Conductive paste and electronic component

Abstract

To provide a conductive paste capable of suppressing thickness variation in an internal electrode layer and also suppressing common material separation.SOLUTION: There is provided a conductive paste in which composite particles are dispersed in a binder and a solvent, wherein the composite particles have large particles and small particles which are adhering to the surface of the large particles and have a smaller average particle diameter than the large particles, the dispersion degree of dispersed particles, which are dispersed in the conductive paste and have a smaller average particle diameter than the large particles, is 0% or more and 50% or less and the agglomeration index of the composite particles in the conductive paste is less than 1.2.SELECTED DRAWING: Figure 2b

Description

[Technical Field]

[0001] The present invention relates to an electronic component having an electrode layer and a conductive paste used to form the electrode layer of the electronic component. [Background technology]

[0002] In ceramic electronic components such as multilayer ceramic capacitors, the ceramic layers and internal electrode layers are becoming thinner in response to demands for smaller size and higher capacitance. However, when the internal electrode layers are made thinner, cracks and discontinuities can occur in the internal electrode layers after sintering due to the difference in sintering start temperatures between the ceramic layers and the internal electrode layers, which can reduce the continuity rate of the internal electrode layers relative to the ceramic layers (the coverage rate of the internal electrode layers).

[0003] As a measure to reduce the difference in sintering start temperature, a method of forming internal electrode layers using a conductive paste to which ceramic common material powder is added has been proposed (for example, Patent Document 1). Adding ceramic common material powder to the conductive paste is expected to have the effect of delaying the sintering of the internal electrode layers (sintering delay effect). However, in such conductive paste, the ceramic common material powder is prone to agglomeration, and the metal components become spherical during the process of sintering the internal electrode layers, which may prevent a sufficient sintering delay effect from being obtained. In addition, the ceramic common material powder may diffuse into the ceramic layer and affect the composition of the ceramic layer.

[0004] In addition to the above measures, a method has also been proposed in which composite particles, in which minute ceramic particles are fixed to the surface of metal particles, are used as raw material powder for conductive pastes (for example, Patent Document 2). The thermal shrinkage onset temperature of such composite particles is higher than that of uncomposite metal particles. Furthermore, ceramic particles fixed to the surface are less likely to agglomerate than ceramic core powders added individually to the conductive paste.

[0005] However, when composite particles are used as raw powder for a conductive paste, it can be difficult to improve the smoothness of the coating film. This is because it is difficult to disperse each dried and agglomerated composite particle when forming the composite particles into a paste. In other words, when attempting to disperse the dried and agglomerated composite particles without breaking them, the dispersibility may remain low. As a result, the composite particles are formed into a sheet with low dispersibility, which can deteriorate the smoothness of the internal electrode pattern layer and increase the thickness variation of the internal electrode layer.

[0006] On the other hand, attempts to improve the dispersibility of dried and agglomerated composite particles can sometimes result in the destruction of the composite particles. Furthermore, when such conductive pastes are left standing, a phenomenon known as "composite particle separation" can occur, in which free particles derived from small particles detached from the composite particles appear on the surface of the conductive paste. Such conductive pastes require stirring before use, complicating the manufacturing process. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-55314 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-282102 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of an exemplary embodiment of the present invention is to provide a conductive paste that can suppress variations in thickness of internal electrode layers and can also suppress material separation. [Means for solving the problem]

[0009] In order to achieve the above object, the conductive paste according to the present invention comprises: A conductive paste in which composite particles are dispersed in a binder and a solvent, The composite particles have large particles and small particles attached to the surfaces of the large particles and having an average particle size smaller than that of the large particles, the degree of liberation of free particles dispersed in the conductive paste and having an average particle size smaller than that of the large particles is 0% or more and 50% or less, The liberation degree is defined by the following formula (1): Freedom (%) = 100 × MF / (MF + MS) (1) where MF is the total mass of free particles, MS is the total mass of the small particles; the composite particles in the conductive paste have an aggregation index of less than 1.2; The aggregation index is defined by the following formula (2): Aggregation index = Ra / (average DL) (2) DL is the particle size of the large particle, The Ra is the coating film smoothness.

[0010] When the conductive paste has the above-mentioned properties, it is possible to suppress variations in thickness of the internal electrode layers and also to suppress material separation.

[0011] Preferably, the large particles are metal particles; The main component of the metal particles is nickel, copper, silver, palladium, or an alloy containing at least one selected from these metal elements.

[0012] Preferably, the average coverage of the small particles attached to the surfaces of the large particles is 3% or more and 60% or less.

[0013] Preferably, the small particles and / or free particles are at least one selected from the group consisting of barium titanate, silicon oxide, titanium oxide, aluminum oxide, zinc oxide, praseodymium oxide, cobalt oxide, chromium oxide, bismuth oxide, boron oxide, calcium oxide, magnesium oxide, strontium oxide, bismuth ferrite, bismuth titanate, potassium sodium niobate, bismuth sodium titanate, potassium bismuth titanate, Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, and zirconium oxide.

[0014] Preferably, the viscosity of the conductive paste is 0.5 Pa·s to 30 Pa·s (100 rpm).

[0015] Preferably, the concentration of the large particles in the conductive paste is 20% by mass to 60% by mass.

[0016] The electronic component according to the present invention has an electrode layer formed using the conductive paste. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing a multilayer ceramic electronic component according to one embodiment. [Figure 2a] FIG. 2a is a schematic diagram showing a conductive paste according to one embodiment. [Figure 2b] FIG. 2b is a schematic diagram showing an internal electrode pattern layer according to an embodiment. [Figure 3] FIG. 3 is a schematic diagram showing a cross section of a composite particle according to one embodiment. [Figure 4] FIG. 4 is a schematic diagram for explaining a method for measuring the coverage of a composite particle. [Figure 5] FIG. 5 is a schematic diagram for explaining a method for measuring the coverage of a composite particle. [Figure 6] FIG. 6 is a schematic diagram for explaining a method for measuring the coverage of a composite particle. [Figure 7a] FIG. 7a is a schematic diagram showing a conventional conductive paste. [Figure 7b] FIG. 7b is a schematic diagram showing a conventional internal electrode pattern layer. [Figure 8a] FIG. 8a is a schematic diagram showing a conventional conductive paste. [Figure 8b] FIG. 8b is a schematic diagram showing a conventional internal electrode pattern layer. [Figure 9] FIG. 9 is a schematic diagram for explaining a method for measuring the thermal shrinkage starting temperature by the tangent method. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] First embodiment As an example of a multilayer ceramic electronic component that uses the conductive paste 11 according to this embodiment, a multilayer ceramic capacitor 2 shown in FIG. 1 will be described.

[0020] The multilayer ceramic capacitor 2 has an element body 4 and a pair of external electrodes 6 formed on the outer surface of the element body 4. The element body 4 has ceramic layers 20 and internal electrode layers 10 that are substantially parallel to a plane including the X-axis and Y-axis, and inside the element body 4, the ceramic layers 20 and internal electrode layers 10 are alternately stacked along the Z-axis direction. Here, "substantially parallel" means that most of the portions are parallel, but there may be some portions that are not parallel, and the ceramic layers 20 and internal electrode layers 10 may have some irregularities or be tilted.

[0021] The ceramic layer 20 includes a dielectric composition. The composition of the dielectric composition is not particularly limited. For example, the ceramic layer 20 may include BaTiO3, CaTiO3, SrTiO3, CaZrO3, (K 1-x Na x )Sr2Nb5O 15 , Ba3TiNb4O 15, and (Ba 1-x Ca x )(Ti 1-y Zr y )O3, etc. as a main component. In addition to the main component, the ceramic layer 20 may also contain one or more accessory components. Examples of accessory components of the ceramic layer 20 include manganese compounds, magnesium compounds, chromium compounds, cobalt compounds, nickel compounds, compounds containing rare earth elements, silicon compounds, and lithium compounds.

