Copper oxide-coated copper particles and sintering materials containing them, sintered bodies and joints using this sintering material

Abstract

A micro-coated copper oxide particle, comprising copper particles as a core and Cu-containing... 64 The shell of micro-copper oxide, which is one or more of O and Cu8O, wherein, in the scanning electron microscope image of the core copper particles, when the maximum length of the particle is set as the long side, the arithmetic mean of the long side is greater than 1 μm, and in the scanning electron microscope image, when the arithmetic mean length of the particles orthogonal to the long side is set as the thickness, the arithmetic mean of the thickness as a ratio of the long side to the long side is less than 0.4, the arithmetic mean of the thickness as a ratio of the long side to the long side is less than 0.25.

Description

Technical Field

[0001] This invention relates to micro-coated copper particles and sintering materials containing them, sintered bodies and joints using the sintering material. Background Technology

[0002] In recent years, printed electronics has garnered significant attention in printed circuit board (PCB) manufacturing due to its clean technology that eliminates the need for traditional exposure and etching processes and avoids the emission of harmful chemicals. This technology, known as printing, directly forms microwires using inkjet printing or other printing methods. Solder is used for bonding components, such as the substrate and components of semiconductor devices, and the interconnection of circuits. High-melting-point lead solder is commonly used as the bonding material in the bonding of power semiconductors and LSIs, which operate at temperatures above 150°C. However, with the emergence of silicon carbide (SiC)-based power semiconductors in recent years, the operating temperature of semiconductors has risen to 250–300°C, approaching the melting point of high-melting-point lead solder. Ensuring connection reliability and heat dissipation design have become critical challenges. Furthermore, with the strengthening of RoHS restrictions, lead-free bonding materials are needed. To date, techniques such as 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 discloses a silver microparticle composition that can achieve high bond strength at a low bonding temperature. However, silver microparticles are expensive, and the effect of wiring short circuits caused by ion migration is a concern. As an alternative to silver microparticles, inexpensive copper microparticles with high resistance to ion migration have attracted attention, but there is the problem that copper microparticles are difficult to sinter at low temperatures.

[0004] To address the aforementioned issues, the inventors have attempted to use copper oxides to obtain particles for low-temperature sintering. Known copper oxides include CuO, Cu₂O, Cu₄O₃, Cu₈O, and Cu. 64 There are five types of O. Among them, Cu 64 Compared to the stable phases CuO and Cu2O, O and Cu8O have a lower proportion of oxygen atoms and are less stable, allowing for reduction to metallic copper at low energy. Therefore, the use of Cu... 64 O and / or Cu8O are used to achieve low-temperature sintering below 250°C. Also, in this specification, Cu with a lower proportion of oxygen atoms... 64 O and Cu8O are specifically referred to as "micro-copper oxide" to distinguish them from other oxides such as CuO, Cu2O, and Cu4O3.

[0005] For example, Patent Document 2 discloses a copper microparticle containing an oxide, which comprises Cu 64 O and Cu2O as required, and coated with carboxylic acids, wherein Cu 64O relative to Cu, Cu 64 The total mass ratio of O and Cu2O is 0.5 to 2.0 by mass.

[0006] In recent years, electrical components have demanded superior conductivity. Besides the copper microparticles containing submicron oxides described in Patent Document 2, which improve surface necking characteristics through carboxylic acid coating, Patent Documents 3 and 4 also cite this as a conductive material technology that utilizes nanoscale dimensions to lower the melting point. Patent Document 3 discloses a copper oxide particle composition containing Cu 64 At least one of O particles and Cu8O particles, wherein the Cu 64 At least one of the O particles and the Cu8O particles has an average particle size of 20 nm or less. Additionally, Patent Document 4 discloses a mixed particle comprising copper clusters with an average particle size of 0.1 nm or more and 1 nm or less, and copper oxide particles with an average particle size greater than 1 nm and less than 20 nm, wherein the copper oxide particles are Cu... 64 At least one of the O particles and the Cu8O particles, or the mixed particles comprise copper clusters with an average particle size of 0.1 nm to 1 nm, copper oxide particles with an average particle size of 1 nm to 20 nm, and metallic copper particles with an average particle size of 20 nm to 1 μm, wherein the copper oxide particles are Cu 64 At least one of the O particles and the Cu8O particles.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2016 / 166948

[0010] Patent Document 2: International Publication No. 2022 / 045252

[0011] Patent Document 3: Japanese Patent Application Publication No. 2020-29392

[0012] Patent Document 4: Japanese Patent Application Publication No. 2020-100893 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] In patent documents 2-4, the particle sizes shown for copper microparticles are all relatively small (e.g., below 1 μm). Submicron-sized microparticles have strong agglomeration, requiring special manufacturing processes to pulverize and refine these agglomerated particles when processing (adjusting) them into a coating paste. Furthermore, since submicron-sized microparticles are prone to oxidation, this must be carefully controlled during the manufacturing process. Moreover, these manufacturing process adjustments also result in increased manufacturing costs.

[0015] In view of the above circumstances, the present invention is proposed, and one of its objectives is to provide a particle containing micro-copper oxide and a sintering material containing it, wherein the particle containing micro-copper oxide can be increased in size (e.g., the long side is greater than 1 μm) and can be fully sintered even at low temperature.

[0016] Problem-solving methods

[0017] Method 1 of the present invention is a micro-coated copper oxide copper particle, which has copper particles as a core and contains Cu. 64 A shell of micro-copper oxides, including O and Cu8O, wherein...

[0018] In the scanning electron microscope image of the said copper particles, when the maximum length of the particle is set as the long side, the arithmetic mean of the long side is higher than 1 μm. Furthermore, in the scanning electron microscope image, when the arithmetic mean length of the particles whose arithmetic mean length of the portion orthogonal to the long side is less than 0.4 is set as the thickness, the arithmetic mean of the thickness relative to the long side is less than 0.25.

[0019] In embodiment 2 of the present invention, copper particles coated with micro-copper oxide according to embodiment 1 are copper particles with an arithmetic mean of equivalent circle diameter greater than 1 nm and less than 20 nm.

[0020] In embodiment 3 of the present invention, copper particles coated with micro-copper oxide according to embodiment 1 or 2 are wherein, in the scanning electron microscope image of the copper particles, the arithmetic mean of the fractal dimension of the particle surface roughness is 1.00 to 1.05.

[0021] The fourth embodiment of the present invention is a sintering material, wherein it contains copper particles coated with micro-copper oxide as described in any one of embodiments 1 to 3.

[0022] In embodiment 5 of the present invention, the sintering material according to embodiment 4 is a paste.

