Copper powder, paste, method for producing low-temperature co-fired ceramic substrate, and method for producing multilayer ceramic capacitor

Abstract

A copper powder having a surface treatment layer, the copper powder containing at least one organic acid salt from among organic acid salts containing Al and organic acid salts containing Ti.

Description

Method for producing copper powder, paste, low-temperature co-fired ceramic substrate, and method for producing multilayer ceramic capacitor

[0001] This specification describes copper powders, pastes, methods for producing low temperature co-fired ceramic substrates, and methods for producing multilayer ceramic capacitors.

[0002] In recent years, in order to realize miniaturization and high performance of electronic devices, there has been a demand for finer, smoother, denser, etc. wiring in, for example, low temperature co-fired ceramics (LTCC) substrates, multi-layer ceramic capacitors (MLCC), and other electronic substrates or electronic components mounted on electronic devices. To meet such demands, it is believed that using fine copper powder for forming 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] In the manufacture of LTCC substrates, a paste is applied onto a green sheet containing ceramic powder, and the two are then fired simultaneously, sintering both the ceramic powder in the green sheet and the copper powder in the paste.

[0006] Here, during firing, the temperature ranges of the shrinkage behavior of the ceramic powder and the copper powder may not match, and in this case, the stress associated with the difference in shrinkage may lead to peeling or cracking of the wiring. Generally, ceramic powders have high sintering temperatures, while metal powders with smaller particle sizes tend to be sintered at lower temperatures, so the difference in shrinkage becomes more pronounced when fine copper powder is used to manufacture LTCC substrates.

[0007] Furthermore, in the firing process during the manufacture of LTCC substrates or MLCCs, heating is carried out in a water vapor atmosphere in order to thoroughly remove organic matter contained in the paste or the like, and decomposition products of the organic matter may be separated as gas.

[0008] This specification discloses copper powder, paste, a method for producing an LTCC substrate, and a method for producing an MLCC that can be sintered at a relatively high temperature when heated in an atmosphere containing water vapor.

[0009] The copper powder disclosed in this specification has a surface treatment layer, which contains at least one organic acid salt of an Al-containing organic acid salt and a Ti-containing organic acid salt.

[0010] The paste disclosed in this specification contains the above copper powder.

[0011] The method for producing an LTCC substrate disclosed in this specification is to produce a low-temperature co-fired ceramic substrate using the above paste.

[0012] The method of manufacturing an MLCC disclosed in this specification is to manufacture a multilayer ceramic capacitor using the paste described above.

[0013] The copper powder can be sintered at a relatively high temperature when heated in an atmosphere containing water vapor.

[0014] The copper powder, paste, method for producing a low-temperature co-fired ceramic substrate, and method for producing a multilayer ceramic capacitor are described in detail below. In one embodiment, the copper powder has a surface treatment layer, and the surface treatment layer mainly contains at least one organic acid salt selected from the group consisting of an organic acid salt containing Al and an organic acid salt containing Ti.

[0015] It is believed that when copper powder is heated in a water vapor atmosphere, the Al-containing organic acid salt and / or the Ti-containing organic acid salt decomposes at a relatively low temperature to produce Al oxide and / or Ti oxide. The presence of these oxides between the copper powder particles is expected to suppress sintering of the copper powder until temperatures reach a certain level. Therefore, it can be said that the above copper powder sinters at a certain level when heated in a water vapor-containing atmosphere.

[0016] (Copper Powder) Copper powder contains Cu (copper) and is often composed mostly of Cu. The Cu content of the copper powder excluding copper oxide is, for example, 90.0 mass% or more, and typically 99.0 mass% or more. The Cu content of the copper powder and the Cu content can be confirmed and measured by X-ray diffraction (XRD).

[0017] The copper powder has a surface treatment layer. More specifically, the copper powder is composed of surface-treated 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 an organic acid salt containing Al (aluminum) and / or an organic acid salt containing Ti (titanium) (hereinafter simply referred to as "organic acid salt"). As a result, the organic acid salt is contained in the copper powder, typically by adhering to the surface of the copper particle. The copper powder contains an organic acid salt, which can effectively form Al oxide and / or Ti oxide, which increases the sintering temperature, when heated.

[0018] An organic acid salt is a salt formed by bonding an acidic organic compound with Al or Ti. Organic acid salts tend to form metal oxides when heated at relatively low temperatures compared to inorganic compounds. The temperature at which an organic acid salt forms a metal oxide is close to the temperature at which sintering of copper particles begins. Therefore, in copper powder containing an organic acid salt, a metal oxide is formed when sintering of copper particles begins during heating, and this can effectively suppress the sintering. In the case of copper powder that has been surface-treated with an inorganic compound instead of an organic acid salt, a metal oxide is not formed when sintering of copper particles begins, which may lead to necking between copper particles.

