Copper particles coated with slightly oxidized copper, material for sintering containing same, sintered body using said material for sintering, and joined body

Abstract

Disclosed are copper particles coated with slightly oxidized copper, which each comprise: a copper particle that serves as a core; and a shell that contains slightly oxidized copper which is one or more of Cu64O and Cu8O. With respect to scanning electron microscope images of the core copper particles, if the maximum length of each particle is defined as the long side, the arithmetic average value of the long sides is more than 1 μm, and with respect to the scanning electron microscope images, if the arithmetic average length of each particle having a ratio of the arithmetic average length of a portion that is orthogonal to the long side to the long side at 0.4 or less is defined as the thickness, the arithmetic average value of the ratio of the thickness to the long side is 0.25 or less.

Description

Copper particles coated with fine copper oxide, sintering material containing the same, sintered body and joined body using the sintering material

[0001] The present disclosure relates to finely-coated copper particles, a sintering material containing the same, and a sintered body and a joined body using the sintering material.

[0002] In recent years, printable electronics, a technology that directly forms fine wiring using inkjet or printing methods, has attracted attention in the manufacture of printed circuit boards. This technology eliminates the need for conventional exposure and etching processes and does not emit harmful chemicals. Solder has traditionally been used to bond components, such as between substrates and components in semiconductor devices and between circuits. High-melting-point lead solder has been used as a bonding material for power semiconductors and LSIs that operate at temperatures above 150°C. In contrast, with the recent emergence of silicon carbide (SiC)-based power semiconductors, the operating temperature of semiconductors has risen to 250-300°C, close to the melting point of high-melting-point lead solder, making ensuring connection reliability and heat dissipation design significant challenges. Furthermore, with the tightening of RoHS regulations, lead-free bonding materials are in demand. For example, techniques that involve low-temperature sintering of silver nanoparticles to form a sintered silver layer have been proposed as lead-free bonding materials.

[0003] As a bonding material using silver, Patent Document 1 proposes a silver microparticle composition that can obtain high adhesive strength at low bonding temperatures. However, silver microparticles are expensive and there are concerns about the influence of wiring short circuits due to ion migration. As an alternative to silver microparticles, copper microparticles, which are inexpensive and highly resistant to ion migration, have attracted attention. However, copper microparticles have the problem of being difficult to sinter at low temperatures.

[0004] To address the above-mentioned problems, the present inventors have attempted to obtain particles for low-temperature sintering using copper oxides. ２ O, Cu ４ O ３ , Cu ８ O and Cu ６４ Five types of Cu are known. ６４ O and Cu ８O is a stable phase such as CuO or Cu ２ Compared to O, the proportion of oxygen atoms is smaller, the stability is low, and it can be reduced to metallic copper with low energy. ６４ O and / or Cu ８ It is thought that by using O, low-temperature sintering at 250°C or less can be realized. ６４ O and Cu ８ O is specifically called "fine copper oxide", and other oxides such as CuO and Cu ２ O, Cu ４ O ３ Distinguish from.

[0005] For example, Patent Document 2 discloses Cu ６４ O and Cu as needed ２ O and coated with a carboxylic acid, ６４ O and Cu ２ Cu relative to the total mass of O ６４ Oxide-containing copper fine particles having an O mass ratio of 0.5 to 2.0 mass % are disclosed.

[0006] In recent years, electrical components have been required to have better electrical conductivity. In addition to the submicron oxide-containing copper particles described in Patent Document 2, which have improved surface necking characteristics due to a carboxylic acid coating, the following Patent Documents 3 and 4 are cited as conductive material technologies that utilize a nano-sized melting point depression. Patent Document 3 describes Cu ６４ O particles and Cu ８ O particles, and the Cu ６４ O particles and the Cu ８ Patent Document 4 discloses a copper oxide particle composition containing copper clusters having an average particle size of 0.1 nm or more and 1 nm or less, and copper oxide particles having an average particle size of more than 1 nm and 20 nm or less, and the copper oxide particles are Cu ６４ O particles and the Cu ８or copper clusters having an average particle size of 0.1 nm or more and 1 nm or less, copper oxide particles having an average particle size of more than 1 nm and 20 nm or less, and metallic copper particles having an average particle size of more than 20 nm and 1 μm or less, wherein the copper oxide particles are Cu ６４ O particles and the Cu ８ Mixed particles are shown, at least one of which is O particles.

[0007] International Publication No. 2016 / 166948 International Publication No. 2022 / 045252 Japanese Patent Application Laid-Open No. 2020-29392 Japanese Patent Application Laid-Open No. 2020-100893

[0008] In all of Patent Documents 2 to 4, the copper fine particles are relatively small in particle size (e.g., 1 μm or less). Because fine particles of submicron size or less have strong cohesion, a special manufacturing process for pulverizing and refining the agglomerated particles is required when processing (preparing) them into a coating paste. Furthermore, because fine particles of submicron size or less are easily oxidized, care must be taken to prevent this during the manufacturing process. Furthermore, adjusting the manufacturing process results in problems such as high manufacturing costs. The present disclosure has been made in light of the above circumstances, and one of its purposes is to provide fine copper oxide-containing particles that can be sufficiently sintered at low temperatures while having a large particle size (e.g., a long side exceeding 1 μm), and a sintering material containing the same.

[0009] Aspect 1 of the present invention is a composite material comprising a copper particle as a core and a Cu ６４ O and Cu ８ and a shell containing fine copper oxide of one or more of O, wherein the core copper particles have, in a scanning electron microscope image, when the maximum length of the particle is taken as the long side, an arithmetic mean value of the long side exceeds 1 μm, and when the arithmetic mean length of the particle orthogonal to the long side is taken as the thickness in the scanning electron microscope image, the ratio of the arithmetic mean length of the part orthogonal to the long side to the long side is 0.4 or less, the arithmetic mean value of the ratio of the thickness to the long side is 0.25 or less.

[0010] A second aspect of the present invention is the fine copper oxide-coated copper particles according to the first aspect, wherein the fine copper oxide is fine copper oxide particles having an arithmetic mean equivalent circle diameter of more than 1 nm and not more than 20 nm.

[0011] A third aspect of the present invention is the finely oxide-coated copper particles according to the first or second aspect, wherein, in a scanning electron microscope image of the core copper particles, the arithmetic mean value of the fractal dimension of the particle surface roughness is 1.00 to 1.05.

[0012] A fourth aspect of the present invention is a material for sintering, comprising the fine copper oxide-coated copper particles according to any one of the first to third aspects.

