Copper powder, paste, sintered body, composite, low-temperature co-fired ceramic substrate and multilayer ceramic capacitor

Abstract

To provide a copper powder to sinter at a temperature high to a certain extent and, after sintering, turn into a sintered body having comparatively high density, paste, a sintered body, a low-temperature co-fired ceramic substrate and a multilayer ceramic capacitor.SOLUTION: A copper powder having a surface-treated layer contains a Si compound having a Si-O bond, amphoteric metal X and alkali earth metal Y. The Si, the amphoteric metal X and the alkali earth metal Y having mole numbers α(mol), β(mol) and γ(mol) respectively satisfy Expressions (I): α / β≥0.8, (II): γ / β≥0.4 and (III): 4α≥2.4β+1.6γ.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This specification describes copper powders, pastes, sintered bodies, composites, low-temperature co-fired ceramic substrates, and multilayer ceramic capacitors. [Background technology]

[0002] In recent years, in order to realize miniaturization and high performance of electronic devices, there has been a demand for finer, smoother, denser wiring in, for example, low temperature co-fired ceramic (LTCC) substrates, multilayer ceramic capacitors (MLCC), and other electronic substrates or electronic components used in electronic devices. To meet such demands, it is believed that using fine copper powder for forming the wiring is effective.

[0003] In such applications, copper powder may be mixed in advance with organic materials such as a solvent and an organic binder to form a paste. In this case, the paste is printed in a predetermined pattern by screen printing or the like, and then fired to remove the organic materials from the paste and sinter the copper powder. This results in the formation of wiring as a sintered body of copper powder.

[0004] To produce this type of fine copper powder, for example, a chemical reduction method or a disproportionation method may be used from a slurry in which cuprous oxide powder is dispersed.

[0005] As a related technology, for example, Patent Document 1 addresses the issue of "obtaining copper powder for conductive paste for external electrodes that is simultaneously excellent in oxidation resistance and sinterability," and proposes "copper powder for conductive paste for external electrodes that is excellent in oxidation resistance and sinterability, characterized in that the copper powder used as a conductive filler in the conductive paste contains 5% by weight or less of Si, substantially all of which is adhered to the copper particle surfaces as an SiO2-based gel coating film, and this SiO2-based gel coating film contains at least one glass-forming component." [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-101276 Summary of the Invention [Problem to be solved by the invention]

[0007] In the manufacture of LTCC substrates, a paste is applied to a green sheet containing ceramic powder, and then the two are fired simultaneously, sintering both the ceramic powder in the green sheet and the copper powder in the paste.

[0008] Here, the temperature ranges of the shrinkage behavior of the ceramic powder and the copper powder may not match during firing, and in this case, the stress associated with the difference in shrinkage may lead to peeling or cracking of the wiring.In general, ceramic powders have a high sintering temperature, while metal powders with smaller particle sizes tend to be sintered at lower temperatures, so the above-mentioned difference in shrinkage becomes more pronounced when relatively fine copper powder is used in the production of LTCC substrates.

[0009] Furthermore, firing during the manufacture of LTCC substrates and MLCCs involves heating in an atmosphere containing water vapor to thoroughly remove organic matter contained in pastes, etc., which can result in the separation of decomposition products of the organic matter as gas. If the copper powder is sintered at a relatively low temperature, the gas generated inside the copper powder during sintering may not be released to the outside, which can result in the formation of voids inside the wiring obtained after sintering the copper powder (the so-called blister phenomenon). The voids formed in the wiring pose a risk of reducing product reliability, such as by allowing plating solution to seep in.

[0010] Patent Document 1 is recognized to have an object of providing copper powder that can be sintered at low temperatures (see paragraphs 0005, 0007, and 0025, etc.), and does not pay any attention to the above-mentioned points.

[0011] This specification discloses copper powder, paste, sintered body, composite, low-temperature co-fired ceramic substrate and multilayer ceramic capacitor that are sintered at a relatively high temperature to form a sintered body with a relatively high density after sintering. [Means for solving the problem]

[0012] The copper powder disclosed in this specification has a surface treatment layer and contains a Si compound having a Si-O bond, an amphoteric metal X, and an alkaline earth metal Y, wherein the amount of substance α (mol) of the Si, the amount of substance β (mol) of the amphoteric metal X, and the amount of substance γ (mol) of the alkaline earth metal Y satisfy the following relations: (I) α / β≧0.8, (II) γ / β≧0.4, and (III) 4α≧2.4β+1.6γ.

[0013] The paste disclosed in this specification contains the above copper powder.

[0014] The sintered body disclosed in this specification is a sintered body of copper powder, and the copper powder contains the above-mentioned copper powder.

[0015] The composite disclosed in this specification comprises a sintered body of ceramic powder and the above-mentioned sintered body of copper powder formed on the sintered body of ceramic powder.

[0016] The low-temperature co-fired ceramic substrate disclosed in this specification comprises the above composite.

[0017] The multilayer ceramic capacitor disclosed in this specification comprises the above composite. [Effects of the Invention]

[0018] The above-mentioned copper powder is sintered at a relatively high temperature, and after sintering, it becomes a sintered body with a relatively high density. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the above-mentioned copper powder, paste, sintered body, composite, low-temperature co-fired ceramic substrate, and multilayer ceramic capacitor will be described in detail.

[0020] In one embodiment, the copper powder has a surface treatment layer. The copper powder mainly contains, in the surface treatment layer, a Si compound having an Si-O bond (hereinafter also referred to as "Si compound"), an amphoteric metal X, and an alkaline earth metal Y. Typically, at least a portion of the amphoteric metal X is contained as a compound of the amphoteric metal X (hereinafter also referred to as "X compound"), and at least a portion of the alkaline earth metal Y is contained as a compound of the alkaline earth metal Y (hereinafter also referred to as "Y compound"), but the forms of the amphoteric metal X and the alkaline earth metal Y in the copper powder are not important. When the amounts of substance α, β, and γ of Si (silicon), amphoteric metal X, and alkaline earth metal Y in copper powder having such a surface treatment layer are measured, the amount of substance α (mol) of Si, the amount of substance β (mol) of amphoteric metal X, and the amount of substance γ (mol) of alkaline earth metal Y satisfy the following equations: (I) α / β≧0.8, (II) γ / β≧0.4, and (III) 4α≧2.4β+1.6γ.

[0021] When copper powder bearing a surface treatment layer containing a silicon compound, an amphoteric metal X, and an alkaline earth metal Y is heated, a glass network consisting primarily of oxides containing silicon, amphoteric metal X, alkaline earth metal Y, and oxygen is believed to form on the surface of the copper powder at a certain temperature. This glass network, provided that silicon, amphoteric metal X, and alkaline earth metal Y are present in a predetermined amount or ratio, exists between the copper powder particles at low temperatures and effectively inhibits sintering of the copper powder. At high temperatures, however, it acquires a moderate fluidity and can be expelled and removed. More specifically, when the above formulas (I), (II), and (III) are satisfied, the formation of triclusters, which have a structure in which three tetrahedra bond to one oxygen atom, is suppressed. This is expected to prevent triclusters from impeding vitrification and reducing the density of sintered copper powder. The triclusters are believed to function as crystal nuclei for mullite (3Al2O3·2SiO2 or 2Al2O3·SiO2), a type of ceramic. It is believed that when mullite is generated on the surface of copper powder due to triclusters during sintering, the poor fluidity of mullite causes the mullite to remain on the surface of the copper powder after sintering. Therefore, the formation of triclusters is thought to result in a decrease in the density of the sintered copper powder.

