Aggregation of fine metal wires

Abstract

Provided is a fine metal linear body having a lower sintering temperature than the conventional one. The fine metal linear body has a length of 0.5-200 µm and a thickness of 30 nm or more and 10 µm or less. Where the length of a metal crystal constituting the fine metal linear body along the extension direction of the fine metal linear body is denoted by X and the length along the direction orthogonal to said direction is denoted by Y, the value of X / Y, which is the ratio of X to Y, is 4 or less at three points in boundary regions obtained when the length of the fine metal linear body is divided into four equal parts along the extension direction thereof.

Description

[Technical Field]

[0001] The present invention relates to fine metal filaments. [Background technology]

[0002] Nanowires, due to their minute size, high aspect ratio, etc., are expected to exhibit physical and chemical properties (e.g., electrical conductivity, thermal conductivity, luminescence properties, catalytic activity, etc.) that are not found in conventional materials. Conventional techniques for producing such nanowires are known from Patent Document 1 and Non-Patent Document 1.

[0003] Patent Document 1 describes a method for producing copper nanowires by an electroless method, in which hydrazine is added as a reducing agent to an aqueous solution containing ethylenediamine, o-phenylenediamine, and copper nitrate. In this method, ethylenediamine and o-phenylenediamine are easily adsorbed to the (001) and (111) faces of copper, but are less likely to adsorb to the (110) face, and copper is selectively deposited on the (110) face to form a wire-like shape. Non-Patent Document 1 also describes a method for producing copper nanowires by an electroless method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 097808 Brochure [Non-patent literature]

[0005] [Non-Patent Document 1] MJ Kim, et. al., Journal of the American Chemical Society, 2017, vol139, p277-284 Summary of the Invention

[0006] In copper nanowires produced by the method described in Patent Document 1, due to the mechanism of production, the copper crystals are elongated and large single crystals with the <0110> orientation preferentially oriented in the longitudinal direction of the wire. It is known that the sintering temperature of metal powder shifts to a lower value as the crystal size becomes smaller. However, it is not easy to lower the sintering temperature of copper nanowires produced by the method described in Patent Document 1, which inevitably results in larger crystal sizes.

[0007] Therefore, an object of the present invention is to provide fine metal filaments which can be sintered at a lower temperature than conventional ones, or which have a lower electrical resistance in the sintered portion after heat treatment when the heating temperature is the same.

[0008] The present invention provides a fine metal filament having a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, The present invention provides a fine metal filamentous body in which, when the length of the metal crystals constituting the fine metal filamentous body along the extension direction is defined as X and the length along the direction perpendicular to that direction is defined as Y, the arithmetic mean value of the X / Y ratio, which is the ratio of X to Y, is 4 or less at three boundary regions obtained by dividing the length of the fine metal filamentous body along its extension direction into four equal parts.

[0009] The present invention provides a fine metal filament having a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, The present invention provides a fine metal filamentous body in which, when the length of the metal crystals constituting the fine metal filamentous body along a direction perpendicular to the extension direction of the fine metal filamentous body is defined as Y, the arithmetic mean value of Y of the crystals is 10 nm or less at three boundary regions obtained by dividing the length of the fine metal filamentous body along its extension direction into four equal parts.

[0010] The present invention also provides a fine metal filament having a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, The present invention provides a fine metal filament, in which, at three boundary regions when the length of the fine metal filament is divided into four equal parts along its extension direction, the proportion of crystal grains of the metal constituting the fine metal filament that have a

[0110] orientation is 50% or less, as evaluated by electron diffraction using a transmission electron microscope or electron backscatter diffraction within a range of ±30° in the extension direction of the fine metal filament.

[0011] The present invention further provides a method for producing fine metal filaments having a metal base material, the method comprising the step of depositing a metal on a cathode by electrolytic reduction using an electrolyte containing a metal element source, the method comprising the steps of: The present invention provides a method for producing fine metal filaments, in which electrolytic reduction is carried out in a state in which an oily substance is present on the surface of the cathode. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a scanning electron microscope image of the fine metal filaments obtained in Example 1. [Figure 2] FIG. 2 is a scanning electron microscope image of the fine metal filaments obtained in Comparative Example 1. [Figure 3] FIG. 3 is an electron backscatter diffraction grain map (EBSD grain map) of the fine metal filaments obtained in Example 1. [Figure 4] FIG. 4 is an electron backscatter diffraction grain map (EBSD grain map) of the fine metal filaments obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described below based on preferred embodiments. The present invention relates to fine metal filaments. In the following description, the term "fine metal filaments" may refer to an individual filament or to a collection of multiple filaments, depending on the context. The fine metal filaments of the present invention are made of metal. Fine metal filaments typically extend in one direction. The state in which the filament extends in one direction varies depending on the state of the filament when observed. For example, the filament may extend in a straight line or in a curved, meandering manner in one direction. This filament is characterized by its long length despite being very thin.

[0014] The fine metal filaments are very thin, preferably having a thickness of 30 nm to 10 μm, more preferably 30 nm to 1000 nm, even more preferably 40 nm to 500 nm, and even more preferably 45 nm to 300 nm. Despite being very thin, the fine metal filaments are long, preferably having a length of 0.5 μm to 200 μm, even more preferably 1 μm to 100 μm, and even more preferably 2 μm to 70 μm. By combining these thicknesses and lengths, the fine metal filaments are easy to handle and can have excellent filling properties when used, for example, as a bonding material. Furthermore, the aspect ratio of the fine metal filaments (length [m] of the fine metal filaments / thickness [m] of the fine metal filaments) is preferably 5 or more and 5,000 or less, more preferably 10 or more and 5,000 or less, even more preferably 20 or more and 5,000 or less, even more preferably 20 or more and 3,000 or less, and even more preferably 20 or more and 1,500 or less. The diameter of the fine metal filaments is determined by arithmetically averaging the diameters of 10 or more fine metal filaments in an electron microscope image, and the length is determined by arithmetically averaging the lengths of 20 or more fine metal filaments in an electron microscope image.

[0015] The fine metal filaments may have a shape in which the thickness is substantially uniform throughout their entire length, or in which the thickness is not uniform but is beaded. It is preferable that at least one end of the fine metal filaments has a tapered shape. The "tapered shape" refers to a shape in which, when observing the end region of the fine metal filaments, the thickness gradually decreases toward the tip. By tapering at least one end of the fine metal filaments, when the fine metal filaments are used, for example, as a raw material for wiring, connections in the direction of extension of the fine metal filaments (hereinafter also referred to as the "longitudinal direction") can be made on the side of the tapered portion rather than on the cross section of the fine metal filaments. In other words, since the side surface area is larger than the cross section of the filaments, there is an advantage in that the contact area of ​​the fine metal filaments can be increased and the resistance at the interface can be reduced. In addition, the ability to reduce the gap between the fine metal filaments is also advantageous for reducing resistance. To make this advantage even more pronounced, the angle of the tip of the tapered shape is preferably 60 degrees or less, more preferably 50 degrees or less, and even more preferably 45 degrees or less. The "direction in which the fine metal filaments extend" refers to the longitudinal direction of the fine metal filaments as described above, and if there is a curved portion, refers to the tangential direction of the curved portion.