[0013] A fifth aspect of the present invention is the material for sintering according to the fourth aspect, which is a paste.

[0014] A sixth aspect of the present invention is a sintered body obtained by sintering the material for sintering according to the fourth or fifth aspect.

[0015] A seventh aspect of the present invention is a joined body formed by joining a plurality of materials with the sintering material according to the fourth or fifth aspect.

[0016] According to the present disclosure, it is possible to provide fine copper oxide-containing particles that can be sufficiently sintered even at low temperatures while having a large particle size (for example, a long side of more than 1 μm), and a sintering material containing the same.

[0017] FIG. 1 is a scanning electron microscope (SEM) image of raw copper particles. FIG. 2 is an SEM image of raw copper particles after processing (flattening treatment). FIG. 3 is an enlarged view of the SEM image of raw copper particles after processing (flattening treatment). FIG. 4 is an XRD pattern of raw copper particles (before processing (raw material) and after processing (flattened)), Levels 1 and 2 (after oxidation and after reaction (after synthesis)) of an example. FIG. 5 is a TEM image of particles of Level 2 of an example. FIG. 6 is an enlarged view of the TEM image of particles of Level 2 of an example. FIG. 7 is a TG-DTA measurement result of Level 1 of an example. FIG. 8 is a TG-DTA measurement result of Level 2 of an example. FIG. 9 is an XRD pattern of raw copper particles (raw material) and spherical particles after reaction (after synthesis) of a comparative example. FIG. 10 is a TEM image of spherical particles of a comparative example. FIG. 11 is a TG-DTA measurement result of spherical particles of a comparative example. FIG. 12 is a diagram showing the procedure for producing a sample for bond firing evaluation. FIG. 13A is a schematic diagram of a copper test piece used to produce the sample for bond firing evaluation. FIG. 13B is a schematic diagram of a metal mask used to produce the sample for bond firing evaluation. FIG. 13C is a schematic diagram illustrating hot pressing in a bond firing evaluation test. FIG. 13D is a schematic cross-sectional view illustrating a method for the bond firing evaluation test. FIG. 14 is a diagram showing the results of the bond firing evaluation test. FIG. 15 is an SEM image of a fracture surface after a bond firing evaluation test at level 1 of an example. FIG. 16 is an SEM image of a cross section after a bond firing evaluation test at level 1 of an example. FIG. 17 is an SEM image of a fracture surface after a bond firing evaluation test of spherical particles of a comparative example.

[0018] The present inventors have conducted extensive research to realize fine copper oxide-containing particles that can be sintered sufficiently even at low temperatures while increasing the particle size of the core copper particles (for example, to make the long side larger than 1 μm). As a result of their research, the present inventors have found that when conventional spherical copper particles are used as core copper particles, adjacent core copper particles are sintered at points. Therefore, simply increasing the particle size of the core copper particles to the micron level reduces the number of sintered contact points per unit volume, and also increases the voids associated with the interparticle gaps, resulting in a brittle structure of the sintered body. It has been found that when such particles are used for bonding purposes, sufficient adhesive strength cannot be obtained. Further research by the present inventors has revealed that when the core copper particles and Cu ６４O and Cu ８ and a shell containing fine copper oxide, which is one or more of O. The core copper particles have a long side exceeding 1 μm when the long side is the maximum length of the particle and the short side is the arithmetic mean length of the part perpendicular to the long side in a scanning electron microscope (SEM) image, and for particles in which the ratio of the short side to the long side in the SEM image is 0.4 or less, when the short side is the thickness, the arithmetic mean value (hereinafter also referred to as the "average first aspect ratio") of the ratio of the thickness to the long side (hereinafter also referred to as the "first aspect ratio") is a predetermined value or less, and are found to be useful as sintering materials. When such finely-coated copper particles are used as a sintering material, sintering is dramatically promoted by a reduction reaction accompanied by a change in the crystalline structure of the shell containing the finely-coated copper oxide. In addition, since the average first aspect ratio of the core copper particles is small, when the sintering material is applied to a substrate or the like, the long sides of the core copper particles tend to be oriented approximately parallel to the surface of the substrate (and the thickness direction is approximately perpendicular to the surface of the substrate), and even if the particle size of the core copper particles is large, they are stacked without (or with few) gaps, making it easier to suppress voids, and it is thought that this makes it possible to obtain a bonded body with sufficient adhesive strength. The requirements of this embodiment are described in detail below.

[0019] The fine copper oxide-coated copper particles according to this embodiment comprise a core copper particle and Cu ６４ O and Cu ８ and a shell containing fine copper oxide of one or more of O. In the core copper particles, when the maximum length of the particle is taken as the long side and the arithmetic mean length of the part perpendicular to the long side is taken as the short side in a scanning electron microscope (SEM) image, the long side exceeds 1 μm, and when the ratio of the short side to the long side in the SEM image is 0.4 or less, when the short side is taken as the thickness, the arithmetic mean value of the ratio of the thickness to the long side is 0.25 or less. This makes it possible to obtain a sintering material that has sufficient adhesive strength while increasing the particle size of the copper microparticles (for example, making the major axis greater than 1 μm).

[0020] The copper particles constituting the core may have a composition mainly composed of copper, for example, a copper content of 80% by mass or more, 90% by mass or more, or 95% by mass or more. The composition preferably consists of copper and inevitable impurity elements. This can improve the conductivity of the sintered body. The total amount of inevitable impurity elements may be, for example, 1.0% by mass or less. The size and shape of the copper particles constituting the core are not particularly limited as long as they satisfy the requirements of this embodiment.

[0021] Cu ６４ O and Cu ８ Regarding the shell containing copper oxide, which is one or more of Cu, as in the prior art, ６４ O particles and Cu ８ In the case of a mixture of fine copper oxide particles, which are at least one of copper oxide particles, metallic copper particles, and copper clusters, it has been difficult to uniformly disperse these. In particular, when the fine copper oxide particles are fine particles with an average particle size of 20 nm or less, the fine particles tend to aggregate and are difficult to disperse. In contrast, the fine copper oxide-coated copper particles according to this embodiment have a Cu ６４ O and Cu ８ The copper oxide particles have a structure (core-shell structure) in which one or more of the copper oxides, O, are attached to the surface of the copper metal particles as a shell-like coating, for example, and the dispersion problem is resolved. Furthermore, during sintering, the Cu on the particle surface is easily removed. ６４ O and the like are easily reduced, promoting sintering between particles.

