Conductive materials, and methods for manufacturing these conductive materials.

Abstract

Invention details;

Description

Conductive material and method for producing the same

[0001] The present disclosure relates to conductive materials and methods for making the same.

[0002] Due to the increasing use and sophistication of electronic controls in automobiles, the number of poles in automotive terminals is increasing, and as a result, the insertion force of the terminals is also increasing. Therefore, from the perspective of reducing the burden on workers in the automobile assembly process and preventing mating errors, the conductive material used in the terminals needs to have a low dynamic friction coefficient. In addition, since automotive terminals can be used for long periods at high temperatures, the conductive material used in the terminals needs to have sufficient heat resistance.

[0003] Patent Document 1 discloses a conductive material with a low dynamic friction coefficient, in which the arithmetic mean roughness of the material surface is within a predetermined range when the cutoff value is set to, for example, 0.8 mm, and the area ratio of the area where the Cu—Sn alloy layer is exposed to the area where it is not exposed is within a predetermined range. Patent Document 1 also describes that the increase in contact resistance of the material is suppressed after long-term use at high temperatures.

[0004] Japanese Patent Application Laid-Open No. 2017-115210

[0005] With the recent trend toward autonomous driving and electrification of automobiles, on-board terminals have become increasingly smaller. As terminals become smaller, their spring structures become smaller, resulting in a decrease in terminal contact pressure. Therefore, there is a demand for conductive materials that exhibit high conductivity (i.e., low contact resistance) even at low contact pressure. However, conventional technologies such as those described in Patent Document 1 do not address contact resistance at low contact pressures (<2N), and it has been found that there is room for further improvement.

[0006] The present disclosure has been made in view of these circumstances, and one of its objectives is to provide a conductive material that has a sufficiently low coefficient of dynamic friction and sufficient heat resistance, while being able to sufficiently reduce contact resistance under low contact pressure (<2 N), and a method for manufacturing the same.

[0007] A first aspect of the present invention is a conductive material comprising, in this order: a base material made of copper or a copper alloy; one or more underlayers composed of at least one type selected from the group consisting of Ni, Co, and Fe; a Cu—Sn alloy layer; and a Sn layer, wherein a portion of the Cu—Sn alloy layer is exposed on the Sn layer side surface of the conductive material; and an arithmetic mean height, evaluated with a cutoff value of 25 μm, of 0.03 μm or more in a 250 μm square region of the Sn layer side surface of the conductive material that includes 50 area % or more of the Sn layer is the conductive material.

[0008] A second aspect of the present invention is the conductive material according to the first aspect, wherein the arithmetic mean height is 0.05 μm or more.

[0009] A third aspect of the present invention is the conductive material according to the first or second aspect, wherein the base material has an arithmetic mean roughness of 0.15 μm or more in at least one direction and an arithmetic mean roughness of 3.0 μm or less in all directions on the surface of the base material facing the undercoat layer.

[0010] A fourth aspect of the present invention is a method for producing a conductive material, comprising: forming, on a base material made of copper or a copper alloy, one or more underlayers composed of one or more elements selected from the group consisting of Ni, Co, and Fe; forming a Cu layer and a Sn layer in this order on the underlayer, and then performing a reflow treatment to obtain a Cu—Sn alloy layer; forming, after the reflow treatment, a matte Sn plating layer having a plating thickness of 0.025 to 0.25 μm; and exposing a portion of the Cu—Sn alloy layer on the surface of the matte Sn plating layer.

[0011] A fifth aspect of the present invention is the manufacturing method according to the fourth aspect, wherein the matte Sn plating layer has a plating thickness of 0.05 to 0.20 μm.

[0012] A sixth aspect of the present invention is the manufacturing method according to the fourth or fifth aspect, wherein the formation of the underlayer is carried out by forming the underlayer on a surface of the base material that has been roughened so that the arithmetic mean roughness in at least one direction is 0.15 μm or more and the arithmetic mean roughness in all directions is 3.0 μm or less.

[0013] According to an embodiment of the present invention, it is possible to provide a conductive material that has a sufficiently low coefficient of dynamic friction and sufficient heat resistance, while also being able to sufficiently reduce contact resistance under low contact pressure (<2N), and a method for manufacturing the same.

[0014] FIG. 1A is an optical microscope image of the Sn layer side surface of the conductive material of Test No. 1. FIG. 1B is an optical microscope image of the Sn layer side surface of the conductive material of Test No. 2. FIG. 1C is an optical microscope image of the Sn layer side surface of the conductive material of Test No. 3. FIG. 1D is an optical microscope image of the Sn layer side surface of the conductive material of Test No. 4. FIG. 2A is a secondary electron (SE) image of the Sn layer side surface of the conductive material of Test No. 1 taken by an SEM. FIG. 2B is a backscattered electron (BSE) image of the Sn layer side surface of the conductive material of Test No. 1 taken by an SEM. FIG. 3A is a cross-sectional SEM image of the conductive material of Test No. 1 taken parallel to the stacking direction of each layer. FIG. 3B is a cross-sectional SEM image of the conductive material of Test No. 4 taken parallel to the stacking direction of each layer, including a portion where a portion of the Cu—Sn alloy layer is exposed from the Sn layer side surface. Figure 3C is a cross-sectional SEM image parallel to the lamination direction of each layer of a portion of the conductive material of Test No. 4 where the Cu—Sn alloy layer is not exposed from the Sn layer side surface. Figure 4 is a schematic diagram of the device used to evaluate the dynamic friction coefficient. Figure 5 is a schematic diagram of the device used to evaluate fretting wear resistance.