[0022] As a result, the copper powder is coated with a polymeric, highly fluid glass network, allowing it to be sintered at a relatively high temperature. Furthermore, as the sintering temperature increases, the decomposition gases of organic substances contained in the paste are sufficiently released before the sintering temperature is reached, making it less likely for blistering to occur. Additionally, the suppression of a decrease in the fluidity of the glass network makes it easier for the glass network to be released to the outside during the copper powder firing process. As a result, a high-density sintered body or wiring with suppressed void formation can be obtained.

[0023] (copper powder) Copper powder contains Cu (copper), and in many cases is composed mostly of Cu. The Cu content of copper powder excluding copper oxide is, for example, 99.0 mass% or more, and typically 99.5 mass% or more. The presence and Cu content of copper powder can be confirmed and measured by X-ray diffraction (XRD).

[0024] The copper powder has a BET specific surface area of ​​0.13 m 2 / g or more, preferably 0.22m 2 / g or more, more preferably 0.67m 2 / g or more. The copper powder has a BET specific surface area of ​​15m 2 / g or less, preferably 10m 2 / g or less, more preferably 5m 2 / g or less. Even with copper powder having a large specific surface area and a relatively small particle size, in this embodiment, the sintering temperature can be increased by forming a predetermined surface treatment layer. Note that the smaller the BET specific surface area, in other words, the larger the particle size of the copper powder, the higher the sintering temperature of the copper powder and the higher the density of the sintered body. On the other hand, the larger the BET specific surface area, in other words, the smaller the particle size of the copper powder, the more fine wiring can be formed. The BET specific surface area here refers to the value measured on copper powder that has been surface-treated and has a surface treatment layer formed thereon.

[0025] The BET specific surface area of ​​copper powder can be measured in accordance with JIS Z8830:2013 using a BELSORP-mini II manufactured by Microtrac-Bell Co., Ltd. More specifically, a 3 g sample of copper powder is degassed for 5 hours at 70°C in a vacuum of 10 Pa or less absolute pressure, and then the nitrogen adsorption isotherm is measured by the static volumetric method. The results obtained are analyzed by the BET method to calculate the BET specific surface area.

[0026] The copper powder has a surface treatment layer. More specifically, the copper powder is composed of surface-treated particles (also simply referred to as "particles") having a copper particle as a core particle and a surface treatment layer that covers at least a portion, typically almost the entire surface, of the copper particle. The surface treatment layer contains a Si compound having an Si-O bond, an amphoteric metal X, and an alkaline earth metal Y, and the copper powder therefore contains a Si compound having an Si-O bond, an amphoteric metal X, and an alkaline earth metal Y. At least a portion of the amphoteric metal X may be in the form of an X compound. At least a portion of the alkaline earth metal Y may be in the form of a Y compound. By including the Si compound, amphoteric metal X, and alkaline earth metal Y, a glass network that increases the sintering temperature when the copper powder is heated can be effectively formed.

[0027] The copper powder of this embodiment is such that the amount of substance α (mol) of Si, the amount of substance β (mol) of amphoteric metal X, and the amount of substance γ (mol) of alkaline earth metal Y contained in the copper powder due to the above-mentioned surface treatment layer, etc., satisfy the following relations: (I) α / β≧0.8, (II) γ / β≧0.4, and (III) 4α≧2.4β+1.6γ.

[0028] If at least one of the above formulas (I), (II), and (III) is not satisfied, there is a concern that the amount of substance β of the amphoteric metal X and / or the amount of substance γ of the alkaline earth metal Y will be too large relative to the amount of substance α of Si, or that the amount of substance β of the amphoteric metal X will be too large relative to the amount of substance γ of the alkaline earth metal Y, resulting in the formation of triclusters, which will inhibit vitrification and make the glass network less fluid. If the fluidity of the glass network decreases, it will remain inside the sintered copper powder, which can cause a decrease in its density.

[0029] The closer the α / β value is to 1.0, the closer the γ / β value is to 0.5, and the closer the 4α value is to 3β + 2γ, respectively. In this case, the proportion of non-bridging oxygen is thought to be sufficiently low, resulting in a high softening temperature of the glass network. Sintering of copper powder begins when exposed copper particles come into contact with each other at high temperatures. When the softening temperature approaches the glass transition temperature, the glass component coats the copper particles at high temperatures, effectively suppressing sintering. In other words, the sintering initiation temperature of the copper powder can be increased. The copper powder preferably has substance amounts α and β that satisfy the formula (I'): α / β ≦ 3.0, preferably the formula (I"): α / β ≦ 2.0, and particularly the formula (I'"): α / β ≦ 1.6. The copper powder preferably has substance amounts β and γ that satisfy the formula (II'): γ / β ≦ 2.0, preferably the formula (II"): γ / β ≦ 1.0, and particularly the formula (II'"): γ / β ≦ 0.7. The copper powder preferably has substance amounts α, β, and γ satisfying the formula (III'): 4α≦3.6β+2.4γ, and more preferably the formula (III''): 4α≦3.3β+2.2γ.

[0030] To ensure a sufficiently high sintering initiation temperature, the Si content, the amphoteric metal X content, and the alkaline earth metal Y content in the copper powder are each preferably 0.01 atomic % or more, more preferably 0.05 atomic % or more, and even more preferably 0.10 atomic % or more. It is possible to add the components of the surface treatment layer of the copper powder of this embodiment to the paste as a glass frit, rather than forming such a surface treatment layer on the copper powder. However, adding the components as a glass frit would likely require a larger amount of addition to increase the sintering temperature compared to forming a surface treatment layer, potentially resulting in a lower density of the sintered body. Therefore, this embodiment has the advantage that an effective surface treatment layer can be formed with a relatively small amount. On the other hand, if the Si content, the amphoteric metal X content, or the alkaline earth metal Y content in the copper powder are too high, there is a concern that the resistivity of the sintered copper powder may increase and the density of the sintered copper powder may not be significantly increased. Therefore, the content of Si, the content of the amphoteric metal X, and the content of the alkaline earth metal Y are each preferably 5.0 atomic % or less, more preferably 3.0 atomic % or less, and particularly preferably 1.5 atomic % or less.

[0031] The Si compounds contained in copper powder contain Si-O bonds and are typically in a gel state. Because a SiO2 network is formed in the Si compounds in a gel state, when they coat the surface of copper particles in a gel state, they may have higher oxidation resistance than when they are not in a gel state.