[0022] Cu forming the shell ６４ O and Cu ８ The copper oxide, which is one or more of CuO, may be in the form of a film or a plurality of particles. The thickness of the shell (the thickness of the film or the thickness of the plurality of particles) may be, for example, more than 1 nm and 20 nm or less. Cu ６４ O and Cu ８The shell containing fine copper oxide, which is one or more of O, is reduced to copper by sintering, but its crystallinity is not as high as that of the core copper particles, so if the shell is too thick, there is a concern that the mechanical strength and electrical conductivity will decrease. From these perspectives, the shell thickness is preferably 20 nm or less as described above. The fine copper oxide is preferably a plurality of particles, which can have a certain degree of fluidity during sintering and make it easier to fill voids, making it easier to sinter at low temperatures. Note that the plurality of particles may be arranged in a single particle or multiple particles in the thickness direction. When the fine copper oxide is a plurality of particles, the arithmetic mean value of the circle-equivalent diameters of the particles (primary particles) (hereinafter also referred to as the "average particle size") may be, for example, more than 1 nm and 20 nm or less, preferably more than 1 nm and 10 nm or less. The average particle size can be obtained, for example, by obtaining a TEM image of the fine copper oxide-coated copper particles, randomly selecting at least 50 or more particles from the TEM image, determining the circle-equivalent diameters, and calculating the arithmetic mean value. Furthermore, when the fine copper oxide is a plurality of particles, Cu ８ O and Cu ６４ With respect to one or more selected from the group consisting of Cu and O, the crystallite diameter measured by the Scherrer method is preferably more than 1 nm and not more than 20 nm, more preferably more than 1 nm and not more than 10 nm. ８ O and Cu ６４ For each of O, the crystallite diameter measured by the Scherrer method is more preferably more than 1 nm and not more than 20 nm, and even more preferably more than 1 nm and not more than 10 nm. The XRD pattern measured by the Scherrer method is obtained by powder X-ray diffraction (X-ray source: CuKα radiation).

[0023] The shell contains Cu ６４ O and Cu ８ In addition to the fine copper oxide, which is one or more of O, for example, CuO, Cu ２ It is acceptable for copper oxides such as CuO and CuO to be present in trace amounts at a level that does not impair sinterability and electrical conductivity. ２ The shell preferably does not contain copper oxide such as Cu. ６４ O and Cu ８O, and more preferably Cu ６４ O or Cu ６４ O and Cu ８ It is formed from copper oxide consisting of O.

[0024] In the fine copper oxide-coated copper particles according to this embodiment, when the maximum length of the particle is taken as the long side, the arithmetic mean value of the long side exceeds 1 μm in an SEM image of the core copper particle. By satisfying this requirement, a step of pulverizing and fining aggregated particles is not required during processing into a coating paste, thereby reducing production costs. The upper limit of the arithmetic mean value of the long side is not particularly limited, but may be, for example, 50 μm or less. The arithmetic mean value of the long side can be obtained, for example, by obtaining an SEM image of the fine copper oxide-coated copper particles, randomly selecting 10 or more particles from the SEM image, determining the long sides, and calculating the arithmetic mean value. The SEM image may be observed under any observation conditions as long as the shape of the core copper particle can be clearly confirmed. For example, a secondary electron image (SEI) may be obtained under imaging conditions of an acceleration voltage of 15 kV and a magnification of 5000x. The long side of the core copper particle from the finely oxide-coated copper particle may be measured directly from an SEM image, or the long side may be determined by measuring the maximum length of the finely oxide-coated copper particle from an SEM image and subtracting from that value the thickness of the finely oxide shell (the thickness of the coating or the thickness of multiple particulate matter) measured by TEM or the like.

[0025] In the SEM image of the finely oxide-coated copper particles according to this embodiment, the maximum length of the core copper particle is defined as the long side, and the arithmetic mean length of the portion perpendicular to the long side is defined as the short side. For particles with a ratio of the short side to the long side of 0.4 or less, the short side is defined as the thickness. The arithmetic mean value of the thickness (first aspect ratio) relative to the long side (average first aspect ratio) is 0.25 or less. This ensures that when the sintering material is applied to a substrate, the long sides of the core copper particles are oriented substantially parallel to the surface of the substrate (and the thickness direction is substantially perpendicular to the surface of the substrate). Even large core copper particles with an arithmetic mean long side length exceeding 1 μm are stacked without gaps, allowing for a large sintered surface between particles and reducing voids, resulting in a bonded structure with sufficient adhesive strength. The arithmetic mean length of the portion perpendicular to the long side (i.e., the short side) can be obtained by randomly selecting three or more points perpendicular to the long side from the SEM image and calculating the arithmetic mean length. The lower limit of the average first aspect ratio is not particularly limited, but may be, for example, 0.01 or more, 0.05 or more, or 0.10 or more. The average first aspect ratio can be obtained, for example, by obtaining an SEM image of the fine copper oxide-coated copper particles, randomly selecting 10 or more particles from the SEM image, determining the long side and thickness, and calculating the first aspect ratio (thickness / long side) and its arithmetic average value. The SEM image can be observed under any observation conditions as long as the shape of the core copper particles can be clearly confirmed. For example, the SEM image is a secondary electron image (SEI) obtained under imaging conditions of an acceleration voltage of 15 kV and a magnification of 5000x.

[0026] In the micro-oxide-coated copper particles according to this embodiment, the average ratio of the short side to the long side (hereinafter also referred to as the "second aspect ratio") is preferably 0.40 or more, but is not particularly limited thereto, when the maximum length of the particle is the long side and the arithmetic mean length of the portion perpendicular to the long side is the short side. This facilitates surface contact between the surface of the substrate or the like and between particles and between individual particles when the micro-oxide-coated copper particles are applied to a substrate or the like, thereby ensuring a wide sintered area for each particle during sintering while further suppressing voids. The upper limit of the average second aspect ratio is not particularly limited and can be 1.00 or less. The average second aspect ratio can be obtained, for example, by obtaining an SEM image of the micro-oxide-coated copper particles, randomly selecting 10 or more particles from the SEM image, determining the long side and short side, and calculating the second aspect ratio (short side / long side) and its arithmetic mean value. The SEM image may be taken under any observation conditions as long as the shape of the core copper particle can be clearly confirmed, but for example, a secondary electron image (SEI) is taken under imaging conditions of an acceleration voltage of 15 kV and a magnification of 5000. The surface SEM image is a secondary electron image (SEI) and is taken under imaging conditions of an acceleration voltage of 15 kV and a magnification of 5000.

