Metal powders and conductive pastes

Abstract

To provide metal powder capable of preventing occurrence of peeling and crack between a dielectric layer and a conductor layer, when being used for a conductive paste for producing a laminate ceramic electronic component, and in the metal powder, a sintering temperature and a contraction degree due to sintering match those of ceramic powder to a certain degree.SOLUTION: In powder metal, a compound expressed by the following formula (1) is adhered to surfaces of particles, and when performing thermomechanical analysis (TMA) in which a temperature is raised from 25°C to 900°C at a temperature raising speed of 10°C / minute, various physical properties are in a specific range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to metal powders and related technologies. [Background technology]

[0002] Conventionally, metal powders such as copper powder and silver powder have been used as materials for conductive pastes that form internal electrodes in multilayer ceramic electronic components such as multilayer ceramic capacitors (MLCCs) and multilayer ceramic inductors (MLCIs).

[0003] Conductive paste is made by dispersing metal powder in an organic vehicle such as a resin or solvent, and multilayer ceramic electronic components are manufactured through processes such as firing a laminate in which dielectric films (green sheets) that form dielectric layers and conductive paste coatings are alternately stacked.

[0004] In the firing process, the laminate is heated from a low temperature, for example, room temperature, to the firing temperature and maintained at that temperature for a predetermined period of time. Sintering of the dielectric (ceramic powder) and metal powder usually begins before the firing temperature is reached, but if the sintering temperatures and the degree of shrinkage due to sintering differ significantly, stress may occur between the dielectric layer and the conductor layer, resulting in peeling between the layers and cracks in each layer.

[0005] In response to recent demands for miniaturization of electronic components, metal powders have become finer, and the temperature at which sintering begins is often lower than that of the ceramic powder that forms the dielectric layer. As the metal powder sinters first, peeling and cracking are more likely to occur.

[0006] To address this problem, it has been proposed to treat the particle surfaces of metal powders with a surface treatment in order to raise the temperature at which sintering of metal powders begins, so as to bring the temperature at which sintering of metal powders begins closer to the temperature at which sintering of ceramic powders begins. For example, Patent Documents 1 and 2 disclose copper powders and silver powders whose particle surfaces are coated with a silicon compound. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-262916 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-079269 Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Documents 1 and 2 state that the sintering initiation temperature is increased by coating copper powder or silver powder with a silicon compound. Each document defines the sintering initiation temperature as the temperature at which the amount of shrinkage reaches a predetermined value when copper powder or silver powder is sintered under predetermined conditions.

[0009] However, as mentioned above, if the temperature at which the ceramic powder and the metal powder sinter and the degree of shrinkage due to sintering differ significantly, stress may occur between the dielectric layer and the conductor layer, which may result in peeling between the layers or cracks in each layer. The sintering start temperatures focused on in Patent Documents 1 and 2 cannot be said to have been fully taken into consideration of the temperature at which the sintering occurs (which has a predetermined temperature range) or the degree of shrinkage due to sintering.

[0010] Therefore, taking these factors into consideration, an object of the present invention is to provide a metal powder that is more than somewhat consistent with the ceramic powder in terms of the sintering temperature and the degree of shrinkage due to sintering (hereinafter also referred to as "sintering behavior"), and that, when used in a conductive paste for producing a multilayer ceramic electronic component, can prevent peeling and cracking from occurring between the dielectric layer and the conductor layer. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that when a predetermined compound is adhered to the particle surfaces of a metal powder and the metal powder is subjected to thermomechanical analysis (TMA) by heating from 25°C to 900°C at a heating rate of 10°C / min, the maximum value of dTMA from 400 to 700°C is 5 to 20 μm / min, the temperature at which dTMA becomes maximum from 400 to 700°C is 600°C or higher, and when the temperature at which the shrinkage rate becomes 1% in the thermomechanical analysis is defined as the sintering start temperature (°C), the sintering start temperature is 480°C or higher, and the volume-based cumulative 50% particle diameter (D 50 The cumulative 90% particle diameter (D 90 diameter) and the volume-based cumulative 10% particle diameter (D 10 Diameter) and the ratio of difference ((D 90 diameter)-(D 10 diameter) / (D 50 When the particle size distribution difference (particle diameter) is defined as the particle size distribution difference, the inventors have found that by adjusting the value X obtained by dividing the sintering initiation temperature (°C) by the particle size distribution difference to be 390 (°C) or higher, the sintering behavior of the metal powder becomes more or less consistent with the sintering behavior of the ceramic powder, and peeling and cracking can be prevented between the dielectric layer and the conductor layer, thereby completing the present invention.

[0012] That is, the present invention is as follows. [1] A metal powder having a compound represented by the following general formula (1) attached to the particle surface: When thermomechanical analysis (TMA) is performed by heating from 25°C to 900°C at a heating rate of 10°C / min, the maximum value of dTMA from 400 to 700°C is 5 to 20 μm / min, and the temperature at which dTMA reaches a maximum from 400 to 700°C is 600°C or higher; When the temperature at which the shrinkage rate reaches 1% in the thermomechanical analysis is defined as the sintering start temperature (°C), the sintering start temperature is 480°C or higher, The volume-based cumulative 50% particle diameter (D 50 The cumulative 90% particle diameter (D 90diameter) and the volume-based cumulative 10% particle diameter (D 10 Diameter) and the ratio of difference ((D 90 diameter)-(D 10 diameter) / (D 50 When the particle size distribution difference is defined as the particle size distribution difference (diameter), the value X obtained by dividing the sintering start temperature (°C) by the particle size distribution difference is 390 (°C) or more. [ka] (In formula (1), R 1 ,R 2 and R 3 are each independently an alkyl group having 1 to 5 carbon atoms, and R is an alkylene group having 1 to 5 carbon atoms).

