Terminal material and electrical connection terminal

Abstract

To provide a terminal material and an electrical connection terminal with reduced contact resistance on the surface of an Ag coating layer and improved wear resistance.SOLUTION: A terminal material 1 includes a substrate 11, an intermediate layer 14 composed of Ag or an Ag alloy and covering the surface of the substrate 11, and a surface layer 15 that includes Ag and at least one of sulfur-containing organic compounds and carbon materials, contacts the surface of the intermediate layer 14 and covers the surface of the intermediate layer 14, where the intermediate layer 14 has a higher Ag purity than the surface layer 15, and the surface layer 15 has a surface roughness Rz of less than 1.2 μm. Furthermore, an electrical connection terminal is configured to include the terminal material 1, in which the intermediate layer 14 and the surface layer 15 is formed on the surface of the base material 11 at least at the electrical contact portion contacting the opposing conductive member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

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

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

[0005] As disclosed in Patent Documents 1 and 2, the wear resistance can be improved by adding an additive made of an organic compound or a carbon material such as graphene to the Ag coating layer provided on the electrical connection terminal. However, in electrical connection terminals having an Ag coating layer, further improvement in wear resistance and a reduction in the surface friction coefficient are desired from the viewpoints of reducing the insertion force required for mating and connecting with a mating electrical connection terminal and extending the life of the electrical connection terminal.

[0006] In view of the above, an object of the present invention is to provide a terminal material and an electrical connection terminal in which the contact resistance on the surface of the Ag coating layer is reduced and the wear resistance is improved. [Means for solving the problem]

[0007] The terminal material of the present disclosure comprises a substrate, an intermediate layer made of Ag or an Ag alloy and covering the surface of the substrate, and a surface layer containing Ag and at least one of a sulfur-containing organic compound and a carbon material, in contact with the surface of the intermediate layer and covering the surface of the intermediate layer, wherein the intermediate layer has a higher Ag purity than the surface layer, and the surface layer has a surface roughness Rz of less than 1.2 μm.

[0008] The electrical connection terminal of the present disclosure is configured to include the terminal material, and at least in the electrical contact portion that comes into contact with the mating conductive member, the intermediate layer and the surface layer are formed on the surface of the base material. [Effects of the Invention]

[0009] The terminal material and electrical connection terminal of the present disclosure have reduced contact resistance on the surface of the Ag coating layer and improved wear resistance. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating the configuration of a terminal material according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view showing the structure of an electrical connection terminal according to one embodiment of the present disclosure. [Figure 3] 3A and 3B are electron microscope images of a cross section of the terminal material. Fig. 3A is a low-magnification image, and Fig. 3B is a high-magnification image of the vicinity of the intermediate layer in Fig. 3A. [Figure 4] Figure 4 shows in table form the evaluation results of surface roughness, friction coefficient, and wear resistance for several samples with different intermediate layer thicknesses. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] [1] The terminal material of the present disclosure comprises a substrate, an intermediate layer made of Ag or an Ag alloy and covering the surface of the substrate, and a surface layer containing Ag and at least one of a sulfur-containing organic compound and a carbon material, in contact with the surface of the intermediate layer and covering the surface of the intermediate layer, wherein the intermediate layer has a higher Ag purity than the surface layer, and the surface layer has a surface roughness Rz of less than 1.2 μm.

[0013] In the terminal material, the Ag-containing surface layer contains at least one of a sulfur-containing organic compound and a carbon material as an additive. This gives the surface layer high wear resistance. In particular, the surface roughness Rz of the surface layer is less than 1.2 μm, which reduces the coefficient of friction on the surface of the surface layer. Furthermore, wear resistance is effectively enhanced, making the surface layer less susceptible to wear even when subjected to friction. Furthermore, in the terminal material, an intermediate layer with a higher Ag purity than the surface layer is formed below the surface layer. This intermediate layer contributes to reducing the surface roughness of the surface layer.