[0016] The angle of the tapered tip is measured using the following procedure. First, the thickness of the fine metal filament is measured based on an electron microscope image as described above. Next, an arc with a diameter equal to the thickness of the fine metal filament is drawn with the end tip of the fine metal filament as its center, and two points of contact between the arc and the fine metal filament are obtained. The angle between the two points of contact and the end tip of the fine metal filament is measured as the tip angle. Note that if the cross section of the end of the fine metal filament is linear or approximately linear, the center of the end tip is taken as the tip of the end. Furthermore, if the cross section of the end of the fine metal filament is linear or approximately linear and the cross-sectional length exceeds half the thickness of the fine metal filament, the fine metal filament is excluded from the measurement. This measurement is performed on 10 or more fine metal filaments, and the arithmetic average value is taken as the angle of the tapered tip.

[0017] The shape of the fine metal filaments is typically a linear body extending in one direction, and the fine metal filaments may or may not have a main chain extending in one direction and a branched structure branching from the main chain. From the viewpoint of imparting sufficient conductivity to an object with a small amount and from the viewpoint of making it difficult for the conductivity of the object to decrease when the conductive object is stretched, contracted, or bent, it is preferable that the fine metal filaments have an unbranched structure having only a main chain. On the other hand, from the viewpoint of making the aggregate of the fine metal filaments present a bulky structure, it is preferable that the fine metal filaments have one or more branched portions.

[0018] The type of metal constituting the fine metal filaments is not particularly limited, and various metals can be used. Considering the balance between high conductivity and ease of industrial use, the metal is preferably at least one metal selected from the group consisting of copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc, or an alloy containing such a metal. Alternatively, the filaments may be formed in a state in which crystals of multiple metals or alloys are mixed. Among these, filaments made of copper or a copper alloy, or zinc or a zinc alloy, are particularly preferred, and filaments made of copper or a copper alloy are particularly preferred. Note that "made of copper or zinc" means that the proportion of copper or zinc in the fine metal filaments is 80% by mass or more. An example of a state in which crystals of multiple metals or alloys are mixed is a state in which crystals of different metals are connected together, such as Cu crystal-Zn crystal-Cu crystal-Zn crystal.

[0019] The fine metal filaments may have a structure having a main body made of a first metal element or an alloy containing the first metal element, and a coating layer of a second metal element other than the first metal element arranged on the surface of the main body. Examples of the first metal element include copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc, as described above. Examples of the second metal element include, provided that it is different from the first metal element, silver, cobalt, iron, nickel, zinc, lead, tin, platinum, gold, palladium, copper, bismuth, etc., and alloys containing one or more of these metals (e.g., nickel alloys, iron alloys, etc.). In particular, it is preferable for the second metal element to have a higher conductivity than the first metal element or alloy of the first metal element constituting the main body, in order to further increase the conductivity imparted to the target object. From this perspective, when the first metal element is, for example, copper or zinc, the second metal element is preferably silver.

[0020] To form a coating layer on the surface of the main body, for example, the main body may be formed by a method described below, followed by electroplating in an electrolytic solution containing the metal element used for coating, or by applying a catalyst that enables displacement plating or electroless plating to the fine metal filaments and then plating the desired metal, or by a dry method. Alternatively, the surface of the filaments may be treated with an organic agent.

[0021] The fine metal filaments of the present invention have a crystal structure different from that of previously known fine metal filaments. Specifically, the fine metal filaments of the present invention have a polycrystalline structure in which multiple crystals are connected along the extension direction of the filaments. In contrast to this, previously known fine metal filaments, such as those produced by an electroless method described in Patent Document 1, have a single-crystal-like structure with large, elongated crystals along the extension direction of the filaments. Furthermore, the fine metal filaments of the present invention have a characteristic crystal structure that allows the sintering temperature to be lower than conventional ones. Furthermore, when the fine metal filaments are heat-treated at the same heating temperature as conventional fine metal filaments, the electrical resistance of the sintered portion after heat treatment can be made lower than conventional ones.

[0022] To describe in detail the crystal structure of the fine metal filaments of the present invention, when the length of the metal crystals constituting the fine metal filaments along the longitudinal direction of the fine metal filaments is X and the length along the direction perpendicular to the longitudinal direction (hereinafter also referred to as the "width direction") is Y, the ratio of X to Y, that is, X / Y, is preferably 4 or less. As described above, the metal crystals constituting the fine metal filaments of the present invention have a substantially isotropic shape with no significant difference between their longitudinal and transverse lengths. Since the thickness of the fine metal filaments of the present invention is 30 nm or more and 10 μm or less, as described above, it is understood that the metal crystals constituting the fine metal filaments are fine. Because the metal crystals constituting the fine metal filaments of the present invention have such a structure, as described above, the fine metal filaments of the present invention can be sintered at a lower temperature than conventionally. Alternatively, when the fine metal filaments are heat-treated at the same heating temperature as conventional fine metal filaments, the electrical resistance of the sintered portion after heat treatment can be made lower than conventionally. To make this advantage even more pronounced, the value of X / Y is more preferably 3 or less. The above-mentioned X / Y value is the arithmetic mean of the X / Y values ​​of the crystals at three boundary regions when the length of the fine metal filament is divided into four equal parts along the longitudinal direction. The arithmetic mean value is rounded to the nearest tenth.

[0023] The term "crystal" as used herein refers to crystal grains, and their size can be obtained from a grain map obtained by electron backscatter diffraction (hereinafter also referred to as "EBSD"). It should be noted that the concept of crystal grains is different from the crystallite size determined from an XRD pattern. When the crystal referred to herein is a twin crystal, each crystal constituting the twin is defined as a different crystal, and the value of X / Y is determined for each crystal.

[0024] When the value of X / Y is 4 or less, there are no restrictions on the values ​​of X and Y, but from the viewpoint of being able to lower the sintering temperature compared to conventional methods, the value of X itself is preferably 10 μm or less, more preferably 5 nm or more and 2 μm or less, and even more preferably 10 nm or more and 500 nm or less. From the same viewpoint, the value of Y itself is preferably 3 μm or less, more preferably 5 nm or more and 1 μm or less, more preferably 10 nm or more and 400 nm or less, and even more preferably 10 nm or more and 200 nm or less.