[0013] [2] The metal powder according to [1], wherein the metal is copper or silver.

[0014] [3] The metal powder according to [1] or [2], wherein in the thermomechanical analysis, the maximum value of dTMA at temperatures above 700°C and below 900°C is 23 μm / min or more.

[0015] [4] In the general formula (1), R 1 ,R 2 and R 3 are each independently an alkyl group having 1 to 3 carbon atoms.

[0016] [5] The metal powder according to any one of [1] to [4], wherein in the general formula (1), R is an alkylene group having 1 to 3 carbon atoms.

[0017] [6] The cumulative 50% particle diameter (D) on a volume basis measured using a laser diffraction particle size distribution analyzer 50 The metal powder according to any one of [1] to [5], wherein the diameter of the particles is 1 to 15 μm.

[0018] [7] A conductive paste, in which the metal powder according to any one of [1] to [6] is dispersed in at least one selected from the group consisting of organic solvents and binder resins.

[0019] [8] The method for producing a metal powder according to [1], comprising mixing a core powder made of a metal powder with a compound represented by the following general formula (1) to adhere the compound to the particle surfaces of the core powder: [ka] (In formula (1), R 1 ,R 2 and R 3 are each independently an alkyl group having 1 to 5 carbon atoms, and R is an alkylene group having 1 to 5 carbon atoms).

[0020] [9] The method for producing a metal powder according to [8], wherein the metal is copper or silver.

[0021]

[10] The volume-based cumulative 50% particle diameter (D 50 The method for producing a metal powder according to [8] or [9], wherein the diameter of the particles is 1 to 15 μm. [Effects of the Invention]

[0022] According to the present invention, there is provided a metal powder which has a sintering behavior more or less consistent with that of a ceramic powder and which, when used in a conductive paste for producing a multilayer ceramic electronic component, can prevent peeling and cracking from occurring between a dielectric layer and a conductor layer. [Brief explanation of the drawings]

[0023] [Figure 1] The results of observing a heat-treated product obtained by heating a coating film formed using the conductive paste containing Cu powder of Comparative Example 1 at 600°C using a scanning electron microscope (SEM) at a magnification of 5000 times are shown. [Figure 2] The results of observing the heat-treated coating film formed using the conductive paste containing Cu powder of Example 1 at 600°C or 700°C using an SEM at a magnification of 5000x are shown ((a) heated at 600°C, (b) heated at 700°C). [Figure 3]The results of observing the heat-treated coating film formed using the conductive paste containing Cu powder of Comparative Example 8 at 600°C or 700°C using an SEM at a magnification of 5000x are shown ((a) heated at 600°C, (b) heated at 700°C). [Figure 4] The results of observing a heat-treated product obtained by heating a coating film formed using the conductive paste containing Cu powder of Comparative Example 10 at 600°C using a scanning electron microscope (SEM) at a magnification of 5000 times are shown. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described. [Metal powder] The metal powder of the present invention has the compound represented by the above general formula (1) adhered to the particle surface.

[0025] <Metal type> The metal type of the metal powder of the present invention is not particularly limited, but specific examples include Au (gold), Ag (silver), Cu (copper), Ni (nickel), and Zn (zinc). Powders made of these single metals or alloy powders of multiple metals may be used. Among these, silver and copper are preferred because of their excellent conductivity.

[0026] <Compound represented by general formula (1)> General formula (1) is shown again. [ka]

[0027] The compound represented by this formula is believed to adhere to the particle surface of the metal powder via the amino group bonded to R, making the sintering behavior of the metal powder similar to that of ceramic powder.

[0028] In general formula (1), R 1 ,R 2 and R 3are each independently an alkyl group having 1 to 5 carbon atoms, and R is an alkylene group having 1 to 5 carbon atoms. From the viewpoint of making the sintering behavior of the metal powder similar to that of the ceramic powder, R 1 ,R 2 and R 3 are preferably each independently an alkyl group having 1 to 3 carbon atoms, and R is preferably an alkylene group having 1 to 3 carbon atoms. An example of the compound represented by general formula (1) is aminopropyltrimethoxysilane.

[0029] The amount of the compound of formula (1) that is suitable for adhering to the particle surface in order to make the sintering behavior of a metal powder similar to that of a ceramic powder varies depending on the metal species of the metal powder, etc., but by experimentally testing different amounts of the compound of formula (1) that are adhering, it is possible to determine the suitable amount for each metal powder.

[0030] For example, for roughly spherical copper powder, the amount of the compound of formula (1) attached is preferably 50 to 200 ppm, preferably 75 to 160 ppm, calculated as silicon (Si). For flaky copper powder, the amount of the compound of formula (1) attached is preferably 90 to 350 ppm, preferably 100 to 280 ppm, calculated as silicon (Si). For roughly spherical silver powder, the amount of the compound of formula (1) attached is preferably 30 ppm or more, preferably 80 to 550 ppm, calculated as silicon (Si).

[0031] In the present invention, the amount of the compound of formula (1) attached is the amount of silicon (the mass ratio of silicon in the metal powder including the mass of the compound of formula (1)) determined for the metal powder by the method described in the Examples below.

[0032] <Thermomechanical analysis (TMA) characteristics> When the metal powder of the present invention is subjected to thermomechanical analysis (TMA) by heating from room temperature (25°C) to 900°C, the dTMA, sintering initiation temperature, and the value obtained by dividing the sintering temperature by the particle size distribution difference (described later) at 400 to 700°C fall within a predetermined range. The TMA is carried out as follows.

