Method for producing silver-plated material, silver-plated material, and terminal

Abstract

This method for producing a silver-plated material includes:a step for performing electroplating in a first plating solution containing benzothiazoles or derivatives thereof to form, at a predetermined film thickness on a metal material, a first silver-plated layer composed of silver containing carbon and sulfur; a step for forming, on the first silver-plated layer under predetermined plating conditions, a second silver-plated layer having a silver concentration of 95 to 100 at% inclusive; and a step for forming, on the second silver-plated layer, an organic coating layer containing a predetermined compound.

Description

Method for manufacturing silver-plated material, silver-plated material, and terminals

[0001] This invention relates to a method for manufacturing silver-plated material, silver-plated material, and terminals for electrical contacts, which are useful as materials for connectors, switches, relays, and other contacts and terminal components used in electrical wiring for automotive and consumer applications. In this invention, "silver-plated material" refers to a metal material on which a silver-plated layer is formed. The silver-plated layer consists of one or more silver-plated layers, and includes silver-plated layers obtained by applying an organic coating layer formation treatment to these silver-plated layers.

[0002] Traditionally, for connectors, switches, and other contact and terminal components, relatively inexpensive materials with excellent corrosion resistance and mechanical properties, such as copper, copper alloys, and stainless steel, have been used. These materials are then plated with tin, silver, or gold depending on the required electrical properties and solderability. Of these, tin-plated materials are inexpensive but have poor corrosion resistance in high-temperature environments. Gold-plated materials offer excellent corrosion resistance and high reliability but are expensive. Silver-plated materials, on the other hand, are less expensive than gold-plated materials and have superior corrosion resistance compared to tin-plated materials.

[0003] The materials used for contacts and terminal components such as connectors and switches require abrasion resistance to withstand the insertion and removal of connectors and the sliding of switches. However, silver-plated materials are soft and easily abraded. Therefore, when silver-plated materials are used for contacts and terminal components, problems arise such as the silver adhering to the surface during insertion, removal, and sliding, leading to adhesive wear, or the surface being worn down during insertion of connection terminals, increasing the coefficient of friction and thus increasing the insertion force.

[0004] To resolve these problems, Patent Document 1 discloses that by performing electroplating in a plating solution comprising an aqueous solution containing potassium silver cyanide or silver cyanide, potassium cyanide or sodium cyanide, and benzothiazoles or their derivatives, a silver plating layer can be obtained on a material that exhibits good peel resistance in severely bent areas and also has good durability against sliding wear.

[0005] Japanese Patent Publication No. 2024-77764

[0006] However, according to the inventors' research, the silver-plated material disclosed in Patent Document 1 is manufactured by electroplating a material using a plating solution that contains sulfide compounds such as benzothiazoles or their derivatives. Although this manufacturing method improves wear resistance, it has the problem that the contact resistance deteriorates because the silver-plated layer contains components other than silver, such as carbon and sulfur.

[0007] The object of the present invention is to provide a silver-plated material that has wear resistance and good contact resistance, a method for manufacturing the same, and a terminal made of the silver-plated material.

[0008] The inventors have diligently conducted research to achieve the above-mentioned objectives and have completed the present invention described below.

[0009] In other words, the first invention for achieving the above-mentioned objectives comprises the steps of: forming a first silver plating layer with a thickness of 0.5 μm to 5.0 μm on a metal material by electroplating with a cyanide plating solution containing benzothiazoles or benzothiazole derivatives; forming a second silver plating layer on the first silver plating layer by electroplating with a plating solution having a carbon concentration of 0 at% to 1 at% and a silver concentration of 95 at% to 100 at%; and forming an organic coating layer by contacting the second silver plating layer with a solution containing one or more organic substances selected from thiol compounds, fatty acid compounds, and fluorine compounds, wherein the current density in the step of forming the second silver plating layer is 3 A / dm ２ It is less than the product of the current density and the plating time (A × sec / dm²). ２ ) to 0.1 (A × sec / dm ２ ) or more 2.0 (A x sec / dm ２The invention relates to a method for manufacturing a silver-plated material, provided that the following conditions are met. The second invention relates to the method for manufacturing a silver-plated material according to the first invention, wherein the carbon concentration in the first silver-plated layer is 5 at% or more and 24 at% or less, and the sulfur concentration is 0.7 at% or more and 5.0 at% or less. The third invention is a silver-plated material having a first or second silver-plated layer on a metal base material, wherein the first or second silver-plated layer contains carbon and sulfur, with a carbon concentration of 5 at% to 24 at% and a sulfur concentration of 0.7 at% to 5.0 at% and a silver concentration of 75 at% to 93 at%. The invention relates to a silver-plated material in which two pieces of the silver-plated material are prepared, one of the silver-plated materials is indented (inner radius = 1.5 mm) and used as an indenter, and when the indenter is pressed against the other silver-plated material with a load of 5 N using a precision sliding test apparatus, and a reciprocating sliding operation is performed at a sliding distance of 5 mm and a sliding speed of 1.67 mm / s, the metal base material is not exposed on the other silver-plated material up to 300 reciprocating sliding cycles, and the contact resistance between the indenter and the other silver-plated material up to 200 reciprocating sliding cycles does not exceed 0.4 mΩ. The fourth invention is the silver-plated material described in the third invention, wherein the metal material is copper or a copper alloy. The fifth invention is a terminal using the silver-plated material described in the third or fourth invention.

[0010] According to the present invention, it is possible to provide a method for manufacturing a silver-plated material having excellent wear resistance and good contact resistance, the silver-plated material itself, and a terminal composed of the silver-plated material.

[0011] This figure schematically illustrates the cross-sectional structure of the silver-plated material according to the present invention. This is the elemental concentration profile in the depth direction obtained by XPS in the silver-plated material according to Example 2.