[0015] The present inventors have conducted research from various angles in order to realize a conductive material that has a sufficiently low coefficient of dynamic friction, sufficient heat resistance, and can sufficiently reduce contact resistance under low contact pressure (<2N).

[0016] They then discovered that by configuring the conductive material to have a base material, a base layer, a Cu-Sn alloy layer, and a Sn layer in this order, and by exposing a portion of the Cu-Sn alloy layer, which has a relatively high hardness, from the surface of the Sn layer, it is possible to impart sufficient heat resistance to the conductive material while sufficiently reducing the coefficient of dynamic friction of the conductive material.

[0017] Furthermore, it was found that by setting the cutoff value at a very narrow interval of 25 μm in a 250 μm square region containing 50 area % or more of the Sn layer on the Sn layer side surface (i.e., excluding the effects of irregularities with wider intervals than 25 μm, such as surface irregularities of the base material), and by setting the arithmetic mean height (hereinafter also referred to as "Sa") to 0.03 μm or more, contact resistance can be sufficiently reduced even under low contact pressure (<2 N). This is thought to be because, although contact resistance can normally be increased by oxides that can form on the surface of the Sn layer, the above-mentioned surface shape makes the oxides more susceptible to destruction even under low contact pressure, thereby enabling contact resistance to be reduced even under low contact pressure.

[0018] Furthermore, in a method for manufacturing the conductive material, the inventors discovered that a conductive material having the above-mentioned Sa can be obtained by forming a matte Sn plating layer of a predetermined thickness when forming the outermost Sn layer, unlike the conventional bright Sn plating layer disclosed in Patent Document 1. As a result, a conductive material has been realized that has a sufficiently low dynamic friction coefficient, sufficient heat resistance, and can sufficiently reduce contact resistance under low contact pressure (<2N). Note that the above mechanism does not limit the technical scope of the embodiments of the present invention.

[0019] The following provides details of each requirement stipulated by the embodiment of the present invention.

[0020] A conductive material according to an embodiment of the present invention comprises, in this order, a base material made of copper or a copper alloy, one or more underlayers composed of at least one element selected from the group consisting of Ni, Co, and Fe, a Cu—Sn alloy layer, and a Sn layer, wherein a portion of the Cu—Sn alloy layer is exposed on the Sn layer side surface of the conductive material, and the arithmetic mean height, evaluated with a cutoff value of 25 μm, of a 250 μm square region of the Sn layer side surface of the conductive material containing at least 50 area% of the Sn layer is 0.03 μm or greater. As a result, the conductive material can have a sufficiently low dynamic friction coefficient and sufficient heat resistance, while also achieving sufficiently low contact resistance under low contact pressures (<2 N). Each layer is described in detail below.

[0021] In an embodiment of the present invention, the base material is made of copper or a copper alloy. Examples of materials that can be used for the base material include pure copper, as well as various copper alloys such as Cu-Ni-Si, Cu-Ni-Sn-P, Cu-Fe-P, Cu-Zn, Cu-Cr-Ti-Si, and Cu-Mg.

[0022] The shape of the base material is not particularly limited, and may be, for example, plate-like, strip-like, or processed into the shape of a terminal. The surface shape of the base material is also not particularly limited, and may be flat or uneven. In the manufacturing method of a conductive material according to an embodiment of the present invention described below, from the viewpoint of easily exposing a portion of the Cu—Sn alloy layer from the surface, it is preferable that the arithmetic mean roughness (hereinafter also referred to as "Ra") of the base material's undercoat layer side surface is 0.15 μm or more in at least one direction and 3.0 μm or less in all directions, when the cutoff value is 0.8 μm. The Ra of the base material's undercoat layer side surface can be measured, for example, using a surface roughness meter in accordance with JIS B0601:2001. The Ra of the base material's undercoat layer side surface can also be determined from a cross-sectional image parallel to the stacking direction of each layer of the conductive material. When the base material is plate-like, the thickness is not particularly limited, and may be, for example, 0.05 mm or more and 2 mm or less.

[0023] <Underlayer> The underlayer is one or more layers composed of any one pure metal selected from the group consisting of Ni, Co, and Fe, or two or more alloys. This underlayer prevents Cu and alloy elements in the base material from diffusing to the material surface, thereby preventing an increase in contact resistance even after prolonged use at high temperatures. The diffusion of the underlayer itself to the material surface can be prevented by a Cu—Sn alloy layer, etc., as described below. Furthermore, the formation of the underlayer improves the sulfur dioxide corrosion resistance of the material.