[0033] 0.5 g of metal powder was mixed with 2% by mass of a vehicle (a mixture of Mitsubishi Plastics BR-105 (manufactured by Mitsubishi Plastics, Inc.) and terpineol in a mass ratio of 3:7 (BR-105:terpineol)) and compressed using a press with a load of 360 N for 20 seconds to prepare a measurement sample (5 mm diameter). This measurement sample was packed into an alumina pan with a diameter of 5 mm and a height of 3 mm and placed in the sample holder (cylinder) of a thermomechanical analysis (TMA) device (TMA / SS6200 manufactured by Seiko Instruments Inc.). A measurement load of 49 mN was applied using the measurement probe in a N2 atmosphere, and the temperature was raised from room temperature to 900 °C at a heating rate of 10 °C / min to measure the shrinkage of the measurement sample.

[0034] The amount of shrinkage and the temperature at that time are recorded every 2 seconds from the start of measurement (heating). To calculate dTMA at temperature T (℃), find the time when the temperature is T (the elapsed time after the start of heating) from the measurement results, and then calculate the amount of shrinkage (S) 2 seconds before that time. -2 ) and the contraction amount after 2 seconds (S +2 ) dTMA can be calculated using the following formula: dTMA=(S +2 -S -2 ) / 4(seconds)

[0035] The dTMA after 2 seconds from the start of measurement is calculated by S in the above formula, which is the contraction amount after 2 seconds from the start of measurement. +2 Substituting into, S -2 dTMA at the end of the measurement is calculated by substituting 0 for , and changing the denominator from 4 to 2. The dTMA at the end of the measurement is calculated by subtracting the amount of shrinkage at the end of the measurement from S in the above formula. +2 and the contraction amount 2 seconds before the end of measurement is S -2 Substitute into the equation and change the denominator from 4 to 2 to find the answer.

[0036] (Maximum dTMA temperature between 400°C and 700°C) Because ceramic powders begin to sinter at high temperatures, sintering of ceramic powders does not substantially occur at the lower end of the 400-700°C temperature range. Therefore, if the dTMA value of a metal powder becomes large early in the temperature range below 600°C, the sintering behavior of the metal powder and the ceramic powder will differ significantly. Therefore, the metal powder of the present invention is designed so that the temperature at which dTMA is maximized (maximum dTMA temperature) in the 400-700°C temperature range when subjected to thermomechanical analysis is 600°C or higher (i.e., 600-700°C). By varying the amount of the compound represented by general formula (1) attached to the powder particles depending on the metal type of the metal powder, the maximum dTMA temperature of the metal powder at 400-700°C can be increased to 600°C or higher. The greater the amount of attachment, the higher the maximum dTMA temperature tends to be.

[0037] (Maximum dTMA between 400℃ and 700℃) For the metal powder of the present invention, the maximum dTMA value (maximum dTMA) in the temperature range of 400 to 700°C when subjected to thermomechanical analysis is in the range of 5 to 20 μm / min. As mentioned above, the maximum dTMA temperature of the metal powder of the present invention in the temperature range of 400 to 700°C when subjected to thermomechanical analysis is 600°C or higher, and sintering of the ceramic powder begins in this temperature range. In order to match the degree of shrinkage (shrinkage rate) due to sintering of the ceramic powder and the degree of shrinkage due to sintering of the metal powder, the maximum dTMA value of the metal powder is set to be in the above range. The maximum value is preferably 6 to 18 μm / min.

[0038] By varying the amount of the compound represented by general formula (1) attached to the particles of the metal powder depending on the metal species of the metal powder, the maximum dTMA value of the metal powder at 400 to 700°C can be kept within the above range. The greater the amount of attachment, the smaller the maximum dTMA value tends to be.

[0039] (sintering start temperature) When the sintering start temperature (°C) is defined as the temperature at which the shrinkage rate of a measurement sample reaches 1% during thermomechanical analysis, the metal powder of the present invention has a sintering start temperature of 480°C or higher, and its sintering behavior is similar to that of ceramic powder, which begins sintering at high temperatures.From the viewpoint of aligning the sintering behavior of ceramic powder with that of metal powder, the sintering start temperature is preferably 550 to 800°C, and more preferably 590 to 750°C.

[0040] The sintering initiation temperature can be controlled within the above range by varying the amount of the compound represented by general formula (1) attached to the powder particles depending on the metal type of the metal powder. The sintering initiation temperature tends to increase as the amount of attachment increases.

[0041] (Value X (sintering start temperature / particle size distribution difference)) The volume-based cumulative 50% particle diameter (D 50 The cumulative 90% particle diameter (D 90 The cumulative 10% particle diameter (D 10 Diameter) and the ratio of difference ((D 90 diameter)-(D 10 diameter) / (D 50 When the particle size distribution difference is defined as the particle size distribution difference, the value obtained by dividing the sintering start temperature (°C) by the particle size distribution difference (sintering start temperature / particle size distribution difference) is 390 (°C) or more.

[0042] When the particle size distribution difference is small, the particle size distribution of the metal powder is sharp, and in this case, close-packing of the powder is unlikely to occur, and the sintering start temperature tends to be high. The value X is an index of sinterability that excludes the effect of the particle size distribution difference on the sintering start temperature. From the viewpoint of aligning the sintering behavior of the ceramic powder and the sintering behavior of the metal powder, the value X is preferably 450 to 700 (°C), and more preferably 500 to 650 (°C).