[0019] The organic acid salt may be an organic acid salt containing Al and / or an organic acid salt containing Ti, but an organic acid salt containing Al is particularly preferred. This is because Al oxide, which is generated during heating, has a higher melting point than Ti oxide and is thought to act more effectively in retarding the sintering of copper particles. However, this does not mean that any metal element with a high melting point will do. Although the reason is not necessarily clear, the test results in the examples described below have shown that Al and Ti are effective.

[0020] The organic acid salt is preferably, but not limited to, one having a carboxyl group, i.e., a carboxylate. Carboxylate salts have a lower thermal decomposition temperature than inorganic salts, and therefore tend to form Al oxide and / or Ti oxide at low temperatures. For example, the thermal decomposition temperature of aluminum sulfate, an inorganic salt, is about 800°C, while the thermal decomposition temperature of aluminum lactate, a carboxylate salt, is about 400°C. Carboxylate salts also have the advantage that, even if they remain after sintering, they do not leave impurities such as chlorine or sulfur that are undesirable for electronic devices. Carboxylate groups can be confirmed by mass spectrometry, which will be described later.

[0021] The copper powder may contain at least one organic acid salt selected from the group consisting of aluminum lactate, titanium lactate, aluminum acetate, aluminum citrate, aluminum tartrate, basic aluminum formate, and potassium titanium oxalate dihydrate.

[0022] The presence of an organic acid salt 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 aqueous solution is added to 0.5 mL of this solution. This solution is used as the sample solution, and mass spectrometry is performed. As the mass spectrometer, a liquid chromatography-Orbitrap mass spectrometer (Orbitrap Explorer 240 manufactured by Thermo Fisher Scientific) can be used, with a scan range of 50-500 (m / z) and a resolution of 60,000. For sample ionization, a NanoMate manufactured by Advion Interchim Scientific can be used, with a spray voltage of 1.4 kV, a gas type of nitrogen, and a gas pressure of 0.3 psi.

[0023] As an example, the m / z value of the monoisotopic mass in positive ion detection mode is shown below. The monoisotopic mass of an element is the calculated exact mass of the isotope with the greatest natural abundance for each element. In the above mass analysis, for example, when aluminum lactate is contained, [M+H] is detected near 295.0604 as the m / z value in positive ion detection mode. + A peak is detected as an ion of [M+H]. + The ion represents an ion in which a proton is added to the molecule of the target compound. When aluminum acetate is contained, [M+H] is detected near the m / z value of 205.0293 in the positive ion detection mode. + When aluminum citrate is contained, a peak is detected as an ion of [M+H] in the vicinity of m / z value 223.0398 in positive ion detection mode. +When aluminum tartrate is contained, a peak of [M+H] is detected near the m / z value of 498.9733 in the positive ion detection mode. + When basic aluminum formate is contained, a peak of [M+H] is detected near the m / z value of 118.9925 in the positive ion detection mode. + When potassium titanium oxalate dihydrate is contained, a peak is detected as an ion [M+H] in the vicinity of m / z value 318.8374 in positive ion detection mode. + When titanium lactate is contained, a peak of [M+H] is detected near the m / z value of 227.0035 in the positive ion detection mode. + A peak is detected as an ion of the formula (I). The "near m / z value" mentioned above refers to a range within ±0.1%. Note that there may be cases where no peak is detected at the m / z value of the monoisotopic mass. In this case, a peak containing an organic acid derived from an organic acid salt and Al or Ti may be detected. As an example, when copper powder contains aluminum lactate ([CHCH(OH)COO]Al), instead of a peak near the monoisotopic mass of 295.061, a peak may be detected near the calculated value of 205.0293, which corresponds to the structure [CHCH(OH)COO]Al in which one lactic acid moiety [CHCH(OH)COO] is removed from aluminum lactate, or a peak may be detected near the calculated value of 179.0136, which corresponds to the structure [CHCH(OH)COO(COH)]Al in which 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 organic acid salt contained in the copper powder is a lactate (carboxylate).

[0024] When the copper powder is subjected to thermogravimetry (TG) while being heated in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa, the temperature at which the weight loss rate first reaches 0.5% is preferably 500° C. or lower. More preferably, the temperature at which the weight loss rate first reaches 0.5% is 300° C. or lower. If this temperature is relatively low, when the copper powder is heated, the organic acid salt decomposes when sintering of the copper particles begins, and Al oxide and / or Ti oxide that suppress sintering can be effectively formed.