[0022] The average thickness of each ceramic layer 20 is not particularly limited, and is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. The lower limit of the average thickness of the ceramic layer 20 is not particularly limited, and may be, for example, about 0.3 μm. The number of layers of the ceramic layer 20 may be determined appropriately depending on the desired properties, and is not particularly limited. For example, the number of layers of the ceramic layer 20 is preferably 20 or more, and more preferably 50 or more.

[0023] The internal electrode layers 10 are formed by sintering composite particles 12, which will be described later, and the large particles 14 in the composite particles 12 become the conductive components of the internal electrode layers 10 after sintering.

[0024] On the other hand, the small particles 16a of the composite particle 12 shown in FIG. 3 and / or the free particles 16b described later may remain as insulating material inside the internal electrode layer 10 after sintering. When the total of the conductor components and insulating material in the internal electrode layer 10 is taken as 100 mass%, the content of the insulating material in the internal electrode layer 10 may be, for example, 0.4 mass% to 20 mass%, and preferably 3 mass% to 15 mass%. Some of the small particles 16a and / or free particles 16b may be diffused into the ceramic layer 20 after sintering. By using barium titanate particles as the small particles 16a and / or free particles 16b, even if the small particles 16a and / or free particles 16b diffuse into the ceramic layer 20, fluctuations in the composition of the ceramic layer 20 can be suppressed.

[0025] The internal electrode layers 10 are laminated between the ceramic layers 20, and the number of layers is determined according to the number of ceramic layers 20. The average thickness of each internal electrode layer 10 is not necessarily limited, and is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. By using the composite particles 12 shown in FIG. 3 as raw material powder, the internal electrode layers 10 can be made thin (for example, 0.8 μm or less) while suppressing the occurrence of cracks and discontinuities. The lower limit of the average thickness of the internal electrode layers 10 is not particularly limited, and may be, for example, about 0.3 μm. The average thickness t E In order to form the internal electrode layer 10, E It is preferable to use large particles 14 having an average particle size (DL) of 0.2 times or less.

[0026] The internal electrode layers 10 are stacked such that one end is alternately exposed on two end faces of the element body 4. A pair of external electrodes 6 are formed on both end faces of the element body 4 and electrically connected to the exposed ends of the alternately arranged internal electrode layers 10. By connecting the internal electrode layers 10 and the external electrodes 6 in the manner shown in FIG. 1, a capacitor circuit is formed by the external electrodes 6 and the internal electrode layers 10. In other words, the ceramic layers 20 present in the capacitance region are sandwiched between internal electrode layers 10 of opposite polarity, and a voltage can be applied to the ceramic layers 20.

[0027] The pair of external electrodes 6 can include a baked electrode layer, a resin electrode layer, a plated electrode layer, etc., and can be composed of a single electrode layer or a laminate of multiple electrode layers. For example, the external electrodes 6 can have a three-layer structure of a baked electrode layer containing copper, a nickel-plated layer, and a tin-plated layer (laminated in the order listed). When the external electrodes 6 are formed with this three-layer structure, the tin-plated layer is located on the outermost surface of the external electrodes 6, which improves the solder wettability of the external electrodes 6.

[0028] The conductive paste 11 shown in FIG. 2a constitutes the internal electrode layer 10 after firing.

[0029] As shown in Fig. 2a, the conductive paste 11 according to this embodiment is produced by kneading the composite particles 12 shown in Fig. 3, a binder, and a solvent. In addition to the above, the conductive paste 11 may contain additives such as a dispersant, an antioxidant, a ceramic powder, and an organometallic solution.

[0030] Furthermore, free particles 16b having an average particle size smaller than that of large particles 14 may be dispersed in conductive paste 11. Free particles 16b are not combined with large particles 14 but are particles dispersed independently in the paste. Free particles 16b may or may not be derived from small particles 16a.

[0031] The primary component of the free particles 16b, like the primary component of the small particles 16a, is preferably at least one selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide, zinc oxide, praseodymium oxide, cobalt oxide, chromium oxide, and zirconium oxide, more preferably silicon oxide, and even more preferably barium titanate. Alternatively, the free particles 16b may contain one or more primary components selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os. By including one or more primary components selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os, the sintering suppression effect is more likely to be improved. In addition, when "free particles 16b contain one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as a main component," this also includes cases where free particles 16b contain any one or more elements selected from the above group of elements as a main component. For example, the term "free particles 16b containing one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as the primary component" applies to free particles 16b containing Ir as the primary component, Rh as the primary component, Ir and Rh as the primary component, Ir, Ag, and V as the primary component, or Cu, Co, and Zr as the primary component. The term "primary component" refers to a component that accounts for 20 or more moles of the total elements constituting free particles 16b, given that the total elements constituting free particles 16b is 100 moles. Each free particle 16b may be made of the same material, or free particles 16b may contain two or more types of particles made of different materials (i.e., two or more types of free particles 16b made of different materials may be mixed).

[0032] The free particles 16b and the small particles 16a may be made of the same material or different materials.

[0033] It is preferable that the thermal shrinkage initiation temperature of the free particles 16b when mixed with the large particles 14 and fired is 500°C or higher, and it is also preferable that the thermal shrinkage initiation temperature when mixed with the large particles 14 and fired is equal to the thermal shrinkage initiation temperature of the ceramic particles that make up the ceramic layer 20.

[0034] The average particle size of the free particles 16b is, for example, preferably 3 nm to 30 nm, more preferably 3 nm to 20 nm. When the free particles 16b include two or more particle groups made of different materials, each particle group may have a different particle size distribution, but it is preferable that the average particle size of each particle group be within the above range.

[0035] The free particles 16b and the small particles 16a may have the same average particle size or may have different average particle sizes.

[0036] The degree of liberation of the free particles 16b is 0% or more and 50% or less.

[0037] The degree of liberation of the free particles 16b is preferably 5% or more and 45% or less. When the conductive paste 11 contains the predetermined free particles 16b, the dispersibility of each component in the conductive paste 11 is improved. From the above viewpoint, the degree of liberation of the free particles 16b is more preferably 5% or more and 20% or less. Examples of methods for controlling the degree of liberation include controlling the amount of the free particles 16b added to the "mixture of the solvent and the composite particles 12 that constitute the conductive paste 11" and controlling the strength of the shear treatment applied to the "mixture of the solvent and the composite particles 12 that constitute the conductive paste 11".

[0038] The degree of liberation is defined by the following formula (1). Freedom (%) = 100 × MF / (MF + MS) (1)

[0039] Here, MF is the total mass of the free particles 16b, and MS is the total mass of the small particles 16a. In other words, the degree of freeness is the ratio of the "total mass of the free particles 16b" to the sum of the "total mass of the free particles 16b" and the "total mass of the small particles 16a attached to the surface of the large particle 14 and which are part of the composite particle 12."

[0040] The "total mass of free particles 16b" and the "total mass of small particles 16a attached to the surface of large particles 14 and forming part of composite particles" can be determined, for example, by the following method.

[0041] First, the free particles 16b and the composite particles 12 are physically separated. For example, the separation method utilizes the difference in sedimentation velocity between the free particles 16b and the composite particles 12, causing the composite particles 12 to settle and separating the free particles 16b as the supernatant. This separation method is based on Stokes' law. According to Stokes' law, the sedimentation velocity of particles in a liquid is proportional to the square of their particle size and proportional to the particle density.

[0042] In the above separation method, separation may be achieved by leaving the mixture to stand or by centrifugation.

[0043] Furthermore, if only the large particles 14 are magnetic, magnetic separation can also be performed.

[0044] In addition, since any of the above separation methods requires a long time for separation in the case of a highly viscous paste, separation may be performed by diluting the paste by adding a paste solvent or the like.

[0045] The total mass (MF) of the free particles 16b separated by the above method and the total mass (MS) of the small particles 16a that are part of the composite particles 12 can be quantified by inductively coupled plasma emission spectroscopy (ICP) or the like, and the degree of liberation can be calculated using the above formula (1).