[0014] [2] In the above aspect [1], the thickness of the intermediate layer is preferably 1.0 μm or more, which is particularly effective in reducing the surface roughness of the surface layer, thereby lowering the coefficient of friction and improving wear resistance.

[0015] [3] In the above-described embodiment [1] or [2], the terminal material may further include a strike layer between the substrate and the intermediate layer, the strike layer being thinner than the intermediate layer, and the intermediate layer being in contact with the surface of the strike layer. The strike layer has the effect of enhancing the adhesion of the intermediate layer and the surface layer to the substrate. The improved adhesion of the surface layer also leads to further reduction in the surface roughness of the surface layer.

[0016] [4] In any one of the above aspects [1] to [3], the terminal material may further include a base layer made of Ni or a Ni alloy between the substrate and the intermediate layer and in contact with the surface of the substrate. Materials with a Ni or Ni alloy base layer on the surface of a Cu or Cu substrate are commonly used as base materials for terminal materials. However, by forming an intermediate layer on the surface of the base material and then forming a surface layer, a terminal material with excellent adhesion of the layers to the base material can be obtained. Improved adhesion also leads to reduced surface roughness in the surface layer.

[0017] [5] The electrical connection terminal of the present disclosure is configured to include any one of the terminal materials [1] to [4] above, and at least in the electrical contact portion that contacts the mating conductive member, the intermediate layer and the surface layer are formed on the surface of the substrate. This electrical connection terminal is configured to include the terminal material described above, which has a low coefficient of friction on the surface of the surface layer and high wear resistance, so that the electrical contact portion can utilize these low coefficient of friction and high wear resistance. As a result, the insertion force required to connect the electrical connection terminal to the mating electrical connection terminal can be reduced, and a long life can be expected.

[0018] [Details of the embodiments of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0019] <Terminal material> A terminal material according to an embodiment of the present disclosure will be described below. A cross section of a terminal material 1 according to an embodiment of the present disclosure is shown schematically in FIG.

[0020] (Outline of terminal material composition) The terminal material 1 has a substrate 11 and a plurality of metal coating layers that coat the surface of the substrate 11. The coating layers include, from the substrate 11 side, an underlayer 12, a strike layer 13, an intermediate layer 14, and a surface layer 15. Of these, the underlayer 12 and the strike layer 13 are optional. The strike layer 13, the intermediate layer 14, and the surface layer 15 are each composed of a layer whose main component is Ag (a layer containing 50% or more by mass of Ag).

[0021] The substrate 11 is formed as a metal plate. The type of metal forming the substrate 11 is not particularly limited, and various metal materials generally applicable as substrates for electrical connection members such as terminals can be used. Preferably, the substrate 11 is formed of Cu or a Cu alloy, which is commonly used as a substrate for terminals.

[0022] The underlayer 12 is an optional layer. However, when the substrate 11 is made of Cu or a Cu alloy, it is preferable to provide the underlayer 12 made of Ni or a Ni alloy in contact with the surface of the substrate 11. The underlayer 12 then serves to enhance the adhesion of the strike layer 13, intermediate layer 14, and surface layer 15 to the substrate 11. The enhanced adhesion between the intermediate layer 14 and the surface layer 15 also contributes to the smoothing of the surface layer 15, as described below. Additionally, the underlayer 12 serves to prevent the diffusion of constituent elements of the substrate 11, such as Cu, into the strike layer 13, intermediate layer 14, and surface layer 15. If the constituent elements of the substrate 11 diffuse to these upper layers and reach the surface of the surface layer 15, they may be oxidized, potentially increasing the contact resistance of the surface layer 15. The thickness of the underlayer 12 can be, for example, in the range of 0.5 μm to 10 μm.