[0025] When copper powder is subjected to thermogravimetry (TG), the organic acid salts present on the surface of the copper powder gradually decompose as the temperature rises, causing the weight of the copper powder to decrease. The weight at the start of the measurement is taken as 100%, and the temperature at which the copper powder first loses 99.5% of its weight as the temperature rises is the temperature at which the weight loss rate first reaches 0.5%. More specifically, a copper powder sample (150 mg ± 10 mg) is placed in an alumina pan, weighed using a balance capable of displaying to 0.1 mg, and set on the balance of a thermogravimetry device (NETZSCH STA2500 Regulus). Then, gas replacement is performed by flowing atmospheric gas at a flow rate of 300 mL / min and nitrogen gas at a flow rate of 50 mL / min for at least 15 minutes, and measurement is then initiated. The measurement conditions are as follows: starting temperature: 50°C ± 10°C, reaching temperature: 900°C, temperature rise rate: 10°C / min, atmospheric gas used: nitrogen gas containing water vapor (dew point temperature: 30°C).

[0026] The organic acid salt in the copper powder is preferably water-soluble. In the case of a water-soluble organic acid salt, when surface treating untreated copper powder, the organic acid salt can be prepared by dissolving it in water such as pure water rather than in an organic solvent such as ethanol. In this case, since water is less likely to evaporate than ethanol, the surface treatment can be performed with a surface treatment agent of the desired concentration. A surface treatment agent prepared in an organic solvent such as ethanol is likely to concentrate due to the evaporation of the organic solvent, and adjustments are required to perform surface treatment at the desired concentration. Furthermore, for example, when surface treating a slurry containing copper particles, a surface treatment agent dissolved in an organic solvent is diluted with the water content of the slurry upon addition, which may cause the organic acid salt to precipitate, making it difficult to coat the surfaces of the copper particles.

[0027] To confirm that the organic acid salts in the copper powder are water-soluble, 47.5 g of pure water is added to 2.5 g of the surface treatment agent corresponding to the organic acid salt contained in the copper powder, and after thorough stirring, 10 mL of the supernatant is filtered with a syringe through a syringe filter (RephiQuik® Syringe Filter (material: hydrophilic PTFE, pore size: 0.22 μm), manufactured by Rephile Corporation), and the filtrate is collected. The filtrate is dropped onto an aluminum dish and dried at 100°C for 1 hour. The dried weight is measured on a balance capable of displaying to the nearest 0.1 mg. A surface treatment agent is defined as water-soluble if the weight after drying, including the aluminum dish, minus the weight of the aluminum dish, is 10 mg or more.

[0028] The copper powder preferably has a total Al and Ti content of 400 ppm by mass or more. If the Al or Ti content is too low, there is a concern that the sintering retardation effect in a water vapor atmosphere may not be sufficient. However, if the Al or Ti content is too high, a large amount of surface treatment agent will adhere to the copper powder, resulting in a large amount of organic matter, and a large amount of carbon will remain in the sintered copper powder, which may increase the resistivity. In this case, there is also a possibility that the sintering temperature will be low. From this perspective, the total Al and Ti content is preferably 9000 ppm by mass or less.

[0029] The Al and Ti contents in copper powder were determined by alkaline fusion of copper powder using sodium peroxide and sodium carbonate, dissolving the resulting molten material in hydrochloric acid, and measuring the solution diluted to a certain volume with ultrapure water using ICP atomic emission spectroscopy to determine the mass (μg) of Al and Ti per unit mass (g) of copper powder. Specifically, calibration curves for Al and Ti concentrations were created using a Hitachi High-Tech Science ICP-OES: PS3500UVDDII, and then measuring sample solutions adjusted to fall within the calibration curve ranges. The standard solutions used for measurement were adjusted to concentrations of 0 μg / mL, 0.1 μg / mL, and 1 μg / mL, respectively, to create the calibration curves. A 0.5 g sample solution was prepared, and the Al or Ti concentration in the sample was adjusted to fall within the calibration curve range. The standard solutions used were the same sodium peroxide, sodium carbonate, and hydrochloric acid used to prepare the sample solutions. The sodium peroxide, sodium carbonate, and hydrochloric acid contained in the standard solution are matched to the sodium peroxide, sodium carbonate, and hydrochloric acid contained in the sample solution so that their molar concentrations are the same. The standard solution for Al can be Kanto Chemical's JCSS Chemical Analysis Standard Solution (Aluminum Standard Solution (Al 1000), specifications: for atomic absorption spectrometry, ICP analysis), and the standard solution for Ti can be Kanto Chemical's standard solution (Titanium Standard Stock Solution (Ti 1000), specifications: for atomic absorption spectrometry). Measurement wavelengths are selected that do not cause spectral interference, and measurements are performed using off-peak background correction. The crucible used during alkali fusion is made of a material that does not dissolve the measured elements and does not form hardly soluble substances with the crucible components, such as zirconium.