[0027] The finely oxide-coated copper particles according to this embodiment preferably have smooth upper and lower base surfaces perpendicular to the thickness direction of the core copper particle. This facilitates surface contact between the surface of the substrate and the particles, and between the particles themselves, ensuring a wide sintering area for each particle during sintering while suppressing voids. As a result, a sintered body with a strong structure can be obtained, resulting in a bonded body with high adhesive strength. As an index of particle smoothness, the arithmetic mean value of the fractal dimension of the particle surface is preferably 1.00 to 1.05. The arithmetic mean value of this ratio can be determined, for example, by obtaining an SEM image capturing the thickness direction of the finely oxide-coated copper particles, randomly selecting 10 or more particles from the SEM image, creating surface roughness curves for the upper and lower base surfaces perpendicular to the thickness direction of the particles, and then using image processing software (ImageJ 1.54 g, manufactured by NIH) to calculate the fractal dimension using the box counting method. The box sizes used in the fractal dimension calculation are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 μm per side. The SEM image can be observed under any observation conditions as long as the shape of the core copper particle can be clearly confirmed. For example, a secondary electron image (SEI) is obtained under imaging conditions of an acceleration voltage of 15 kV and a magnification of 5000x. Furthermore, for the surface roughness curves of the upper and lower surfaces of the particle, particles with a clear contour in the thickness direction are selected, and the contour of the long side (the white bright line observed in the secondary electron image) caused by the edge effect perpendicular to the thickness direction is regarded as the surface roughness curve of the upper and lower surfaces of the particle, and these surface roughness curves are created. For example, particles that can be used as particles having a thickness direction captured in an SEM observation image of finely oxide-coated copper particle powder can have a ratio of the short side to the long side of 0.4 or less, preferably about 0.2, where the long side is the maximum length of the particle and the short side is the arithmetic mean length of the part perpendicular to the long side.

[0028] By using the fine copper oxide-coated copper particles according to this embodiment, sufficient sintering can be achieved at low temperatures of 250°C or less, and even 200°C or less, under normal pressure (preferably a higher pressure).

[0029] The present disclosure also includes a sintering material containing the finely oxide-coated copper particles according to this embodiment. Examples of the sintering material include a paste or ink containing the finely oxide-coated copper particles according to this embodiment, intended for forming a conductive film or the like. Known materials can be used as the dispersion medium contained in the paste or ink. Examples of such known materials include 2-(dimethylamino)ethanol, N-butyldiethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, diethanolamine, triethanolamine, 1-[bis(2-hydroxyethyl)amino]-2-propanol, and ethylenediamine-N,N,N',N'-tetraethanol. A bonded body with high adhesive strength can be obtained by, for example, applying a sintering material containing the finely oxide-coated copper particles according to this embodiment to the bonding surfaces of multiple materials, such as metals (pure metals, alloys), ceramics, etc., and bonding them together. The sintered body according to this embodiment is obtained by sintering a sintering material containing the finely oxide-coated copper particles according to this embodiment. The bonded body according to this embodiment is obtained by bonding multiple materials together with a sintering material containing the finely oxide-coated copper particles according to this embodiment.

[0030] The method for producing fine copper oxide-containing particles according to this embodiment includes: processing raw copper particles so that, when the maximum length of the particles is taken as the long side in an SEM image, the arithmetic mean value of the long side exceeds 1 μm, and when the arithmetic mean ratio of the arithmetic mean length of the portion perpendicular to the long side to the long side in the SEM image is 0.4 or less, when the arithmetic mean length is taken as the thickness of the particles, the arithmetic mean ratio of the thickness to the long side is 0.25 or less; and mixing the raw copper particles with a solution containing a solvent, an amine compound, and a complexing agent, and then adding a reducing agent to cause a reaction. If necessary, the raw copper particles after the processing and before the reaction may be subjected to an oxidation treatment, or cuprous oxide (Cu ２ Alternatively, copper oxide particles (CuO) or copper oxide particles (CuO) may be added. The fine copper oxide-coated copper particles according to this embodiment can be obtained by the above method, and the fine copper oxide-coated copper particles may be particles each having a plurality of fine copper oxide particles contained in the shell. The conditions for the production method according to this embodiment will be described in detail below.

[0031] [Processing Raw Copper Particles] The raw copper particles are processed (hereinafter sometimes referred to as "flattening") so that, in an SEM image, the arithmetic mean value of the long sides exceeds 1 μm and the arithmetic mean ratio of the thickness to the long sides is 0.25 or less. As a processing (flattening) method, the raw copper particles can be processed using a thin-film swirling high-speed mixer to adjust them to particles having the above dimensions (and the arithmetic mean values ​​of the average second aspect ratio and fractal dimension according to an embodiment of the present invention). Examples of thin-film swirling high-speed mixers that can be used include the Filmix 56-L manufactured by Primix. A peripheral speed of 5 to 50 m / s and a processing time of 10 to 60 minutes are preferred to obtain particles having the above dimensions. Other methods, such as bead milling or ball milling, may also be used. In this case, for example, by selecting media with a diameter at least 10 times the particle size of the raw copper particles, particles having the above dimensions can be obtained efficiently. The method of flattening is not limited to these, and various methods such as rolling using a three-roll mill can be used.

[0032] The method for obtaining the raw copper particles is not particularly limited, and for example, commercially available products can be used. The size of the raw copper particles before processing can be such that the arithmetic mean value of the long sides in an SEM image is greater than 1 μm, preferably greater than 2 μm. The shape of the raw copper particles before processing is not particularly limited, but from the viewpoint of cost, it is preferable to use dendritic copper particles produced by, for example, an electrolytic method.

[0033] [Oxidation Treatment Step] The surface of the raw material copper particles is formed with CuO and Cu. ２ Copper oxide (preferably Cu) containing one or more of O ２ A copper oxide coating consisting of CuO may be present due to natural oxidation or the like. In this embodiment, an oxidation treatment may be performed as needed so that the copper oxide coating of the raw copper particles is larger than the natural oxide coating. Examples of the oxidation treatment method include a method of heating in water and a method of heating in the atmosphere. By performing the oxidation treatment, for example, the CuO and CuO content in the raw copper particles may be reduced. ２The proportion of copper oxide containing one or more of O can be 1 mass % or more. ６４ O and Cu ８ When it is desired to form a thick shell containing fine copper oxide, which is one or more of O, the raw material particles may be actively oxidized. In this case, if the amount of copper oxide on the surface of the raw material particles is too large, Cu may be present in the core copper particle. ６４ O and Cu ８ The shell containing copper oxide, which is one or more of Cu, is less likely to adhere. ６４ O and Cu ８ The shell containing fine copper oxide, which is one or more of CuO, has lower crystallinity when sintered at low temperatures compared to the core copper particles with high crystallinity, and therefore, if the shell is thick, there is a concern that the mechanical strength and / or electrical conductivity may decrease. ２ The proportion of copper oxide containing one or more of CuO and O is preferably 10 mass % or less. ２ The same effect can be obtained by adding copper oxide particles containing one or more of O in the reaction step described in the next section. In this case, too, the proportion of the copper oxide particles added to the raw copper particles is preferably 10 mass% or less.