[0024] The average thickness of the underlayer (if there are two underlayers, the average of the total thickness of the two layers) is preferably 0.1 μm or more in order to suppress pit defects in the underlayer and to further demonstrate the above-mentioned effects. On the other hand, in order to reduce costs and ensure moldability, the average thickness of the underlayer is preferably 3.0 μm or less. The average thickness of the underlayer can be measured, for example, using a fluorescent X-ray film thickness meter. The surface shape of the underlayer is not particularly limited, and can reflect, for example, the shape of the underlayer-side surface of the base material.

[0025] <Cu—Sn alloy layer> The Cu—Sn alloy layer is made of an alloy of Cu and Sn. The Cu—Sn alloy layer is made of, for example, an η phase (Cu ６ Sn ５ ) only or ε phase (Cu ３ The Cu—Sn alloy layer may be composed of an ε phase and an η phase. When the Cu—Sn alloy layer is composed of an ε phase and an η phase, the ε phase may be formed between the underlayer and the η phase and may be in contact with the underlayer. Since the ε phase is harder than the η phase, the presence of the ε phase is preferable because it makes the Cu—Sn alloy layer harder and further reduces the friction coefficient. Also, in the case of a Ni underlayer, for example, after reflow treatment, the (Cu, Ni) ６ Sn ５ An alloy layer may be formed.

[0026] A portion of the Cu—Sn alloy layer is exposed from the Sn layer side surface of the conductive material according to an embodiment of the present invention, and is not entirely covered by the Sn layer. This allows the kinetic friction coefficient of the conductive material to be sufficiently reduced. The exposure of a portion of the Cu—Sn alloy layer from the Sn layer side surface of the conductive material can be confirmed, for example, by obtaining a backscattered electron (BSE) image of the Sn layer side surface of the conductive material using a scanning electron microscope (SEM). FIG. 2B shows an example of a BSE image of a conductive material according to an embodiment of the present invention (Test No. 1). In FIG. 2B, a relatively dark region due to the Cu—Sn alloy layer 1 and a relatively bright region due to the Sn layer (here, the matte plating layer 2b) are observed. Thus, when a relatively dark region due to the Cu—Sn alloy layer 1 is observed in the BSE image of the Sn layer side surface of the conductive material, it can be determined that a portion of the Cu—Sn alloy layer is exposed from the Sn layer side surface of the conductive material.

[0027] The area ratio of the exposed portion of the Cu—Sn alloy layer on the surface of the conductive material facing the Sn layer is preferably 10% or more. This allows for a further reduction in the dynamic friction coefficient of the conductive material. On the other hand, the area ratio of the exposed portion of the Cu—Sn alloy layer on the surface of the conductive material facing the Sn layer is preferably 50% or less, more preferably 40% or less. This allows for a further reduction in the contact resistance of the conductive material. The area ratio of the exposed portion of the Cu—Sn alloy layer on the surface of the conductive material facing the Sn layer can be calculated by acquiring the above-mentioned BSE image, binarizing the obtained BSE image using image analysis software (free software ImageJ 1.49), and then analyzing the image.

[0028] The average thickness of the Cu—Sn alloy layer is preferably 3.0 μm or less in order to reduce costs and ensure formability. On the other hand, from the viewpoint of suppressing diffusion of the materials (Ni, Co, and Fe) of the underlayer into the Sn layer, the average thickness of the Cu—Sn alloy layer is preferably 0.2 μm or more. The average thickness of the Cu—Sn alloy layer can be measured, for example, using a fluorescent X-ray film thickness meter. Specifically, the value of the Sn component in the Cu—Sn alloy layer can be measured using fluorescent X-rays, and the average of the obtained Sn plating thicknesses can be used as the average thickness of the Cu—Sn alloy layer.

[0029] The Cu—Sn alloy layer may be continuous or discontinuous in a plane perpendicular to the stacking direction. If the Cu—Sn alloy layer is discontinuous, the Sn layer as the upper layer may be in direct contact with the lower layer (e.g., the underlayer) in a region where the Cu—Sn alloy layer is not present.

[0030] <Sn Layer> The Sn layer is disposed on the surface of the conductive material. The Cu—Sn alloy layer is partially exposed from the surface. That is, the Sn layer is discontinuous on the surface of the conductive material (in a plane perpendicular to the stacking direction).

[0031] In a 250 μm square region on the surface of the Sn layer side of the conductive material, which includes 50% or more of the Sn layer by area, the arithmetic mean height (Sa) evaluated with a cutoff value of 25 μm (i.e., excluding the influence of widely spaced irregularities greater than 25 μm, such as surface irregularities of the base material) is 0.03 μm or greater. This allows for sufficient reduction in the contact resistance of the conductive material due to factors such as the susceptibility of the oxide film that may form on the surface to destruction. Sa is preferably 0.05 μm or greater, and more preferably 0.07 μm or greater. Note that, for example, when evaluated with a cutoff value greater than 25 μm, the widely spaced irregularities that are less likely to destroy the oxide film are also reflected in the arithmetic mean height. Therefore, when evaluated with a cutoff value greater than 25 μm, even if the arithmetic mean height is 0.03 μm or greater, the contact resistance of the conductive material may not be sufficiently reduced. The Sa can be determined by measurement using a laser microscope in accordance with ISO 25178. Whether the Sn layer comprises 50% or more by area can be confirmed from a BSE image of the Sn layer side surface of the conductive material, in the same manner as in the method for determining the area ratio of the exposed portion of the Cu-Sn alloy layer described above.

