Method for manufacturing conductive powder, conductive paste, and electronic components, with copper as the main component.

Abstract

Provided is a conductive powder containing copper as a main component, in which D50 is 0.3 to 7.5 μm inclusive, the ratio of a major axis X to a medium diameter Y is between 1.0 and 3.0 (both inclusive), the ratio of the major axis X to a minor axis Z is between 1.5 and 8.0 (both inclusive), and an aliphatic amine is included in at least a part of a surface of the conductive powder. The aliphatic amine is one such that at least one peak is detected in a chromatogram for a mass number of 44 when the conductive powder containing copper as a main component is heated from 38°C to 900°C at a heating rate of 10°C / min in an inert atmosphere by TG-MS, and the ratio of an area of the peak in a range between 250°C and 400°C (both inclusive) to an area of the peak in a range between 250°C and 900°C (both inclusive) is 0.9 or more. A conductive paste obtained by using the conductive powder can remove a surface treatment agent by low-temperature firing, and can form a dense conductor film.

Description

Copper-based conductive powder 【0001】 The present invention relates to a copper-based conductive powder, and more particularly to a copper-based conductive powder suitable for forming terminal electrodes of multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer inductors, and multilayer piezoelectric actuators. 【0002】 Multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer inductors, and multilayer piezoelectric actuators are generally manufactured as follows. 【0003】 First, a conductive paste for the internal electrodes is printed in a predetermined pattern on a dielectric ceramic green sheet such as a barium titanate-based ceramic. Then, multiple such sheets are stacked and pressed together to obtain an unfired laminate in which ceramic green sheets and internal electrode paste layers are alternately stacked. The resulting laminate is cut into chips of a predetermined shape to obtain a laminated body. The laminated body may be fired at a high temperature at this stage, or it may not be fired at this stage but may be co-fired later with a terminal electrode paste layer formed using a conductive paste for the terminal electrodes. In either case, the laminated body in its state before the terminal electrode paste layer is formed is referred to as a "laminated body." 【0004】 Thereafter, a conductive paste for terminal electrodes, which contains components such as conductive powder, binder resin, organic solvent, and glass frit, is printed on the exposed ends of the internal electrodes of the laminated body by a dip printing method or the like to form a conductive paste layer, which is then dried as necessary and further fired at a high temperature to form the terminal electrodes. 【0005】 Furthermore, thereafter, a plating layer of nickel, tin, or the like may be formed on the terminal electrodes by electroplating or the like, if necessary. 【0006】Traditionally, precious metals such as palladium, silver-palladium, and platinum have been used as internal electrode materials. However, there are demands for resource conservation and cost reduction, and particularly for sintered types, there is a demand for preventing delamination and cracking caused by oxidative expansion of palladium and silver-palladium during sintering. In recent years, therefore, the use of base metals such as nickel, cobalt, and copper has become mainstream. For this reason, copper, nickel, cobalt, or alloys of these metals, which easily form good electrical connections with base metal internal electrodes, have been used as terminal electrode materials instead of the conventional silver and silver-palladium. 【0007】 When base metals are used for the internal electrodes and terminal electrodes in this way, the terminal electrodes are usually fired in a non-oxidizing atmosphere with as low an oxygen partial pressure as possible, for example, in an inert gas atmosphere with an oxygen content of several ppm to several tens of ppm, at a high peak temperature of 800°C, so as to prevent the base metals from being oxidized during firing. 【0008】 However, particularly when firing a metal powder whose main component is copper in a low-oxygen atmosphere, it is difficult to properly remove the binder to combust, decompose, and scatter organic components such as binder resin. If the binder is not removed sufficiently at the relatively low temperature in the early stages of firing, before the glass fluidizes and the copper powder sinters, carbon and organic residues become trapped in the film after sintering begins, and the organic decomposition products gasify at the subsequent high-temperature stage, causing blisters (air bubbles) and various other problems that impair the density of the fired film. 【0009】 Therefore, in the past, an important issue for conductive pastes using metal powders whose main component is base metals, particularly copper, was how to efficiently remove the binder in the early stages of firing and reduce residual carbon before the sintering of the copper powder progresses at high temperatures. 【0010】 As a method for solving this problem, for example, Patent Document 1 discloses a conductor paste for terminal electrodes that uses an aliphatic amine as a surface treatment agent for copper-based conductive powder, thereby improving the dispersibility of the conductive powder and significantly improving the binder removal properties, thereby making it possible to form dense terminal electrodes that are excellent in adhesion and conductivity. 【0011】 Japanese Patent Application Laid-Open No. 2006-004734 【0012】 Recently, there has been a demand for lower firing temperatures when forming the terminal electrodes in order to reduce environmental impact, manufacturing costs, and thermal stress on the laminated body, and therefore there is a demand for the surface treatment agent as well as the binder resin to be removable at low temperatures. 【0013】 Therefore, an object of the present invention is to provide a conductive powder containing copper as its main component, which can be suitably used in a conductive paste that can form a dense conductor film even when fired at a low temperature, and from which a surface treatment agent can be removed at a low temperature. 【0014】 As a result of extensive research to solve the above problems, the present inventors have found that by using a conductive powder containing copper as a main component and having the following composition, the powder can be suitably used in a conductive paste that can form a dense conductor film even when fired at a low temperature, and that the surface treatment agent can be removed at a low temperature. 