[0023] Embodiment 6 of the present invention is a sintered body, wherein the sintering material described in Embodiment 4 or 5 is sintered.

[0024] The present invention, in embodiment 7, is a joint in which multiple materials are joined together by the sintering material described in embodiment 4 or 5.

[0025] The effects of the invention

[0026] According to the present invention, it is possible to provide particles containing micro-copper oxide and sintering materials containing the same, wherein the particles containing micro-copper oxide can be sintered fully even at low temperatures while increasing the particle size (e.g., making the long side higher than 1 μm). Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the raw copper particles.

[0028] Figure 2 It is an SEM image of the raw copper particles after processing (flattening).

[0029] Figure 3 This is a magnified SEM image of the raw copper particles after processing (flattening).

[0030] Figure 4 The images show the XRD patterns of the raw copper particles in the examples (before processing (raw material) and after processing (flattening)), and levels 1 and 2 (after oxidation and after reaction (after synthesis)).

[0031] Figure 5 This is a TEM image of the particles at level 2 of the embodiment.

[0032] Figure 6 This is a magnified view of the TEM image of the particles in level 2 of the embodiment.

[0033] Figure 7 This is the TG-DTA measurement result of level 1 in the embodiment.

[0034] Figure 8 This is the TG-DTA measurement result of level 2 in the embodiment.

[0035] Figure 9 These are the XRD patterns of copper particles (raw material) and spherical particles (after synthesis) from the comparative example.

[0036] Figure 10 This is a TEM image of a comparative example of spherical particles.

[0037] Figure 11 These are the TG-DTA measurement results for the spherical particles used in the comparative example.

[0038] Figure 12 This is a diagram showing the preparation steps of the sample for evaluation of bonding firing.

[0039] Figure 13AThis is a schematic diagram of a copper test piece used to prepare samples for evaluating the bonding firing process.

[0040] Figure 13B This is a schematic diagram of a metal mask used to create samples for evaluating the bonding process.

[0041] Figure 13C This is a schematic diagram illustrating the hot pressing process in the bonding firing evaluation test.

[0042] Figure 13D This is a schematic cross-sectional view illustrating the method of evaluating the bonding firing process.

[0043] Figure 14 This is a graph showing the results of the bonding firing evaluation test.

[0044] Figure 15 The image shows a SEM image of the fracture surface after the bonding firing evaluation test of Level 1 in the observation example.

[0045] Figure 16 This is an SEM image of the cross section after the bonding firing evaluation test of Level 1 in Example 1.

[0046] Figure 17 These are SEM images of the fracture surfaces of the comparative example spherical particles after the bonding and firing evaluation test. Detailed Implementation

[0047] The inventors have conducted intensive research to achieve micro-copper oxide particles that can be fully sintered at low temperatures while simultaneously increasing the particle size of the core copper particles (e.g., making the long side greater than 1 μm). Their research revealed that when existing 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 micrometer level reduces the number of sintering contact points per unit volume, and also increases the porosity of the interparticle gaps, resulting in a brittle sintered body. It is known that using such particles for bonding applications cannot achieve sufficient adhesive strength. Further research by the inventors has shown that a combination of copper particles as a core and Cu... 64Copper oxide-coated particles containing one or more of O and Cu8O, wherein the core copper particles, in their scanning electron microscope (SEM) images, when the maximum length of the particle is taken as the long side and the arithmetic mean length of the orthogonal portion thereto is taken as the short side, such that the long side is greater than 1 μm, and in the same SEM image, among particles where the ratio of the short side to the long side is 0.4 or less, when the short side is taken as the thickness, the arithmetic mean (hereinafter also referred to as the "average first aspect ratio") of the ratio of the thickness to the long side is below a specified value, are useful for sintering materials. When such micro-coated copper particles are used in sintering materials, the sintering process is significantly accelerated due to the reduction reaction that accompanies the change in the crystal structure of the shell containing micro-coated copper. Furthermore, since the average first aspect ratio of the core copper particles is small, when the sintering material is applied to a substrate, for example, the long side of the core copper particles is easily oriented approximately parallel to the surface of the substrate (and the thickness direction is approximately perpendicular to the surface of the substrate). Even if the particle size of the core copper particles is large, they can be stacked without gaps (with few gaps), and pores are easily suppressed. Therefore, it is believed that a bond with sufficient adhesive strength can be obtained.

[0048] The requirements of this embodiment will be described in detail below.

[0049] The micro-coated copper particles of this embodiment have copper particles as the core and contain Cu. 64 A shell of micro-copper oxide, selected from O and Cu8O, wherein the core copper particles, in their scanning electron microscope (SEM) images, have a long side greater than 1 μm when the maximum length of the particle is taken as the long side and the arithmetic mean length of the orthogonal portion thereto is taken as the short side, and in the SEM images, among particles where the ratio of the short side to the long side is 0.4 or less, the arithmetic mean ratio of the thickness to the long side when the short side is taken as the thickness is 0.25 or less. Thus, a sintering material can be obtained that still possesses sufficient adhesive strength even when the particle size of the copper microparticles is increased (e.g., the major axis is greater than 1 μm).

[0050] The composition of the copper particles constituting the core can be primarily copper, for example, with a copper content of 80% by mass or more, 90% by mass or more, or 95% by mass or more. Preferably, this composition consists of copper and unavoidable impurity elements. This improves the electrical conductivity of the sintered body. The total amount of unavoidable impurity elements can, for example, be 1.0% by mass or less. The size and shape of the copper particles constituting the core are not particularly limited as long as the requirements of this embodiment are met.

[0051] Regarding the presence of Cu 64A shell of one or more of O and Cu8O micro-copper oxides, for example, as in the prior art, in Cu 64 It is difficult to uniformly disperse at least one of the following: copper oxide particles, copper particles, or even mixtures of copper particles and copper clusters, including O particles and Cu8O particles. In particular, when the copper oxide particles are microparticles with an average particle size of less than 20 nm, these microparticles tend to aggregate and are difficult to disperse. In contrast, the copper oxide-coated copper particles of this embodiment have Cu... 64 With one or more micro-copper oxides, such as O and Cu8O, attached as a shell-like coating to the surface of the copper particles (core-shell structure), the aforementioned dispersion problem is eliminated. Furthermore, during sintering, the Cu on the particle surface... 64 O and other substances are also easily reduced, which can promote sintering between particles.

[0052] Cu forming a shell 64 Micro-copper oxides of one or more of O and Cu8O can be in the form of a film or multiple granules. The thickness of the shell (the thickness of the film or the thickness of the multiple granules) can, for example, be greater than 1 nm and less than 20 nm. Containing Cu 64 A shell of micro-copper oxide, consisting of one or more of O and Cu8O, is reduced to copper through sintering. However, its crystallinity is not as high as that of the copper particles in the core. Therefore, if the shell is too thick, the mechanical strength and electrical conductivity may decrease. From these perspectives, the shell thickness, as described above, is preferably below 20 nm.