[0032] The Sn layer preferably has, in at least one cross section parallel to the stacking direction, convex portions on its surface where H / W is ≧0.15, where H is the height and W is the bottom width. This further reduces the contact resistance of the conductive material. Here, the bottom width W is the width along the surface of the Sn layer, and the height H is the height perpendicular to the surface. The average value of H is preferably 0.1 μm or more. The upper limit of the average value of H is not particularly limited, but may be, for example, 1 μm or less. The average value of W is preferably 5 μm or less, more preferably 3 μm or less. The lower limit of the average value of W is not particularly limited, but may be, for example, 0.1 μm or more. By satisfying these ranges, the contact resistance of the conductive material can be further reduced. For example, if the convex portions of the Sn layer are linearly formed in the surface image of the Sn layer side of the conductive material, a cross-sectional sample can be prepared near the center of the linear convex portions in a direction perpendicular to the linear convex portions and observed horizontally to confirm whether the convex portions have the above-mentioned shape.

[0033] The conductive material according to the embodiment of the present invention may include layers other than the base material, underlayer, Cu—Sn alloy layer, and Sn layer, as long as the object thereof is achieved.

[0034] The conductive material according to the embodiment of the present invention, thanks to the above-described configuration, has a sufficiently low coefficient of dynamic friction and sufficient heat resistance, while also being able to sufficiently reduce contact resistance under low contact pressure (<2N). Furthermore, in recent years, a phenomenon known as fretting wear, in which fretting occurs between contacts due to engine vibrations and / or vibrations caused by vehicle operation, resulting in wear of the contacts and increased contact resistance, has become a problem. The conductive material according to the embodiment of the present invention, thanks to the above-described configuration, also has sufficient fretting wear resistance. That is, fretting wear can destroy and peel off oxides on the surface of the Sn layer, and the accumulation of these exfoliated materials can further accelerate wear. In the embodiment of the present invention, a portion of the Cu—Sn alloy layer is exposed from the surface, so that wear of the Sn layer and (the accumulation of oxides peeled off by wear) become intermittent. This allows the conductive material according to the embodiment of the present invention to reduce wear associated with fretting wear.

[0035] A method for producing a conductive material according to an embodiment of the present invention includes forming the underlayer on the base material, forming a Cu layer and a Sn layer on the underlayer in this order, and then performing a reflow treatment to obtain the Cu—Sn alloy layer, forming a matte Sn plating layer having a plating thickness of 0.025 to 0.25 μm after the reflow treatment, and exposing a portion of the Cu—Sn alloy layer on the Sn layer side surface of the conductive material. Each step is described in detail below.

[0036] <Forming an Underlayer on a Base Material> A base material made of copper or a copper alloy as described above is prepared, and an underlayer is formed thereon, which is one or more layers composed of at least one element selected from the group consisting of Ni, Co, and Fe. From the perspective of ease of manufacturing, the underlayer is preferably one or two layers selected from the group consisting of a Ni layer, a Co layer, and an Fe layer. The method for forming the underlayer is not particularly limited, and it may be formed by a known method such as plating. In this case, it is preferable to form the underlayer on a base material surface roughened so that the arithmetic mean roughness in at least one direction is 0.15 μm or more and the arithmetic mean roughness in all directions is 3.0 μm or less. This allows the Cu—Sn alloy layer to be exposed from the surface of the conductive material facing the Sn layer, as described below. The base material can be roughened by, for example, rolling (using a work roll roughened by polishing or shot blasting, etc.) or mechanical methods such as polishing or shot blasting. Physical methods such as ion etching or chemical methods such as etching or electropolishing can also be used.

[0037] <Forming a Cu layer and a Sn layer in this order on an underlayer, followed by a reflow treatment to obtain a Cu—Sn alloy layer> The Cu layer and the Sn layer may be formed by a known method, such as plating. By forming the Cu layer and the Sn layer in this order and then performing a reflow treatment, the Cu in the Cu layer and the Sn in the Sn layer interdiffuse to form a Cu—Sn alloy layer. At this time, the Cu layer may disappear entirely, or a portion may remain between the Cu—Sn alloy layer and the underlayer. Similarly, the Sn layer may disappear entirely, or a portion may remain. Note that when the thickness of the Sn plating layer before the reflow treatment (ts) is defined as the thickness of the Cu plating layer (tc), if ts / tc = 2, both the Cu layer and the Sn layer are likely to disappear. Furthermore, when ts / tc < 2, the Cu layer is likely to remain, and when ts / tc > 2, the Sn layer is likely to remain (the remaining Sn layer may be referred to as the "residual Sn layer"). Furthermore, when ts / tc>2, only the η phase can be formed in an equilibrium state, but depending on the reflow treatment conditions, the ε phase, a non-equilibrium phase, can also be formed. It is preferable that ts and tc satisfy ts / tc>2, with tc being 0.1 to 1.5 μm and ts being 0.35 to 3.15 μm. This allows the Cu—Sn alloy layer to be adjusted to a preferred average thickness (0.2 to 3.0 μm) while forming the ε phase. The reflow treatment conditions are preferably a temperature between the melting point of the Sn plating layer and 600°C for 3 to 30 seconds.