[0043] The value X can be set within the above range by varying the amount of the compound represented by general formula (1) attached to the powder particles depending on the metal type of the metal powder, etc. The value X tends to increase as the attached amount increases.

[0044] (dTMA at temperatures between 400°C and 600°C) From the viewpoint of aligning the sintering behavior of the metal powder with that of the dielectric powder, the metal powder of the present invention preferably has a dTMA of 12 μm / min or less, more preferably 5 μm / min or less, and even more preferably 3 μm / min or less at 400° C. or more but less than 600° C. From the same viewpoint, the maximum dTMA value at 400° C. or more but less than 600° C. is preferably 9 / 10 or less, more preferably 1 / 2 or less, and even more preferably 1 / 5 or less of the maximum dTMA value at 400 to 700° C.

[0045] (dTMA at temperatures above 700°C and below 900°C) As described above, in thermomechanical analysis, the metal powder of the present invention exhibits a predetermined maximum dTMA at temperatures above 600°C in the range of 400 to 700°C. Furthermore, sintering of the metal powder of the present invention proceeds further in the temperature range above 700°C to 900°C. Therefore, the maximum value of dTMA in this temperature range (maximum dTMA) is preferably 23 μm / min or greater. The upper limit of the maximum dTMA is not particularly limited, but is typically about 100 μm / min. Furthermore, the shrinkage due to sintering of powders in this temperature range is typically stronger than that of powders at 400 to 700°C. Therefore, the maximum dTMA value in the range above 700°C to 900°C is preferably 2 to 10 times the maximum dTMA value in the range of 400 to 700°C.

[0046] (dTMA at room temperature (25°C) or higher but less than 400°C) From the perspective of aligning the sintering behavior of the metal powder with that of the dielectric powder, it is desirable that the metal powder of the present invention does not substantially sinter in the temperature range from room temperature (25°C) to less than 400°C. However, in the thermomechanical analysis conducted in the present invention, since a vehicle is used for preparing the measurement sample, shrinkage due to evaporation or decomposition of the vehicle may be observed in the above temperature range. Therefore, in the above temperature range, the maximum value of dTMA may be about 10 μm / min.

[0047] That the metal powder of the present invention does not substantially sinter in the temperature range less than 400°C can be directly observed by microscopic observation of the metal powder heated up to 400°C and finding that the metal powder has not undergone necking. It can also be indirectly observed by confirming that the metal powder shows a predetermined maximum dTMA in the range of 400 - 700°C and also shows a predetermined high maximum dTMA in the range exceeding 700°C up to 900°C.

[0048] <Average particle size> The volume-based cumulative 50% particle size (D 50 iameter) measured by the laser diffraction particle size distribution measuring device of the metal powder of the present invention is preferably 1 - 15 μm, and when used as a material for a conductive paste for forming internal electrodes of electronic components with further miniaturized metal powder, it is more preferably 1 - 8 μm.

[0049] <Oxygen content, carbon content, nitrogen content> The oxygen content in the metal powder of the present invention is preferably 1 mass% or less, and more preferably 0.02 - 0.7 mass%. The carbon content in the metal powder of the present invention is preferably 0.5 mass% or less, and more preferably 0.01 - 0.35 mass%. The nitrogen content in the metal powder of the present invention is preferably 0.1 mass% or less, and more preferably 0.04 mass% or less.

[0050] <BET specific surface area> The BET specific surface area of the metal powder of the present invention is preferably 0.05 - 1.2 m 2 / g, and more preferably 0.1 - 1.0 m2 / g is more preferred.

[0051] <Filling rate> The filling rate of the metal powder of the present invention (the ratio of the tap density of the metal powder to the density of the corresponding bulk metal) is preferably 35% or more in order to increase the powder filling ability and form a conductive layer with good conductivity when the metal powder is used as a material for a conductive paste to form a conductive layer, and is more preferably 40 to 75% because of the above points and the fact that there is a limit to how much the filling rate can be improved.

[0052] <Shape> The shape of the metal powder of the present invention may be any of spherical, flake, and granular shapes, or may be irregular in shape.

[0053] [Metal powder manufacturing method] Next, an embodiment of the method for producing metal powder of the present invention will be described. In this method, a metal powder is produced by adhering a compound represented by the general formula (1) to the particle surfaces of core powder. When the produced metal powder is subjected to thermomechanical analysis (TMA) by heating from 25°C to 900°C, the maximum value of dTMA from 400 to 700°C is 5 to 20 μm / min, the temperature at which dTMA is maximum from 400 to 700°C is 600°C or higher, the sintering start temperature is 480°C or higher, and the value X (sintering start temperature / particle size distribution difference) is 390°C or higher. Each component of the method for producing metal powder of the present invention will be described below.

[0054] <Core powder> The core powder is the target to which the compound of general formula (1) is attached, and its metal species and shape are the same as those of the metal powder of the present invention. Core powders can be produced by conventionally known methods such as wet reduction, atomization, and gas phase methods, and are also commercially available.

[0055] The cumulative 50% particle diameter (D) of the core powder was measured by a laser diffraction particle size distribution analyzer. 50The diameter of the core powder is preferably 1 to 15 μm. When the produced metal powder is used as a material for a conductive paste for forming an internal electrode of a further miniaturized electronic component, the diameter of the core powder is preferably 1 to 15 μm. 50 The diameter is more preferably 1 to 8 μm.

[0056] <Attachment of the compound represented by general formula (1)> By mixing the core powder with the compound represented by general formula (1), the compound can be attached to the particle surface of the core powder. The mixing method is not particularly limited, and either dry mixing or wet mixing may be used.

