Tin-plated product and method for producing the same

Abstract

A tin-plated product, wherein a surface of a substrate (10) is plated with tin, the tin-plated product comprising: a substrate (10) made of copper or a copper alloy; a base (12) formed on a surface of the substrate (10), the base (12) being formed of nickel and / or a copper-nickel alloy; and an outermost layer formed on a surface of the base layer (12), the outermost layer being composed of a copper-tin alloy layer (14) and tin layers (16), the copper-tin alloy layer (14) being formed of a large number of crystal grains of a copper-tin alloy, each of the tin layers (16) being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of crystal grains of the copper-tin alloy, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, wherein an area ratio occupied by the tin layers (16) on the outermost surface is 20 to 80%, and a maximum thickness of the tin layers (16) is smaller than an average particle diameter of the crystal grains of the copper-tin alloy, and wherein the outermost surface has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers and a maximum roughness depth Ry of 0.3 to 1.5 micrometers.

Description

TECHNICAL FIELD

[0001] The present invention generally relates to a tin-plated product and a method for producing the same. More particularly, the invention relates to a tin-plated product used as the material of an insertable connection terminal or the like and a method for producing the same. TECHNICAL BACKGROUND

[0002] As conventional materials for insertable connecting terminals, tin-plated products are used, in which a tin plating layer is formed as the outermost layer from a conductive material such as copper or a copper alloy. In particular, tin-plated products are used as materials for information transmission equipment for automobiles, portable telephones and personal computers, control base plates for industrial equipment such as robots, terminals / terminals such as connectors, lead frames, relays and switches, and bus bars due to their low contact resistance, contact reliability, corrosion resistance, solderability, and cost-effectiveness.

[0003] As such a tin-plated product, a plated copper or plated copper alloy is proposed in which a nickel or nickel alloy layer is formed on the surface of copper or a copper alloy, and a tin or tin alloy layer is formed on the outermost surface thereof, wherein at least one layer of intermediate layers containing copper and tin as main components, or intermediate layers containing copper, nickel, and tin as main components, is formed between the nickel or nickel alloy layer and the tin or tin alloy layer, and at least one intermediate layer of these intermediate layers includes a layer containing 50% by weight or less of copper and 20% by weight or less of nickel (see, for example, Japanese Patent Publication JP 2003 - 293 187 A). Another tin-plated product can be found, for example, in US 2014 / 0 004 373 A1.

[0004] A conductive material for connecting parts is also proposed, wherein a copper-tin alloy plating layer containing 20 to 70 atomic% of copper and having an average thickness of 0.2 to 3.0 micrometers, and a tin plating layer having an average thickness of 0.2 to 5.0 micrometers are formed on the surface of a base material of a copper plate or a copper rod in this order, and the surface thereof is reflow-treated, wherein the arithmetic mean roughness Ra in at least one direction is 0.15 micrometers or more, the arithmetic mean roughness Ra in all directions is 3.0 micrometers or less, a part of the copper-tin alloy plating layer is exposed to the surface of the tin plating layer, and the ratio of the exposed areas of the copper-tin alloy plating layer is 3 to 75% with respect to the surface of the conductive material (see, for example,Japanese patent publication JP 2006 - 183 068 A).

[0005] However, in the tin-plated product proposed in Japanese Patent Publication No. 2003-293187, there is a problem in that the insertion force of an insertable connection terminal or the like is increased during insertion when the tin-plated product is used as the material of the insertable connection terminal or the like, although the tin-plated product has good solderability, whisker resistance, heat resistance reliability, and formability. In the tin-plated product proposed in Japanese Patent Publication No. 2006-183068, since a substrate is plated after its surface is roughened to reduce the insertion force of an insertable connection terminal or the like, its production cost is increased when the tin-plated product is used as the material of the insertable connection terminal or the like. DISCLOSURE OF THE INVENTION

[0006] It is therefore an object of the present invention to eliminate the above-mentioned problems and to provide a tin-plated product having a low insertion force when used as the material of an electrical element such as an insertable connecting terminal, and a method for manufacturing the tin-plated product at low cost.

[0007] In order to achieve the above-mentioned object, the inventors conducted extensive studies and found that it is possible to manufacture a tin-plated product at low cost, the tin-plated product having a low insertion force when used as the material of an electrical element such as an insertable connecting terminal, when a tin-plated product is provided in which a surface of a substrate is plated with tin, the tin-plated product comprising: a substrate made of copper or a copper alloy; an undercoat formed on a surface of the substrate, the undercoat being made of nickel and / or a copper-nickel alloy;and an outermost layer formed on a surface of the base layer, the outermost layer being composed of a copper-tin alloy layer and tin layers, the copper-tin alloy layer being formed of a large number of copper-tin alloy crystal grains, each of these tin layers being arranged in a corresponding one of the recessed portions, each of which is formed between adjacent ones of the large number of copper-tin alloy crystal grains, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, an area ratio occupied by the tin layers on the outermost surface being 20 to 80%, and a maximum thickness of the tin layers being smaller than an average particle diameter of the copper-tin alloy crystal grains. Thus, the inventors have completed the present invention.

[0008] According to the present invention, there is provided a tin-plated product wherein a surface of a substrate is plated with tin, the tin-plated product comprising: a substrate made of copper or a copper alloy; a sub-base formed on a surface of the substrate, the sub-base being formed of nickel and / or a copper-nickel alloy;and an outermost layer formed on a surface of the subbase, the outermost layer being composed of a copper-tin alloy layer and tin layers, the copper-tin alloy layer being formed of a large number of copper-tin alloy crystal grains, each of these tin layers being arranged in a corresponding one of the recessed portions, each formed between adjacent ones of the large number of copper-tin alloy crystal grains, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, an area ratio occupied by the tin layers on the outermost surface being 20 to 80%, and a maximum thickness of the tin layers being smaller than an average particle diameter of the copper-tin alloy crystal grains.

[0009] In this tin-plated product, the copper-tin alloy layer is preferably formed of a copper-tin alloy or a copper-nickel-tin alloy. In this case, the copper-tin alloy is preferably Cu 6 Sn 5 and the copper-nickel-tin alloy is preferred (Cu, Ni) 6 Sn 5The copper-tin alloy crystal grains preferably have an average particle diameter of 1.5 to 3 micrometers. The tin layers preferably have a maximum thickness of 0.2 to 1.0 micrometers, and the tin layers preferably have an average thickness of 0.05 to 0.4 micrometers. The copper-tin alloy layer preferably has a thickness of 0.4 to 1.5 micrometers, and the base layer preferably has a thickness of 0.05 to 0.5 micrometers. The outermost surface of the tin-plated product according to the invention has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers and a maximum roughness Ry of 0.3 to 1.5 micrometers.

[0010] According to the present invention, there is provided a method for producing a tin-plated product whose outermost surface has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers and a maximum roughness Ry of 0.3 to 1.5 micrometers, the method comprising the steps of: treating a surface of a substrate made of copper or a copper alloy; forming a nickel plating layer, a copper plating layer, and a tin plating layer on the treated surface of the substrate in this order;and thereafter performing a heat treatment to form an outermost layer composed of a copper-tin alloy layer and tin layers, wherein the copper-tin alloy layer is formed of a large number of copper-tin alloy crystal grains, each of the tin layers being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of copper-tin alloy crystal grains, adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, wherein the heat treatment causes an area ratio occupied by the tin layers on the outermost surface to be 20 to 80% and causes a maximum thickness of the tin layers to be smaller than an average particle diameter of the copper-tin alloy crystal grains.

