Electric contact pair and terminal pair

Abstract

To provide an electric contact pair formed by a pair of electric contact points having a coated layer containing Ag in a front surface and a terminal pair having such an electric contact pair, capable of suppressing damages of the coated layer caused by processing while improving an abrasion resistance.SOLUTION: An electric contact pair 1 contains: an expansion-like electric contact point 2 that is expanded toward a front surface side; and a flat-plate like electric contact point 3 of which a curvature is smaller than the expansion-like electric contact point 2, and which can be electrically contacted in the front surface with the expansion-like electric contact point 2. The expansion-like electric contact point 2 contains Ag, includes a high purity Ag coated layer 24 of which a content amount of Ag is 99.9 mass% or larger. Meanwhile, the flat-plate like electric contact point 3 contains Ag and a sulfur-containing organic compound in the front surface, and includes a low purity Ag coated layer 34 of which a content amount of Ag is 97.0 mass% or more and 99.5 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In automobiles, terminals with an Ag coating layer on the surface are sometimes used as electrical connection terminals for large currents. Terminals with an Ag coating layer on the surface have excellent heat resistance, corrosion resistance, and electrical conductivity, but because Ag is soft and prone to adhesion, the surface is prone to wear when subjected to sliding. Therefore, as one of the means to suppress wear while utilizing the excellent properties of Ag, such as heat resistance and electrical conductivity, a method is sometimes used in which the Ag coating layer contains additive elements such as Se to increase the hardness of the Ag coating layer and turn it into a hard silver layer.

[0003] However, there may be cases where the wear resistance cannot be sufficiently improved by making the Ag coating layer on the terminal surface into a hard silver layer by adding an additive element such as Se. For example, as the current of the terminal increases, it becomes necessary to apply a high contact load to the electrical contact, but when the electrical contact is slid by applying such a high contact load, the conventional hard silver layer may not be able to fully meet the required wear resistance. In such a case, it is considered to apply an Ag coating layer having better wear resistance than the conventional 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 a method of manufacturing a silver-plated material by forming a surface layer made of silver on a material using a silver plating solution containing benzothiazoles or derivatives thereof. It is said that this method can obtain a silver-plated material having better wear resistance than the conventional one. [Prior art documents] [Patent documents]

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

[0005] As disclosed in Patent Document 1, it is expected that a high effect in improving wear resistance can be obtained by adding an additive made of an organic compound such as benzothiazoles to the Ag coating layer provided on the electrical contact and keeping the Ag concentration in the Ag coating layer low. It is believed that the low Ag concentration suppresses adhesion of Ag and keeps the friction coefficient of the surface of the Ag coating layer low.

[0006] On the other hand, when an additive made of an organic compound is added to the Ag coating layer in an amount sufficient to obtain the effect of improving wear resistance, the Ag coating layer is likely to become brittle compared to conventional hard silver layers. Then, when a metal material with an Ag coating layer is processed into a predetermined shape by mechanical processing such as pressing, damage such as cracks is likely to occur on the surface of the Ag coating layer. When such damage occurs, the metal material present in the layer below the Ag coating layer, such as the base layer or base material, is likely to undergo denaturation such as oxidation, which causes a decrease in the durability of the terminal. In particular, when forming an embossed electrical contact, cracks are likely to occur on the surface of the bulging part of the electrical contact. In this way, when cracks occur in the Ag coating layer and oxidation progresses in the electrical contact, it becomes difficult to maintain the desired electrical connection characteristics for a long period of time.

[0007] In view of the above, an object of the present invention is to provide an electrical contact pair consisting of a set of electrical contacts having a coating layer containing Ag on the surface thereof, and a terminal pair having such an electrical contact pair, which can suppress damage to the coating layer due to processing while improving abrasion resistance, and a terminal pair. [Means for solving the problem]

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

[0009] The terminal pair of the present disclosure includes a first terminal having a first contact portion and a second terminal having a second contact portion, and the set of the first contact portion and the second contact portion constitutes the electrical contact pair and are capable of electrical contact with each other. Effect of the Invention

[0010] The electrical contact pairs and terminal pairs disclosed herein are electrical contact pairs consisting of a set of electrical contacts having a coating layer containing Ag on the surface thereof, and terminal pairs having such electrical contact pairs, and are electrical contact pairs and terminal pairs that can suppress damage to the coating layer associated with processing while improving abrasion resistance. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic diagram of an electrical contact pair according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view illustrating an example of a structure of a terminal pair according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a STEM image of a cross section of the low-purity Ag coating layer (organic-containing Ag layer 1). [Figure 4] FIG. 4 is a table showing the results of measuring the coefficient of friction while sliding a bulge-shaped electrical contact and a flat electrical contact against each other for a number of samples having different types of Ag coating layers provided on the surfaces of the two contacts. [Diagram 5]Figures 5A and 5B are SEM images of the surfaces of bulging electrical contacts. Figure 5A shows the case where a metal material with a high-purity Ag coating layer (hard Ag layer) was used, and Figure 5B shows the case where a metal material with a low-purity Ag coating layer (organic-containing Ag layer 1) was used. In both cases, the upper images show the entire surface of the bulging electrical contact, and the lower images show an enlarged view of the vicinity of the top of the bulging electrical contact. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Description of the embodiments of the present disclosure] First, an embodiment of the present disclosure will be described.

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

[0014] The electrical contact pair has good electrical contact properties and durability by having a coating layer containing Ag on the surfaces of both the bulging electrical contact and the flat electrical contact, utilizing the properties of Ag such as heat resistance, corrosion resistance, and high conductivity. The bulging electrical contact is processed into a shape that bulges toward the surface side, and compared to a flat electrical contact having a shape with a small curvature, damage such as cracks is more likely to occur in the Ag coating layer on the surface as a result of processing. However, the high-purity Ag coating layer provided on the surface of the flat electrical contact contains 99.9 mass% or more of Ag and does not contain additives or contains only a small amount of additives, so embrittlement due to the addition of additives is unlikely to occur. Therefore, even if it is processed into a bulging shape, damage such as cracks is unlikely to occur on the surface of the high-purity Ag coating layer as a result of processing, and deterioration of durability due to damage such as oxidation of the underlying metal from the cracks is unlikely to occur.

