobiles, as electrical connection terminals for high currents, terminals provided with an Ag coating layer on the surface may be used. Terminals provided 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 for suppressing wear while utilizing the excellent properties of Ag such as heat resistance and conductivity, a method may be taken 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 into 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 by applying such a high contact load, a conventional general hard silver layer may not sufficiently satisfy the required wear resistance. In such a case, it may be considered 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 having better wear resistance than before can be obtained thereby.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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, a protruding electrical contact 2 is provided on the female terminal 5, and a flat electrical contact 3 is provided on the male terminal 6. When mating a terminal pair having a protruding electrical contact and a flat electrical contact in this way, the protruding electrical contact slides along the surface of the flat electrical contact. During this sliding, the area of ​​the flat electrical contact that is in contact with the protruding electrical contact moves with the sliding, while the same area at the top of the protruding shape of the protruding electrical contact remains in constant contact with the surface of the flat electrical contact. Therefore, wear due to sliding is less likely to progress at each position on the surface of the flat electrical contact, while wear is more likely to progress significantly at the top of the protruding electrical contact.

[0006] By applying an Ag coating layer to the surface of an electrical contact pair, the heat resistance, corrosion resistance, conductivity, and other properties of Ag can be utilized. In the case of flat electrical contacts, even if the coating layer is not formed to be very thick, wear does not progress easily at each position, so the properties of the Ag coating layer are easily retained even after sliding. On the other hand, in the case of bulging electrical contacts, wear progresses easily at the top, so if the Ag coating layer is not formed to be thick, after sliding, the properties of the Ag coating layer may not be fully utilized due to the effects of wear. If wear of the Ag coating layer on the surface of bulging electrical contacts can be suppressed, it is expected that wear of the Ag coating layer will be suppressed for the entire electrical contact pair, and the properties of the Ag coating layer can be retained for a long period of time even after sliding. If wear of the Ag coating layer is suppressed, the need to form the Ag coating layer thickly in advance in anticipation of wear will decrease, which will also lead to a reduction in material costs.

[0007] 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 an additive consisting of an organic compound to the Ag coating layer. However, according to the inventors' studies, in a terminal pair equipped with a bulging electrical contact and a flat electrical contact, it was found that simply forming an Ag coating layer in an arbitrary shape on the surface of both electrical contacts, which is said to be effective in improving their wear resistance, is insufficient to effectively suppress wear of the Ag coating layer of the bulging electrical contact. The shape of the Ag coating layer to be formed needs to be carefully considered.

[0008] 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 surface, which can effectively suppress wear on the surface of the bulging electrical contact. [Means for solving the problem]

[0009] 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 at its surface, wherein the bulging electrical contact and the flat electrical contact each have an Ag coating layer on their surface, which is a metal layer mainly composed of Ag, and the Ag coating layer on at least one surface of the bulging electrical contact and the flat electrical contact has a containing Ag coating layer containing Ag and a sulfur-containing organic compound, and the Ag coating layer on at least one surface of the bulging electrical contact and the flat electrical contact has a modified Ag surface layer as the outermost layer, the modified Ag surface layer is a thinner layer than the containing Ag coating layer and has a higher Ag concentration and a lower concentration of the sulfur-containing organic compound compared to the containing Ag coating layer.

[0010] 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. [Effects of the Invention]

[0011] 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 effectively suppress wear on the surface of the bulging electrical contact. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing an electrical contact pair according to one embodiment of the present disclosure. [Figure 2] Figures 2A and 2B are schematic cross-sectional views showing an example of the layer structure of the metal material constituting the above electrical contact pair. 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] 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] Figure 4A shows SEM images of the cross-sections of both electrical contacts for sample 1, and Figure 4B shows the same for sample 5 (magnification ×50,000, scale bar 100 nm). Figure 4B shows SEM images of the cross-sections of both electrical contacts for sample 5 (magnification ×30,000, scale bar 100 nm). In each image, the upper row shows the bulging electrical contact with the surface side facing down, and the lower row shows the flat electrical contact with the surface side facing up. [Figure 5] Figure 5 shows SEM images of the cross-section of the bulging electrical contacts in sample 4. The upper panel shows a low-magnification image (magnification ×10,000, scale bar 1 μm), and the lower panel shows a high-magnification image (magnification ×50,000, scale bar 100 nm). [Figure 6] Figure 6 shows the results of the analysis of the surface composition of sample 1. The images in the left column are STEM images, and the graphs in the right column show the depth distribution of Ag, C, S, and O concentrations obtained by EDX. The upper row shows bulging electrical junctions with the surface side down, and the lower row shows flat electrical junctions with the surface side up. [Figure 7] Figure 7 shows the relationship between sliding amount and wear depth. The data points indicated by circles represent the wear of flat electrical contacts in a sample with a silver-containing coating layer on both electrical contacts, while the data points indicated by squares represent the wear of bulging electrical contacts in a sample with a high-purity silver-containing coating layer on both electrical contacts. The inset shows a magnified view of the low sliding amount region. [Modes for carrying out the invention]

[0013] [Description of Embodiments in this Disclosure] First, embodiments of this disclosure will be described.

[0014] [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 at its surface, wherein the bulging electrical contact and the flat electrical contact each have an Ag coating layer on their surface which is a metal layer mainly composed of Ag, and the Ag coating layer on at least one surface of the bulging electrical contact and the flat electrical contact has a containing Ag coating layer which contains Ag and a sulfur-containing organic compound, and the Ag coating layer on at least one surface of the bulging electrical contact and the flat electrical contact has a modified Ag surface layer as the outermost layer, the modified Ag surface layer is a thinner layer than the containing Ag coating layer which has a higher Ag concentration and a lower concentration of the sulfur-containing organic compound.

[0015] The above electrical contact pair has an Ag coating layer on the surfaces of both the bulged electrical contact and the flat electrical contact. By utilizing the properties of Ag such as heat resistance, corrosion resistance, and high conductivity, it has good electrical contact characteristics and durability. Further, the Ag coating layer on the surface of at least one of the electrical contacts has a containing organic Ag coating layer containing a sulfur-containing organic compound, and moreover, the Ag coating layer on the surface of at least one of the electrical contacts has a modified Ag surface layer as the outermost layer. Thus, when the electrical contacts are slid relative to each other, wear of the Ag coating layer occurs in the flat electrical contact, and surface wear is suppressed in the bulged electrical contact. Instead of the bulged electrical contact where the same location at the top of the bulged shape always contributes to sliding, wear progresses in the flat electrical contact where the location contributing to sliding moves. By doing so, wear of the Ag coating layer can be suppressed for the entire electrical contact pair. Then, the properties of the Ag coating layer can be maintained in the electrical contact pair over a long period even after sliding. The material cost required for forming the Ag coating layer can also be suppressed. The modified Ag surface layer can be formed by applying processing strain to the surface layer portion of the containing organic Ag coating layer by sliding with the mating electrical contact, etc., and constitutes the outermost layer of the Ag coating layer on the surface of at least one of the electrical contacts through appropriate transfer.

[0016] [2] In the aspect of [1] above, it is preferable that the Ag concentration is higher on the outermost surface of the bulged electrical contact than on the outermost surface of the flat electrical contact. Then, the effect of suppressing wear of the bulged electrical contact can be enhanced.

[0017] [3] In the aspect of [1] or [2] above, it is preferable that the modified Ag surface layer is provided to cover at least the surface of the containing organic Ag coating layer. Then, the modified Ag surface layer can be easily formed by applying processing strain to the surface of the containing organic Ag coating layer, etc., and can effectively contribute to suppressing wear in the flat electrical contact.