[0011] In this method for manufacturing a tin-plated product, the treatment of the surface of the substrate causes the surface of the substrate to have an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers, a maximum roughness Ry of 0.4 to 1.5 micrometers, and a ten-point mean roughness Rz of 0.15 to 1.0 micrometers. The nickel plating layer preferably has a thickness of 0.05 to 0.5 micrometers, the copper plating layer preferably has a thickness of 0.1 to 0.7 micrometers, and the tin plating layer preferably has a thickness of 0.5 to 1.5 micrometers. The ratio of the thickness of the tin plating layer to the thickness of the copper plating layer is preferably 1.5 to 5, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer is preferably 1 to 3.5.The heat treatment is carried out according to the invention by adjusting the temperature and time in a temperature range of 300 to 800°C to cause the average particle diameter of the crystal grains of the copper-tin alloy to be 1.5 to 3 micrometers, while causing the maximum thickness of the tin layers to be 0.2 to 1.0 micrometer.

[0012] The heat treatment is preferably carried out by adjusting the temperature and time within a temperature range of 300 to 800°C to cause the tin layers to have an average thickness of 0.05 to 0.4 micrometers. In this case, the temperature and time in the heat treatment are preferably adjusted such that the thickness (µm) of the tin plating layer consumed after being melted by the heat treatment is {thickness (µm) of the tin plating layer before heat treatment - 0.7 (µm)} or more and {thickness (µm) of the tin plating layer before heat treatment - 0.35 (µm)} or less.

[0013] According to the present invention, there is provided an electrical element using the above-described tin-plated product as its material.

[0014] According to the present invention, it is possible to produce a tin-plated product at low cost, the tin-plated product having a low insertion force when used as the material of an electrical element such as an insertable connecting terminal. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view schematically showing the preferred embodiment of a tin-plated product according to the present invention; and Fig.2 is a view illustrating an angle θ between the outermost surface of a copper-tin alloy layer and a straight line intersecting the point of maximum depth of a tin layer and the intersection point of the outermost surface and a substantially central portion of the copper-tin alloy layer adjacent to the tin layer, in a cross section substantially perpendicular to the outermost surface of the preferred embodiment of a tin-plated product according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0015] In the preferred embodiment of a tin-plated product according to the present invention, wherein a surface of a substrate 10 made of copper or a copper alloy is plated with tin, as shown in Fig.1, a sub-base 12 is formed on the surface of the substrate 10, the sub-base 12 being formed of nickel and / or a copper-nickel alloy, and an outermost layer is formed on a surface of the sub-base 12, the outermost layer being composed of a copper-tin alloy layer 14 and tin layers 16, the copper-tin alloy layer 14 being formed of a large number of crystal grains of a copper-tin alloy, each of the tin layers 16 being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of crystal grains of the copper-tin alloy, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, the area ratio occupied by the tin layers 16 on the outermost surface being20 to 80% (preferably 30 to 75%, more preferably 30 to 70%), and the maximum thickness of the tin layers 16 is smaller than an average particle diameter of the crystal grains of the copper-tin alloy. When a tin-plated product with such a structure is used as the material of an insertable connecting terminal, it is possible to prevent cutting of the copper-tin alloy layer of the outermost layer, thereby producing a connecting terminal that has a low insertion force and that has low electrical resistance during slight sliding.

[0016] In this tin-plated product, the copper-tin alloy layer 14 is preferably formed from a copper-tin alloy and a copper-nickel-tin alloy. In this case, the copper-tin alloy is preferably Cu 6 Sn 5 , and the copper-nickel-tin alloy is preferred (Cu,Ni) 6 Sn 5(an intermetallic compound where Ni in Cu 6 Sn 5is present). The crystal grains of the copper-tin alloy preferably have an average particle diameter of 1.5 to 3 micrometers. The tin layers 16 preferably have a maximum thickness of 0.2 to 1.0 micrometers, and more preferably have a maximum thickness of 0.3 to 0.9 micrometers. The ratio (D / T) of the average particle diameter (D) of the crystal grains of the copper-tin alloy layer of the outermost layer to the maximum thickness (T) of the tin layers 16 is preferably 1.5 to 10, more preferably 2 to 7, and most preferably 2 to 6. The tin layers 16 preferably have an average thickness of 0.05 to 0.4 micrometers, and more preferably have an average thickness of 0.05 to 0.3 micrometers. The copper-tin alloy layer 14 preferably has a thickness of 0.4 to 1.5 micrometers, and more preferably has a thickness of 0.5 to 1.2 micrometers.The substrate 12 preferably has a thickness of 0.05 to 0.5 micrometers, and more preferably has a thickness of 0.1 to 0.4 micrometers. The outermost surface preferably has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers and a maximum roughness depth Ry of 0.3 to 1.5 micrometers.

[0017] Thus, in the preferred embodiment of a tin-plated product according to the present invention, the undercoat 12 is formed of nickel and / or a copper-nickel alloy on the surface of the substrate 10, the outermost layer of the copper-tin alloy layer 14 and the tin layers 16 are formed on the surface of the undercoat 12, and there is preferably no layer of copper between the undercoat 12 and the outermost layer as an intermediate layer.

[0018] On a cross section substantially perpendicular to the outermost surface of the tin-plated product, an angle θ between the outermost surface of the copper-tin alloy layer and a straight line passing through the point of maximum depth of the tin layer and the intersection point of the outermost surface and a substantially central portion of the copper-tin alloy layer adjacent to the tin layer is preferably 25 to 45°C. That is, as shown in Fig.As shown in Fig. 2, on the cross section substantially perpendicular to the outermost surface of the tin-plated product, a straight line L1 is drawn parallel to the outermost surface from a point A1 at which a copper-tin alloy crystal grain of the copper-tin alloy layer 14 contacts one of the copper-tin alloy crystal grains on both sides thereof and at which the depth of a tin layer 16 between these crystal grains is maximum. Then, a straight line L2 is drawn parallel to the outermost surface from a point A2 at which the copper-tin alloy crystal grain of the copper-tin alloy layer 14 contacts the other of the copper-tin alloy crystal grains on both sides thereof and at which the depth of the tin layers 16 between these crystal grains is maximum.Then, a straight line L3 is drawn parallel to the outermost surface such that the distance from both straight lines L1 and L2 is equal between the straight lines L1 and L2 (the straight line L3 denotes an average depth of the points A1 and A2 at which the depth of each of the tin layers 16 on both sides of a crystal grain of the copper-tin alloy is maximum). Then, an intersection point B1 of the straight line L3 and a normal to the outermost surface drawn to pass through the point A1, and an intersection point B2 of the straight line L3 and a normal to the outermost surface drawn to pass through the point A2 are obtained. Then, an intersection point B3 of the outermost surface and a normal to the outermost surface drawn from a midpoint of a line segment between the intersection points B1 and B2 is obtained.The angle θ between the outermost surface and a straight line drawn between the intersection points B1 and B3 is preferably 25 to 45°C. For example, this angle θ can be calculated as follows. First, the tin-plated product is cut with a focused ion beam (FIB) instrument to expose a cross-section substantially perpendicular to the outermost surface of the tin-plated product and parallel to its rolling direction (or a cross-section substantially perpendicular to the outermost surface of the tin-plated product and perpendicular to its rolling direction). Then, the cross-section is observed (for example, at a magnification of 10,000) using a scanning electron microscope (SEM).The angle θ can be calculated from tan θ = H / (L / 2) since tan θ is essentially equal to H / (L / 2), assuming that L is the length of the line segment between the points shown in . Fig. 2 and that H is the length between a midpoint (between the intersection points B1 and B2) and the intersection point of the outermost surface and a normal to the outermost surface, the normal being drawn from the midpoint between the intersection points B1 and B2.