[0053] The micro-copper oxide is preferably composed of multiple particles, which allows for a certain degree of fluidity during sintering, making it easier to fill pores. Consequently, it is easier to sinter at low temperatures. Furthermore, the multiple particles can be arranged in a single particle along the thickness direction, or multiple particles can be arranged. When the micro-copper oxide consists of multiple particles, the arithmetic mean of the equivalent circular diameter of each particle (primary particle) (hereinafter also referred to as the "average particle size") can, for example, be greater than 1 nm and less than 20 nm, preferably greater than 1 nm and less than 10 nm. This average particle size can be obtained, for example, by obtaining a TEM image of copper particles coated with micro-copper oxide, randomly selecting at least 50 particles from the TEM image, obtaining the equivalent circular diameter, and calculating their arithmetic mean.

[0054] Additionally, when this micro-copper oxide consists of multiple particles, regarding the relationship between Cu8O and Cu... 64 The crystallite diameter, preferably greater than 1 nm and less than 20 nm as measured by the Scherrer method, is selected from one or more of the groups consisting of O, and more preferably greater than 1 nm and less than 10 nm. Regarding Cu8O and Cu... 64For each of the O atoms, the crystallite diameter measured by the Scherrer method is more preferably greater than 1 nm and less than 20 nm, and even more preferably greater than 1 nm and less than 10 nm. The XRD pattern measured by the Scherrer method is obtained by powder X-ray diffraction (X-ray source: CuKα line).

[0055] In addition to Cu 64 In addition to one or more of copper oxides, such as CuO and Cu8O, trace amounts of copper oxides, such as CuO and Cu2O used as raw materials, are permitted at levels that do not impede sintering and conductivity. Preferably, no copper oxides, such as CuO and Cu2O used as raw materials, are present. The shell is preferably made of Cu... 64 The micro-copper oxide is formed from one or more of O and Cu8O, more preferably from Cu. 64 Micro-copper oxide composed of O or Cu 64 Micro-copper oxide is formed by O and Cu8O.

[0056] In this embodiment, the arithmetic mean of the longest side of the copper particles coated with micro-copper oxide, taken as the maximum length of the particle in the SEM image of the core copper particles, is higher than 1 μm. By satisfying the above requirement, the process of miniaturizing the aggregated particles is eliminated during the processing into a coating paste, thereby reducing manufacturing costs. There is no particular upper limit to the arithmetic mean of the longest side; for example, it can be less than 50 μm. The arithmetic mean of the longest side can be obtained, for example, by obtaining an SEM image of the copper particles coated with micro-copper oxide, randomly selecting more than 10 particles from the SEM image, obtaining the longest side, and calculating its arithmetic mean. As long as the shape of the core copper particles can be clearly identified in the SEM image, the observation conditions are irrelevant; for example, it can be a secondary electron image (SEI) obtained under imaging conditions of 15 kV acceleration voltage and 5000x magnification.

[0057] As a method for measuring the long side of the core copper particle from copper particles coated with micro-copper oxide, the long side of the core copper particle can be measured directly from an SEM image, or the maximum length of the copper particles coated with micro-copper oxide can be measured from an SEM image. The result is obtained by subtracting the thickness of the micro-copper oxide shell (the thickness of the coating, or the thickness of multiple particle-like structures) measured by TEM or the like from this value.

[0058] In this embodiment, the micro-coated copper particles are characterized by a maximum length of the core copper particle as the long side and the arithmetic mean length of the portion orthogonal to the long side as the short side in SEM images. For particles where the ratio of the short side to the long side is 0.4 or less, when the short side is considered as the thickness, the arithmetic mean of the thickness relative to the long side (first aspect ratio) (average first aspect ratio) is 0.25 or less. Therefore, when this sintering material is applied to a substrate or similar material, the long side of the core copper particles tends to be oriented substantially parallel to the surface of the substrate or similar material (and the thickness direction is substantially perpendicular to the surface of the substrate or similar material). Even larger core copper particles with an arithmetic mean of the long side exceeding 1 μm can be stacked without gaps. This increases the sintering surface between particles and easily suppresses porosity, thereby obtaining a bond with sufficient adhesive strength. The arithmetic mean length of the portion perpendicular to the long side (i.e., the short side) is obtained by randomly selecting three or more points perpendicular to the long side from the SEM image and calculating their arithmetic mean length. There is no particular limitation on the lower limit of the average first aspect ratio; for example, it can be greater than 0.01, 0.05, or 0.10. This average first aspect ratio can be obtained, for example, by acquiring a SEM image of copper particles coated with micro-copper oxide, randomly selecting more than 10 particles from the SEM image to determine the long side and thickness, and calculating the first aspect ratio (thickness / long side) and its arithmetic mean. The observation conditions are irrelevant as long as the shape of the copper particles in the SEM image can be clearly identified; for example, it can be a secondary electron image (SEI) obtained under conditions of 15kV accelerating voltage and 5000x magnification.

[0059] In this embodiment, when the maximum length of the copper particles coated with copper oxide is taken as the long side and the arithmetic mean length of the portion orthogonal to it is taken as the short side in an SEM image, the average of the ratio of the short side to the long side (hereinafter also referred to as the "second aspect ratio") is preferably 0.40 or higher (hereinafter also referred to as the "average second aspect ratio"), but it is not particularly limited to this. Therefore, when these copper-coated copper oxide particles are applied to a substrate, for example, the surface of the substrate / particles and the particles themselves can easily make surface contact, ensuring a large sintering area for each particle during sintering, while further suppressing porosity. There is no particular upper limit to this average second aspect ratio, which can be 1.00 or lower. This average second aspect ratio can be obtained, for example, by obtaining an SEM image of the copper-coated copper oxide particles, randomly selecting 10 or more particles from the SEM image to obtain the long and short sides, and calculating the second aspect ratio (short side / long side) and its arithmetic mean. The observation conditions are irrelevant as long as the shape of the copper nuclei can be clearly identified in the SEM images mentioned above. For example, it can be a secondary electron image (SEI) obtained under the conditions of an accelerating voltage of 15 kV and a magnification of 5000x. The surface SEM images mentioned above are secondary electron images (SEI) obtained under the conditions of an accelerating voltage of 15 kV and a magnification of 5000x.

