Conductive material and method for producing the same

Abstract

To provide a conductive material that possesses sufficient heat resistance while enabling sufficiently low contact resistance under low contact pressure (<2 N).SOLUTION: A conductive material having a base material made of copper or a copper alloy, one or more ground layers each composed of one or more elements selected from the group consisting of Ni, Co, and Fe, a Cu-Sn alloy layer, and a Sn layer in the given order where the skewness evaluated with a cutoff value of 25 μm in a 250 μm square area containing 50% or more of the Sn layer on the Sn layer side surface of the conductive material is -3.50 to 3.50.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

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

[0002] The increasing use and sophistication of electronic controls in automobiles has led to an increase in the number of poles in automotive terminals. This increase in the number of poles also increases the mounting density of terminals, creating an environment in which heat tends to build up (and is difficult to dissipate). Furthermore, since terminals are likely to be used in such environments for long periods of time, the conductive materials used in the terminals must have sufficient heat resistance.

[0003] Patent Document 1 discloses a material in which the arithmetic mean roughness of the material surface is set within a predetermined range when the cutoff value is set to 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 set 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 these circumstances, and one of its objectives is to provide a conductive material that has sufficient heat resistance and can 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 having, 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, The conductive material has a skewness of -3.50 to 3.50 evaluated with a cutoff value of 25 μm in a 250 μm square region that includes 50 area % or more of the Sn layer on the surface of the conductive material on the Sn layer side.

[0008] Aspect 2 of the present invention is The conductive material according to aspect 1, wherein, in a 250 μm square region of the surface of the conductive material on the Sn layer side, which region contains the Sn layer at 50% or more by area, the arithmetic mean height evaluated with a cutoff value of 25 μm is 0.03 μm or more.

[0009] Aspect 3 of the present invention is 3. The conductive material according to claim 1, wherein the Cu—Sn alloy layer is partly exposed on the surface of the conductive material on the Sn layer side.

[0010] A fourth aspect of the present invention is The conductive material according to any one of aspects 1 to 3, 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.

[0011] A fifth 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, cooling is performed to 50°C or less. After the cooling, a matte Sn plating process is performed to form a matte Sn plating layer having a plating thickness of 0.01 to 0.50 μm; The matte plating treatment is Within 30 seconds of cooling to 50°C, or After pickling using sulfuric acid at a temperature of 40 to 60 ° C and a concentration of 30 mass % or more, A method for producing a conductive material.

[0012] A sixth aspect of the present invention is A manufacturing method according to aspect 5, further comprising exposing a portion of the Cu—Sn alloy layer on the surface of the matte Sn plating layer.

[0013] A seventh aspect of the present invention is In the manufacturing method according to aspect 5 or 6, 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]

[0014] According to an embodiment of the present invention, it is possible to provide a conductive material that has sufficient heat resistance and can sufficiently reduce contact resistance under low contact pressure (<2N), and a method for manufacturing the same. [Brief explanation of the drawings]

[0015] [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. 7. [Figure 2A] FIG. 2A is a secondary electron (SE) image of the surface of the Sn layer side of the conductive material of Test No. 1, taken by SEM. [Figure 2B] FIG. 2B is a backscattered electron (BSE) image of the surface of the Sn layer side 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. 7, 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. 7, 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. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present inventors have conducted research from various angles in order to realize a conductive material that has sufficient heat resistance and can sufficiently reduce contact resistance under low contact pressure (<2N).

[0017] Then, by forming a structure having a base material, a base layer, a Cu-Sn alloy layer, and an Sn layer in that order, and further by evaluating the skewness (hereinafter also referred to as "Ssk") in a 250 μm square area on the surface of the Sn layer, which includes 50% or more of the Sn layer by area, with a cutoff value of 25 μm at a very narrow interval (i.e., excluding the effects of irregularities with a wide interval of more than 25 μm, such as surface irregularities of the base material), to -3.50 to 3.50, it was found that sufficient heat resistance can be imparted while also achieving sufficiently low contact resistance even under low contact pressure (<2 N). Here, Ssk is a parameter expressed by the following formula (1), and indicates the degree of deviation (skewness) of the histogram of the height distribution on the contour curved surface.