[0023] The strike layer 13 is an optional layer that covers the surface of the substrate 11 via an appropriate underlayer 12. The strike layer 13 is composed of Ag or an Ag alloy and has a higher Ag purity than the surface layer 15. Preferably, the strike layer 13 has an Ag purity of 99.0% by mass or more, and even 99.5% by mass or more. The strike layer 13 may contain only Ag and unavoidable impurities, or may contain, in addition to Ag and unavoidable impurities, an additive element that hardens the Ag layer. Examples of such additive elements include Se, Sb, C, N, and S.

[0024] The thickness of the strike layer 13 is smaller than that of the intermediate layer 14. The specific thickness of the strike layer 13 is not particularly limited, but a range of 0.01 μm to 0.1 μm is a suitable example. The strike layer 13 serves to enhance the adhesion of the intermediate layer 14 and the surface layer 15 to the substrate 11 and the underlayer 12. In particular, when the strike layer 13 is provided on the surface of the underlayer 12 made of Ni or a Ni alloy, the strike layer 13 is formed in close contact with the surface of the underlayer 12 while reducing Ni oxide on the surface of the underlayer 12. The enhanced adhesion of the intermediate layer 14 and the surface layer 15 to the substrate 11 and the underlayer 12 also has an effect on smoothing the surface of the surface layer 15, which will be described later.

[0025] The intermediate layer 14 is a layer that covers the surface of the substrate 11. If the terminal material 1 has an underlayer 12 and / or a strike layer 13, the intermediate layer 14 is provided to cover the surfaces of these layers. In particular, if the terminal material 1 has a strike layer 13, the intermediate layer 14 is provided in contact with the surface of the strike layer 13. The intermediate layer 14 is composed of Ag or an Ag alloy and has a higher Ag purity than the surface layer 15. Like the strike layer 13, the intermediate layer 14 also preferably has an Ag purity of 99.0% by mass or more, and even 99.5% by mass or more. The intermediate layer 14 may contain only Ag and unavoidable impurities, or may contain an additive element that hardens the Ag layer in addition to Ag and unavoidable impurities. Examples of such additive elements include Se, Sb, C, N, and S.

[0026] The thickness of the intermediate layer 14 is not particularly limited, but is preferably 1.0 μm or more. It is also preferable to set the thickness to approximately 10 μm or less, or 5.0 μm or less. As will be explained in detail later, providing the intermediate layer 14 can reduce the surface roughness of the surface layer 15. Furthermore, providing the intermediate layer 14 can suppress corrosion of the terminal material 1 and improve the corrosion resistance of the terminal material 1.

[0027] The surface layer 15 is a layer that contacts the surface of the intermediate layer 14 and coats the surface of the intermediate layer 14. The surface layer 15 contains Ag and an additive. The additive contains at least one of a sulfur-containing organic compound and a carbon material. The type of sulfur-containing organic compound is not particularly limited, but suitable examples include sulfur-containing polymers such as benzothiazoles, thiols, sulfides, disulfides, and sulfonated anionic polymers, as well as derivatives thereof. The sulfur-containing organic compound may be used alone or in combination of two or more. The type of carbon material is also not particularly limited, and graphite, graphene, carbon fiber, fullerene, carbon nanotubes, etc. can be used. Graphite is particularly preferred. The carbon material may also be used alone or in combination of two or more. The surface layer 15 is preferably composed only of Ag and the additive, excluding unavoidable impurities, but may also contain metal elements other than Ag as long as their amount is less than that of Ag. As will be described in detail later, the surface roughness Rz of the surface layer 15 is less than 1.2 μm. Because the surface layer 15 has such a highly smooth surface, the surface layer 15 has a low coefficient of friction and high wear resistance.

[0028] In the terminal material 1 according to this embodiment, an intermediate layer 14 and a surface layer 15 are formed in this order on the surface of a substrate 11, and other layers may be included, including an underlayer 12 and a strike layer 13, as long as the intermediate layer 14 and the surface layer 15 are in direct contact with each other. The surface layer 15 is preferably exposed on the outermost surface of the terminal material 1, but a thin film (not shown), such as an organic layer, may be provided on the surface of the surface layer 15 as long as it does not significantly affect the properties of the surface layer 15.