【0015】That is, the present invention (1) provides a copper-based conductive powder, characterized in that the conductive powder has a volume-based cumulative 50% particle diameter D50 measured by laser diffraction particle size distribution measurement of 0.3 μm to 7.5 μm, a ratio of a major diameter X (defined below) to a median diameter Y (defined below) of 1.0 to 3.0, and a ratio of a major diameter X (defined below) to a minor diameter Z (defined below) of 1.5 to 8.0, and the conductive powder has an aliphatic amine on at least a portion of its surface, and the aliphatic amine is an aliphatic amine that, when the copper-based conductive powder is heated from 38°C to 900°C at a heating rate of 10°C / min in an inert atmosphere by TG-MS, detects at least one peak in a chromatogram with a mass number of 44, and the ratio of the area of ​​the peak in the range of 250°C to 400°C to the area of ​​the peak in the range of 250°C to 900°C is 0.9 or more. (Major diameter X and median diameter Y) One hundred particles are randomly selected by observation with a scanning electron microscope, and the average length of the long side of a rectangle circumscribing each particle so as to have the smallest area is defined as the major diameter X, and the average length of the short side is defined as the median diameter Y. (Minor diameter Z) 100 parts by mass of the copper-based conductive powder and 7 parts by mass of an acrylic resin dissolved in terpineol are mixed, then kneaded using a three-roll mill, then diluted with terpineol, and kneaded at 25°C at a shear rate of 4 s －１ A paste-like composition is prepared by adjusting the viscosity at 250 Pa s, and the paste-like composition is cast onto a PET film using an applicator to form a coating film with a thickness of 250 μm. The coating film is dried in an air atmosphere at 150°C for 10 minutes to form a dry film. A cross section of the dry film is exposed using an ion milling device, and the cross section of the dry film is observed with a scanning electron microscope. 100 particles are randomly selected, and the average value of the length of the short sides of the rectangles circumscribing each particle so as to minimize its area is defined as the short diameter Z. 【0016】 The present invention (2) also provides a copper-based conductive powder according to (1), in which the aliphatic amine includes at least one of a secondary amine and a tertiary amine. 【0017】 The present invention (3) provides a copper-based conductive powder according to (1) or (2), in which, when the peak with the strongest peak intensity among the peaks in the range of 250°C or higher and 400°C or lower is taken as the main peak, neither a peak nor a shoulder peak exists within the range of higher than the peak top temperature of the main peak and lower than 400°C. 【0018】 The present invention (4) provides a copper-based conductive powder according to any one of (1) to (3), in which, in a differential graph obtained by differentiating the chromatogram, an upwardly projecting peak exists in the range of 250°C or more and 350°C or less, and when the peak with the strongest peak intensity among the upwardly projecting peaks is defined as the main peak of the differential graph, no upwardly projecting peak exists in the range of more than the peak top temperature of the main peak of the differential graph and less than 400°C. 【0019】 The present invention (5) also provides a copper-based conductive powder according to any one of (1) to (4), wherein the aliphatic amine is dimethylstearylamine. 【0020】 According to the present invention, it is possible to provide a conductive powder containing copper as a main component, which can be suitably used in a conductive paste that can form a dense conductor film even when fired at a low temperature, and from which a surface treatment agent can be removed at a low temperature. 【0021】 FIG. 1 is a diagram for explaining how to determine the minor axis Z in the present invention. 【0022】<Conductive Powder Containing Copper as a Main Component> The conductive powder of the present invention containing copper as a main component has a volume-based cumulative 50% particle diameter D50 of 0.3 μm or more and 7.5 μm or less as measured by laser diffraction particle size distribution measurement, a ratio of the major axis X to the median axis Y of 1.0 or more and 3.0 or less, and a ratio of the major axis X to the minor axis Z of 1.5 or more and 8.0 or less, and contains an aliphatic amine on at least a portion of the surface of the conductive powder, and the aliphatic amine is an aliphatic amine that, when the copper-based conductive powder is heated from 38°C to 900°C at a heating rate of 10°C / min in an inert atmosphere by TG-MS, at least one peak is detected in a chromatogram of mass number 44, and the ratio of the area of ​​the peak in the range of 250°C to 400°C to the area of ​​the peak in the range of 250°C to 900°C is 0.9 or more. This allows the paste to be suitably used for a conductive paste that can form a dense conductor film even when fired at a low temperature, and also allows the surface treatment agent to be removed at a low temperature. 【0023】 When using conventional flake-shaped powders with a large ratio of the long diameter to the short diameter, firing at a high temperature such as 800°C was necessary to form a dense conductive film; firing at a low temperature such as 720°C did not produce a dense conductive film. In contrast, the copper-based conductive powder of the present invention has a volume-based cumulative 50% particle diameter D50 measured by laser diffraction particle size distribution measurement of 0.3 μm to 7.5 μm, a ratio of the long diameter X to the median diameter Y of 1.0 to 3.0, and a ratio of the long diameter X to the short diameter Z of 1.5 to 8.0, and contains an aliphatic amine on at least a portion of its surface. Therefore, when used in a conductive paste, the filling ability of the conductive powder in the coating film of the conductive paste is improved, which facilitates sintering of the conductive powder even when firing at a low temperature, making it easier to obtain a dense conductive film. 【0024】 However, based on this finding, the inventors further investigated the matter and found that while favorable results were obtained from the viewpoint of low-temperature firing, it may become difficult to remove the aliphatic amine from the conductive powder, i.e., firing at temperatures even lower than the aforementioned temperatures is not favorable. 【0025】 As a result of further investigations, the present inventors found that the aliphatic amine can be removed at low temperatures if it is an aliphatic amine such that, when the copper-based conductive powder is heated from 38°C to 900°C at a heating rate of 10°C / min in an inert atmosphere by TG-MS, at least one peak is detected in a chromatogram of mass number 44, and the ratio of the area of ​​the peak in the range of 250°C to 400°C to the area of ​​the peak in the range of 250°C to 900°C is 0.9 or greater, thereby completing the present invention. 