[0038] Here, when a base layer is formed on the above-mentioned roughened base material, the base layer and the Cu—Sn alloy layer may also have irregularities reflecting the shape of the base layer. Furthermore, if a portion of the Sn layer remains after the reflow treatment, the remaining Sn layer may be unevenly distributed in areas corresponding to the recesses of the roughened base material due to molten Sn flowing into the recesses during reflow. In other words, the layer structure in areas corresponding to the protrusions of the roughened base material may be base material / base layer / Cu—Sn alloy layer, and the layer structure in areas corresponding to the recesses of the roughened base material may be base material / base layer / Cu—Sn alloy layer / residual Sn layer.

[0039] <Forming a matte Sn plating layer with a plating thickness of 0.025 to 0.25 μm after reflow treatment> By forming a matte Sn plating layer so that the plating thickness is 0.025 to 0.25 μm, a Sn layer with fine convex portions can be obtained, and in a 250 μm square region containing 50 area % or more of the Sn layer, the arithmetic mean height evaluated with a cutoff value of 25 μm can be 0.03 μm or more. Here, the matte Sn plating layer refers to a Sn plating layer formed using a plating bath that does not contain additives such as brighteners that refine crystal grains, and the plating bath can be, for example, SnSO ４ and H ２ SO ４ Preferably, a matte Sn plating layer having a plating thickness of 0.05 to 0.20 μm is formed. This allows the arithmetic mean height, evaluated with a cutoff value of 25 μm, to be 0.05 μm or more in a 250 μm square region containing 50 area% or more of the Sn layer. More preferably, the matte Sn plating layer is formed so that the plating thickness is 0.07 to 0.15 μm. This allows the arithmetic mean height, evaluated with a cutoff value of 25 μm, to be 0.07 μm or more in a 250 μm square region containing 50 area% or more of the Sn layer.

[0040] Here, when an underlayer is formed on the above-mentioned roughened base material, the matte Sn plating layer can grow on the residual Sn layer that can be present in the areas corresponding to the recesses of the roughened base material. In other words, the layer structure in the areas corresponding to the protrusions of the roughened base material can be base material / underlayer / Cu-Sn alloy layer, and the layer structure in the areas corresponding to the recesses of the roughened base material can be base material / underlayer / Cu-Sn alloy layer / Sn layer (i.e., residual Sn layer + matte Sn plating layer).

[0041] <Exposing a Portion of the Cu—Sn Alloy Layer on the Sn Layer-Side Surface of the Conductive Material> Various methods can be used to expose a portion of the Cu—Sn alloy layer on the Sn layer-side surface of the conductive material. For example, by forming an underlayer on the above-described roughened base material, a portion of the Cu—Sn alloy layer can be exposed on the Sn layer-side surface of the conductive material at locations corresponding to the convex portions of the roughened base material. Even when the underlayer is formed on a flat base material, a portion of the Cu—Sn alloy layer can be exposed by roughening the underlayer in the same manner as the base material. Furthermore, as disclosed in JP 2013-174006 A, for example, a Cu—Sn alloy layer with a steep profile can be formed by adjusting the elements of the underlayer and the reflow treatment. Furthermore, after forming the base material / underlayer / Cu—Sn alloy layer / Sn layer, a portion of the Cu—Sn alloy layer can be exposed by mechanically removing a portion of the Sn layer.

[0042] The method for producing a conductive material according to an embodiment of the present invention may include other steps within the scope in which the object of the method is achieved.

[0043] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0044] The base material used was a copper alloy plate (Cu-Ni-Sn-P system) with a thickness of 0.25 mm, which had been rolled with a roughened roll. The average arithmetic roughness Ra of the base material rolled with the roughened roll was 0.48 μm in one direction and 0.49 μm in all directions. The surface roughness (arithmetic mean roughness Ra) of the base material was measured in accordance with JIS B0601:2001 using a contact surface roughness meter (Tokyo Seimitsu Co., Ltd.; Surfcom 1400). The surface roughness measurement conditions were a cutoff value of 0.8 mm, a reference length of 0.8 mm, an evaluation length of 4.0 mm, a measurement speed of 0.3 mm / s, and a stylus tip radius of 5 μmR. The surface roughness measurement direction was perpendicular to the rolling direction (which may be the direction in which the surface roughness is calculated to be greatest).

[0045] Next, a Ni plating layer was formed as a base layer on the surface of the roughened base material by a known method so as to have an average thickness of 0.3 μm. Specifically, the Ni plating solution used before the reflow treatment was that described in JP-A-2004-68026, and the plating conditions were a current density of 5 A / dm ２ The bath temperature was set to 60°C.