[0029] (Surface details) In the surface layer 15, the sulfur-containing organic compound and the carbon material serve to improve the wear resistance of the surface layer 15. That is, when an electrical contact made of the terminal material 1 according to this embodiment is brought into contact with another electrical contact (including one made of the terminal material 1) and the electrical contacts are caused to slide against each other, the sulfur-containing organic compound and the carbon material suppress adhesion between the two electrical contacts. The surface layer 15 also contributes to maintaining a low coefficient of friction between the two electrical contacts. The effects of improving the wear resistance and reducing the coefficient of friction are mainly achieved by increasing the hardness of the surface layer 15 due to the refinement of Ag crystals and by reducing the Ag concentration in the surface layer 15. The sulfur-containing organic compound and the carbon material can be contained in the surface layer 15 by adding them to a plating solution used when forming the surface layer 15 by plating. The sulfur-containing organic compound and carbon material contained in the surface layer 15 in this manner often maintain the molecular structure of the sulfur-containing organic compound and the skeletal structure of the carbon material even within the surface layer 15. However, even when at least a part of the molecular structure of the sulfur-containing organic compound or the skeletal structure of the carbon material has changed or disappeared, the sulfur-containing organic compound and the carbon material are still considered to be contained in the surface layer 15.

[0030] The content of the additive in the surface layer 15 is not particularly limited, but the purity of Ag in the surface layer 15 is preferably 99.5% by mass or less, and more preferably 99.4% by mass or less. Furthermore, when the additive is a sulfur-containing organic compound, the purity of Ag is preferably 99.0% by mass or less, and even more preferably 98.5% by mass or less. In this way, by containing a sufficient amount of additive in the surface layer 15, the effects of improving wear resistance and reducing the friction coefficient can be significantly achieved. On the other hand, the purity of Ag in the surface layer 15 is preferably 97.0% by mass or more, and even more preferably 98.0% by mass or more. Furthermore, when the additive is made of a carbon material, the purity of Ag is preferably 99.0% by mass or more. In this way, the properties exhibited by Ag, such as heat resistance, corrosion resistance, and conductivity, can be fully utilized as properties of the surface layer 15.

[0031] The surface roughness Rz (maximum height) of the surface layer 15 is less than 1.2 μm. Because the surface layer 15 has such a highly smooth surface, the surface layer 15 exhibits a particularly low coefficient of friction and excellent wear resistance. The surface roughness Rz is preferably 1.1 μm or less, and even more preferably 1.0 μm or less. The smaller the surface roughness Rz, the more preferable it is. While there is no particular lower limit, the surface roughness Rz of an actual Ag coating layer is generally 0.5 μm or more. The surface roughness Rz of the surface layer 15 can be reduced, for example, by providing an intermediate layer 14 below the surface layer 15 and further by forming the intermediate layer 14 thicker. Furthermore, plating conditions for forming the surface layer 15 by plating can be achieved by reducing the current density, increasing the metal ion concentration in the plating solution, increasing the temperature of the plating solution, increasing the agitation rate of the plating solution, adding a brightener, etc.

[0032] The thickness of the surface layer 15 is not particularly limited, but can be, for example, 0.5 μm or more and 10 μm or less. By forming the surface layer 15 to a thickness of 0.5 μm or more, the properties of the constituent material of the surface layer 15 can be utilized to significantly reduce the friction coefficient and improve wear resistance. It is more preferable to make the thickness of the surface layer 15 1.0 μm or more. On the other hand, by keeping the thickness of the surface layer 15 to 10 μm or less, it is easier to improve the surface smoothness, and the effect of providing the intermediate layer 14 is more effectively utilized, making it easier to enhance the effects of reducing the friction coefficient and improving wear resistance. It is more preferable to make the thickness of the surface layer 15 5.0 μm or less.