[0015] On the other hand, the low-purity Ag coating layer formed on the surface of the flat electrical contact contains a sulfur-containing organic compound, and the Ag content is suppressed to a relatively low purity range of 97.0 mass% to 99.5 mass%, so that the surface has high wear resistance and the friction coefficient between the electrical contacts is suppressed to a low level. As shown in the following examples, when the flat electrical contact has this low-purity Ag coating layer on its surface, even if the metal layer formed on the surface of the bulging electrical contact that serves as the mating electrical contact is a high-purity Ag coating layer that does not show high wear resistance by itself, a high wear resistance improvement effect is obtained to the same extent as in the case of a low-purity Ag coating layer. Unlike the bulging electrical contact, the flat electrical contact is not processed into a shape with a large curvature, so that even if the low-purity Ag coating layer has a property that is easily damaged during processing, the occurrence of damage to the electrical contact and the associated decrease in durability are suppressed to a small level.

[0016] In this way, by forming an Ag coating layer having a predetermined composition on the surfaces of the bulging electrical contact and the flat electrical contact, the wear resistance of the electrical contact pair can be improved while suppressing damage to the coating layer caused by processing. Furthermore, the sulfur-containing organic compound contained in the low-purity Ag coating layer not only improves the wear resistance but also prevents discoloration of the Ag coating layer, eliminating the need to apply a separate discoloration inhibitor to the surfaces of both electrical contacts.

[0017] [2] In the above aspect [1], the content of the sulfur-containing organic compound in the low-purity Ag coating layer may be 0.5% by mass or more and 3.0% by mass or less, so that the wear resistance of the electrical contact pair can be improved by the sulfur-containing organic compound, and the contact resistance between the electrical contacts can be kept low.

[0018] [3] In the above-mentioned aspect [1] or [2], the high-purity Ag coating layer may be configured as a hard silver layer. In this case, when the metal material is processed into a bulged shape to form the bulged electrical contact, the formation of cracks on the surface of the high-purity Ag coating layer is effectively suppressed. As a result, the electrical contact pair has high durability.

[0019] [4] In any one of the above-mentioned [1] to [3], in the bulging electric contact and the flat electric contact, the surface of the base material made of Cu or Cu alloy is covered with a base layer made of Ni or Ni alloy, and the surface of the base layer is covered with the high-purity Ag coating layer and the low-purity Ag coating layer, respectively. The base layer made of Ni or Ni alloy plays a role of improving the adhesion of the Ag coating layer to the base material made of Cu or Cu alloy and suppressing the diffusion of the base metal into the Ag coating layer. If a crack occurs in the Ag coating layer, the base layer made of Ni or Ni alloy may be oxidized from the crack, which may cause an effect such as an increase in contact resistance in the electric contact pair. However, since the high-purity Ag coating layer is formed on the surface of the bulging electric contact, damage such as cracks is unlikely to occur even after processing into a bulging shape, and such effects are unlikely to occur, and the electric contact pair exhibits high durability.

[0020] [5] 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 set of the first contact portion and the second contact portion is configured with any one of the electrical contact pairs [1] to [4] above and can be in electrical contact with each other. By having the above-mentioned electrical contact pair as a set of contact portions that can be in electrical contact with each other, this terminal pair is capable of improving wear resistance while suppressing damage to the coating layer caused by processing.

[0021] [6] In the above aspect [5], the first terminal may be configured as a mating type female terminal having the bulging electrical contact, and the second terminal may be configured as a male terminal having the flat electrical contact and matable with the first terminal. In a mating type terminal pair consisting of a female terminal and a male terminal, it is common for an embossed bulging electrical contact to be provided as a contact portion of the female terminal, and a tab-type flat electrical contact to be provided as a contact portion of the male terminal. By providing the bulging electrical contact and the flat electrical contact constituting the electrical contact pair as the contact portions, respectively, it is possible to obtain high wear resistance at the electrical contact portion between the two contacts and suppress damage caused by processing.

[0022] [Details of the embodiment of the present disclosure] Hereinafter, electrical contact pairs and terminal pairs according to embodiments of the present disclosure will be described in detail with reference to the drawings. Hereinafter, unless otherwise specified, values ​​indicating various characteristics are values ​​obtained at room temperature in the atmosphere.

[0023] <Electrical contacts> 1 is a schematic cross-sectional view of an electrical contact pair 1 according to an embodiment of the present disclosure. The electrical contact pair 1 according to an 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 be in electrical contact with each other on their respective surfaces.

[0024] The bulging electrical contact 2 has a shape bulging (embossed) on the surface side. The specific bulging shape of the bulging electrical contact 2 is not particularly limited, but it is preferable that the bulging shape is approximate to a partial elliptical sphere (elliptical cap; a shape obtained by cutting a part of an elliptical sphere on a flat surface; an elliptical sphere includes a true sphere), such as a semi-elliptical sphere. More preferably, the bulging electrical contact 2 has a partial sphere (spherical cap; a shape obtained by cutting a part of a sphere on a flat surface), such as a hemisphere. In this specification, approximating a certain shape refers to a shape in which the dimensional deviation from the shape is within 10%.