[0018] [4] In any of the aspects [1] to [3] above, the Ag coating layer of the flat electrical contact includes the organic Ag-containing coating layer and the modified Ag surface layer, the Ag coating layer of the bulged electrical contact contains Ag, and it preferably includes a high-purity Ag coating layer with a higher Ag concentration than the organic Ag-containing coating layer of the flat electrical contact. In this case, the effect of suppressing wear of the bulged electrical contact is highly obtained. Also, the Ag coating layer of the bulged electrical contact has high strength, and the occurrence of damage such as cracks associated with the formation of the bulged shape is suppressed.

[0019] [5] Alternatively, in any of the aspects [1] to [3] above, the Ag coating layers on the surfaces of the bulged electrical contact and the flat electrical contact preferably both include the organic Ag-containing coating layer and the modified Ag surface layer. In this case as well, the effect of suppressing wear of the bulged electrical contact is highly obtained.

[0020] [6] In any of the aspects [1] to [5] above, the bulged electrical contact is preferably capable of sliding a distance of 200 μm or more on the surface of the flat electrical contact. As described above, the modified Ag surface layer can be formed by sliding with the mating electrical contact with respect to the organic Ag-containing coating layer. By setting the sliding distance to 200 μm or more, during the sliding, the formation of the modified Ag surface layer proceeds sufficiently, and a high effect of suppressing wear of the bulged electrical contact can be obtained.

[0021] [7] 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, and the pair of the first contact portion and the second contact portion is composed of any one of the electrical contact pairs [1] to [6] above and is electrically contactable with each other. By having the above electrical contact pair as a pair of contact portions that can be electrically contacted with each other, wear of the Ag coating layer can be effectively suppressed in the terminal having the bulged electrical contact.

[0022] [8] In the embodiment described in [7] 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 contact portion of the female terminal is generally provided with an embossed bulging electrical contact, and the contact portion of the male terminal is generally provided with a tab-shaped flat electrical contact. By providing the bulging electrical contact and the flat electrical contact that constitute the above electrical contact pair as their respective contact portions, wear of the Ag coating layer on the bulging electrical contact of the female terminal can be effectively suppressed.

[0023] [9] In the embodiment described in [8] above, it is preferable that the sliding distance of the bulging electrical contact on the surface of the flat electrical contact when mating the first terminal and the second terminal is 200 μm or more. This allows for sufficient formation of the modified Ag surface layer during sliding, resulting in a terminal pair that is highly effective in suppressing wear of the bulging electrical contact. Similarly, it is preferable that the amplitude of the micro-sliding when vibration is applied to the mated terminal pair is also 200 μm or more.

[0024]

[10] In the embodiment of [8] or [9] above, the sliding amount is the product of the load applied to press the bulging electrical contact against the flat electrical contact and the sliding distance of the bulging electrical contact on the surface of the flat electrical contact when mating the first terminal and the second terminal, and it is preferable that the sliding amount be 14 N mm or more. Then, the formation of the modified Ag surface layer progresses sufficiently during sliding, resulting in a terminal pair that is highly effective in suppressing wear of the bulging electrical contact. As shown in the example, the content of sulfur-containing organic compounds in the modified Ag surface layer has a negative correlation with the sliding amount, and the larger the sliding amount, the more effective it is in suppressing wear of the bulging electrical contact due to the progress of the formation of the modified Ag surface layer.

[0025] [Details of the embodiments of this disclosure] The electrical contact pairs and terminal pairs according to embodiments of this 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.

[0026] <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 electrically contact each other on their respective surfaces.

[0027] 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 can approximate 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 is preferable that it has 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%.

[0028] 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 contacts the surface of the flat electrical contact 3 at its top.

[0029] 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 (in the lateral direction in the figure), thereby reversibly forming and dissolving electrical contact between the two electrical contacts 2 and 3.

[0030] As shown in Figure 1, the bulging electrical contact 2 is made of a metal material 20 having a bulging-side Ag coating layer 2A on its surface. The flat electrical contact 3 is made of a metal material 30 having a flat-side Ag coating layer 3B 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 bulging-side Ag coating layer 2A and flat-side Ag coating layer 3A. Both the bulging-side Ag coating layer 2A and the flat-side Ag coating layer 3A are made of metal layers mainly composed of Ag. At least one of the bulging-side Ag coating layer 2A and the flat-side Ag coating layer 3A has a containing Ag coating layer. Furthermore, at least one of the bulging-side Ag coating layer 2A and the flat-side Ag coating layer 3A has a modified Ag surface layer as its outermost layer. Below, as an example, we will sequentially describe the details of the configuration of the bulging electrical contact 2 and the flat electrical contact 3 in a configuration in which the flat-side Ag coating layer 3A is composed of the contained Ag coating layer and the modified Ag surface layer, and the bulging-side Ag coating layer 2A is composed of a high-purity Ag coating layer with a higher Ag purity than the contained Ag coating layer.

[0031] (Configuration of bulging electrical contacts) As shown in Figure 2A, the bulging electrical contact 2 is composed of a metal material 20 having a base material 21 and a high-purity Ag coating layer 24 as the bulging Ag coating layer 2A. The high-purity Ag coating layer 24 is formed by coating 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 are commonly used as base materials for terminals.

[0032] The high-purity Ag coating layer 24 contains Ag, and the concentration of Ag is higher than that of the Ag coating layer 34 containing the flat plate-shaped electrical contact 3, which will be described later. Preferably, the Ag content is 99.0% by mass or more. More preferably, the high-purity Ag coating layer 24 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 24 is higher than the surface hardness of the Ag coating layer 34 containing the flat plate-shaped electrical contact 3.

[0033] The high-purity Ag coating layer 24 may contain only Ag and unavoidable impurities, but it is preferable that it contains, in addition to Ag and unavoidable impurities, additive elements that have the 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 amount of these additive elements added should be kept within a range of 0.1 mass% or less of the total high-purity Ag coating layer 24.

[0034] Because the high-purity Ag coating layer 24 has high Ag purity, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and conductivity, can be effectively utilized as properties of the high-purity Ag coating layer 24. Furthermore, because the high-purity Ag coating layer 24 has high purity, unlike the contained Ag coating layer 34 which contains additives made of organic compounds and has low Ag purity, as will be explained later, it is less likely to cause the metal structure to become brittle due to the inclusion of additives. Therefore, even if the metal material 20 equipped with the high-purity Ag coating layer 24 is subjected to machining such as press working and formed into a bulging shape, damage such as cracks is less likely to occur on the surface of the high-purity Ag coating layer 24 due to the load associated with processing. There is no particular upper limit set for the Ag concentration in the high-purity Ag coating layer 24, but it is preferable to keep it at a concentration that allows for the addition of additive elements that harden the Ag layer, such as Se.

[0035] The thickness of the high-purity Ag coating layer 24 is not particularly limited, but for example, from the viewpoint of fully exhibiting the properties of the high-purity Ag coating layer 24, it is preferably 1 μm or more, and more preferably 3 μm or more. On the other hand, from the viewpoint of ensuring the processability of the metal material 20, it is preferably 10 μm or less.

[0036] In the metal material 20 constituting the bulging electrical contact 2, the high-purity Ag coating layer 24 may be directly formed on the surface of the substrate 21. However, another type of metal layer may be formed between the substrate 21 and the high-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 substrate 21, such as Cu, into the high-purity Ag coating layer 24, and also enhances the adhesion of the high-purity Ag coating layer 24 to the substrate 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. In the metal material 20, at the interface of each adjacent layer, some of the metal atoms constituting the layers on both sides may form an alloy.