[0018]

number

[0019] In equation (1), Sq represents the root mean square height (i.e., the standard deviation of the height distribution), A represents the evaluation area (i.e., a 250 μm square area), Z represents the height in the evaluation area, and x and y represent the coordinates of the xy plane perpendicular to the Z (height) direction in the evaluation area.

[0020] Ssk is also described in ISO25178-2:2012, and indicates that when Ssk<0, the unevenness is biased toward the convex side (upward) (i.e., the area of ​​the convex parts is larger than the area of ​​the concave parts when viewed from above), and when Ssk>0, the unevenness is biased toward the concave side (downward) (i.e., the area of ​​the concave parts is larger than the area of ​​the convex parts when viewed from above).

[0021] The reason why the contact resistance can be reduced by the above configuration is considered to be as follows. If Ssk is biased toward a positive value, the contact area becomes too small, resulting in increased contact resistance. On the other hand, if Ssk is biased toward a negative value, the contact area becomes too large, resulting in increased contact resistance without destroying the oxide film that increases contact resistance. Therefore, by controlling Ssk within the above specified range so that the contact area is neither too large nor too small, it is believed that contact resistance can be sufficiently reduced even under low contact pressure (<2N).

[0022] The present inventors have also discovered that a method for producing the above-mentioned conductive material includes a reflow treatment to form a Cu-Sn alloy layer, followed by cooling to 50°C or below, and performing a matte Sn plating treatment to form a matte Sn plating layer with a plating thickness of 0.01 to 0.50 μm, and that the matte plating treatment can be performed within 30 seconds after cooling to 50°C, or after performing an acid pickling treatment using sulfuric acid at a temperature of 40 to 60°C and a concentration of 30 mass% or more, thereby obtaining a conductive material having the above-mentioned Ssk. As a result, a conductive material was realized that has 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.

[0023] The following provides details of each requirement stipulated by the embodiment of the present invention.

[0024] A conductive material according to an embodiment of the present invention is a conductive material having, 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, and in the surface of the conductive material on the Sn layer side, in a 250 μm square region that includes at least 50 area% of the Sn layer, the skewness evaluated with a cutoff value of 25 μm is -3.50 to 3.50. As a result, the contact resistance under low contact pressure (<2N) can be sufficiently reduced while maintaining sufficient heat resistance. Each layer will be described in detail below.

[0025] <Base material> In an embodiment of the present invention, the base material is made of copper or a copper alloy. 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.

[0026] 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 on the underlayer side 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 on the underlayer side can be measured, for example, using a surface roughness meter in accordance with JIS B0601:2001. The Ra of the base material surface on the underlayer side 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.

[0027] <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, suppressing an increase in initial contact resistance and also suppressing an increase in contact resistance after prolonged use at high temperatures. The diffusion of the underlayer itself to the material surface can be suppressed 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.

[0028] 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 may reflect, for example, the shape of the surface of the base material on the underlayer side.

[0029] <Cu-Sn alloy layer> The Cu-Sn alloy layer is made of an alloy of Cu and Sn. The Cu-Sn alloy layer can consist of, for example, only the η-phase (Cu6Sn5) or 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 is preferable because the Cu-Sn alloy layer becomes harder and the coefficient of friction is further reduced. Also, for example, in the case of a Ni underlying layer, a (Cu,Ni)6Sn5 alloy layer may be formed after the reflow treatment.

[0030] It is preferable that a part of the Cu-Sn alloy layer is exposed from the surface on the Sn layer side of the conductive material according to an embodiment of the present invention, that is, it is preferable that the entire surface is not covered by the Sn layer. Thereby, the coefficient of kinetic friction of the conductive material can be reduced. The fact that a part of the Cu-Sn alloy layer is exposed from the surface on the Sn layer side of the conductive material can be confirmed, for example, by acquiring a backscattered electron (BSE) image of the surface on the Sn layer side of the conductive material using a SEM (scanning electron microscope). FIG. 2B shows an example of a BSE image of a conductive material (Test No. 1) according to an 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 on 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 on the Sn layer side of the conductive material.