[0025] The flat electrical contact 3 has a planar structure with a smaller curvature (larger radius of curvature) than the bulging electrical contact 2. The specific shape of the flat electrical contact 3 is not particularly limited, and may have a curved shape that is gentler than the bulging shape of the bulging electrical contact 2, but is preferably a plane or a flat shape that can be approximated to it. The bulging electrical contact 2 and the flat electrical contact 3 are electrically contacted 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 an electrical contact between the two electrical contacts 2 and 3, the bulging electrical contact 2 comes into contact with the surface of the flat electrical contact 3 at its top, as shown in the figure.

[0026] A combination of a partially ellipsoidal bulging electrical contact 2 and a flat, planar electrical contact 3 is often used in a male-female mating type terminal pair as will be described later with reference to Figure 2. By inserting and removing a terminal (male terminal 6) having a planar electrical contact 3 into a terminal (female terminal 5) having a bulging electrical contact 2, the bulging electrical contact 2 and the planar electrical contact 3 are caused to slide relative to each other within the plane of the planar electrical contact 3 (horizontal direction in the figure), and electrical contact between the two electrical contacts 2, 3 can be reversibly made / broken.

[0027] As shown in Fig. 1, the bulging electrical contact 2 is made of a metal material 20 having a high-purity Ag coating layer 24 on its surface. The flat electrical contact 3 is made of a metal material 30 having a low-purity Ag coating layer 34 on its surface. The bulging electrical contact 2 and the flat electrical contact 3 are in contact with each other at the surfaces of the high-purity Ag coating layer 24 and the low-purity Ag coating layer 34, respectively. Both the high-purity Ag coating layer 24 and the low-purity Ag coating layer 34 are made of metal layers mainly composed of Ag, but have different component compositions. The configurations of the bulging electrical contact 2 and the flat electrical contact 3 will be described in detail below.

[0028] (Structure of bulging electrical contacts) As shown in Fig. 1, 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 that coats 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 such as terminals can be used. Preferably, the base material 21 is composed of Cu or a Cu alloy, which is widely used as a base material for terminals.

[0029] The high-purity Ag coating layer 24 is a layer exposed on the outermost surface of the metal material 20. The high-purity Ag coating layer 24 contains Ag, and the Ag content is 99.9 mass % or more. Preferably, the high-purity Ag coating layer 24 is configured as a hard silver layer. Here, the hard silver layer is a layer of Ag or an Ag alloy having a surface hardness of about 90 HV or more, preferably 110 HV or more, in Vickers hardness. In addition, the surface hardness of the high-purity Ag coating layer 24 is preferably higher than the surface hardness of the low-purity Ag coating layer 34 of the flat electrical contact 3.

[0030] The high purity Ag coating layer 24 may contain only Ag and inevitable impurities, but preferably contains, in addition to Ag and inevitable impurities, an additive element that acts to harden the Ag layer. Examples of such additive elements include Se, Sb, C, N, and S. In particular, it is preferable to use Se as the additive element. The amount of these additive elements added is limited to 0.1 mass% or less of the entire high purity Ag coating layer 24.

[0031] Since the high purity Ag coating layer 24 has a high Ag purity of 99.9 mass % or more, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and electrical conductivity, can be effectively utilized as the properties of the high purity Ag coating layer 24. Furthermore, since the high purity Ag coating layer 24 has a high purity, as described later, unlike the low purity Ag coating layer 34 which contains an additive made of an organic compound and has a low Ag purity, the metal structure is less likely to become brittle due to the inclusion of the additive. Therefore, even if the metal material 20 provided with the high purity Ag coating layer 24 is subjected to mechanical processing such as pressing to form the metal material 20 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 the processing. Therefore, even if the bulging electrical contact 2 is used for a long period of time in an environment where corrosion is likely to occur, the metal material present in the underlayer 22 and the layer below the high-purity Ag coating layer 24 is unlikely to be oxidized or degenerated through damage such as cracks in the high-purity Ag coating layer 24, which would cause an increase in contact resistance and other degradation of the electrical characteristics of the bulging electrical contact 2. In other words, the bulging electrical contact 2 has high durability. There is no particular upper limit for the Ag concentration in the high-purity Ag coating layer 24, but it is preferable to keep it at a concentration that allows the addition of an additive element that hardens the Ag layer, such as Se.

[0032] The thickness of the high purity Ag coating layer 24 is not particularly limited, but from the viewpoint of fully exerting the properties of the high purity Ag coating layer 24, such as the effect of suppressing damage during processing, the thickness 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, the thickness is preferably 10 μm or less. In addition, the thickness of the high purity Ag coating layer 24 is preferably larger than the thickness of the low purity Ag coating layer 34 of the flat electrical contact 3.

[0033] In the metal material 20 constituting the bulging electrical contact 2, the high purity Ag coating layer 24 may be formed directly 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 metal layer is the underlayer 22 made of Ni or a Ni alloy. The underlayer 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 plays a role in increasing the adhesion of the high purity Ag coating layer 24 to the substrate 21. The thickness of the underlayer 22 may be, for example, in the range of 0.5 μm or more and 10 μm or less.

[0034] Further, an intermediate layer 23 having a higher Ag purity than the high purity Ag coating layer 24 and a thinner layer than the high purity Ag coating layer 24 may be provided directly below the high purity Ag coating layer 24, that is, between the underlayer 22 and the high purity Ag coating layer 24. The intermediate layer 23 plays a role in increasing the adhesion of the high purity Ag coating layer 24 to the underlayer 22. The intermediate layer 23 also prevents elements such as C and S contained in the high purity Ag coating layer 24 from diffusing from the high purity Ag coating layer 24 to the underlayer 22. In the metal material 20, at the interface between adjacent layers, some of the metal atoms constituting the layers on both sides may form an alloy. Furthermore, the high purity Ag coating layer 24 is preferably exposed on the outermost surface of the metal material 20, but a coating composed of an organic material or the like may be formed on the surface of the high purity Ag coating layer 24 as long as the properties of the high purity Ag coating layer 24 are not significantly impaired. However, as described later, the sulfur-containing organic compound contained in the low-purity Ag coating layer 34 of the flat electrical contact 3 can function as a discoloration inhibitor, so there is no need to provide a separate layer of a discoloration inhibitor on the surface of the high-purity Ag coating layer 24.

