Conductive material and method for producing the same

Abstract

To provide a conductive material that can realize a sufficient low contact resistance under a low contact pressure (<2 N) while having a sufficient low dynamic friction coefficient and a sufficient heat resistance.SOLUTION: A conductive material comprises: a base material made of copper or a copper alloy; a ground layer composed of one or more layers comprising one or more metals selected from a group consisting of Ni, Co, and Fe; a Cu-Sn alloy layer; and a Sn layer in this order. A part of the Cu-Sn alloy layer is exposed on the Sn layer-side surface of the conductive material. On the Sn layer-side surface of the conductive material, in an area of 250 square μm including 50 area% or more of the Sn layer, an arithmetical average height is 0.03 μm or more when evaluated so that a cut-off value is 25 μm.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

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

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-115210 Summary of the Invention [Problem to be solved by the invention]

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

[0006] The present invention has been made in view of the above 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 also being able to sufficiently reduce contact resistance under low contact pressure (<2N), and a method for manufacturing the same. [Means for solving the problem]

[0007] Aspect 1 of the present invention is A conductive material comprising, in this order: a base material made of copper or a copper alloy; an underlayer which is one or more layers made of at least one kind selected from the group consisting of Ni, Co, and Fe; a Cu-Sn alloy layer; and an Sn layer; a part of the Cu-Sn alloy layer is exposed on the Sn layer side surface of the conductive material, The conductive material has an arithmetic mean height of 0.03 μm or more, evaluated with a cutoff value of 25 μm, in a 250 μm square region of the Sn layer side surface of the conductive material that includes the Sn layer at 50 area % or more.

[0008] Aspect 2 of the present invention is A conductive material according to aspect 1, wherein the arithmetic mean height is 0.05 μm or more.

[0009] Aspect 3 of the present invention is The conductive material according to aspect 1 or 2, wherein the surface of the base material facing the undercoat layer 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.

[0010] A fourth aspect of the present invention is forming one or more underlayers composed of one or more elements selected from the group consisting of Ni, Co, and Fe on a base material made of copper or a copper alloy; 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; After the reflow treatment, forming 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 Aspect 5 is the manufacturing method according to aspect 4, 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 In the manufacturing method according to aspect 4 or 5, the underlayer is formed 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

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

[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 that order, and by exposing a portion of the relatively hard Cu-Sn alloy layer 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 to a very narrow interval of 25 μm in a 250 μm square region containing 50% 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 low contact resistance even under low contact pressure.

[0018] Furthermore, in the method for manufacturing the above-mentioned conductive material, it was discovered that when forming the outermost Sn layer, a matte Sn plating layer having a predetermined thickness, unlike the conventional bright Sn plating layer disclosed in Patent Document 1, can be formed, thereby obtaining a conductive material having the above-mentioned Sa. As a result, it has become possible 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). 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 type selected from the group consisting of Ni, Co, and Fe, a Cu-Sn alloy layer, and an 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, in a 250 μm square region of the Sn layer side surface of the conductive material that includes at least 50 area% of the Sn layer is 0.03 μm or more. As a result, the contact resistance under low contact pressure (<2N) can be sufficiently reduced while maintaining a sufficiently low dynamic friction coefficient and sufficient heat resistance. Each layer will be described in detail below.

[0021] <Base material> In an embodiment of the present invention, the base material is made of copper or a copper alloy, and examples of the material 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 surface facing the undercoat layer 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 surface facing the undercoat layer can be measured, for example, using a surface roughness meter in accordance with JIS B0601:2001. The Ra of the base material surface facing the undercoat layer 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 in the form of a plate, the thickness is not particularly limited, but 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 a 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, 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, which will be described later. Furthermore, the formation of the underlayer improves the material's resistance to sulfur dioxide corrosion.