[0034] [Reaction step] The raw copper particles after processing (or oxidation treatment) are mixed with a solution containing a solvent, an amine compound, and a complexing agent, and then a reducing agent is added to react (synthesize). Instead of oxidizing the raw copper particles, CuO and Cu ２ Alternatively, copper oxide particles containing one or more of O may be added. The complex-forming agent and the like necessary for this reaction will be described below.

[0035] (Complexing Agent) In this embodiment, a complexing agent is reacted with copper oxide contained in the raw copper particles after processing (or oxidation treatment), or copper oxide added as particles, to form copper complex ions. By ionizing the copper in the raw copper particles in this way, the rate of reduction by a reducing agent can be significantly faster than the reduction of solid copper oxide. Examples of the complexing agent include carboxylic acids. Examples of carboxylic acids include formic acid, saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, and terpene carboxylic acids. These may be monocarboxylic acids or dicarboxylic acids. These may be used alone or in combination of two or more. The aliphatic monocarboxylic acid may be either linear or branched, and may be either saturated or unsaturated aliphatic monocarboxylic acids. Examples of linear saturated aliphatic monocarboxylic acids include acetic acid (2 carbon atoms), propionic acid (3 carbon atoms), butyric acid (4 carbon atoms), valeric acid (5 carbon atoms), caproic acid (6 carbon atoms), enanthic acid (7 carbon atoms), caprylic acid (8 carbon atoms), pelargonic acid (9 carbon atoms), capric acid (10 carbon atoms), lauric acid (12 carbon atoms), myristic acid (14 carbon atoms), palmitic acid (16 carbon atoms), margaric acid (17 carbon atoms), and stearic acid (18 carbon atoms).

[0036] The aliphatic dicarboxylic acid may be either linear or branched, and may be either saturated or unsaturated. The aliphatic dicarboxylic acids may be used alone or in combination of two or more. Examples of aliphatic dicarboxylic acids include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,0-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, brassylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, thapsic acid, 1,15-pentadecanedicarboxylic acid, and 1,16-hexadecanedicarboxylic acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, and trimesic acid. Terpene carboxylic acids that can be used include those contained in rosin. Examples include abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, and desidroabietic acid.

[0037] Among these, it is preferable to use acetic acid, which is easy to handle and easy to treat after the reaction.

[0038] The amount of the complexing agent used in the reaction is not particularly limited. ６４ O and Cu ８ From the viewpoint of promoting the formation of copper complex ions to promote the generation of O, the molar ratio of the amount of copper contained in the starting material particles is preferably 0.05 to 15 times.

[0039] (Amine Compound) A compound having an amino group (hereinafter referred to as "amine compound") is added as a protective agent. The amine compound also contributes to the formation of copper complex ions. The amine compound is not particularly limited, and it is preferable to use, for example, alkanolamine, diamine, aminocarboxylic acid, etc. Among them, it is more preferable to use alkanolamine. Examples of alkanolamine include 2-amino-1-butanol, 1-amino-2-propanol, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-hydroxymethyl-1,3-propanediol, 1,3-diamino-2-propanol, 1-amino-2-butanol, and 2-aminoethanol.

[0040] The amount of the amine compound used in the reaction is not particularly limited. ６４ O and Cu ８ From the viewpoint of promoting the generation of O, the molar ratio of the amine compound to the copper contained in the raw material particles is preferably 0.1 or more. The molar ratio may be, for example, 20 or less.

[0041] (Solvent) The solvent is not particularly limited, and examples thereof include polyhydric alcohols such as ethylene glycol, lower alcohols such as methanol, ethanol, and 2-propanol, ketones such as acetone, and water.

[0042] (Reducing Agent) The reducing agent is not particularly limited, and examples thereof include hydrazine-based reducing agents such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, and hydrazine hydrate, as well as citric acid, ascorbic acids, and borohydrides such as sodium borohydride. The reducing agent may be added after the raw materials containing the raw material particles, complexing agent, amine compound, and solvent are charged and mixed. After adding the reducing agent, stirring may be carried out until the formation of the desired copper oxide is confirmed. In either production method, stirring is preferably carried out until the reducing agent disappears, allowing the reaction to proceed sufficiently.

[0043] (Cooling during reaction) In the production method according to the present embodiment, for example, when hydrazine is used as a reducing agent, heat is generated by the addition of the reducing agent, such as a decomposition reaction of hydrazine, and the temperature of the reaction solution may rise. ６４ O and Cu ８ From the viewpoint of suppressing the reduction of O to metallic copper, it is preferable to provide a temperature control means, such as cooling the reaction solution, so that the reaction proceeds at 50° C. or less. For example, as shown in the examples described later, it is preferable to add the reducing agent while the reaction vessel is in a room-temperature water bath.

[0044] (Atmosphere during reaction) In the manufacturing method according to this embodiment, the atmosphere during the reaction is limited to an oxygen-containing atmosphere such as the air, and it is necessary to always expose the reaction vessel to the oxygen-containing atmosphere during the reaction. When an inert gas atmosphere such as nitrogen gas or argon gas is used, or when the reaction vessel is sealed even in the air, Cu ６４ O or Cu ８ This is not preferable because the reaction of forming oxides to O does not proceed and metallic copper particles are formed.

[0045] (Other Steps) The manufacturing method of this embodiment may further include steps other than those described above. For example, Cu obtained by the reduction may be ６４ O and Cu ８ The method may include a step of recovering fine copper oxide-containing particles by, for example, centrifuging and / or filtering a slurry containing particles having fine copper oxide, which is one or more of O, followed by a purification step, a drying step, etc. In the purification step, purification is preferably performed using a washing solvent. The washing solvent is not particularly limited, and for example, an organic solvent such as N,N-dimethylacetamide, toluene, or hexane can be used.