[0046] Furthermore, on the underlayer, a Cu plating layer and a Sn plating layer were formed in this order by a known method. Here, the thickness (tc) of the Cu plating layer and the thickness (ts) of the Sn plating layer before the reflow treatment were set to tc: 0.15 μm and ts: 0.9 μm so that the Cu—Sn alloy layer would have a preferred average thickness (0.2 to 3.0 μm) while forming the ε phase. Specifically, the Cu plating solution and the Sn plating solution used were those described in JP 2004-68026 A, and the plating conditions were as follows: for Cu plating, a current density of 3.5 A / dm ２ The bath temperature was 35°C, and the current density for Sn plating was 3.0 A / dm ２ The bath temperature was set to 35° C. Thereafter, a reflow treatment was carried out at a temperature of 232° C. or higher (substantial temperature) at which Sn melts.

[0047] After the reflow treatment, a matte Sn plating layer was formed to obtain a conductive material of Test No. 1. Specifically, the matte Sn plating layer was formed of SnSO ４ (80 g / L) and H ２ SO ４ (80 g / L) was prepared, and the current density was 3 A / dm ２ The conductive material of Test No. 1 was subjected to electrical conduction for 2 to 8 seconds at a temperature of 1000 K. Here, the average Sn layer thickness before and after matte Sn plating was measured using a fluorescent X-ray film thickness meter, and the increase in the average thickness of the matte Sn plating layer was determined to be 0.10 μm.

[0048] The thickness of the matte Sn plating layer was changed from the conductive material of Test No. 1 to produce Test No. 2 (matte Sn plating layer 0.05 μm), Test No. 3 (matte Sn plating layer 0.025 μm), and Test No. 4 (no matte Sn plating layer). Furthermore, the base material of Test No. 1 was changed to a material obtained by rolling a 0.20 mmt copper alloy sheet (Cu—Ni—Sn system) with a flat roll, and no undercoat layer was formed, thereby producing the conductive material of Test No. 5. Furthermore, the matte Sn plating layer of Test No. 1 was changed to a bright Sn plating layer to produce the conductive material of Test No. 6. The bright Sn plating layer was formed of SnSO ４ (80 g / L) and H ２ SO ４ A plating bath containing 80 g / L of copper and 35 g / L of brightener was prepared at a current density of 3 A / dm ２ The film was formed by applying current for 2 to 8 seconds.

[0049] The Sn layer side surfaces of the conductive materials of Test Nos. 1 to 6 were observed using an optical microscope. As an example, FIGS. 1A to 1C show optical microscope images of the conductive materials of Test Nos. 1 to 3, respectively, on which a matte Sn plating layer was formed, and FIG. 1D shows an optical microscope image of the conductive material of Test No. 4, which does not have a matte Sn plating layer. As shown in FIG. 1D, the conductive material of Test No. 4 has a flat surface due to the absence of a matte Sn plating layer. Note that in FIG. 1D, the relatively dark areas are the Cu—Sn alloy layer 1, and the relatively light areas are the residual Sn layer 2a. Compared to the conductive material of Test No. 4 in FIG. 1D, the conductive materials of Test Nos. 1 to 3 in FIGS. 1A to 1C have a matte Sn plating layer 2b, indicated by the darker areas, and are therefore found to have greater surface roughness.

[0050] The Sn layer side surfaces of the conductive materials of Test Nos. 1 to 6 were observed using an SEM. As an example, FIG. 2A shows a secondary electron (SE) image of the Sn layer side surface of the conductive material of Test No. 1, and FIG. 2B shows a backscattered electron (BSE) image. The SE image of FIG. 2A reveals that the Sn layer side surface of the conductive material has at least a matte Sn plating layer 2b with fine protrusions and a flat Cu—Sn alloy layer 1. The BSE image of FIG. 2B more clearly reveals that a portion of the Cu—Sn alloy layer 1 (a relatively dark region) is exposed on the Sn layer side surface of the conductive material. Similarly, Test Nos. 2 to 4 and 6 also confirmed that a portion of the Cu—Sn alloy layer 1 was exposed on the Sn layer side surface of the conductive material, but no exposure of the Cu—Sn alloy layer 1 was confirmed in Test No. 5. This is because the manufacturing method of the conductive material of Test No. 5 did not include the manufacturing method of Test No. 5. This is thought to be because, unlike Tests Nos. 1 to 4 and 6, no means for exposing a part of the Cu—Sn alloy layer 1, such as roughening the base material, was included. In addition, the entire surface of the Sn layer side of the conductive materials of Tests Nos. 1 to 6 was observed using an SEM, and it was confirmed that the area ratio of the Sn layer was 50 area % or more across the entire surface (i.e., in any 250 μm square region).