[0024] The average thickness of the underlying layer (when there are two underlying layers, it is the average of the total thickness of the two layers) is preferably 0.1 μm or more from the viewpoint of suppressing pit defects in the underlying layer and further exerting the above effects. On the other hand, in order to reduce costs and ensure moldability, the average thickness of the underlying layer is preferably 3.0 μm or less. The average thickness of the underlying layer can be measured using, for example, a fluorescent X-ray film thickness meter. The surface shape of the underlying layer is not particularly limited, and for example, the shape of the surface of the base material on the underlying layer side can be reflected.

[0025] <Cu-Sn alloy layer> The Cu-Sn alloy layer is composed of an alloy of Cu and Sn. The Cu-Sn alloy layer can consist of, for example, only the η-phase (Cu6Sn5) or a combination of the ε-phase (Cu3Sn) and the η-phase. When the Cu-Sn alloy layer consists of the ε-phase and the η-phase, the ε-phase can be formed between the underlying layer and the η-phase and can contact the underlying layer. Since the ε-phase is harder than the η-phase, the presence of the ε-phase makes the Cu-Sn alloy layer harder and the coefficient of friction is further reduced, which is preferable. Also, for example, in the case of a Ni underlying layer, a (Cu,Ni)6Sn5 alloy layer may be formed after the reflow treatment.

[0026] A part of the Cu-Sn alloy layer is exposed from the surface of the Sn layer side of the conductive material according to the embodiment of the present invention, and the entire surface is not covered by the Sn layer. Thereby, the dynamic friction coefficient of the conductive material can be sufficiently reduced. The fact that a part of the Cu-Sn alloy layer is exposed from the surface of the Sn layer side of the conductive material can be confirmed, for example, by obtaining a backscattered electron (BSE) image of the surface of the Sn layer side of the conductive material using a SEM (scanning electron microscope). FIG. 2B shows an example of a BSE image of the conductive material (Test No. 1) according to the embodiment of the present invention. 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 surface of the Sn layer side of the conductive material, it can be determined that a part of the Cu-Sn alloy layer is exposed from the surface of the Sn layer side of the conductive material.

[0027] The area ratio of the exposed portion of the Cu-Sn alloy layer on the surface of the Sn layer side of the conductive material is preferably 10% or more. Thereby, the coefficient of kinetic friction of the conductive material can be further reduced. On the other hand, the area ratio of the exposed portion of the Cu-Sn alloy layer on the surface of the Sn layer side of the conductive material is preferably 50% or less, and more preferably 40% or less. Thereby, the contact resistance of the conductive material can be further reduced. The area ratio of the exposed portion of the Cu-Sn alloy layer on the surface of the Sn layer side of the conductive material can be obtained by acquiring the above-mentioned BSE image, binarizing the obtained BSE image using image analysis software (free software ImageJ 1.49), and calculating the area ratio of the exposed portion of the Cu-Sn alloy layer by image analysis.

[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 the diffusion of the base layer materials (Ni, Co, and Fe) 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 using, for example, 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 thickness 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 the plane perpendicular to the stacking direction. In the case of being discontinuous, in some regions where the Cu-Sn alloy layer does not exist, the upper Sn layer may be in direct contact with the lower layer (for example, the base layer).

[0030] <Sn layer> The Sn layer is disposed on the surface of the conductive material. From the surface, the Cu-Sn alloy layer is partially exposed. That is, the Sn layer is discontinuous on the surface of the conductive material (in the 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, the arithmetic mean height (Sa) is evaluated at a cutoff value of 25 μm (i.e., excluding the influence of widely spaced irregularities exceeding 25 μm, such as surface irregularities of the base material), and is 0.03 μm or greater. This sufficiently reduces the contact resistance of the conductive material, due to factors such as the ease of destruction of an oxide film that may form on the surface. Sa is preferably 0.05 μm or greater, and more preferably 0.07 μm or greater. Note that, for example, when the cutoff value is evaluated at more 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 the cutoff value is evaluated at more 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 above Sa can be determined by measurement using a laser microscope in accordance with ISO 25178. Whether or not 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, similar to the method for determining the area ratio of the exposed part 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, protrusions on its surface such that H / W≧0.15, where H is the height and W is the width of the bottom. 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 protrusions of the Sn layer are linear in a surface image of the Sn layer side of the conductive material, a cross-sectional sample can be prepared near the center of the linear protrusion in a direction perpendicular to the linear protrusion and observed horizontally to confirm whether the protrusions 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. However, 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 an 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 part of the Cu-Sn alloy layer on the Sn layer side surface of the conductive material. Each step will be described in detail below.