[0037] Furthermore, similar to the metal material 30 that constitutes the flat electrical contact 3 described later, an intermediate layer and / or strike layer made of high-purity Ag may be provided between the high-purity Ag coating layer 24 and the base layer 22. If provided, the configuration may be the same as that described for the metal material 30 below. However, in the case of the metal material 20 of the bulging electrical contact 2, the need to provide an intermediate layer or strike layer is low, given that the high-purity Ag coating layer 24 is provided on the surface. Also, similar to how a modified Ag surface layer 35 is formed on the surface of the containing Ag coating layer 34 in the flat-side Ag coating layer 3A, a modified Ag surface layer, that is, a layer with a higher Ag concentration than the containing Ag coating layer 34 of the flat-side Ag coating layer 3A and containing sulfur-containing organic compounds as appropriate, may be formed as the outermost layer on the surface of the high-purity Ag coating layer 24 as the bulging-side Ag coating layer 2A. Thus, the modified Ag surface layer constituting the outermost layer of the bulging Ag coating layer 2A may be formed by alteration of the high-purity Ag coating layer 24 due to the application of processing strain, similar to the modified Ag surface layer 35 of the flat plate side Ag coating layer 3A, or, instead or in addition to that, it may be formed by the transfer of the modified Ag surface layer 35 of the flat plate side Ag coating layer 3A.

[0038] The high-purity Ag coating layer 24 is preferably exposed to the outermost surface of the metal material 20, excluding the modified Ag surface layer. However, a coating made of organic material or the like may be formed on the surface of the high-purity Ag coating layer 24, as long as it does not significantly impair the properties of the high-purity Ag coating layer 24. However, as will be described later, the sulfur-containing organic compound contained in the Ag coating layer 3A on the flat side of the flat electrical contact 3 can act as a discoloration inhibitor, so it is not necessary to separately provide a layer of discoloration inhibitor on the surface of the high-purity Ag coating layer 24.

[0039] The high-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. 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 22 can be formed on the surface of the substrate 21 as appropriate, and then the high-purity Ag coating layer 24 can be formed to form a flat metal material 20. A bulge-shaped electrical contact 2 can then be manufactured by pressing the metal material 20 to form a bulge shape.

[0040] (Configuration of flat-plate 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 flat-side Ag coating layer 3A 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 plate-side Ag coating layer 3A includes an organic Ag coating layer 34 and a modified Ag surface layer 35. The modified Ag surface layer 35 is configured as a layer that covers the surface of the organic Ag coating layer 34 and is thinner than the organic Ag coating layer 34.

[0042] The containing Ag coating layer 34 contains Ag and a sulfur-containing organic compound. In the containing Ag coating layer 34, it is preferable that the Ag content is in the range of 96.0% by mass or more and 99.5% by mass or less.

[0043] The type of sulfur-containing organic compound contained in the Ag coating layer 34 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.

[0044] The sulfur-containing organic compounds contained in the Ag coating layer 34 play a role in improving wear resistance. Specifically, when the flat electrical contact 3 is brought into contact with the bulging electrical contact 2 and slid, they suppress adhesion between the bulging side Ag coating layer 2A and the flat side Ag coating layer 3A, 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 Ag coating layer 34 and thereby improving wear resistance by refining the Ag crystals. In this specification, the sulfur-containing organic compounds contained in the Ag coating layer 34 (and modified Ag surface layer 35) include all components derived from organic molecules containing sulfur atoms, including forms in which the shape of the sulfur atom-containing organic molecule is maintained, forms in which at least a portion of such molecules undergo intramolecular bond cleavage or rearrangement, and forms in which at least a portion of the constituent atoms, including sulfur atoms, form bonds with external atoms such as Ag. The content of sulfur-containing organic compounds also refers to the total amount of all those components combined.

[0045] Since the contained Ag coating layer 34 is composed mainly of Ag, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and conductivity, can be fully utilized as properties of the contained Ag coating layer 34. In particular, by ensuring high conductivity in the contained Ag coating layer 34, the contact resistance on the surface of the flat electrical contact 3 is reduced, and a good electrical connection can be formed between it and the mating bulging electrical contact 2. Furthermore, because the contained Ag coating layer 34 has high conductivity, the heat generated when a large current flows through the metal material 30 can be kept to a minimum, making it easier to apply the flat electrical contact 3 to applications where a large current is applied, such as high-current terminals. These effects are especially enhanced if the contained Ag coating layer contains Ag at a concentration of 96.0% by mass or higher. Furthermore, when manufacturing electrical connection members such as terminals having flat electrical contacts 3, although less severe than with electrical connection members including bulging electrical contacts 2, a certain amount of load is applied to the metal material 30 by machining, such as press molding, to form the terminal shape. However, if the containing Ag coating layer 34 contains Ag with a purity of 96.0% by mass or higher, the ductility of Ag can be used to suppress damage to the containing Ag coating layer 34 caused by machining of the metal material 30. From the viewpoint of further enhancing these effects, it is more preferable that the Ag concentration in the containing Ag coating layer 34 be 97.0% by mass or higher, and even more preferably 99.0% by mass or higher.

[0046] On the other hand, if the concentration of Ag in the containing Ag coating layer 34 is kept below 99.5% by mass, the wear resistance of the containing Ag coating layer 34 can be effectively improved. This is because, in the containing Ag coating layer 34, 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 containing Ag coating layer 34. 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 flat plate side Ag coating layer 3A. From the viewpoint of further enhancing these effects, it is more preferable that the concentration of Ag in the containing Ag coating layer 34 be below 99.4% by mass.

[0047] In the flat plate side Ag coating layer 3A, the containing Ag coating layer 34 may contain other components in addition to Ag and sulfur-containing organic compounds. However, from the viewpoint of minimizing the influence of the properties imparted by the sulfur-containing organic compounds, it is preferable that the containing Ag coating layer 34 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 24 described above and have the effect of hardening the Ag layer, are not contained in the containing Ag coating layer 34, 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 containing Ag coating layer 34 is 0.5% by mass or more and 3.0% by mass or less. This allows for a high improvement in wear resistance due to the addition of sulfur-containing organic compounds, while minimizing the decrease in conductivity of the containing Ag coating layer 34 due to the addition of a large amount of sulfur-containing organic compounds.

[0048] As described above, in the containing Ag coating layer 34, 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 containing Ag coating layer 34 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 containing Ag coating layer 34, and it is preferable that the hardness of the containing Ag coating layer 34 is 90 HV or more and 150 HV or less on a Vickers hardness scale.

[0049] The thickness of the contained Ag coating layer 34 is not particularly limited. For example, a thickness of 0.5 μm or more, or 5 μm or less, can be exemplified. The contained Ag coating layer 34 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.

[0050] As described above, the modified Ag surface layer 35 is a layer that covers the surface of the containing Ag coating layer 34, but has a higher Ag concentration and a lower concentration of sulfur-containing organic compounds compared to the containing Ag coating layer 34. To that extent, the modified Ag surface layer 35 may be configured as a layer that substantially does not contain sulfur-containing organic compounds, like the high-purity Ag coating layer 24 that constitutes the bulging Ag coating layer 2A, or it may contain sulfur-containing organic compounds at a lower concentration than the containing Ag coating layer 34. Furthermore, when the modified Ag surface layer 35 contains sulfur-containing organic compounds, those sulfur-containing organic compounds may be the same as those contained in the containing Ag coating layer 34, or they may be different. However, from the viewpoint of ease of formation of the modified Ag surface layer 35, it is preferable that the modified Ag surface layer 35 contains the same sulfur-containing organic compounds as the containing Ag coating layer 34, but at a lower concentration than the containing Ag coating layer 34. It is preferable that the modified Ag surface layer 35 is integrally continuous with the containing Ag coating layer 34.