【0026】 The terms "major diameter X," "intermediate diameter Y," and "minor diameter Z" used in this specification (the present invention) are defined as follows. (Major diameter X and intermediate diameter Y) One hundred particles are randomly selected through scanning electron microscope observation, and the average length of the long side of a rectangle circumscribing each particle so as to minimize its area is defined as the major diameter X, and the average length of the short side of the rectangle is defined as the intermediate diameter Y. (Minor diameter Z) 100 parts by mass of the copper-based conductive powder and 7 parts by mass of an acrylic resin dissolved in terpineol are mixed, kneaded using a three-roll mill, diluted with terpineol, and kneaded at 25°C at a shear rate of 4 s －１ A paste-like composition is prepared by adjusting the viscosity at 250 Pa s, and the paste-like composition is cast onto a PET film using an applicator to form a coating film with a thickness of 250 μm. The coating film is dried in an air atmosphere at 150°C for 10 minutes to form a dry film. A cross section of the dry film is exposed using an ion milling device, and the cross section of the dry film is observed with a scanning electron microscope. 100 particles are randomly selected, and the average value of the length of the short sides of the rectangles circumscribing each particle so as to minimize its area is defined as the short diameter Z. 【0027】 The method for determining the minor axis Z will be explained using Figure 1. Figure 1 is a diagram of the cross section of a dried film obtained by drying a coating film, observed with a scanning electron microscope. The minor axis Z is the average value of the length of the short side 3 of the rectangle 2 circumscribing the cross section 1 of the conductive particle, which has the smallest area. 【0028】The conductive powder of the present invention may be any powder containing copper as its main component. In this specification, the term "main component" refers to a component exceeding 50% by mass relative to the total. In particular, in a conductive powder containing copper as its main component, the copper component exceeds 50% by mass relative to the total conductive powder, including the mixed powder and alloy powder described above. The copper content in the conductive powder is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, and particularly preferably 100% by mass (pure copper). Having the copper content in the conductive powder within the above range facilitates sintering of the conductive powder particles, thereby making it easier to obtain a dense sintered film. As long as the conductive powder contains copper as its main component, it may be a mixed powder of copper powder and other elemental metal powders such as nickel powder or silver powder, or an alloy powder of copper and other elemental metals such as nickel or silver. Furthermore, it may be a composite powder in which copper powder is coated with glass, ceramic, or the like, or may have an oxide film on its surface. Furthermore, the conductive powder may be surface-treated with an organometallic compound, a surfactant, or the like, and two or more of these conductive powders may be mixed and used. 【0029】 The copper-based conductive powder of the present invention may have a volume-based cumulative 50% particle diameter D50 of 0.3 μm or more and 7.5 μm or less in laser diffraction particle size distribution measurement, but is preferably 0.3 μm or more and 7.0 μm or less, more preferably 0.3 μm or more and 6.5 μm or less, more preferably 0.3 μm or more and 6.0 μm or less, more preferably 0.3 μm or more and 5.5 μm or less, more preferably 0.3 μm or more and 5.0 μm or less, even more preferably 0.3 μm or more and 4.5 μm or less, and particularly preferably 0.3 μm or more and 4.0 μm or less. When the copper-based conductive powder has a D50 within the above range, sintering of the conductive powder proceeds easily even when fired at a low temperature, making it easier to form a dense fired film. 【0030】The copper-based conductive powder of the present invention may have a ratio of the major diameter X to the median diameter Y of 1.0 or more and 3.0 or less, preferably 1.0 or more and 2.5 or less. When the ratio of the major diameter X to the median diameter Y of the copper-based conductive powder is within the above range, sintering proceeds easily even when firing at low temperatures, making it easier to form a dense fired film. The major diameter X and median diameter Y can both be measured, for example, by scanning electron microscope observation. That is, 100 conductive particles are randomly selected by scanning electron microscope observation, and the average length of the long side of the rectangle circumscribing each particle so as to minimize its area can be measured as the major diameter X and the average length of the short side of the rectangle. 【0031】 The copper-based conductive powder of the present invention may have a ratio of the major axis X to the minor axis Z of 1.5 or more and 8.0 or less, preferably 2.0 or more and 7.5 or less, more preferably 2.5 or more and 7.0 or less, more preferably 3.0 or more and 6.5 or less, even more preferably 3.5 or more and 6.0 or less, and particularly preferably 4.0 or more and 5.5 or less. When the ratio of the major axis X to the minor axis Z of the copper-based conductive powder is within the above range, sintering proceeds easily even when sintering is performed at a low temperature, and a dense sintered film can be easily formed. 【0032】 The minor axis Z can be measured, for example, by scanning electron microscopy of the cross section of a dried film formed using a paste composition containing the conductive powder of the present invention. More specifically, for example, 100 parts by mass of the conductive powder of the present invention and 7 parts by mass of an acrylic resin (e.g., Dianall MB-2677, manufactured by Mitsubishi Chemical Corporation) dissolved in terpineol are mixed, kneaded using a three-roll mill (e.g., manufactured by Inoue Seisakusho), diluted with terpineol, and heated at 25°C and a shear rate of 4 s －１A paste-like composition is prepared by adjusting the viscosity at 250 Pa s, and the paste-like composition is cast onto a PET film using an applicator to form a coating film with a thickness of 250 μm. The coating film is dried in an air atmosphere at 150°C for 10 minutes to form a dry film. A cross section of the dry film is exposed using an ion milling device (e.g., IM4000 manufactured by Hitachi High-Technologies Corporation). The cross section of the dry film is observed using a scanning electron microscope (e.g., SU-8020 manufactured by Hitachi High-Technologies Corporation). 100 conductive particles are randomly selected from the observation, and the average value of the length of the short sides of the rectangles circumscribing the conductive particles can be measured as the short diameter Z. 【0033】 The copper-based conductive powder of the present invention has an aliphatic amine on at least a portion of its surface. By having an aliphatic amine on at least a portion of its surface, the copper-based conductive powder can be prevented from oxidizing and can improve the dispersibility of the conductive powder in the paste, thereby improving the packing of the conductive powder in the coating film of the conductive paste of the present invention, and thereby forming a fired film with excellent density even when fired at a low temperature. 