[0036] <Forming a base layer on the base material> A base material made of copper or a copper alloy as described above is prepared, and a base layer 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 viewpoint of ease of manufacturing, the base layer 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 base layer 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 base layer 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] <After forming a Cu layer and an Sn layer in this order on the underlayer, a reflow process is performed to obtain a Cu-Sn alloy layer> The Cu layer and Sn layer may be formed by known methods, such as plating. After forming the Cu layer and Sn layer in this order, reflow treatment causes the Cu in the Cu layer and the Sn in the Sn layer to interdiffuse, forming 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. When the thickness of the Sn plating layer before reflow treatment (ts) is defined as the thickness of the Cu plating layer (tc), and when 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 is sometimes referred to as the "residual Sn layer"). When ts / tc>2, only the η phase is formed in equilibrium, but depending on the reflow treatment conditions, the ε phase, a non-equilibrium phase, may also be formed. It is preferable that ts and tc satisfy the relationship ts / tc>2, with tc being 0.1 to 1.5 μm and ts being 0.35 to 3.15 μm. This allows the ε phase to be formed while adjusting the Cu—Sn alloy layer to a preferred average thickness (0.2 to 3.0 μm). 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 an underlayer is formed on the above-mentioned roughened base material, the underlayer and the Cu—Sn alloy layer may also have irregularities reflecting the shape of the underlayer. 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 / underlayer / Cu—Sn alloy layer, and the layer structure in areas corresponding to the recesses of the roughened base material may be base material / underlayer / Cu—Sn alloy layer / residual Sn layer.

[0039] <After reflow treatment, a matte Sn plating layer with a plating thickness of 0.025 to 0.25 μm is formed.> By forming a matte Sn plating layer with a plating thickness of 0.025 to 0.25 μm, a Sn layer with fine protrusions can be obtained, and the arithmetic mean height, evaluated with a cutoff value of 25 μm, can be 0.03 μm or more in a 250 μm square region containing 50% or more of the Sn layer. 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. The plating bath may consist of, for example, SnSO4 and H2SO4. Preferably, a matte Sn plating layer with a plating thickness of 0.05 to 0.20 μm can be 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% or more of the Sn layer. More preferably, a matte Sn plating layer with a plating thickness of 0.07 to 0.15 μm can be formed. 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% or more of the Sn layer by area.

[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 may be present in the areas corresponding to the recesses of the roughened base material. In other words, the layer structure at the areas corresponding to the protrusions of the roughened base material can be base material / underlayer / Cu-Sn alloy layer, and the layer structure at 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 part 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 from 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 from 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. [Example]

[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. [Example]