[0035] The high-purity Ag coating layer 24 may be formed by any method such as plating or vapor deposition. The use of plating is particularly preferred from the viewpoint of simplicity and the like. For example, electrolytic plating may be performed using an Ag plating solution containing an additive element such as Se that acts to harden the Ag layer. After a metal layer such as an underlayer 22 is appropriately formed on the surface of the base material 21, the high-purity Ag coating layer 24 is formed to form a flat metal material 20, and the metal material 20 is pressed to form a bulging shape, whereby the bulging electrical contact 2 can be produced.

[0036] (Configuration of flat electrical contacts) 1, the flat electrical contact 3 is made of a metal material 30 having a base material 31 and a low-purity Ag coating layer 34 that coats the surface of the base material 31. As with 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 the type of metal, but is preferably made of Cu or a Cu alloy.

[0037] The low-purity Ag coating layer 34 contains Ag and a sulfur-containing organic compound. The low-purity Ag coating layer 34 has an Ag content in the range of 97.0 mass % or more and 99.5 mass % or less.

[0038] The type of sulfur-containing organic compound contained in the low-purity Ag coating layer 34 is not particularly limited, but suitable examples include sulfur-containing polymers such as benzothiazoles, thiols, sulfides, disulfides, and sulfonated anionic polymers, and derivatives thereof. The sulfur-containing organic compound may be used alone or in combination of two or more. In particular, it is preferable to use mercaptobenzothiazole and its derivatives, and thiodiethanol. The type of derivative is not particularly limited, but metal salts such as sodium salts can be used.

[0039] In the low-purity Ag coating layer 34, the sulfur-containing organic compound plays a role in improving wear resistance. That is, when the flat electrical contact 3 is in contact with the bulging electrical contact 2 and slid, it suppresses adhesion between the low-purity Ag coating layer 34 and the high-purity Ag coating layer 24, and contributes to keeping the friction coefficient between the two electrical contacts 2, 3 low. In particular, the above-mentioned benzothiazoles and their derivatives are highly effective in improving the hardness of the low-purity Ag coating layer 34 and thereby improving its wear resistance by making the Ag crystals finer. In this specification, the sulfur-containing organic compound contained in the low-purity Ag coating layer 34 includes all components derived from organic molecules containing sulfur atoms, such as a form in which the shape of the organic molecule containing sulfur atoms is maintained, a form in which at least a part of such molecules has undergone cleavage or recombination of intramolecular bonds, and a form in which at least a part of the constituent atoms, including sulfur atoms, forms bonds with external atoms such as Ag. The content of the sulfur-containing organic compound also refers to the total amount of all of these components.

[0040] Since the low-purity Ag coating layer 34 contains Ag at a concentration of 97.0 mass % or more, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and electrical conductivity, can be fully utilized as the properties of the low-purity Ag coating layer 34. In particular, by ensuring high electrical conductivity in the low-purity 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 with the mating bulging electrical contact 2. In addition, since the low-purity Ag coating layer 34 has high electrical conductivity, heat generation when a large current flows through the metal material 30 can be suppressed to a small amount, and the flat electrical contact 3 can be easily applied to applications in which a large current is applied, such as a large-current terminal. Furthermore, when manufacturing an electrical connection member such as a terminal having the flat electrical contact 3, a certain amount of load is applied to the metal material 30 by forming the metal material 30 into a terminal shape by mechanical processing such as press forming, although the load is lighter than that of an electrical connection member including the bulging electrical contact 2. However, since the low-purity Ag coating layer 34 contains Ag at a purity of 97.0% by mass or more, the ductility of Ag can be utilized to suppress damage to the low-purity Ag coating layer 34 associated with the mechanical processing of the metal material 30. From the viewpoint of further enhancing these effects, the Ag concentration in the low-purity Ag coating layer 34 is preferably 98.0% by mass or more, and more preferably 99.0% by mass or more.

[0041] On the other hand, by suppressing the Ag concentration in the low-purity Ag coating layer 34 to 99.5 mass% or less, the wear resistance of the low-purity Ag coating layer 34 can be effectively improved. This is because the Ag concentration in the low-purity Ag coating layer 34 is suppressed low and components other than Ag, such as sulfur-containing organic molecules, are contained at a certain concentration, thereby improving the hardness of the low-purity Ag coating layer 34, and the contact probability between Ag atoms is reduced, making it difficult for Ag to adhere to each other, thereby reducing the friction coefficient of the surface of the low-purity Ag coating layer 34. From the viewpoint of further enhancing these effects, it is more preferable that the Ag concentration in the low-purity Ag coating layer 34 is 99.4 mass% or less.

[0042] In the low-purity Ag coating layer 34, the low-purity Ag coating layer 34 may contain other components in addition to Ag and the sulfur-containing organic compound as long as the Ag content is in the range of 97.0 mass% or more and 99.5 mass% or less. However, from the viewpoint of suppressing the influence on the characteristics imparted by the sulfur-containing organic compound, it is preferable that the low-purity Ag coating layer 34 is composed only of Ag and the sulfur-containing organic compound, excluding unavoidable impurities. In particular, it is preferable that the additive element such as Se, which is suitably added to the high-purity Ag coating layer 24 described above and has the effect of hardening the Ag layer, is not contained in the low-purity Ag coating layer 34, excluding unavoidable impurities and excluding atoms such as C, S, and N derived from the added sulfur-containing organic compound. In addition, the content of the sulfur-containing organic compound in the low-purity Ag coating layer 34 is preferably 0.5 mass% or more and 3.0 mass% or less. As a result, the effect of improving the wear resistance by adding the sulfur-containing organic compound can be significantly obtained, and the decrease in electrical conductivity of the low-purity Ag coating layer 34 caused by adding a large amount of the sulfur-containing organic compound can be suppressed to a minimum.