【0034】 The aliphatic amine in the present invention preferably includes at least one of a secondary amine and a tertiary amine, preferably a secondary amine or a tertiary amine, and particularly preferably a tertiary amine. Examples of secondary amines include distearylamine, N-methylstearylamine, and di-n-octylamine, and examples of tertiary amines include triethylamine, dimethyloctylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dimethylbehenylamine, dimethyllaurylamine, and trioctylamine. Of these, dimethylstearylamine and di-n-octylamine are more preferred, and dimethylstearylamine is particularly preferred. This allows the effects of the present invention to be suitably achieved. 【0035】 The molecular weight of the aliphatic amine in the present invention may be, for example, 100 or more and 400 or less, or 150 or more and 350 or less. 【0036】 The boiling point or thermal decomposition temperature of the aliphatic amine in a nitrogen atmosphere in the present invention is preferably 500° C. or lower, more preferably 450° C. or lower, and even more preferably 400° C. or lower. This makes it easier to achieve the effects of the present invention. The lower limit of the thermal decomposition temperature is not particularly limited, and for example, an aliphatic amine having a thermal decomposition temperature of 200° C. or higher can be used. 【0037】 The number of carbon atoms in the main chain of the aliphatic amine in the present invention is preferably 8 or more and 20 or less, more preferably 10 or more and 20 or less, still more preferably 12 or more and 20 or less, still more preferably 14 or more and 20 or less, still more preferably 16 or more and 20 or less, and particularly preferably 17 or more and 19 or less. 【0038】 The aliphatic amine in the present invention may be a saturated aliphatic amine or an unsaturated aliphatic amine, but is preferably a saturated aliphatic amine. 【0039】 The alkyl group of the aliphatic amine in the present invention may be linear or branched. 【0040】 The content of the aliphatic amine in the copper-based conductive powder of the present invention is preferably 0.01 part by mass to 1.0 part by mass, more preferably 0.02 part by mass to 0.10 part by mass, even more preferably 0.02 part by mass to 0.08 part by mass, and particularly preferably 0.02 part by mass to 0.06 part by mass, per 100 parts by mass of the copper-based conductive powder. When the amount of the aliphatic amine is within the above range, the dispersibility of the conductive powder in the paste is improved and the aliphatic amine is easily removed during firing, making it easier to form dense terminal electrodes. 【0041】 Furthermore, when the peak with the strongest intensity among the peaks in the range of 250° C. to 400° C. is defined as the main peak, it is preferable that neither the peak nor the shoulder peak exists within the range of more than the peak top temperature of the main peak to 400° C. This allows the effects of the present invention to be suitably obtained. 【0042】Furthermore, in a differential graph obtained by differentiating the chromatogram, when an upwardly projecting peak exists in the range of 250° C. to 350° C. and the peak with the strongest peak intensity among the upwardly projecting peaks is defined as the main peak of the differential graph, it is preferable that no upwardly projecting peak exists in the range of more than the peak top temperature of the main peak of the differential graph to 400° C. or less. This allows the effects of the present invention to be suitably achieved. 【0043】 As the TG-MS, for example, a STA2500 Regulus manufactured by NETZSCH can be used as a TG-DTA for heating the sample, and a JMS-Q1500GC manufactured by JEOL Ltd. can be used as an MS for mass spectrometry of substances vaporized by heating the sample. 【0044】 The copper-based conductive powder of the present invention preferably has a carbon content of 0.00% by mass or more and 0.10% by mass or less, and particularly preferably 0.00% by mass or more and 0.08% by mass or less. Having a carbon content within the above range makes it easier to form highly dense terminal electrodes. The carbon content (%) can be measured using a carbon / sulfur analyzer (EMIA-320V, manufactured by HORIBA). 【0045】 The copper-based conductive powder of the present invention preferably has a bottom surface and a surface facing the bottom surface, and can be, for example, flat, cylindrical, elliptical cylindrical, truncated conical, truncated conical, rectangular parallelepiped, or other shapes. This facilitates sintering even when fired at low temperatures, making it easier to form a dense fired film. It is preferable that both the bottom surface and the surface facing the bottom surface are completely flat, but they may have irregularities as long as the effects of the present invention are not impaired. The average angle of the surface facing the bottom surface is preferably 0° to 45°, more preferably 0° to 30°, and even more preferably 0° to 15°. 0°, i.e., parallel, is particularly preferred. 【0046】In this specification (the present invention), of the two opposing surfaces, the surface with the larger area is referred to as the "bottom surface," and the other surface is referred to as the "surface opposite the bottom surface." When the areas of the two opposing surfaces are the same, one arbitrarily selected is referred to as the "bottom surface," and the other is referred to as the "opposing surface." Note that the conductive powder of the present invention does not exclude powders of other shapes, such as spherical, as long as the "ratio of major diameter X to median diameter Y," "ratio of major diameter X to minor diameter Z," and "D50" of the entire conductive powder satisfy the above-mentioned numerical ranges. In this case, the content of the conductive powder satisfying the numerical ranges relative to the total conductive powder is not particularly limited, but is preferably more than 50% by mass, more preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. 【0047】 In the copper-based conductive powder of the present invention, where D10 is the cumulative 10% particle diameter on a volume basis in laser diffraction particle size distribution measurement and D90 is the cumulative 90% particle diameter, the ratio (D90-D10) / D50 is preferably 7.5 or less, more preferably 6.5 or less, more preferably 5.0 or less, more preferably 4.0 or less, even more preferably 3.0 or less, and particularly preferably 2.0 or less. The lower limit of (D90-D10) / D50 is not particularly limited, but can be, for example, 0.2 or more. 【0048】 The (D90-D10) / D50 ratio of the copper-based conductive powder is within the above range, i.e., the particle size distribution of the conductive powder is narrow, allowing the conductive powder to be sintered uniformly throughout the entire film. This means that localized sintering within the film can be suppressed, ensuring an appropriate binder removal path throughout the film, resulting in the formation of a highly dense terminal electrode. Furthermore, the terminal electrode can be prevented from becoming too thick due to excessively large conductive powder particles. 