[0030] The C (carbon) content in the copper powder is preferably 5.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 1.0 mass% or less. The C content in the copper powder is preferably 0.05 mass% or more, more preferably 0.10 mass% or more, and even more preferably 0.15 mass% or more. The C content is preferably 0.2 mass% or more and 4.0 mass% or less. If the C content is too low, Al oxide and / or Ti oxide cannot be formed at a low temperature, and a high sintering temperature may not be achieved. On the other hand, if the C content is too high, the amount of carbon remaining after sintering increases, which may adversely affect the resistivity of the sintered body.

[0031] The carbon content of copper powder is measured by a high-frequency induction heating furnace combustion-infrared absorption method. Specifically, using a carbon-sulfur analyzer such as the LECO CS844 model, a sample of 0.2 g is collected, adjusted to fall within the calibration curve intensity range, and the carbon content of the copper powder can be measured using a LECO LECOCEL II and Fe chips as combustion improvers and a standard steel pin 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 heating rate over two hours and then holding it at 1000°C for two hours before being used to measure the carbon content of the copper powder.

[0032] The copper powder may have a Na (sodium), Cl (chlorine), and S (sulfur) content all less than 10 ppm by mass. This is because the organic acid salts of copper powder often do not contain any of these elements. The almost complete absence of S reduces the generation of harmful gases (SOx) during firing. If the Cl content is high, the Cl content in the sintered body of the copper powder may also be high. Since Cl has the property of corroding copper, reducing the Cl content in the copper powder can improve the reliability of the sintered body. When forming fine wiring using copper powder, a high Na content may cause the wiring to short-circuit.

[0033] The sulfur content of copper powder is measured by high-frequency induction heating furnace combustion-infrared absorption method. Specifically, using a carbon / sulfur analyzer such as the LECO CS844 model, the sample amount is adjusted to 0.5 g so that it falls within the intensity range of the calibration curve, 1.40 g of Cu chips as a combustion improver is added, and the sulfur content of copper powder can be measured using Cu as a certified reference material for the calibration curve. The alumina crucible used for the measurement is preheated in air at 1000°C for 2 hours.

[0034] The Cl content of copper powder can be measured by combustion-ion chromatography. Specifically, a combustion-ion chromatograph such as a Metrohm 930 Combustion IC is used to create a calibration curve for Cl concentration using a standard solution, and then the sample solution adjusted to fall within the calibration curve range is measured. The standard solution is prepared by diluting Kanto Chemical's JCSS standard solution for chemical analysis (chloride ion standard solution for ion chromatography) with ultrapure water to achieve chloride ion concentrations of 20, 100, or 200 mg / L. The combustion temperature in the combustion section is set to 1100°C, and 0.1% HO is used as the absorption solution in the absorption section. The ion chromatography in the analysis section uses a Metrohm Metrosep A sup-p 5-250 / 4.0 separation column, 3.2 mM NaCO3 + 1.0 mM NaHCO3 as the eluent, and an electrical conductivity detector as the detector. The sample solution was introduced in an amount of 250 μL, the column temperature was 35°C, and no gradient was used. A suppressor was used to reduce background, and the suppressor regeneration solution was 100 mM H2SO4. Prior to measuring the sample, the components used (combustion boat, combustion capsule, quartz wool) were washed with ultrapure water and then dried. A blank measurement was also performed using the washed components, and measurements were performed after confirming that the blank value was 0.01 μg / mL or less.