[0060] In this embodiment, the copper particles coated with micro-copper oxide preferably have smooth upper and lower surfaces orthogonal to the thickness direction of the core copper particles. This allows for easy surface contact between the substrate surface / particles and between individual particles during sintering, ensuring a large sintering area for each particle and suppressing porosity. The result is a sintered body with a robust structure and a bond with high adhesive strength. As one indicator of particle smoothness, the arithmetic mean of the fractal dimension of the particle surface is preferably 1.00 to 1.05. This arithmetic mean can be obtained, for example, by acquiring an SEM image capturing the thickness direction of the copper particles coated with micro-copper oxide, randomly selecting 10 or more particles from the SEM image, creating surface roughness curves for the upper and lower surfaces orthogonal to the thickness direction of the particles, calculating the fractal dimension using box counting with image processing software (NIH ImageJ 1.54g), and obtaining its arithmetic mean. Furthermore, the box dimensions used for 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 on each side. The observation conditions are irrelevant as long as the shape of the copper nucleus in the SEM images can be clearly identified; for example, a secondary electron image (SEI) can be obtained under conditions of 15 kV acceleration and 5000x magnification. Additionally, regarding the surface roughness curves of the upper and lower surfaces of the particles, particles with clear outlines that capture the thickness direction are selected. The long side outlines orthogonal to the thickness direction, generated by edge effects (the bright white lines observed in the secondary electron image), are considered as the surface roughness curves of the upper and lower surfaces of the particles, and their surface roughness curves are created. To capture particles in the thickness direction, for example, based on SEM images of copper particle powder coated with micro-copper oxide, when the maximum length of the particle is taken as the long side and the arithmetic mean length of the portion orthogonal to it is taken as the short side, the ratio of the short side to the long side is less than 0.4. It is desirable to use particles with a ratio of about 0.2 to capture particles in the thickness direction.

[0061] By using the micro-coated copper particles of this embodiment, sintering can be fully achieved even at atmospheric pressure (preferably above atmospheric pressure) and at low temperatures below 250°C or even below 200°C.

[0062] This invention also includes sintering materials containing copper-coated micro-copper oxide particles as described in this embodiment. Examples of sintering materials include pastes or inks containing copper-coated micro-copper oxide particles as described in this embodiment, intended for forming conductive films. The dispersion medium contained in the paste or ink can be a known material. Examples of such known materials include 2-(dimethylamino)ethanol, N-butyldiethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, diethanolamine, triethanolamine, 1-[bis(2-hydroxyethyl)amino]-2-propanol, ethylenediamine-N,N,N',N'-tetraethanolamine, etc. By coating the sintering material containing copper-coated micro-copper oxide particles as described in this embodiment onto the bonding surfaces of multiple materials, such as metals (pure metals, alloys), ceramics, etc., and bonding them together, a bond with high adhesive strength can be obtained. The sintered body of this embodiment is formed by sintering the sintering material containing copper-coated micro-copper oxide particles as described in this embodiment. The bonding body of this embodiment is formed by bonding multiple materials using a sintering material containing copper particles coated with micro-copper oxide as described in this embodiment.

[0063] The method for manufacturing particles containing micro-copper oxide in this embodiment includes:

[0064] In the SEM image, when the maximum length of the particle is taken as the long side, the arithmetic mean of the long side is higher than 1 μm. Furthermore, in the SEM image, when the arithmetic mean length of the particle with a length ratio of 0.4 or less to the length of the portion perpendicular to the long side is taken as the thickness, the raw copper particles are processed in such a way that the arithmetic mean of the ratio of the thickness to the long side is 0.25 or less.

[0065] The raw material copper particles are mixed with a solution containing a solvent, an amine compound and a complexing agent, and then a reducing agent is added to allow the mixture to react.

[0066] Alternatively, depending on the needs, the raw copper particles after processing and before reaction can be subjected to oxidation treatment, or cuprous oxide (Cu2O) or copper oxide particles (CuO) can be added as a copper oxide source.

[0067] According to the above method, copper particles coated with micro-copper oxide can be obtained in this embodiment. The micro-copper oxide particles contained in the shell can be multiple particles.

[0068] The conditions for the manufacturing method of this embodiment will be described in detail below.

[0069] [Process for processing raw copper particles]

[0070] The raw copper particles are processed in a manner that, in the SEM image, makes the arithmetic mean of the long side greater than 1 μm and the arithmetic mean of the ratio of thickness to the long side less than 0.25 (hereinafter referred to as "flattening").

[0071] As a processing (flattening) method, by using a thin-film rotary high-speed mixer, the raw copper particles can be adjusted to have the aforementioned dimensions (and, in the embodiments of the present invention, the arithmetic mean of the average second aspect ratio and fractal dimension, etc.). As a thin-film rotary high-speed mixer, a Primix FILMIX56-L or similar mixer can be used. For obtaining particles with the aforementioned dimensions, a peripheral speed of 5 to 50 m / s for 10 to 60 minutes is preferred. Other methods include processing with a bead mill or ball mill, for example. In this case, for example, by selecting a medium with a diameter approximately 10 times or more than the particle size of the raw copper particles, particles with the aforementioned dimensions can be effectively obtained. The flattening process is not limited to these methods; various methods such as rolling with a three-roll mill can be used.

[0072] There are no particular restrictions on the method for obtaining the raw copper particles; for example, commercially available products can be used. Regarding the size of the raw copper particles before processing, the arithmetic mean of the long side in the SEM image can be greater than 1 μm, preferably greater than 2 μm. There are no particular restrictions on the shape of the raw copper particles before processing, but from a cost perspective, it is preferable to use, for example, dendritic copper particles manufactured by electrolysis.

[0073] [Oxidation treatment process]

[0074] On the surface of the raw copper particles, a copper oxide film (preferably composed of Cu2O) containing one or more of CuO and Cu2O may exist due to natural oxidation. In this embodiment, an oxidation treatment may be performed as needed to increase the copper oxide film on the raw copper particles compared to natural oxidation. Examples of oxidation treatment methods include heating in water and heating under atmospheric conditions.

[0075] By implementing oxidation treatment, for example, the proportion of copper oxide containing one or more of CuO and Cu2O in the raw copper particles can reach more than 1% by mass. If the desired final core-shell micro-coated copper oxide particles containing Cu... 64 A thick shell of one or more of the copper oxides, such as O and Cu8O, can actively oxidize the raw material particles. In this case, if the surface copper oxide occupies too much of the raw material particles, it will contain Cu. 64 The shells of micro-copper oxides, such as O and Cu8O, are difficult to adhere to the copper particles that serve as the core. Additionally, those containing Cu... 64A shell containing one or more of copper oxides, such as O and Cu8O, exhibits reduced crystallinity during low-temperature sintering compared to copper particles with a highly crystalline core. Therefore, if the shell is thick, the mechanical strength and / or electrical conductivity may decrease. From these perspectives, the proportion of copper oxides containing one or more of CuO and Cu2O in the raw material particles is preferably less than 10% by mass.