[0025] The fine metal filaments of the present invention are characterized only by the above-mentioned value of Y. That is, the value of Y is preferably 10 nm or less. When Y is 10 nm or less, it means that the width is as narrow as 100 or fewer metal atoms. This is the same as the design concept of setting the X / Y value to 4 or less, and it also means that the crystals are fine. Due to this, the fine metal filaments of the present invention can be sintered at a lower temperature than conventional ones. Alternatively, when heat-treated at the same heating temperature as conventional fine metal filaments, it is possible to reduce the electrical resistance of the sintered portion after heat treatment. Note that as long as Y is 10 nm or less, the value of X / Y does not matter. The above-mentioned value of Y is determined by calculating the Y values ​​of the crystals at three boundary regions when the length of the fine metal filament is divided into four equal parts along the longitudinal direction, and then taking the arithmetic mean of these values. The arithmetic mean value is rounded to the nearest tenth.

[0026] The fine metal filaments of the present invention are also characterized by the crystal orientation of the metal that constitutes them. Specifically, when the length of the fine metal filament of the present invention is divided into four equal parts along its extension direction, and attention is focused on the crystals present in three boundary regions, the proportion of crystal grains having a

[0110] orientation as evaluated by electron diffraction using a transmission electron microscope (hereinafter also referred to as "TEM") or EBSD within a range of ±30° along the extension direction of the fine metal filament is preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less. Satisfying this relationship means that the

[0110] orientation of the crystals is not preferentially oriented in the longitudinal direction of the fine metal filament.

[0110] The proportion of oriented crystal grains is calculated by randomly selecting two or more fine metal filaments, drawing boundary lines along the longitudinal direction of each of the fine metal filaments to divide the length into four equal parts, and measuring the three boundary regions of the boundaries. When evaluated by electron diffraction in a TEM, this is the percentage of crystal grains with a

[0110] orientation measured at a total of six or more midpoints of the boundary lines for one boundary region (for example, six locations if two fine metal filaments are extracted, or 15 locations if five fine metal filaments are extracted). When evaluating using EBSD, measurements are taken at a total of 18 or more locations for each boundary region, consisting of three points that divide the boundary line into four equal parts (for example, 18 locations if two fine metal filaments are extracted, and 45 locations if five fine metal filaments are extracted). Percentages shall be rounded to the nearest tenth. When observing crystal grains with a

[0110] orientation using a TEM, electrons are passed through the fine metal filament to perform the observation. However, if the thickness of the fine metal filament is 200 nm or more, the electrons do not pass through the fine metal filament, and the desired electron diffraction pattern cannot be obtained. Therefore, if the thickness of the fine metal filament is 200 nm or more, the proportion of crystal grains with a

[0110] orientation is evaluated using EBSD.

[0027] In contrast to this, previously known fine metal filaments, such as those manufactured by the electroless method described in Patent Document 1, have a preferred orientation of the

[0110] direction in the longitudinal direction of the filament due to their manufacturing method. Non-Patent Document 1 also reports the synthesis of fine metal filaments by an electroless method. As described in the comparative example below, the inventor's experiments have revealed that the fine metal filaments synthesized by the electroless method of Non-Patent Document 1 also have a preferred longitudinal orientation of the

[0110] orientation. This document also describes that the side surfaces of these fine metal filaments are (100) planes. This document also describes that the (100) plane is more easily oxidized than other planes, resulting in the formation of an oxide film on the surface. In other words, the side surfaces of fine metal filaments with a preferred longitudinal orientation of the

[0110] orientation are more easily oxidized, which contributes to an increase in the resistance of the fine metal filaments in the width direction. Therefore, the fine metal filaments of the present invention, which are fine metal filaments that do not grow in the longitudinal direction with a

[0110] orientation, have the advantage of being less susceptible to oxidation. The fine metal filaments of the present invention, in which the crystals are not preferentially oriented in the longitudinal direction in the

[0110] direction, have a characteristic crystal structure that allows the sintering temperature to be lower than that of conventional fine metal filaments. Alternatively, when the fine metal filaments are heat-treated at the same heating temperature as conventional fine metal filaments, the electrical resistance of the sintered portion after heat treatment can be made lower than that of conventional fine metal filaments.

[0028] From the viewpoint of lowering the sintering temperature compared to conventional methods, it is preferable that the proportion of crystal grains with a

[0111] orientation evaluated by TEM electron diffraction or EBSD within a range of ±30° in the extension direction of the fine metal filament is 50% or more, more preferably 52% or more, even more preferably 60% or more, and even more preferably 70% or more, in the three crystals present in the boundary region when the length of the fine metal filament is divided into four equal parts along its extension direction.

[0111] The proportion of oriented crystal grains is calculated by randomly selecting two or more fine metal filaments, drawing boundary lines along the longitudinal direction of each of the fine metal filaments to divide the length into four equal parts, and measuring the three boundary regions of the boundaries. When evaluated by electron diffraction in a TEM, this is the percentage of crystal grains with a

[0111] orientation measured at a total of six or more midpoints of the boundary lines for one boundary region (for example, six locations if two fine metal filaments are extracted, or 15 locations if five fine metal filaments are extracted). When evaluating using EBSD, measurements are taken at a total of 18 or more locations for each boundary region, consisting of three points that divide the boundary line into four equal parts (for example, 18 locations if two fine metal filaments are extracted, and 45 locations if five fine metal filaments are extracted). Percentages shall be rounded to the nearest tenth. This relationship means that the <0111> orientation is preferentially oriented in the longitudinal direction of the fine metal filaments. Crystallographically, the <0111> orientation of the crystals in the longitudinal direction is preferable because it means that the (100) plane is not exposed on the side surfaces.

[0029] Furthermore, when the length of the fine metal filament is divided into four equal parts along its extension direction, the three crystals present in the boundary region preferably have a proportion of crystal grains with the

[0100] orientation, the

[0110] orientation, and the

[0111] orientation evaluated by TEM electron diffraction or EBSD within a range of ±30° in the extension direction of the fine metal filament, of 50% or less, and more preferably 40% or less. The proportion of crystal grains with the

[0110] ,

[0111] , and

[0100] orientations is calculated by randomly selecting two or more fine metal filaments, drawing boundary lines along the longitudinal direction of each of the fine metal filaments to divide their length into four equal parts, and measuring the three boundary regions of the boundaries. When evaluated by electron diffraction in a TEM, this is the percentage of crystal grains with the

[0110] ,

[0111] , or

[0100] orientation measured at a total of six or more locations at the midpoints of the boundary lines for each boundary region (for example, six locations if two fine metal filaments are extracted, or 15 locations if five fine metal filaments are extracted). When evaluating using EBSD, measurements are taken at a total of 18 or more locations for each boundary region, consisting of three points that divide the boundary line into four equal parts (for example, 18 locations if two fine metal filaments are extracted, and 45 locations if five fine metal filaments are extracted). Percentages shall be rounded to the nearest tenth.