[0035] The Na content of copper powder can be measured by atomic absorption spectrometry. Specifically, a calibration curve of Na concentration is created using a standard solution using an atomic absorption spectrophotometer such as the Z2310 manufactured by Hitachi High-Tech Science Corporation, and then a sample solution adjusted to the range of the calibration curve is measured. A 1-g sample is collected, decomposed with hydrochloric acid and nitric acid, and then the volume is adjusted to a constant volume in a 100-mL measuring flask to obtain the sample solution. The standard solution uses the same hydrochloric acid and nitric acid reagents as those used to prepare the sample solution. The hydrochloric acid and nitric acid contained in the standard solution are matched to the hydrochloric acid and nitric acid contained in the sample solution so that they have the same molar concentrations, respectively. More specifically, the standard solutions were prepared by diluting Kanto Chemical's JCSS standard solution for chemical analysis (sodium standard solution (Na 1000), specifications: for atomic absorption spectrometry, for ion chromatography) with ultrapure water, hydrochloric acid, and nitric acid to give solutions with Na concentrations of 0.5 μg / mL and 1.0 μg / mL, and a solution with a Na concentration of 0 μg / mL to which Kanto Chemical's JCSS standard solution for chemical analysis had not been added. The measurement conditions for the instrument were a measurement wavelength of 589 nm and an Air-C2H2 flame type.

[0036] The copper powder has a BET specific surface area of ​​0.13 m 2 / g or more, preferably 0.22 m 2 / g or more, more preferably 0.67m 2 The copper powder has a BET specific surface area of ​​15 m 2 / g or less, preferably 10m 2 / g or less, more preferably 5m 2 / g or less. Copper powder with a large BET specific surface area and a relatively small particle size usually tends to be sintered at a low temperature, but in this embodiment, by forming a predetermined surface treatment layer, the sintering temperature can be increased. 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 tends to be. The BET specific surface area of ​​the copper powder is 0.13 m 2 / g to 15m 2 The BET specific surface area herein means a value measured on copper powder that has been surface-treated and on which a surface treatment layer has been formed.

[0037] 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, Inc. More specifically, a 3 g sample of copper powder is degassed for 5 hours at a temperature of 70°C in a vacuum of an absolute pressure of 10 Pa or less, 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.

[0038] The copper powder preferably has a 10% shrinkage temperature of 700°C or higher, and more preferably 800°C or higher, which is the temperature at which the copper powder shrinks by 10% when heated from room temperature (25°C) to 1000°C in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa in thermomechanical analysis (TMA). When the 10% shrinkage temperature is high, the shrinkage behavior of the copper powder tends to match the shrinkage behavior of the ceramic powder during the production of an LTCC substrate, thereby suppressing peeling and cracking of the wiring.

[0039] More specifically, the 10% shrinkage temperature is measured 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 (e.g., a Mitutoyo Coolant-Proof Micrometer MDC-25MX, maximum allowable error ±1 μm), and this is used as the initial height. This pellet is placed in a thermomechanical analyzer (e.g., a NETZSCH TMA4000SE), evacuated to -0.1 MPa or less, and then N2 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 flow rate of nitrogen from the thermomechanical analyzer is then changed to 50 mL / min. In this state, gas was allowed to flow for 15 minutes to stabilize the measurement atmosphere. The gas from the water vapor generator and the gas from the thermomechanical analyzer were mixed to create an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa. While gas was flowing from the water vapor generator and the thermomechanical analyzer, the temperature was increased from room temperature (25°C) to 1000°C at a heating rate of 10°C / min while applying a load of 10 g. During this heating from 40°C to 1000°C, the pellet height was measured every second, and the temperature at which the pellet had shrunk by 10% relative to the maximum shrinkage width from the initial pellet height to the minimum pellet height was defined as the 10% shrinkage temperature. For example, if the initial pellet height was 3 mm and the minimum pellet height upon heating to 1000°C was 2 mm, the temperature at which the pellet height first reached 2.9 mm was defined as the 10% shrinkage temperature.

[0040] (Production Method) The copper powder can be produced by subjecting untreated copper powder to a predetermined surface treatment. The untreated copper powder referred to here means copper powder before the predetermined surface treatment is applied, and may be copper powder that has already been subjected to a surface treatment other than the predetermined surface treatment.

[0041] 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.

[0042] In the chemical reduction method, for example, a copper salt aqueous solution such as a copper sulfate aqueous solution is used as a raw material 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 4CuSO + N H + 8NaOH → 2CuO + 4NaSO + 6H O + N. 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 2CuO + N H → 4Cu + 2H O + N, producing copper particles in the liquid.

[0043] 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 thereto, thereby generating copper particles in the liquid through the disproportionation reaction of CuO + HSO → Cu↓ + CuSO + HO.

[0044] In the predetermined surface treatment applied to the untreated copper powder, the untreated copper powder is brought into contact with a liquid surface treatment agent containing an Al-containing organic acid salt and / or a Ti-containing organic acid salt by adding the liquid to the surface treatment agent and stirring the mixture, etc. In this case, if the organic acid salt is water-soluble, water such as pure water can be used as the solvent instead of an organic solvent such as ethanol.