[0057] The relationship between the amount of compound of general formula (1) added and the amount of adhesion to the particle surface of the core powder can vary depending on the mixing method, but can be determined experimentally. The relationship is such that the amount of adhesion increases as the amount of addition increases. In the present invention, the amount of adhesion of the compound of formula (1) is the amount of silicon determined for the metal powder by the method described in the Examples below.

[0058] [Conductive paste] When the metal powder according to the present invention is used as a material for a conductive paste, the conductive paste can be prepared by dispersing the metal powder in at least one organic vehicle selected from the group consisting of organic solvents and binder resins. Examples of the organic solvent include saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, ketones, aromatic hydrocarbons, glycol ethers, esters, and alcohols. Examples of the binder resin include cellulose resins such as ethyl cellulose and acrylic resins. Two or more organic solvents and binder resins may be used in combination.

[0059] If necessary, glass frit, inorganic oxides, dispersants, etc. may be added to the conductive paste.

[0060] The content of the metal powder of the present invention in the conductive paste is preferably 4.5 to 97.5 mass %, more preferably 70 to 95 mass %, from the viewpoints of the production cost of the conductive paste and the conductivity of the conductor layer.

[0061] The conductive paste may also contain one or more other metal powders (metal powders such as silver-tin alloy powders and tin powders that do not satisfy the requirements for the metal powder of the present invention with respect to thermomechanical analysis; hereinafter, these may also be referred to as "optional powders"). The optional powders may have different shapes and particle sizes from the metal powders according to the present invention.

[0062] The cumulative 50% particle size (D) of any powder measured by a laser diffraction particle size distribution analyzer 50 The diameter of the optional powder is preferably 0.5 to 20 μm in order to form a thin conductive layer by firing the conductive paste. The content of the optional powder in the conductive paste is preferably 1 to 94 mass %, more preferably 3 to 28 mass %. The total content of the metal powder and optional powder in the conductive paste is preferably 60 to 98.5 mass %, more preferably 74 to 98 mass %.

[0063] Furthermore, in consideration of the dispersibility of the metal powder in the conductive paste and the appropriate viscosity of the conductive paste, the content of the organic solvent is preferably 0.8 to 20 mass%, more preferably 0.8 to 15 mass%, and the content of the binder resin in the conductive paste is preferably 0.1 to 10 mass%, more preferably 0.1 to 6 mass%, in consideration of the dispersibility of the metal powder in the conductive paste and the conductivity of the conductive paste.

[0064] From the viewpoint of sinterability of the conductive paste, the content of the glass frit in the conductive paste is preferably 0.1 to 20 mass %, more preferably 0.1 to 10 mass %. Two or more types of glass frit may be mixed and used.

[0065] Such a conductive paste can be prepared, for example, by weighing each component, placing it in a designated container, pre-mixing it using a mixing machine, a universal mixer, a kneader, or the like, and then performing main mixing using a three-roll mill. If necessary, an organic solvent may be added thereafter to adjust the viscosity. Alternatively, glass frit or inorganic oxide may be mixed with an organic solvent or binder resin to reduce the particle size, and then metal powder may be added and the mixture may be main mixed.

[0066] [Multilayer ceramic electronic components] For example, a laminate obtained by stacking a coating film formed by applying the conductive paste of the present invention and a dielectric film (green sheet) is fired to sinter the metal powder in the coating film to form a conductor layer, and sinter the ceramic powder such as barium titanate in the dielectric film to form a dielectric layer (ceramic layer), and external electrodes are formed on the side surfaces of the conductor layer and dielectric layer in the stacking direction of the laminate that has undergone this firing process, thereby producing a multilayer ceramic electronic component.

[0067] In the firing step, the metal powder and the ceramic powder have sintering behaviors that are similar to each other to a certain extent, so that peeling between the conductive layer and the dielectric layer and cracks in the layers are unlikely to occur.

[0068] The firing temperature in the firing step can be, for example, about 600 to 1000°C, and more preferably about 700 to 900°C. Furthermore, prior to firing, pre-drying, such as by vacuum drying, may be performed to remove volatile components such as organic solvents in the conductive paste coating and the dielectric film. Furthermore, if these contain a binder resin, a debindering step to reduce the binder resin content is preferably performed by heating at a low temperature of 250 to 400°C prior to firing. [Example]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. <<Spherical Cu powder>> [Comparative Example 1] In an atmospheric environment, carbon powder was added as a reducing agent to a molten metal obtained by heating 40 kg of electrolytic copper to 1600 °C in a tundish furnace. While dropping the molten metal from the lower part of the tundish furnace, high-pressure water (water pressure: 150 MPa, water volume: 160 L / min, pH: 10) was sprayed in the atmosphere by a water atomization device to pulverize and solidify it. The obtained powder was filtered, washed with water, dried, crushed, and classified to obtain Cu powder.

[0070] The following evaluations were performed on the Cu powder according to this Comparative Example 1.

[0071] <Si content> Si was analyzed by the gravimetric method as follows. First, hydrochloric acid and perchloric acid were added to the sample (Cu powder) and heated for decomposition until white smoke of perchloric acid was generated. Subsequently, heating was continued until dryness. After cooling, water and hydrochloric acid were added and heated to dissolve soluble salts. Subsequently, the insoluble residue was filtered using filter paper, and the residue was transferred to a crucible together with the filter paper, dried, and ashed. After cooling, the crucible was weighed. A small amount of sulfuric acid and hydrofluoric acid were added, heated until dryness, and then strongly heated. After cooling, the crucible was weighed. Then, the second weighing value was subtracted from the first weighing value, and the weight difference was calculated as SiO2 to determine the Si content. As a result, the Si content was below the detection limit. Therefore, it can be said that the electrolytic copper used in the preparation of this sample (Cu powder) also substantially contained no Si.