[0076] Alternatively, adding copper oxide particles containing one or more of CuO and Cu2O to the reaction step described in the next step, instead of oxidizing the raw copper particles, can achieve the same effect. In this case, the proportion of the copper oxide particles added to the raw copper particles is preferably 10% by mass or less.

[0077] [Reaction process]

[0078] The processed (or oxidized) copper particles are mixed with a solution containing a solvent, an amine compound, and a complexing agent, and then a reducing agent is added to initiate the reaction (synthesis). Alternatively, copper oxide particles containing one or more of CuO and Cu2O may be added to replace the oxidation treatment of the copper particles. The complexing agents required for this reaction will be described below.

[0079] (Complexing agent)

[0080] In this embodiment, copper oxide contained in the processed (or oxidized) raw copper particles, or copper oxide added as particles, reacts with a complexing agent to form copper complex ions. Thus, by ionizing the copper in the raw copper particles, the reduction rate brought about by the reducing agent is significantly faster than the reduction of solid copper oxide. Carboxylic acids can be used as complexing agents. Examples of carboxylic acids include formic acid, saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, and terpene carboxylic acids. They can also be monocarboxylic acids or dicarboxylic acids. Furthermore, one type can be used alone, or two or more can be used in combination. Aliphatic monocarboxylic acids can be linear or branched, and can also be any type of saturated or unsaturated aliphatic monocarboxylic acids. Examples of linear saturated aliphatic monocarboxylic acids include acetic acid (2 carbons), propionic acid (3 carbons), butyric acid (4 carbons), valeric acid (5 carbons), hexanoic acid (6 carbons), heptanoic acid (7 carbons), octanoic acid (8 carbons), nonanoic acid (9 carbons), decanoic acid (10 carbons), lauric acid (12 carbons), myristic acid (14 carbons), palmitic acid (16 carbons), heptadecanic acid (17 carbons), and stearic acid (18 carbons).

[0081] Aliphatic dicarboxylic acids can be either straight-chain or branched, and can also be either saturated or unsaturated. Aliphatic dicarboxylic acids can be used alone or in combination of two or more. Examples of aliphatic dicarboxylic acids include adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, 1,0-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, brassic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, tetradecanedicarboxylic acid, 1,15-pentadecanedicarboxylic acid, and 1,16-hexadecanedicarboxylic acid. Examples of aromatic carboxylic acids include benzoic acid, ortho-phenylenediic acid, iso-phenylenediic acid, terephthalic acid, semi-phenyltriglyceric acid, trimellitic acid, and pyromellitic acid. Terpenoid carboxylic acids can be those contained in rosin, etc. Examples include abietic acid, neo-rosinic acid, longleaf abietic acid, piratic acid, isopiratic acid, and dehydrorosinic acid.

[0082] Acetic acid, which is easy to process and also easy to handle after the reaction, is preferred.

[0083] There is no particular limitation on the amount of complexing agent added for the reaction, but in order to promote Cu 64 From the viewpoint of promoting the formation of copper complex ions, the molar ratio of O and Cu8O to the copper contained in the starting material particles is preferably 0.05 times or more and 15 times or less.

[0084] (Amine compounds)

[0085] A compound containing an amino group (hereinafter referred to as "amine compound") is added as a protecting agent. Amine compounds also contribute to the formation of copper complex ions. The amine compound is not particularly limited; for example, alkanolamines, diamines, and aminocarboxylic acids are preferred. Alkanolamines are more preferably used. Examples of alkanolamines 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.

[0086] The amount of amine compounds added for the reaction is not particularly limited, but it can promote the reaction of Cu. 64 From the perspective of the formation of O and Cu8O, the molar ratio of the amine compound to the copper contained in the raw material particles is preferably 0.1 times or more. This molar ratio can, for example, be 20 times or less.

[0087] (solvent)

[0088] As a solvent, there are no particular limitations; for example, polyols such as ethylene glycol, lower alcohols such as methanol, ethanol, and 2-propanol, ketones such as acetone, and water can be used.

[0089] (reducing agent)

[0090] There are no particular limitations on the reducing agent used; hydrazine-based reducing agents such as hydrazine hydrochloride, hydrazine sulfate, and hydrazine hydrate, as well as borohydride salts such as citric acid, ascorbic acid, and sodium borohydride, can be used. During the addition of the reducing agent, the raw materials containing the aforementioned raw material particles, complexing agent, amine compound, and solvent are added and mixed. After adding the reducing agent, stirring is performed until the desired micro-copper oxide is formed. Regardless of the manufacturing method, stirring until the reducing agent disappears and the reaction is fully realized is preferred.

[0091] (Cooling during the reaction)

[0092] In the manufacturing method of this embodiment, for example, when hydrazine is used as a reducing agent, the addition of the reducing agent, such as the decomposition reaction of hydrazine, generates heat, and the temperature of the reaction solution may rise. To suppress the temperature rise of the reaction solution, the pre-formed Cu... 64 From the viewpoint that O and Cu8O are reduced to metallic copper, it is preferable to provide a temperature control mechanism, such as a cooling reaction solution, to ensure that the reaction proceeds below 50°C. For example, as shown in the embodiments described later, it is preferable to add the reducing agent while the reaction vessel is immersed in room temperature water.

[0093] (Atmosphere during the reaction)

[0094] In the manufacturing method of this embodiment, the reaction atmosphere is, for example, limited to an oxygen-containing atmosphere such as the atmosphere, and the reaction needs to be continuously exposed to this oxygen-containing atmosphere. If the atmosphere is an inert gas such as nitrogen or argon, or if the reaction vessel is sealed even in the atmosphere, Cu 64 The oxide formation reaction of O or Cu8O did not progress; instead, metallic copper particles were formed, which is therefore not preferred.

[0095] (Other processes)

[0096] The manufacturing method of this embodiment may also include steps other than those described above. For example, it may include processing the product obtained after the reduction described above, which contains Cu. 64 The process involves recovering copper oxide-containing particles from a slurry containing one or more micro-copper oxide particles, such as O and Cu8O, through methods such as centrifugation and / or filtration. This process may also include subsequent purification and drying steps. In the purification step, purification is preferably performed using a washing solvent. The washing solvent is not particularly limited; for example, organic solvents such as N,N-dimethylacetamide, toluene, and hexane can be used.