[0051] By forming a modified Ag surface layer 35 on the surface of the containing Ag coating layer 34, which has a higher Ag concentration and a lower concentration of sulfur-containing organic compounds than the containing Ag coating layer 34, the effect of the containing Ag coating layer 34 in improving wear resistance between electrical contacts 2 and 3 is further enhanced. In particular, the presence of the modified Ag surface layer 35 makes wear of the Ag coating layers 2A and 3A more likely to occur on the surface of the flat electrical contact 3 than on the bulging electrical contact 2, and effectively suppresses wear on the surface of the bulging electrical contact 2.

[0052] The Ag concentration in the modified Ag surface layer 35 is not particularly limited, as long as it is higher than the Ag concentration in the containing Ag coating layer 34. However, from the viewpoint of enhancing the effect of providing the modified Ag surface layer 35, it is preferable that the Ag concentration in the modified Ag surface layer 35 be 1.01 times or more, and more preferably 1.03 times or more, than the Ag concentration in the containing Ag coating layer 34. There is no particular upper limit to this ratio, but it is generally preferable to keep it at 1.1 times or less. Furthermore, it is preferable that the Ag concentration in the modified Ag surface layer 35 be 94% by mass or more, and more preferably 97% by mass or more. There is no particular upper limit to the Ag concentration in the modified Ag surface layer 35.

[0053] The concentration of sulfur-containing organic compounds in the modified Ag surface layer 35 is not particularly limited, as long as it is lower than the concentration of sulfur-containing organic compounds in the containing Ag coating layer 34. However, from the viewpoint of enhancing the effect of providing the modified Ag surface layer 35, it is preferable to set the concentration of sulfur-containing organic compounds in the modified Ag surface layer 35 to 0.7 times or less, and more preferably 0.5 times or less, the concentration of sulfur-containing organic compounds in the containing Ag coating layer 34. There is no particular lower limit for this ratio. Furthermore, it is preferable to set the concentration of sulfur-containing organic compounds in the modified Ag surface layer 35 to 6.0% by mass or less, and more preferably 3.0% by mass or less. There is no particular lower limit for the concentration of sulfur-containing organic compounds in the modified Ag surface layer 35.

[0054] The modified Ag surface layer 35 tends to exhibit higher hardness than the contained Ag coating layer 34 because it has a higher Ag concentration. The thickness of the modified Ag surface layer 35 is not particularly limited as long as it is thinner than the contained Ag coating layer 34, but from the viewpoint of enhancing the effects of providing the modified Ag surface layer 35, it is preferable to have a thickness of 40 nm or more.

[0055] In the metal material 30 constituting the flat electrical contact 3, the laminated structure of the contained Ag coating layer 34 and the modified Ag surface layer 35 may be directly formed on the surface of the base material 31. Alternatively, another type of metal layer may be formed between the base material 31 and the contained Ag coating layer 34. An example of such another type of metal layer is a base layer 32 made of Ni or a Ni alloy. The base layer 32 can have a configuration similar to that of the base layer 22 optionally provided on the metal material 20 constituting the bulging electrical contact 2.

[0056] Furthermore, an intermediate layer 33a may be provided directly beneath the containing Ag coating layer 34, that is, between the base layer 32 and the containing Ag coating layer 34, consisting of a layer with a higher Ag purity than the containing Ag coating layer 34. The intermediate layer 33a plays a role in suppressing corrosion of the substrate 31 and the base layer 32 due to the influence of sulfur-containing organic compounds contained in the containing Ag coating layer 34. Furthermore, a strike layer 33b may be provided below the intermediate layer 33a, that is, between the base layer 32 and the intermediate layer 33a. The strike layer 33b is provided as a layer with a higher Ag purity than the containing Ag coating layer 34 and a thinner layer than the intermediate layer 33a. It is preferable that the strike layer 33b is composed of smaller crystal grains than the intermediate layer 33a. The strike layer 33b plays a role in improving the adhesion between the containing Ag coating layer 34 and the intermediate layer 33a to the base layer 32. A configuration in which only the strike layer 33b is provided without the intermediate layer 33a is also possible. In the metal material 30, at the interface of each adjacent layer, some of the metal atoms constituting the layers on both sides may form an alloy. Furthermore, while it is preferable that the modified Ag surface layer 35 is exposed to the outermost surface of the metal material 30, a coating made of organic material or the like may be formed on the surface of the modified Ag surface layer 35, as long as it does not significantly impair the properties of the containing Ag coating layer 34 and the modified Ag surface layer 35. However, as with the case of the metal material 20 constituting the bulging electrical contact 2, it is not necessary to provide a layer of discoloration inhibitor on the surface.

[0057] The preferred configuration of the containing Ag coating layer 34 is as described above, but for example, the Ag plating layer disclosed in Patent Document 1 can be suitably applied as the containing Ag coating layer 34. The containing 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, etc. For example, electroplating can be performed using an Ag plating solution containing a sulfur-containing organic compound.

[0058] The method for forming the modified Ag surface layer 35 is not particularly limited. For example, the modified Ag surface layer 35 may be formed separately from the contained Ag coating layer 34 on the surface of the contained Ag coating layer 34 by a plating method using a plating solution containing Ag at a higher concentration than that used to form the contained Ag coating layer 34. However, it is preferable to alter the surface of the contained Ag coating layer 34 and the surrounding area to form the modified Ag surface layer 35, from the viewpoint of improving adhesion between the contained Ag coating layer 34 and the modified Ag surface layer 35 and the ease of forming the modified Ag surface layer 35. As a method for altering the contained Ag coating layer 34 to form the modified Ag surface layer 35, a method of applying a mechanical load to the surface of the contained Ag coating layer 34 and applying processing strain can be considered. By applying processing strain, some of the sulfur-containing organic compounds are discharged to the outside of the coating layer from the surface of the contained Ag coating layer 34 and the surrounding area. This results in a decrease in the concentration of sulfur-containing organic compounds and a corresponding increase in the Ag concentration, forming a modified Ag surface layer 35 as a processed altered layer.

[0059] When applying processing strain to the containing Ag coating layer 34 to form a modified Ag surface layer 35, the method of applying the processing strain is not particularly limited and can include machining such as press working, or surface friction due to sliding with other components. Among these, from the viewpoint of efficiency and simplicity in forming the modified Ag surface layer 35, it is preferable to use surface friction due to sliding with other components. Surface friction can be carried out as one step in the manufacturing process of the metal material 30, such as before processing the metal material 30 into a predetermined terminal shape. In that case, a metal layer such as an underlayer 32, a strike layer 33b, or an intermediate layer 33a can be formed on the surface of the base material 31 as appropriate, then the containing Ag coating layer 34 can be formed, and then processing strain by surface friction can be applied to form a modified Ag surface layer 35 to produce the metal material 30, and the metal material 30 can be processed into a predetermined shape to form a flat plate-shaped electrical contact 3. Alternatively, the metal material 30 can be manufactured without forming the modified Ag surface layer 35, and a flat electrical contact 3 can be formed from the metal material 30 with the contained Ag coating layer 34 already formed, and then slid between it and the bulging electrical contact 2. The friction resulting from this sliding between the flat electrical contact 3 and the bulging electrical contact 2 applies processing strain to the contained Ag coating layer 34, allowing the modified Ag surface layer 35 to form on the surface of the contained Ag coating layer 34. As a result of this sliding forming of the modified Ag surface layer 35, the effect of the modified Ag surface layer 35 can be enjoyed to suppress wear on the surface of the bulging electrical contact 2 from the next sliding onward. The sliding with the bulging electrical contact 2 to form the modified Ag surface layer 35 may be performed independently of the sliding required for use before the electrical contact pair 1 is put into actual use, or it may be performed when the electrical contact pair 1 is put into actual use, combined with the sliding required for use.