[0046] As described above, the method for producing fine copper oxide-coated copper particles according to this embodiment has been described. However, a person skilled in the art who understands the desired properties of the fine copper oxide-coated copper particles according to this embodiment may, through trial and error, find a method for producing fine copper oxide-coated copper particles according to this embodiment other than the above-described production method.

[0047] The method for producing a sintered body according to this embodiment includes the steps of preparing a sintering material containing the fine copper oxide-coated copper particles according to this embodiment and sintering the sintering material. The step of preparing the sintering material can be performed by appropriately mixing the fine copper oxide-coated copper particles according to this embodiment with a dispersion medium. The dispersion medium is not particularly limited and any known dispersion medium can be used, such as 2-(dimethylamino)ethanol, N-butyldiethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, diethanolamine, triethanolamine, 1-[bis(2-hydroxyethyl)amino]-2-propanol, or ethylenediamine-N,N,N',N'-tetraethanol. The step of sintering the sintering material can be performed using a known method. The sintering method is not particularly limited, but can be, for example, sintering under atmospheric pressure (preferably at a higher pressure) at a low temperature of 250°C or less, or even 200°C or less. The method for producing a joined body according to this embodiment includes the steps of preparing a sintering material containing the fine copper oxide-coated copper particles according to this embodiment and joining multiple materials using the sintering material. The process of preparing a sintering material containing fine copper oxide-coated copper particles according to this embodiment is as described above. The process of joining multiple materials using the sintering material is not particularly limited, but can be carried out by, for example, applying the sintering material to the joining surfaces of multiple materials, such as metals (pure metals, alloys), ceramics, etc., and joining them. The joining conditions can be, for example, sintering the sintering material present between the multiple materials under atmospheric pressure (preferably higher pressure) at a low temperature of 250°C or lower, or even 200°C or lower.

[0048] The present embodiment will be described in more detail below with reference to examples. The present embodiment is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present embodiment.

[0049] (Step of processing raw copper particles) Kanto Chemical copper particles 07439-01 (particle size 75 μm to 150 μm, 100 mesh to 200 mesh provided by the manufacturer) were used as raw copper particles. 70 g of these particles were mixed with 60 ml of ethanol (manufactured by Japan Alcohol Sales) as a dispersion medium, and then processed intermittently for 30 minutes at a peripheral speed of 30 m / s using a thin film swirling high-speed mixer (Filmix 56-L manufactured by Primix). The amount of ethanol that volatilized during processing was appropriately replaced. The supernatant of the resulting solution was removed and dried to obtain processed raw copper particles.

[0050] FIG. 1 is an SEM image of raw copper particles before processing, obtained using a scanning electron microscope (JEOL JSM-6701F). As shown in FIG. 1, the raw copper particles before processing were dendritic copper particles with long sides of approximately 10 to 100 μm. FIG. 2 is an SEM image of raw copper particles after processing, obtained using the scanning electron microscope. FIG. 3 is an example of an enlarged view of particles in which the ratio of the short side to the long side is 0.4 or less, where the long side is the maximum length of the particle and the arithmetic mean length of the portion perpendicular to the long side is the short side. Particles such as those shown in FIG. 3 were used to calculate the parameters described below as particles captured in the thickness direction. Note that the SEM images are secondary electron images (SEI), and were taken at an accelerating voltage of 15 kV. Figure 2 was taken at a magnification of 500x for Figure 2 and 5000x for Figure 3. As shown in FIG. 2, it was found that the raw copper particles after processing were flattened by processing. A plurality of SEM images such as those shown in FIG. 3 were obtained, and the arithmetic mean value of the long sides, the average first aspect ratio, the average second aspect ratio, and the arithmetic mean value of the fractal dimension were determined by the method described in detail in the "Description of Embodiments." The results were as follows: arithmetic mean value of the long sides: 18.9 μm, average first aspect ratio: 0.18, average second aspect ratio: 0.50, and arithmetic mean value of the fractal dimension, which indicates the surface roughness of the upper and lower surfaces of the particles: 1.014.

[0051] XRD patterns (Figure 4) of the raw copper particles before (raw material) and after (flattened) processing were obtained using a powder X-ray diffractometer (XRD, Rigaku Miniflex II, D / teX Ultra). Measurements were performed using Cu-Kα radiation at a scan rate of 20° (2θ) min. －１ I went there.

[0052] (Oxidation Treatment Step) The processed raw copper particles were subjected to an oxidation treatment. In Level 1, 114 g of the processed raw copper particles were mixed with 1 L of pure water and boiled in air for 42 hours. The supernatant of the mixture was then removed and dried. An XRD pattern (FIG. 4, Level 1, after oxidation) was obtained for the obtained particles using a powder X-ray diffractometer (XRD, Rigaku Miniflex II, D / teX Ultra). The measurement was performed using Cu-Kα radiation at a scan rate of 20° (2θ) min －１ As a result of carrying out RIR quantitative analysis from the XRD pattern, it was found that 2 mass % of Cu ２ The presence of an oxide film of O was confirmed. In level 2, 120 g of the processed raw copper particles was placed in a muffle furnace (FT-101FM manufactured by Furutech) and heated at 200°C for 2 hours in air. The XRD pattern (Figure 4, level 2 after oxidation) of the obtained particles was obtained using the powder X-ray diffractometer. The measurement was performed using Cu-Kα radiation at a scan rate of 20° (2θ) min －１ As a result of carrying out RIR quantitative analysis from the XRD pattern, it was found that 5 mass % of Cu ２ The presence of an oxide film of O was confirmed.

[0053] (Reaction Step) Fine copper oxide-coated copper microparticles of Levels 1 and 2 were synthesized by the following reaction. 1,390 g (22.4 mol) of ethylene glycol (Kanto Chemical) as a solvent, 1,182 g (15.7 mol) of 1-amino-2-propanol (Kanto Chemical) as a protective agent, and 473 g (7.87 mol) of acetic acid (Junsei Chemical) as a complexing agent were placed in a reaction vessel and stirred thoroughly, followed by the addition of 100 g (1.57 mol) of the particles after oxidation treatment of Levels 1 or 2. With the reaction vessel in a room-temperature water bath, 788 g (15.7 mol) of hydrazine monohydrate (Kanto Chemical) as a reducing agent was added, and the mixture was allowed to react while stirring at 1,100 rpm. The reaction was carried out in the air. After the reaction, the mixture was purified by centrifugation multiple times using N,N-dimethylacetamide, toluene, and hexane to obtain a slurry containing the product. The yield of fine copper oxide-coated copper microparticles in the slurry was calculated using the following formula (1):

[0054]

[0055] In formula (1), Y: weight of particles in the slurry (g) M ｓ V: Slurry weight (g) ｓ : Slurry volume (cm ３ ) ρ ｍ : Solvent density (g / cm ３ ) ρ Ｃｕ : Copper density (g / cm ３ )

[0056] (X-ray Diffraction Measurement) Using the slurry containing the product, X-ray diffraction measurement was carried out using a powder X-ray diffractometer (XRD, Rigaku MiniFlex II, D / teX Ultra). The measurement was carried out using Cu-Kα radiation at a scan rate of 20° (2θ) min －１ The results are shown in Figure 4 (after synthesis).