[0097] The manufacturing method of micro-coated copper particles with copper oxide as described above has been explained. However, those skilled in the art who understand the required characteristics of the micro-coated copper particles with copper oxide involved in this embodiment may, through repeated attempts, discover methods other than those described above in the manufacturing method of micro-coated copper particles with copper oxide as described in this embodiment.

[0098] The method for manufacturing a sintered body according to this embodiment includes the following steps: a step of preparing a sintering material containing copper micro-coated copper particles of this embodiment; and a step of sintering the sintering material. Regarding the step of preparing the sintering material, it can be performed by appropriately mixing the copper micro-coated copper particles of this embodiment with a dispersion medium. There are no particular limitations on the dispersion medium; known dispersion media can be used, such as 2-(dimethylamino)ethanol, N-butyldiethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, diethanolamine, triethanolamine, 1-[bis(2-hydroxyethyl)amino]-2-propanol, ethylenediamine-N,N,N',N'-tetraethanol, etc. In the step of sintering the sintering material, sintering can be performed using known methods. There are no particular limitations on the sintering method; for example, sintering can be performed at atmospheric pressure (preferably a pressure higher than atmospheric pressure) and at a low temperature of 250°C or even 200°C or lower.

[0099] The method for manufacturing the bonded body according to this embodiment includes the following steps: a step of preparing a sintering material containing copper particles coated with micro-copper oxide as described in this embodiment; and a step of bonding multiple materials using the sintering material. The step of preparing the sintering material containing copper particles coated with micro-copper oxide as described in this embodiment is as described above. Regarding the step of bonding multiple materials using the sintering material, there are no particular limitations; it can be performed by coating the bonding surfaces of multiple materials, such as metals (pure metals, alloys), ceramics, etc., and then bonding them. As bonding conditions, for example, it can be performed by sintering the sintering material existing between the multiple materials at a low temperature of 250°C or below, or even 200°C, under normal pressure (preferably a pressure higher than normal pressure).

[0100] Example

[0101] The following examples illustrate this embodiment in more detail. This embodiment is not limited to the examples described below; appropriate modifications may be made to achieve the objectives described above and below, and all such modifications are included within the technical scope of this embodiment.

[0102] (Process for processing raw copper particles)

[0103] Copper particles, manufactured by Kanto Chemicals (07439-01, with a particle size of 75μm to 150μm and a mesh size of 100 to 200 mesh), were used as the raw material. 70g of these particles were mixed with 60ml of ethanol (manufactured by Nippon Alcohol Sales Co., Ltd.) as the dispersion medium, and the mixture was processed intermittently at a rotation speed of 30m / s for 30 minutes using a thin-film rotary high-speed mixer (Primix FILMIX56-L). Ethanol was added as needed to account for any evaporation during processing. The supernatant of the resulting solution was removed and dried to obtain the processed raw material copper particles.

[0104] Figure 1 These are SEM images of raw copper particles before processing, obtained using a scanning electron microscope (JSM-6701F, Nippon Electron). Figure 1 As shown, the raw copper particles before processing are dendritic copper particles with a long side of about 10 to 100 μm.

[0105] Figure 2 These are SEM images of the processed raw copper particles obtained using the aforementioned scanning electron microscope. Figure 3 This is an example of an enlarged view of a particle whose ratio of the short side to the long side is 0.4 or less, when the maximum length of the particle is taken as the long side and the arithmetic mean length of the portion orthogonal to it is taken as the short side. Figure 3 The particles shown are used to capture particles in the thickness direction for the calculation of the parameters described later. Furthermore, this SEM image is a secondary electron image (SEI) with an accelerating voltage of 15 kV. Figure 2 Shot at 500x magnification. Figure 3 Shot at 5000x magnification. (Example) Figure 2 As shown, the processed raw copper particles are flattened during processing. Multiple [items / processes] were obtained. Figure 3 The SEM image shown, when the arithmetic mean of the long side, the average first aspect ratio, the average second aspect ratio, and the arithmetic mean of the fractal dimension are obtained using the method detailed in "Means for Carrying Out the Invention", has the following arithmetic mean: long side: 18.9 μm, average first aspect ratio: 0.18, average second aspect ratio: 0.50, and arithmetic mean of the fractal dimension representing the surface roughness of the bottom surface of the particle: 1.014.

[0106] XRD patterns were obtained using a powder X-ray diffraction apparatus (XRD, Rigaku MiniFlexII, D / teX Ultra) before and after the processing of the raw copper particles (raw material) and after processing (flattening). Figure 4 Measurements were performed using Cu-Kα rays at a scanning speed of 20° (2θ) min. －1 And so it is carried out.

[0107] (Oxidation treatment process)

[0108] The processed raw copper particles are subjected to oxidation treatment.

[0109] In Level 1, 114 g of processed copper particles were mixed with 1 L of pure water and boiled under atmospheric pressure for 42 hours. The supernatant was then removed and the mixture was dried. The resulting particles were analyzed using powder X-ray diffraction (XRD, Rigaku MiniFlexII, D / teX Ultra) to obtain XRD patterns. Figure 4 (Level 1, after oxidation). Measurements were performed using Cu-Kα rays at a scan rate of 20° (2θ) min. －1 The XRD pattern was then analyzed using RIR quantification, which confirmed the presence of a 2% (w / w) Cu₂O oxide coating.

[0110] In level 2, 120g of the processed raw copper particles were added to a muffle furnace (Fotex FT-101FM) and heated at 200°C for 2 hours under atmospheric conditions. The resulting particles were then analyzed using the powder X-ray diffraction apparatus described above to obtain XRD patterns. Figure 4 (Level 2, after oxidation). Measurements were performed using Cu-Kα rays at a scan rate of 20° (2θ) min. －1 The XRD pattern was then analyzed using RIR quantification, which confirmed the presence of a 5% (w / w) Cu₂O oxide coating.

[0111] (Reaction process)

[0112] Copper microparticles coated with copper oxide at levels 1 and 2 were synthesized by reacting them in the following manner.

[0113] 1390 g (22.4 mol) of ethylene glycol (manufactured by Kanto Chemical) as solvent, 1182 g (15.7 mol) of 1-amino-2-propanol (manufactured by Kanto Chemical) as protective agent, and 473 g (7.87 mol) of acetic acid (manufactured by Junsei Chemical) as complexing agent were placed in a reaction vessel and stirred thoroughly. Then, 100 g (1.57 mol) of particles after oxidation treatment at level 1 or 2 were added. With the reaction vessel immersed in room temperature water, 788 g (15.7 mol) of hydrazine hydrate (manufactured by Kanto Chemical) as reducing agent was added and stirred at 1100 rpm to allow the reaction to proceed. The reaction was carried out in the atmosphere. After the reaction, the product was purified by multiple centrifugations using N,N-dimethylacetamide, toluene, and hexane to obtain a slurry containing the product. The yield of copper microparticles coated with copper oxide in the slurry was calculated by the following formula (1).