[0072] <TMA evaluation> The thermomechanical analysis (TMA) of Cu powder was carried out as follows. 0.5 g of Cu powder was mixed with a vehicle (a mixture of Mitsubishi Plastics BR-105 (manufactured by Mitsubishi Plastics Inc.) and terpineol at a mass ratio of 3:7 (BR-105:terpineol)) at a mass ratio of 2% with respect to the powder, and pressed firmly with a press machine at a load of 360 N for 20 seconds to prepare a measurement sample with a diameter of 5 mm. This measurement sample was packed into an alumina pan with a diameter of 5 mm and a height of 3 mm, set in a sample holder (cylinder) of a thermomechanical analysis (TMA) apparatus (TMA / SS6200 manufactured by Seiko Instruments Inc.), and a load of 49 mN was applied under a N2 atmosphere with a measurement probe, and the temperature was raised from room temperature (25 °C) to 900 °C at a heating rate of 10 °C / min to measure the shrinkage of the measurement sample.

[0073] The shrinkage and the temperature at that time were recorded every 2 seconds from the start of measurement (heating). When obtaining dTMA at temperature T (°C), the time (elapsed time after the start of heating) at which the temperature was T was obtained from the measurement results, and the shrinkage amount (S -2 ) 2 seconds before that time and the shrinkage amount (S +2 ) 2 seconds after that time were used to obtain dTMA according to the following formula. dTMA=(S +2 -S -2 ) / 4 (seconds)

[0074] As a result of the above evaluation, the sintering start temperature (temperature at 1% shrinkage) was 503 °C, the maximum dTMA temperature in the range of 400 to 700 °C was 501 °C, and the dTMA value (maximum dTMA value) at that time was 51.4 μm / min. Also, the maximum value of dTMA at room temperature to 400 °C was 7.4 μm / min, the maximum value of dTMA at 400 °C to 600 °C was 51.4 μm / min, and the maximum value of dTMA at 700 °C to 900 °C was 8.8 μm / min.

[0075] <BET specific surface area> The BET specific surface area of ​​the Cu powder was measured using a BET specific surface area analyzer (Macsorb manufactured by Mountec Co., Ltd.). After degassing the powder by flowing nitrogen gas through the analyzer at 105°C for 20 minutes to remove impurities from the particle surface, the BET specific surface area was measured by the single-point BET method while flowing a mixed gas of nitrogen and helium (N: 30% by volume, He: 70% by volume). The BET specific surface area was found to be 0.80 m. 2 / g.

[0076] <Filling rate> The tap density of the Cu powder was determined by filling a bottomed cylindrical die with Cu powder up to 80% of its capacity, with an inner diameter of 6 mm and a height of 11.9 mm, in the same manner as in the method described in JP 2007-263860 A, to form a Cu powder layer, and applying a pressure of 0.160 N / m 2 The Cu powder was compressed at this pressure until it could no longer be packed densely, and the height of the Cu powder layer was then measured. The tap density of the Cu powder was calculated from the measured height of the Cu powder layer and the weight of the packed Cu powder. As a result, the tap density was 4.2 g / cm. 3 This value and the bulk density of copper, 8.96 g / cm 3 From this, the filling rate of the Cu powder was calculated to be 47.3%.

[0077] <Oxygen and nitrogen content> The oxygen and nitrogen contents of the Cu powder were measured using an oxygen / nitrogen / hydrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.), and the oxygen content was 0.38 mass % and the nitrogen content was less than 0.01 mass %.

[0078] <Carbon content> The carbon content in the Cu powder was measured using a carbon / sulfur analyzer (EMIA-920V2 manufactured by Horiba, Ltd.), and was found to be 0.01% by mass.

[0079] <Particle size distribution> Using a laser diffraction particle size distribution analyzer (SYMPATEC's HELOS particle size distribution analyzer (HELOS & RODOS (airflow dispersion module))), the Cu powder was dispersed with nitrogen gas at a dispersion pressure of 5 bar to evaluate the particle size distribution, and the cumulative 10% particle diameter (D 10 diameter), cumulative 50% particle diameter (D 50 diameter), cumulative 90% particle diameter (D 90 diameter) and cumulative 99% particle diameter (D 99 As a result, D 10 The diameter is 0.60 μm, and D 50 The diameter is 1.55 μm, and D 90 The diameter is 2.71 μm, and D 99 The diameter is 4.99 μm, and the particle size distribution difference ((D 90 diameter)-(D 10 diameter) / (D 50 The diameter was 1.36.

[0080] The above evaluation results are summarized in Table 1 below.

[0081] Comparative Example 2 The Cu powder according to Comparative Example 1 was coated with TEOS (tetraethyl orthosilicate), specifically as follows.

[0082] To 80 g of Cu powder, 0.06 g of TEOS (0.074 parts by mass per 100 parts by mass of Cu powder, equivalent to 101 ppm of Si) was added as a surface treatment agent, and while the Cu powder was being crushed, the Cu powder and the surface treatment agent were mixed to obtain Cu powder surface-treated with 3-aminopropyltrimethoxysilane.