[0045] As the organic acid salt of the surface treatment agent, for example, one having a carboxy group can be used, such as aluminum lactate, titanium lactate, aluminum acetate, aluminum citrate, aluminum tartrate, basic aluminum formate, and potassium titanium oxalate dihydrate.

[0046] After contacting the untreated copper powder with the surface treatment agent, the copper powder having a surface treatment layer is obtained by drying.

[0047] (Paste) The paste contains the copper powder described above and may also be called a conductive paste. This paste may contain a binder resin and a solvent in addition to the copper powder.

[0048] 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.

[0049] Examples of the solvent 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).

[0050] (LTCC Substrate and MLCC) To use copper powder in an LTCC substrate or MLCC, for example, in the co-firing method, the above paste may be applied by printing or the like onto a green sheet containing ceramic powder, and the paste and green sheet may be alternately stacked and then heated and fired at the same time.

[0051] The 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. Because the copper powder in this embodiment has a high sintering temperature, it shrinks during sintering, similar to the behavior of the ceramic powder in the green sheet. As a result, peeling and cracking of the wiring due to shrinkage differences after sintering are effectively suppressed.

[0052] 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.

[0053] (Example 1) 2.5 g of aluminum lactate was added to 47.5 g of pure water to prepare a 5 mass % aqueous aluminum lactate solution. 2 To 20 g of untreated copper powder (wt. / g), 2.18 g of a 5 mass% aluminum lactate aqueous solution was added, and 2.0 g of pure water was further 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 rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0054] (Example 2) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Example 1, except that 4.36 g of a 5 mass % aqueous aluminum lactate solution was added to 20 g of untreated copper powder having a surface-treated layer of 100 wt %.

[0055] (Example 3) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Example 1, except that 6.54 g of a 5 mass % aqueous aluminum lactate solution was added to 20 g of untreated copper powder having a surface-treated layer of 100 wt %.

[0056] (Example 4) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Example 1, except that 8.72 g of a 5 mass % aqueous aluminum lactate solution was added to 20 g of untreated copper powder having a surface-treated layer of 1 / g.

[0057] (Example 5) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Example 1, except that 21.81 g of a 5 mass % aqueous aluminum lactate solution was added to 20 g of untreated copper powder having a surface-treated layer of 1 / g.

[0058] (Example 6) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Example 1, except that 43.62 g of a 5 mass % aqueous aluminum lactate solution was added to 20 g of untreated copper powder having a surface-treated layer of 1000 kJ / g.

[0059] Example 7 12.5 g of Orgatix TC-310 (titanium lactate, manufactured by Matsumoto Fine Chemical Co., Ltd.) was added to 37.5 g of pure water to prepare an 11% by mass aqueous solution of TC-310. 2 To 20 g of untreated copper powder (wt. / g), 7.34 g of a 10 mass % TC-310 aqueous solution was added, followed by 2.0 g of pure water. The mixture was kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) with a revolution speed of 2000 rpm, a rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0060] (Example 8) BET specific surface area: 2.0 m 2 The same procedure as in Example 7 was carried out except that 4.08 g of a 10 mass % TC-310 aqueous solution was added to 20 g of untreated copper powder having a surface-treated layer.

[0061] (Example 9) BET specific surface area: 2.0 m 2 The same procedure as in Example 7 was carried out except that 3.26 g of a 10 mass % TC-310 aqueous solution was added to 20 g of untreated copper powder having a surface-treated layer.

[0062] (Example 10) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Example 7, except that 10.1 g of a 10 mass % TC-310 aqueous solution was added to 20 g of untreated copper powder having a surface-treated layer of 10.1 mass % TC-310.

[0063] (Comparative Example 1) BET specific surface area: 2.0 m 2The untreated copper powder having a porosity of 1 / g was not subjected to any surface treatment and was used as the copper powder.