[0033] By reducing the coefficient of friction of the surface of the surface layer 15, the force required for sliding the surface of the terminal material 1 against another object can be reduced. For example, when an electrical connection terminal is formed from the terminal material 1 and the electrical connection terminal is mated with a mating electrical connection terminal, the insertion force required for connection can be reduced. The coefficient of friction can be reduced to 0.5 or less under the measurement conditions shown in the examples. Furthermore, by improving the wear resistance of the surface of the surface layer 15, the surface of the terminal material 1 is less likely to suffer from wear associated with adhesion, even when the surface of the terminal material 1 is brought into contact with another object and slid. As a result, the durability of the terminal material 1 can be maintained high even in a sliding environment. For example, even when an electrical connection terminal made of the terminal material 1 is repeatedly inserted and removed from a mating electrical connection terminal, the surface layer 15 can remain exposed on the surface of the electrical contact for a long period of time.

[0034] (Details of the middle layer) In the terminal material 1 according to this embodiment, the intermediate layer 14 is provided below the surface layer 15, which increases the smoothness of the surface of the surface layer 15 and makes it easier to reduce the surface roughness. This is because the intermediate layer 14 fills in and smooths the unevenness of the lower layer. As described above, reducing the surface roughness of the surface layer 15 effectively reduces the coefficient of friction and improves the wear resistance of the surface of the surface layer 15. This effect increases as the thickness of the intermediate layer 14 increases. Therefore, it is preferable that the thickness of the intermediate layer 14 be 1.0 μm or more. More preferably, the thickness of the intermediate layer 14 is 2.0 μm or more, and even more preferably 3.0 μm or more.

[0035] The intermediate layer 14 not only smooths the surface of the surface layer 15, but also inhibits corrosion of the terminal material 1. The surface layer 15 contains an additive composed of at least one of a sulfur-containing organic compound and a carbon material, which provides high abrasion resistance. However, the additives, which result in a lower Ag purity, make the terminal material 1 more susceptible to corrosion than a material without additives. However, the presence of the intermediate layer 14 below the surface layer 15, inhibits corrosion of the terminal material 1. In particular, if the thickness of the intermediate layer 14 is 1.0 μm or more, corrosion of the terminal material 1 caused by liquid corrosive substances can be effectively inhibited. On the other hand, if the thickness of the intermediate layer 14 is 3.0 μm or less, corrosion of the terminal material 1 caused by gaseous corrosive substances can be effectively inhibited.

[0036] When terminal material 1 has strike layer 13, intermediate layer 14 and strike layer 13 are both composed of Ag or Ag alloy layers with a higher Ag purity than surface layer 15, and intermediate layer 14 and strike layer 13 may have the same composition. However, intermediate layer 14 and strike layer 13 are formed independently by separate plating processes, etc. In other words, strike layer 13 is formed first, and then intermediate layer 14 is formed on the surface of strike layer 13. Therefore, as shown in FIG. 3B, in many cases, a clear interface can be confirmed at the boundary between strike layer 13 and intermediate layer 14 by electron microscope observation. The strike layer 13 is a thin layer formed to improve adhesion between the lower and upper layers, and to enhance its functionality, it is formed at a low speed using a plating solution with a low Ag concentration, whereas the intermediate layer 14 is suitable for formation at a relatively high speed to ensure a certain degree of thickness. Differences in these plating conditions often result in differences in the structural state of the strike layer 13 and the intermediate layer 14.

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

[0038] However, depending on the conditions for forming strike layer 13 and intermediate layer 14, a clear interface may not be formed between strike layer 13 and intermediate layer 14. Even in such cases, if the thickness of the region corresponding to intermediate layer 14, which has a higher Ag purity than surface layer 15 and corresponds to the combined region of strike layer 13 and intermediate layer 14, is 1.0 μm or more, intermediate layer 14 can effectively smooth the surface of surface layer 15. As described above, the thickness of strike layer 13 is preferably 0.1 μm or less, and therefore the thickness of the region corresponding to strike layer 13 and intermediate layer 14, which has a higher Ag purity than surface layer 15, is preferably 1.1 μm or more.