[0019] The preferred embodiment of a method for producing a tin-plated product according to the present invention comprises the steps of: treating a surface of a substrate made of copper or a copper alloy; forming a nickel plating layer, a copper plating layer, and a tin plating layer on the treated surface of the substrate in this order;and thereafter performing a heat treatment to form an outermost layer composed of a copper-tin alloy layer and tin layers, wherein the copper-tin alloy layer is formed of a large number of copper-tin alloy crystal grains, each of the tin layers being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of copper-tin alloy crystal grains, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, wherein the heat treatment causes an area ratio occupied by the tin layers on the outermost surface to be 20 to 80% (preferably 30 to 75%, more preferably 30 to 70%), and causes a maximum thickness of the tin layers to be smaller than an average particle diameter of the copper-tin alloy crystal grains.

[0020] In this method for manufacturing a tin-plated product, the treatment of the surface of the substrate preferably causes the surface of the substrate to have an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers, a maximum roughness Ry of 0.4 to 1.5 micrometers, and a ten-point mean roughness Rz of 0.15 to 1.0 micrometers. As a method for treating the surface of the substrate in this way to reduce the unevenness of the surface of the substrate by reducing the surface roughness of the substrate (to a desired value), chemical polishing such as electrolytic polishing, rolling the substrate using a work roll with a surface roughness reduced by polishing or the like, mechanical polishing such as buffing or shot blasting, etc. can be used.

[0021] The nickel plating layer preferably has a thickness of 0.05 to 0.5 micrometers, and more preferably has a thickness of 0.05 to 0.4 micrometers. The copper plating layer preferably has a thickness of 0.1 to 0.7 micrometers, and more preferably has a thickness of 0.1 to 0.5 micrometers. The tin plating layer preferably has a thickness of 0.5 to 1.5 micrometers, and more preferably has a thickness of 0.6 to 1.2 micrometers. The ratio (Sn thickness / Cu thickness) of the thickness of the tin plating layer to the thickness of the copper plating layer is preferably 1.5 to 5, and more preferably 2 to 5. The ratio (Sn thickness / Cu thickness + Ni thickness)) of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer is preferably 1 to 3.5.

[0022] The heat treatment is preferably carried out at a temperature of 300 to 800°C for 1 to 1800 seconds in the atmosphere (until the heat treatment forms an outermost layer composed of a copper-tin alloy layer and tin layers, wherein the copper-tin alloy layer is formed of a large number of crystal grains of a copper-tin alloy, each of the tin layers being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of crystal grains of the copper-tin alloy, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, wherein the heat treatment causes an area ratio occupied by the tin layers on the outermost surface to be 20 to 80%, and causesthat a maximum thickness of the tin layers becomes smaller than an average particle diameter of the crystal grains of the copper-tin alloy). The heat treatment is preferably carried out by adjusting the temperature and time in a temperature range of 300 to 800 °C to cause the average particle diameter of the crystal grains of the copper-tin alloy to be 1.5 to 3 micrometers, while causing the maximum thickness of the tin layers to be 0.2 to 1.0 micrometer.

[0023] The heat treatment is more preferably carried out by setting the temperature and time in a temperature range of 300 to 800°C to cause the tin layers to have an average thickness of 0.5 to 0.4 micrometers (in order to reduce the amount of adhesion to the contact point when the tin-plated product is used as the material of an insertable connecting terminal or the like). If the heat treatment is continued until the average thickness of the tin layers remaining after tin melting is 0.05 to 0.4 micrometers, it is possible to cause the average thickness of the tin layers to be 0.05 to 0.4 micrometers by the heat treatment in the temperature range of 300 to 800°C.That is, when the heat treatment is carried out in the temperature range of 300 to 800°C after the nickel plating layer, the copper plating layer, and the tin plating layer are formed on the surface of the substrate in this order, the thickness of the tin plating layer consumed until a temperature (232°C) reaches the melting point of tin is 0.3 micrometers (as a value evaluated in a previous experiment), and the thickness of the tin plating layer consumed by the diffusion of liquid tin after the melting of tin is {2 × diffusion coefficient D (m. 2 / s) × holding time t(s)} 1 / 2 (m). Therefore, if the temperature and time during heat treatment are adjusted such that {thickness T Sn(µm) of the tin plating layer before heat treatment - thickness (0.3 µm) of the tin plating layer consumed until the tin melts - average thickness (0.4 µm) of the tin plating layer remaining after the tin melts} ≦ {2 x diffusion coefficient D x holding time t} 1 / 2 (µm) ≦ {thickness T Sn (µm) of the tin plating layer before heat treatment - thickness (0.3 µm) of the tin plating layer consumed until the tin melts - average thickness (0.05 µm) of the tin plating layer remaining after the tin melts}, it is possible to make the average thickness of the tin layers by heat treatment 0.05 to 0.4 micrometers. That is, if the temperature and time during heat treatment are adjusted so that the thickness (µm) of the tin plating layer consumed after the tin plating layer melts by heat treatment is not less than {thickness T Sn(µm) of the tin plating layer before heat treatment - 0.7 (µm)} and not larger than {thickness T Sn (µm) of the tin plating layer before heat treatment is -0.35 (µm)}, it is possible to make the average thickness of the tin layers by heat treatment 0.05 to 0.4 micrometers. In addition, since the diffusion coefficient D (m 2 / s) D = D 0 exp(-Q / RT) from the frequency factor D 0 (=1.7×10 -11 (m 2 / s)), the activation energy Q (= -19.4 (J / mol)), the gas constant (=8.314 J / mol·K) and the temperature T (K), the thickness (µm) of the tin plating layer consumed by the heat treatment after the tin plating layer is melted is a function of temperature and time, so it is possible to adjust the temperature and time during the heat treatment.

[0024] Examples of a tin-plated product and a method for producing the same according to the present invention will be described in detail below. Example 1

[0025] First, a Cu-Ni-Sn-P alloy conductive substrate plate (a copper alloy substrate containing 1.0 wt% nickel, 0.9 wt% tin, 0.05 wt% phosphorus, and the balance copper) with a thickness of 0.25 mm was prepared. The surface of the substrate was treated with a ceramic mill roller (a mill roller polished with a 400-grit grindstone using a mill roller grinder to reduce the maximum roughness Ry and ten-point centerline roughness Rz of its surface) to reduce the surface roughness of the substrate.Regarding the surface roughness of the substrate thus surface-treated, the arithmetic mean roughness Ra, the maximum roughness depth Ry, and the ten-point mean roughness Rz, which are parameters indicating the surface roughness, were calculated based on JIS B0601 (1994) from the results measured in the direction perpendicular to the rolling direction on the rolling surface using a contact surface roughness measuring device (Surfcoder SE4000, manufactured by Kosaka Laboratory Ltd.). As a result, the arithmetic mean roughness Ra was 0.15 micrometers, the maximum roughness depth Ry was 1.05 micrometers, and the ten-point mean roughness Rz was 0.71 micrometers. Using the contact surface roughness measuring device (Surfcoder SE4000, manufactured by Kosaka Laboratory Ltd.), the mean interval Sm between adjacent concavities or convexities on the substrate surface was measured.As a result, the mean interval Sm was 80 micrometers.