[0012] [1] Structure of the Silver-Plated Material The structure of the silver-plated material according to the present invention will be explained with reference to Figure 1, which schematically illustrates the cross-sectional structure of the silver-plated material according to the present invention. In the silver-plated material 10 according to the present invention, a first silver-plated layer 5 is formed on a metal material 1, a second silver-plated layer 6 is formed on the first silver-plated layer 5, and an organic coating layer 7 is formed on the second silver-plated layer 6. Between the metal material 1 and the first silver-plated layer 5, an undercoat plating layer 2, a silver strike plating layer 3, and a silver undercoat plating layer 4, which will be described later, can be appropriately formed as a surface treatment for forming the first silver-plated layer, as needed. The following describes each structure constituting the silver-plated material 10 according to the present invention.

[0013] (1) Metal material The metal material 1 on which a silver plating layer is formed is preferably a material that can be silver plated and has the conductivity required for materials such as switches and connectors that are sliding electrical contacts. Furthermore, from the viewpoint of cost, Cu (copper) and Cu alloys are preferred as the constituent material of the metal material 1, and Cu is preferred in the present invention. As for the Cu alloy, from the viewpoint of conductivity and strength, an alloy composed of Cu and at least one selected from the group consisting of Si (silicon), Fe (iron), Mg (magnesium), P (phosphorus), Ni (nickel), Sn (tin), Co (cobalt), Zn (zinc), Be (beryllium), Pb (lead), Te (tellurium), Ag (silver), Zr (zirconium), Cr (chromium), Al (aluminum), and Ti (titanium), and unavoidable impurities is preferred. The amount of Cu in the Cu alloy is preferably 85% by mass or more, more preferably 92% by mass or more, and preferably 99.95% by mass or less.

[0014] As will be described later, metal material 1 is used as a silver-plated material with a silver plating layer formed on it for applications such as terminals. In some cases, metal material 1 itself may have a shape suitable for such applications, while in other cases, metal material 1 may be flat but be molded into the desired shape after being silver-plated.

[0015] (2) Structure of the first silver plating layer and method of forming the same <1> Structure of the first silver plating layer The first silver plating layer 5 is formed on the metal material 1, or if necessary, by first forming an undercoat plating layer 2, a silver strike plating layer 3, and a silver undercoat plating layer 4 on the metal material 1, and then performing electroplating on these plating layers.

[0016] The first silver plating layer 5 is made of silver containing carbon and sulfur, and the carbon concentration in the first silver plating layer 5 is preferably 5 at% to 24 at%, and more preferably 7.0 at% to 20 at%. The sulfur concentration in the first silver plating layer 5 is preferably 0.7 at% to 5.0 at%, and more preferably 1.0 at% to 1.5 at%. The inclusion of unavoidable impurities other than carbon and sulfur is permitted.

[0017] Furthermore, the carbon and sulfur content in the first silver plating layer 5 is derived from benzothiazoles or their derivatives. The inventors believe that by adding the benzothiazoles or their derivatives as organic additives to the plating solution and performing electroplating (silver plating), a portion of the organic additives is incorporated into the film of the first silver plating layer 5 made of silver, and the organic additives incorporated into the film act as lubricating components, thereby improving wear resistance.

[0018] In other words, in the present invention, the carbon and sulfur components exist in the first silver plating layer 5 in the form of sulfide compound molecules. Therefore, unlike silver plating layers formed with solid carbon particles and sulfur particles, the first silver plating layer 5 according to the present invention does not contain carbon particles and sulfur particles with a particle size of 10 nm or larger.

[0019] The silver concentration in the first silver plating layer 5 is less than the silver concentration in the second silver plating layer 6 described later, and is preferably 75 at% to 93 at%, and more preferably 77 at% to 92 at%.

[0020] <2> Method for forming the first silver plating layer The first silver plating layer 5 is preferably formed to a thickness of 0.5 μm or more and 5 μm or less by electroplating using a cyanide plating solution containing benzothiazoles or their derivatives. A thickness of 0.5 μm or more for the first silver plating layer 5 is preferable because it is possible to obtain a plating material with wear resistance. On the other hand, a thickness of 5 μm or less for the first silver plating layer 5 is preferable because it is possible to obtain a plating material with wear resistance and good resistance while keeping the amount of silver used low. From this viewpoint, it is more preferable that the thickness of the first silver plating layer 5 be 0.5 μm or more and 3.0 μm or less, and most preferable that it be 0.8 μm or more and 2.3 μm or less.

[0021] The benzothiazole (C ７ H ５ Benzothiazoles (NS) are heterocyclic compounds having a benzene skeleton and a thiazole skeleton. Benzothiazoles can be used as derivatives of azoles such as 2-mercaptobenzothiazole, including sodium 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)), zinc-2-mercaptobenzothiazole, 5-chloro-2-mercaptobenzothiazole, and 6-amino-2-mercapto-5-methoxybenzothiazole. Among these derivatives of benzothiazoles, alkali metal salts of benzothiazoles are preferred, and sodium salts of benzothiazoles such as 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)) are preferred.

[0022] As a method for forming the electroplating of the first silver plating layer 5 containing benzothiazoles or derivatives thereof, it is preferable to form the first silver plating layer 5 on the metal material 1 by performing electroplating in a plating solution consisting of an aqueous solution containing potassium silver cyanide or silver cyanide, potassium cyanide or sodium cyanide, and benzothiazoles or derivatives thereof.

[0023] The concentration of free cyanide in the plating solution is preferably 3 g / L or more and 60 g / L or less, more preferably 4 g / L or more and 57 g / L or less, and still more preferably 4 g / L or more and 40 g / L or less. The concentration of benzothiazole moiety in the plating solution is preferably 2 g / L or more and 30 g / L or less, more preferably 2.5 g / L or more and 25 g / L or less, still more preferably 5 g / L or more and 22 g / L or less, and most preferably 7 g / L or more and 20 g / L or less. In the present invention, the "benzothiazole moiety" refers to a moiety corresponding to the benzothiazole (C ７ H ５ NS structure) (molecular weight: 135.19) in a given organic compound (benzothiazoles or derivatives thereof).