[0030] Such a relationship means that the crystals of the metal that make up the fine metal filaments are randomly oriented. Random orientation of the crystals of the metal that make up the fine metal filaments means that the metal crystals that make up the fine metal filaments are polycrystalline, meaning that the crystals are small. As mentioned above, small crystals lead to lower sintering temperatures. Furthermore, "random orientation of the crystals" means that the (100) plane is not preferentially exposed on the side of the filaments, meaning that oxidation of the side of the fine metal filaments is not promoted.

[0031] When the fine metal filaments of the present invention are an assembly containing a plurality of fine metal filaments, the number of fine metal filaments having curved portions with a radius of curvature of not more than 5 times the length of the fine metal filaments in the assembly preferably accounts for 5% or more of the total number of fine metal filaments in the assembly, more preferably 20% or more, even more preferably 40% or more, and even more preferably 60% or more. This makes it easier to achieve contact across the plurality of fine metal filaments in the lateral (width) direction of the fine metal filaments, which is preferable in that the assembly of fine metal filaments has low resistance. The radius of curvature is calculated as follows. The fine metal filament is observed using a scanning electron microscope (hereinafter also referred to as "SEM"). A straight line is drawn between both ends of the fine metal filament, and its length (chord length) is measured. Furthermore, an auxiliary line perpendicular to the line is drawn from the midpoint of the line toward the fine metal filament, and the distance (arrow height) between the midpoint and the point where it intersects with the fine metal filament is measured. The radius of curvature is calculated using the following formula. r = (C × C) / (8 × h) + h / 2 (In the formula, r represents the radius of curvature, C represents the chord length, and h represents the arrow height.) The above-mentioned radius of curvature is preferably 0.5 μm or more and 1000 μm or less. If the fine metal filamentary object is bent, the radius of curvature is calculated from the above formula by approximating the shape of the fine metal filamentary object as having a curved portion. If a line connecting both ends of the fine metal filamentary object crosses the fine metal filamentary object, the radius of curvature is measured as if the fine metal filamentary object were a different fine metal filamentary object, with the crossing point as the boundary.

[0032] When the fine metal filaments of the present invention are an aggregate containing a plurality of fine metal filaments, the aggregate may contain particles having a shape other than that of the filaments, although it is preferable that particles having a shape other than that of the filaments are as few as possible present in the aggregate from the viewpoint of preventing a decrease in conductivity even when subjected to deformation such as bending or stretching. When the proportion of particles in the aggregate having a shape other than that of filaments is defined as the "irregularity rate," the irregularity rate is preferably 50% or less, more preferably 40% or less, even more preferably 30% or less, even more preferably 10% or less, and even more preferably 2% or less. If fine metal filaments are produced by the production method described below, it is possible to easily achieve an irregularity rate of 50% or less. The irregularity rate is determined by observing the sample under SEM in a field of view that is 5 to 30 times the average length of the fine metal filaments in both the vertical and horizontal directions, and calculating the percentage of [area of ​​irregularly shaped objects / area of ​​filaments]. "Irregular shapes" refers to shapes other than filaments (e.g., spheres, lumps, fern-like leaves, etc.).

[0033] Next, a preferred method for producing the fine metal filaments of the present invention will be described. An electrolytic method is preferably used to produce the fine metal filaments. This is because electrolytic methods not only facilitate control into the desired shape, but also allow the repeated use of electrolyte, reducing the amount of liquid required to produce the fine metal filaments and simultaneously reducing the amount of waste liquid to be treated. Another method for producing metal powder is atomization, but it cannot produce anisotropic shapes such as fine metal filaments. Another method is wet reduction (electroless reduction), but this method does not allow the solution to be reused and it is impossible to increase the concentration of the target metal element above a certain level, making it difficult to produce fine metal filaments with high productivity.

[0034] When producing fine metal filaments by electrolysis, for example, an example of a process involves immersing an anode and a cathode in a sulfuric acid electrolyte containing a metal element source, passing a direct current through the electrolyte to perform electrolytic reduction, depositing fine metal filaments on the surface of the cathode, scraping off and recovering the deposited fine metal filaments using a mechanical or electrical method, washing the recovered fine metal filaments with water or an organic solvent, drying, and, if necessary, sieving.

[0035] The metal element used in this manufacturing method is not particularly limited as long as it allows for the production of fine metal filaments by this manufacturing method. Considering the balance between high conductivity and ease of industrial use, examples of suitable metal elements include copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc. These metal elements have in common the fact that they can be electrolytically deposited from aqueous solutions, and therefore, regardless of which metal element is used, they can be produced in the same manner according to this manufacturing method. Among these, it is particularly preferable to use copper or a copper alloy, or zinc or a zinc alloy, as the base material. The fine metal filaments obtained by this manufacturing method may be composed of only the target metal element, excluding unavoidable impurities, or may be composed of an alloy of the target metal element, excluding unavoidable impurities, or may be composed of a combination of two or more of the above-mentioned metal elements, excluding unavoidable impurities.

[0036] The inventors have found that when manufacturing fine metal filaments using the above-mentioned procedure, it is advantageous to carry out electrolytic reduction while an oily substance is attached to the surface of the cathode. Reducing the ions of the metal elements under such conditions has the advantage of being able to control the reduction reaction. The details are as follows. The amount of oily substance deposited on the cathode surface, expressed in thickness, is several hundred nanometers or more on average, preferably several micrometers to several hundred micrometers. However, the thickness varies locally due to fluctuations in the electrolyte. Although almost no metal ions coexist in the oily substance, electrolyte containing metal ions may float in the form of droplets on the oily substance, or a very small amount of electrolyte may be intermittently drawn to the vicinity of the electrode by the force of the electric field formed by applying electricity. Under such circumstances, a reduction reaction of the metal occurs on the surface of the cathode, resulting in the formation of locally deposited metal protrusions. The thickness of the oily substance directly above these protrusions is thinner than in other areas, reducing the electrical resistance in those areas, causing current to concentrate there, and the protrusions to grow into filaments. In this way, fine metal filaments are formed by electrolysis. As the growth of the fine metal filaments progresses, they tend to sag under their own weight and take on a curved shape. Alternatively, linear growth is hindered by electrical resistance due to the oily substance, making the fine metal filaments prone to curved shapes. While the fine metal filaments are essentially formed by electrolysis using the mechanism described above, the detailed shape and structure also vary depending on the type of oily substance used. As with normal metal electrolytic deposition, they also vary depending on the composition and additives of the electrolyte.