[0032] Examples of the amphoteric metal X contained in the copper powder include aluminum (Al), zinc (Zn), tin (Sn), and lead (Pb), which can form a glass network, but it is particularly preferable for the copper powder to contain Al as the amphoteric metal X. Aluminosilicate glass containing Al has good thermal stability and mechanical properties, so it is used in substrate glass for liquid crystal displays and cover glass for smartphones, and also has a high glass transition temperature, which is close to the softening temperature, and this is thought to contribute to improving sintering retardation.

[0033] The compound of the amphoteric metal X can include, for example, at least one selected from the group consisting of oxycarboxylic acid salts, carboxylate salts (preferably basic carboxylate salts), and compounds having an XO bond. The oxycarboxylic acid and basic carboxylic acid of the amphoteric metal X are water-soluble and do not evaporate easily, which facilitates the formation of a uniform surface treatment layer, and is expected to further enhance sintering retardation. Furthermore, because they are water-soluble, there is no need to use solvents such as organic solvents that have a high environmental impact.

[0034] In particular, the compound of amphoteric metal X preferably contains at least one selected from the group consisting of lactate, citrate, and tartrate among oxycarboxylates, and in addition to or instead of these, contains basic formate and / or basic acetate among carboxylates. These compounds have short carbon chains, which suppress the generation of decomposition gases or residues that can hinder the improvement of sintered density.

[0035] Compounds having an XO bond are typically produced by hydrolysis of the alkoxide used during surface treatment and can be contained in the surface treatment layer, and ultimately in the copper powder. When the alkoxide is hydrolyzed, in addition to the compound having an XO bond, alcohol is produced as a by-product. Because alcohol has a low boiling point, it can be easily removed by heat drying or the like, and is unlikely to remain as carbon on the copper powder surface. From this perspective, it is preferable to use an alkoxide having an alkoxy group with 4 or fewer carbon atoms for the surface treatment. Examples of such alkoxides include methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide, sec-butoxide, and tert-butoxide. In this case, compounds having an XO bond as decomposition products of the hydrolysis of such alkoxides are contained in the copper powder. The presence of compounds having an XO bond can be confirmed by mass spectrometry, as described below.

[0036] The alkaline earth metal Y preferably contains at least one selected from the group consisting of Ca (calcium), Ba (barium), Sr (strontium), and Ra (radium). Ca, Ba, and Sr have relatively high softening temperatures, and by including at least one of them, the sintering initiation temperature of the copper powder can be increased. Ca is particularly preferred, followed by Ba.

[0037] The alkaline earth metal Y compound may include at least one selected from the group consisting of hydroxides, carboxylates, oxycarboxylates, nitrates, and compounds having a Y-O bond. Hydroxides, carboxylates, and oxycarboxylates of alkaline earth metal Y are preferred because they are less likely to generate corrosive gases during thermal decomposition. Hydroxides, which produce HO as a decomposition by-product, are particularly preferred.

[0038] In particular, the compound of alkaline earth metal Y preferably contains a formate and / or acetate among carboxylates, and in addition to or instead of these, a lactate among oxycarboxylates. These compounds have short carbon chains, which suppress the generation of decomposition gases or residues that can hinder the improvement of sintered density.

[0039] Compounds having a Y-O bond are typically produced by hydrolysis of the alkoxide used in the surface treatment, and the hydrolysis of the alkoxide produces an alcohol as a by-product. Because alcohol has a low boiling point, it can be easily removed by heat drying or the like, and is unlikely to remain as carbon on the copper powder surface. From this perspective, it is preferable to use an alkoxide having an alkoxy group having 4 or less carbon atoms for the surface treatment. Examples of such alkoxides include methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide, sec-butoxide, and tert-butoxide. In this case, the copper powder contains compounds having a Y-O bond as decomposition products of the hydrolysis of such alkoxides.

[0040] To confirm the presence of Si-O bonds in copper powder, copper powder was placed in an aluminum pan (Hitachi High-Tech Science, GAA-0068, Al open-type sample container, φ5.2 H2.5mm) approximately halfway up the pan, and then pressed under wrapping paper to form a tablet. This tablet was then analyzed by X-ray photoelectron spectroscopy (XPS) using a PHI 5000 VersaProbe II (ULVAC-PHI, Inc.). The X-ray source used was monochromated AlKα radiation (X-ray energy: 1486.6 eV), with a power output of 25 W, a beam diameter of 100 μm, an X-ray incidence angle of 90°, and a photoelectron take-off angle of 45°. The measurements were performed with electron and Ar ion beams irradiated for charge neutralization. Data analysis was performed using MultiPak Version 9.5.0.8, and the spectra were corrected for charge by Cu2p 3 / 2 The peak is used and correction is performed assuming that the peak position is 932.7 eV. Then, Si2p, Ca2p 3 / 2 , Ca2p 1 / 2 ,Ba3d 5 / 2 , Sr3d 5 / 2 , Sr3d 3 / 2 The background intensity of the peaks is calculated and peak fitting is performed using the iterative Shirley method, and the peak top of each spectrum obtained is used as the binding energy. The Si2p peak is used to evaluate the presence or absence of Si-O bonds. The Si2p peak position changes depending on the Si bonding state, and a peak is detected between 102 eV and 104 eV for Si-O bonds. The presence of Si-O bonds is determined by detecting a peak in this range.

[0041] The presence of Y-O bonds in copper powder can be confirmed by the XPS analysis described above. The peak position changes depending on the bonding state of the alkaline earth metal Y. For Ca-O bonds, Ca2p 3 / 2 A peak was detected at 345-350 eV in the Sr-O bond. 5 / 2 A peak was detected at 132-137 eV in the bond energy of Ba-O bond. 5 / 2A peak is detected at a bond energy of 778 to 783 eV. By detecting a peak in this range, it is determined that a Y-O bond is present. For example, when copper powder contains calcium lactate, Ca2p 3 / 2 When the copper powder contains barium acetate, a peak is detected at a bond energy of 347.2 to 348.2 eV. 5 / 2 A peak is detected at binding energy of 780.6 to 781.6 eV.

[0042] The presence of compounds X and Y in copper powder can be confirmed as follows. 5 mL of pure water is added to 1 g of copper powder, and ultrasonic irradiation (frequency: 24 or 31 Hz, output: 110 W, temperature: 20°C to 40°C) is performed for 20 minutes. After centrifugation, the supernatant is collected and mixed with 3 mL of acetonitrile. The mixture is filtered through a syringe filter (RephiQuik® Syringe Filter (material: hydrophilic PTFE, pore size: 0.22 μm), manufactured by Rephile), and the filtrate is collected. 0.5 mL of a 0.1% by mass formic acid solution is added to 0.5 mL of this solution. This solution is used as the sample solution and subjected to mass spectrometry. A liquid chromatography-Orbitrap mass spectrometer (Thermo Fisher Scientific Orbitrap Exploris 240 mass spectrometer) can be used as the mass spectrometer, with a scan range of 50-500 (m / z) and a resolution of 60,000. NanoMate manufactured by Advion Interchim Scientific can be used to ionize the sample, with a spray voltage of 1.4 kV, nitrogen gas, and a gas pressure of 0.3 psi.