[0024] The silver concentration in the plating solution is preferably 15 g / L or more and 85 g / L or less, and more preferably 20 g / L or more and 82 g / L or less. The concentration of potassium silver cyanide or silver cyanide in the plating solution is preferably 30 g / L or more and 170 g / L or less, and more preferably 35 g / L or more and 150 g / L or less.

[0025] Further, the concentration of potassium cyanide or sodium cyanide in the plating solution is preferably 30 g / L or more and 150 g / L or less, more preferably 35 g / L or more and 145 g / L or less, and still more preferably 38 g / L or more and 100 g / L or less.

[0026] Further, the plating is preferably performed at a solution temperature of 15°C or more and 50°C or less, and more preferably performed at a solution temperature of 18°C or more and 47°C or less. In addition, the plating is performed at a current density of 0.5 A / dm ２ or more and 10 A / dm ２ or less, and more preferably performed at 0.5 A / dm ２ or more and 8 A / dm ２ or less. In order to form a favorable first silver plating layer, it is preferable that the current density is relatively high, being 1.5 A / dm ２ or more, and it is more preferable that the current density is 2.5 A / dm ２ or more.

[0027] (3) Structure of the second silver plating layer and method for forming the same <1> Structure of the second silver plating layer The second silver plating layer 6 is formed on the first silver plating layer 5, and is an extremely thin high-purity silver plating layer considered to have a film thickness of 0.7 nm or more and 15 nm or less. Since the second silver plating layer 6 is an extremely thin plating layer, it is difficult to directly measure characteristics such as film thickness and purity of the second silver plating layer 6. However, unlike the first silver plating layer 5, the silver concentration in the silver plating layer is considered to be 95 at% or more and 100 at% or less, and the second silver plating layer 6 is formed for the purpose of ensuring the good contact resistance exhibited by the silver-plated material according to the present invention.

[0028] <2> Method for controlling the film thickness of the second silver plating layer As described above, the second silver plating layer 6 is considered to be an extremely thin high-purity silver plating layer having a film thickness of about 0.7 nm or more and 15 nm or less. However, even when various observation devices and analyzers are used, it is difficult to directly measure or control the film thickness thereof.

[0029] Therefore, in the present invention, a preliminary test was conducted, and the conditions for achieving the target film thickness were confirmed using a plating solution in which the silver concentration in the silver plating layer is 95 at% or more and 100 at% or less. Specifically, in advance, using a plating solution capable of forming a second silver plating layer on a metal material 1 such that the silver concentration in the obtained silver plating layer is 95 at% or more and 100 at% or less, the film thickness of the obtained silver plating layer and the product of current density and plating time (A × sec / dm ２ ) are determined in advance. Using the corresponding relationship, the value of the product of current density and plating time for forming the second silver plating layer is determined so as to form the target film thickness on the metal material using the second plating solution. Then, from the determined value of the product of current density and plating time, feasible current density values and feasible plating time values are set, and the second silver plating layer having the target film thickness is formed on the first silver plating layer 5 using an indirect method with a plating solution capable of forming a silver plating layer having a silver concentration of 95 at% or more and 100 at% or less in the obtained silver plating layer.

[0030] Specifically, to form a very thin second silver plating layer with a silver concentration of 95 at% to 100 at% and a film thickness of approximately 0.7 nm to 15 nm, the current density is set to 0.1 A / dm ２ 3.0A / dm or more ２ The product of current density and plating time (A × seconds / dm²) is set to be less than the product of current density and plating time. ２ ) to 0.1 (A x sec / dm ２ ) or more 2.0 (A x sec / dm ２ ) Less than or equal to, preferably 0.1 (A × seconds / dm ２ ) or more 1.5 (A x sec / dm ２ The following conditions shall apply. In this case, for ease of control, the plating time is preferably 0.5 seconds or more as the feasible plating time.

[0031] As mentioned above, the composition of the second plating solution is not particularly limited, as long as it is a plating solution capable of forming a silver plating layer in which the silver concentration in the resulting silver plating layer is between 95 at% and 100 at%. Therefore, if the above requirement is met, the first plating solution described above can also be used as the second plating solution.

[0032] <3> Method for forming the second silver plating layer Prepare a plating solution capable of forming a silver plating layer in which the silver concentration in the resulting silver plating layer is 95 at% or more and 100 at% or less. Then, using the prepared plating solution, as explained in "<2> Method for determining the thickness of the second silver plating layer", determine the thickness of the silver plating layer and the product of the current density and the plating time (A × seconds / dm²). ２ The correspondence with ) is determined. Then, from the product of the determined current density and plating time, the feasible current density value and plating time value are set, and a second silver plating layer 6 is formed on the first silver plating layer 5 using the second plating solution, with a silver concentration of 95 at% to 100 at% and a target film thickness in the range of 0.7 nm to 15 nm.

[0033] <4> Effects exhibited by a second silver plating layer having a predetermined thickness The inventors prepared samples by forming a second silver plating layer 6 having various thicknesses on the first silver plating layer 5 using the indirect method described above, and measured the wear resistance and contact resistance of the samples. They found that when the thickness of the second silver plating layer 6 is considered to be 0.7 nm or more, the silver plating material according to the present invention exhibits good contact resistance. On the other hand, they found that when the thickness of the second silver plating layer 6 is considered to be 15 nm or less, the silver plating material according to the present invention exhibits wear resistance.

[0034] It is easy to understand that the silver plating material according to the present invention exhibits good contact resistance when the thickness of the second silver plating layer 6 is considered to be above a predetermined value. On the other hand, the reason why the wear resistance decreases when the thickness of the second silver plating layer 6 is considered to be above a predetermined value is thought to be because the second silver plating layer is made of high-purity silver, making it prone to silver adhesion at the contact points. In other words, it is presumed that when the thickness of the second silver plating layer 6 is above a predetermined value, areas are created where the surface of the silver layer adheres and is gouged when subjected to sliding, and these areas become the starting point for a decrease in wear resistance.