[0051] Cross sections parallel to the lamination direction of each layer of the conductive materials of Test Nos. 1 to 6 were observed using an SEM. As an example, FIG. 3A shows a cross-sectional SEM image of the conductive material of Test No. 1, FIG. 3B shows a cross-sectional SEM image of a portion of the conductive material of Test No. 4 where a portion of the Cu—Sn alloy layer 1 is exposed from the surface, and FIG. 3C shows a cross-sectional SEM image of a portion of the conductive material of Test No. 4 where the Cu—Sn alloy layer 1 is not exposed from the surface. As shown in FIGS. 3B and 3C, the conductive material of Test No. 4 has a Sn layer side surface composed of the Cu—Sn alloy layer 1 and the residual Sn layer 2a, or the residual Sn layer 2a, and it can be seen that the surface is flat. On the other hand, as shown in FIG. 3A, the conductive material of Test No. It can be seen that the conductive material No. 1 has a matte Sn plating layer 2b on its surface and forms convex portions with a ratio H / W≧0.15, where H is the height and W is the width at the bottom (as an example, FIG. 3A shows one convex portion with H (≈0.53) and W (≈1.33), and it can be seen that the H / W ratio for this convex portion is ≈0.40). It can also be seen from FIG. 3A that the convex portions resulting from the matte Sn plating layer 2b grow not on the Cu—Sn alloy layer 1 but on the residual Sn layer 2a. Furthermore, in FIGS. 3A to 3C, a base layer 3 is confirmed below the Cu—Sn alloy layer 1. At least for the conductive material No. 1, the average value of H was within the range of 0.1 to 1 μm and the average value of W was within the range of 0.1 to 3 μm.

[0052] The conductive materials of Test Nos. 1 to 6 were further evaluated as follows.

[0053] <Evaluation of arithmetic surface height (Sa)> Using a laser microscope (Olympus Corporation; OLS-4100), Sa of the Sn layer side surface of the conductive materials of Test Nos. 1 to 6 was measured in accordance with ISO 25178. The surface roughness measurement conditions were a cutoff value of 25 μm and an evaluation area of ​​250 μm square.

[0054] <Contact Resistance Evaluation> The contact resistance of the conductive materials in Tests No. 1 to 6 was evaluated using an electrical contact simulator (manufactured by Yamazaki Seiki Kenkyusho). The contact resistance measurement probe in this device was a gold wire. However, in this test, a separate probe material (Cu-Ni-based base material (0.2 mm) / Cu-Sn alloy layer (0.3 μm) / Sn layer (0.7 μm)) was prepared, and a jig was fabricated to attach a female test piece, a hemispherical processed material (outer diameter: 0.55 mm). The female test piece was used as the contact resistance measurement probe, allowing it to contact the Sn layer side surface of a male test piece, which was a plate material cut from each conductive material. Three measurements were then performed using the four-terminal method under conditions of an open circuit voltage of 20 mV, a current of 10 mA, and a load of 1 N, and the average value was used as the contact resistance value. The male test piece was also heated in air at 160°C for 120 hours, and the contact resistance before and after heating was measured. The evaluation criteria for initial contact resistance were as follows: ◎ (very excellent): 2.3 mΩ or less, ○ (excellent): 2.4 to 6.3 mΩ, △ (sufficient): 6.4 to 6.8 mΩ, × (insufficient): 6.9 mΩ or more; and for contact resistance after heating: ◎ (very excellent): 2.9 mΩ or less, ○ (excellent): 3.0 to 6.9 mΩ, △ (sufficient): 7.0 to 9.9 mΩ, × (insufficient): 10.0 mΩ or more.

[0055] <Evaluation of Dynamic Friction Coefficient> The shape of the indented portion of an electrical contact in a mating connection component was simulated, and the dynamic friction coefficients of the conductive materials of Test Nos. 1 to 6 were evaluated using an apparatus such as that shown in FIG. 4. As shown in FIG. 4, male test pieces 10 made of plate material cut from each conductive material were fixed to a horizontal table 11, and female test pieces 12 made of hemispherical processed material (outer diameter: 0.55 mm) of the above-mentioned probe material were placed on top of them, with the Sn layer sides of each test piece brought into contact with each other. Next, a 1.0 N load (weight 13) was applied to the female test piece 12 to hold down the male test piece 10, and the maximum friction force (unit: N) was measured when the male test piece 10 was slid horizontally once using a horizontal load measuring device (Aiko Engineering Co., Ltd.; Model-2152). The sliding distance was 5 mm, and the sliding speed was 80 mm / min. In Figure 4, 14 indicates a load cell, the arrow indicates the sliding direction, and for both the male test piece 10 and the female test piece 12, the rolling perpendicular direction was parallel to the sliding direction. When the normal force (load) is P (= 1.0 N) and the maximum friction force is F, the dynamic friction coefficient μ' is expressed as μ' = F / P. Measurement tests were performed four times for each conductive material, and the average value of the dynamic friction coefficients was calculated and used as the dynamic friction coefficient of the conductive material. The evaluation criteria for the dynamic friction coefficient were ◎ (very excellent): 0.19 or less, ○ (excellent): 0.20 to 0.44, △ (sufficient): 0.45 to 0.59, and × (insufficient): 0.60 or more.