[0046] Hereinafter, among the components contained in the conductive paste 11, components other than the composite particles 12, the large particles 14, and the free particles 16b may be referred to as binders, etc. 19. That is, the binders, etc. 19 include a solvent.

[0047] The conductive paste 11 may be an organic paint or a water-based paint, and the binder and solvent used in the conductive paste 11 are not particularly limited.

[0048] For example, when the conductive paste 11 is an organic paint, polyvinyl butyral, acrylic, ethyl cellulose, etc. may be used as the binder, and an organic solvent such as methyl ethyl ketone, methanol, ethanol, acetone, toluene, terpineol, butyl carbitol, acetate, etc. may be used as the solvent. When the conductive paste 11 is a water-based paint, water may be used as the solvent, and polyvinyl alcohol, water-soluble acrylic resin, water-soluble polyvinyl butyral resin, etc. may be used as the binder.

[0049] In this embodiment, the cohesion index of the composite particles 12 in the conductive paste 11 is less than 1.2, preferably 0.3 or less, and more preferably 0.2 or less. Examples of methods for controlling the cohesion index include controlling the type and concentration of the binder contained in the conductive paste 11, and controlling the strength of a shear treatment applied to the "mixture of the solvent and composite particles 12 that constitute the conductive paste 11."

[0050] The aggregation index is defined by the following formula (2): Aggregation index = Ra / (average DL) (2)

[0051] Here, DL is the particle diameter of the large particles 14. Furthermore, Ra is the coating smoothness, in other words, the arithmetic mean roughness of the coating interface 110a of the internal electrode pattern layer described later.

[0052] The coating film smoothness can be measured, for example, by the following method. Conductive paste 11 is applied by screen printing onto a film such as PET to obtain a film on which an internal electrode pattern is formed. The coating thickness of conductive paste 11 is adjusted so that the thickness of an internal electrode pattern layer (dried paste film) 110, which will be described later, is 1 μm to 5 μm.

[0053] Next, the internal electrode pattern on the film is dried for 90 minutes at a temperature of 80° C. The coating film smoothness (Ra) of the coating interface 110a of the internal electrode pattern layer (paste dried film) having a thickness of 1 μm to 5 μm after drying is determined using a contact type step measuring device in accordance with the "arithmetic mean roughness" of JIS B 0601-1994.

[0054] Here, the "coating interface 110a of the internal electrode pattern layer" refers to the surface of the two surfaces of the internal electrode pattern layer 110 that faces the surface in contact with the PET film.

[0055] The reference length of the arithmetic mean roughness may be about 0.5 mm to 1 mm.

[0056] The viscosity of the conductive paste 11 is preferably 0.5 Pa·s to 30 Pa·s, and more preferably 0.5 Pa·s to 10 Pa·s. The viscosity of the conductive paste 11 is measured at a liquid temperature of 25°C using a B-type rotational viscometer with an S14 rotor at 100 rpm.

[0057] In the conductive paste 11, the concentration of the large particles 14 is preferably 20% by mass to 60% by mass, more preferably 25% by mass to 55% by mass, and even more preferably 30% by mass to 50% by mass.

[0058] As shown in FIG. 3, each composite particle 12 according to this embodiment has one large particle 14 and a plurality of small particles 16a attached to the surface of the large particle 14.

[0059] The large particles 14 are conductive metal particles and may contain, as a main component, nickel, copper, silver, palladium, or an alloy containing at least one selected from these metal elements. The large particles 14 are preferably nickel particles or nickel alloy particles containing tin (hereinafter referred to as NiSn-based alloy particles).

[0060] When the large particles 14 are nickel particles, the purity of the nickel is preferably, for example, 98% by mass or more, and in addition to nickel, trace elements such as iron, cobalt, chromium, manganese, copper, palladium, magnesium, silicon, calcium, sodium, potassium, chlorine, oxygen, carbon, and nitrogen may be contained. When the large particles 14 are NiSn-based alloy particles, the above trace elements may also be contained. The ratio of nickel to tin in the NiSn-based alloy large particles 14 is not particularly limited, and the tin content may be, for example, 1% by mass or more and 50% by mass or less.

[0061] In the composite particle 12, each large particle 14 may have the same material, or the large particle 14 may contain two or more types of particles made of different materials (i.e., two or more types of large particles 14 made of different materials may be mixed together). In this embodiment, "different materials" refers to cases where the elements constituting the particles are different, or cases where the elements constituting the particles are the same but have different composition ratios.

[0062] The average particle diameter (DL) of the large particles 14 may be 200 nm or more, and from the viewpoint of reducing the thickness of the electrode layer formed using the composite particles 12, it is preferably 20 nm or more and 200 nm or less, more preferably 20 nm or more and 150 nm or less, and even more preferably 30 nm or more and 100 nm or less. Furthermore, the coefficient of variation (standard deviation / average particle diameter) in the particle size distribution of the large particles 14 is not particularly limited, but may be, for example, 30% or less. When the large particles 14 include two or more particle groups made of different materials, each particle group may have a different particle size distribution, but it is preferable that the average particle diameter of each particle group be within the above range.

[0063] In this embodiment, the "average particle size" means the arithmetic mean value of the equivalent circle diameter, and the "particle size distribution" means the distribution of the equivalent circle diameter.

[0064] In the composite particle 12 of this embodiment, the crystallite diameter (D C ) is 20 nm or more and 80 nm or less, preferably more than 20 nm and 80 nm or less, more preferably more than 20 nm and 50 nm or less, and even more preferably 30 nm or more and 50 nm or less. Here, the crystallite size refers to the size of the crystals present inside each large particle 14.

[0065] Crystallite diameter (D C The average value of the crystallite diameter (D ) of the large particles 14 can be measured by X-ray diffraction (XRD). Specifically, an X-ray diffraction chart of the composite particles 12 is obtained by 2θ / θ measurement, and the diffraction peaks attributable to the large particles 14 are identified in the X-ray diffraction chart. Then, the crystallite diameter (D ) of the large particles 14 is calculated from the identified diffraction peaks based on the Scherrer equation (the following formula (3)). C ) can be calculated as the average value.

number

[0066] The small particles 16a are particles having a smaller particle size than the large particles 14. The main component of the small particles 16a is preferably at least one selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide, zinc oxide, praseodymium oxide, cobalt oxide, chromium oxide, and zirconium oxide, more preferably barium titanate or silicon oxide, and even more preferably barium titanate. The small particles 16a may also contain one or more main components selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os. The sintering suppression effect is improved when the small particles 16a contain one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as a main component. Note that "when the small particles 16a contain one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as a main component" also includes cases where the small particles 16a contain one or more elements selected from the above element group as a main component. For example, the term "small particles 16a containing one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as the main component" applies to small particles 16a containing Ir as the main component, Rh as the main component, Ir and Rh as the main component, Ir, Ag, and V as the main component, or Cu, Co, and Zr as the main component. The main component of small particles 16 is a component that accounts for 20 or more mole parts when the total number of elements constituting small particles 16 is 100 mole parts. In composite particle 12, each small particle 16a may be made of the same material, or the small particles 16a may contain two or more types of particles made of different materials (i.e., two or more types of small particles 16a made of different materials may be mixed).

[0067] It is preferable that the small particles 16a have a thermal shrinkage initiation temperature of 500°C or higher when mixed with the large particles 14 and fired, and that the thermal shrinkage initiation temperature when mixed with the large particles 14 and fired is equal to the thermal shrinkage initiation temperature of the ceramic particles that make up the ceramic layer 20.

[0068] The average particle size (DS) of the small particles 16a is preferably, for example, 3 nm to 30 nm, more preferably 3 nm to 20 nm. When the small particles 16a include two or more particle groups made of different materials, each particle group may have a different particle size distribution, but the average particle size of each particle group is preferably within the above range. Furthermore, the ratio of the average particle size of the small particles 16a to the average particle size of the large particles 14 (average DS / average DL) is preferably 0.01 to 0.30, more preferably 0.01 to 0.20, and even more preferably 0.03 to 0.17. By setting the average DS / average DL within the above range, the steric hindrance described below can be more effectively exerted.