[0031] 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.

[0032] The Cu-Sn alloy layer preferably has an average crystal grain size of 30 μm or less when analyzed by electron backscatter diffraction (EBSD). This facilitates reducing unevenness of the surface irregularities. The Cu-Sn alloy layer more preferably has an average crystal grain size of 20 μm or less when evaluated by EBSD, more preferably 10 μm or less, and particularly preferably 5 μm or less. The lower limit of the average crystal grain size is not particularly limited, but may be, for example, 0.1 μm or more. Here, the average crystal grain size refers to the average diameter of the area surrounded by crystal grain boundaries, i.e., the average circle equivalent diameter, when the boundaries are defined as grain boundaries where the crystal orientation misorientation (oblique angle) exceeds 15° (also called high-angle grain boundaries) as a result of EBSD analysis.

[0033] The average thickness of the Cu-Sn alloy layer is preferably 3.0 μm or less to reduce costs and ensure formability. On the other hand, the average thickness of the Cu-Sn alloy layer is preferably 0.2 μm or more to prevent the materials of the underlayer (Ni, Co, and Fe) from diffusing into the Sn layer. 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.

[0034] The Cu-Sn alloy layer may be continuous or discontinuous in the plane perpendicular to the stacking direction. When it is 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).

[0035] <Sn layer> The Sn layer is disposed on the surface of the conductive material. The Cu-Sn alloy layer may be partially exposed from the surface. That is, the Sn layer may be discontinuous on the surface of the conductive material (in the plane perpendicular to the stacking direction).

[0036] In a 250-μm square region containing 50 area% or more of the Sn layer on the surface of the conductive material on the Sn layer side, the skewness (Ssk) evaluated with a cut-off value of 25 μm (that is, excluding the influence of irregularities with a wide interval exceeding 25 μm such as the surface irregularities of the base material) is -3.50 to 3.50. Thereby, the contact resistance under a low contact pressure (<2 N) can be reduced. Ssk is preferably -2.50 to 2.50, more preferably -2.00 to 2.00, still more preferably -1.50 to 1.50, even more preferably -1.20 to 1.20, and particularly preferably -1.00 to 1.00. The above Ssk can be obtained by measuring in accordance with ISO25178 using a laser microscope. Whether or not the Sn layer contains 50 area% or more can be confirmed from the BSE image or the like of the surface of the conductive material on the Sn layer side in the same manner as the method for obtaining the area ratio of the exposed portion of the above Cu-Sn alloy layer.

[0037] In a 250 μm square region on the surface of the Sn layer side of the conductive material, which includes at least 50% by area of ​​the Sn layer, the arithmetic mean height (Sa) is preferably 0.03 μm or greater when evaluated using 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). This allows for a further reduction in the contact resistance of the conductive material, due to factors such as the susceptibility to destruction of an oxide film that may form on the surface. Sa is more preferably 0.05 μm or greater, and even more preferably 0.07 μm or greater. Note that, for example, when evaluated using a cutoff value greater than 25 μm, the arithmetic mean height also reflects widely spaced irregularities that are less likely to destroy the oxide film. Therefore, when evaluated using a cutoff value greater than 25 μm, the contact resistance of the conductive material may not be fully reduced even if the arithmetic mean height is 0.03 μm or greater. 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 or the like of the surface of the Sn layer side of the conductive material, in the same way as in the method for determining the area ratio of the exposed part of the Cu-Sn alloy layer described above.

[0038] 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.

[0039] 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.

[0040] 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 in this order on the underlayer, and then performing a reflow treatment to obtain the Cu-Sn alloy layer; After the reflow treatment, cooling is performed to 50°C or less. After the cooling, a matte Sn plating process is performed to form a matte Sn plating layer having a plating thickness of 0.01 to 0.50 μm; The matte plating treatment is Within 30 seconds of cooling to 50°C, or This includes performing pickling treatment using sulfuric acid at a temperature of 40 to 60°C and a concentration of 30 mass % or more. Each step will be described in detail below.