[0043] As described above, in the low-purity Ag coating layer 34, sulfur-containing organic compounds such as benzothiazoles have the effect of refining Ag crystals. For example, it is preferable that the grain size of Ag crystal grains in the low-purity Ag coating layer 34 is 5 nm or more and 20 nm or less. The refining of Ag crystal grains contributes to an increase in the hardness of the low-purity Ag coating layer 34, and it is preferable that the hardness of the low-purity Ag coating layer 34 is 90 HV or more and 150 HV or less in Vickers hardness.

[0044] The thickness of the low-purity Ag coating layer 34 is not particularly limited. For example, the thickness may be 0.5 μm or more and 5 μm or less. Since the low-purity Ag coating layer 34 can sufficiently exhibit the effect of improving the wear resistance even if it is not formed thick, it may be formed thinner than the high-purity Ag coating layer 24 of the bulging electrical contact 2. Also, the thickness may be 2 μm or less.

[0045] The metal material 30 constituting the flat electrical contact 3 may have other metal layers, such as an underlayer 32 and / or an intermediate layer 33, between the low-purity Ag coating layer 34 and the substrate 31, similarly to the metal material 20 having the bulging electrical contact 2. Also, a coating made of an organic material or the like may be provided on the surface of the low-purity Ag coating layer 34. The configurations applicable to the underlayer 32, intermediate layer 33, and coating are the same as those explained above for the metal material 20 constituting the bulging electrical contact 2. The same also applies in that there is no need to provide a layer of anti-tarnish agent on the surface.

[0046] The preferred configuration of the low-purity 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 low-purity Ag coating layer 34. The low-purity Ag coating layer 34 may be formed by any method, such as a plating method or a vapor deposition method. The plating method is particularly preferred from the viewpoint of simplicity and the like. For example, electrolytic plating may be performed using an Ag plating solution containing a sulfur-containing organic compound. After forming a metal layer such as an underlayer 32 on the surface of the base material 31 as appropriate, the low-purity Ag coating layer 34 may be formed to prepare the metal material 30, and the flat electrical contact 3 may be formed from the metal material 30.

[0047] (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 high-purity Ag coating layer 24 on its surface and a flat electrical contact 3 having a low-purity Ag coating layer 34 on its surface, and both electrical contacts 2, 3 can be in electrical contact with each other on the surfaces of both Ag coating layers 24, 34. The high-purity Ag coating layer 24 contains Ag at a concentration of 99.0 mass% or more. On the other hand, the low-purity Ag coating layer 34 contains a sulfur-containing organic compound in addition to Ag, and the Ag concentration is 99.5 mass% or more and 97.0 mass% or less.

[0048] The surfaces of both the bulging electrical contact 2 and the flat electrical contact 3 are covered with a metal layer mainly composed of Ag, which is a metal with excellent properties such as heat resistance, corrosion resistance, and electrical conductivity, so that the electrical contact pair 1 has excellent electrical contact properties and durability. Furthermore, the surface of the flat electrical contact 3 is provided with a low-purity Ag coating layer 34 that contains a sulfur-containing organic compound and has an Ag concentration suppressed within a predetermined range, so that adhesion between the flat electrical contact 3 and the bulging electrical contact 2 is suppressed and the friction coefficient during sliding is suppressed. This allows the electrical contact pair 1 to have high wear resistance. The low-purity Ag coating layer 34 may be easily brittle due to its material properties due to its low Ag purity, but the flat electrical contact 3, unlike the bulging electrical contact 2, has a small curvature and is not subjected to a large load during processing, so the brittleness of the low-purity Ag coating layer 34 is unlikely to lead to damage due to the load during processing.

[0049] On the other hand, a high-purity Ag coating layer 24 having a high Ag purity is formed on the surface of the bulging electrical contact 2. The bulging electrical contact 2 is subjected to a large load when it is formed into a bulging shape by mechanical processing such as pressing, but since the metal layer formed on the surface is the high-purity Ag coating layer 24, it is difficult to cause damage such as cracks even when it is subjected to such load. Therefore, deterioration of the metal material 20 caused by damage such as oxidation of the underlying metal from the cracked area and the associated change in electrical properties is suppressed, and the bulging electrical contact 2 can obtain high durability. If the metal layer formed on the surface of the bulging electrical contact 2 is a brittle metal layer such as the low-purity Ag coating layer 34, the load associated with forming into a bulging shape may cause cracks in the metal layer. Then, over time, the metal present in the underlying layer such as the base layer 22 may be oxidized from the cracked area, which may affect the electrical properties such as an increase in the contact resistance of the surface.

[0050] In this manner, in the electrical contact pair 1 according to the present embodiment, the high-purity Ag coating layer 24 that is resistant to damage during processing is formed on the surface of the bulging electrical contact 2 to which a large load is applied during processing, while the low-purity Ag coating layer 34 that is highly effective in improving abrasion resistance is formed on the surface of the flat electrical contact 3 to which no or small load is applied during processing, so that the electrical contact pair 1 including the bulging electrical contact 2 and the flat electrical contact 3 as a whole can obtain high abrasion resistance while suppressing damage to the surface coating layer caused by processing, and can obtain high durability. This suppresses the effects of abrasion, and a low friction coefficient is obtained between the electrical contacts 2 and 3, and the state exhibiting good electrical properties such as the low friction coefficient can be durably maintained for a long period of time. Since the low-purity Ag coating layer 34 having a high wear resistance improving effect is formed on the surface of the flat electrical contact 3, the high-purity Ag coating layer 24, which does not exhibit a very high wear resistance by itself, is formed on the surface of the bulging electrical contact 2. However, as will be shown later in the examples, the wear resistance between the two electrical contacts 2, 3 is as high as that in the case where the low-purity Ag coating layer 34 is also formed on the bulging electrical contact 2.