[0060] When a modified Ag surface layer 35 is formed by the sliding of an electrical contact pair 1, at least a portion of the modified Ag surface layer 35 formed on the surface of the flat electrical contact 3 may transfer to the surface of the high-purity Ag coating layer 24 of the opposing bulging electrical contact 2. From the viewpoint of effectively suppressing wear on the surface of the flat electrical contact 3, it is preferable that this transfer occurs. It is even more preferable that, as a result of the transfer, the modified Ag surface layer 35 remaining on the surface of the flat electrical contact 3 is thinner than the modified Ag surface layer formed on the surface of the bulging electrical contact 2. Most preferably, as a result of the transfer, substantially no modified Ag surface layer remains on the surface of the flat electrical contact 3.

[0061] When forming a modified Ag surface layer 35 by sliding with a bulging electrical contact 2, it is preferable that the sliding distance of the bulging electrical contact 2 on the surface of the flat electrical contact 3 be 200 μm or more, and more preferably 2 mm or more. This makes it easier to sufficiently promote the formation of the modified Ag surface layer 35 by applying processing strain. Also, from a similar viewpoint, it is preferable that the amount of sliding of the bulging electrical contact 2 on the surface of the flat electrical contact 3 be 14 N mm or more, and more preferably 20 N mm or more. Here, the amount of sliding is defined as the product of the load pressing the bulging electrical contact 2 against the flat electrical contact 3 and the sliding distance of the bulging electrical contact 2 on the surface of the flat electrical contact 3. With the bulging electrical contact 2 and the flat electrical contact 3 in contact due to mating or other means of terminal pair connection, the micro-sliding motion that occurs at the contact point between the electrical contacts 2 and 3 due to vibration or thermal cycles can also be utilized for the formation of the modified Ag surface layer 35, and it is preferable that the amplitude of this micro-sliding motion is 200 μm or more.

[0062] (Characteristics of electrical contact pairs) As described above, the electrical contact pair 1 according to this embodiment includes a bulging electrical contact 2 having a bulging Ag coating layer 2A on its surface and a flat electrical contact 3 having a flat Ag coating layer 3A on its surface, and both electrical contacts 2 and 3 have both Ag coating layers 2A and 3A The surfaces of the two contacts are electrically able to contact each other. Both the bulging electrical contact 2 and the flat electrical contact 3 are coated with a metal layer mainly composed of Ag, a metal with excellent properties such as heat resistance, corrosion resistance, and conductivity, resulting in an electrical contact pair 1 with excellent electrical contact characteristics and durability.

[0063] Furthermore, since at least one of the bulging Ag coating layer 2A and the flat plate side Ag coating layer 3A, in the example described in detail above, the flat plate side Ag coating layer 3A has a sulfur-containing organic compound-containing Ag coating layer 34, adhesion between the flat plate-shaped electrical contact 3 and the bulging electrical contact 2 is suppressed, and the coefficient of friction during sliding is kept low. As a result, the electrical contact pair 1 has high wear resistance. Moreover, since a modified Ag surface layer 35 with a higher Ag concentration and a lower concentration of sulfur-containing organic compound than the containing Ag coating layer 34 is provided on the surface of the containing Ag coating layer 34, wear on the surface of the bulging Ag coating layer 2A is effectively suppressed in particular.

[0064] When an electrical contact pair 1 is provided on a terminal pair, including a bulging electrical contact 2 and a flat electrical contact 3, when sliding occurs between the bulging electrical contact 2 and the flat electrical contact 3, due to the shapes of the electrical contacts 2 and 3, the contact point on the surface of the flat electrical contact 3 moves with the sliding of the bulging electrical contact 2, while the same point at the top of the surface of the bulging electrical contact 2 always contacts the flat electrical contact 3. Therefore, wear of the coating layer 2A is more likely to occur on the surface of the bulging electrical contact 2 than on the flat electrical contact 3, and the effects of wear are more serious. However, in the electrical contact pair 1 according to this embodiment, since a containing Ag coating layer 34 and a modified Ag surface layer 35 are provided as the flat-side Ag coating layer 3A, surface wear due to sliding is more likely to occur on the flat electrical contact 3 than on the bulging electrical contact 2, and the amount of surface wear on the bulging electrical contact 2 can be kept to a minimum. In the bulging electrical contact 2, which has a shape prone to surface wear, suppressing wear reduces the impact of wear on the Ag coating layers 2A and 3A due to sliding on the electrical contact pair 1 as a whole. This allows the effects of heat resistance, corrosion resistance, and improved conductivity provided by the Ag coating layers 2A and 3A to be maintained over a long period even after sliding. Furthermore, by suppressing wear on the bulging electrical contact 2, it becomes unnecessary to form a thicker Ag coating layer 2A on the bulging side in anticipation of wear, thereby reducing the material cost required for the Ag coating layer 2A. In the flat electrical contact 3, wear on the Ag coating layer 3A will occur, but due to the effect of the shape, surface wear on the flat electrical contact 3 is kept to a minimum in the first place. Therefore, the impact of wear on the flat side Ag coating layer 3A and the increase in material cost are limited.

[0065] From the viewpoint of further enhancing the effect of the modified Ag surface layer 35 in suppressing wear of the bulging side Ag coating layer 2A, it is preferable that the Ag concentration at the outermost surface of the bulging electrical contact 2 is higher than that at the outermost surface of the flat electrical contact 3. In other words, it is preferable that the Ag concentration at the outermost surface of the bulging side Ag coating layer 2A is higher than the Ag concentration at the outermost surface of the flat side Ag coating layer 3A. In the specific example described above, it is preferable that the Ag concentration on the surface of the high-purity Ag coating layer 24 constituting the outermost surface of the bulging electrical contact 2 is higher than the Ag concentration on the surface of the modified Ag surface layer 35 constituting the outermost surface of the flat electrical contact 3. The specific relationship between the Ag concentrations at the outermost surfaces of the bulging electrical contact 2 and the flat electrical contact 3 is not particularly limited, but it is preferable that the ratio of the Ag concentration at the outermost surface of the bulging electrical contact 2 to the Ag concentration at the outermost surface of the flat electrical contact 3 (bulging side Ag concentration / flat side Ag concentration) is 1.01 or higher, and more preferably 1.02 or higher. There is no particular upper limit to this ratio, but it is preferable to keep it below 1.10, for example. Regarding the concentration of sulfur-containing organic molecules, it is preferable that the concentration at the outermost surface of the bulging electrical contact 2 is lower than that at the outermost surface of the flat electrical contact 3.

[0066] 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 later, the electrical contact pair 1 according to this embodiment can be suitably applied as a contact pair for an electrical connection terminal.

[0067] (Other configuration examples) In the example described in detail above, a high-purity Ag coating layer 24 was provided as the bulging Ag coating layer 2A, and a containing Ag coating layer 34 and a modified Ag surface layer 35 were provided as the flat plate Ag coating layer 3A. However, in the electrical contact pair 1 according to this embodiment, the configuration of the bulging Ag coating layer 2A and the flat plate Ag coating layer 3A is not limited to these, and it is sufficient that at least one of the two Ag coating layers 2A and 3A contains a containing Ag coating layer, and at least one of the two Ag coating layers 2A and 3A contains a modified Ag surface layer as the outermost layer. In other words, the bulging electrical contact 2 and the flat electrical contact 3 each have an Ag coating layer 2A, 3A on their surface, which is a metal layer mainly composed of Ag, and the Ag coating layer on at least one surface of the bulging electrical contact 2 and the flat electrical contact 3 is a containing Ag coating layer, and the Ag coating layer on at least one surface of the bulging electrical contact 2 and the flat electrical contact 3 is a modified Ag surface layer as the outermost layer. Here, the containing Ag coating layer contains Ag and a sulfur-containing organic compound. The modified Ag surface layer is a thinner layer than the containing Ag coating layer, and has a higher Ag concentration and a lower sulfur-containing organic compound concentration compared to the containing Ag coating layer. Furthermore, it is preferable that the Ag concentration on the outermost surface of the bulging electrical contact 2 is higher than that on the outermost surface of the flat electrical contact 3. As described above, both the contained Ag coating layer and the modified Ag surface layer are included in the Ag coating layer on at least one of the surfaces of the bulging electrical contact 2 and the flat electrical contact 3. However, among the Ag coating layers 2A and 3A of both electrical contacts 2 and 3, the Ag coating layer containing the contained Ag coating layer and the Ag coating layer containing the modified Ag surface layer may be the same or different. If they are the same, the modified Ag surface layer will be provided covering at least the surface of the contained Ag coating layer. Furthermore, whether the contained Ag coating layer constitutes the bulging side Ag coating layer 2A, the flat side Ag coating layer 3A, or both, the specific configuration of the metal material containing the contained Ag coating layer may be the same as the configuration described for the metal material 30 constituting the flat electrical contact 3 in the above example.