[0069] In this embodiment, each large particle 14 is a core particle in the composite particle 12. On the other hand, each small particle 16a has a smaller particle size than the large particles 14 and acts to create steric hindrance in the composite particle 12. Steric hindrance means the function of preventing the surfaces of adjacent large particles 14 from coming into direct contact with each other. In the composite particle 12, the small particles 16a attached to the surface of each large particle 14 are interposed between adjacent large particles 14, thereby creating steric hindrance. Such steric hindrance can make the thermal shrinkage onset temperature of the composite particle 12 higher than the thermal shrinkage onset temperature of a powder consisting only of large particles 14.

[0070] In addition, in the particle structure in which the above-mentioned steric hindrance occurs, the crystallite diameter (D CBy controlling the average value of DL) in the range of 20 nm or more and 80 nm or less, the thermal shrinkage starting temperature can be shifted to a higher temperature side than that of conventional composite particles. In particular, in the composite particle 12 of this embodiment, the thermal shrinkage starting temperature can be sufficiently high not only when the average value of the particle diameter (DL) of the large particles 14 is 200 nm or more, but also when the average value of the particle diameter (DL) of the large particles 14 is reduced to less than 200 nm.

[0071] The reason why the heat shrinkage starting temperature increases by controlling the crystallite size is considered to be, for example, as follows.

[0072] In conventional composite particles, even if steric hindrance is exerted, it is thought that the shape of the core metal particle is easily distorted at high temperatures of 400°C or higher. When the shape of the metal particle is distorted, it is thought that adjacent metal particles will bond together in the gaps between microparticles made of inorganic compounds, etc. In particular, when the average particle size of the metal particles is small, less than 200 nm, the particle shape is easily distorted at high temperatures, and bonding between the metal particles between the microparticles becomes significant, which is thought to prevent sufficient improvement in thermal shrinkage properties.

[0073] In contrast, in the composite particle 12 of this embodiment, the large particle 14 has a diameter of 20 nm or less. C By satisfying the average value of DL≦80 nm, the ratio of the average particle size of the large particles 14 to the average crystallite size of the large particles 14 (average value of DL / D C The average value of the average particle diameter (μm) is lower than that of conventional composite particles. In other words, the volume ratio of each crystallite in each large particle 14 is higher than that of conventional composite particles. In this way, by increasing the volume ratio of each crystallite inside the large particle 14, it is thought that the shape of the large particle 14 is less likely to collapse even at high temperatures. As a result, it is thought that it is possible to prevent the large particles 14 from joining together in the gaps between the small particles 16a, and to increase the thermal shrinkage starting temperature.

[0074] When the average diameter (DL) of large particles 14 is in the range of 20 nm to 100 nm, the average value of DL / D CThe average value of is 5.0 or less, and preferably 3.0 or less. When the average particle diameter (DL) of the large particles 14 is in the range of more than 100 nm and 200 nm or less, the average value of DL / D C The average value of DL / D is 10.0 or less, preferably 8.0 or less, and more preferably 4.0 or less. C The lower limit of the average value of DL is 1.0. C By controlling the average value within the above range, the heat shrinkage properties can be further improved.

[0075] The sulfur content of the composite particles 12 is preferably 3000 ppm by mass or less, and more preferably 10 ppm by mass or less. If the sulfur content is less than 10 ppm by mass, the composite particles 12 can be considered to be substantially free of sulfur. The sulfur contained in the composite particles 12 is considered to be mainly derived from the large particles 14. The sulfur component may be mixed as an impurity during the production of the large particles 14, or may be intentionally added as an additive. By controlling the sulfur content of the composite particles 12 to 3000 ppm by mass or less (preferably 10 ppm or less), it is possible to suppress a decrease in the melting point of the large particles 14 due to sulfurization. The sulfur content may be measured using an ICP, a carbon / sulfur analyzer, or the like.

[0076] In the composite particle 12, the average coverage of the small particles 16a to the large particles 14 is 3% or more and 60% or less, preferably 5% or more and 50% or less, and more preferably 15% or more and 50% or less. By setting the average coverage of the small particles 16a to the large particles 14 to 3% or more and 60% or less, the steric hindrance by the small particles 16a can be more effectively exerted.

[0077] Furthermore, the standard deviation of the coverage of the small particles 16a with respect to the large particles 14 is preferably 0% or more and 20% or less, and more preferably 0% or more and 5% or less.

[0078] Furthermore, the CV of the coverage of the small particles 16a with respect to the large particles 14 is preferably 0% or more and 60% or less, and more preferably 10% or more and 60% or less.

[0079] By reducing the variation in the coverage, the steric hindrance can be exerted more effectively. The above-mentioned standard deviation of the coverage (particularly, 5% or less) can be achieved by producing the composite particles 12 by, for example, an electrostatic adsorption method.

[0080] The method for measuring the "particle size of the large particles 14 and the small particles 16a" and the "coverage ratio of the small particles 16a to the large particles 14" is not necessarily limited, but it is preferable to employ, for example, an image analysis method such as that shown below.

[0081] A liquid containing the composite particles 12 is dropped onto a sample stage and allowed to air dry. Next, the composite particles 12 on the sample stage are observed using a scanning electron microscope (SEM) (a scanning transmission electron microscope (STEM) may also be used) to obtain an SEM image of the composite particles 12. The observation magnification when obtaining the SEM image is not particularly limited and may be determined appropriately depending on the average particle diameter (DL) of the large particles 14. For example, the observation magnification may be set so that the area per field of view is approximately (average DL × 8) × (average DL × 6). Figure 4 shows a schematic diagram of an SEM image.

[0082] Next, "large particles 14 with a visible outline" are selected from the large particles 14 included in the SEM image. In FIG. 5, "large particles 14 with a visible outline" are selected from the large particles 14 included in FIG. 4, and the outlines of the selected large particles 14 are shown in bold. In FIG. 5, the outlines of "small particles 16a with a visible outline" attached to the "large particles 14 with a visible outline" are also shown in bold. Note that "large particles 14 with a visible outline" refers to large particles 14 whose entire outline is included in the SEM image and which are present in the foreground in the SEM image. Therefore, if even a portion of the outline is missing, that large particle 14 does not qualify as a "large particle 14 with a visible outline." Furthermore, if even a portion of a large particle 14 is present behind (behind) another large particle 14, that large particle 14 does not qualify as a "large particle 14 with a visible outline."

[0083] The circle-equivalent diameters of the "large particles 14 with visible outlines" identified by the above method are measured, and the particle size distribution and average particle size (DL) of the large particles 14 are calculated. Furthermore, the circle-equivalent diameters of the "small particles 16a with visible outlines" attached to the "large particles 14 with visible outlines" are measured, and the particle size distribution and average particle size (DS) of the small particles 16a are calculated. The circle-equivalent diameters can be measured using image analysis software, and the average particle sizes (DL and DS) are preferably calculated by measuring the circle-equivalent diameters of at least 1,000 particles.

[0084] When measuring the coverage, first, a particle to be measured is selected from among the "large particles 14 whose outlines can be confirmed." The particle size DL of the particle to be measured is then measured, and the center of gravity G of the particle to be measured is identified. Next, as shown in FIG. 6, a circle with a radius 0.25 times DL is drawn from the center of gravity G, and this circle is designated as a virtual circle 18. Next, the area A0 of the virtual circle 18 and the total area A1 of the small particles 16a contained in the virtual circle 18 are measured, and the coverage of the small particles 16a on the particle to be measured is calculated as the ratio of A1 to A0 (A1 / A0). Using the method described above, the coverage of at least 100 large particles 14 is determined, and the average value is designated as the average coverage.

[0085] The standard deviation of the coverage may be calculated based on the following formula (4).

number

[0086] The CV of the coverage may be calculated based on the following formula (5). CV of coverage = (standard deviation of coverage) / (average coverage) Equation (5)

[0087] In the image analysis described above, the composite particles 12 may contain particles with a coverage of 0%, but the number ratio (number density) of particles with a coverage of 0% in the composite particles 12 is preferably 10% or less.