[0083] The obtained Cu powder according to Comparative Example 2 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0084] Comparative Example 3 A Cu powder according to Comparative Example 3 was obtained in the same manner as in Comparative Example 2, except that the amount of TEOS used in the TEOS coating was changed to 200 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0085] Comparative Example 4 A Cu powder according to Comparative Example 4 was obtained in the same manner as in Comparative Example 2, except that the amount of TEOS used in the TEOS coating was changed to 400 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0086] Comparative Example 5 A Cu powder according to Comparative Example 5 was obtained in the same manner as in Comparative Example 2, except that the amount of TEOS used in the TEOS coating was changed to 800 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0087] Comparative Example 6 In an atmospheric air atmosphere, 40 kg of electrolytic copper was heated to 1600°C in a tundish furnace, and carbon powder was added as a reducing agent to the molten metal. The molten metal was then dropped from the bottom of the tundish furnace, and high-pressure water (water pressure: 150 MPa, water flow rate: 160 L / min, pH: 10) was sprayed onto the molten metal in the atmosphere using a water atomizer to pulverize and solidify it. The resulting powder was filtered, washed with water, dried, and crushed (this crushing was performed by mixing 0.24 parts by mass of stearic acid with 100 parts by mass of Cu powder), and classified to obtain Cu powder.

[0088] The Cu powder according to Comparative Example 6 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. From the evaluation results of the Si content (see Table 1 below), it can be said that the electrolytic copper that was the raw material of the Cu powder did not substantially contain Si.

[0089] [Example 1] The Cu powder obtained in Comparative Example 6 was surface treated using 3-aminopropyltrimethoxysilane (APTMS) in an amount of 100 ppm in terms of Si. Specifically, the procedure is as follows.

[0090] To 120 g of Cu powder, 0.077 g of APTMS (0.064 parts by mass per 100 parts by mass of Cu powder) was added as a surface treatment agent, and while crushing the Cu powder, the Cu powder and the surface treatment agent were mixed to obtain Cu powder surface-treated with APTMS.

[0091] The obtained Cu powder according to Example 1 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0092] Comparative Example 7 A Cu powder according to Comparative Example 7 was obtained in the same manner as in Example 1, except that the amount of APTMS used was changed to 200 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0093] [Comparative Example 8] A Cu powder according to Comparative Example 8 was obtained in the same manner as in Example 1, except that the amount of APTMS used was changed to 400 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0094] <<Flake Cu powder>> Comparative Example 9 The roughly spherical Cu powder produced in Comparative Example 6 was subjected to a flaking treatment, specifically as follows.

[0095] (Flakes) 1.732 kg of Cu powder, 5.2 g of stearic acid (ST5000), 10.5 kg of zirconia beads with a diameter of 0.5 mm, and 0.93 g of industrial alcohol (Solmix AP7, manufactured by Japan Alcohol Sales Co., Ltd.) were placed in an attritor and pulverized in a nitrogen atmosphere at 360 rpm for 180 minutes. The resulting slurry was then filtered and dried to obtain flake copper powder.

[0096] The obtained Cu powder according to Comparative Example 9 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0097] [Comparative Example 10] The Cu powder according to Comparative Example 9 was coated with APTMS in an amount of 50 ppm in terms of Si. Specifically, the coating was performed as follows.

[0098] To 150 g of Cu powder, 0.096 g (0.064 parts by mass per 100 parts by mass of Cu powder) of 3-aminopropyltrimethoxysilane (APTMS) was added as a surface treatment agent, and while the Cu powder was being crushed, the Cu powder and the surface treatment agent were mixed to obtain Cu powder surface-treated with APTMS.

[0099] The obtained Cu powder according to Comparative Example 10 was evaluated for the Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0100] [Example 2] A Cu powder according to Example 2 was obtained in the same manner as in Comparative Example 10, except that the amount of APTMS used was changed to 100 ppm in terms of Si amount. The Cu powder was evaluated for Si amount, TMA, BET specific surface area, packing ratio, oxygen amount, nitrogen amount, carbon amount, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0101] [Example 3] A Cu powder according to Example 3 was obtained in the same manner as in Comparative Example 10, except that the amount of APTMS used was changed to 200 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0102] [Comparative Example 11] A Cu powder according to Comparative Example 11 was obtained in the same manner as in Comparative Example 10, except that the amount of APTMS used was changed to 400 ppm in terms of Si content. The Cu powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 6. The results are shown in Table 1 below.

[0103] <<Spherical Ag powder>> [Comparative Example 12] In an air atmosphere, 40 kg of silver shot was heated to 1400°C in a tundish furnace. The molten metal was dropped from the bottom of the tundish furnace while being pulverized and solidified by spraying high-pressure water (water pressure: 70 MPa, water flow rate: 160 L / min, pH: 5.8) onto the molten metal using a water atomizer. The resulting powder was filtered, washed with water, dried, crushed, and classified to obtain Ag powder.

[0104] The Ag powder according to Comparative Example 12 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below. From the evaluation result of the Si content (see Table 1 below), it can be said that the shot silver, which is the raw material of the Ag powder, did not substantially contain Si.

[0105] [Example 4] The Ag powder according to Comparative Example 12 was coated with 100 ppm of APTMS in terms of Si amount. Specifically, the coating was as follows.

[0106] To 150 g of Ag powder, 0.096 g (0.064 parts by mass per 100 parts by mass of silver powder) of 3-aminopropyltrimethoxysilane (APTMS) was added as a surface treatment agent, and the silver powder and surface treatment agent were mixed while crushing the silver powder to obtain Ag powder surface-treated with APTMS.