[0026] Then, as a pretreatment, the thus surface-treated substrate (a material to be plated) was electrolytically degreased with an alkaline electrolytic degreasing solution for 10 seconds and then washed with water. Subsequently, the substrate was immersed in 5 wt% sulfuric acid for 10 seconds for pickling and then washed with water.

[0027] Thereafter, the thus surface-treated substrate (the material to be plated) and a nickel electrode plate were used as a cathode and an anode, respectively, to electrolyte the substrate at a current density of 5 A / dm 2 and a liquid temperature of 50 °C for 5 seconds in a nickel plating solution containing 80 g / l nickel sulfamate and 45 g / l boric acid to form a nickel plating layer with a thickness of 0.1 micrometers on the substrate.

[0028] Then, the thus nickel-plated substrate and a copper electrode plate were used as a cathode and an anode, respectively, to electrolyte the substrate at a current density of 5 A / dm 2 and a liquid temperature of 30°C for 16 seconds in a copper plating solution containing 110 g / l copper sulfate and 100 g / l sulfuric acid to form a copper plating layer with a thickness of 0.4 micrometers on the substrate.

[0029] Then, the thus copper-plated substrate and a tin electrode plate as a cathode and anode, respectively, were used to electroplate the substrate at a current density of 5 A / dm 2 and a liquid temperature of 25°C for 20 seconds in a tin plating solution containing 60 g / l tin sulfate, 75 g / l sulfuric acid, 30 g / l cresolsulfonic acid, and 1 g / l β-naphthol to form a tin plating layer with a thickness of 1.0 micrometers on the substrate.

[0030] In the plated product after tin plating, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.5, and the ratio of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 2.

[0031] Then, the plated product after tin plating was washed and dried, and then placed in an annealing furnace (manufactured by Koyo Lindberg Co., Ltd.), where the plated product was held at a furnace temperature of 400°C for 150 seconds in the atmosphere for heat treatment. Furthermore, in this example, during the 150-second heat treatment holding time, the holding time after tin melting was calculated as 90 seconds. The average thickness of tin consumed after tin melting was calculated as 0.37 micrometers.

[0032] The outermost layer formed on the outermost surface of the thus prepared tin-plated product was analyzed by electron beam microanalysis (EPMA) and Auger electron spectroscopy (AES). As a result, it was confirmed that the outermost layer was composed of Sn and Cu. 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed of the copper-tin alloy crystal grains, each of the depressed portions having a tin layer therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thicknesses of these layers were measured by an electrolytic film thickness gauge (Thickness Tester TH-11, manufactured by Chuo Seisakusho Ltd.). As a result, the average thickness of the tin layers was 0.23 micrometers, and the thickness of the copper-tin alloy layer was 0.90 micrometers.After peeling off the tin layers on the surface of the tin-plated product with a tin peeling solution (containing p-nitrophenol and sodium hydroxide), the crystal grain size of the copper-tin alloy on the exposed surface was obtained according to the sectioning method based on JIS H0501, and the average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 2.8 micrometers.

[0033] The undercoat layer formed on the surface of the substrate of the tin-plated product was analyzed using AES. As a result, the undercoat layer was composed of nickel and / or a copper-nickel alloy, and the thickness of the undercoat layer was 0.10 micrometers. The presence of an interlayer between the outermost layer and the undercoat layer of the tin-plated product was analyzed using AES. As a result, there was no copper layer as the interlayer, so the outermost layer was formed on the surface of the undercoat layer.

[0034] After gold was deposited on the outermost surface of the tin-plated product to a thickness of approximately 200 nanometers, the tin-plated product was cut with a focused ion beam (FIB) instrument to expose a cross-section perpendicular to the rolling direction of the tin-plated product. Then, ten points on the exposed cross-section were observed with a scanning electron microscope (SEM) at a magnification of 5000 in a field of view with a length L (= 20 micrometers) parallel to the surface of the tin-plated product.In each of the observed areas, the sum (Lm) of lengths of the copper-tin alloy layer contacting the evaporated gold layer was subtracted from the length L (= 20 micrometers) of the entire area to divide this by the length L of the entire area to obtain a value (a ratio (= (L-Lm) / L) of the length of the tin layer contacting the evaporated gold layer in the observed area). Then, an average of the values ​​(the ratio (L-Lm) / L) obtained in eight observed areas, excluding the maximum and minimum values ​​in the ten observed areas, was multiplied by 100 to calculate a value as the area ratio of tin (the area occupied by the tin layer on the outermost surface). As a result, the area ratio of tin was 57%.

[0035] Then, the tin-plated product was cut with a focused ion beam (FIB) instrument to expose a cross-section perpendicular to the rolling direction of the tin-plated product. Then, three points on the cross-section were observed with a scanning electron microscope (SEM) at a magnification of 5000 in a field of view with a length of approximately 30 micrometers parallel to the surface of the tin-plated product to obtain the maximum depth in the depressed portions (the maximum thickness of the tin layer (the depth at which pure tin was present)). As a result, the maximum depth of the depressed portions was 0.75 micrometers. In addition, the ratio (D / T) of the average particle diameter (D) of the crystal grains of the copper-tin alloy of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 3.73.

[0036] Regarding the surface roughness of the tin-plated product, the arithmetic mean roughness Ra and its maximum roughness depth Ry were calculated using the same method as the method described above. As a result, the arithmetic mean roughness Ra on the surface of the tin-plated product was 0.16 micrometers, and its maximum roughness depth Ry was 1.13 micrometers.

[0037] Then, the tin-plated product was cut with a focused ion beam (FIB) instrument to expose two cross sections substantially perpendicular to the outermost surface of the tin-plated product and parallel to its rolling direction, and two cross sections substantially perpendicular to the outermost surface of the tin-plated product and perpendicular to its rolling direction as cross sections substantially perpendicular to the outermost surface of the tin-plated product. Each of the cross sections was observed at a magnification of 10,000 using a scanning electron microscope (SEM).From the observation of these cross sections, it was confirmed that a copper-tin alloy layer and tin layers of tin existed on the outermost surface of the tin-plated product, with the copper-tin alloy layer being formed of crystal grains of a copper-tin alloy, with each of the tin layers being formed between adjacent crystal grains of the copper-tin alloy. On each of the cross sections, as shown in . Fig.As shown in Figure 2, a straight line L1 was drawn parallel to the outermost surface from a point A1 at which a copper-tin alloy crystal grain of the copper-tin alloy layer 14 contacted one of the copper-tin alloy crystal grains on both sides thereof, and at which the depth of a tin layer 16 between these crystal grains was maximum. Then, a straight line L2 was drawn parallel to the outermost surface from a point A2 at which the copper-tin alloy crystal grain of the copper-tin alloy layer 14 contacted the other of the copper-tin alloy crystal grains on both sides thereof, and at which the depth of the tin layer 16 between these crystal grains was maximum. Then, a straight line L3 was drawn parallel to the outermost surface between the straight lines L1 and L2 so as to be equidistant from both the straight lines L1 and L2.Then, an intersection point B1 of the straight line L3 and a normal to the outermost surface drawn to pass through point A1, and an intersection point B2 of the straight line L3 and a normal to the outermost surface drawn to pass through point A2 were obtained. Then, an intersection point B3 of the outermost surface and a normal to the outermost surface drawn from a midpoint of a line segment between the intersection points B1 and B2 were obtained. Then, an angle θ between the outermost surface and a straight line drawn between the intersection points B1 and B3 was calculated. As a result, an average value of the angles θ on the cross sections was 27.7°C.In addition, the angle θ was calculated from tan θ = H / (L / 2) because tan θ was essentially equal to H / (L / 2), assuming that L was the length of the line segment between the intersection points B1 and B2 and that H was the length between a midpoint (between the intersection points B1 and B2) and the intersection point B3 of the outermost surface and a normal to the outermost surface, the normal being drawn from the midpoint between the intersection points B1 and B2.