[0043] As an example, the m / z values ​​of the monoisotopic mass in positive ion detection mode for compounds X and Y used in the tests described in the Examples section below are shown below. The monoisotopic mass of an element is the calculated exact mass of the isotope with the highest natural abundance for each element. Aluminum lactate has an [M+H] near 295.061. + As an ion, aluminum citrate has a [M+H] near 223.040+ As an ion, aluminum tartrate has a [M+H] near 498.973 + As an ion, basic aluminum formate has [M+H] near 250.956 + As an ion, basic aluminum acetate has a [M+H] near 307.019 + As an ion, calcium hydroxide has an [M+H] near 74.976 + As an ion, calcium formate has a [M+H] near 130.966 + As an ion, calcium acetate has a [M+H] near 158.997 + As an ion, calcium lactate has a [M+H] near 219.018 + As an ion, calcium citrate has [M+H] near 498.903 + As an ion, calcium tartrate has an [M+H] near 188.971. + As an ion, calcium nitrate has an [M+H] near 164.946 + As an ion, strontium hydroxide has an [M+H] near 122.919. + As an ion, strontium formate has a [M+H] near 178.909 + As an ion, strontium acetate has a [M+H] near 205.932. + As an ion, strontium lactate has an [M+H] near 266.961. + As an ion, strontium citrate has a [M+H] near 642.732. + As an ion, strontium tartrate has a [M+H] near 236.914. + As an ion, strontium nitrate has an [M+H] near 212.889 + As an ion, barium hydroxide has an [M+H] near 172.919 + As an ion, barium formate has a [M+H] near 228.908 + As an ion, barium acetate has a [M+H] near 256.940 + As an ion, barium lactate has a [M+H] near 316.961. +As an ion, barium citrate has [M+H] near 792.731 + As an ion, barium tartrate has a [M+H] near 286.914 + As an ion, barium nitrate has an [M+H] near 262.889 + The peaks are detected as ions of the above. "Close" means within ±0.1%. [M+H] + The ions refer to ions in which a proton is added to a molecule of the target compound. In some cases, no peak is detected at the m / z value in the monoisotopic mass. In such cases, a peak containing an organic acid derived from the X compound and an amphoteric metal X, or a peak containing an organic acid derived from the Y compound and an alkaline earth metal Y, may be detected. For example, if the copper powder contains aluminum lactate ([CHCH(OH)COO]Al), instead of detecting a peak near the monoisotopic mass of 295.061, a peak may be detected near the calculated mass of 205.0293, which corresponds to the structure [CHCH(OH)COO]Al, where one lactic acid moiety [CHCH(OH)COO] is removed from aluminum lactate; or a peak may be detected near the calculated mass of 179.0136, which corresponds to the structure [CHCH(OH)COO(COH)]Al, where two lactic acid moieties [CHCH(OH)COO] are removed from aluminum lactate and formic acid is added. The latter is thought to be due to the addition of formic acid used as a pretreatment for mass spectrometry. From the results of such mass spectrometry, it can be confirmed that the compound of amphoteric metal X is a lactate, which is a type of oxycarboxylate. In other words, the detection of a peak containing an organic acid derived from compound X and amphoteric metal X, or a peak containing an organic acid derived from compound Y and alkaline earth metal Y, confirms that the compound of amphoteric metal X or the compound of alkaline earth metal Y is the above-mentioned compound.

[0044] The amount of substance α and content of Si in copper powder are determined as follows. Copper powder is alkali-fused using sodium peroxide and sodium carbonate, the resulting molten material is dissolved in hydrochloric acid, and the solution is adjusted to a certain amount with ultrapure water. This solution is then analyzed by ICP atomic emission spectrometry to determine the mass of Si (μg) per unit mass (g) of copper powder. Specifically, a calibration curve of Si concentration is created using a standard solution using a Hitachi High-Tech Science ICP-OES: PS3500UVDDII, and then a sample solution adjusted to fall within the range of the calibration curve is measured. More specifically, Kanto Chemical's JCSS standard solution for chemical analysis (silicon standard solution (Si1000), specifications: for atomic absorption spectrometry, ICP analysis) was added to a solution consisting of sodium peroxide, sodium carbonate, and hydrochloric acid to prepare solutions with Si concentrations of 0.1 μg / mL and 1.0 μg / mL, as well as a solution with a Si concentration of 0 μg / mL without the addition of the Kanto Chemical's JCSS standard solution for chemical analysis. These were used as standard solutions to create a calibration curve. The sodium peroxide, sodium carbonate, and hydrochloric acid contained in the standard solution were adjusted to have the same molar concentrations as those of the sodium peroxide, sodium carbonate, and hydrochloric acid contained in the sample solution. The sample solution was prepared in an amount of 0.5 g, and the Si concentration of the sample solution was adjusted to fall within the range of the calibration curve. A wavelength free of spectral interference was selected for measurement, and off-peak background correction was applied. The crucible used in alkali fusion is selected from a material that does not allow the element to be measured to elute and that does not form hardly soluble substances with the crucible components. For example, a zirconium crucible can be used.

[0045] The amount of substance β and content of amphoteric metal X in copper powder are determined as follows: Copper powder is alkali-fused using sodium peroxide and sodium carbonate, the resulting molten material is dissolved in hydrochloric acid, and the solution is adjusted to a certain amount with ultrapure water. This solution is then measured by ICP atomic emission spectrometry to determine the mass (μg) of amphoteric metal X per unit mass (g) of copper powder. Specifically, a calibration curve of X concentration is created using a standard solution using an ICP-OES: PS3500UVDDII manufactured by Hitachi High-Tech Science Corporation, and then a sample solution adjusted to fall within the range of the calibration curve is measured. More specifically, Kanto Chemical's JCSS standard solution for chemical analysis (aluminum standard solution (Al 1000), zinc standard solution (Zn 1000), tin standard solution (Sn 1000), lead standard solution (Pb 1000), specifications: for atomic absorption spectrometry, ICP analysis) corresponding to the metal species to be measured was added to a solution consisting of sodium peroxide, sodium carbonate, and hydrochloric acid to prepare solutions with X concentrations of 0.1 μg / mL and 1.0 μg / mL, and a solution with an X concentration of 0 μg / mL without the above Kanto Chemical's JCSS standard solution for chemical analysis was also prepared. These were used as standard solutions to create a calibration curve. The sodium peroxide, sodium carbonate, and hydrochloric acid contained in the standard solution were adjusted to have the same molar concentrations as the sodium peroxide, sodium carbonate, and hydrochloric acid contained in the sample solution, respectively. The sample solution was prepared in an amount of 0.5 g, and the X concentration of the sample solution was adjusted to fall within the range of the calibration curve. The measurement wavelength is selected to be free from spectral interference, and off-peak background correction is applied. The crucible used during alkali fusion is selected from a material that does not dissolve the measurement element and does not form hardly soluble substances with the crucible components; for example, a zirconium crucible can be used.