[0044] The base material used was a copper alloy sheet (Cu-Ni-Sn-P system) with a thickness of 0.25 mm, which had been rolled with a surface-roughened roll. The average arithmetic roughness Ra of the base material rolled with the surface-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 using a contact surface roughness meter (Tokyo Seimitsu Co., Ltd.; Surfcom 1400) in accordance with JIS B0601:2001. 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 the 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 of the Cu plating layer (tc) and the thickness of the Sn plating layer (ts) 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 , bath temperature 35℃, for Sn plating, current density 3.0A / 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, and the conductive material of Test No. 1 was obtained. Specifically, the matte Sn plating layer was formed by preparing a plating bath consisting of SnSO4 (80 g / L) and H2SO4 (80 g / L) and applying a current density of 3 A / dm 2 The conductive material of Test No. 1 was subjected to electrical conduction for 2 to 8 seconds. The average thickness of the Sn layer before and after matte Sn plating was measured using a fluorescent X-ray film thickness meter, and the increase in thickness was taken as the average thickness of the matte Sn plating layer, which was 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 0.20 mmt copper alloy sheet (Cu-Ni-Sn system) rolled with a flat roll, and no undercoat layer was formed, 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, producing the conductive material of Test No. 6. The bright Sn plating layer was produced by preparing a plating bath containing SnSO4 (80 g / L), H2SO4 (80 g / L), and a brightener (35 g / L), at a current density of 3 A / dm 2 The formation was carried out 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, which have a matte Sn plating layer, 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 significantly rougher.

[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 in 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 in 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 exposed Cu-Sn alloy layer 1 was observed in Test No. 5. This is thought to be because the manufacturing method of the conductive material of Test No. 5, unlike Test Nos. 1 to 4 and 6, did not include any means for exposing part of the Cu-Sn alloy layer 1, such as roughening the base material. In addition, the entire surface of the Sn layer of the conductive materials of Test 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 over the entire surface (i.e., in every 250 μm square area).

[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, 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. As shown in FIGS. 3B and 3C, the conductive material of Test No. 4 has a flat surface, with the Sn layer side surface composed of the Cu-Sn alloy layer 1 and the residual Sn layer 2a, or the residual Sn layer 2a. On the other hand, as shown in FIG. 3A, the conductive material of Test No. 1 has a matte Sn plating layer 2b on its surface, and it forms protrusions with a ratio H / W≧0.15, where H is the height and W is the width at the base. (As an example, FIG. 3A shows one protrusion with H (≈0.53) and W (≈1.33), indicating that the ratio H / W for that protrusion is ≈0.40.) It can be seen from FIG. 3A that the protrusions resulting from the matte Sn plating layer 2b grow not on the Cu—Sn alloy layer 1 but on the residual Sn layer 2a. Also, in FIGS. 3A to 3C, a base layer 3 is observed below the Cu—Sn alloy layer 1. At least for the conductive material of Test 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] <Arithmetic surface height (Sa) evaluation> Using a laser microscope (Olympus Corporation; OLS-4100), Sa was measured on the Sn layer side surface of the conductive materials of Test Nos. 1 to 6 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 Nos. 1 to 6 was evaluated using an electrical contact simulator (Yamazaki Seiki Kenkyusho). The contact resistance measurement probe in this device is a gold wire. For this test, a separate probe material (Cu-Ni base material (0.2 mm) / Cu-Sn alloy layer (0.3 μm) / Sn layer (0.7 μm)) was prepared. A jig was fabricated to attach a female test piece, a hemispherical material (outer diameter: 0.55 mm), to the Sn layer side of a male test piece cut from each conductive material. Three measurements were 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. The average of these measurements 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 was measured before and after heating. 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] <Dynamic friction coefficient evaluation> The shape of the indented portion of an electrical contact in a mating connector was simulated, and the coefficient of dynamic friction of the conductive materials of Test Nos. 1 to 6 was evaluated using an apparatus such as that shown in Figure 4. As shown in Figure 4, a male test piece 10 made of a plate cut from each conductive material was fixed to a horizontal table 11, and a female test piece 12 made of a hemispherical processed material (outer diameter: 0.55 mm) of the above-mentioned probe material was placed on top of it, with the Sn layer sides of each test piece brought into contact with each other. Next, a load of 1.0 N (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 FIG. 4, 14 denotes a load cell, the arrow indicates the sliding direction, and the rolling direction was parallel to the sliding direction for both the male test piece 10 and the female test piece 12. 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 as follows: ◎ (very excellent): 0.19 or less; ○ (excellent): 0.20 to 0.44; △ (sufficient): 0.45 to 0.59; × (unsatisfactory): 0.60 or more.