[0039] <Electrical connection terminal> An electrical connection terminal according to one embodiment of the present disclosure includes the terminal material 1 according to the embodiment of the present disclosure described above. In the electrical connection terminal, the laminated structure of the intermediate layer 14 and the surface layer 15 is formed at least in the electrical contact portion that comes into contact with a mating conductive member, such as a mating electrical connection terminal. The intermediate layer 14 and the surface layer 15 (as well as the base layer 12 and strike layer 13) may be formed over the entire surface of the electrical connection terminal or only in a partial area including the electrical contact portion, as long as they are formed at least in the electrical contact portion.

[0040] While the specific type and shape of the electrical connection terminal are not particularly limited, FIG. 2 illustrates an example in which the electrical connection terminal is a mating-type male terminal 2. The male terminal 2 has a shape similar to that of a known mating-type male terminal. That is, the male terminal 2 has a terminal connection portion 21 at the front and a wire connection portion 22 at the rear. The terminal connection portion 21 is the portion electrically connected to the mating female terminal and has a flat tab-like structure. The terminal connection portion 21 of the male terminal 2 is inserted from the tip side into the box-shaped interior of a female terminal having a box-shaped terminal connection portion, thereby mating and connecting the male terminal 2 and the female terminal. In the male terminal 2, an electric wire is electrically and physically connected to the wire connection portion 22. In the male terminal 2, an intermediate layer 14 and a surface layer 15 are formed on at least the surface of the terminal connection portion 21, along with an appropriate base layer 12 and strike layer 13. Preferably, the entire male terminal 2 is made of the terminal material 1 having these coating layers.

[0041] In this structure, the surface layer 15 is exposed on the outermost surface of the terminal connection portion 21 of the male terminal 2. Because the surface coefficient of friction of the surface layer 15 is low, when the terminal connection portion 21 of the male terminal 2 is inserted into the box-shaped terminal connection portion of the female terminal with sliding to form an electrical connection, the force required for sliding at the contact portion between the male terminal 2 and the female terminal is reduced. In other words, the insertion force required for inserting the male terminal 2 is reduced. Furthermore, because the surface of the surface layer 15 has high wear resistance, the contact portion between the male terminal 2 and the female terminal is less likely to experience wear accompanied by Ag adhesion, even with repeated sliding. The reduced wear ensures that the contact state between the male terminal 2 and the female terminal via the surface layer 15 is maintained for a long period of time, thereby increasing the durability of the male terminal 2. Furthermore, the presence of the intermediate layer 14 maintains low contact resistance of the terminal material 1 even in a corrosive environment, which, combined with the effect of the high durability, allows for the formation and maintenance of a good electrical connection between the male terminal 2 and the female terminal. The mating female terminal may be made of the terminal material 1 according to the embodiment of the present disclosure having the above-described coating layers, similar to the male terminal 2, or may be made of another metal material. An example of the other metal material is a material formed by exposing a high-purity Ag layer on the outermost surface, as in the intermediate layer 14. [Example]

[0042] Examples are shown below. However, the present invention is not limited to these examples. Here, the influence of the intermediate layer on the friction characteristics of the surface layer was examined. Unless otherwise specified, the preparation and evaluation of samples were carried out at room temperature in the atmosphere.

[0043] <Sample preparation> A 1.0 μm thick Ni layer was formed as an underlayer on the surface of a clean Cu alloy substrate by electroplating. Next, an Ag strike layer was formed on the surface of the Ni layer by electroplating. The Ag strike layer had a thickness of 0.1 μm or less and an Ag purity of 99.9 mass%. Furthermore, an Ag intermediate layer was formed on the surface of the Ag strike layer by electroplating. The thickness of the intermediate layer for each sample was as shown in Table 1 below.