[0041] <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 Ni, Co, and Fe. 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, the base layer is preferably formed 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), or mechanical methods such as polishing or shot blasting. Physical methods such as ion etching, or chemical methods such as etching or electrolytic polishing, can also be used.

[0042] <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 μm or more and 1.5 μm or less, and ts being 0.35 μm or more and 3.15 μm or less. 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.

[0043] 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.

[0044] <After reflow processing, cool to below 50°C> After reflow treatment, the temperature must be cooled to below 50°C. If the temperature exceeds 50°C, the desired matte plating layer cannot be formed in the next step. The cooling method is preferably to immediately cool the product from the reflow treatment temperature range to 50°C or less, preferably 40°C or less, using cooling water. This allows the crystal grains of the residual Sn layer to be uniformly refined throughout the product. The lower limit of the water temperature is not particularly limited, but can be, for example, 5°C or more.

[0045] <After cooling, a matte plating process is carried out to form a matte Sn plating layer with a plating thickness of 0.01 to 0.50 μm> The matte plating treatment is carried out within 30 seconds after the steel is cooled to 50°C, or after pickling treatment using sulfuric acid at a temperature of 40 to 60°C and a concentration of 30 mass % or more. If the time interval between cooling to 50°C and the formation of the matte plating layer is long, oxides and the like may form on the surface, hindering the formation of the matte Sn plating layer, and as a result, Ssk within the above range may not be achieved. To achieve Ssk within the above range, the matte Sn plating layer must be formed immediately (specifically, within 30 seconds) after cooling to 50°C, or the matte Sn plating layer must be formed after pickling treatment using sulfuric acid at a temperature of 40 to 60°C and a concentration of 30% by mass or more to sufficiently remove the oxides and the like. 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 may consist of, for example, SnSO4 and H2SO4. The thickness of the matte Sn plating layer is 0.01 to 0.50 μm. If it is less than 0.01 μm, the amount of convex portions formed in the Sn layer will be small, and Ssk may become less than -3.50. On the other hand, if it is more than 0.50 μm, the convex portions of the Sn layer will bond together to form large, gentle convex portions, and Ssk may become more than 3.50.

[0046] The plating thickness of the matte Sn plating layer is preferably 0.025 μm or more, more preferably 0.05 μm or more, and even more preferably 0.07 μm or more. The plating thickness of the matte Sn plating layer is preferably 0.25 μm or less, more preferably 0.20 μm or less, and even more preferably 0.15 μm or less. This results in an Sn layer having fine protrusions, and in a 250 μm square region containing 50% or more of the Sn layer by area, the arithmetic mean height, evaluated with a cutoff value of 25 μm, can be 0.03 μm or more, more preferably 0.05 μm or more, and even more preferably 0.07 μm or more.

[0047] 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).

[0048] <Exposing part of the Cu-Sn alloy layer on the surface of the conductive material on the Sn layer side> The method for manufacturing a conductive material according to an embodiment of the present invention preferably further includes exposing a portion of the Cu—Sn alloy layer on the surface of the conductive material facing the Sn layer. Various methods can be used to expose a portion of the Cu—Sn alloy layer on the surface of the conductive material facing the Sn layer. For example, by forming an underlayer on the roughened base material, a portion of the Cu—Sn alloy layer can be exposed on the surface of the conductive material facing the Sn layer at locations corresponding to the convex portions of the roughened base material. Even when forming an underlayer 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.

[0049] 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]

[0050] 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]

[0051] 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).

[0052] 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.

[0053] 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.

[0054] After the reflow treatment, the material was water-cooled to 10 to 30°C. After water-cooling, the material was pickled using sulfuric acid at a temperature of 50°C and a concentration of 30 mass% or more. After the pickling treatment, a matte Sn plating treatment was performed to form a matte Sn plating layer, 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.

[0055] Test No. 2 (matte Sn plating layer 0.05 μm) and Test No. 3 (matte Sn plating layer 0.025 μm) were prepared from the conductive material of Test No. 1 by changing the thickness of the matte Sn plating layer.

[0056] The base material of the conductive material of Test No. 1 was changed to a material obtained by rolling a 0.20 mmt copper alloy plate (Cu-Ni-Sn system) with a flat roll, to produce the conductive material of Test No. 4.