[0088] Furthermore, in the image analysis described above, it is preferable that the number of agglomerates of small particles 16a in an area of ​​(average DL value × 80) × (average DL value × 60) is 3 or less, more preferably 1 or less, and even more preferably 0.

[0089] An example of a method for manufacturing the multilayer ceramic capacitor 2 according to this embodiment will now be described.

[0090] First, the large particles 14 and the small particles 16a are prepared.

[0091] The method for producing the large particles 14 is not necessarily limited. C ) can be controlled based on various conditions, such as the type of precursor, the temperature, and the cooling rate, during synthesis of the large particles 14.

[0092] In terms of producing metal particles with small particle sizes, the liquid phase method is more suitable than the gas phase method, and the liquid phase method is generally used to produce metal particles with a particle size of 200 nm or less. In addition, since the current liquid phase method tends to result in small crystallite diameters, the crystallite diameter may be increased by heat treating the large particles 14 at a low temperature that does not destroy the shape of the large particles 14.

[0093] From the viewpoint of producing metal particles with a small particle size to crystallite size ratio, gas phase methods such as PVD and CVD are more suitable than liquid phase methods, and it is preferable to use a gas phase method in producing composite particles 12. However, current gas phase methods tend to produce large particle sizes. For this reason, the base powder is produced under conditions that result in a wide particle size distribution with a predetermined crystallite size. The base powder may then be classified until the desired average particle size (for example, preferably 200 nm or less, more preferably 100 nm or less) is obtained, thereby obtaining large particles 14.

[0094] The sulfur content in the composite particles 12 may be controlled, for example, by carrying out a desulfurization treatment when the large particles 14 are produced.

[0095] There are no particular limitations on the method for producing the small particles 16a, and they may be produced by, for example, a liquid phase synthesis method or a solid phase synthesis method.

[0096] Next, the small particles 16a are attached to the surfaces of the large particles 14 to produce the composite particles 12. In this embodiment, it is preferable to consistently perform the wet process from compounding the large particles 14 and the small particles 16a to forming a paste. The "wet process" refers to a method in which the composite particles 12 are not dried at all from the production of the composite particles 12 to the completion of the conductive paste 11. For this reason, it is preferable to compound the large particles 14 and the small particles 16a by electrostatically adsorbing them in a liquid phase. The electrostatic adsorption method is a method in which the large particles 14 and the small particles 16a are charged with opposite charges and then mixed together to compound the large particles 14 and the small particles 16a by electrical attraction.

[0097] In the electrostatic adsorption method, the small particles 16a can be attached to the surfaces of the large particles 14 in a nearly monodisperse state, and aggregation of the small particles 16a can be suppressed. In addition, in the electrostatic adsorption method, the amount of the small particles 16a attached to the large particles 14 can be easily controlled, and the coverage rate of the small particles 16a with respect to the large particles 14 can be controlled to an optimum range for effectively exerting steric hindrance.

[0098] The nanometer-sized oxide particles used as the small particles 16a have hydroxyl groups on their outermost surfaces, making them generally highly hydrophilic and dispersible in water or highly polar solvents, such as alcohols and glycols. While this depends on the manufacturing and dispersion methods, oxide particles often have a negative surface charge. A dispersion containing the small particles 16a is obtained by dispersing the small particles 16a with such a negative surface charge in an organic solvent, such as an alcohol, glycol, or ketone. To stabilize the dispersion of the small particles 16a, a small amount of additive may be added to the dispersion.

[0099] On the other hand, the metal particles used as the large particles 14 have a very weak positive or negative charge, depending on the element and synthesis method. It is preferable to change the surface potential of the large particles 14 to a strong positive potential using a polymer electrolyte such as polydiallyldimethylammonium chloride (PDDA) or polyethyleneimine (PEI). Then, similar to the small particles 16a, the large particles 14 with a positive surface potential are dispersed in an organic solvent such as an alcohol, glycol, or ketone to obtain a dispersion containing the large particles 14. To stabilize the dispersion of the large particles 14, a small amount of additive may be added to the dispersion.

[0100] Next, a dispersion containing small particles 16a and a dispersion containing large particles 14 are mixed in a desired ratio, and the small particles 16a are electrostatically adsorbed onto the surfaces of the large particles 14 in the slurry to obtain a composite particle slurry.

[0101] In a conventional composite method, the water or organic solvent contained in the composite particle slurry is removed and the resulting mixture is dried to obtain composite particles, in order to selectively select the organic solvent contained in the composite particle slurry and the solvent contained in the conductive paste. However, as a result, the composite particles may aggregate together during the drying process, and such aggregated composite particles are difficult to disperse.

[0102] In contrast to this, in the present embodiment, the "organic solvent constituting the composite particle slurry" is not removed, but the "solvent constituting the conductive paste 11", binder and other additives are added to the "composite particle slurry", and the composite particle slurry is mixed with the "solvent constituting the conductive paste 11", binder and other additives to obtain the conductive paste 11.

[0103] The binder may be added before the dispersant is added, but adding the binder after the dispersant has the advantage that the dispersant and composite particles 12 can be well mixed in a low viscosity state, eliminating the need for strong shearing treatment in subsequent processes.

[0104] The method of mixing the binder is not particularly limited as long as it prevents the composite particles 12 from drying. For example, collision dispersion may be used, a rotation-revolution mixer may be used, or both may be used.

[0105] Then, the conductive paste 11 is subjected to a shearing process to uniformly disperse the composite particles 12.

[0106] According to this embodiment, since the drying aggregation of the composite particles 12 can be suppressed, the conductive paste 11 in which the composite particles 12 are well dispersed can be obtained without strong shearing such as in thick kneading. Furthermore, since strong shearing is not applied, the generation of free particles 16b derived from the small particles 16a can be suppressed.

[0107] Next, the desired conductive paste 11 is obtained by adding free particles 16b and / or additional binders 19, etc., as needed.

[0108] Next, a ceramic layer paste to be used for forming the ceramic layer 20 is prepared.

[0109] The ceramic layer paste may be produced by kneading the main component powder of the dielectric composition, a binder, and a solvent. In addition to the above, additives such as subcomponent powder, a dispersant, and an antioxidant may be added to the ceramic layer paste. The ceramic layer paste may be an organic paint or a water-based paint, and the binder and solvent used in the conductive paste 11 are not particularly limited. The ceramic layer paste may also use the same binder and solvent as the conductive paste 11.

[0110] Next, the ceramic layer paste is formed into a sheet by a method such as a doctor blade method to obtain a ceramic green sheet. Then, the conductive paste 11 is applied in a predetermined pattern onto this ceramic green sheet by various printing methods such as screen printing or a transfer method to obtain a green sheet on which an internal electrode pattern layer 110 is formed. As a method for applying the conductive paste 11, it is preferable to adopt screen printing or gravure printing from the viewpoint of easily maintaining the structure of the composite particles 12.

[0111] A mother laminate is obtained by laminating a plurality of green sheets on which the internal electrode pattern layers 110 are formed and then pressing them in the lamination direction. At this time, one or more green sheets on which the internal electrode pattern layers 110 are not formed are laminated on the top and bottom surfaces of the mother laminate in the lamination direction.

[0112] The mother laminate obtained by the above steps is cut into a predetermined size by dicing or cutting to obtain a plurality of green chips. If necessary, the green chips may be solidified and dried to remove plasticizers, and after solidification and drying, they may be barrel polished using a horizontal centrifugal barrel machine or the like.

[0113] Next, the green chip obtained above is subjected to a binder removal process and a firing process to obtain the element body 4.

[0114] The conditions for the binder removal treatment are not particularly limited and may be appropriately determined depending on the types of binders added to the ceramic layer paste and the conductive paste 11. For example, the temperature increase rate may be preferably 5°C / hour to 300°C / hour, the holding temperature may be preferably 180°C to 800°C, and the temperature holding time may be preferably 0.5 hours to 24 hours. The atmosphere for the binder removal treatment may be an atmospheric atmosphere (i.e., air) or a reducing atmosphere.