[0051] The electrical contact pair 1 according to the present embodiment can be applied as a component of an electrical contact portion of various electrical connection members. The type of electrical connection member is not particularly limited, but it is preferable that the electrical connection member is one in which the electrical contacts 2, 3 slide between each other to form / disconnect the electrical connection. As will be described next, the electrical contact pair 1 according to the present embodiment can be suitably applied as a contact pair of a terminal for electrical connection.

[0052] <Terminal pair> The terminal pair according to the embodiment of the present disclosure includes the above-described electrical contact pair 1 according to the embodiment of the present disclosure. That is, in a terminal pair including a first terminal having a first contact portion and a second terminal having a second contact portion, the set of the first contact portion and the second contact portion may be configured with the electrical contact pair 1 according to the embodiment of the present disclosure, and may be electrically contactable with each other.

[0053] Although the specific type and shape of the terminal pair are not particularly limited, a form consisting of a mating type terminal pair, such as terminal pair 4 shown in Fig. 2, is preferable. Terminal pair 4 is configured as a set of a female terminal 5 and a male terminal 6 that can be mated with the female terminal 5. The female terminal 5 is a first terminal having a bulging electrical contact 2 as a first contact portion, and the male terminal 6 is a second terminal having a flat electrical contact 3 as a second contact portion. A high-purity Ag coating layer 24 is provided on the surface of the contact portion of the female terminal 5, and a low-purity Ag coating layer 34 is provided on the surface of the contact portion of the male terminal 6.

[0054] The female terminal 5 and the male terminal 6 have the same shape as known mating female terminals and male terminals. The female terminal 5 has a clamping portion 53. The clamping portion 53 is formed in a square tube shape with an opening at the front, and has a resilient contact piece 51 that is folded back toward the inside rear on the inside of the bottom surface of the clamping portion 53. On the other hand, the male terminal 6 has a tab portion 61 formed in a flat plate shape at the front. When the tab portion 61 of the male terminal 6 is inserted into the clamping portion 53 of the female terminal 5, the resilient contact piece 51 of the female terminal 5 comes into contact with the tab portion 61 of the male terminal 6 at the embossed portion 51a that bulges toward the inside of the clamping portion 53, and applies an upward force to the tab portion 61. The surface of the ceiling of the clamping portion 53 facing the resilient contact piece 51 serves as the inner facing contact surface 52, and the tab portion 61 of the male terminal 6 is pressed against the inner facing contact surface 52 by the resilient contact piece 51, thereby clamping and holding the tab portion 61 within the clamping portion 53. As a result, electrical contact is formed and maintained between the embossed portion 51a of the female terminal 5 as the bulging electrical contact 2 and the surface of the tab portion 61 of the male terminal 6 as the flat electrical contact 3.

[0055] Here, in the metal material 20 forming the female terminal 5, at least the surface of the embossed portion 51a of the elastic contact piece 51 has a high purity Ag coating layer 24 formed together with an appropriate underlayer 22 and / or intermediate layer 23 (not shown). In addition, in the metal material 30 forming the male terminal 6, at least the surface of the tab portion 61 has a low purity Ag coating layer 34 formed together with an appropriate underlayer 32 and / or intermediate layer 33 (not shown). From the viewpoint of ease of manufacture, etc., it is preferable that the high purity Ag coating layer 24 is formed on the entire surface of the female terminal 5, and the low purity Ag coating layer 34 is formed on the entire surface of the male terminal 6.

[0056] In this way, the high-purity Ag coating layer 24 is formed on the surface of the embossed portion 51a of the elastic contact piece 51 of the female terminal 5 that becomes the bulging electrical contact 2, and the low-purity Ag coating layer 34 is formed on the surface of the tab portion 61 of the male terminal 6 that becomes the flat electrical contact 3. This allows the electrical contact portion between the female terminal 5 and the male terminal 6 to obtain high wear resistance while suppressing damage to the surface coating layer caused by processing, thereby ensuring high durability. Since the electrical contact portion has high wear resistance, even when the male terminal 6 is inserted and removed with sliding relative to the female terminal 5, a state having a low friction coefficient is stably maintained. In addition, since the surface coating layer of the electrical contact portion is not easily damaged by processing, high durability is obtained. For example, even if the terminal pair 4 is used in an environment where metal oxidation is likely to occur, such as a high-temperature environment, the change in electrical characteristics caused by the influence of oxidation can be suppressed to a small extent. Furthermore, compared to male terminal 6, female terminal 5 has other areas that are susceptible to large loads during processing, such as the cylindrical portion of clamping portion 53 and embossed portion 51a. However, since the metal layer coating the surface of metal material 20 constituting female terminal 5 is high-purity Ag coating layer 24, which is not easily brittle, damage due to processing is less likely to occur even at these processed areas. EXAMPLES

[0057] Examples are shown below. Note that the present invention is not limited to these examples. Here, the relationship between the composition of the Ag coating layer of the bulging electrical contact and the flat electrical contact that constitute the electrical contact pair and the characteristics of the electrical contact pair was examined. Unless otherwise specified, the preparation and evaluation of the samples were performed at room temperature in the atmosphere.