[0068] It is preferable that the containing Ag coating layer be provided as at least one layer constituting the flat plate side Ag coating layer 3A. Furthermore, it is preferable that the Ag coating layer on the side without the containing Ag coating layer be a high-purity Ag coating layer. In this case, the specific configuration of the metal material containing the high-purity Ag coating layer may be the same as the configuration described above for the metal material 20 constituting the bulging electrical contact 2. As a particularly preferred form, in addition to the configuration described above, in which a high-purity Ag coating layer 24 is provided as the bulging side Ag coating layer 2A and a containing Ag coating layer 34 is provided as the flat plate side Ag coating layer 3A, both the bulging side Ag coating layer 2A and the flat plate side Ag coating layer 3A may be configured to include a containing Ag coating layer. In this case, the specific configuration of the containing Ag coating layer in the bulging side Ag coating layer 2A and the flat plate side Ag coating layer 3A may be the same or different from each other.

[0069] As described above, the modified Ag surface layer is provided as the outermost layer of the Ag coating layer on at least one of the bulging electrical contact 2 and the flat electrical contact 3, and can be provided on either one or both of these electrical contacts 2 and 3. However, since the modified Ag surface layer is easily formed by the alteration of the containing Ag coating layer due to the application of processing strain, the modified Ag surface layer is more likely to be formed on the Ag coating layer containing the containing Ag coating layer. However, when sliding is applied to the electrical contact pair 1, it is possible that the modified Ag surface layer formed by the alteration of the containing Ag coating layer on the surface of one electrical contact may transfer to the surface of the other electrical contact, for example, the surface of the electrical contact on which the high-purity Ag coating layer is formed. As described above, the modified Ag surface layer may be provided on the surface of only one electrical contact or on both electrical contact surfaces. Even when both the bulging Ag coating layer 2A and the flat plate Ag coating layer 3A contain a material-containing Ag coating layer, the modified Ag surface layer may be formed on the surface of only one of the material-containing Ag coating layers or on the surfaces of both material-containing Ag coating layers. However, it is preferable that the surface of the flat plate electrical contact 3 does not have a modified Ag surface layer, and if it is provided, its thickness is preferably smaller than the thickness of the modified Ag surface layer on the surface of the bulging electrical contact 2. When the modified Ag surface layer is formed on the outermost layer of both material-containing Ag coating layers 2A and 3A, the specific configuration of the modified Ag surface layer in the bulging Ag coating layer 2A and the flat plate Ag coating layer 3A may be the same or different from each other.

[0070] 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.

[0071] <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. In other words, 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 up of the electrical contact pair 1 according to the embodiment of the present disclosure, and is capable of making electrical contact with each other.

[0072] 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 composed 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 bulging side Ag coating layer 2A is provided on the surface of the contact portion of the female terminal 5, and a flat side Ag coating layer 3A is provided on the surface of the contact portion of the male terminal 6.

[0073] 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.

[0074] Here, of the metal material 20 forming the female terminal 5, the bulging side Ag coating layer 2A is formed on the surface of at least the embossed portion 51a of the elastic contact piece 51, along with the base layer 22 and the like as appropriate (figure not shown). Then, of the metal material 30 forming the male terminal 6, the flat plate side Ag coating layer 3A is formed on the surface of at least the tab portion 61, along with the base layer 32, strike layer 33b, intermediate layer 33a and the like as appropriate (figure not shown). As described above for the electrical contact pair 1, at least one of the bulging side Ag coating layer 2A and the flat plate side Ag coating layer 3A has a containing Ag coating layer, and at least one of them has a modified Ag surface layer on its outermost surface. Preferably, the flat plate side Ag coating layer 3A of the male terminal 5 includes a laminated structure of a containing Ag coating layer 34 and a modified Ag surface layer 35, and the bulging side Ag coating layer 2A of the female terminal 5 includes a high-purity Ag coating layer 24. Alternatively, the bulging Ag coating layer 2A of the female terminal 5 may also include a laminated structure of a containing Ag coating layer and a modified Ag surface layer.

[0075] Thus, since at least one of the bulging-side Ag coating layer 2A 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 the flat-side Ag coating layer 3A formed on the surface of the tab portion 61 of the male terminal 6 which becomes a flat-plate electrical contact 3, has a contained Ag coating layer, and at least one of them has a modified Ag surface layer on its outermost surface, high wear resistance can be obtained at the electrical contact portion between the female terminal 5 and the male terminal 6, and in particular, wear can be effectively suppressed at the electrical contact 2 of the female terminal 5. As a result, the effect of wear on the Ag coating layers 2A and 3A can be kept to a minimum for the terminal pair 4 as a whole. In addition, the material cost required for the Ag coating layers 2A and 3A can be reduced.

[0076] In terminal pair 4, as a method for forming a modified Ag surface layer on the surface of the containing Ag coating layer, as described in detail above regarding the manufacturing method of the bulging electrical contact 2, a method can be adopted in which processing strain is applied to the containing Ag coating layer as one step in the manufacturing of the metal materials 20 and 30 constituting the female terminal 5 and male terminal 6. Alternatively, the modified Ag surface layer can be formed without forming the containing Ag coating layer in the manufacturing process of the metal materials 20 and 30, and the metal materials 20 and 30 can be formed into terminal pairs 2 and 3 with the containing Ag coating layer already formed. By sliding between the embossed portion 51a of the female terminal 5 and the tab portion 61 of the male terminal 6, processing strain can be applied to the containing Ag coating layer, thereby forming a modified Ag surface layer on the surface of the containing Ag coating layer. The sliding between the embossed portion 51a and the tab portion 61 may be performed independently of the sliding required for actual use before the terminal pair 4 is put into actual use, or it may be performed when the terminal pair is put into actual use, while also performing the sliding required for actual use, that is, the sliding required for forming / dissolving the mating connection between the male terminal 6 and the female terminal 5. In this case, from the viewpoint of sufficiently promoting the formation of the modified Ag surface layer due to the application of processing strain through sliding, it is preferable to set the sliding distance of the embossed portion 51a on the surface of the tab portion 61 when mating the male terminal 6 and the female terminal 5, that is, the distance the tip of the male terminal 6 moves from the entrance of the clamping portion 53 of the female terminal 5 to the correct connection completion position, to 200 μm or more. It is also preferable to set the sliding amount to 14 N mm or more. Here, the sliding amount is defined as the product of the load that presses the embossed portion 51a of the female terminal 5 against the tab portion 61 of the male terminal 6 and the above sliding distance. The load can be adjusted by the elastic force exerted by the elastic contact piece 51 of the female terminal 5, etc. [Examples]

[0077] 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 bulging and flat electrical contacts constituting an electrical contact pair and surface wear was investigated. Unless otherwise specified, sample preparation and evaluation were carried out at room temperature in air.