[0115] The firing conditions are not particularly limited as long as they are set to conditions under which the internal electrode layers 10 and the ceramic layers 20 are sintered. For example, in the firing process, the temperature rise rate may be 200°C / hour to 50,000°C / hour, and preferably 1,000°C / hour to 10,000°C / hour. The holding temperature in the firing process is preferably 1,200°C to 1,350°C, and more preferably 1,220°C to 1,300°C. The temperature holding time is preferably 0.5 hours to 8 hours, and more preferably 2 hours to 3 hours. The firing process is preferably performed in a reducing atmosphere, and the atmospheric gas is preferably, for example, a humidified mixed gas of N2 and H2.

[0116] The oxygen partial pressure in the firing atmosphere may be appropriately determined depending on the type of conductive component in the conductive paste 11. When the conductive component is a base metal such as nickel or a nickel alloy, the oxygen partial pressure in the firing atmosphere is 1.0×10 -14 MPa~1.0×10 -10 The temperature drop rate in the firing treatment is preferably 50°C / hour to 500°C / hour.

[0117] After firing in a reducing atmosphere, the element body 4 may be subjected to an annealing treatment. The conditions for the annealing treatment are not particularly limited. For example, the oxygen partial pressure in the atmosphere is 1.0×10 -9 MPa~1.0×10 -5The annealing temperature may be 950°C to 1150°C, and the temperature holding time may be 0 to 20 hours. As the atmospheric gas for annealing, for example, humidified N2 gas or the like may be used.

[0118] In the above-mentioned binder removal treatment, firing treatment, and annealing treatment, a wetter or the like may be used to humidify the N2 gas or mixed gas, and in this case, the water temperature is preferably about 5° C. to 75° C. Furthermore, the binder removal treatment, firing treatment, and annealing treatment may be performed consecutively or independently.

[0119] Next, a pair of external electrodes 6 are formed on the outer surfaces of the element body 4 obtained above. The method for forming the external electrodes 6 is not particularly limited. For example, when forming baked electrodes as the external electrodes 6, a conductive paste 11 containing glass frit may be applied to the end surfaces of the element body 4 by a dipping method, and then the element body 4 may be heated at a predetermined temperature. When forming resin electrodes as the external electrodes 6, a conductive paste 11 containing a thermosetting resin may be applied to the end surfaces of the element body 4, and then the element body 4 may be heated at a temperature at which the thermosetting resin hardens. Furthermore, after forming baked electrodes or resin electrodes by the above method, sputtering, vapor deposition, electrolytic plating, electroless plating, or the like may be performed to form external electrodes 6 having a multilayer structure.

[0120] Through the above steps, a multilayer ceramic capacitor 2 having a cross section as shown in FIG. 1 can be manufactured.

[0121] Generally, the organic solvent contained in the slurry for compounding the large particles 14 and the small particles 16a and the solvent contained in the conductive paste 11 are different in type and concentration.

[0122] For this reason, in the prior art, after the large particles 14 and the small particles 16a are composited, the composite particle slurry is dried to obtain the composite particles 12, and then the composite particles 12 are mixed with a binder or the like 19 containing a solvent to obtain the conductive paste 11.

[0123] Furthermore, when composite particles are synthesized by mechanochemical method, it is also necessary to fix the small particles 16a to the large particles 14 by drying.

[0124] However, there is a problem that the composite particles 12 aggregate when the composite particle slurry is dried. When the aggregated composite particles 12 are used to prepare the conductive paste 11, the composite particles 12 also aggregate within the conductive paste 11. Therefore, it is conceivable to perform a shearing treatment to break up the aggregation of the composite particles 12, but since a strong shearing treatment would separate the small particles 16a from the composite particles 12, a weak shearing treatment is generally used.

[0125] In the conductive paste 11 that has been subjected to a weak shearing treatment, the aggregates of the composite particles 12 are not sufficiently loosened, and some of the composite particles 12 may remain aggregated, as shown in Fig. 7a. Furthermore, in such a conductive paste 11, the composite particles 12 cannot be sufficiently mixed with the binder 19 or the like due to the weak shearing treatment.

[0126] When an internal electrode pattern layer (paste dried film) 110 is formed using such a conductive paste 11, as shown in Fig. 7b, the aggregated composite particles 12 form irregularities at the coating interface 110a of the internal electrode pattern layer, which may cause a decrease in the coating film smoothness of the internal electrode pattern layer 110. Furthermore, in the conductive paste 11 shown in Fig. 7a, the dispersibility of the composite particles 12 in the internal electrode pattern layer 110 is low, which may cause unevenness in the distribution of the composite particles 12, resulting in the occurrence of voids or areas where the composite particles 12 are not present and where the binder or the like 19 is mainly unevenly distributed.

[0127] A decrease in the smoothness of the coating film and uneven distribution of the composite particles 12 may cause defects such as short circuits and electrode breaks in the internal electrode layers 10 of the multilayer ceramic capacitor 2.

[0128] On the other hand, if strong shearing is performed to break up the agglomerated composite particles 12 in the conductive paste 11, as shown in Figure 8a, the agglomerated composite particles 12 can be broken up, but small particles 16a may separate from large particles 14, destroying the composite particles 12, and forming a large number of free particles 16b derived from the small particles 16a.

[0129] When an internal electrode pattern layer (paste dried film) 110 is formed using such a conductive paste 11, as shown in Fig. 8b, the large particles 14 come into contact with each other and agglomerate, or the detached small particles 16a, i.e., the free particles 16b agglomerate with each other, resulting in a decrease in the effect of delaying the sintering of the internal electrode layer 20 (sintering delay effect) by the small particles 16a forming the composite particles 12, and may result in a decrease in the thermal shrinkage start temperature of the internal electrode layer 10. If the thermal shrinkage start temperature of the internal electrode layer 10 decreases, cracks or discontinuities may occur in the internal electrode layer 10 after sintering due to the difference in sintering start temperature between the ceramic layer 20 and the internal electrode layer 10, and the continuity rate of the internal electrode layer 10 relative to the ceramic layer 20 may decrease.

[0130] Furthermore, in the conductive paste 11 shown in FIG. 8a, small particles 16a may separate from large particles 14, resulting in the presence of free particles 16b derived from the small particles 16a. Furthermore, since the composite particles 12 have a larger particle size than the free particles 16b and therefore have a higher settling rate, when the conductive paste 11 is left standing, the composite particles 12 tend to be located at the bottom of the conductive paste 11, and the free particles 16b tend to be located at the top of the conductive paste 11. In particular, when the conductive paste 11 is left standing, a phenomenon called "composite material separation" (particularly when the free particles are white, this is called "white floating") may be observed, in which the free particles 16b float on the surface of the conductive paste 11. Such a conductive paste 11 must be stirred before use, complicating the manufacturing process.

[0131] In contrast, in the multilayer ceramic capacitor 2 according to this embodiment, aggregation of the composite particles 12 is suppressed in the conductive paste 11 for forming the internal electrode layers 10, and therefore it is possible to suppress variations in the thickness of the internal electrode layers 10. As a result, it is possible to improve the continuity ratio of the internal electrode layers 10.

[0132] Furthermore, as described above, in the multilayer ceramic capacitor 2 according to this embodiment, aggregation of the composite particles 12 is suppressed in the conductive paste 11 for forming the internal electrode layers 10, so that the conductive paste 11 in which the composite particles 12 are uniformly dispersed can be obtained even if the content of the solvent in the conductive paste 11 is reduced. In other words, in the conductive paste 11 according to this embodiment, the composite particles 12 can be dispersed uniformly at a high concentration.

[0133] In addition, in the multilayer ceramic capacitor 2 according to this embodiment, the amount of free particles 16b in the conductive paste 11 for forming the internal electrode layers 10 is controlled to be within a predetermined range. Therefore, when the conductive paste 11 is left to stand, it is possible to suppress material separation caused by the free particles 16b.