[0037] Examples of methods for attaching an oily substance to the surface of the cathode include directly applying the oily substance to the surface of the cathode, immersing the cathode in a container containing the oily substance to attach it, and floating the oily substance on the electrolyte and immersing the cathode from above to attach the oily substance to the cathode surface. Another method involves suspending the oily substance in the electrolyte and stirring the suspended electrolyte, causing the suspended oily substance to collide with the surface of the cathode and adhere directly to the cathode surface. Furthermore, if the oily substance has the property of dissolving in a small amount in the electrolyte, even if the suspended oily substance does not directly contact the electrode, it will exhibit the same effect as if the oily substance dissolved in the electrolyte were continuously adsorbed onto the electrode surface and ultimately adhered to the surface.

[0038] By manufacturing a fine metal filament using the above method, the fine metal filament has a polycrystalline structure in which multiple crystals are connected along the longitudinal direction. Furthermore, the crystals are less likely to be preferentially oriented in the longitudinal direction in the

[0110] direction. Furthermore, the fine metal filament tends to be more likely to have a preferential orientation in the longitudinal direction in the

[0111] direction, or the crystals are more likely to be randomly oriented. Furthermore, by producing fine metal filaments using the above method, it is possible to minimize the generation of particles having shapes other than those of the filaments.

[0039] The oily substance to be attached to the surface of the cathode may be any organic compound that is poorly soluble or insoluble in water and has a viscosity sufficient to be retained on the surface after being attached to the cathode. Note that "poorly soluble or insoluble in water" means that the compound dissolves in an amount of 100 g or less in 1 L of water at the temperature when the fine metal filaments are produced. The oily substance may be liquid or solid, and may be used by dissolving it in a liquid solvent at room temperature (20 to 30°C). In order to facilitate control of the physical properties of the deposited fine metal filaments, the oily substance may further contain additives such as benzoic acid, fumaric acid, citric acid, benzotriazoles, etc.

[0040] Examples of the organic compound include, provided that it is poorly soluble or insoluble in water, aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic alcohols, aromatic alcohols, aliphatic aldehydes, aromatic aldehydes, aliphatic ethers, aromatic ethers, aliphatic ketones, aromatic ketones, aliphatic carboxylic acids and salts thereof, aromatic carboxylic acids and salts thereof, amides of aliphatic carboxylic acids, amides of aromatic carboxylic acids, esters of aliphatic carboxylic acids, esters of aromatic carboxylic acids, silicones (e.g., dimethyl silicone), aliphatic amines, aromatic amines, nitrogen-containing heterocyclic compounds, tributyl phosphate, thiols, fluorine-based solvents, ionic liquids, etc. In this specification, "aliphatic alcohol" refers to an alcohol having 5 or more carbon atoms. As a result of the inventor's investigations, it was found that fine metal filaments can be more successfully produced by using, as the oily substance, particularly, a fatty acid or its salt, an ester or its amide, an aromatic carboxylic acid, an aliphatic hydrocarbon, an aliphatic alcohol, an aliphatic amine, a silicone (e.g., dimethyl silicone), or a mixture thereof.

[0041] The fatty acids include lower fatty acids and higher fatty acids. Lower fatty acids include saturated or unsaturated aliphatic carboxylic acids preferably having 9 or less carbon atoms. Higher fatty acids include saturated or unsaturated aliphatic carboxylic acids preferably having 10 to 25 carbon atoms, more preferably 10 to 22 carbon atoms, and even more preferably 11 to 20 carbon atoms. Examples of saturated aliphatic carboxylic acids include caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, heneicosylic acid, behenic acid, tricosylic acid, and lignoceric acid.

[0042] The unsaturated aliphatic carboxylic acid may be one having one or more unsaturated carbon bonds in the molecule. Examples of unsaturated aliphatic carboxylic acids having one unsaturated carbon bond in the molecule include crotonic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, and nervonic acid. Examples of unsaturated aliphatic carboxylic acids having two or more unsaturated carbon bonds in the molecule include linoleic acid, eicosadienoic acid, docosadienoic acid, and linolenic acid.

[0043] Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, mellophanic acid, prenitic acid, pyromellitic acid, mellitic acid, diphenic acid, toluic acid, xylyl acid, hemellic acid, mesitylene acid, prenithylic acid, γ-isodurylic acid, durylic acid, β-isodurylic acid, mesitic acid, α-isodurylic acid, cumic acid, ubic acid, α-toluic acid, hydratropic acid, atropic acid, hydrocinnamic acid, cinnamic acid, salicylic acid, anisic acid, cresotic acid, o-phosphatic acid, hydroxybenzoic ... Mosalicylic acid, o-cresotic acid, m-homosalicylic acid, m-cresotic acid, p-homosalicylic acid, p-cresotic acid, o-pyrocatechuic acid, β-resorcylic acid, gentisic acid, γ-resorcylic acid, protocatechuic acid, α-resorcylic acid, vanillic acid, isovanillic acid, veratrum, o-veratric acid, orsellinic acid, m-hemipic acid, gallic acid, syringic acid, asaronic acid, mandelic acid, vanillylmandelic acid, homoanisic acid, homogentisic acid, homoprotocatechuic acid, homovanillic acid, homoisovanillic acid, homoveratric acid, o -Homoveratric acid, homophthalic acid, homoisophthalic acid, homoterephthalic acid, phthalonic acid, isophthalonic acid, terephthalonic acid, benzilic acid, atrolactic acid, tropic acid, mellotic acid, phloretic acid, hydrocaffeic acid, hydroferulic acid, hydroisoferulic acid, p-coumaric acid, umbellic acid, caffeic acid, ferulic acid, isoferulic acid, sinapic acid, benzoyl, phthaloyl, isophthaloyl, terephthaloyl, toluoyl, xyloyl, cumoyl, α-toluoyl, hydroatropoyl, atropoyl, hydrocinnamoyl yl, cinnamoyl, salicyloyl, anisoyl, cresotoyl, o-pyrocatechuyl, β-resorcyloyl, gentisoyl, γ-resorcyloyl, protocatechuyl, α-resorcyloyl, vanilloyl, isovanilloyl, o-veratroyl, veratroyl, galloyl, syringoyl, mandeloyl, vanylmandeloyl, homogentisoyl, homovanilloyl, homoveratroyl, benzyloyl, tropoyl, caffeoyl, feruloyl, perbenzoic acid, ibuprofen, ketoprofen, and felbinac.

[0044] Among the above fatty acids, it is preferable to use saturated aliphatic carboxylic acids or unsaturated aliphatic carboxylic acids, since this allows for more successful production of fine metal filaments.