【0049】 The specific surface area of ​​the copper-based conductive powder of the present invention is preferably 0.2 m ２ / g or more 3.0m ２ / g or less, particularly preferably 0.3m ２ / g or more 2.0m ２ When the specific surface area of ​​the conductive powder containing copper as a main component is in the above range, sintering proceeds easily even when firing is performed at a low temperature, and a dense fired film is easily formed. 【0050】 The method for producing the copper-based conductive powder of the present invention is not particularly limited. For example, a spherical conductive powder can be produced by a wet method such as a liquid-phase reduction method, or a dry method such as an atomization method, a spray pyrolysis method, a physical vapor phase method, or a chemical vapor phase method. If necessary, the conductive powder can then be surface-treated with a surface treatment agent such as an aliphatic amine described below, and then pulverized using a bead mill, ball mill, stamp mill, or the like. If necessary, the particle size distribution can be adjusted by classification before or after the pulverization process. Wet methods are preferred in terms of obtaining powder with a uniform particle size distribution, while dry methods are preferred in terms of obtaining powder with excellent crystallinity. 【0051】 <Conductive Paste> The composition of the present invention, which is a combination of the copper-based conductive powder, glass frit, binder resin, and organic solvent, can be suitably used as a conductive paste. 【0052】 The conductive paste is preferably used by applying the conductive paste to a laminated body or the like to form a coating film, drying the coating film as needed to form a dry film, and then firing the paste. The peak temperature of firing is not particularly limited, and firing is possible at a temperature of 600°C or higher, which is lower than conventional firing temperatures. From the viewpoints of reducing environmental load, reducing manufacturing costs, and reducing thermal stress on the laminated body, a temperature of 600°C or higher and 720°C or lower is preferred, and a temperature of 600°C or higher and 700°C or lower is particularly preferred. 【0053】 <Glass Frit> The glass frit preferably has a volume-based cumulative 50% particle diameter D50 of 0.3 μm or more and 2.0 μm or less, more preferably 0.5 μm or more and 1.5 μm or less, as measured by laser diffraction particle size distribution measurement. When the D50 of the glass frit is in the above range, a dense fired film can be easily formed, and a fired film (terminal electrode) having excellent continuity can be easily formed. 【0054】When the cumulative 10% particle diameter of the glass frit on a volume basis in laser diffraction particle size distribution measurement is D10 and the cumulative 90% particle diameter is D90, (D90-D10) / D50 is preferably 7.5 or less, more preferably 6.5 or less, more preferably 5.0 or less, even more preferably 3.5 or less, and particularly preferably 2.5 or less. The lower limit of (D90-D10) / D50 is not particularly limited, but can be, for example, 0.2 or more. 【0055】 When the glass frit's (D90-D10) / D50 is within the above range, i.e., when the particle size distribution of the glass frit is narrow, uniformly sized glass frit is uniformly distributed within the pre-fired film, which is densely packed with conductive powder, facilitating uniform sintering of the conductive powder throughout the film. This also suppresses localized sintering within the film, ensuring appropriate debindering paths throughout the film, resulting in the formation of highly dense terminal electrodes. The low level of extremely small glass frit, which exists in agglomerates and is prone to softening and flow, facilitates suppression of localized sintering and localized debindering failures resulting from the sintering. Furthermore, the low level of extremely large glass frit suppresses exposure of the laminated body due to voids that form where the glass frit flows during the firing process, thereby improving the continuity of the terminal electrodes. 【0056】 The composition of the glass frit is not particularly limited, and examples thereof include BaO-ZnO, BaO-ZnO-B ２ O ３ RO-ZnO-B ２ O ３ -MnO ２ RO-ZnO system, RO-ZnO-MnO system ２ RO-ZnO-SiO ２ ZnO-B ２ O ３ system, SiO ２ -B ２ O ３ -R' ２ O-based, SiO ２ -RO-R' ２Glasses such as O-based (where R is an alkaline earth metal element and R' is an alkali metal element) can be used. 【0057】 The glass transition point of the glass frit is preferably 400° C. or higher and 550° C. or lower. When the glass transition point of the glass frit is within the above range, the glass easily wets and spreads throughout the film even when fired at a low temperature, making it easier to form a dense fired film. 【0058】 The softening point of the glass frit is preferably 500° C. or higher and 650° C. or lower. When the softening point of the glass frit is in the above range, the glass easily wets and spreads throughout the film even when fired at a low temperature, making it easier to form a dense fired film. 【0059】 The specific surface area of ​​the glass frit is preferably 2.0 m ２ / g or more 7.0m ２ / g or less, particularly preferably 3.0m ２ / g or more 6.0m ２ When the specific surface area of ​​the glass frit is in the above range, the glass frit is easily dispersed uniformly in the film, and therefore a dense fired film is easily formed. 【0060】 The amount of glass frit is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 4 parts by mass or more and 18 parts by mass or less, even more preferably 6 parts by mass or more and 16 parts by mass or less, and particularly preferably 8 parts by mass or more and 14 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the amount of glass frit is within the above range, a dense fired film can be easily formed. 【0061】 <Binder Resin> The binder resin is not particularly limited, but preferably contains an acrylic resin. The ratio of the acrylic resin to the total binder resin is preferably more than 50% by mass, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. When an acrylic resin is used, it has excellent thermal decomposition properties in a nitrogen atmosphere, so the binder resin can be successfully removed without oxidizing copper. 【0062】The amount of binder resin is not particularly limited, but is preferably 3 to 11 parts by mass, more preferably 4 to 10 parts by mass, even more preferably 5 to 9 parts by mass, and particularly preferably 6 to 8 parts by mass, relative to 100 parts by mass of the conductive powder. When the amount of binder resin is within the above range, it becomes easier to form a highly dense terminal electrode. 【0063】 The weight-average molecular weight of the acrylic resin is not particularly limited, but may be, for example, from 20,000 to 1,000,000. Two or more types of acrylic resins having different weight-average molecular weights, structures, etc. may be used in combination. 【0064】 <Organic Solvent> The organic solvent is not particularly limited, and examples thereof include terpineol, dihydroterpineol, dihydroterpineol acetate, secondary butyl alcohol, butyl carbitol, butyl carbitol acetate, and benzyl alcohol. 