[0056] <Fretting wear resistance evaluation> Fretting wear resistance was evaluated using a sliding tester, as shown in Figure 5, simulating the shape of the indented portion of an electrical contact in a mating connector. First, a male test piece 5, a plate cut from each conductive material, was fixed to a horizontal table 6. A female test piece 7, a hemispherical piece (outer diameter: 0.55 mm) of the probe material described above, was placed on top of the male test piece 5, bringing the Sn layers of the test pieces 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. A constant current of 10 mA was applied between the male test piece 5 and the female test piece 8, and the male test piece 5 was slid horizontally using a stepping motor 9 to measure the initial peak value of contact resistance. Measurements were performed three times for each conductive material, and the average was calculated. This average was used as the contact resistance for 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] [Table 1]

[0059] The results in Table 1 can be considered as follows. The conductive materials of Test Nos. 1 to 3 all 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 of 9.9 mΩ or less), and sufficient low contact resistance (initial contact resistance of 6.8 mΩ or less) under low contact pressure (<2 N). They also had sufficient fretting wear resistance (initial peak value of contact resistance of 6.8 mΩ or less). Test Nos. 1 and 2 also satisfied the preferred requirement of Sa≧0.05, thereby enabling further reduction in contact resistance; specifically, both the initial contact resistance and the contact resistance after heating were excellent. Test No. 1 satisfied the more preferred requirement of Sa≧0.07, thereby enabling further reduction in contact resistance; specifically, both the initial contact resistance and the contact resistance after heating were very excellent. On the other hand, all of the conductive materials of Test Nos. 4 to 6 did not satisfy 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, and 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 instead of a matte Sn plating layer, resulting in an Sa of less than 0.03 μm, which resulted in insufficient initial contact resistance. Perhaps due to this influence, the contact resistance after heating was also insufficient. [Explanation of symbols]

[0063] 1 Cu-Sn alloy layer 2 Sn layer 2a Residual Sn layer 2b Matte Sn plating layer 3 Base layer 5, 10 Male test specimens 6, 11 Level stand 7, 12 Female test pieces 8, 13 weight 9 Stepping motor 14 load cells

Claims

1. A laminated structure formed on a base material of a conductive material, the laminated structure comprising, in this order: a base layer which is one or more layers composed of at least one kind selected from the group consisting of Ni, Co, and Fe; a Cu-Sn alloy layer; and an Sn layer; a part of the Cu—Sn alloy layer is exposed on the Sn layer side surface of the laminated structure, A laminated structure in which, in a 250 μm square region of the Sn layer side surface of the laminated structure that contains the Sn layer at 50 area % or more, the arithmetic mean height evaluated with a cutoff value of 25 μm is 0.03 μm or more.

2. The laminate structure according to claim 1 , wherein the arithmetic mean height is 0.05 μm or more.

3. The laminate structure according to claim 1 , wherein the arithmetic mean height is 0.07 μm or more.

4. A method for manufacturing the laminated structure according to claim 1, comprising forming one or more underlayers composed of one or more selected from the group consisting of Ni, Co, and Fe on a base material of a conductive material; forming a Cu layer and an Sn layer in this order on the underlayer, and then performing a reflow treatment to obtain a Cu—Sn alloy layer; After the reflow treatment, a matte Sn plating layer having a plating thickness of 0.025 to 0.25 μm is formed; and exposing a portion of the Cu—Sn alloy layer on the surface of the matte Sn plating layer.

5. The manufacturing method according to claim 4, wherein the matte Sn plating layer has a plating thickness of 0.05 to 0.20 μm.

6. The manufacturing method according to claim 4, wherein the matte Sn plating layer has a plating thickness of 0.07 to 0.15 μm.