[0114] Formula 1

[0115]

[0116] In equation (1),

[0117] Y: Particle weight in the slurry (g)

[0118] M s Slurry weight (g)

[0119] V s : Slurry volume (cm³) 3 )

[0120] ρ m Solvent density (g / cm³) 3 )

[0121] ρ Cu Copper density (g / cm³) 3 )

[0122] (X-ray diffraction measurement)

[0123] X-ray diffraction measurements were performed using a slurry containing the product and a powder X-ray diffractometer (XRD, Rigaku MiniFlexII, D / teX Ultra). Measurements were performed using Cu-Kα rays at a scan rate of 20° (2θ) min. －1 And so it was carried out. The results showed... Figure 4 (After synthesis) in.

[0124] (Observation under an electron microscope)

[0125] The product synthesized using copper particles from level 2 as raw material was observed using transmission electron microscopy (TEM, JEM-2000FX, NEC, accelerating voltage 200kV). The results showed... Figure 5 and Figure 6 middle.

[0126] Based on the above X-ray diffraction measurements and electron microscopy observations, the following was confirmed. Figure 4 The XRD patterns shown (after synthesis) confirm Cu in both levels 1 and 2. 64 The peak of O. Especially in level 2 (5% by mass oxidation), Cu can be clearly identified. 64 Peaks of O and Cu8O.

[0127] The particles at level 2 are composed of Figure 5 The TEM images shown confirm that the copper particles, which act as the nucleus, are surrounded by a shell-like layer of tiny particles, as seen when the shell is magnified. Figure 6 It can be confirmed that the particle size of the nanoparticles constituting the shell is 2–10 nm (the arithmetic mean is also within this range). Based on the XRD pattern of this particle ( Figure 3(After synthesis at level 2), the crystallite diameters measured by the Scherrer method were 3.8 nm for Cu8O and 3.8 nm for Cu. 64 The size of O is 2.1 nm, which is roughly consistent with the size of the nanoparticles constituting the shell observed by TEM. Based on this, it can be concluded that the structure of the obtained particles consists of copper microparticles forming a core, surrounded by a Cu layer. 64 O and Cu8O nanoparticle shells.

[0128] (Manufacturing of paste containing copper microparticles coated with micro-copper oxide)

[0129] By centrifugation, the supernatant of the synthesized slurry containing two levels of copper micro-coated copper oxide particles and hexane was removed, yielding a wet filter cake containing copper micro-coated copper oxide particles. Relative to 85 parts by mass of copper particles in the wet filter cake calculated by equation (1), 15 parts by mass of triethanolamine (Fujifilm and Koujun Pharmaceutical) as a paste solvent were added, along with a small amount of ethanol to adjust the solubility of triethanolamine. The mixture was then vortexed (Heathrow Scientific) and stirred for 30 seconds using a planetary mixer (Thinky AR-100). Subsequently, the mixture was kept in a vacuum at room temperature until no further weight change occurred to remove the ethanol, yielding two levels of paste (copper chip bonding paste). Thermogravimetric-differential thermal analysis (TG-DTA) was performed on the obtained paste using a TG / DTA simultaneous measurement device (Shimadzu Corporation) under a 3% hydrogen-nitrogen mixed gas atmosphere at a heating rate of 5°C / min. The results showed… Figure 7 (Level 1) and Figure 8 (Level 2) The results are as follows. Figure 7 and Figure 8 As shown, based on the weight reduction indicated by the TGA, it can be confirmed that in each paste, Level 1 (2% by mass oxidation) contains 86.0% by mass of micro-coated copper microparticles with copper oxide, and Level 2 (5% by mass oxidation) contains 84.7% by mass of micro-coated copper microparticles with copper oxide.

[0130] (Synthesis of spherical copper oxide-coated copper microparticles)

[0131] As a comparative example, spherical copper oxide-coated copper microparticles that do not meet the requirements of this embodiment were synthesized in the following manner.

[0132] 733 g (11.8 mol) of ethylene glycol (Kanto Chemical) as solvent, 591 g (7.87 mol) of 1-amino-2-propanol (Kanto Chemical) as protective agent, and 236 g (3.93 mol) of acetic acid (Junsei Chemical) as complexing agent were added to a reaction vessel. After thorough stirring, 100 g (1.57 mol) of spherical copper particles (HXR-Cu, 2.5 μm particle size, manufactured by Nippon Atomization Processing) as starting material and 2 g (2% by mass relative to copper particles) of cuprous oxide (Furukawa Chemical) as copper oxide source were added. With the reaction vessel immersed in room temperature water, 394 g (7.87 mol) of hydrazine hydrate (Kanto Chemical) as reducing agent was added, and the reaction was carried out with stirring at 1100 rpm. The reaction was carried out in the atmosphere. After the reaction, the product was purified by multiple centrifugations using N,N-dimethylacetamide, toluene, and hexane to obtain a slurry containing the product.

[0133] Using the slurry containing the product, X-ray diffraction measurements were performed using a powder X-ray diffraction apparatus (XRD, Rigaku MiniFlexII, D / teX Ultra). Measurements were performed using Cu-Kα rays at a scan rate of 20° (2θ) min. －1 And so it was carried out. The results showed... Figure 9 (After synthesis) In addition, X-ray diffraction measurements were also performed on the spherical copper particles (raw material) used as raw materials.

[0134] according to Figure 9 The XRD pattern shown confirms the presence of Cu in the synthesized particles. 64 Peaks of O and Cu8O.

[0135] The resulting product was observed using a transmission electron microscope (TEM, JEM-2000FX, NEC, accelerating voltage 200kV). An example of a TEM image is shown below. Figure 10 middle.

[0136] The TEM images confirm that the spherical particles, which form the core, are surrounded by a shell of tiny particles. Since the particles are spherical, the average first aspect ratio is presumed to be at least higher than 0.25 (less than 1), which does not meet the requirements of this embodiment.