【0065】 <Additives> In addition to the above components, the conductive paste may contain additives such as antifoaming agents, plasticizers, dispersants, and rheology modifiers, as needed, as long as the effects of the present invention are not impaired. Examples of plasticizers include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, butyl benzyl phthalate, dioctyl adipate, diisononyl adipate, dibutyl sebacate, diethyl sebacate, dioctyl sebacate, tricresyl phosphate, chlorinated paraffin, and cyclohexane 1,2-dicarboxylic acid diisononyl ester. Examples of rheology modifiers include silica powder. 【0066】 <Physical properties of conductive paste> The shear rate of the conductive paste measured at 25°C was 4 s －１ The viscosity of the conductive paste is not particularly limited, but is preferably 10.0 Pa·s or more and 80.0 Pa·s or less, and particularly preferably 20.0 Pa·s or more and 60.0 Pa·s or less. When the viscosity of the conductive paste is in the above range, it becomes easier to form highly dense terminal electrodes. 【0067】Conductive paste shear rate 40 s when measured at 25 ° C. －１ Viscosity at a shear rate of 0.4 s －１ The viscosity ratio in the conductive paste is not particularly limited, but is preferably 2.0 or more and 20.0 or less, and particularly preferably 3.0 or more and 8.0 or less. When the viscosity ratio of the conductive paste is in the above range, it becomes easier to form a highly dense terminal electrode. 【0068】 When a strain of 1% is applied to the conductive paste at an angular frequency of 1 Hz, the value of the phase difference δ between the strain and the stress generated by the strain is not particularly limited, but is preferably 45° to 80°, and particularly preferably 45° to 78°. When the value of the phase difference δ of the conductive paste is within the above range, it becomes easier to form a highly dense terminal electrode. 【0069】 The conductive paste can be used to calculate the electrode area ratio of the terminal electrodes described below using an evaluation test sample prepared by, for example, the following method. The evaluation test sample can be prepared, for example, by preparing a rectangular parallelepiped laminated body having a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm, in which a plurality of dielectric layers containing barium titanate and internal electrode layers containing nickel are stacked, and applying the conductive paste to the end of the laminated body where the internal electrodes are exposed by a dip printing method with the laminated body lowered at a rate of 300 μm / s and pulled up at a rate of 100 μm / s, and then holding the laminated body in an air atmosphere at 150°C for 10 minutes, and then heating the laminated body in a nitrogen atmosphere at a heating rate of 50°C / min, and after reaching 700°C, holding the body for 15 minutes to form terminal electrodes, thereby producing 20 electronic components equipped with terminal electrodes, and embedding each of the 20 electronic components in resin. Each electronic component can be prepared by cutting the electronic component so as to pass through the center of each end face of the electronic component and in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross section of the electronic component. 【0070】 <Method for Manufacturing Electronic Component> The conductive paste is suitable as a conductive paste for forming terminal electrodes on a laminated element body for a multilayer ceramic electronic component. 【0071】The method for manufacturing an electronic component using a conductive paste includes a laminated body preparation step of preparing a laminated body for a multilayer ceramic electronic component, which comprises a plurality of ceramic layers and a plurality of internal electrode layers, and a terminal electrode formation step of applying a conductive paste to exposed ends of the internal electrodes of the laminated body and then firing the applied conductive paste to form terminal electrodes. By using the conductive paste of the present invention in the above-described method for manufacturing an electronic component, highly dense terminal electrodes can be formed even when firing is performed at a low temperature in the terminal electrode formation step. In other words, the above-described method for manufacturing an electronic component allows the manufacture of an electronic component having highly dense terminal electrodes, even when firing is performed at a low temperature in the terminal electrode formation step. 【0072】 The laminated element preparing step is a step of preparing a laminated element for a multilayer ceramic electronic component. 【0073】 A laminated element for a multilayer ceramic electronic component comprises a plurality of ceramic layers and a plurality of internal electrode layers. In the laminated element for a multilayer ceramic electronic component, the ceramic layers and the internal electrode layers are alternately stacked. Examples of laminated elements for multilayer ceramic electronic components include laminated elements for multilayer ceramic capacitors, laminated elements for multilayer ceramic inductors, and laminated elements for piezoelectric actuators. 【0074】 Examples of materials for forming the ceramic layers constituting the laminated element for a laminated ceramic electronic component include barium titanate, strontium titanate, calcium titanate, barium zirconate, strontium zirconate, calcium zirconate, and strontium calcium zirconate. 【0075】 Examples of materials for forming the internal electrode layers constituting the laminated body for a multilayer ceramic electronic component include nickel, palladium, silver, copper, and gold, or alloys containing one or more of these (e.g., an alloy of silver and palladium). 【0076】 The terminal electrode forming step is a step of applying the conductive paste of the present invention to the exposed ends of the internal electrodes of a laminated body for a multilayer ceramic electronic component, and firing the applied conductive paste to form terminal electrodes. 【0077】 The method for applying the conductive paste is not particularly limited, and examples thereof include dip printing, screen printing, and roll coating. Among these, dip printing is preferred. After the conductive paste is applied to the laminated body, it may be dried and then fired. 【0078】 In the terminal electrode forming step, after the terminal electrodes are formed, a plating layer can be formed on the surface of the electrodes. 【0079】 In this specification, both ends of the laminated element where the internal electrodes are exposed are referred to as "ends," the surfaces of the ends where the internal electrodes are particularly exposed are referred to as "end faces," and the outer edge portions of the end faces are referred to as "corners." Typically, when applying a conductive paste to the ends in the terminal electrode formation process, the conductive paste is applied so as to cover the end faces and corners. 