[0035] In the silver-plated material according to the present invention, when the thickness of the second silver-plated layer 6 is considered to be 0.7 nm or more and 15 nm or less, it exhibits wear resistance and good contact resistance, as confirmed by the test results of the examples described later.

[0036] (4) Structure of the organic coating layer and method of forming the same <1> Structure of the organic coating layer The organic coating layer 7 is a coating layer formed on the second silver plating layer 6 and contains one or more selected from thiol compounds, fatty acid compounds, and fluorine compounds, and has the effect of improving the wear resistance of the second silver plating layer 6 as described in "(6) Second silver plating layer" and suppressing corrosion of the second silver plating layer 6 in the environment.

[0037] Thiol surface treatment agents, which are thiol compounds, include aqueous solutions consisting of a surfactant, a thiol compound, an organic acid, and ion-exchanged water, and octadecanethiol (C １８Surface treatment agents containing a mixed aqueous solution of SH and benzotriazole (BTA), an alcohol solution (such as ethanol) containing 1-octadecanethiol, or the like can be used. In addition, commercially available rust inhibitors such as fluorine-free CD-9700W (manufactured by Chemical Electronics Co., Ltd.) can be used.

[0038] Furthermore, as fatty acid compounds, fatty acid-based surface treatment agents can be used that include saturated fatty acids such as stearic acid, capric acid, lauric acid, myristic acid, palmitic acid, behenic acid, cerotic acid, and melissic acid, as well as unsaturated fatty acids such as myristoleic acid, palmitoleic acid, oleic acid, nervonic acid, linoleic acid, and α-linolenic acid.

[0039] Furthermore, as a fluorine-based surface treatment agent containing fluorine compounds, commercially available rust inhibitors such as CE-9500W (manufactured by Chemical Electronics Co., Ltd.) can be used.

[0040] <2> Method for forming the organic coating layer The organic coating layer 7 can be formed by immersing a silver-plated material having formed the second silver-plated layer 6 into a water emulsion bath, aqueous solution, or alcohol solution containing one or more selected from thiol-based surface treatment agents, fatty acid-based surface treatment agents, and fluorine-based surface treatment agents, and bringing it into contact with the water emulsion bath.

[0041] (5) Structure of the undercoat plating layer, structure of the silver undercoat plating layer, and method of forming them <1> Structure of the undercoat plating layer and structure of the silver undercoat plating layer The undercoat plating layer is formed as needed for the purpose of preventing copper from the metal material 1 from diffusing onto the plating surface and oxidizing, thereby preventing deterioration of the conductivity of the silver plating material 10, and for the purpose of improving the adhesion of the silver plating layer. Examples of metals constituting the undercoat plating layer include at least one metal or alloy selected from the group consisting of Cu, Ni, Sn, and Ag. In the present invention, if the undercoat plating layer is a metal other than Ag, such as Cu, Ni, or Sn, it will be described as "undercoat plating layer 2", and if the undercoat plating layer consists of Ag, it will be described as "silver undercoat plating layer 4". The undercoat plating layer may be a single layer made of Cu, Ni, Sn, Ag, or alloys thereof, or a layered structure combining them. The formation of the undercoat plating layer 2 and the silver undercoat plating layer 4 on the metal material 1 may be on the entire surface of the metal material 1 or on a part thereof, depending on the intended use of the silver-plated material 10 being manufactured.

[0042] In the present invention, it is preferable to form an undercoat plating layer 2 made of Ni in order to prevent copper in the metal material 1 from diffusing onto the surface of the silver plating layer and degrading its conductivity.

[0043] The silver undercoat plating layer 4 shall be a silver layer that does not contain carbon or sulfur. However, the unavoidable presence of trace amounts of carbon and sulfur is permitted.

[0044] <2> Method for forming the undercoat plating layer The method for forming the undercoat plating layer 2 is not particularly limited. For example, it can be formed by electroplating using a known method with a plating bath containing the metals that constitute the undercoat plating layer 2. Alternatively, for example, the undercoat plating layer 2 can be formed by sequentially laminating layers made of each metal that constitutes the target metal layer on the metal material 1, and then reflowing (heat treating). There are no particular restrictions on the average thickness of the undercoat plating layer 2, but it is preferably 0.2 μm or more and 5.0 μm or less, and more preferably 0.2 μm or more and 3 μm or less.

[0045] <3> Method for forming the silver undercoat plating layer A plating solution that does not contain sulfide compounds is used to form the silver undercoat plating layer 4. As long as the effects of the present invention are not impaired, known methods can be used without particular limitation as a method for forming the silver undercoat plating layer 4. There are no particular limitations on the average thickness of the silver undercoat plating layer 4, but it is preferably 0.2 μm or more and 5.0 μm or less, and more preferably 0.2 μm or more and 3 μm or less.

[0046] (6) Structure of the silver strike plating layer and method of forming the same <1> Structure of the silver strike plating layer Before forming the first silver plating layer 5 described later on the metal material 1, it is preferable to form a very thin intermediate layer with the silver strike plating layer 3 to improve the adhesion between the metal material 1 and the first silver plating layer 5. When the above-mentioned under-plating layer 2 is formed on the metal material 1, it is preferable to form the silver strike plating layer 3 on the under-plating layer 2 to improve the adhesion between the under-plating layer 2 and the first silver plating layer 5.

[0047] The silver strike plating layer 3 is preferably a silver plating layer that does not contain carbon or sulfur. However, the unavoidable presence of trace amounts of carbon and sulfur is acceptable.