[0045] The ester of the fatty acid is preferably an ester with a saturated aliphatic alcohol or an unsaturated aliphatic alcohol. The carbon number of this alcohol is preferably 1 to 18. The ester of the fatty acid is more preferably an ester with a saturated aliphatic alcohol having 1 to 18 carbon atoms. Such an ester includes, for example, ethyl acetate.

[0046] The amount of oily substance to be attached to the surface of the cathode is 0.1 g / m per unit surface area of ​​the cathode. 2 More than 500g / m 2 It is preferable that the density is 1 g / m or less. 2 More than 500g / m 2 It is more preferable that the concentration is 3 g / m or less. 2 More than 200g / m 2 It is more preferable that the concentration is 5 g / m or less. 2 More than 100g / m 2 It is more preferable that:

[0047] The anode and cathode may be made of any known material without any particular limitations. For example, anodes and cathodes made of titanium or copper may be used. An insoluble metal electrode (DSE) may also be used for the anode. In this regard, the current density during reduction was 5 A / m 2 More than 3000A / m 2 It is preferable that the current is less than 10 A / m 2 More than 1000A / m 2 It is more preferable that the current is 50 A / m or less. 2 More than 500A / m 2 It is more preferable that:

[0048] Typically, in metal deposition by electrolysis, a good surface shape can be obtained by passing an amount of electricity corresponding to a reduction rate that is slower than the supply rate of metal ions from the electrolyte (for example, in plating, a state in which a metallic luster is obtained on the surface). Similarly, in the electrolysis of the present invention, the concentration of ions of metal elements in the electrolyte is preferably a concentration that can supply metal ions without excess or deficiency to the reaction rate of the reduction of the metal ions, and from this viewpoint, the concentration of metal ions is preferably 1 g / L or more and 80 g / L or less, and more preferably 1 g / L or more and 60 g / L or less. From the same viewpoint, it is preferable to stir or circulate the electrolytic solution in the electrolytic cell during electrolysis. The electrolytic solution may be used in an unheated state, such as at room temperature (25° C.), or in a heated state. From the same viewpoint, it is also preferable to adjust the size of the electrolytic cell, the number of electrodes, the shape of the electrodes (plate-like, drum-like), the distance between the electrodes, the oscillation of the electrodes, and the circulation rate of the electrolyte so as to maintain a high metal ion concentration in the electrolyte near the electrodes at all times.

[0049] The fine metal filaments of the present invention obtained by the above method can be composited with other substances to impart electrical conductivity to the substances. For example, the fine metal filaments of the present invention can be combined with particles of the same or different metal element to form a bonding material. Alternatively, a composition containing the fine metal filaments of the present invention and a dispersion medium can be used as a bonding material. These bonding materials can also be sintered to form sintered bodies. These bonding materials and sintered bodies are used, for example, as materials for bonding semiconductor elements and substrates.

[0050] Specifically, in a bonded structure including a first member, a second member, and a bonded portion joining the first member and the second member, the bonded portion can be made of a sintered body of a composition containing the fine metal filaments of the present invention and a dispersion medium. Alternatively, in a semiconductor device including a first member, a second member, and a bonded portion joining the first member and the second member, a semiconductor element can be used as at least one of the first member and the second member, and the bonded portion can be made of a sintered body of a composition containing the fine metal filaments of the present invention and a dispersion medium.

[0051] The fine metal filaments of the present invention can also be used to manufacture electronic circuit components. For example, in an electronic circuit component comprising a substrate and a conductive pattern formed on the substrate, the conductive pattern can be composed of a sintered body of a composition containing the fine metal filaments of the present invention and a dispersion medium.

[0052] The dispersion medium contained in the composition can be, for example, various organic solvents. Examples of such organic solvents include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, esters, ketones, nitrogen-containing heterocyclic compounds, amides, amines, saturated hydrocarbons, etc. These organic solvents can be used alone or in combination of two or more.

[0053] The fine metal filaments of the present invention can be incorporated into a resin to obtain a resin composition containing the fine metal filaments and the resin. The resin composition exhibits electrical conductivity due to the inclusion of the fine metal filaments. To impart electrical conductivity to a resin, for example, fine metal filaments may be dispersed in the resin. Alternatively, a layer containing fine metal filaments may be formed on the surface of a substrate containing a resin. In either embodiment, the resin composition can be molded into various shapes. For example, it can be molded into one-dimensional shapes such as fibers, two-dimensional shapes such as films, plates, and strips, and various three-dimensional shapes. Regardless of the shape, the resin composition exhibits sufficient electrical conductivity with the addition of a relatively small amount of fine metal filaments. The resin composition differs from conventional conductive resin compositions containing copper powder as a filler in that its electrical conductivity decreases little before and after stretching or bending the resin composition. From this perspective, the properties of the fine metal filaments of the present invention are effectively exhibited when the resin composition is stretchable or bendable. Conventional conductive resin compositions tend to exhibit a decrease in electrical conductivity when stretched or bent.

[0054] As described above, the fine metal filaments of the present invention can be used in various embodiments. Specific uses of the fine metal filaments of the present invention include uses that require electrical conductivity and that are subject to deformation due to external forces, such as wearable devices and flexible displays that are attached to living bodies. The fine metal filaments of the present invention can also be used in low-linear expansion wiring materials, anisotropic conductive films, anisotropic heat transfer films, anode current collectors for lithium batteries, via-hole filling materials for printed wiring boards, sensors, switches, adsorption / separation devices, electrode catalysts for various electrochemical reactions, and current collectors for power generation elements. [Example]

[0055] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0056] Example 1 In this example, a wire made of copper was manufactured. An electrolyte solution was prepared from copper sulfate and sulfuric acid so that the copper ion concentration was 4 g / L and the free sulfuric acid concentration was 5 g / L. 800 mL of this solution was placed in an electrolytic cell measuring 10 cm x 8 cm x 12 cm (capacity approximately 1000 mL) and stirred. The temperature of the electrolyte solution was 40°C. An 8 cm x 8 cm copper plate was used as the cathode. Oleic acid was evenly applied to the surface of the cathode. The amount of application was 7 g / m. 2 An 8 cm x 8 cm copper plate was used as the anode. The cathode and anode were suspended in the electrolytic cell so that the gap between them was 8 cm. Current density: 160A / m 2 The temperature was adjusted to 50°C and electrolysis was carried out for 30 minutes. In this way, copper was electrodeposited on the surface of the cathode. The copper electrodeposited on the cathode surface was collected and washed with ethanol. The deposit was observed using an SEM, revealing the formation of filaments. Each end of the filaments was tapered. An SEM image of the linear bodies obtained in this example is shown in Figure 1. In this figure, the SEM image at 30,000 magnification is shown to observe the tip shape of the linear bodies.