[0046] The amount of substance γ and content of alkaline earth metal Y in copper powder are determined as follows: Copper powder is dissolved using hydrochloric acid and nitric acid, and the solution is adjusted to a certain amount with ultrapure water. By measuring the solution using ICP atomic emission spectrometry, the mass (μg) of alkaline earth metal Y per unit mass (g) of copper powder can be determined. Specifically, a calibration curve of Y concentration is created using a standard solution using an ICP-OES: PS3500UVDDII manufactured by Hitachi High-Tech Science Corporation, and then a sample solution adjusted to fall within the range of the calibration curve is measured. More specifically, the JCSS standard solution for chemical analysis manufactured by Kanto Chemical (calcium standard solution 1 (Ca 1000), strontium standard solution (Sr 1000), barium standard solution (Ba 1000), specifications: for atomic absorption spectrometry, ICP analysis) corresponding to the metal species to be measured was added to a solution consisting of hydrochloric acid and nitric acid to prepare solutions with Y concentrations of 1 μg / mL and 10 μg / mL, and a solution with a Y concentration of 0 μg / mL without the JCSS standard solution manufactured by Kanto Chemical. These were used to prepare a calibration curve. The hydrochloric acid and nitric acid contained in the standard solution were adjusted to the same molar concentrations as those of the hydrochloric acid and nitric acid contained in the sample solution. The sample solution was prepared in a volume of 0.5 g, and the Y concentration of the sample solution was adjusted so that it was within the range of the calibration curve. Measurement wavelengths with no spectral interference were selected, and measurements were performed using off-peak background correction.

[0047] The carbon (C) content in the copper powder is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less. The oxygen (O) content in the copper powder is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 2.0% by mass or less. If the C or O content is too high, copper oxide (CuO) or cuprous oxide (CuO) is likely to be generated. Copper oxide and cuprous oxide tend to remain in the sintered compact without being reduced in a water vapor atmosphere. As a result, the resistivity of the sintered compact may increase, and the density of the sintered compact may decrease. While there are no particular drawbacks to a low C or O content, the copper powder of this embodiment often contains C or O derived from the compounds in the surface treatment layer.

[0048] The carbon content of copper powder is measured using a high-frequency induction furnace combustion-infrared absorption method. Specifically, a carbon-sulfur analyzer such as the LECO CS844 is used to measure the carbon content of copper powder. The sample is adjusted to a 0.2 g weight within the calibration curve intensity range, and the combustion improver is LECO CEL II and Fe chips. A standard steel pin is used for the calibration curve. When measuring the sample in an alumina crucible, the alumina crucible can be pretreated by heating it in air from room temperature to 1000°C at a constant rate over two hours and then holding it at 1000°C for two hours before measuring the carbon content of the copper powder.

[0049] The O content of copper powder is measured using the inert gas fusion-infrared absorption method. Specifically, an oxygen / nitrogen analyzer such as the LECO TC600 is used, and the test sample amount is adjusted to 0.02g to 0.05g so that it falls within the strength range of the calibration curve. A certified reference material steel pin is used for the calibration curve, and the copper powder is placed in a nickel capsule and measured. To prevent oxidation by oxygen in the air, measurements should be taken immediately after opening.

[0050] The copper powder preferably has a 2% shrinkage temperature of 500°C or higher, and more preferably 700°C or higher, as measured by thermomechanical analysis (TMA) at which it shrinks by 2% when heated from room temperature to 1000°C in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa. Such a high 2% shrinkage temperature makes it easier for the shrinkage behavior of the copper powder to match that of the ceramic powder during the production of LTCC substrates, thereby suppressing peeling and cracking of wiring. Furthermore, when the copper powder is made into a paste and sintered, sintering is less likely to occur until sufficient decomposition products of organic matter are released as gas, thereby suppressing the occurrence of blistering.

[0051] Furthermore, when the copper powder is heated from room temperature to 1000°C in a nitrogen and water vapor atmosphere with a water vapor pressure of 3.6 kPa in a thermomechanical analysis, the minimum value of the linear expansion coefficient during this temperature rise is preferably 95% or more, and more preferably 96% or more, of the theoretical ideal linear expansion coefficient calculated from the true density and thermal expansion coefficient of copper at the temperature at which this minimum value is obtained. This means that the copper powder is sintered densely, which suppresses the formation of voids in the sintered compact and reduces the risk of deterioration in product reliability due to factors such as penetration of plating solution.

[0052] The thermomechanical analysis is performed as follows. Copper powder (approximately 0.3 g) is placed in a pellet die with a 5 mm diameter hole and compressed with a force of 1 kN to produce a cylindrical copper powder pellet (height: approximately 3 mm, diameter: approximately 5 mm). The height is measured using a micrometer (such as a coolant-proof micrometer MDC-25MX, with a maximum allowable error of ±1 μm), and this is the initial pellet height. The pellet is placed in a thermomechanical analyzer (such as a NETZSCH TMA4000SE), evacuated to a gauge pressure of -0.1 MPa or less, and then nitrogen is introduced to create an inert atmosphere. A water vapor generator (NETZSCH HC9800) is then connected to the thermomechanical analyzer, and nitrogen gas containing water vapor set to a dew point temperature of 30°C is introduced at a flow rate of 300 mL / min. The nitrogen flow rate from the thermomechanical analyzer is then changed to 50 mL / min. The gas is allowed to flow in this state for 15 minutes to stabilize the measurement atmosphere. While gas is flowing from the steam generator and the thermomechanical analyzer, the temperature is increased from room temperature (25°C) to 1000°C at a rate of 10°C / min while a 10g load is applied. During this heating from room temperature to 1000°C, the pellet height is measured every second, and the temperature at which the pellet shrinks by 2% from the initial height is defined as the 2% shrinkage temperature.

[0053] The linear expansion coefficient can be calculated by dividing the height of the copper powder pellets during heating, obtained by the thermomechanical analysis described above, by the initial height of the pellets, subtracting 1 from the result, and then multiplying the result by 100. Because the pellet height decreases during heating, the linear expansion coefficient becomes a negative value. Copper powder pellets shrink as the temperature increases, and their linear expansion coefficient changes accordingly. When the linear expansion coefficient reaches its minimum during heating from room temperature to 1000°C, the copper powder pellets can be considered to have undergone the most advanced sintering and experienced the greatest shrinkage. If this minimum linear expansion coefficient is close to the theoretically ideal linear expansion coefficient of bulk copper at the temperature at which this minimum value is obtained, the copper powder will become a high-density sintered body after sintering. The theoretically ideal linear expansion coefficient is calculated based on the true density of copper (8.96 g / cm). 3 ) and thermal expansion coefficient (1.77×10 -5 / K), the linear expansion coefficient of an object having the same dimensions and shape as the copper powder pellet can be calculated as a value that changes with temperature.