[0044] Next, a surface layer was formed on the surface of the intermediate layer by electroplating. DuPont's "SILVERON GT-210 Durability Silver," a plating solution containing a sulfur-containing organic compound, was used as the plating solution ("SILVERON" is a registered trademark). The thickness of the surface layer was 1.0 μm for all samples. For the formation of the surface layer by electroplating, samples B to E were plated in a beaker. On the other hand, sample A was plated using a hoop plating apparatus. Plating using a hoop plating apparatus is characterized by the fact that plating can be performed at a higher current density than plating in a beaker.

[0045] <Evaluation method> (1) Confirmation of the laminated structure The cross-section of each sample was observed using a scanning electron microscope (SEM), and it was confirmed that a laminated structure consisting of a base layer, a strike layer, an intermediate layer, and a surface layer had been formed.

[0046] (2) Confirmation of the composition of the intermediate and surface layers The composition of the intermediate and surface layers of each sample was confirmed. Specifically, the elemental content in the intermediate and surface layers was analyzed using a glow discharge optical emission spectrometer (GD-OES).

[0047] (3) Measurement of surface roughness Rz The surface roughness Rz of the surface layer of each sample was measured. Specifically, the surface of each sample was observed using confocal measurement with a three-dimensional laser microscope. Then, based on the observed image, the surface roughness was evaluated as the maximum height Rz. The surface roughness Rz was measured at five points on the surface of each sample, and the average value was recorded.

[0048] (4) Measurement of friction coefficient The coefficient of friction on the surface of each sample was measured. The friction coefficient was measured by contacting and sliding an embossed contact point with each sample plate. The embossed contact point was placed at its top on the surface of the surface layer of each sample plate, and then slid across the surface of the plate. A contact load of 5 N was applied, and the sliding was repeated 10 times over a distance of 2 mm. During the sliding, a load cell was used to measure the dynamic friction force acting between the electrical contacts. The dynamic friction force was then divided by the load to obtain the dynamic friction coefficient, which was recorded for each cycle. If the friction coefficient remained below 0.5 during the 10 cycles, the friction coefficient was considered to be sufficiently reduced.

[0049] (5) Evaluation of appearance after sliding In the friction test to measure the coefficient of friction (4) above, the embossed contact point was slid back and forth 10 times, and then the surface of each sample plate was observed using an optical microscope. The state of the sliding marks and whether or not the base layer was exposed were then observed. If no sliding marks extending long in the sliding direction were formed and the base layer was not exposed, the surface layer could be evaluated as having sufficiently high wear resistance. As described above, for samples in which the base layer was not exposed in the friction test involving 10 sliding strokes at a contact load of 5 N, a friction test was conducted under high-load conditions, involving 100 sliding strokes at a contact load of 7 N, and the presence or absence of base layer exposure was also confirmed after that.

[0050] <Test Results> Table 1 below shows the manufacturing method of the surface layer, the thickness of the surface layer and the intermediate layer, as well as the analysis results of the component composition of the surface layer and the intermediate layer for Samples A to E.

[0051] [Table 1]

[0052] Table 1 shows that the intermediate layer of each sample has a high Ag purity of 99.9 mass%. The surface layer contains a coating layer with a low Ag purity that contains C and S, reflecting the addition of sulfur-containing organic compounds.

[0053] Figures 3A and 3B show representative SEM images of the cross section of sample C. Figure 3A is a low-magnification image, while Figure 3B is a high-magnification image of the intermediate layer (14) and its vicinity in Figure 3A. As shown in Figure 3A, the underlayer (12), intermediate layer (14), and surface layer (15) are layered on the surface of the substrate (11). Furthermore, Figure 3B shows that a thin strike layer (13) is formed between the underlayer (12) and intermediate layer (14). Crystal grains with diameters ranging from several hundred nanometers to several micrometers are formed in the intermediate layer. In each sample, including sample C, the average diameter of the crystal grains constituting the intermediate layer was 0.14 μm or more and 0.32 μm or less. In contrast, the surface and strike layers above and below the intermediate layer did not contain crystal grains large enough to be detected by SEM, and the intermediate layer had a structure clearly distinguishable from the layers above and below it.