[0056] <Evaluation of Fretting Wear Resistance> Fretting wear resistance was evaluated using a sliding tester as shown in FIG. 5, simulating the shape of the indented portion of an electrical contact in a fitting-type connecting component. First, a male test piece 5 made of a plate material cut from each conductive material was fixed to a horizontal table 6, and a female test piece 7 made of a hemispherical processed material (outer diameter: 0.55 mm) of the above-mentioned probe material was placed on top of it, bringing the Sn layer sides of each test piece into contact. A load of 1.0 N (weight 8) was applied to the female test piece 7 to hold down the male test piece 5, and a constant current of 10 mA was applied between the male test piece 5 and the female test piece 8. The male test piece 5 was slid horizontally using a stepping motor 9 to measure the initial peak value of contact resistance. For each conductive material, the measurement test was performed three times to obtain an average value, which was used as the contact resistance of each conductive material. The sliding distance was 50 μm, and the sliding frequency was 1 Hz. The arrow in the figure indicates the sliding direction. The evaluation criteria for fretting wear resistance (initial peak value of contact resistance) were as follows: ◎ (very excellent): 2.3 mΩ or less, ○ (excellent): 2.4 to 6.3 mΩ, △ (sufficient): 6.4 to 6.8 mΩ, × (insufficient): 6.9 mΩ or more.

[0057] The above results are summarized in Table 1.

[0058]

[0059] The results in Table 1 can be considered as follows. All of the conductive materials in Test Nos. 1 to 3 satisfied the requirements defined in the embodiment of the present invention, having a sufficiently low dynamic friction coefficient (0.59 or less), sufficient heat resistance (contact resistance after heating: 9.9 mΩ or less), and sufficient low contact resistance (initial contact resistance: 6.8 mΩ or less) under low contact pressure (<2 N). They also had sufficient fretting wear resistance (initial peak value of contact resistance: 6.8 mΩ or less). Furthermore, Test Nos. 1 and 2 satisfied the preferred requirement of Sa≧0.05, thereby further reducing contact resistance; specifically, both initial contact resistance and contact resistance after heating were excellent. Test No. 1 satisfied the more preferred requirement of Sa≧0.07, thereby further reducing contact resistance; specifically, both initial contact resistance and contact resistance after heating were extremely excellent. On the other hand, Test No. None of the conductive materials Nos. 4 to 6 satisfied the requirements defined in the embodiment of the present invention, and the initial contact resistance, contact resistance after heating, or dynamic friction coefficient was insufficient.

[0060] The conductive material of Test No. 4 did not have a matte Sn plating layer formed thereon, and the Sa was less than 0.03 μm, resulting in insufficient initial contact resistance.

[0061] The conductive material of Test No. 5 did not have a base layer formed, and the contact resistance after heating was insufficient. Furthermore, the Cu—Sn alloy layer was not exposed from the surface of the Sn layer side, and the dynamic friction coefficient was also insufficient.

[0062] The conductive material of Test No. 6 had a bright Sn plating layer formed instead of a matte Sn plating layer, and Sa was less than 0.03 μm, resulting in insufficient initial contact resistance. Perhaps due to this influence, the contact resistance after heating was also insufficient.

[0063] This application claims priority from Japanese Patent Application No. 2022-134358, filed August 25, 2022. Japanese Patent Application No. 2022-134358 is incorporated herein by reference.

[0064] REFERENCE SIGNS LIST 1 Cu—Sn alloy layer 2 Sn layer 2a Residual Sn layer 2b Matte Sn plating layer 3 Undercoat layer 5, 10 Male test piece 6, 11 Horizontal base 7, 12 Female test piece 8, 13 Weight 9 Stepping motor 14 Load cell

Claims

DEPCT6820 / 05 / 25681. Conductive material comprising: a base material consisting of copper or copper alloy; an underlying layer of one or more elements composed of one or more elements selected from a group consisting of Ni, Co, and Fe; a Cu-Sn alloy layer; and a Sn layer, respectively, where a portion of the Cu-Sn alloy layer is exposed on the Sn layer surface of the conductive material, and the estimated arithmetic height with a cutoff of 25 µm is 0.03 µm or more in an area of ​​250 sq µm where 50 percent or more of the area of ​​the Sn layer is on the Sn layer surface of the conductive material.

2. Conductive material according to Relief 1 where the arithmetic height is 0.05 µm or more.

3. Conductive material according to Relief 1 or 2 where the arithmetic surface roughness in at least one direction is 0.15 µm or more and the arithmetic surface roughness in all directions is 3.0 µm or less on the underlying surface of the base material.4.The method for producing conductive materials includes: creating one or more underlying layers composed of one or more elements selected from groups consisting of Ni, Co, and Fe on a copper or copper alloy base material; creating Cu and Sn layers, respectively, on the underlying layer, followed by a refluxing process to obtain a Cu-Sn alloy layer; creating a non-shiny Sn plating layer with a plating thickness of 0.025 to 0.25 micrometers after the refluxing process; and making a portion...

5. The manufacturing method according to claim 4, where the underlayer is formed by creating an underlayer on the surface of a non-glossy Sn plating layer; 6. The manufacturing method according to claim 4 or 5, where the underlayer is formed by creating an underlayer on the surface of a roughened base material to achieve an arithmetic mean surface roughness in at least one direction of 0.15 micrometers or more, and an arithmetic mean surface roughness in all directions of 3.0 micrometers or less.