[0057] Example 2 The copper ion concentration was changed to 1 g / L to prepare the electrolyte, and the current density was set to 63 A / m 2 Electrolysis was carried out with the above changes. Except for these changes, the same procedure as in Example 1 was carried out to obtain an electrodeposit. The resulting electrodeposit was observed using an SEM, and filamentous bodies were confirmed, each end of which was tapered.

[0058] Example 3 The copper ion concentration was changed to 7 g / L to prepare the electrolyte, and the current density was set to 63 A / m 2 Electrolysis was carried out with the above changes. Except for these changes, the same procedure as in Example 1 was carried out to obtain an electrodeposit. The resulting electrodeposit was observed using an SEM, and filamentous bodies were confirmed, each end of which was tapered.

[0059] Example 4 The electrolytic solution was prepared by changing the copper ion concentration to 10 g / L. Except for this, the same procedure as in Example 1 was carried out to obtain an electrodeposit. The resulting electrodeposit was observed using an SEM, and filamentous bodies were confirmed, each end of which was tapered.

[0060] Example 5 The concentration of copper ions was changed to 40 g / L to prepare the electrolyte, and the current density was set to 310 A / m 2 Electrolysis was carried out with the above changes. Except for these changes, the same procedure as in Example 1 was carried out to obtain an electrodeposit. The resulting electrodeposit was observed using an SEM, and filamentous bodies were confirmed, each end of which was tapered.

[0061] Comparative Example 1 This comparative example corresponds to Non-Patent Document 1. A 100 mL four-neck flask was charged with 40 mL of 15 mol / L aqueous sodium hydroxide, 0.30 mL of ethylenediamine, and 2.0 mL of 0.1 mol / L aqueous copper nitrate solution, and stirred with a stirrer. The ethylenediamine concentration in the copper salt solution was 137 mmol / L. The heater was set to 40°C and the temperature was raised. 50 μL of 35% aqueous hydrazine solution was injected into the flask with a syringe. After stirring with the stirrer for 60 minutes, the heater was turned off. The mixture was then cooled to below 30°C in a water bath to obtain linear particles. The particles were separated by filtration, dispersed in ethanol, and ultrasonically dispersed. The mixture was then left for 10 minutes to separate the supernatant (floating matter) and precipitate. An SEM image of the linear bodies obtained in this comparative example is shown in Figure 2. In this figure, the SEM image at 30,000 magnification is shown to observe the tip shape of the linear bodies.

[0062] [Rating 1] The length, thickness, and radius of curvature were measured by the above-described method for the linear bodies obtained in Examples 1 to 5 and Comparative Example 1. In particular, the thickness of the linear bodies was measured by reading the thickness of 10 or more linear bodies at magnifications at which the thickness could be sufficiently measured, specifically, from a 20,000x SEM image for Example 1, from a 80,000x SEM image for Example 2, from a 10,000x SEM image for Example 3, from a 10,000x SEM image for Example 4, from a 100x SEM image for Example 5, and from a 20,000x SEM image for Comparative Example 1, and then arithmetically averaging the readings. The lengths were also measured at magnifications sufficient to measure the lengths, specifically, 20 or more lengths were read from 10,000x SEM images in Example 1, 20,000x SEM images in Example 2, 5,000x SEM images in Example 3, 1,000x, 2,000x, and 5,000x SEM images in Example 4, 100x, 200x, and 500x SEM images in Example 5, and 5,000x SEM images in Comparative Example 1, and the lengths were then calculated as an arithmetic average. The irregularity rates of the aggregates of linear bodies obtained in Examples 1 to 5 and Comparative Example 1 were measured by the method described above. Furthermore, the X, Y, and X / Y values ​​of the crystals and the crystal orientation were measured by the following methods, and the results are shown in Table 1 below.

[0063] [X, Y and X / Y values ​​for the crystal and the crystal orientation] The X, Y, and X / Y values ​​for the crystals were determined using the following method. The fine metal filaments were coated on a copper plate using carbon paste, and the coating was cross-sectionally processed using an argon ion beam cross-section polisher (JEOL Cross Section Polisher (CP)). An EBSD grain map of the cross section was then created and observed. The carbon paste used was Colloidal Graphite (Isopropanol Base) from Electron Microscopy Sciences. EBSD was performed using a Carl Zeiss SEM Crossbeam 540 equipped with an Oxford Symmetry EBSD detector. In the obtained grain map, the fine metal filaments were divided into four equal parts along their longitudinal direction. The X and Y values ​​of the crystals present at each boundary were measured at three locations using the scale in the figure, and the X / Y value was calculated. The arithmetic mean was then calculated. The arithmetic mean was rounded to the nearest tenth. EBSD grain maps measured for the linear bodies of Example 1 and Comparative Example 1 are shown in FIGS. 3 and 4, respectively.

[0064] The crystal orientation was determined by the following method. In the fine metal filaments of Examples 1 to 4 and Comparative Example 1, the fine metal filaments were supported by sprinkling them on a copper grid. Observations were performed using a JEM-ARM200F manufactured by JEOL Ltd. Boundary lines were drawn along the direction of extension of the fine metal filaments to divide their length into four equal parts, and shape observations were performed using a TEM at the midpoints of the boundary lines in the three boundary regions, and electron diffraction patterns were obtained. Orientation analysis by electron diffraction was performed using a digital micrograph manufactured by GATAN Corporation. Furthermore, for the fine metal filaments of Example 5, the material was mixed with carbon paste, applied to a copper plate, and the coating was cross-sectionally processed using an argon ion beam cross-section processing device (a cross-section polisher (CP) manufactured by JEOL Ltd.). Observations were performed using an SEM Crossbeam540 and the EBSD detector: Symmetry installed thereon. Boundary lines were drawn on the fine metal filaments along their extension direction to divide their length into four equal parts. In the three boundary regions of the boundary, the crystal orientation was determined by EBSD at the three points that divide the boundary lines into four equal parts. The crystal orientation was analyzed by EBSD using AZtec Crystal 2.0 manufactured by Oxford. It was determined whether each orientation (0100, 0110, and 0111) evaluated by TEM electron diffraction or EBSD fell within a range of ±30° of the extension direction or tangent direction of the fine metal filaments (each orientation was judged based on a normal closest to the range of ±30° in the longitudinal direction. If two or more orientations fell within the range of ±30°, the orientation closest to 0° was selected. Furthermore, if all three orientations were outside the range of ±30°, it was determined that there was no preferred orientation). For Examples 1 to 4 and Comparative Example 1, five randomly selected fine metal filaments were evaluated, and the percentage of crystal grains preferentially oriented in each direction (

[0100] orientation,

[0110] orientation, and

[0111] orientation) was calculated from a total of 15 evaluation results. For Example 5, five randomly selected fine metal filaments were evaluated, and the percentage of crystal grains preferentially oriented in each direction (

[0100] orientation,

[0110] orientation, and

[0111] orientation) was calculated from a total of 45 evaluation results.