[0054] Figure 4 summarizes the surface roughness Rz and friction coefficient measurements for each sample, micrographs showing the appearance after sliding, and whether the base layer is exposed. Figure 4 shows that the thicker the intermediate layer, the smaller the surface roughness Rz, and the smoother the surface of the outer layer. Samples C to E, which have intermediate layer thicknesses of 1.0 μm or more, have surface roughness Rz of less than 1.2 μm.

[0055] Looking at the results of the friction coefficient measurements, samples A and B, which have a surface roughness Rz of 1.2 μm or more, show large fluctuations in the friction coefficient during sliding, with the measured values ​​increasing. Both the fluctuation range and value of the friction coefficient exceed 0.5. In particular, sample A, which has a large surface roughness Rz, shows large fluctuation range and value of the friction coefficient. In contrast, samples C to E, which have a surface roughness Rz below 1.2 μm, all show small fluctuation ranges in the friction coefficient, and the values ​​are also small. Over the entire sliding range, the friction coefficient values ​​are 0.5 or less. Except for the very early stages of sliding, the fluctuation range also remains below 0.5.

[0056] Next, examining the appearance after sliding and whether or not the base layer was exposed, specimens A and B, which have a surface roughness Rz of 1.2 μm or greater, have sliding marks that extend horizontally, indicating the sliding direction. Furthermore, the color contrast within the sliding marks is large, indicating that the surface layer has worn away. In particular, specimen A, which has a high surface roughness Rz, has sliding marks that occupy a large area. Furthermore, specimens A and B have exposed the base layer. In contrast, specimens C to E, which have a surface roughness Rz below 1.2 μm, all have wear marks, but their area is small and they do not extend horizontally, indicating the sliding direction. The color contrast within the sliding marks is also kept low. These findings indicate that surface wear is significantly suppressed in specimens C to E compared to specimens A and B. Furthermore, specimens C to E do not have exposed the base layer. Furthermore, even under high load conditions, the base layer does not become exposed.

[0057] These results show that the surface roughness Rz of the surface layer can be reduced by forming a sufficiently thick intermediate layer. Furthermore, it was confirmed that by keeping the surface roughness Rz of the surface layer below 1.2 μm, the friction coefficient of the surface layer can be stabilized at a small value and wear can be suppressed.

[0058] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0059] 1 Terminal material 11 Base material 12 Base layer 13 Strike layer 14 Middle Class 15 Surface layer 2 Male terminals (electrical connection terminals) 21 Terminal connection part 22 Wire connection

Claims

1. A substrate; an intermediate layer made of Ag or an Ag alloy and covering the surface of the substrate; a surface layer that contains Ag and at least one of a sulfur-containing organic compound and a carbon material, and that is in contact with the surface of the intermediate layer and covers the surface of the intermediate layer; the intermediate layer has a higher Ag purity than the surface layer, The surface layer has a surface roughness Rz of less than 1.2 μm.

2. The terminal material according to claim 1 , wherein the intermediate layer has a thickness of 1.0 μm or more.

3. the terminal material further includes a strike layer between the substrate and the intermediate layer, the strike layer having a thickness smaller than that of the intermediate layer; The termination material of claim 1 , wherein the intermediate layer contacts a surface of the strike layer.

4. the substrate is made of Cu or a Cu alloy; 2. The terminal material according to claim 1, further comprising an underlayer made of Ni or a Ni alloy between the substrate and the intermediate layer and in contact with the surface of the substrate.

5. An electrical connection terminal comprising the terminal material according to any one of claims 1 to 4, wherein the intermediate layer and the surface layer are formed on the surface of the substrate at least in an electrical contact portion that comes into contact with a mating conductive member.

Images