[0057] The base material of the conductive material of Test No. 1 was changed to a material obtained by rolling a 0.80 mmt copper alloy plate (Cu-Fe-P system) with a flat roll, to produce the conductive material of Test No. 5.

[0058] Conductive material Test No. 6 was produced from the conductive material Test No. 1 by changing the process so that the pickling treatment was not performed, but rather the matte Sn plating treatment was performed within 30 seconds after the reflow treatment and cooling to 50°C.

[0059] Test No. 7 was prepared using the conductive material of Test No. 1 without the matte Sn plating layer.

[0060] The conductive material of Test No. 8 was produced by changing the base material from the conductive material of Test No. 1 to a material made by rolling a 0.20 mmt copper alloy plate (Cu-Ni-Sn system) with a flat roll and not forming an underlayer.

[0061] The conductive material of Test No. 9 was produced by changing the matte Sn plating layer of the conductive material of Test No. 1 to a bright Sn plating layer. 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), and the plating was carried out at a current density of 3 A / dm 2 The formation was carried out by applying current for 2 to 8 seconds.

[0062] The conductive material of Test No. 10 was produced by changing the base material from the conductive material of Test No. 1 to a material made by rolling a 0.20 mmt copper alloy plate (Cu-Ni-Sn system) with a flat roll and not forming an undercoat layer.

[0063] When the surfaces of Test Nos. 1 to 10 after reflow treatment (before the formation of the Sn plating layer) were analyzed by EBSD, the average crystal grain size was all 5 μm or less (and 0.1 μm or more).

[0064] The surfaces of the Sn layer side of the conductive materials of Test Nos. 1 to 10 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. 7, which does not have a matte Sn plating layer. As shown in FIG. 1D, the conductive material of Test No. 7 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. 7 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.

[0065] The surfaces of the Sn layer side of the conductive materials of Test Nos. 1 to 10 were observed using an SEM. As an example, FIG. 2A shows a secondary electron (SE) image of the surface of the Sn layer side 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 surface of the Sn layer side 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 surface of the Sn layer side of the conductive material. Similarly, Test Nos. 2 to 4, 6 to 7, and 9 also confirmed that a portion of the Cu-Sn alloy layer 1 was exposed on the surface of the Sn layer side of the conductive material. However, no exposed Cu-Sn alloy layer 1 was observed in Test Nos. 5, 8, and 10. This is thought to be because the manufacturing methods of the conductive materials of Test Nos. 5, 8 and 10, unlike Test Nos. 1 to 4, 6 to 7 and 9, 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 side of the conductive materials of Test Nos. 1 to 10 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 area).

[0066] Cross sections parallel to the lamination direction of each layer of the conductive materials of Test Nos. 1 to 10 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. 7 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. 7 where the Cu-Sn alloy layer 1 is not exposed. As shown in FIGS. 3B and 3C, the surface of the conductive material of Test No. 7 on the Sn layer side is 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. 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.

[0067] The conductive materials of Test Nos. 1 to 10 were further evaluated as follows.

[0068] <Skewness (Ssk) evaluation> Using a laser microscope (Olympus Corporation; OLS-4100), Ssk was measured on the surface on the Sn layer side of the conductive materials of test Nos. 1 to 10 based on ISO 25178. The surface roughness measurement conditions were a cutoff value of 25 μm and an evaluation area of ​​250 μm square.

[0069] <Arithmetic surface height (Sa) evaluation> Using a laser microscope (Olympus Corporation; OLS-4100), Sa was measured on the surface on the Sn layer side of the conductive materials of test Nos. 1 to 10 based on ISO 25178. The surface roughness measurement conditions were a cutoff value of 25 μm and an evaluation area of ​​250 μm square.

[0070] <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. However, 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 and 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.

[0071] <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 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 that conductive material. The evaluation criteria for the dynamic friction coefficient were as follows: ⊚ (very excellent): 0.50 or less; ◯ (excellent): 0.51 to 0.64; △ (sufficient): 0.65 to 0.74; × (unsatisfactory): 0.75 or more.

[0072] The above results are summarized in Table 1.