[0064] Comparative Example 2 5.0 g of Orgatix AL-3001 (aluminum secondary butoxide, manufactured by Matsumoto Fine Chemical Co., Ltd.) was added to 45.0 g of ethanol to prepare a 10 mass % aqueous solution of AL-3001. 2 To 20 g of untreated copper powder (wt. / g), 1.82 g of a 10 mass % AL-3001 aqueous solution was added, followed by 2.0 g of pure water. The mixture was kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) with a revolution speed of 2000 rpm, a rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0065] Comparative Example 3 5.0 g of Orgatix TA-8 (titanium tetraisopropoxide, manufactured by Matsumoto Fine Chemical Co., Ltd.) was added to 45.0 g of ethanol to prepare a 10% by mass aqueous solution of TA-8. 2 To 20 g of untreated copper powder (wt. / g), 1.19 g of a 10 mass% TA-8 aqueous solution was added, followed by 2.0 g of pure water. The mixture was kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) with a revolution speed of 2000 rpm, a rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0066] Comparative Example 4 5.0 g of magnesium acetate tetrahydrate was added to 45.0 g of pure water to prepare a 10 mass % aqueous solution of magnesium acetate tetrahydrate. 2To 20 g of untreated copper powder (wt. / g), 0.48 g of a 10 mass % aqueous solution of magnesium acetate tetrahydrate was added, followed by 2.0 g of pure water. The mixture was kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) with a revolution speed of 2000 rpm, a rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0067] (Comparative Example 5) BET specific surface area: 2.0 m 2 Copper powder having a surface-treated layer was prepared by the same procedure as in Comparative Example 1, except that 0.72 g of a 10 mass % aqueous solution of magnesium acetate tetrahydrate was added to 20 g of untreated copper powder having a surface-treated layer of 10 mass %.

[0068] Comparative Example 6 2.5 g of DL-calcium lactate pentahydrate was added to 47.5 g of pure water to prepare a 5 mass % aqueous solution of DL-calcium lactate pentahydrate. 2 To 20 g of untreated copper powder (wt. / g), 3.08 g of a 5 mass% aqueous solution of calcium DL-lactate pentahydrate was added, followed by 2.0 g of pure water. The mixture was then kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) at a revolution speed of 2000 rpm, a rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder with a surface-treated layer.

[0069] Comparative Example 7 6.7 g of Orgatix ZA-45 (zirconium tetra-normal propoxide, manufactured by Matsumoto Fine Chemical Co., Ltd.) was added to 43.3 g of ethanol to prepare a 10 mass % aqueous solution of ZA-45. 2To 20 g of untreated copper powder (wt. / g), 1.19 g of a 10 mass % ZA-45 aqueous solution was added, followed by 2.0 g of pure water. The mixture was kneaded in a planetary centrifugal mixer (model: ARE-310, manufactured by Thinky Corporation) with a revolution speed of 2000 rpm, a rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0070] (Comparative Example 8) 5.0 g of barium acetate was added to 45.0 g of pure water to prepare a 10 mass % aqueous solution of barium acetate. 2 To 20 g of untreated copper powder having a solubility of 1 / g, 0.37 g of a 10 mass % barium acetate aqueous solution was added, and 2.0 g of pure water was further 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 rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0071] (Comparative Example 9) 1.0 g of ammonium tungstate was added to 99.0 g of pure water to prepare a 1 mass % aqueous solution of ammonium tungstate. 2 To 20 g of untreated copper powder having a solubility of 1 / g, 4.62 g of a 1 mass % ammonium tungstate aqueous solution was added, and 2.0 g of pure water was further 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 rotation speed of 800 rpm, and a kneading time of 5 minutes. After kneading, the slurry was recovered. The recovered slurry was vacuum-dried in a vacuum dryer (model: AVO-250-SB) at a temperature of 70°C for 5 hours. After vacuum drying, the temperature was confirmed to have dropped, and the mixture was roughly crushed in a mortar. This yielded copper powder having a surface-treated layer.

[0072] (Comparative Example 10) BET specific surface area: 2.0 m2 The same procedure as in Comparative Example 9 was carried out except that 6.93 g of a 1 mass % aqueous solution of ammonium tungstate was added to 20 g of untreated copper powder having a surface-treated layer.

[0073]

[0074] (Evaluation) The water solubility of the surface treatment agents used in Examples 1 to 10 and Comparative Examples 2 to 10 was confirmed by the method described above. In Table 1, a "○" indicates that the surface treatment agent is water soluble, and an "×" indicates that the surface treatment agent is water insoluble. Furthermore, for each of the copper powders of Examples 1 to 10 and Comparative Examples 1 to 10, the BET specific surface area was measured and the components were analyzed by the method described above, and the results are shown in Table 2. Furthermore, when the copper powder of Example 6 was subjected to mass spectrometry as described above, peaks were detected at m / z values ​​of 295.0614 (near the monoisotopic mass of aluminum lactate, 295.061) and 205.0293 (near the calculated value of 205.0293, which corresponds to the structure [CHCH(OH)COO]Al, in which one lactic acid moiety [CHCH(OH)COO] is removed from aluminum lactate). From this, it is presumed that it can be confirmed that the specified organic acid salts are attached to other copper powders that have been subjected to surface treatment.