[0078] <Sample preparation> First, two types of metal materials were prepared: a high-purity Ag coating material and a material containing Ag. 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, thereby forming the high-purity Ag coating material and the material containing Ag coating material. The layered structure for the high-purity Ag coating material is shown in Figure 2A, and for the material containing Ag coating material, it is shown in Figure 2B, except that a modified Ag surface layer is not initially formed. The Ag concentration in each Ag layer was evaluated by glow discharge emission spectrometry (GD-OES) or energy-dispersive X-ray spectrometry (EDX). • 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) • Contains 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), containing Ag coating layer (thickness 1.0 μm, Ag purity 97.0% by mass) The contained Ag coating layer was fabricated using DuPont's "SILVERON GT-210 Durability Silver," a plating that contains sulfur-containing organic compounds.

[0079] 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, the flat metal material was used as the flat electrical contact. For each sample, the combination of Ag coating material shown in Table 1 was used as the metal material constituting the bulging and flat specimens.

[0080] For each model electrical contact pair created, the top of the bulging electrical contact of the bulging test piece and the surface of the flat electrical contact of the flat test piece were brought into contact and slid. The set of test pieces after sliding was adopted as the final sample. As shown in Table 1, samples 1 to 3 all consist of a bulging test piece and a flat test piece contained in an Ag coating material, but the amount of sliding was varied between them. Sliding was performed by applying a load that pressed the bulging electrical contact against the surface of the flat electrical contact, and then moving the bulging electrical contact back and forth on the surface of the flat electrical contact at a predetermined amplitude for a predetermined number of sliding movements. For all samples, the load was set to 7N and the amplitude to 2mm, and the amount of sliding was set according to the selection of the number of sliding movements, as shown in Table 1.

[0081] <Evaluation Method> • Check the layer structure The cross-sections of the bulging and flat electrical contacts of each sample were observed using a scanning electron microscope (SEM). The layer structure of the coating on the surface of each electrical contact was confirmed based on the observation results. In particular, it was confirmed whether a modified Ag surface layer was formed on the surface of the Ag coating layer of the Ag-containing coating material.

[0082] • Detailed analysis of the surface For each sample of bulging and flat electrical contacts, cross-sections were observed using a scanning transmission electron microscope (STEM) to further examine the layer structure of the surface. Furthermore, the composition of the surface layer was analyzed by energy-dispersive X-ray spectroscopy (EDX). From the EDX results, the depth distribution of the concentrations of each element, Ag, C, S, and O, was obtained. From this depth distribution, the ratio of the Ag concentration at the outermost surface of the bulging electrical contact to the Ag concentration at the outermost surface of the flat electrical contact (bulging side Ag concentration / flat side Ag concentration) was calculated.

[0083] • Check the condition of wear and tear For each sample, the wear state of the Ag coating layer was confirmed using an X-ray fluorescence film thickness gauge. Specifically, the wear of the Ag coating layer was investigated by sliding, which was performed as the final step in sample preparation, and whether it occurred on the flat or bulging surface of the electrical contact. This was recorded as a wear mode. In this process, if the film thickness of the Ag coating layer on the electrical contact after sliding was thinner than that of the surrounding area of ​​the electrical contact, it was determined that wear had occurred. If the film thickness of the Ag coating layer on the electrical contact after sliding had not changed compared to that of the surrounding area of ​​the electrical contact, it was determined that no wear had occurred. Furthermore, for electrical contacts where wear was determined to have occurred, the wear depth of the Ag coating layer was measured.

[0084] <Test Results> Table 1 below shows the type of Ag coating material and sliding amount constituting the bulging and flat specimens, as well as the Ag concentration and ratio at the outermost surface of both electrical contacts, and the wear state (wear mode and wear depth at the worn electrical contact). Furthermore, as representative examples, Figure 4A shows cross-sectional SEM images of both electrical contacts for sample 1, and Figure 4B shows cross-sectional SEM images of sample 5. As shown in correspondence with the schematic diagrams, the upper panel shows the bulging electrical contact with the surface side down, and the lower panel shows the flat electrical contact with the surface side up. Figure 5 shows a cross-sectional SEM image of the bulging electrical contact for sample 4. The upper panel is a low-magnification image, and the lower panel is a high-magnification image observing the vicinity of the surface. Figure 6 shows the results of detailed analysis of the surface layer for sample 1. The images in the left column show cross-sectional STEM images, and the graphs in the right column show the depth distribution of Ag, C, S, and O concentrations obtained by EDX at the locations indicated by dotted lines in the STEM images. As shown in correspondence with the schematic diagram, the upper section shows a bulging electrical contact with the surface side facing downwards, and the lower section shows a flat electrical contact with the surface side facing upwards. Furthermore, Figure 7 shows the relationship between the amount of sliding (product of sliding distance and load) and the wear depth. The data points indicated by circles indicate the wear depth of the flat electrical contacts for Examples 1 to 3, in which both electrical contacts were provided with a silver-containing coating layer, and for samples with different amounts of sliding. The data points indicated by squares indicate the wear depth of the bulging electrical contacts for Comparative Example 1, in which both electrical contacts were provided with a high-purity silver coating layer, and for samples with different amounts of sliding. The inset shows a magnified view of the low insertion depth region.

[0085] [Table 1]

[0086] First, let's look at the SEM image in Figure 4A for sample 1, which consists of both a bulging and a flat specimen made of a containing Ag coating material. In the SEM image, on the surface of the bulging electrical contact, in addition to the Ag intermediate layer (L1) and the containing Ag coating layer (L2), a thin layer (L3) is formed on the outermost surface, covering the surface of the containing Ag coating layer (L2). On the flat electrical contact as well, although not as clear as on the bulging electrical contact, a thin layer (L5) is formed on the outermost surface, covering the surface of the containing Ag coating layer (L4).

[0087] In the STEM image in Figure 6, the thin outermost layers (L3, L5) are observed even more clearly. Furthermore, looking at the depth distribution of elemental concentrations by EDX in Figure 4, it can be seen that in the regions corresponding to these thin layers (L3, L5), the Ag concentration is higher and the concentrations of C and S are lower than in the underlying Ag-containing coating layers (L2, L4). In particular, the changes in these elemental concentrations are more pronounced in the bulging specimens. From these analysis results, it is confirmed that the thin outermost layers (L3, L5) correspond to a modified Ag surface layer with a higher Ag concentration and a lower concentration of sulfur-containing organic compounds than the Ag-containing coating layers (L2, L4). Furthermore, as indicated by the dashed guide line, in the modified Ag surface layer (L3) constituting the outermost layer of the bulging electrical contact, the Ag concentration is higher and the concentration of sulfur-containing organic compounds is lower than in the modified Ag surface layer (L5) constituting the outermost layer of the flat electrical contact.

[0088] In addition to sample 1, in samples 2 to 4, in which at least one of the bulging and flat specimens was made of the contained Ag coating material, it was confirmed that, similar to sample 1, a modified Ag surface layer was formed on the surface of the electrical contacts of the specimens made of the contained Ag coating material, covering the surface of the contained Ag coating layer and having a higher Ag concentration and a lower concentration of sulfur-containing organic compounds than the contained Ag coating layer. Furthermore, it was confirmed that the Ag concentration was higher and the concentration of sulfur-containing organic compounds was lower on the outermost surface of the bulging electrical contacts than on the outermost surface of the flat electrical contacts. The ratio of Ag concentrations on the outermost surfaces of both electrical contacts is shown in Table 1, and the fact that the value of this ratio exceeds 1 in all samples 1 to 4 reflects that the Ag concentration on the outermost surface is higher in the bulging electrical contacts.