[0038] In order to evaluate the insertion force of the tin-plated product when used as the material of an insertable connecting terminal or the like, the tin-plated product was mounted as a sample for evaluation on a horizontal table of a horizontal load measuring device (a device manufactured by combining an electrical contact simulator manufactured by Yamazaki Seiki Co., Ltd., a table controller, a load cell, and a load cell amplifier) ​​to cause the tin-plated product to contact a pusher, and then the tin-plated product was pulled horizontally at a friction speed of 80 mm / min over a sliding distance of 10 mm while the pusher was pressed against the surface of the tin-plated product with a load of 0.7 N and 5 N, respectively.Then, forces applied in the horizontal direction from 1 mm to 4 mm (measuring distance of 3 mm) were measured to calculate an average value F thereof, and the dynamic friction coefficient (µ) between the test pieces was calculated from µ = F / N. As a result, the dynamic friction coefficient was 0.25 and 0.23 when the load was 0.7 N and 5 N, respectively.

[0039] The contact resistance of a test piece cut from the tin-plated product was measured. As a result, the contact resistance of the tin-plated product was 1.1 mΩ. To evaluate the contact reliability of the tin-plated product after being allowed to stand at room temperature, after a test piece cut from the tin-plated product was kept in a constant-temperature chamber at 120°C for 120 hours in the atmosphere, the test piece was removed from the constant-temperature chamber, and then the constant resistance of the surface of the test piece (the constant resistance after being allowed to stand at the high temperature) was measured at 20°C in a measuring room. As a result, the constant resistance after being allowed to stand at the high temperature was 25 mΩ.In addition, the constant resistance was measured five times by means of a micro-ohmmeter (manufactured by Yamazaki Seiki Co., Ltd.) at an open-circuit voltage of 20 mV, a current of 10 mA, and a maximum load of 10 gf using a U-shaped gold wire probe with a diameter of 0.5 mm under sliding (1 mm / 100 gf), and its average value was obtained (when the maximum load of 100 gf was applied).

[0040] Then, one of two test pieces cut from the tin-plated product was used as a plate test piece (a test piece serving as a plug terminal), and the other test piece was indented (imprinted in a hemispherical shape of R = 1 mm) for use as an indented test piece (a test piece serving as a socket terminal). The plate test piece was mounted on the table of an electrical precision sliding wear tester, and the indentation of the indented test piece was brought into contact with the plate test piece.Then, a sliding test was performed, in which the table on which the plate test piece was mounted was slid back and forth in the horizontal direction for 70 cycles at a friction speed of one cycle per second within a range of 50 micrometers, while the indented test piece was pressed against the surface of the grooved plate test piece with a load of 0.7 N. After the sliding test, the electrical resistance at the contact point of the grooved plate test piece with the indented test piece was measured sequentially using the four-terminal method. As a result, the maximum electrical resistance value of the tin-plated product during the sliding test was a low 8.5 mΩ. Example 2

[0041] A tin-plated product was manufactured using the same method as in Example 1, except that the thickness of the copper plating layer was 0.2 micrometers. Furthermore, in this example, during the 150-second holding time in the heat treatment, the holding time after tin melting was 90 seconds, so the thickness of tin consumed after tin melting was calculated to be 0.37 micrometers.

[0042] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Moreover, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 5, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 3.3.

[0043] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed from the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.22 micrometers, and the thickness of the copper-tin alloy layer was 0.55 micrometers. It was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 1.7 micrometers.In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 3.09. The area (area ratio of tin) occupied by the tin layer on the top surface was 56%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.55 micrometers.

[0044] The base layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the base layer was 0.10 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the base layer of the tin-plated product, so the outermost layer was formed on the surface of the base layer.

[0045] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.14 micrometers, its maximum roughness Ry was 0.85 micrometers, and the mean value of the angle θ was 38.8°. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.29 and 0.24, respectively. The contact resistance of the tin-plated product was 1.5 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at room temperature was 21 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a low 18 mΩ. Example 3

[0046] A tin-plated product was manufactured using the same method as in Example 1, except that the arithmetic mean roughness Ra, the maximum roughness Ry, and the ten-point mean roughness Rz of the substrate after surface treatment were 0.08 micrometers, 0.69 micrometers, and 0.53 micrometers, respectively. The thickness of the nickel plating layer was 0.3 micrometers, the thickness of the copper plating layer was 0.3 micrometers, the thickness of the tin plating layer was 0.7 micrometers, and the holding time in the heat treatment was 105 seconds. In addition, in this example, during the holding time of 105 seconds in the heat treatment, the holding time after tin melting was 45 seconds, so the thickness of tin consumed after tin melting was calculated to be 0.26 micrometers.

[0047] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Furthermore, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.3, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 1.16.

[0048] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed of the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.08 micrometers, and the thickness of the copper-tin alloy layer was 0.70 micrometers. It was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 1.6 micrometers.In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 5.33. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 35%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.30 micrometers.

[0049] The undercoat layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the undercoat layer was 0.30 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the undercoat layer of the tin-plated product, so the outermost layer was formed on the surface of the undercoat layer.

[0050] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.14 micrometers, its maximum roughness Ry was 1.01 micrometers, and the mean value of the angle θ was 35.5°. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.24 and 0.23, respectively. The contact resistance of the tin-plated product was 1.3 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 48 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a low 9.5 mΩ. Example 4

[0051] A tin-plated product was manufactured using the same method as Example 1, except that the thickness of the copper plating layer was 0.3 micrometers, the thickness of the tin plating layer was 0.7 micrometers, the heat treatment temperature was 600°C, and the heat treatment holding time was 40 seconds. Furthermore, in this example, during the 40-second heat treatment holding time, the holding time after tin melting was 30 seconds, so the thickness of tin consumed after tin melting was calculated to be 0.32 micrometers.

[0052] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Furthermore, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.3, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 1.75.

[0053] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed from the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.07 micrometers, and the thickness of the copper-tin alloy layer was 0.70 micrometers. It was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 1.5 micrometers.In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 4.29. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 51%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.35 micrometers.

[0054] The base layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the base layer was 0.10 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the base layer of the tin-plated product, so the outermost layer was formed on the surface of the base layer.

[0055] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.16 micrometers, its maximum roughness Ry was 1.19 micrometers, and the mean angle θ was 32.2°. The dynamic friction coefficient under a load of 0.7 N and 5 N was 0.22 and 0.25, respectively. The contact resistance of the tin-plated product was 1.2 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 10 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a low 8.0 mΩ. Example 5

[0056] A tin-plated product was manufactured using the same method as in Example 1, except that the arithmetic mean roughness Ra, maximum roughness Ry, and ten-point mean roughness Rz of the substrate after surface treatment were 0.12 micrometers, 0.95 micrometers, and 0.68 micrometers, respectively, and the heat treatment temperature was 700°C, with a heat treatment holding time of 13 seconds. Furthermore, in this example, during the 13-second heat treatment holding time, the holding time after tin melting was 6.5 seconds, so the thickness of tin consumed after tin melting was calculated to be 0.31 micrometers.