[0058] <Sample preparation> First, a plurality of kinds of metal materials were prepared. Specifically, a 1 μm thick Ni layer was formed as a base layer on the surface of a clean 0.25 mm thick Cu alloy substrate by electrolytic plating. Next, a 0.2 μm thick intermediate layer made of pure Ag was formed on the surface of the Ni layer by electrolytic plating. Furthermore, the following plurality of kinds of Ag coating layers were formed on the surface of the intermediate layer by electrolytic plating. The Ag concentration in each Ag coating layer was evaluated by X-ray photoelectron spectroscopy (XPS). Hard Ag layer - Ag concentration: 99.9% by mass, Se added, thickness: 5 μm Organic-containing Ag layer 1 - Ag concentration: 99.4% by mass, sodium 2-mercaptobenzothiazole added, thickness: 1 μm Organic-containing Ag layer 2 - Ag concentration: 98.6% by mass, thiodiethanol added, thickness: 1 μm Organic-containing Ag layer 3 - Ag concentration: 97.0 mass%, sodium 2-mercaptobenzothiazole added, thickness: 1 μm Organic-containing Ag layer 4 - Ag concentration: 96.0 mass%, sodium 2-mercaptobenzothiazole added, thickness: 1 μm Ni-containing Ag layer - Ag concentration: 99.8 mass%, Ni added, thickness: 1 μm

[0059] Using the prepared metal materials, pairs of bulging test pieces and flat test pieces were made as models of electrical contact pairs, as shown in Figure 1. For the bulging test pieces, the metal material was pressed to form a hemispherical bulging electrical contact with a radius of 3 mm. For the flat test pieces, the flat metal material was used as is as a flat electrical contact. For each sample, the metal materials constituting the bulging test pieces and flat test pieces had Ag coating layers in the combinations shown in Table 1.

[0060] <Evaluation method> -Condition of Ag coating layer containing sulfur-containing organic compounds As a representative example of a low-purity Ag coating layer containing sulfur-containing organic compounds, a cross-sectional sample was cut in the thickness direction of the metal material on which the organic-containing Ag layer 1 was formed, and observed with a scanning transmission electron microscope (STEM). This confirmed the state of the low-purity Ag coating layer.

[0061] ·Initial contact resistance The contact resistance was measured for the electrical contact pairs in the initial state before sliding between the electrical contacts. Specifically, for the electrical contact pairs of each sample, the bulging electrical contact of the bulging test piece was brought into contact at its top with the flat electrical contact of the flat test piece, and the contact resistance was measured while applying a contact load of 30 N. The measurement was performed using the four-terminal method. The open circuit voltage was 20 mV and the current was 10 mA. When the obtained contact resistance was less than 0.2 mΩ, the initial contact resistance was evaluated as being sufficiently low (A). On the other hand, when the contact resistance was 0.2 mΩ or more, the initial contact resistance was evaluated as being high (B).

[0062] Abrasion resistance Wear resistance was evaluated by measuring the coefficient of friction while sliding a pair of bulging test pieces and flat test pieces for each sample. For the electrical contact pair of each sample, the bulging test piece was slid on the surface of the flat test piece while the bulging electrical contact of the bulging test piece was in contact with the flat electrical contact of the flat test piece at the top. At this time, the contact load was 5N, and the sliding was repeated over a distance of 2mm. During the sliding, the dynamic friction force acting between the electrical contacts was measured using a load cell. The dynamic friction force was then divided by the load to obtain the (dynamic) friction coefficient.

[0063] In the obtained friction coefficient measurement results, if the friction coefficient remained within a range of less than 0.3 during 30 sliding cycles, the wear resistance was evaluated as high (A). On the other hand, if the friction coefficient increased to 0.3 or more during the sliding, the wear resistance was evaluated as low (B). Furthermore, if the friction coefficient increased to 1.0 or more during the sliding, the wear resistance was evaluated as very low (B-).

[0064] Damage to bulging electrical contacts The surface of the bulging test piece of the electrical contact pair of each sample was observed by a scanning electron microscope (SEM). In the obtained SEM image, if there was no crack more than 0.5 μm wide on the surface of the bulging electrical contact, it was evaluated as having small damage due to processing (A). On the other hand, if there was a crack more than 0.5 μm wide, it was evaluated as having large damage due to processing (B).

[0065] <Test Results> Figure 3 shows a STEM image (magnification 1,000,000 times) of a cross section of the organic-containing Ag layer 1. The gray areas in the image correspond to the Ag coating layer, and it can be seen that many crystal grains are aggregated within the layer. The grain size of the crystal grains is small, about 10 nm.

[0066] FIG. 4 shows the results of measuring the friction coefficients while sliding the sample A1 and samples B1 to B3 as representative examples. The type of Ag coating layer of both electrical contacts and the evaluation results of wear resistance are also shown in table form. In all samples shown in FIG. 4, the initial friction coefficient is kept low, but in sample B1, the friction coefficient fluctuates up and down drastically with sliding and tends to increase with the number of sliding cycles. In sample B3, the friction coefficient also tends to increase with the number of sliding cycles, although not as much as in sample B1. In contrast, in sample A1 and sample B2, the change and increase in the friction coefficient with sliding is kept small, and the friction coefficient remains almost unchanged even after 50 sliding cycles.

[0067] Furthermore, Figs. 5A and 5B show representative examples of SEM images taken to evaluate damage in bulging electrical contacts. Fig. 5A shows an observation of a bulging electrical contact made of a metal material with a hard Ag layer, which constitutes sample A1, etc. On the other hand, Fig. 5B shows an observation of a bulging electrical contact made of a metal material with an organic-containing Ag layer 1, which constitutes sample B1, etc. In both cases, the upper images are observed at a magnification of 50 times, and the lower images are observed at a magnification of 500 times, in which the vicinity of the top of the bulging electrical contact is enlarged. When the metal material with the organic-containing Ag layer 1 in Fig. 5B is used, many cracks are observed as dark stripes over a wide area of ​​the surface of the bulging electrical contact. In contrast, when the metal material with the hard Ag layer in Fig. 5A is used, no clear cracks that can be confirmed in the SEM image are generated over the entire area of ​​the bulging electrical contact.