[0137] (Manufacturing of a paste containing spherical micro-coated copper microparticles)

[0138] The supernatant of the synthesized spherical copper oxide-coated copper microparticles and hexane slurry was removed by centrifugation to obtain a wet filter cake of spherical copper oxide-coated copper microparticles. Relative to 90 parts by mass of copper particles in the wet filter cake calculated by equation (1), 10 parts by mass of triethanolamine (Fujifilm and Koujun Pharmaceutical) as a paste solvent were added, along with a small amount of ethanol to adjust the solubility of triethanolamine. The mixture was then vortexed (Heathrow Scientific) and stirred for 30 seconds using a planetary mixer (Thinky AR-100). Subsequently, the mixture was kept in a vacuum at room temperature until no further weight change occurred to remove the ethanol, yielding a paste (copper chip bonding paste). Thermogravimetric-differential thermal analysis (TG-DTA) was performed on the obtained paste using a TG / DTA simultaneous measurement device (Shimadzu Corporation) under a 3% hydrogen-nitrogen mixed gas atmosphere at a heating rate of 5°C / min. The results showed… Figure 11 The result is as follows. Figure 11 As shown, the weight reduction indicated by the TGA confirms that the resulting paste contains 89.0% by mass of micro-coated copper microparticles with copper oxide.

[0139] (Evaluation of the bonding and firing process)

[0140] Using the obtained paste, two copper test pieces were glued together, and a bonding evaluation sample was made by firing the paste to make the bonded joint, and the bond strength was measured.

[0141] 1. Preparation of samples for evaluation of bonding firing

[0142] The preparation steps for samples used in the evaluation of bonding firing are as follows: Figure 12 As shown. First, a circular copper test piece is prepared from a 5mm thick oxygen-free copper plate (C1020P), as follows. Figure 13A As shown, copper test pieces 1 (12 mm in diameter) and 2 (5 mm in diameter) were cut. Copper test pieces 1 and 2 were prepared as copper test pieces. The surfaces of each copper test piece were polished with P4000 water-resistant sandpaper (SiC paper), then mirror-finished using a polishing cloth impregnated with a 0.5 μm alumina powder suspension, 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 cleaned with pure water and methanol, and then dried.

[0143] Next, metal mask printing is performed. Specifically, using... Figure 13B The schematic diagram shows an opening in a metal mask with a diameter of 5mm and a thickness of 0.15mm. Figure 13C As shown, the above-mentioned paste (paste containing copper micro-coated copper microparticles with micro-copper oxide) 3 is applied to the center of a copper test piece 1 with a diameter of 12 mm, so that it is bonded together with a copper test piece 2 with a diameter of 5 mm. Then, a hot press is used to press the two bonded copper test pieces together along the... Figure 13C A load of 15 MPa was applied in the direction of the arrow, and the temperature was rapidly increased to 200 °C at a rate of 90 °C / min. After reaching 200 °C, the temperature was held for 15 minutes, then removed from the hot press and rapidly cooled by water to obtain a sample for evaluation of the bonded sintering. All operations were performed in a nitrogen atmosphere.

[0144] 2. Bonding and firing evaluation test (measurement of bond strength)

[0145] The bond strength of the samples used for bonding and firing evaluation was evaluated using a 5kN material testing machine (manufactured by Shimadzu Corporation). Specifically, as follows... Figure 13D The schematic cross-sectional view shown illustrates the application of a load parallel to the coating surface at a speed of 1 mm / min to a bonding evaluation sample fixed by clamp 4 of the testing machine. The fracture load of the copper test piece is measured as the bond strength. The results are shown in... Figure 14 middle. Figure 14 The longitudinal width shown in the measurements represents the deviation from multiple measurements. For example... Figure 14 As shown, the average bond strength is 30.3 MPa in level 1 (2% by mass oxidation) which satisfies the requirements of this embodiment, and 26.4 MPa in level 2 (5% by mass oxidation) which satisfies the requirements of this embodiment, showing a sufficiently practical value. In contrast, the comparative example using spherical particles that do not satisfy the requirements of this embodiment shows a low value of 11.8 MPa.

[0146] SEM images of the fracture surface of the sample after the test for evaluation of the bonding firing process are shown in Figure 15 (In the example, level 1). For example... Figure 15 As shown, in level 1, which satisfies the requirements of this embodiment, traces of bonding are visible across the entire surface of the sintered body. SEM images of the cross-section of the sample used for evaluating the bonding sintering in level 1 after testing are shown. Figure 16 The cross-section was prepared by cutting the center of the sample used for evaluation after bonding and firing using a low-speed cutting machine (made by BUEHLER). Figure 16 The observed image confirms the dense sintering along the thickness direction.

[0147] SEM images of the fracture surface of the sample after the test for evaluation of the bonding firing process are shown in Figure 17 (Comparative example, spherical particles). For example... Figure 17 As shown, in the comparative example that uses spherical particles that do not meet the requirements of this embodiment, the adhesion traces are only seen at the endpoints of the spherical particles, and the sintering state between the particles is also only confirmed at the endpoints.

[0148] Industrial availability

[0149] The copper oxide-containing particles of this embodiment can be fully sintered even at low temperatures, such as below 200°C or even below 250°C, under normal pressure (preferably above normal pressure). Therefore, the copper oxide-containing particles of this embodiment, in addition to being used as circuit forming materials for printed circuit boards (especially flexible circuit boards) and other micro-wiring materials, can also be used for thermal conductivity and as chip bonding materials for power semiconductors, as shown in this embodiment. Furthermore, they can also be used as antistatic materials, electromagnetic wave shielding materials, infrared blocking materials, etc.

[0150] This application is based on the priority claim of Japanese Patent Application No. 2024-006167, filed on January 18, 2024. Japanese Patent Application No. 2024-006167 is incorporated herein by reference.

[0151] Explanation of reference numerals in the attached figures

[0152] 1, 2 Copper test pieces

[0153] 3. Paste containing micro-coated copper microparticles of copper oxide

[0154] 4. Fixtures for fixing the testing machine

Claims

1. A micro-coated copper oxide copper particle, comprising copper particles as a core and Cu... 64 A shell of micro-copper oxides, including O and Cu8O, wherein... In the scanning electron microscope image of the said copper particles, when the maximum length of the particle is set as the long side, the arithmetic mean of the long side is higher than 1 μm. Furthermore, in the scanning electron microscope image, when the arithmetic mean length of the particles whose arithmetic mean length of the portion orthogonal to the long side is less than 0.4 is set as the thickness, the arithmetic mean of the thickness relative to the long side is less than 0.

25.

2. The micro-coated copper particles according to claim 1, wherein, The micro-copper oxide refers to micro-copper oxide particles whose arithmetic mean of equivalent circular diameter is higher than 1 nm and lower than 20 nm.

3. The micro-coated copper particles according to claim 1 or 2, wherein, In the scanning electron microscope images of the said copper particles, the arithmetic mean of the fractal dimension of the particle surface roughness is 1.00 to 1.

05.

4. A sintering material comprising copper particles coated with micro-copper oxide as described in any one of claims 1 to 3.

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

6. A sintered body formed by sintering the sintering material as described in claim 4 or 5.

7. A joint comprising a plurality of materials joined by the sintering material as described in claim 4 or 5.

Images