[0075]

[0076] For each of the copper powders, thermomechanical analysis (TMA) was performed using the method described above to determine the 10% shrinkage temperature. However, for the copper powder of Example 7, an analysis was also performed under similar conditions except for the nitrogen atmosphere not containing water vapor. Furthermore, for the copper powders of Example 8 and Comparative Examples 1 to 3 and 7, only an analysis was performed under similar conditions except for the nitrogen atmosphere. The results are shown in Table 3.

[0077] The results of Example 7 show that the introduction of water vapor lowers the sintering temperature. Although no test results were obtained in Comparative Examples 1 to 3 and 7 under an atmosphere containing water vapor, the results of Example 7 suggest that if the copper powders of Comparative Examples 1 to 3 and 7 were analyzed under an atmosphere containing water vapor, the 10% shrinkage temperature would be lower than that under a nitrogen atmosphere. Furthermore, if the copper powder of Example 8 were analyzed under an atmosphere containing water vapor, the 10% shrinkage temperature would be predicted to be between that of Examples 7 and 9, taking into account the content of the surface treatment agent. Therefore, it can be said that the copper powders of Examples 1 to 10 have higher 10% shrinkage temperatures than the copper powders of Comparative Examples 1 to 10. This indicates that the copper powders of Examples 1 to 10 are capable of suppressing sintering up to relatively high temperatures.

[0078] Thermogravimetry (TG) was also performed on each of the copper powders of Examples 1, 6, 9, and 10 according to the method described above. The results are also shown in Table 3. The temperature at which the weight loss rate first reached 0.5% in the thermogravimetry was 250°C or lower for all of them. Among Examples 1 to 6, which used aluminum lactate, Example 1 had the lowest Al, C, and O contents, while Example 6 had the highest Al, C, and O contents. Therefore, the copper powders of Examples 2 to 5 are also likely to have the temperature at which the weight loss rate first reached 0.5% in the thermogravimetry below 250°C. Furthermore, among Examples 7 to 10, which used titanium lactate, Example 9 had the lowest Ti, C, and O contents, while Example 10 had the highest Ti, C, and O contents. Therefore, the copper powders of Examples 7 to 8 are also likely to have the temperature at which the weight loss rate first reached 0.5% in the thermogravimetry below 250°C.

[0079]

[0080] From the above, it was suggested that the copper powder described above may be capable of being sintered at a relatively high temperature when heated in an atmosphere containing water vapor.

[0081] (Potential Contribution to SDGs) The copper powder of the above-described embodiment can be sintered at a relatively high temperature when heated in an atmosphere containing water vapor, which may prevent 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 copper powder containing at least one organic acid salt selected from the group consisting of an organic acid salt containing Al and an organic acid salt containing Ti.

2. The copper powder according to claim 1, wherein the organic acid salt is water-soluble.

3. Copper powder according to claim 1 or 2, wherein the temperature at which the weight loss rate first reaches 0.5% when subjected to thermogravimetry (TG) while heating in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa is 500°C or lower.

4. The copper powder according to claim 1 or 2, wherein the organic acid salt has a carboxyl group.

5. The copper powder according to claim 1 or 2, wherein the organic acid salt comprises at least one of aluminum lactate, titanium lactate, aluminum acetate, aluminum citrate, aluminum tartrate, basic aluminum formate, and potassium titanium oxalate dihydrate.

6. The copper powder according to claim 1 or 2, wherein the total content of Al and Ti is 400 mass ppm or more.

7. Copper powder according to claim 1 or 2, wherein the C content is 0.2 mass % or more and 4.0 mass % or less.

8. BET specific surface area is 0.13m 2 / g~15m 2 The copper powder according to claim 1 or 2, wherein the copper powder has a molecular weight of 1 / g.

9. The copper powder according to claim 1 or 2, which, when analyzed by thermomechanical analysis (TMA), has a 10% shrinkage temperature of 700°C or higher in an atmosphere containing nitrogen and water vapor with a water vapor pressure of 3.6 kPa.

10. The copper powder according to claim 1 or 2, which is used in a low-temperature co-fired ceramic substrate or a multilayer ceramic capacitor.

11. A paste containing the copper powder according to claim 1 or 2.

12. A method for producing a low-temperature co-fired ceramic substrate using the paste according to claim 11.

13. A method for manufacturing a multilayer ceramic capacitor using the paste according to claim 11.

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