[0134] Furthermore, in the multilayer ceramic capacitor 2 according to this embodiment, the composite particles 12 contained in the conductive paste 11 for forming the internal electrode layers 10 maintain the shape of the large particles 14 coated with the small particles 16a at a predetermined coverage rate, so that the small particles 16a can exert an effect of delaying the sintering of the internal electrode layers 10 (sintering delay effect), and can increase the thermal shrinkage start temperature of the internal electrode layers 10. As a result, the difference in sintering start temperature between the ceramic layers 20 and the internal electrode layers 10 becomes small, so that it is possible to suppress the occurrence of cracks or discontinuities in the internal electrode layers 10 after sintering, and it is possible to improve the continuity rate of the internal electrode layers 10 relative to the ceramic layers 20.

[0135] Furthermore, when the internal electrode layer 10 is formed using the composite particles 12, it is possible to suppress the diffusion of the small particles 16a into the ceramic layer 20. As a result, it is possible to suppress deviation of the composition of the ceramic layer 20 from the target composition.

[0136] Second embodiment The second embodiment is the same as the first embodiment except that the composite particle 12 has the following characteristics.

[0137] The large particles 14 are conductive metal particles containing nickel or a nickel-containing alloy as the main component. Here, the main component of the large particles 14 is a component that preferably accounts for 90 to 100 parts by mass, and more preferably 95 to 100 parts by mass, when the total of the elements constituting the large particles 14, excluding oxygen, is taken as 100 parts by mass.

[0138] The large particles 14 are preferably nickel particles or nickel alloy particles containing tin (hereinafter referred to as NiSn-based alloy particles).

[0139] The surfaces of the large particles 14 according to this embodiment are oxidized. In other words, the surfaces of the large particles 14 according to this embodiment are covered with an extremely thin oxide layer. Specifically, the average oxidation degree of the outermost surfaces 14a of the large particles 14 is 30% or more and 90% or less, preferably 50% or more and 90% or less, and more preferably 70% or more and 90% or less.

[0140] The degree of oxidation is defined by the following formula (6): Oxidation degree (%)=100×M / (L+M+M) ··· Formula (6)

[0141] Here, L, M, and N are the X-ray photoelectron images of the outermost surface 14a of the large particle 14 shown in FIG. It is obtained by measuring by spectroscopy (XPS), where L is the atomic ratio calculated by multiplying the peak area of ​​the metallic nickel peak by the "conversion factor for the metallic nickel peak," M is the atomic ratio calculated by multiplying the peak area of ​​the nickel oxide peak by the "conversion factor for the nickel oxide peak," and N is the atomic ratio calculated by multiplying the peak areas of the satellite peaks derived from metallic nickel and nickel oxide by the "conversion factor for the satellite peak."

[0142] The L slope of the large particles 14 is preferably greater than 0%, more preferably 0.1% or more and 40% or less, and even more preferably 2% or more and 15% or less.

[0143] The L slope is defined by the following equations (7) and (8). L ratio=L / (L+M+N) Equation (7) L slope (%) = 100 × (IL ratio - SL ratio) / 2 ··· Formula (8)

[0144] Here, the SL ratio is the L ratio at the outermost surface 14a of the large particle 14 shown in Figure 3, and the IL ratio is the L ratio at a depth 14b of 2 nm from the outermost surface 14a of the large particle 14 toward the center G of the large particle 14 shown in Figure 3.

[0145] The degree of oxidation and L slope of the outermost surface 14a of the large particle 14 are measured by XPS. Specifically, the composite particle 12 is formed into a pellet using a press, and the outermost surface 14a of the large particle 14 and a depth 14b of 2 nm from the outermost surface 14a of the large particle 14 toward the center G of the large particle 14 are measured by sputtering, as shown in Figure 3.

[0146] The obtained XPS data is then analyzed. Specifically, an XPS spectrum of the Ni2p orbital is obtained, and the Ni2p peak is separated into a metallic nickel peak, a nickel oxide peak, and a satellite peak. A preferred separation method is peak separation analysis using the least squares method, or a comprehensive judgment based on literature and databases.

[0147] Among the metallic nickel peak, nickel oxide peak, and satellite peak, the peak located on the lowest energy side can be determined to be the metallic nickel peak. The peak range of the metallic nickel peak is affected by correction of the charging state and the influence of the substrate, but is often in the range of 851.5 to 852.9 eV.

[0148] Satellite peaks and nickel oxide peaks can be close in energy, making it difficult to distinguish them strictly. However, peaks higher in energy than the lowest-energy peak can be considered to be derived from nickel oxide peaks or satellite peaks. Nickel oxide peaks include NiO, Ni2O3, and Ni(OH)2, but it is preferable to make a comprehensive judgment based on literature and databases when separating these peaks and their satellite peaks. Nickel oxide peaks often fall within the range of 853.5-854.4 eV and 855.8-857.3 eV.

[0149] In some cases, multiple nickel oxide peaks are detected, and in such cases, the peak area of ​​the nickel oxide peak is determined as the sum of the peak areas of the individual nickel oxide peaks.

[0150] Similarly, multiple satellite peaks may be detected, and in such cases, the peak area of ​​the satellite peak is determined as the sum of the peak areas of the individual satellite peaks.

[0151] The areas of the metallic nickel peak, nickel oxide peak, and satellite peak obtained by peak separation analysis are used as detection intensities (signal intensities).

[0152] The atomic ratio (L) derived from the metallic nickel peak is calculated by multiplying the peak area of ​​the metallic nickel peak by the conversion factor of the metallic nickel peak.

[0153] The atomic ratio (M) derived from the nickel oxide peak is calculated by multiplying the peak area of ​​the nickel oxide peak by the conversion factor of the nickel oxide peak.

[0154] The atomic ratio (N) derived from the satellite peak is calculated by multiplying the peak area of ​​the satellite peak by the conversion factor of the satellite peak.

[0155] The degree of oxidation can be calculated using the above formula (6).

[0156] Furthermore, the L slope can be calculated using the above formulas (7) and (8).

[0157] In this embodiment, it is preferable to use a charge adjusting agent such as the above-mentioned polymer electrolyte or a predetermined acid for the metal particles used as the large particles 14 to change the surface potential of the large particles 14 to a strong positive potential.

[0158] The predetermined acid may be a carboxylic acid, hydrochloric acid, nitric acid, or the like.

[0159] The degree of oxidation and L slope of the outermost surface 14a of the large particles 14 can be controlled by subjecting the large particles 14 to an acid treatment using the charge adjusting agent. That is, in this embodiment, the large particles 14 are subjected to charge adjustment and acid treatment.

[0160] The degree of oxidation of the outermost surface 14a of the large particle 14 and the L gradient can be controlled by changing the temperature during the acid treatment, the acid concentration, the treatment time, and the amount of acid added.

[0161] The large particles 14, which have a positive surface potential as a result of charge adjustment and have also been treated with acid, are then dispersed in an organic solvent such as an alcohol, glycol, or ketone, similar to the small particles 16a, to obtain a dispersion containing the large particles 14. To stabilize the dispersion of the large particles 14, a small amount of additive may be added to the dispersion.

[0162] Next, a dispersion containing the small particles 16a and a dispersion containing the large particles 14 are mixed in a desired ratio, and the small particles 16a are electrostatically adsorbed onto the surfaces of the large particles 14 to obtain a composite particle slurry.

[0163] The present inventors have discovered that the catalytic activity of the metallic nickel contained in the conductive paste 11 causes the binder to rapidly decompose during the binder removal process, which causes cracks to occur in the green chip during the binder removal process. In contrast, in this embodiment, the average oxidation degree of the outermost surfaces 14a of the large particles 14 is 30% or more, which inhibits the catalytic activity of the metallic nickel and causes the binder to decompose slowly during the binder removal process, thereby preventing cracks from occurring in the green chip.