[0048] <2> Method for forming the silver strike plating layer A plating solution that does not contain sulfide compounds is used to form the silver strike plating layer 3. As for the method for forming the silver strike plating layer, known methods can be used without particular limitation as long as they do not impair the effects of the present invention. The silver strike plating layer 3 is an extremely thin electroplated silver layer with an average thickness of, for example, 1 nm to 50 nm, preferably 1 nm to 20 nm.

[0049] (7) Formation sequence of the undercoat, silver undercoat, and silver strike plating layer It is preferable to form a silver undercoat 4 on the metal material 1 before forming the first silver plating layer 5 to improve adhesion between the metal material 1 and the first silver plating layer 5. When the undercoat 2 is formed on the metal material 1, it is preferable to form the silver undercoat 4 on the undercoat 2 to improve adhesion between the undercoat 2 and the first silver plating layer 5.

[0050] Furthermore, when forming the aforementioned silver strike plating layer 3 on the undercoat plating layer 2 or on the metal material 1, it is preferable to form a silver undercoat plating layer 4 or a first silver plating layer 5 on the silver strike plating layer 3 to further improve the adhesion between the undercoat plating layer 2 and the silver undercoat plating layer 4 or the first silver plating layer 5.

[0051] [2] Evaluation of the silver-plated material As described above, the silver-plated material 10 according to the present invention, obtained by sequentially forming a first silver-plated layer 5, a second silver-plated layer 6, and an organic film layer 7 on a metal material 1, has significantly improved durability against sliding wear and excellent properties such as low contact resistance after sliding wear.

[0052] Specifically, as will be explained in the examples, two pieces of silver-plated material according to the present invention are prepared, one of which is indented (inner radius = 1.5 mm) and used as an indenter. Using a precision sliding test apparatus, the indenter is pressed against the other silver-plated material with a load of 5 N, and slid back and forth at a sliding distance of 5 mm and a sliding speed of 1.67 mm / s, and the contact resistance at the contact point between the indenter and the other silver-plated material is measured after each back and forth. When the contact resistance between the indenter and the other silver-plated material is measured up to 200 back and forth sliding cycles, it is 0.4 mΩ or less, and the metal material is not exposed up to 300 back and forth sliding cycles, indicating that the silver-plated material has a film thickness of 0.5 μm or more and 5 μm or less.

[0053] Here, the thickness of the silver plating is the thickness of the layers including the first silver plating layer 5, the second silver plating layer 6, and the organic coating layer 7. Furthermore, if a silver strike plating layer 3 and a silver undercoat plating layer 4 are applied, the thickness of those layers is also included. In this invention, the thickness of the plating layer was measured using an X-ray fluorescence thickness meter.

[0054] Furthermore, the thickness of the first silver plating layer of the plated material obtained in this invention can be determined by converting the region where the carbon concentration is 5 at% to 24 at%, the sulfur concentration is 0.7 at% to 5 at% and the silver concentration is 75 at% to 93 at% to Si equivalent (20 nm / min) from the profile results obtained by depth profiling using XPS, as described later.

[0055] [3] Terminals The terminal according to the present invention is formed from a silver-plated material 10 obtained by the process of sequentially forming a first silver plating layer 5, a second silver plating layer 6, and an organic coating layer 7 on a metal material 1 as described above. Compared to conventional terminals, the terminal according to the present invention has significantly improved durability against sliding wear and excellent characteristics such as low contact resistance after sliding wear.

[0056] The silver-plated material and terminals according to the present invention will be described in detail below with reference to the examples. However, the present invention is not limited to these examples. (Example 1) (1) Metal material A pure copper metal substrate (C1020-1 / 2H) measuring 67 mm × 50 mm × 0.3 mm was prepared as the metal material. This metal material and a SUS plate were placed in an alkaline degreasing solution, and electrolytic degreasing was performed for 30 seconds by applying a voltage of 5 V with the metal material as the cathode and the SUS plate as the anode. Next, the metal material was pickled in 3% sulfuric acid for 15 seconds to obtain the plated material according to Example 1. Note that 15 seconds of water rinsing was performed between each step.

[0057] (2) Formation of the undercoat In a plating solution consisting of 504 g / L nickel sulfamate tetrahydrate, 25 g / L nickel chloride, and 35 g / L boric acid, the material to be plated is used as the cathode and the SK nickel electrode plate as the anode, and the plating is carried out while stirring at 500 rpm with a magnetic stirrer at a current density of 5 A / dm ２ Electroplating was performed at a liquid temperature of 55°C until the nickel film thickness reached 1 μm, and a nickel undercoat was applied.

[0058] (3) Formation of silver strike plating layer In a plating solution consisting of 3 g / L of silver potassium cyanide and 90 g / L of potassium cyanide, the material to be plated is used as the cathode and a platinum-coated titanium electrode plate as the anode, and the solution is stirred at 500 rpm with a stirrer while the current density is 2 A / dm ２ Electroplating was performed for 10 seconds, and a silver strike plating layer was applied on top of the Ni underplating layer.

[0059] (4) Silver underplating layer In Example 1, no silver underplating layer was formed on the material to be plated.

[0060] (5) Formation of the first silver plating layer In a silver plating bath containing 175 g / L of potassium silver cyanide, 95 g / L of potassium cyanide, and 30 g / L of sodium 2-mercaptobenzothiazole, the material to be plated with the silver strike plating layer is used as the cathode, and a silver electrode plate with a purity of 99.99% or higher is used as the anode, and the plating is performed while stirring at 500 rpm with a stirrer, with a current density of 7 A / dm ２ The solution temperature was set to 35°C, and electroplating was performed until the silver film thickness reached 1 μm, thereby applying the first silver plating layer. After silver plating, the material was rinsed with water for 15 seconds and dried with an air gun.