[0065] [Rating 2] The resistivity of sintered bodies produced from the filaments and particles obtained in Examples 1 to 5 and Comparative Example 1 was measured by the method described below. The results are shown in Table 1.

[0066] [Measurement of resistivity] The linear bodies and particles obtained in Examples 1 to 5 and Comparative Example 1 were mixed with varnish (terpineol and ethyl cellulose), degassed, and dispersed using a triple roll mill to obtain compositions. The solid content in the compositions was 60% in Example 1, 55% in Example 2, 51% in Example 3, 57% in Example 4, 39% in Example 5, and 62% in Comparative Example 1. This composition was coated on an alumina substrate and heated in a nitrogen atmosphere at a heating rate of 10°C / min to 220°C, 240°C, 260°C, and 300°C, respectively. After reaching the target temperature, the sintered body was allowed to cool naturally to obtain a sintered body. The resistivity of the sintered body was measured by the four-probe method using a resistivity meter (Mitsubishi Chemical Corporation MCP-T600). In Comparative Example 1, the sintered bodies sintered at 220°C and 240°C had a resistance of 10 6 Measurement was not possible because the value exceeded Ω·cm. 6 " was written.

[0067] [Table 1]

[0068] As is clear from the results shown in Table 1, the sintered bodies formed from the linear bodies obtained in the examples have good low-temperature sintering properties. Furthermore, the linear bodies obtained in the examples have lower electrical resistance in the sintered parts after heat treatment than the linear bodies obtained in the comparative examples when heated at the same temperature. [Industrial Applicability]

[0069] According to the present invention, there is provided a fine metal filament that can be sintered at a lower temperature than conventional ones, or that has a lower electrical resistance in the sintered portion after heat treatment when the heating temperature is the same.

Claims

1. An aggregate of fine metal wires having a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, Regarding the metal crystals constituting the fine metal filaments, when the length of the fine metal filaments along the extension direction is defined as X and the length along the direction perpendicular to the extension direction is defined as Y, the length of the fine metal filaments is divided into four equal parts along the extension direction, and at three boundary regions, the crystals have an arithmetic average value of X / Y, which is the ratio of X to Y, of 4 or less; the metal constituting the fine metal filaments is at least one metal selected from the group consisting of copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc, or an alloy containing the metal; An aggregate of fine metal filaments, in which the number of fine metal filaments having curved portions with a radius of curvature of 5 times or less the length of the fine metal filaments accounts for 40% or more of the total number of the fine metal filaments.

2. An aggregate of fine metal wires having a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, Regarding the metal crystals constituting the fine metal filaments, when the length along the direction perpendicular to the extension direction of the fine metal filaments is defined as Y, the crystals have an arithmetic average value of Y of 10 nm or less at three boundary regions obtained by dividing the length of the fine metal filaments into four equal parts along the extension direction; the metal constituting the fine metal filaments is at least one metal selected from the group consisting of copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc, or an alloy containing the metal; An aggregate of fine metal filaments, in which the number of fine metal filaments having curved portions with a radius of curvature of 5 times or less the length of the fine metal filaments accounts for 40% or more of the total number of the fine metal filaments.

3. An aggregate of fine metal wires having a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, the metal crystals constituting the fine metal filaments have a proportion of crystal grains with a [110] orientation of 50% or less at three boundary regions when the length of the fine metal filaments is divided into four equal parts along the direction of extension of the fine metal filaments, as evaluated by electron diffraction using a transmission electron microscope or electron backscatter diffraction within a range of ±30° along the direction of extension of the fine metal filaments; the metal constituting the fine metal filaments is at least one metal selected from the group consisting of copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc, or an alloy containing the metal; An aggregate of fine metal filaments, in which the number of fine metal filaments having curved portions with a radius of curvature of 5 times or less the length of the fine metal filaments accounts for 40% or more of the total number of the fine metal filaments.

4. The length of the fine metal filaments is divided into four equal parts along the direction of extension, and at three boundary regions, the metal crystals constituting the fine metal filaments are The proportion of crystal grains having a [111] orientation evaluated by electron diffraction using a transmission electron microscope or electron backscatter diffraction within a range of ±30° of the extension direction of the fine metal filaments is 50% or more, or 4. An aggregate of fine metal filaments according to claim 1, wherein the proportions of crystal grains having the [100] orientation, the [110] orientation, and the [111] orientation evaluated by electron diffraction using a transmission electron microscope or electron backscatter diffraction within a range of ±30° in the extension direction of the fine metal filaments are all 50% or less.

5. An assembly of fine metal filaments described in any one of claims 1 to 4, wherein at least one end of the fine metal filaments is tapered, and the angle of the tip of the tapered shape is 60 degrees or less.

6. A method for producing fine metal filaments using a metal as a base material, the method comprising the step of depositing a metal on a cathode by electrolytic reduction using an electrolyte containing a metal element source, the metal constituting the fine metal filaments is at least one metal selected from the group consisting of copper, silver, gold, nickel, lead, palladium, platinum, cobalt, tin, iron, bismuth, and zinc, or an alloy containing the metal; The fine metal filaments have a length of 0.5 μm or more and 200 μm or less and a thickness of 30 nm or more and 10 μm or less, Regarding the metal crystals constituting the fine metal filaments, when the length of the fine metal filaments along the extension direction is defined as X and the length along the direction perpendicular to the extension direction is defined as Y, the length of the fine metal filaments is divided into four equal parts along the extension direction, and at three boundary regions, the crystals have an arithmetic average value of X / Y, which is the ratio of X to Y, of 4 or less; Electrolytic reduction is carried out in a state where an oily substance is adhered to the surface of the cathode, The method for producing fine metal filaments, wherein the oily substance is a fatty acid having from 10 to 25 carbon atoms, or a salt, ester, or amide thereof.

7. An aggregate of fine metal filaments described in any one of claims 1 to 5, wherein the proportion of particles having shapes other than filaments in the aggregate is 50% or less.

8. A composition comprising the aggregate of fine metal filaments according to any one of claims 1 to 5 and 7 and a dispersion medium.

9. a first member, a second member, and a joint portion that joins the first member and the second member; A bonded structure, wherein the bonded portion comprises a sintered body of the composition according to claim 8.

10. a first member, a second member, and a joint portion that joins the first member and the second member; The joint is made of a sintered body of the composition according to claim 8, At least one of the first member and the second member is a semiconductor element.

11. An electronic circuit component comprising a substrate and a conductive pattern formed on the substrate, An electronic circuit component, wherein the conductive pattern comprises a sintered body of the composition according to claim 8.

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