[0068] The evaluation results for each of Samples A1 to A3 and Samples B1 to B5 are summarized in Table 1 below, along with the combinations of the Ag coating layers.

[0069] [Table 1]

[0070] From Table 1, the following can be seen. In all of the samples A1 to A3, a hard Ag layer, i.e., a high-purity Ag coating layer containing Ag at a concentration of 99.9% by mass or more, is provided on the surface of the bulging electrical contact, and an organic-containing Ag layer 1, 2, or 3, i.e., a low-purity Ag coating layer containing Ag and a sulfur-containing organic compound and having an Ag concentration of 97.0% by mass or more and 99.5% by mass or less, is provided on the surface of the flat electrical contact. In all of the samples A1 to A3, the initial contact resistance is kept sufficiently low and high wear resistance is obtained. Damage to the bulging electrical contact is also kept small. These results are also shown in Fig. 4 and Fig. 5A for sample A1.

[0071] On the other hand, in the samples B1 to B5, the Ag coating layer provided on the surface of the bulging electrical contact is not a high-purity Ag coating layer containing Ag at a concentration of 99.9% by mass or more, or the Ag coating layer provided on the surface of the flat electrical contact is not a low-purity Ag coating layer containing Ag and a sulfur-containing organic compound and having an Ag concentration of 97.0% by mass or more and 99.5% by mass or less, or both. In all of the samples B1 to B5, at least one of low initial contact resistance, high wear resistance, and small damage to the bulging electrical contact does not reach a sufficiently high level.

[0072] In sample B1, both electrical contacts have a hard Ag layer on the surface. As shown in FIG. 4, sample B1 has low wear resistance. In samples B2 and B3, an organic-containing Ag layer 1 is provided at least on the surface of the bulging electrical contact. As shown in FIG. 5B, in samples B2 and B3, damage to the surface of the bulging electrical contact is large. From the above comparison of samples A1 to A3 and samples B1 to B3, it can be seen that in order to simultaneously improve wear resistance and suppress damage to the surface of the bulging electrical contact due to processing, it is necessary to form a coating layer that is less likely to cause damage, such as a hard Ag layer, on the surface of the bulging electrical contact, and to form a coating layer that has a high wear resistance improving effect, such as a low-purity Ag coating layer containing a sulfur-containing organic compound, on the surface of the flat electrical contact. As can be seen from the friction coefficient measurement results in Figure 4, sample B3, in which the combination of the surface coating layers of the bulging electrical contacts and the flat electrical contacts is reversed from that of sample A1, has lower wear resistance than sample A1. This is thought to be due to the effect of damage that occurred to the surfaces of the bulging electrical contacts.

[0073] In samples B4 and B5, similarly to samples A1 to A3, a hard Ag layer is provided on the surface of the bulging electrical contact, and an Ag coating layer with a lower Ag concentration than the hard Ag layer is provided on the surface of the flat electrical contact. However, unlike samples A1 to A3, sample B4 has an Ag concentration of less than 97.0 mass% in the Ag coating layer provided on the surface of the flat electrical contact. In sample B1, the initial contact resistance is high. This is considered to be due to the Ag concentration being too low in the Ag coating layer, resulting in low electrical conductivity. In sample B5, unlike samples A1 to A3, no sulfur-containing organic compound is added to the Ag coating layer on the surface of the flat electrical contact. Also, the Ag concentration is more than 99.5 mass%. In sample B5, the wear resistance is low. This is considered to be due to the Ag concentration in the Ag coating layer being too high, resulting in insufficient suppression of the increase in the friction coefficient due to adhesion of Ag. Comparing Samples A1 to A3 with Samples B4 and B5, it can be said that in order to obtain the effects of improving the wear resistance of the electrical contact pair and suppressing damage to the bulging electrical contacts due to processing while keeping the contact resistance sufficiently low, it is effective to use a low-purity Ag coating layer that contains a sulfur-containing organic compound and has an Ag concentration of 97.0% by mass or more and 99.5% by mass or less as the Ag coating layer to be provided on the surface of the bulging electrical contacts.

[0074] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0075] 1 Electrical contact pair 2 Bulged electrical contacts 3 Flat Electrical Contacts 20,30 Metal materials 21,31 Base material 22,32 Base layer 23,33 Middle class 24 High purity Ag coating layer 34 Low purity Ag coating layer 4-Terminal Pair 5 Female Terminal 51 Elastic contact piece 51a Embossed section 52 Internal facing contact surface 53 Clamping section 6 Male Terminal 61 Tab section

Claims

1. A bulging electrical contact that bulges toward the front surface side; a flat-shaped electrical contact having a smaller curvature than the bulging electrical contact and capable of electrically contacting the bulging electrical contact at a surface thereof; The bulging electrical contact has a surface, Contains Ag, The high-purity Ag coating layer has an Ag content of 99.9% by mass or more. The flat electrical contact has a surface having Ag, and a sulfur-containing organic compound, A pair of electrical contacts having a low-purity Ag coating layer having an Ag content of 97.0 mass % or more and 99.5 mass % or less.

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

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

4. In the bulge-shaped electrical contact and the flat-shaped electrical contact, A surface of a base material made of Cu or a Cu alloy is coated with a base layer made of Ni or a Ni alloy, 2. The electrical contact pair according to claim 1, wherein the high purity Ag coating layer and the low purity Ag coating layer are formed by coating the surfaces of the underlayer, respectively.

5. a first terminal having a first contact portion and a second terminal having a second contact portion; A set of the first contact portion and the second contact portion is constituted by the electrical contact pair according to any one of claims 1 to 4, and is capable of making electrical contact with each other. Terminal pair.

6. the first terminal is configured as a mating type female terminal having the bulging electrical contact, The terminal pair according to claim 5 , wherein the second terminal has the flat electrical contact and is configured as a male terminal capable of mating with the first terminal.

Images