[0057] (Electron Microscope Observation) The product obtained by synthesis using the raw material copper particles of Level 2 was observed with a transmission electron microscope (TEM, JEM-2000FX manufactured by JEOL Ltd., accelerating voltage 200 kV). The results are shown in Figs. 5 and 6.

[0058] From the X-ray diffraction measurement and the electron microscope observation, the following was confirmed. From the XRD patterns (after synthesis) shown in FIG. 4, both Levels 1 and 2 have Cu. ６４ In particular, in level 2 (5 mass% oxidation), the peak of Cu ６４ O and Cu ８ The peak of O was clearly confirmed. In the TEM image shown in Figure 5, the particles of level 2 have a core copper particle surrounded by a shell of minute particles, and from the enlarged view of the shell portion shown in Figure 6, it was confirmed that the particle size of the nanoparticles constituting the shell was 2 to 10 nm (the arithmetic mean value was also within this range). From the XRD pattern of this particle (Figure 3, level 2, after synthesis), the crystallite diameter measured by the Scherrer method was 2 to 10 nm. ８ O is 3.8 nm, Cu ６４ The particle diameter was 2.1 nm, which roughly matched the size of the nanoparticles constituting the shell observed by TEM. ６４ O and Cu ８It is believed that the nanoparticles are covered with a shell of O nanoparticles.

[0059] (Production of paste containing finely oxide-coated copper microparticles) The two levels of finely oxide-coated copper microparticles and hexane slurry synthesized were centrifuged to remove the supernatant, thereby obtaining a wet cake of finely oxide-coated copper microparticles. 15 parts by mass of triethanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a paste solvent to 85 parts by mass of copper particles in the wet cake calculated by formula (1), and a small amount of ethanol was added to adjust the solubility of triethanolamine. After mixing with a vortex mixer (manufactured by Heathrow Scientific), the mixture was stirred for 30 seconds with a planetary mixer (AR-100 manufactured by Thinky). The mixture was then held at room temperature in a vacuum until no weight change occurred, and the ethanol was removed to obtain two levels of paste (copper die attach paste). The obtained paste was subjected to thermogravimetry and differential thermal analysis (TG-DTA) at a heating rate of 5 ° C. / min under a 3% hydrogen / nitrogen mixed gas using a TG / DTA simultaneous measurement device (manufactured by Shimadzu Corporation). The results are shown in Figure 7 (Level 1) and Figure 8 (Level 2). As shown in Figures 7 and 8, from the weight loss indicated by TGA, it was confirmed that each paste contained 86.0 mass% of finely oxide-coated copper particles in Level 1 (2 mass% oxidation) and 84.7 mass% in Level 2 (5 mass% oxidation).

[0060] (Synthesis of spherical copper oxide-coated copper microparticles) As a comparative example, spherical copper oxide-coated copper microparticles not satisfying the requirements of this embodiment were synthesized as follows. 733 g (11.8 mol) of ethylene glycol (manufactured by Kanto Chemical Co., Ltd.) as a solvent, 591 g (7.87 mol) of 1-amino-2-propanol (manufactured by Kanto Chemical Co., Ltd.) as a protective agent, and 236 g (3.93 mol) of acetic acid (manufactured by Junsei Chemical Co., Ltd.) as a complexing agent were placed in a reaction vessel and stirred thoroughly. 100 g (1.57 mol) of spherical copper particles (HXR-Cu, particle size 2.5 μm, manufactured by Nippon Atomize Kako) as a starting material and 2 g (2% by mass relative to the copper particles) of cuprous oxide (manufactured by Furukawa Chemical Co., Ltd.) as a copper oxide source were added. With the reaction vessel in a room temperature water bath, 394 g (7.87 mol) of hydrazine monohydrate (manufactured by Kanto Chemical Co., Ltd.) as a reducing agent was added, and the mixture was allowed to react while stirring at 1100 rpm. After the reaction, purification was carried out by centrifugation multiple times using N,N-dimethylacetamide, toluene, and hexane to obtain a slurry containing the product.

[0061] X-ray diffraction measurement was carried out on the slurry containing the product using a powder X-ray diffractometer (XRD, Rigaku MiniFlex II, D / teX Ultra). The measurement was carried out using Cu-Kα radiation at a scan rate of 20° (2θ) min －１ The results are shown in Figure 9 (after synthesis). X-ray diffraction measurement was also carried out on the spherical copper particles (raw material) used as the raw material. From the XRD pattern shown in Figure 9, it can be seen that Cu was extracted from the synthesized particles. ６４ O and Cu ８ The O peak was confirmed.

[0062] The obtained product was observed with a transmission electron microscope (TEM, JEOL Ltd., JEM-2000FX, accelerating voltage 200 kV). An example of a TEM image is shown in FIG. 10. From the TEM image, it was confirmed that the periphery of a spherical particle serving as a core was covered with a shell of minute particles. Since the particles were spherical, the average first aspect ratio was estimated to be at least greater than 0.25 (1 or less), which did not satisfy the requirements of this embodiment.

[0063] (Production of a paste containing spherical copper oxide-coated copper microparticles) The supernatant was removed from a slurry of the synthesized spherical copper oxide-coated copper microparticles and hexane by centrifugation to obtain a wet cake of spherical copper oxide-coated copper microparticles. To 90 parts by mass of copper particles in the wet cake calculated by formula (1), 10 parts by mass of triethanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a paste solvent, and a small amount of ethanol was added to adjust the solubility of triethanolamine. The mixture was mixed using a vortex mixer (manufactured by Heathrow Scientific), and then stirred for 30 seconds using a planetary centrifugal mixer (AR-100, manufactured by Thinky). The mixture was then held at room temperature in a vacuum until no weight change occurred, and the ethanol was removed to obtain a paste (copper die attach paste). The obtained paste was subjected to thermogravimetry and differential thermal analysis (TG-DTA) at a heating rate of 5°C / min under a 3% hydrogen / nitrogen mixed gas using a TG / DTA simultaneous measurement device (manufactured by Shimadzu Corporation). The results are shown in Figure 11. As shown in Figure 11, it was confirmed from the weight loss indicated by TGA that the obtained paste contained 89.0 mass % of fine copper oxide-coated copper particles.