[0089] For sample 4, in which the bulging test specimen was made from high-purity silver coating material and the flat test specimen was made from the contained silver coating material, Figure 5 shows a cross-sectional SEM image of the bulging test specimen made from high-purity silver coating material. The upper row is a low-magnification image, and the lower row is a high-magnification image. Here, too, a thin layer (L9) is observed on the surface of the high-purity silver coating layer (L8). This thin layer (L9) can be identified as the modified silver surface layer, and it is thought that the modified silver surface layer, which was generated by sliding on the surface of the contained silver coating layer of the flat electrical contact, was transferred to the bulging electrical contact.

[0090] On the other hand, for sample 5, which used a high-purity Ag coating material instead of a contained Ag coating material for both the bulging and flat test specimens, as shown in Figure 4B, no layer distinct from the high-purity Ag coating layers (L6, L7) that corresponds to the modified Ag surface layer was formed on the surface of the high-purity Ag coating layer (L6) on the surface of the bulging electrical contact, nor on the surface of the high-purity Ag coating layer (L7) on the surface of the flat electrical contact. Furthermore, as shown in Table 1, the ratio of Ag concentrations at the outermost surfaces of both electrical contacts is exactly 1, indicating that the Ag concentrations in the high-purity Ag coating layers constituting the outermost surfaces of both electrical contacts remain equal. Note that the layer (Ni) observed beneath the high-purity Ag coating layer (L6) of the bulging electrical contact is the underlayer.

[0091] Table 1 shows the evaluation results of the wear modes. In samples 1 to 4, where a silver-containing coating layer is provided on at least one surface of the bulging electrical contact and the flat electrical contact, and a modified silver surface layer is formed, wear occurred on the flat electrical contact, but not on the bulging electrical contact. On the other hand, in sample 5, where a high-purity silver coating layer is provided on both the bulging and flat electrical contacts, and there is no modified silver surface layer, wear occurred on the bulging electrical contact. Furthermore, as shown in Table 1, the wear depth for each sample is significantly smaller on the flat electrical contact side of samples 1 to 4 than on the bulging electrical contact side of sample 5. Thus, by providing a silver-containing coating layer on at least one surface of the bulging and flat electrical contacts, and further forming a modified silver surface layer, wear on the surface of the bulging electrical contact can be suppressed, and wear on the surface of the flat electrical contact can also be kept shallow. Although the results are not shown here, it was also confirmed that when a silver-containing coating layer was applied to the surface of both electrical contacts, and the sliding amount was set to 80 N mm with a load of 2 N and an amplitude of 200 μm, wear occurred only on the flat electrical contact, and the wear depth was kept to a minimum.

[0092] In Figure 7, the data points indicated by circles show the wear depth of the wear that progressed only on the flat electrical contact due to sliding when a silver-containing coating layer was applied to the surface of both electrical contacts. Looking at the relationship between the amount of sliding and the wear depth, the wear depth increases as the amount of sliding increases. However, compared to the case where a high-purity silver-containing coating layer was applied to the surface of both electrical contacts, indicated by squares, the increase in wear depth with respect to the amount of sliding is significantly smaller. Furthermore, compared with the ratio of Ag concentrations on the outermost surface in Table 1, it can be said that the concentration of sulfur-containing organic compounds in the modified silver surface layer formed on the surface of the bulging electrical contact has a negative correlation with the amount of sliding. In addition, as the amount of sliding increases, wear of the electrical contact progresses due to the sliding itself, but on the other hand, when sliding occurs between electrical contacts where a silver-containing coating layer is formed on at least one of the surfaces of the electrical contacts, the formation of the modified silver surface layer progresses with increasing sliding. When the amount of sliding increases, if the degree of increase in the effect of suppressing wear of the bulging electrical contact due to the formation of the modified Ag surface is sufficiently large compared to the degree of wear progression, then the progression of wear in the bulging electrical contact can be suppressed when the amount of sliding increases. As a result of this effect, in Figure 7, in Comparative Example 1, the wear depth of the bulging electrical contact increases with a small amount of sliding, while in the cases marked with circles, including Examples 1 to 3, although the wear depth of the flat electrical contact also increases with increasing sliding, the gradient is kept small.

[0093] 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. [Explanation of Symbols]

[0094] 1 Electrical contact pair 2. Bulging electrical contacts 3. Flat electrical contacts 2A Ag coating layer on bulging side 3A Ag coating layer on flat plate side 20,30 Metal materials 21,31 Base material 22,32 Base layer 24 High purity Ag coating layer 33a middle class 33b Strike Layer 34 Ag-containing machine Ag coating layer 35. Modified Ag surface 4 terminal pairs 5 Female terminals 51 Elastic contact piece 51a Embossed area 52 Internal opposing contact surfaces 53 Clamping section 6 Male connectors 61 Tab section L1 Ag interlayer L2,L4 Ag-containing Ag coating layer L3, L5, L9 Degenerated Ag surface L6,L7,L8 High purity Ag coating layer

Claims

1. A bulging electrical contact that protrudes toward the surface, It includes a flat electrical contact having a smaller curvature than the aforementioned bulging electrical contact and capable of making electrical contact with the aforementioned bulging electrical contact on its surface, The bulging electrical contact and the flat electrical contact each have an Ag coating layer on their surface, which is a metal layer mainly composed of Ag. The Ag coating layer on at least one surface of the bulging electrical contact and the flat electrical contact has an Ag coating layer containing Ag and a sulfur-containing organic compound. The Ag coating layer on at least one surface of the bulging electrical contact and the flat electrical contact has a modified Ag surface layer as the outermost layer. The modified Ag surface layer is a thinner layer than the containing Ag coating layer, and has a higher Ag concentration and a lower concentration of the sulfur-containing organic compound compared to the containing Ag coating layer, in an electrical contact pair.

2. The pair of electrical contacts according to claim 1, wherein the Ag concentration is higher on the outermost surface of the bulging electrical contact than on the outermost surface of the flat electrical contact.

3. The electrical contact pair according to claim 1, wherein the modified Ag surface layer is provided so as to cover at least the surface of the containing Ag coating layer.

4. The Ag coating layer of the flat electrical contact comprises the contained Ag coating layer and the modified Ag surface layer. The pair of electrical contacts according to claim 1, wherein the Ag coating layer of the bulging electrical contact contains Ag, and includes a high-purity Ag coating layer having a higher concentration of Ag than the Ag-containing Ag coating layer of the flat electrical contact.

5. The pair of electrical contacts according to claim 1, wherein the Ag coating layer on the surface of the bulging electrical contact and the flat electrical contact both include the contained Ag coating layer and the modified Ag surface layer.

6. The pair of electrical contacts according to claim 1, wherein the bulging electrical contact is slidable over a distance of 200 μm or more on the surface of the flat electrical contact.

7. It includes 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 composed of an electrical contact pair as described in any one of claims 1 to 6, and is electrically contactable with each other. Terminal pair.

8. The first terminal is configured as a mating-type female terminal having the bulging electrical contact, The terminal pair according to claim 7, wherein the second terminal has the flat electrical contact and is configured as a male terminal that can be mated with the first terminal.

9. The terminal pair according to claim 8, wherein the sliding distance of the bulging electrical contact on the surface of the flat electrical contact when mating the first terminal and the second terminal is 200 μm or more.

10. The sliding amount is defined as the product of the load applied to press the bulging electrical contact against the flat electrical contact and the sliding distance of the bulging electrical contact on the surface of the flat electrical contact when mating and connecting the first terminal and the second terminal. The terminal pair according to claim 8 or claim 9, wherein the sliding amount is 14 N mm or more.

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