[0061] (6) Formation of the second silver plating layer <1> Preliminary test: Understanding the relationship between the value of "current density × plating time" and the thickness of the silver plating layer under predetermined conditions A plating material for Example 1, similar to that described in "(1) Metal material", was prepared. In a plating solution containing 175 g / L of silver potassium cyanide, 95 g / L of potassium cyanide, and 20 mg / L of selenocyanate, the plating material was used as the cathode and a silver electrode plate with a purity of 99.99% or higher as the anode, and while stirring at 500 rpm with a stirrer, the current density was set to 0.5 A / dm ２ Plating was performed for 266 seconds at a solution temperature of 18°C. When measured with an X-ray fluorescence film thickness gauge, the resulting silver plating layer thickness was 1.0 μm, the carbon concentration in the film was 0.39 at%, the oxygen concentration was 0.26 at%, the sulfur concentration was 0.28 at%, and the silver concentration was 98.2 at%.

[0062] In the plating process, according to Faraday's law, the amount of metal deposited (i.e., the film thickness) is proportional to the amount of electricity flowing (the product of current and time). Using this relationship, the proportionality constant between the film thickness in the preliminary test and the product of current density and plating time can be expressed as the value obtained by dividing the film thickness obtained in the preliminary test by the product of the current density and plating time in the preliminary test (7.5 nm / second A / dm²). ２ Therefore, the assumed value of the film thickness formed per second under the conditions of the preliminary test can be calculated from the following equation (1): Assumed film thickness = 7.5 (nm / (second・A / dm ２ )) × current density (A / dm ２) × plating time (seconds) ... Equation (1) The results are shown in Table 1.

[0063]

[0064] <2> Formation of the second silver plating layer Based on this correspondence, the material to be plated with the first silver plating layer was used as the cathode, and a silver electrode plate with a purity of 99.99% or higher was used as the anode. Silver plating was performed under the same conditions as in preliminary test 1, except that the plating time was set to 3 seconds, and the second silver plating layer was applied on top of the first silver plating layer. The product of the current density and plating time when the second silver plating was applied in Example 1 was 1.5 (seconds・A / dm²). ２ The expected thickness of the second silver plating layer is 11.3 nm. After silver plating, the sample was rinsed with water for 15 seconds and dried with an air gun.

[0065] (7) Formation of the organic coating layer The plated material with the second silver plating layer was immersed for 10 seconds in an aqueous solution containing 200 mL / L of a commercially available surface treatment agent (CE-9500W manufactured by Chemical Electronics Co., Ltd.), which is a fluorine-based surface treatment agent, at a liquid temperature of 30°C to form the organic coating layer and obtain the silver plated material according to Example 1. After immersion in the surface treatment agent, it was rinsed with water for 15 seconds and dried with an air gun. The state of the plating layer of the silver plated material according to Example 1 is shown in Table 2. The same procedure was followed for Examples 2 to 5. Comparative Examples 1 to 6 are shown in Table 3, and Comparative Examples 7 to 11 are shown in Table 4.

[0066] (8) Evaluation of Silver-Plated Material The following tests were performed using the silver-plated material obtained for Example 1 as the test material. <1> Reciprocating Sliding Durability Test Two pieces of silver-plated material from Example 1 were prepared. One was indented (inner radius = 1.5 mm) and used as an indenter, and the other was used as a flat evaluation sample. Using a precision sliding test apparatus (CRS-G2050-DWA, manufactured by Yamazaki Seiki Kenkyusho Co., Ltd.), the indenter was pressed against the evaluation sample with a constant load (5 N) and a reciprocating sliding motion (sliding distance 5 mm, sliding speed 1.67 mm / s) was continued until the material was exposed. Then, the wear resistance was evaluated by performing an abrasion test to check the wear state of the silver-plated material by observing the center of the sliding marks on the silver-plated material at a magnification of 100x using a microscope (VHX-1000, manufactured by Keyence Corporation). Specifically, a score of ○ (good wear resistance) was given if the material was not exposed after 300 reciprocating slides, and a score of × (poor wear resistance) was given if the material was exposed after fewer than 300 reciprocating slides. A score of ○ was considered a pass. The silver-plated material in Example 1 received a score of ○. The evaluation results of the reciprocating sliding durability test for the silver-plated material in Example 1 are shown in Table 2. The same applies to Examples 2 and 3 and Comparative Examples 1 to 9 below.

[0067] <2> Measurement of Contact Resistance Using the precision sliding test apparatus described above, the change in contact resistance between the indenter and the other silver-plated material during each reciprocating motion of the silver-plated material according to Example 1 was measured. After 200 reciprocating slides, a contact resistance of 0.4 mΩ or less between the indenter and the other silver-plated material was judged as ○ (good contact resistance), and a contact resistance of 0.4 mΩ or more was judged as × (poor contact resistance), with ○ being the pass / fail evaluation. The silver-plated material according to Example 1 received a ○ evaluation. The evaluation results of the contact resistance of the silver-plated material according to Example 1 are shown in Table 2. The same applies to Examples 2 and 3 and Comparative Examples 1-9 below.

[0068] (Example 2) In Example 2, a silver plated material according to Example 2 was prepared in the same manner as in Example 1, except that a silver undercoat was formed on the silver strike plating layer by a method described later, and a first silver plating layer was formed on the silver undercoat.

[0069] (1) Formation of the silver underplating layer In a plating solution containing 175 g / L of potassium silver cyanide, 95 g / L of potassium cyanide, and 16 mg / L of selenium, the material to be plated with a silver strike plating layer formed on it is used as the cathode, and a silver electrode plate with a purity of 99.99% or higher is used as the anode, and the plating is performed while stirring at 500 rpm with a magnetic stirrer, with a current density of 7 A / dm ２ At a liquid temperature of 18°C, electroplating was performed until the thickness of the silver undercoat plating layer reached 0.2 μm, thereby forming a silver undercoat plating layer on top of the silver strike plating layer.

[0070] Using the silver-plated material obtained in Example 2, the following tests were performed in the same manner as in Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance".