[0064] (Bonding and Firing Evaluation) Two copper test pieces were bonded together using the paste, and a bonded and sintered bonding evaluation sample was prepared by sintering the paste, and the adhesive strength was measured.

[0065] 1. Preparation of Samples for Bonding and Sintering Evaluation The procedure for preparing samples for bonding and sintering evaluation is as shown in FIG. 12 . First, circular copper test pieces, Copper Test Piece 1 with a diameter of 12 mm and Copper Test Piece 2 with a diameter of 5 mm, were cut from a 5 mm thick oxygen-free copper plate (C1020P) as shown in FIG. 13A . Copper test pieces 1 and 2 were prepared. The surface of each copper test piece was polished with waterproof abrasive paper (SiC paper) P4000, then mirror-finished with a polishing cloth soaked in a suspension of 0.5 μm alumina powder, and degreased. Before applying the paste, each copper test piece was immersed in 2.5 M hydrochloric acid to remove the copper oxide film on the surface, thoroughly washed with pure water and methanol, and then dried.

[0066] Next, metal mask printing was performed. Specifically, a metal mask having an opening size of 5 mm in diameter × 0.15 mm in thickness, as shown in FIG. 13B, was used. As shown in FIG. 13C, the paste (paste containing copper fine particles coated with fine copper oxide) 3 was applied to the center of a 12 mm diameter copper test piece 1, and then bonded to a 5 mm diameter copper test piece 2. Then, a load of 15 MPa was applied to the two bonded copper test pieces in the direction of the arrow in FIG. 13C by hot pressing, and the temperature was rapidly increased to 200 ° C. at a rate of 90 ° C. / min. After reaching 200 ° C., the test pieces were held for 15 minutes. Then, the test pieces were removed from the hot press and rapidly cooled by water cooling to obtain a sample for bond firing evaluation. This series of operations was performed in a nitrogen atmosphere.

[0067] 2. Bonding and Sintering Evaluation Test (Adhesion Strength Measurement) The adhesive strength of the bonding and sintering evaluation sample was evaluated using a 5 kN materials testing machine (Shimadzu Corporation). Specifically, as shown in the schematic cross-sectional view of FIG. 13D , a load was applied parallel to the coated surface of the bonding and sintering evaluation sample fixed to the fixture 4 of the testing machine at a rate of 1 mm / min, and the breaking load of the copper test piece was measured as the adhesive strength. The results are shown in FIG. 14 . The vertical width of each measurement value in FIG. 14 indicates the variation in the results obtained from multiple measurements. As shown in FIG. 14 , the average adhesive strength was 30.3 MPa for Level 1 (2% by mass oxidation), which satisfied the requirements of this embodiment, and 26.4 MPa for Level 2 (5% by mass oxidation), which also satisfied the requirements of this embodiment, both of which were sufficient for practical use. However, the comparative example using spherical particles, which did not satisfy the requirements of this embodiment, showed a low value of 11.8 MPa.

[0068] FIG. 15 (Example, Level 1) shows an SEM image of the fracture surface of the bonded and sintered evaluation sample after testing. As shown in FIG. 15, in Level 1, which meets the requirements of this embodiment, adhesion marks were observed over the entire surface of the sintered body. FIG. 16 shows an SEM image of the cross section of the bonded and sintered evaluation sample of Level 1 after testing. The cross section was prepared by cutting the center of the bonded and sintered evaluation sample with a low-speed cutter (manufactured by BUEHLER). The observation image shown in FIG. 16 confirms that the sample was densely sintered in the thickness direction. FIG. 17 (Comparative Example, Spherical Particles) shows an SEM image of the fracture surface of the bonded and sintered evaluation sample after testing. As shown in FIG. 17, in the Comparative Example, which used spherical particles that did not meet the requirements of this embodiment, adhesion marks were observed only at the ends of the spherical particles, and similarly, sintering was only observed between the particles at the ends.

[0069] The fine copper oxide-containing particles according to this embodiment can be sufficiently sintered at atmospheric pressure (preferably higher pressure) at temperatures of 250°C or lower, even at temperatures as low as 200°C or lower. Therefore, the fine copper oxide-containing particles according to this embodiment can be used, for example, as circuit-forming materials for printed circuit boards (particularly flexible boards) and other microwiring materials, as well as for heat conduction applications such as die bonding materials for power semiconductors, as shown in this example. They can also be used as antistatic materials, electromagnetic wave blocking materials, infrared blocking materials, etc.

[0070] This application claims priority from Japanese Patent Application No. 2024-006167, filed January 18, 2024. Japanese Patent Application No. 2024-006167 is incorporated herein by reference.

[0071] 1, 2 Copper test piece 3 Paste containing copper fine particles coated with copper oxide 4 Fixing jig for testing machine

Claims

1. Copper particles as the core and a shell containing cuprous oxide which is one or more of Cu ６４ O and Cu ８ O, the cuprous oxide-coated copper particles, wherein the core copper particles have an arithmetic mean value of the major axis length exceeding 1 μm when the major axis length of the particles is the major axis in their scanning electron microscope image, and in the scanning electron microscope image, when the arithmetic mean length of the portion orthogonal to the major axis with respect to the major axis is 0.4 or less, the cuprous oxide-coated copper particles having an arithmetic mean value of the ratio of the thickness to the major axis of 0.25 or less when the arithmetic mean length is the thickness.

2. The copper suboxide-coated copper particles according to claim 1, wherein the copper suboxide is copper suboxide particles having an arithmetic mean value of the equivalent circle diameter exceeding 1 nm and not exceeding 20 nm.

3. The copper suboxide-coated copper particles according to claim 1 or 2, wherein in the scanning electron microscope image of the core copper particles, the arithmetic mean value of the fractal dimension of the particle surface roughness is 1.00 to 1.

05.

4. A sintering material containing the copper suboxide-coated copper particles according to any one of claims 1 to 3.

5. The sintering material according to claim 4, which is a paste.

6. A sintered body obtained by sintering the sintering material according to claim 4 or 5.

7. A joined body obtained by joining a plurality of materials with the sintering material according to claim 4 or 5.

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