【0080】 The size of the laminated element in which the conductive paste is used is not particularly limited, and the conductive paste can be used, for example, for laminated elements for 2012 size laminated ceramic capacitors, laminated elements for 1608 size laminated ceramic capacitors, laminated elements for 1005 size laminated ceramic capacitors, laminated elements for 0603 size laminated ceramic capacitors, laminated elements for 0402 size laminated ceramic capacitors, and laminated elements for 0201 size laminated ceramic capacitors. 【0081】 The electrode area ratio of the terminal electrodes of the multilayer ceramic electronic component obtained by the present invention is not particularly limited, but is preferably 90% or more, and particularly preferably 99% or more. This makes it easier to prevent the plating solution from penetrating into the laminated body when plating the terminal electrodes. The electrode area ratio can be calculated, for example, by the following method. That is, 20 electronic components are embedded in resin, and each electronic component is cut through the center of each end face of the electronic component in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross section of each electronic component. The cross section is then observed using a scanning electron microscope in 10 fields of view for each electronic component, and the ratio of the electrode area to the observed field of view can be calculated as the electrode area ratio. 【0082】 The present invention will be described below based on specific experimental examples, but the present invention is not limited to these. 【0083】 <Production of Copper Powder> First, spherical copper powder produced by a known dry method (atomization) was prepared as the raw powder. Next, zirconia beads with a diameter of 0.1 mm, the spherical copper powder, secondary butyl alcohol, and a predetermined lubricant (aliphatic amine) were mixed together. Using a bead mill, physical force was applied to the spherical copper powder by adjusting the flow rate and number of passes as appropriate until the ratio of the major axis X to the minor axis Z reached the values ​​shown in Table 1, yielding copper powders of Experimental Examples 1 to 10. Table 1 shows the physical properties of the copper powders of Experimental Examples 1 to 10, measured by the following measurement methods, and the evaluation results of electronic components fabricated using the copper powders of Experimental Examples 1 to 10, measured by the following evaluation methods. In Table 1, experimental examples marked with an "*" are outside the scope of the present invention. Furthermore, "present (shoulder)" in Table 1 indicates that there is no peak, but a shoulder peak is present. 【0084】 <D50> The volume-based cumulative 50% particle diameter D50 (μm) was measured using a laser diffraction particle size distribution analyzer (LA-960, manufactured by HORIBA). 【0085】 <Ratio of major diameter X to median diameter Y and ratio of major diameter X to minor diameter Z> The ratio of major diameter X to median diameter Y and the ratio of major diameter X to minor diameter Z were calculated using the values ​​of major diameter X, median diameter Y, and minor diameter Z measured by the following method. (Major diameter X and median diameter Y) 100 particles were randomly selected by observation with a scanning electron microscope, and the average length of the long side of a rectangle circumscribing each particle so as to minimize its area was measured as the major diameter X and the average length of the short side as the median diameter Y. (Minor diameter Z) 100 parts by mass of copper powder and 7 parts by mass of an acrylic resin (Dianal MB-2677, manufactured by Mitsubishi Chemical Corporation) dissolved in terpineol were mixed, then kneaded using a three-roll mill (manufactured by Inoue Seisakusho), then diluted with terpineol, and kneaded at 25°C and a shear rate of 4 s －１A paste-like composition was prepared by adjusting the viscosity at 2000 kJ / min to 30 Pa s, and the paste-like composition was cast onto a PET film using an applicator to form a coating film with a thickness of 250 μm. The coating film was dried in an air atmosphere at 150°C for 10 minutes to form a dry film. The cross section of the dry film was exposed using an ion milling device (IM4000 manufactured by Hitachi High-Technologies Corporation). The cross section of the dry film was observed with a scanning electron microscope (SU-8020 manufactured by Hitachi High-Technologies Corporation). Based on the observation, 100 copper particles were randomly selected, and the average value of the length of the short side of a rectangle circumscribing each particle so as to minimize the area was measured as the short diameter Z. 【0086】 <TG-MS> For copper powder, the transition of the amount of gas generated (peak intensity) with respect to temperature change for molecules with a mass number of 44 was measured by TG-MS (thermogravimetry-mass spectrometry) when the temperature was raised from 38°C to 900°C at a heating rate of 10°C / min in an inert helium atmosphere, and the peak area was measured in each temperature range. Table 1 also shows the peak-top temperatures of predetermined peaks, and the presence or absence of peaks and shoulders in predetermined temperature ranges. The transition of the amount of gas generated (peak intensity) with respect to temperature change for the molecule with a mass number of 44 was differentiated, and the peak-top temperatures and presence or absence of peaks for upwardly convex peaks in predetermined temperature ranges in the graph obtained by this differentiation are shown in Table 1. Note that EI (electron ionization) was used as the ionization method for MS. NETZSCH's STA2500 Regulus was used as the TG-DTA for heating the sample, and JEOL's JMS-Q1500GC was used as the MS for mass spectrometry of the substances vaporized by heating the sample. 【0087】 <Density> (Preparation of Conductive Paste) 100 parts by mass of copper powder, 7 parts by mass of an acrylic resin (Dianal MB-2677, manufactured by Mitsubishi Chemical Corporation) dissolved in terpineol as a resin, and 10 parts by mass of glass frit (BaO-ZnO-based glass) were mixed, then kneaded using a three-roll mill (manufactured by Inoue Seisakusho), then diluted with terpineol, and kneaded at 25°C at a shear rate of 4 s －１ The viscosity at 1000 kJ / min was adjusted to 30 Pa·s to prepare a conductive paste. 【0088】 (Fabrication of Electronic Component with Terminal Electrodes) A ​​roughly rectangular parallelepiped laminated element having a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm was prepared, in which multiple dielectric layers containing barium titanate and internal electrode layers containing nickel were stacked. A conductive paste was applied to the end of this laminated element where the internal electrodes were exposed by dip printing, with the laminated element lowered at a rate of 300 μm / s and raised at a rate of 100 μm / s. The laminated element was then held at 150°C in an air atmosphere for 10 minutes. The temperature was then increased at a rate of 50°C / min in a nitrogen atmosphere, and after reaching 700°C, the temperature was held for 15 minutes to form terminal electrodes, thereby fabricating an electronic component with terminal electrodes. 