[0054] The surface treatment layer of the copper powder may contain polypropylene glycol, polyethylene glycol, polyoxyethylene alkyl ether, or alkylcarboxylic acid, which can improve the dispersibility of the copper powder in the paste.

[0055] (Manufacturing method) The copper powder can be produced by subjecting untreated copper powder to a predetermined surface treatment. The term "untreated copper powder" used herein refers to copper powder that has not yet been subjected to a predetermined surface treatment, and may be copper powder that has already been subjected to a surface treatment other than the predetermined surface treatment.

[0056] The untreated copper powder to be subjected to the predetermined surface treatment may be purchased or may be prepared by generating copper particles by a liquid phase method such as a chemical reduction method or a disproportionation method.

[0057] In the chemical reduction method, for example, a copper salt aqueous solution such as a copper sulfate aqueous solution is used as a raw solution, and after adjusting the pH by adding sodium hydroxide or other alkali, a reducing agent such as hydrazine is added to produce cuprous oxide powder in a slurry based on a reduction reaction such as 4CuSO4 + N2H4 + 8NaOH → 2Cu2O + 4Na2SO4 + 6H2O + N2. Next, this slurry is heated, and while the pH is adjusted, hydrazine is further added to reduce the cuprous oxide to copper through a reaction such as 2Cu2O + N2H4 → 4Cu + 2H2O + N2, producing copper particles in the liquid.

[0058] In the disproportionation method, for example, an aqueous solution containing a dispersant such as gum arabic, gelatin, or collagen peptide is mixed with a slurry containing cuprous oxide powder, and sulfuric acid is added to the mixture, causing the disproportionation reaction Cu2O+H2SO4→Cu↓+CuSO4+H2O to generate copper particles in the liquid.

[0059] In the predetermined surface treatment performed on the untreated copper powder, the untreated copper powder is brought into contact with a liquid surface treatment agent containing at least SiO or a glass precursor that generates SiO by thermal decomposition, polymerization, condensation, etc., a glass-forming intermediate oxide precursor, and a glass-forming modifier oxide precursor, by adding the liquid to the surface treatment agent and stirring the mixture. The untreated copper powder may be contacted with at least two of the SiO or glass precursor, the glass-forming intermediate oxide precursor, and the glass-forming modifier oxide precursor simultaneously, or may be contacted sequentially in any order.

[0060] Among the surface treatment agents, examples of glass precursors that can be used include tetraethoxysilane (TEOS) or tetraethyl orthosilicate, which are compounds represented by the formula Si(OC2H5)4. The glass-forming intermediate oxide precursor contains an amphoteric metal X, specific examples of which include aluminum lactate, aluminum citrate, aluminum tartrate, basic aluminum formate, basic aluminum acetate, zinc acetate, tin acetate (tin diacetate, tin tetraacetate), and lead acetate. These specific compounds can produce Al2O3, ZnO, SnO, or PbO upon thermal decomposition. The glass-forming modifier oxide precursor contains an alkaline earth metal Y, specific examples of which include calcium acetate and barium acetate. These specific compounds can produce CaO or BaO upon thermal decomposition.

[0061] After contacting the untreated copper powder with the surface treatment agent, the copper powder having a surface treatment layer is obtained by drying.

[0062] (paste) The paste contains the copper powder described above and may also be called a conductive paste. In addition to the copper powder, the paste may also contain a binder resin and a solvent.

[0063] Examples of binder resins include cellulose-based resins, acrylic resins, alkyd resins, polyvinyl alcohol-based resins, polyvinyl acetal, ketone resins, urea resins, melamine resins, polyesters, polyamides, and polyurethanes.

[0064] Examples of the solvent that can be used include alcohol solvents (e.g., one or more selected from the group consisting of terpineol, dihydroterpineol, isopropyl alcohol, butyl carbitol, terpineloxyethanol, and dihydroterpineloxyethanol), glycol ether solvents (e.g., butyl carbitol), acetate solvents (e.g., one or more selected from the group consisting of butyl carbitol acetate, dihydroterpineol acetate, dihydrocarbitol acetate, carbitol acetate, linalyl acetate, and terpinyl acetate), ketone solvents (e.g., methyl ethyl ketone), hydrocarbon solvents (e.g., one or more selected from the group consisting of toluene and cyclohexane), cellosolves (e.g., one or more selected from the group consisting of ethyl cellosolve and butyl cellosolve), diethyl phthalate, and propionate solvents (e.g., one or more selected from the group consisting of dihydroterpinyl propionate, dihydrocarbyl propionate, and isobornyl propionate).

[0065] (LTCC substrate and MLCC) To manufacture LTCC substrates or MLCCs, for example, the co-firing method may involve applying the above paste onto a green sheet containing ceramic powder by printing or the like, stacking the paste and green sheet alternately, and then simultaneously heating and firing them.

[0066] This heating may be performed in an atmosphere containing oxygen atoms, typically water vapor, to remove organic substances such as binder resins and solvents that may be contained in the paste or green sheet. In this case, gas generated inside the copper powder contained in the paste during sintering may be released to the outside. Because the copper powder of the above-described embodiment has a high sintering temperature, the gas inside is sufficiently released to the outside before sintering is complete. This effectively prevents the occurrence of blistering, and the copper powder can form wiring as a high-density sintered body after sintering.

[0067] Furthermore, because the sintering temperature of this copper powder is high, it shrinks during sintering in a manner similar to that of the ceramic powder in the green sheet, effectively preventing peeling and cracking of the wiring due to the difference in shrinkage after sintering.

[0068] The LTCC substrate or MLCC thus manufactured comprises a sintered body of ceramic powder and a sintered body of copper powder formed on the sintered body of ceramic powder. [Example]

[0069] Next, the above-mentioned copper powder was produced as a prototype and its performance was confirmed, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0070] (Preparation of aqueous solution of surface treatment agent) Tetraethoxysilane (TEOS) and a 0.25 mass % aqueous solution of citric acid were mixed at an arbitrary weight ratio and stirred at room temperature for 2 hours or more to prepare a TEOS aqueous solution.

[0071] Aluminum lactate and pure water were mixed at an arbitrary weight ratio and stirred at room temperature for 2 hours or more to prepare an aqueous solution of aluminum lactate.

[0072] DL-calcium lactate pentahydrate and pure water were mixed in an arbitrary weight ratio and stirred at room temperature for 2 hours or more to prepare an aqueous calcium lactate solution.

[0073] Barium acetate and pure water were mixed in an arbitrary weight ratio and stirred at room temperature for 2 hours or more to prepare a barium acetate aqueous solution.

[0074] Calcium acetate and pure water were mixed in an arbitrary weight ratio and stirred at room temperature for 2 hours or more to prepare a barium acetate aqueous solution.

[0075] Polypropylene glycol and pure water were mixed in an arbitrary weight ratio and stirred at room temperature for 2 hours or more to prepare an aqueous polypropylene glycol solution.