[0057] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out using the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained using the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained using the same method as that in Example 1. Furthermore, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.5, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 2.

[0058] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed of the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.29 micrometers, and the thickness of the copper-tin alloy layer was 0.95 micrometers. It was confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 1.9 micrometers.In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 2.11. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 67%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.90 micrometers.

[0059] The base layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the base layer was 0.10 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the base layer of the tin-plated product, so the outermost layer was formed on the surface of the base layer.

[0060] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.17 micrometers, its maximum roughness Ry was 1.18 micrometers, and the mean value of the angle θ was 28.5°. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.25 and 0.24, respectively. The contact resistance of the tin-plated product was 1.3 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 22 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a low 7.5 mΩ. Example 6

[0061] A tin-plated product was manufactured using the same method as in Example 1, except that the arithmetic mean roughness Ra, maximum roughness Ry, and ten-point mean roughness Rz of the substrate after substrate treatment were 0.08 micrometers, 0.69 micrometers, and 0.53 micrometers, respectively. The thickness of the nickel plating layers was 0.3 micrometers, the thickness of the copper plating layer was 0.3 micrometers, the thickness of the tin plating layer was 0.7 micrometers, and the holding time in the heat treatment was 120 seconds. In addition, in this example, during the 120-second holding time in the heat treatment, the holding time after tin melting was 60 seconds, so the thickness of the tin consumed after tin melting was calculated to be 0.31 micrometers.

[0062] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Furthermore, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.3, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 1.16.

[0063] As a result, it was confirmed that the outermost layer of Sn and (Cu,Ni) 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed of the copper-tin alloy crystal grains, each of the depressed portions having a tin layer therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.07 micrometers, and the thickness of the copper-tin alloy layer was 0.70 micrometers. It was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 1.7 micrometers.

[0064] In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 5.67. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 45%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.30 micrometers.

[0065] The undercoat layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the undercoat layer was 0.30 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the undercoat layer of the tin-plated product, so the outermost layer was formed on the surface of the undercoat layer.

[0066] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.15 micrometers, its maximum roughness Ry was 1.15 micrometers, and the mean value of the angle θ was 35.5°. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.25 and 0.25, respectively. The contact resistance of the tin-plated product was 1.2 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 50 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a low 9.0 mΩ. Example 7

[0067] A tin-plated product was manufactured by the same method as that in Example 1, except that the arithmetic mean roughness Ra, the maximum roughness Ry, and the ten-point mean roughness Rz of the substrate after surface treatment were 0.07 micrometers, 0.52 micrometers, and 0.41 micrometers, respectively, and that the thickness of the nickel plating layer was 0.1 micrometers, the thickness of the copper plating layer was 0.3 micrometers, the thickness of the tin plating layer was 0.6 micrometers, the heat treatment temperature was 700°C, and the heat treatment holding time was 5 seconds.

[0068] With respect to the thus-manufactured tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Furthermore, in the tin-plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 1.5.

[0069] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed of the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.14 micrometers, and the thickness of the copper-tin alloy layer was 0.70 micrometers. It was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 2.5 micrometers.In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 6.76. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 63%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.37 micrometers.

[0070] The undercoat layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the undercoat layer was 0.1 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the undercoat layer of the tin-plated product, so the outermost layer was formed on the surface of the undercoat layer.

[0071] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.06 micrometers, and its maximum roughness Ry was 0.45 micrometers. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.21 and 0.22, respectively. The contact resistance of the tin-plated product was 1.5 mΩ, and the maximum electrical resistance of the tin-plated product during the sliding test was a low 16.1 mΩ. Comparison example 1

[0072] A tin-plated product was manufactured by the same method as that in Example 1, except that the surface of the substrate was treated with a ceramic mill roll whose surface was not polished to cause the arithmetic mean roughness Ra, the maximum roughness Ry, and the ten-point mean roughness Rz of its surface to be 0.15 micrometers, 1.75 micrometers, and 1.15 micrometers, respectively, and that the thickness of the nickel plating layer was 0.3 micrometers, the thickness of the copper plating layer was 0.7 micrometers, the thickness of the tin plating layer was 0.7 micrometers, the heat treatment temperature was 600°C, and the heat treatment holding time was 20 seconds.In addition, in this comparative example, during the holding time of 20 seconds in the heat treatment, the holding time after the tin melting was 10 seconds, so the thickness of the tin consumed after the tin melting was calculated as 0.19 micrometers.

[0073] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Moreover, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 1, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 0.7.

[0074] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed from the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.04 micrometers, and the thickness of the copper-tin alloy layer was 0.95 micrometers. The shape of the copper-tin alloy layer grains was not confirmed by SEM, and it was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer by bonding the crystal grains to each other.The area (area ratio of tin) occupied by the tin layer on the outermost surface was 8%, and the maximum depth of the recessed portions (the maximum thickness of the tin layers) was 0.15 micrometers.

[0075] The undercoat layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the undercoat layer was 0.30 micrometers. A copper layer with a thickness of 0.20 micrometers was formed as the intermediate layer between the outermost layer and the undercoat layer of the tin-plated product, so that the outermost layer was formed on the surface of the intermediate layer.

[0076] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.23 micrometers, and its maximum roughness Ry was 1.85 micrometers. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.38 and 0.29, respectively. The contact resistance of the tin-plated product was 1.4 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 24 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a high value of 150 mΩ. Comparison example 2

[0077] A tin-plated product was manufactured by the same method as that in Example 1, except that the surface of the substrate was treated with a ceramic mill roll whose surface was not polished to cause the arithmetic mean roughness Ra, the maximum roughness Ry, and the ten-point mean roughness Rz of its surface to be 0.15 micrometers, 1.65 micrometers, and 0.94 micrometers, respectively, and that nickel plating and copper plating were not performed, the heat treatment temperature was 700°C, and the heat treatment holding time was 6.5 seconds. In addition, in this comparative example, during the heat treatment holding time of 6.5 seconds, the holding time after tin melting was 0 seconds, so the thickness of tin consumed after tin melting was calculated as 0 micrometers.

[0078] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, the calculation of the mean value of the angles θ and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1.

[0079] As a result, it was confirmed that the outermost layer was composed of Sn, and the thickness of the tin layer was 0.57 micrometers. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 100%, and the maximum depth of the recessed portion (the maximum thickness of the tin layer) was 1.00 micrometers.

[0080] As the base formed on the surface of the tin-plated product, a copper-tin alloy layer of CuSn was 5with a thickness of 0.90 micrometers. The outermost tin layer was removed to observe the surface of the copper-tin alloy layer by SEM to calculate the average particle diameter of the copper-tin alloy crystal grains. As a result, the average particle diameter was 1.1 micrometers. In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 1.10. As the intermediate layer between the outermost layer and the substrate of the tin-plated product, there was no copper layer, so the outermost layer was formed on the surface of the subbase.