[0073] [Table 1]

[0074] The results in Table 1 can be considered as follows: All of the conductive materials of Test Nos. 1 to 6 satisfied the requirements defined in the embodiment of the present invention, and while they had sufficient heat resistance (contact resistance after heating of 9.9 mΩ or less), they were able to achieve sufficiently low contact resistance (initial contact resistance of 6.8 mΩ or less) under low contact pressure (<2 N), and also had a sufficiently low dynamic friction coefficient (0.74 or less). On the other hand, all of the conductive materials of Test Nos. 7 to 10 did not satisfy the requirements defined in the embodiment of the present invention, and the initial contact resistance and / or the contact resistance after heating was insufficient.

[0075] The conductive material of Test No. 7 did not have a matte Sn plating layer formed, and the Ssk exceeded 3.50, resulting in insufficient initial contact resistance.

[0076] The conductive material of Test No. 8 did not have a base layer formed, and the contact resistance after heating was insufficient.

[0077] The conductive material of Test No. 9 had a bright Sn plating layer instead of a matte Sn plating layer, and Sska was over 3.50, meaning the initial contact resistance was insufficient. Perhaps due to this influence, the contact resistance after heating was also insufficient.

[0078] The conductive material of Test No. 10 did not have an underlayer formed, and the initial contact resistance and the contact resistance after heating were insufficient.

[0079] The results of the initial contact resistance and the contact resistance after heating are further discussed. Tests Nos. 1, 2, and 4 to 6 satisfied the preferred conditions of -1.20≦Ssk≦1.20 or -2.50≦Ssk≦2.50 and Sa≧0.05, thereby enabling further reductions in contact resistance. Specifically, both the initial contact resistance and the contact resistance after heating were excellent. Tests Nos. 1 and 4 to 6 satisfied the more preferred conditions of -1.00≦Ssk≦1.00 or -2.00≦Ssk≦2.00 and Sa≧0.07, thereby enabling further reductions in contact resistance. Specifically, either the initial contact resistance or the contact resistance after heating was excellent. Tests Nos. 1 and 4 satisfied the even more preferred conditions of -1.00≦Ssk≦1.00 and Sa≧0.07, thereby enabling further reductions in contact resistance. Specifically, both the initial contact resistance and the contact resistance after heating were excellent.

[0080] The results of the dynamic friction coefficient will be further considered. Tests Nos. 1 to 3 and 6 satisfied the preferable requirement that a portion of the Cu-Sn alloy layer be exposed on the surface of the Sn layer side of the conductive material, and therefore had very excellent dynamic friction coefficients. [Explanation of symbols]

[0081] 1 Cu-Sn alloy layer 2 Sn layer 2a Residual Sn layer 2b Matte Sn plating layer 3 Base layer 10 male specimens 11 Level platform 12 Female test pieces 13 weight 14 load cells

Claims

1. 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, In a 250 μm square region of the surface of the conductive material on the Sn layer side that contains 50 area % or more of the Sn layer, the skewness evaluated with a cutoff value of 25 μm is −3.50 to 3.50, A conductive material, wherein an arithmetic mean height evaluated with a cutoff value of 25 μm is 0.03 μm or more in a 250 μm square region of the surface of the conductive material on the Sn layer side, the region including the Sn layer at 50 area % or more.

2. 2. The conductive material according to claim 1, wherein a part of the Cu—Sn alloy layer is exposed on a surface of the conductive material on the Sn layer side.

3. 3. The conductive material according to claim 1, 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.

4. 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 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, cooling to 50°C or less; After the cooling, performing a matte Sn plating process to form a matte Sn plating layer having a plating thickness of 0.01 to 0.50 μm; The matte plating treatment is Within 30 seconds of cooling to 50°C, or After pickling using sulfuric acid at a temperature of 40 to 60°C and a concentration of 30% by mass or more, A method for producing the conductive material according to claim 1 .

5. The method for producing a conductive material according to claim 4, further comprising exposing a part of the Cu—Sn alloy layer on the surface of the matte Sn plating layer.

6. 6. The manufacturing method according to claim 4 or 5, 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.

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