[0076] Example 1 The BET specific surface area is 2.0m 2 20 g of untreated copper powder (wt. / g) was prepared, and 4.5 g of a 5 wt.% TEOS aqueous solution, 4.8 g of a 5 wt.% aluminum lactate aqueous solution, and 3.1 g of a 5 wt.% calcium lactate aqueous solution were added. A small amount of pure water was then added. The mixture was kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) with a revolution speed of 2000 rpm, a planetary centrifugal speed of 800 rpm, and a kneading time of 5 minutes. The kneaded sample was then dried in a vacuum dryer (model: AVO-250-SB) at a gauge pressure of -0.1 MPa or less and a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was returned to atmospheric pressure. The sample was then removed and crushed in a mortar to obtain the surface-treated copper powder of Example 1.

[0077] Example 2 The BET specific surface area is 2.0m 2 50 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 11.1 g of a 5 mass % TEOS aqueous solution, 12.0 g of a 5 mass % aluminum lactate aqueous solution, and 7.7 g of a 5 mass % calcium lactate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, to obtain the surface-treated copper powder of Example 2.

[0078] Example 3 The BET specific surface area is 2.0m 2 30 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 11.4 g of a 5 mass % TEOS aqueous solution, 11.7 g of a 5 mass % aluminum lactate aqueous solution, and 6.3 g of a 5 mass % barium acetate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, to obtain the surface-treated copper powder of Example 3.

[0079] Example 4 The BET specific surface area is 2.0m 2 30 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 1.7 g of a 5 mass % TEOS aqueous solution, 1.0 g of a 5 mass % aluminum lactate aqueous solution, and 1.7 g of a 5 mass % barium acetate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, to obtain the surface-treated copper powder of Example 4.

[0080] Example 5 The specific surface area is 1.6m 2 To a slurry containing 45.6% by mass of untreated copper powder (wt. / g), 50.6 g of a 20% by mass TEOS aqueous solution, 224.2 g of a 5% by mass aluminum lactate aqueous solution, 21.0 g of a 20% by mass calcium acetate aqueous solution, and 16.5 g of a 20% by mass polypropylene glycol aqueous solution were added per 1 kg of untreated copper powder. The slurry was dried in a nitrogen atmosphere and crushed to obtain the surface-treated copper powder of Example 5.

[0081] Example 6 The specific surface area is 1.6m 2 A slurry containing 46.1% by mass of untreated copper powder (wt. / g) was prepared, and 50.6 g of a 20% by mass TEOS aqueous solution, 224.2 g of a 5% by mass aluminum lactate aqueous solution, 30.4 g of a 20% by mass barium acetate aqueous solution, and 16.5 g of a 20% by mass polypropylene glycol aqueous solution were added per 1 kg of untreated copper powder. The slurry was dried in a nitrogen atmosphere and crushed to obtain the surface-treated copper powder of Example 6.

[0082] (Comparative Example 1) The BET specific surface area is 2.0m 2 / g of untreated copper powder.

[0083] (Comparative Example 2) The BET specific surface area is 2.0m 2 20 g of untreated copper powder having a molecular weight of 1 / g was prepared, 0.74 g of a 10 mass % TEOS aqueous solution was added, and a small amount of pure water was further added. The subsequent steps were carried out in the same manner as in Example 1, and a surface-treated copper powder of Comparative Example 2 was obtained.

[0084] (Comparative Example 3) The BET specific surface area is 2.0m 2 20 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 12.6 g of a 5 mass % TEOS aqueous solution, 6.2 g of a 5 mass % aluminum lactate aqueous solution, and 2.5 g of a 5 mass % calcium lactate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, and a surface-treated copper powder of Comparative Example 3 was obtained.

[0085] Comparative Example 4 The BET specific surface area is 2.0m 2 20 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 1.7 g of a 5 mass % TEOS aqueous solution, 34.1 g of a 5 mass % aluminum lactate aqueous solution, and 1.6 g of a 5 mass % calcium lactate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, and a surface-treated copper powder of Comparative Example 4 was obtained.

[0086] (Comparative Example 5) The BET specific surface area is 2.0m 2 20 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 1.9 g of a 5 mass % TEOS aqueous solution, 4.2 g of a 5 mass % aluminum lactate aqueous solution, and 1.0 g of a 5 mass % barium acetate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, and a surface-treated copper powder of Comparative Example 5 was obtained.

[0087] (Comparative Example 6) The BET specific surface area is 2.0m 2 20 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 0.8 g of a 5 mass % TEOS aqueous solution, 0.7 g of a 5 mass % aluminum lactate aqueous solution, and 1.9 g of a 5 mass % barium acetate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, and a surface-treated copper powder of Comparative Example 6 was obtained.

[0088] (Comparative Example 7) The BET specific surface area is 2.0m 2 20 g of untreated copper powder having a molecular weight of 1 / g was prepared, and 4.5 g of a 5 mass % TEOS aqueous solution and 4.8 g of a 5 mass % aluminum lactate aqueous solution were added, followed by the addition of a small amount of pure water. The subsequent steps were carried out in the same manner as in Example 1, and a surface-treated copper powder of Comparative Example 7 was obtained.

[0089] [Table 1]

[0090] (evaluation) For each of the copper powders of Examples 1 to 6 and Comparative Examples 1 to 7, the BET specific surface area and the contents of C, O, Si, Al, Ca, and Ba were measured according to the methods described above. Here, Al corresponds to the amphoteric metal X, and Ca and Ba correspond to the alkaline earth metal Y. The remainder was assumed to be Cu. The results are shown in Table 2.

[0091] From the above contents of Si, Al, Ca, and Ba, the molar masses of Si (28.09 g / mol), Al (26.98 g / mol), Ca (40.08 g / mol), and Ba (137.33 g / mol) were used to calculate the masses of these substances α, β, and γ, as well as the values ​​of α / β, γ / β, 4α, and 2.4β+1.6γ. The results are also shown in Table 2.

[0092] The copper powders of Examples 5 and 6 were confirmed to have Si-O bonds by the method described above. The copper powders of Examples 5 and 6 were also confirmed to have Y-O bonds and to contain X compounds and Y compounds by the method described above. As a result, in mass spectrometry, peaks containing aluminum and an organic acid derived from aluminum lactate were detected in Examples 5 and 6, peaks containing calcium and an organic acid derived from calcium acetate were detected in Example 5, and peaks containing barium and an organic acid derived from barium acetate were detected in Example 6. From these results, it can be said that there is a high probability that the copper powders of Examples 5 and 6 and the copper powders of Examples 1 to 4, which were subjected to the same surface treatments with respect to Si, X compound, and Y compound, also have Si-O bonds, Y-O bonds, and peaks containing aluminum and an organic acid derived from aluminum lactate, and peaks containing calcium and an organic acid derived from calcium acetate or peaks containing barium and an organic acid derived from barium acetate are detected.