[0071] Furthermore, the following tests were performed using the silver-plated material obtained in Example 2 as the test material. <3> Depth profiling analysis by XPS The structure of the silver-plated material in Example 2 was investigated by analyzing the depth profiling concentrations of specified elements C, O, S, Ag, and Ni using XPS (X-ray photoelectron spectroscopy: PH5000 VersaProbe III manufactured by ULVAC-PHI, Inc.).

[0072] XPS measurements were performed under X-ray irradiation conditions with a target vacuum level of 10 ―７ The Pa excitation source was monochromatic AlKα, the output was 25A, the acceleration voltage was 15kV, the beam size was 100μmφ, and the incident angle was 90deg. Then, an electron beam was irradiated using an electron neutralization gun with an emission current of 20μA, a bias voltage of 1.0V, and an acceleration voltage of 30.0V, while the ion species was converted using an argon gun. ＋ Measurements were performed while irradiating with argon ions at an acceleration voltage of 0.11 kV and emission current of 7 mA, with a photoelectron extraction angle of 45 deg, integration count of 5 times, differentiation time of 40 ms (20 ms x 2), pulse energy of 140 eV, and measurement energy interval of 0.25 eV / step.

[0073] Furthermore, the depth profile is obtained by using an argon gun to separate ion species into Ar ＋Ion sputtering was performed with an acceleration voltage of 4 kV, an emission current of 20 mA, and a sweep area of ​​2.7 mm × 2.7 mm. Surface etching for depth profiling was then performed, and the results were obtained by alternately repeating this surface etching and XPS measurements.

[0074] Figure 2 shows the depth-direction concentration profile of XPS in the plated material according to Example 2. The atomic concentration of carbon in the plated material according to Example 2 immediately after the start of measurement (outermost surface) was 73.8 at%, the average atomic concentration of carbon from 10 to 20 minutes after the start of measurement (between a depth of 200 nm and 400 nm in Si equivalent) was 9.3 at%, the average atomic concentration of sulfur was 1.1 at%, and the average atomic concentration of silver was 89.6 at%. These values ​​are shown in Table 4.

[0075] The abrasion resistance of the silver-plated material in Example 2 was rated as ○, and the contact resistance measurement also received a ○ rating.

[0076] (Example 3) A silver-plated material was prepared in the same manner as in Example 2, except that the thickness of the silver undercoat plating layer on the silver strike plating layer was 1.0 μm. Using the silver-plated material obtained in Example 3, the following tests were performed in the same manner as in Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The wear resistance of the silver-plated material in Example 3 was rated as ○, and the measurement of contact resistance was also rated as ○.

[0077] (Example 4) A silver-plated material was prepared in the same manner as in Example 2, except that the material to be plated with a second silver-plated layer was immersed for 10 seconds at a liquid temperature of 30°C in an aqueous solution containing 120 mL / L of a commercially available rust inhibitor (CD-9700W, manufactured by Chemical Electronics Co., Ltd.) that does not contain fluorine, to form an organic coating layer. Using the silver-plated material obtained in Example 4, the following tests were performed in the same manner as in Example 1: "<1> Reciprocating sliding durability test" and "<2> Measurement of contact resistance". The abrasion resistance of the silver-plated material in Example 4 was rated as ○, and the measurement of contact resistance was also rated as ○.

[0078] (Example 5) A silver-plated material was prepared in the same manner as in Example 2, except that the current density when forming the second silver plating layer was set to 0.1 A / dm² and the plating time was set to 1 second. The product of the current density and plating time when the second silver plating was applied in Example 5 was 0.1 (seconds・A / dm²). ２ ) and the expected thickness of the second silver plating layer is 0.8 nm. Using the silver-plated material obtained in Example 4, the following tests were performed in the same manner as in Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The wear resistance of the silver-plated material in Example 5 was rated as ○, and the measurement of contact resistance was also rated as ○.

[0079] (Comparative Examples 1-3) In Comparative Example 1, no silver underplating layer was formed, similar to Example 1. In Comparative Example 2, a silver underplating layer with a thickness of 0.2 μm was formed on the silver strike plating layer, similar to Example 2. In Comparative Example 3, a silver underplating layer with a thickness of 1.0 μm was formed on the silver strike plating layer, similar to Example 3. In Comparative Examples 1-3, the second silver plating layer and the organic coating layer were not formed. Except for these, the silver-plated materials according to Comparative Examples 1-3 were prepared by the same method as in Example 1. Using the obtained silver-plated materials according to Comparative Examples 1-3, the following tests were performed, similar to Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The wear resistance results for the silver-plated materials according to Comparative Examples 1-3 were rated as ○, and the contact resistance measurement was rated as ×.

[0080] (Comparative Examples 4-6) In Comparative Example 4, no silver underplating layer was formed, similar to Example 1. In Comparative Example 5, a silver underplating layer with a thickness of 0.2 μm was formed on the silver strike plating layer, similar to Example 2. In Comparative Example 6, a silver underplating layer with a thickness of 1.0 μm was formed on the silver strike plating layer, similar to Example 3. In Comparative Examples 4-6, no second silver plating layer was formed. Except for these, the silver-plated materials according to Comparative Examples 4-6 were prepared by the same method as in Example 1. Using the obtained silver-plated materials according to Comparative Examples 4-6, the following tests were performed, similar to Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The wear resistance results for the silver-plated materials according to Comparative Examples 4-6 were rated as ○, and the contact resistance measurement was rated as ×.

[0081] (Comparative Examples 7-9) In Comparative Example 7, no silver underplating layer was formed, similar to Example 1. In Comparative Example 8, a silver underplating layer with a thickness of 0.2 μm was formed on the silver strike plating layer, similar to Example 2. In Comparative Example 9, a silver underplating layer with a thickness of 1.0 μm was formed on the silver strike plating layer, similar to Example 3. In Comparative Examples 7-9, no organic coating layer was formed. Except for these, the silver-plated materials according to Comparative Examples 7-9 were prepared by the same method as in Example 1. Using the obtained silver-plated materials according to Comparative Examples 7-9, the following tests were performed, similar to Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The wear resistance results for the silver-plated materials according to Comparative Examples 7-9 were rated as ×, while the contact resistance measurement was rated as ○.