[0107] The obtained Ag powder according to Example 4 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0108] [Comparative Example 14] In an air atmosphere, 40 kg of silver shot was heated to 1600°C in a tundish furnace. The molten metal was dropped from the bottom of the tundish furnace while being pulverized and solidified by spraying high-pressure water (water pressure: 150 MPa, water flow rate: 160 L / min, pH: 5.8) onto the molten metal using a water atomizer. The resulting powder was filtered, washed with water, dried, crushed, and classified to obtain Ag powder.

[0109] The Ag powder according to Comparative Example 14 was evaluated for the Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0110] [Example 5] The Ag powder according to Comparative Example 14 was coated with 100 ppm of APTMS in terms of Si amount. Specifically, the coating was performed as follows.

[0111] To 150 g of Ag powder, 0.096 g (0.064 parts by mass per 100 parts by mass of silver powder) of 3-aminopropyltrimethoxysilane (APTMS) was added as a surface treatment agent, and the silver powder and surface treatment agent were mixed while crushing the silver powder to obtain Ag powder surface-treated with APTMS.

[0112] The obtained Ag powder according to Example 5 was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0113] [Comparative Example 15] An Ag powder according to Comparative Example 15 was obtained in the same manner as in Example 5, except that the amount of APTMS used was changed to 1000 ppm in terms of Si content. The Ag powder was evaluated for Si content, TMA, BET specific surface area, packing ratio, oxygen content, nitrogen content, carbon content, and particle size distribution in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0114] [Table 1]

[0115] <Paste evaluation> A conductive paste was prepared by mixing 9 g of the Cu powders of Comparative Example 1, Example 1, Comparative Example 8, and Comparative Example 10 with 1 g of BCA (diethylene glycol monobutyl ether acetate) in a kneader at 1400 rpm for 30 seconds, and then coated onto an alumina substrate. The coating film formed on the substrate was then heated to a specified temperature (600°C or 700°C) at a rate of 5°C / min in a nitrogen atmosphere, and held at that temperature for 10 minutes. After that, heating was stopped and the film was allowed to cool naturally in a nitrogen atmosphere.

[0116] The heat-treated coating film was observed under a scanning electron microscope (SEM) at a magnification of 5000. The results are shown in Figure 1 (Comparative Example 1 (heated at 600°C)), Figure 2 (Example 1 ((a) heated at 600°C, (b) heated at 700°C)), Figure 3 (Comparative Example 8 ((a) heated at 600°C, (b) heated at 700°C)), and Figure 4 (Comparative Example 10 (heated at 600°C)).

[0117] In Comparative Example 1, sintering progressed upon heating at 600°C. In Example 1, sintering did not substantially occur upon heating at 600°C, but sintering progressed upon heating at 700°C. In Comparative Example 8, sintering did not substantially occur upon heating at 600°C, but sintering did occur, but only slightly, upon heating at 700°C. In Comparative Example 10, sintering progressed upon heating at 600°C.

Claims

1. A metal powder having a compound represented by the following general formula (1) attached to the particle surface, When thermomechanical analysis (TMA) is performed by heating from 25°C to 900°C at a heating rate of 10°C / min, the maximum value of dTMA from 400 to 700°C is 5 to 20 μm / min, and the temperature at which dTMA becomes maximum from 400 to 700°C is 600°C or higher, When the temperature at which the shrinkage rate reaches 1% in the thermomechanical analysis is defined as the sintering start temperature (°C), the sintering start temperature is 480°C or higher, The volume-based cumulative 50% particle diameter (D ５０ The volume-based cumulative 90% particle diameter (D ９０ diameter) and the volume-based cumulative 10% particle diameter (D １０ The ratio of difference between the diameter and ９０ diameter) - (D １０ diameter) / (D ５０ When the particle size distribution difference (particle diameter) is defined as the particle size distribution difference, the value X obtained by dividing the sintering initiation temperature (°C) by the particle size distribution difference is 390 (°C) or more, A metal powder having a nitrogen content of less than 0.01% by mass. 【Chemistry 1】 (In formula (1), R １ , R ２ and R ３ are each independently an alkyl group having 1 to 5 carbon atoms, and R is an alkylene group having 1 to 5 carbon atoms).

2. 2. The metal powder of claim 1, wherein the metal is copper or silver.

3. The metal powder according to claim 1 or 2, wherein in the thermomechanical analysis, the maximum value of dTMA at temperatures exceeding 700°C and not exceeding 900°C is 23 µm / min or more.

4. In the general formula (1), R １ , R ２ and R ３ The metal powder according to any one of claims 1 to 3, wherein each independently represents an alkyl group having 1 to 3 carbon atoms.

5. The metal powder according to any one of claims 1 to 4, wherein in the general formula (1), R is an alkylene group having 1 to 3 carbon atoms.

6. The cumulative 50% particle diameter (D) on a volume basis measured by a laser diffraction particle size distribution analyzer ５０ The metal powder according to any one of claims 1 to 5, wherein the diameter of the particles is 1 to 15 µm.

7. A conductive paste comprising the metal powder according to any one of claims 1 to 6 dispersed in at least one selected from the group consisting of organic solvents and binder resins.

8. 2. The method for producing a metal powder according to claim 1, wherein a core powder made of a metal powder is mixed with a compound represented by the following general formula (1) to adhere the compound to particle surfaces of the core powder: 【Chemistry 2】 (In formula (1), R １ , R ２ and R ３ are each independently an alkyl group having 1 to 5 carbon atoms, and R is an alkylene group having 1 to 5 carbon atoms).

9. The method for producing metal powder according to claim 8, wherein the metal is copper or silver.

10. The volume-based cumulative 50% particle diameter (D ５０ The method for producing metal powder according to claim 8 or 9, wherein the diameter of the particles is 1 to 15 μm.

Images