[0093] [Table 2]

[0094] In addition, thermomechanical analysis (TMA) was performed for each copper powder using the procedure and conditions described above, and the temperature at each shrinkage rate, the density after sintering, the minimum linear expansion coefficient, and the ratio of that to the ideal linear expansion coefficient were calculated. The results are shown in Table 3. As an example, Example 1 will be described. In Example 1, the initial pellet had a height of 3.303 mm, a diameter of 5.000 mm, and a weight of 0.3014 g. Since the pellet was cylindrical, the density was 4.65 g / cm 3 When the height and diameter of the copper powder pellet are assumed to shrink at the same rate, the true density of copper (8.96 g / cm 3 ), the linear expansion coefficient must be -19.64%, at which point the height is calculated to be 2.654 mm, the diameter to be 4.018 mm, and the weight to be 0.3014 g. This is the size of the fully sintered body at room temperature (25°C). Note that a fully sintered body is a sintered body that does not contain impurities such as voids or surface treatment agents, and has the same density as the true density of copper. Since the pellet expands due to heat, the pellet height of the fully sintered body at the temperature where sintering has progressed most in the TMA measurement results (902°C) is calculated using the thermal expansion coefficient of copper (1.77 x 10 -5 / K), the linear expansion coefficient is calculated as 2.695 mm, which is the initial length + (initial length × thermal expansion coefficient × temperature difference). When the pellet height changes from the initial 3.303 mm to the fully sintered pellet height of 2.695 mm, the linear expansion coefficient is -18.09%, so the theoretically ideal linear expansion coefficient at 902°C is -18.09%.

[0095] [Table 3]

[0096] As can be seen from Table 3, the 2% shrinkage temperatures of all the copper powders of Examples 1 to 6 were relatively high. In particular, the copper powders of Examples 1 to 3, 5, and 6 had even higher 2% shrinkage temperatures than the copper powder of Example 4. This is thought to be because the copper powders of Examples 1 to 3, 5, and 6 had α / β values ​​closer to 1.0, γ / β values ​​closer to 0.5, and 4α values ​​closer to 3β+2γ than the copper powder of Example 4. Furthermore, since the copper powders of Examples 1 to 4 all had a high ratio of the linear expansion coefficient to the theoretical value, it can be said that they will form sintered bodies with high density.

[0097] The copper powders of Comparative Examples 1, 2, 4, and 6 had low 2% shrinkage temperatures. In addition, the copper powders of Comparative Examples 1 to 7, including Comparative Examples 3, 5, and 7, which had high 2% shrinkage temperatures, also had low ratios of the linear expansion coefficient to the theoretical value.

[0098] From the above, it was suggested that the copper powder described above is sintered at a relatively high temperature, and after sintering, it becomes a sintered body with a relatively high density.

[0099] (Potential contribution to SDGs) The copper powder of the embodiment described above is sintered at a relatively high temperature and becomes a sintered body with a relatively high density after sintering, which may suppress wiring peeling and cracking, thereby improving product yield. Improving product yield leads to a stable supply of products and reduced loss of metal raw materials, which are limited resources. Therefore, the copper powder of one embodiment may contribute to the achievement of Goal 9 "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" and Goal 12 "Ensure sustainable consumption and production patterns" of the United Nations-led Sustainable Development Goals (SDGs).

Claims

1. Copper powder having a surface treatment layer, The present invention comprises a compound of Si having a Si—O bond, an amphoteric metal X, and an alkaline earth metal Y, The amount of substance α (mol) of the Si, the amount of substance β (mol) of the amphoteric metal X, and the amount of substance γ (mol) of the alkaline earth metal Y satisfy the following formulas: (I): α / β≧0.8, (II): γ / β≧0.4, and (III): 4α≧2.4β+1.6γ.

2. The copper powder according to claim 1 , wherein the amphoteric metal X comprises Al.

3. BET specific surface area is 0.13m 2 The copper powder according to claim 1, wherein the copper powder has a molecular weight of 1 / g or more.

4. In XPS analysis, Ca2p with a binding energy in the range of 345 to 350 eV 3 / 2 peak, Sr3d with a binding energy in the range of 132 to 137 eV 5 / 2 peak, Ba3d with binding energy in the range of 778 to 783 eV 5 / 2 The copper powder according to claim 1, having at least one peak selected from the group consisting of:

5. At least a part of the amphoteric metal X is contained as a compound of the amphoteric metal X, 3. The copper powder according to claim 2, wherein the compound of the amphoteric metal X comprises at least one selected from the group consisting of oxycarboxylates, carboxylates, and compounds having an X—O bond.

6. the compound of the amphoteric metal X includes the oxycarboxylate; The copper powder according to claim 5, wherein the oxycarboxylate salt comprises at least one selected from the group consisting of lactate salts, citrate salts, and tartrate salts.

7. the compound of the amphoteric metal X comprises the carboxylate; The copper powder according to claim 5 , wherein the carboxylate comprises a basic formate and / or a basic acetate.

8. 2. The copper powder according to claim 1, wherein the alkaline earth metal Y comprises at least one selected from the group consisting of Ca, Ba, and Sr.

9. At least a portion of the alkaline earth metal Y is contained as a compound of the alkaline earth metal Y, The copper powder according to claim 8, wherein the compound of the alkaline earth metal Y comprises at least one selected from the group consisting of hydroxides, carboxylates, oxycarboxylates, nitrates, and compounds having a Y—O bond.

10. the compound of the alkaline earth metal Y comprises the carboxylate; The copper powder according to claim 9 , wherein the carboxylate comprises a formate and / or an acetate.

11. the compound of the alkaline earth metal Y includes the oxycarboxylate; The copper powder according to claim 9, wherein the oxycarboxylate comprises a lactate.

12. The copper powder according to any one of claims 1 to 11, wherein the 2% shrinkage temperature when heated from room temperature to 1000°C in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa, as determined by thermomechanical analysis (TMA), is 500°C or higher.

13. The copper powder according to any one of claims 1 to 11, wherein the minimum value of the linear expansion coefficient during heating from room temperature to 1000°C in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa, as measured by thermomechanical analysis (TMA), is 95% or more of the theoretical ideal linear expansion coefficient calculated from the true density and thermal expansion coefficient of copper at the temperature at which the minimum value is obtained.

14. The copper powder according to any one of claims 1 to 11, which is used for firing in an atmosphere containing oxygen atoms.

15. The copper powder according to any one of claims 1 to 11, wherein the amounts of substance α, β, and γ satisfy the formula (I'): α / β≦3.0, the formula (II'): γ / β≦2.0, and the formula (III'): 4α≦3.6β+2.4γ.

16. The copper powder according to any one of claims 1 to 11, wherein the content of Si, the content of the amphoteric metal X, and the content of the alkaline earth metal Y are each 5.0 atomic % or less.

17. A paste comprising the copper powder according to any one of claims 1 to 11.

18. A sintered body of copper powder, wherein the copper powder comprises the copper powder according to any one of claims 1 to 11.

19. A composite comprising a sintered body of ceramic powder and the sintered body of copper powder according to claim 18 formed on the sintered body of ceramic powder.

20. A low-temperature co-fired ceramic substrate comprising the composite of claim 19.

21. A multilayer ceramic capacitor comprising the composite of claim 19.

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