[0081] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.06 micrometers, its maximum roughness Ry was 0.49 micrometers, and the mean value of the angle θ was 56.0°. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.41 and 0.32, respectively. The contact resistance of the tin-plated product was 1.2 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 110 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a low 25 mΩ. Comparison example 3

[0082] A tin-plated product was manufactured using the same method as Example 1, except that the thickness of the copper plating layer was 0.2 micrometers, the thickness of the tin plating layer was 0.5 micrometers, the heat treatment temperature was 600°C, and the heat treatment holding time was 30 seconds. Furthermore, in this comparative example, during the 30-second heat treatment holding time, the holding time after tin melting was 20 seconds, so the thickness of tin consumed after tin melting was calculated to be 0.26 micrometers.

[0083] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, and the calculation of the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. In addition, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.5, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 1.7.

[0084] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed from the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.04 micrometers, and the thickness of the copper-tin alloy layer was 0.45 micrometers. The shape of the grains of the copper-tin alloy layer was not confirmed by SEM, and it was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer formed by bonding the crystal grains together.The area (area ratio of tin) occupied by the tin layer on the outermost surface was 15%, and the maximum depth of the recessed portions (the maximum thickness of the tin layers) was 0.20 micrometers.

[0085] The undercoat layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the undercoat layer was 0.15 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the undercoat layer of the tin-plated product, so the outermost layer was formed on the surface of the undercoat layer.

[0086] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.15 micrometers, and its maximum roughness Ry was 1.10 micrometers. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.23 and 0.23, respectively. The contact resistance of the tin-plated product was 1.3 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 32 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a high value of 53 mΩ. Comparison example 4

[0087] A tin-plated product was manufactured by the same method as in Example 1, except that the surface of the substrate was treated with a ceramic mill roll whose surface was not polished to cause the arithmetic mean roughness Ra, the maximum roughness Ry, and the ten-point mean roughness Rz of its surface to be 0.20 micrometers, 2.30 micrometers, and 1.58 micrometers, respectively. The thickness of the copper plating layer was 0.3 micrometers, the thickness of the tin plating layer was 0.7 micrometers, and the holding time in the heat treatment was 120 seconds. Furthermore, in this comparative example, during the 120-second holding time in the heat treatment, the holding time after tin melting was 60 seconds, so the thickness of the tin consumed after tin melting was calculated to be 0.31 micrometers.

[0088] With respect to the thus-prepared tin-plated product, the analysis of the plating layers, the calculation of the arithmetic mean roughness Ra and the maximum roughness Ry of its surface, the calculation of the mean value of the angles θ, and the dynamic friction coefficient were carried out by the same methods as those in Example 1. In addition, the contact resistance of the tin-plated product was obtained by the same method as that in Example 1, and the maximum value of the electrical resistance of the tin-plated product during the sliding test was obtained by the same method as that in Example 1. Furthermore, in the plated product after being plated with tin, the ratio of the thickness of the tin plating layer to the thickness of the copper plating layer was 2.3, and the ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer was 1.75.

[0089] As a result, it was confirmed that the outermost layer of Sn and Cu 6 Sn 5(copper-tin alloy), and that depressed portions (between adjacent copper-tin alloy crystal grains) were formed on the surface of the copper-tin alloy layer formed from the copper-tin alloy crystal grains, each of the depressed portions having a tin layer containing tin therein, so that the copper-tin alloy layer and the tin layers were present on the outermost surface. The thickness of the tin layers was 0.07 micrometers, and the thickness of the copper-tin alloy layer was 0.55 micrometers. It was also confirmed by SEM that the depressed portions (in which tin remained) were formed on the surface of the copper-tin alloy layer. The average particle diameter of the copper-tin alloy crystal grains on the outermost surface was calculated. As a result, their average particle diameter was 1.6 micrometers.In addition, the ratio (D / T) of the average particle diameter (D) of the copper-tin alloy crystal grains of the outermost layer to the maximum thickness (T) of the tin layer was calculated. As a result, the ratio (D / T) was 6.40. The area (area ratio of tin) occupied by the tin layer on the outermost surface was 10%, and the maximum depth of the depressed portions (the maximum thickness of the tin layers) was 0.25 micrometers.

[0090] The base layer formed on the surface of the substrate of the tin-plated product was composed of nickel and / or a copper-nickel alloy, and the thickness of the base layer was 0.10 micrometers. There was no copper layer as the intermediate layer between the outermost layer and the base layer of the tin-plated product, so the outermost layer was formed on the surface of the base layer.

[0091] The arithmetic mean roughness Ra of the surface of the tin-plated product was 0.22 micrometers, its maximum roughness Ry was 1.78 micrometers, and the mean angle θ was 35.5°. The dynamic friction coefficient under the load of 0.7 N and 5 N was 0.36 and 0.26, respectively. The contact resistance of the tin-plated product was 2.5 mΩ, and the contact resistance of the tin-plated product after being allowed to stand at high temperature was 40 mΩ. The maximum electrical resistance of the tin-plated product during the sliding test was a high value of 120 mΩ.

[0092] The manufacturing conditions and properties of the tin-plated products in these examples and comparative examples are shown in Tables 1 to 5. Table 1 Ra (µm) Ry (µm) Rz (µm) Sn (µm) Cu (µm) Ni (µm) Ratio of the thickness of the cladding layers Example 1 0,15 1,05 0,71 1,0 0,4 0,1 Sn / Cu=2.5 Sn / (Cu+Ni)=2 Example 2 0,15 1,05 0,71 1,0 0,2 0,1 Sn / Cu=5 Sn / (Cu+Ni)=3.3 Example 3 0,08 0,69 0,53 0,7 0,3 0,3 Sn / Cu=2.3 Sn / (Cu+Ni)=1.75 Example 4 0,15 1,05 0,71 0,7 0,3 0,1 Sn / Cu=2.3 Sn / (Cu+Ni)=1.16 Example 5 0,12 0,95 0,68 1,0 0,4 0,1 Sn / Cu=2.5 Sn / (Cu+Ni)=12 Example 6 0,08 0,69 0,53 0,7 0,3 0,3 Sn / Cu=2.3 Sn / (Cu+Ni)=1.16 Example 7 0,07 0,52 0,41 0,6 0,3 0,1 Sn / Cu=2 Sn / (Cu+Ni)=1.5 See example 1 0,14 1,78 1,15 0,7 0,7 0,3 Sn / Cu=1 Sn / (Cu+Ni)=0.7 See example 2 0,15 1,65 0,94 1,0 - - - See example 3 0,15 1,05 0,71 0,5 0,2 0,1 Sn / Cu=2.5 Sn / (Cu+Ni)=1.7 See example 4 0,20 2,30 1,58 0,7 0,3 0,1 Sn / Cu=2.3 Sn / (Cu+Ni)=1.75 Table 2 Temperature in oven (°C) Holding time (s) Holding time after melting the tin (s) Thickness of the plating layers consumed after melting the tin (µm) Example 1 400 150 90 0,37 Example 2 400 150 90 0,37 Example 3 400 105 45 0,26 Example 4 600 40 30 0,32 Example 5 700 13 6,5 0,31 Example 6 400 120 60 0,31 Example 7 700 5 See example 1 600 20 10 0,19 See example 2 700 6,5 0 0 See example 3 600 30 20 0,26 See example 4 400 120 60 0,31 Table 3 Construction of the outermost layer Thickness (µm) Sn CuSn alloy Cu Ni, CuNi alloy Example 1 Sn+Cu 6 Sn 5 0,23 0,90 0 0,10 Example 2 Sn+Cu 6 Sn 5 0,22 0,55 0 0,10 Example 3 Sn + Cu 6 Sn 5 0,08 0,70 0 0,30 Example 4 Sn+Cu 6 Sn 5 0,07 0,70 0 0,10 Example 5 Sn+Cu 6 Sn 5 0,29 0,95 0 0,10 Example 6 Sn+(Cu,Ni) 6 Sn 5 0,07 0,70 0 0,30 Example 7 Sn+Cu 6 Sn 5 0,14 0,70 0 0,10 See example 1 Sn+Cu 6 Sn 5 0,04 0,95 0,20 0,30 See example 2 Sn 0,57 0,90 - - See example 3 Sn+Cu 6 Sn 5 0,04 0,45 0 0,15 See example 4 Sn+Cu 6 Sn 5 0,07 0,55 0 0,10 Table 4 Average particle diameter of the Sn alloy on the outermost layer (µm) Sn position Average particle diameter of the Sn alloy on the outermost layer / Maximum thickness of the Sn layer Surface roughness (µm) θ (°) Area ratio of Sn (%) Maximum thickness (µm) Ra Ry Example 1 2,8 57 0,75 3,73 0,16 1,13 27,7 Example 2 1,7 56 0,55 3,09 0,14 0,85 38,8 Example 3 1,6 35 0,30 5,33 0,14 1,01 35,5 Example 4 1,5 51 0,35 4,29 0,16 1,19 32,2 Example 5 1,9 67 0,90 2,11 0,17 1,18 28,5 Example 6 1,7 45 0,30 5,67 0,15 1,15 35,5 Example 7 2,5 63 0,37 6,76 0,06 0,45 See example 1 - 8 0,15 - 0,23 1,85 - See example 2 1,1 100 1,00 1,10 0,06 0,49 56,0 See example 3 - 15 0,20 - 0,15 1,10 - See example 4 1,6 10 0,25 6,40 0,22 1,78 35,5 Table 5 Coefficient of friction Contact resistance (mΩ) Contact resistance after stand at high temperature (mΩ) Maximum value of electrical resistance during sliding test (mΩ) 0,7 N 5 N Example 1 0,25 0,23 1,1 25 8,5 Example 2 0,29 0,24 1,5 21 18 Example 3 0,24 0,23 1,3 48 9,5 Example 4 0,22 0,25 1,2 10 8,0 Example 5 0,25 0,24 1,3 22 7,5 Example 6 0,25 0,25 1,2 50 9,0 Example 7 0,21 0,22 1,5 16,1 See example 1 0,38 0,29 1,4 24 1,50 See example 2 0,41 0,32 1,2 110 25 See example 3 0,23 0,23 1,3 32 53 See example 4 0,36 0,26 2,5 40 120