[0082] (Comparative Example 10) When forming the second silver plating layer, the current density is 0.5 A / dm ２ A silver-plated material according to Comparative Example 10 was prepared in the same manner as in Example 2, except that the plating time was set to 5 seconds and no organic film layer was formed. The product of the current density and plating time when the second silver plating was performed in Comparative Example 10 was 2.5 (seconds・A / dm²). ２) and the expected thickness of the second silver plating layer is 18.8 nm. Using the silver-plated material obtained in Comparative Example 10, the following tests were performed in the same manner as in Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The abrasion resistance result of the silver-plated material obtained in Comparative Example 10 was rated as ×, and the measurement of contact resistance was rated as ○.

[0083] (Comparative Example 11) When forming the second silver plating layer, the current density is 0.5 A / dm ２ A silver-plated material according to Comparative Example 11 was prepared in the same manner as in Example 2, except that the plating time was set to 5 seconds. The product of the current density and plating time when the second silver plating was performed in Comparative Example 11 was 2.5 (seconds・A / dm²). ２ ) and the expected thickness of the second silver plating layer is 18.8 nm. Using the silver plating material obtained for Comparative Example 11, the following tests were performed in the same manner as in Example 1: "(1) Reciprocating sliding durability test" and "(2) Measurement of contact resistance". The abrasion resistance result for the silver plating material obtained for Comparative Example 11 was a × rating, and the contact resistance result was a ○ rating.

[0084]

[0085]

[0086]

[0087] The elemental concentration profiles in the depth direction of silver, carbon, and sulfur in the silver-plated material according to Example 2 were measured by XPS and are shown in Figure 2. The elemental concentration profiles in the depth direction of silver, carbon, and sulfur in the silver-plated layer of the silver-plated material shown in Figure 2 were examined. Here, the second silver-plated layer according to Example 2 has a film thickness of 11.3 nm, and it was difficult to distinguish the film thickness of the second silver-plated layer from the first silver-plated layer based on the silver concentration profile. Note that Figure 2 shows the profile results up to an etching time of 20 minutes, and shows the etching results from the surface to partway through the first silver-plated layer. In the obtained silver-plated material, the etching time can be increased as appropriate to confirm the film thickness of the first silver-plated layer.

[0088] Furthermore, the elemental concentration profile in the depth direction of carbon in the silver plating layer of the silver-plated material shown in Figure 2 was examined using XPS. Here, although the silver-plated material according to Example 2 has an organic film layer formed on it, it was difficult to confirm the thickness of the organic film layer in the silver-plated material according to Example 2 based on the carbon concentration profile.

[0089] In the silver-plated material according to Example 2, the elemental concentration profiles of silver, carbon, and sulfur in the depth direction were measured by XPS and are shown in Figure 2. Figure 2 shows the profile results up to an etching time of 20 minutes by XPS, and indicates the concentration profiles of each element from the surface layer of the silver-plated material to the middle of the first silver-plated layer.

[0090] The silver concentration profile was examined using Figure 2. As a result, although the thickness of the second silver plating layer in Example 2 is estimated to be 11.3 nm, it was difficult to distinguish the thickness of the second silver plating layer from the first silver plating layer using the silver concentration profile obtained with XPS. Next, the carbon concentration profile in Figure 2 was examined. As a result, it was difficult to measure the thickness of the organic coating layer in the silver plating material in Example 2 using the carbon concentration profile obtained with XPS.

[0091] 1. Metal material 2. Undercoat plating layer 3. Silver strike plating layer 4. Silver undercoat plating layer 5. First silver plating layer 6. Second silver plating layer 7. Organic coating layer 10. Silver plating material

Claims

1. The process comprises the steps of: forming a first silver plating layer with a thickness of 0.5 μm to 5.0 μm on a metal material by electroplating with a cyanide plating solution containing benzothiazoles or benzothiazole derivatives; forming a second silver plating layer on the first silver plating layer by electroplating with a plating solution having a carbon concentration of 0 at% to 1 at% and a silver concentration of 95 at% to 100 at%; and forming an organic coating layer by contacting the second silver plating layer with a solution containing one or more organic substances selected from thiol compounds, fatty acid compounds, and fluorine compounds, wherein the current density in the step of forming the second silver plating layer is 3 A / dm ２ It is less than the product of the current density and the plating time (A × sec / dm²). ２ ) to 0.1 (A × sec / dm ２ ) or more 2.0 (A x sec / dm ２ A method for manufacturing silver-plated material, provided the following conditions are met.

2. The method for producing a silver-plated material according to claim 1, wherein the carbon concentration in the first silver-plated layer is 5 at% or more and 24 at% or less, and the sulfur concentration is 0.7 at% or more and 5.0 at% or less.

3. A silver-plated material having a first silver-plated layer on a metal base material containing carbon and sulfur, wherein the carbon concentration is 5 at% to 24 at%, the sulfur concentration is 0.7 at% to 5.0 at%, and the silver concentration is 75 at% to 93 at%, wherein two of the silver-plated materials are prepared, and one of the silver-plated materials is indented (inner radius = 1.5 mm) and used as an indenter. When the indenter is pressed against the other silver-plated material with a load of 5 N using a precision sliding test apparatus, and a reciprocating sliding operation is performed at a sliding distance of 5 mm and a sliding speed of 1.67 mm / s, the metal base material is not exposed on the other silver-plated material up to 300 reciprocating sliding cycles, and the contact resistance between the indenter and the other silver-plated material up to 200 reciprocating sliding cycles does not exceed 0.4 mΩ.

4. The silver-plated material according to claim 3, wherein the metal material is copper or a copper alloy.

5. A terminal using the silver-plated material described in claim 3 or 4.

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