【0089】 (Preparation of Evaluation Test Samples) In each experimental example, 20 of the above-described electronic components were prepared. Each electronic component was embedded in resin, and cut through the center of each end face of each electronic component in the lamination direction (perpendicular to the dielectric layers and internal electrode layers) to expose the cross section of each electronic component, thereby preparing an evaluation test sample. The following evaluations were performed. 【0090】 (Evaluation of Density (Electrode Area Ratio)) The above-mentioned evaluation test samples were observed with a scanning electron microscope, with 10 visual fields per sample, for a total of 200 visual fields, and the ratio of the electrode area to the visual fields was calculated as the electrode area ratio. The electrode area ratio value was evaluated based on the following evaluation criteria. 【0091】 A: Electrode area ratio is 90% or more B: Electrode area ratio is less than 90% 【0092】 <Removability of Surface Treatment Agent> For copper powder, the temperature was raised from 38°C to 900°C at a heating rate of 10°C / min in an inert helium atmosphere, and the transition of the amount of gas generated (peak intensity) with respect to temperature change for molecules with a mass number of 44 was measured by TG-MS, and the ratio of the peak area from 250°C to 400°C to the peak area from 250°C to 900°C was calculated. The peak area ratio was evaluated based on the following evaluation criteria. Note that the larger the peak area ratio, the better the removability of the surface treatment agent. 【0093】 A: Peak area ratio is 0.9 or more B: Peak area ratio is less than 0.9 【0094】 <Sinterability (Shrinkage Rate Measured by Thermomechanical Analysis (TMA))> 200 mg of copper powder was pressed at a pressure of 1.0 kN for 3 minutes to form a cylindrical sample with a diameter of 5 mm and a height of 2 mm. Using a TMA apparatus (TMA4000S, manufactured by Bruker), the sample was heated from room temperature to 900°C at a rate of 10°C / min in a nitrogen atmosphere. The percentage (%) of the sample height at each temperature (each time) relative to the sample height (2 mm) was measured as the shrinkage rate. The change in sample height with respect to time was differentiated to measure the shrinkage rate [µm / sec] at each temperature (each time). From the measurement results, the absolute value of the maximum shrinkage rate [µm / sec] (maximum value (absolute value) of ΔTMA) and the temperature [°C] at this maximum value (temperature at the peak top of ΔTMA) were obtained. 【0095】 【0096】 1 Cross section of conductive particle 2 Rectangle circumscribing the cross section of the conductive particle 3 Short side of the rectangle 4 Long side of the rectangle

Claims

[Claim 1] A conductive powder having copper as its main component, The conductive powder has a volume-based cumulative 50% particle size D50 of 0.3 μm or more and 7.5 μm or less in laser diffraction particle size distribution measurement, a ratio of the major axis X defined below to the medium axis Y defined below is 1.0 or more and 3.0 or less, and a ratio of the major axis X defined below to the minor axis Z defined below is 1.5 or more and 8.0 or less. The conductive powder has an aliphatic amine on at least a portion of its surface, The aliphatic amine is such that, when the copper-based conductive powder is heated from 38°C to 900°C at a heating rate of 10°C / min in an inert atmosphere by TG-MS, at least one peak is detected in the chromatogram of mass number 44, and the ratio of the area of ​​the peak in the range of 250°C to 400°C to the area of ​​the peak in the range of 250°C to 900°C is 0.9 or more. A conductive powder having copper as its main component, characterized by the following features. (Longest axis X and medium axis Y) Using a scanning electron microscope, 100 particles are randomly selected, and the average length of the longer side of the rectangle circumscribing each particle to minimize its area is defined as the major axis X, and the average length of the shorter side is defined as the medium axis Y. (Short axis Z) 100 parts by mass of conductive powder mainly composed of copper and 7 parts by mass of acrylic resin dissolved in terpineol are mixed, then kneaded using a three-roll mill, then diluted with terpineol, and processed at 25°C and a shear rate of 4s. －１ A paste-like composition is prepared by adjusting the viscosity to 30 Pa·s, the paste-like composition is cast onto a PET film using an applicator to form a coating film with a thickness of 250 μm, the coating film is dried in an air atmosphere at 150°C for 10 minutes to form a dried film, the cross-section of the dried film is exposed using an ion milling apparatus, the cross-section of the dried film is observed with a scanning electron microscope, 100 particles are randomly selected, and the average length of the short side of the rectangle circumscribing each particle to minimize its area is defined as the minor axis Z. [Claim 2] The copper-based conductive powder according to claim 1, wherein the aliphatic amine comprises at least one aliphatic amine from among secondary amines and tertiary amines. [Claim 3] The copper-based conductive powder according to claim 1, wherein when the peak with the strongest peak intensity among the peaks within the range of 250°C to 400°C is designated as the main peak, neither peaks nor shoulder peaks exist within the range exceeding the peak top temperature of the main peak but not exceeding 400°C. [Claim 4] The conductive powder mainly composed of copper according to claim 1, wherein in the differential graph obtained by differentiating the chromatogram, there is an upwardly convex peak in the range of 250°C to 350°C, and when the peak with the strongest peak intensity among the upwardly convex peaks is taken as the main peak of the differential graph, there are no upwardly convex peaks in the range exceeding the peak top temperature of the main peak of the differential graph and up to 400°C. [Claim 5] The copper-based conductive powder according to claim 1, wherein the aliphatic amine includes dimethylstearylamine. [Claim 6] The copper-based conductive powder according to Claim 1, wherein the aliphatic amine is an aliphatic amine whose peak area ratio is 0.9 or more and 1.0 or less. [Claim 7] A conductive paste comprising a conductive powder mainly composed of copper as described in any one of claims 1 to 6, glass frit, a binder resin, and an organic solvent. [Claim 8] A laminated body preparation step for preparing a laminated body for a multilayer ceramic electronic component consisting of multiple ceramic layers and multiple internal electrode layers, A terminal electrode forming step involves applying the conductive paste described in claim 7 to the exposed end of the internal electrode of the laminated body, and then firing the applied conductive paste to form a terminal electrode, A method for manufacturing electronic components, comprising: [Claim 9] The method for manufacturing an electronic component according to claim 8, wherein the peak temperature when firing the conductive paste is 600°C or more and 720°C or less.