Claims

[1] A tin-plated product, wherein a surface of a substrate (10) is plated with tin, the tin-plated product comprising: a substrate (10) made of copper or a copper alloy; a base (12) formed on a surface of the substrate (10), the base (12) being formed of nickel and / or a copper-nickel alloy; and an outermost layer formed on a surface of the base layer (12), the outermost layer being composed of a copper-tin alloy layer (14) and tin layers (16), the copper-tin alloy layer (14) being formed of a large number of crystal grains of a copper-tin alloy, each of the tin layers (16) being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of crystal grains of the copper-tin alloy, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, wherein an area ratio occupied by the tin layers (16) on the outermost surface is 20 to 80%, and a maximum thickness of the tin layers (16) is smaller than an average particle diameter of the crystal grains of the copper-tin alloy, and wherein the outermost surface has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers and a maximum roughness depth Ry of 0.3 to 1.5 micrometers. [2] The tin-plated product according to claim 1, wherein the copper-tin alloy layer (14) comprises a copper-nickel-tin alloy. [3] The tin-plated product according to claim 2, wherein the copper-tin alloy is Cu6Sn5, and the copper-nickel-tin alloy is (Cu,Ni)6Sn5. [4] The tin-plated product according to any one of claims 1 to 3, wherein the crystal grains of the copper-tin alloy have an average particle diameter of 1.5 to 3 micrometers. [5] A tin-plated product according to any one of claims 1 to 4, wherein the tin layers (16) have a maximum thickness of 0.2 to 1.0 micrometer. [6] A tin-plated product according to any one of claims 1 to 5, wherein the tin layers (16) have an average thickness of 0.05 to 0.4 micrometers. [7] A tin-plated product according to any one of claims 1 to 6, wherein the copper-tin alloy layer (14) has a thickness of 0.4 to 1.5 micrometers. [8] A tin-plated product according to any one of claims 1 to 7, wherein the base (12) has a thickness of 0.05 to 0.5 micrometers. [9] A method for producing a tin-plated product whose outermost surface has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers and a maximum roughness depth Ry of 0.3 to 1.5 micrometers, the method comprising the steps of: Treating a surface of a substrate (10) made of copper or a copper alloy such that the surface of the substrate (10) has an arithmetic mean roughness Ra of 0.05 to 0.2 micrometers, a maximum roughness depth Ry of 0.4 to 1.5 micrometers and a ten-point mean roughness Rz of 0.15 to 1.0 micrometers; forming a nickel plating layer, a copper plating layer and a tin plating layer on the treated surface of the substrate (10) in this order; and then performing a heat treatment to form an outermost layer composed of a copper-tin alloy layer (14) and tin layers (16), wherein the copper-tin alloy layer (14) is formed from a large number of crystal grains of a copper-tin alloy, each of the tin layers (16) being arranged in a corresponding one of depressed portions, each of which is formed between adjacent crystal grains of the large number of crystal grains of the copper-tin alloy, the adjacent crystal grains being adjacent to each other on an outermost surface of the outermost layer, wherein the heat treatment causes an area ratio occupied by the tin layers (16) on the outermost surface to be 20 to 80%, and causes a maximum thickness of the tin layers (16) to be smaller than an average particle diameter of the crystal grains of the copper-tin alloy, wherein the heat treatment is carried out by adjusting the temperature and time in a temperature range of 300 to 800°C such that the average particle diameter of the crystal grains of the copper-tin alloy is 1.5 to 3 micrometers, while causing the maximum thickness of the tin layers (16) to be 0.2 to 1.0 micrometer. [10] A method of manufacturing a tin-plated product according to claim 9, wherein the nickel plating layer has a thickness of 0.05 to 0.5 micrometers and the copper plating layer has a thickness of 0.1 to 0.7 micrometers, the tin plating layer having a thickness of 0.5 to 1.5 micrometers. [11] A method for producing a tin-plated product according to claim 9 or 10, wherein a ratio of the thickness of the tin plating layer to the thickness of the copper plating layer is 1.5 to 5, and a ratio of the thickness of the tin plating layer to the sum of the thickness of the copper plating layer and the thickness of the nickel plating layer is 1 to 3.

5. [12] A method for producing a tin-plated product according to any one of claims 9 to 11, wherein the heat treatment is carried out by setting a temperature and time in a temperature range of 300 to 800 °C to cause the tin layers (16) to have an average thickness of 0.05 to 0.

4. [13] A method for producing a tin-plated product according to claim 12, wherein the temperature and time in the heat treatment are adjusted such that the heat treatment causes a thickness (µm) of the tin plating layer consumed after melting to be {thickness (µm) of the tin plating layer before the heat treatment - 0.7 (µm)} or more and {thickness (µm) of the tin plating layer before the heat treatment - 0.35 (µm)} or less. [14] An electric element using a tin-plated product according to any one of claims 1 to 8 as one of its materials.

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