[0164] Furthermore, in this embodiment, since the average oxidation degree of the outermost surface 14a of the large particles 14 is 90% or less, the composite particles 12a can be well dispersed in the conductive paste 11 for forming the internal electrode layer 10, and as a result, the occurrence of cracks in the green chip during the binder removal process can be suppressed.

[0165] Specifically, in the multilayer ceramic capacitor 2 using the composite particles 12a, the crack occurrence rate of the green chip during the binder removal process can be suppressed to 2% or less.

[0166] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention.

[0167] The electronic components to which the conductive paste 11 is applied are not limited to multilayer ceramic capacitors, and the conductive paste 11 can be applied to other electronic components as well. The other electronic components include all electronic components in which ceramic layers are laminated via internal electrode layers, such as bandpass filters, inductors, multilayer three-terminal filters, piezoelectric elements, PTC thermistors, NTC thermistors, and varistors.

[0168] The internal electrode layer 10 may also be formed using a conductive paste 11 containing composite particles 12 and conductive particles other than the composite particles 12. The conductive particles other than the composite particles 12 are not particularly limited, and may be, for example, nickel particles, nickel-based alloy particles, copper particles, or copper-based alloy particles that are not composited with the small particles 16a. In this case, the conductive paste 11 used preferably contains 20% by mass or more and 60% by mass or less, and more preferably 25% by mass or more and 45% by mass or less, of the composite particles 12, with the total content of the composite particles 12 and the conductive particles being 100% by mass.

[0169] Furthermore, the composite particles 12 may be used to form the external electrodes 6. For example, the external electrodes 6 may be formed using a conductive paste 11 containing the composite particles 12 and a thermosetting resin. [Example]

[0170] The present disclosure will be described below in more detail based on examples, but the present disclosure is not limited to these examples.

[0171] (Experiment 1A) In Experiment 1A, a conductive paste was obtained by a wet process, and the "average coverage rate," "freedom," and "aggregation index" were changed to produce the conductive pastes shown in each sample number other than sample number 12 and sample number 16.

[0172] The mother powder was produced by the CVD method (vapor phase method) using nickel as the raw material. Note that the mother powder was subjected to desulfurization treatment during the production by the CVD method.

[0173] Next, the mother powder was classified to obtain multiple large particles (hereinafter referred to as Ni particles) with a particle diameter (DL) equal to the average value of the specified large particles. Small particles made of barium titanate (hereinafter referred to as BT particles) were attached to the surfaces of the Ni particles using electrostatic adsorption. Specifically, the Ni particles were mixed with an aqueous solution containing PDDA, and the surfaces of the Ni particles were positively charged. Next, the BT particles, which originally had a negative surface potential, were introduced into an aqueous solution containing positively charged Ni particles, and the Ni particles and BT particles were composited by electrostatic adsorption.

[0174] The composite particle slurry was obtained by mixing a binder etc. The compounding ratio of the composite particles in the obtained conductive paste was set to 45 mass %, the compounding ratio of the binder to 10 mass %, and the compounding ratio of the solvent to 45 mass %.

[0175] In addition, the coverage was changed by changing the blending ratio of BT particles during electrostatic adsorption for each sample.

[0176] (Experiment 1B) Experiment 1B concerns sample number 12. In Experiment 1B, a conductive paste was obtained in the same manner as Experiment 1A, except that instead of a wet process, a conventional process was used in which the composite particle slurry was dried to obtain composite particles, and then a binder or the like was added, and a strong shearing treatment was performed to break up the dried agglomerations of the composite particles to obtain a conductive paste.

[0177] (Experiment 1C) Experiment 1C concerns sample number 16. In Experiment 1C, a conductive paste was obtained in the same manner as Experiment 1A, except that instead of using a wet process, a conventional process was used in which the composite particle slurry was dried to obtain composite particles, and then a binder or the like was added, and a weak shearing treatment was performed to break up the dry aggregation of the composite particles without causing small particles to detach from the composite particles.

[0178] (Experiment 2) In Experiment 2, multilayer ceramic capacitors were manufactured using the conductive pastes manufactured in Experiments 1A to 1C according to the following procedure.

[0179] A ceramic layer green sheet containing BaTiO3 as the main component was prepared, and a conductive paste was applied to the green sheet to form an internal electrode pattern. Then, multiple layers of the green sheets with the internal electrode patterns were stacked and pressed in the stacking direction to obtain a mother laminate. At this time, protective green sheets without internal electrode patterns were stacked on the top and bottom surfaces of the mother laminate. The mother laminate was then cut to a predetermined size by dicing to obtain multiple green chips.

[0180] Next, the green chip was subjected to binder removal, firing, and annealing to obtain an element body (fired body). Next, a pair of external electrodes was formed by applying and firing an external electrode paste to two end faces of the element body, resulting in a multilayer ceramic capacitor (hereinafter referred to as a capacitor sample) having the structure shown in Figure 1. The dimensions of the element body in the capacitor sample were 12 mm wide x 20 mm deep x 12 mm high. In addition, the average thickness of each ceramic layer in the capacitor sample was 0.80 μm, the average thickness of each internal electrode layer was 0.50 μm, and the number of ceramic layers sandwiched between the internal electrode layers was four.

[0181] The composite particles of each sample were evaluated as follows.

[0182] Average particle size of large particles (Ni particles), average particle size of small particles (BT particles) and average coverage rate The composite particle slurry was dried to obtain composite particles, and then the composite particles were added to ethanol at a ratio of 0.5% by mass and mixed using a vortex mixer for 1 minute. The ethanol solution containing the composite particles was left to stand for 1 to 2 hours to allow the composite particles to settle. The supernatant of the ethanol solution was then removed by decantation, and the remaining liquid was added to ethanol again and mixed. The obtained composite particle-containing liquid was dropped onto an SEM stage and air-dried. The composite particles remaining on the SEM stage were then observed using an SEM, and SEM images of the composite particles were obtained.

[0183] The SEM images were analyzed using image analysis software. The particle sizes of 100 or more Ni particles were measured and averaged. The particle sizes of 100 or more BT particles were measured and averaged. The coverage of BT particles with respect to Ni particles was measured and averaged. The results are shown in Table 1A.

[0184] The average diameter (DL) of Ni particles is shown in Table 1A.

[0185] The average diameter of the BT particles (DS) was 8 nm to 40 nm in all samples, which means that the average diameter of the BT particles (DS) was smaller than the average diameter of the Ni particles (DL) in all samples.

[0186] Average particle size of free particles The conductive paste was poured into ethanol and mixed for 1 minute using a vortex mixer. The solution containing the conductive paste was separated by centrifugation, and the supernatant liquid containing free particles was dropped onto the SEM stage and air-dried. The free particles remaining on the SEM stage were then observed using an SEM, and SEM images of the free particles were obtained.

[0187] The SEM images were analyzed using image analysis software, and the particle sizes of more than 100 free particles were measured and the average value was calculated. As a result, the average particle size of the free particles was 8 nm to 40 nm for all samples. In other words, it was confirmed that the average particle size of the free particles was smaller than the average particle size (DL) of the Ni particles for all samples.

[0188] Conductive paste viscosity The viscosity of the conductive paste for all samples was 0.5 Pa·s to 30 Pa·s.

[0189] Concentration of large particles (Ni particles) In all samples, the concentration of large particles in the conductive paste was 20% by mass to 60% by mass.

[0190] Freedom The degree of liberation of the obtained conductive paste was measured by the method described in embodiment 1. The results are shown in Table 1A.

[0191] agglomeration index For the obtained conductive paste, the coating film smoothness (Ra) of the coating interface of the internal electrode pattern layer was measured by the method described in the first embodiment, and the cohesion index was calculated. The results are shown in Table 1A.

[0192] Number of days (months) required for separating co-materials The number of days (months) required for the resulting conductive paste to be left to stand for separation of the co-materials is shown in Table 1B as "Number of days (months) required for co-material separation." Co-material separation was confirmed using the following method: the surface layer of the conductive paste was sampled, the concentration of small particle components was measured using ICP analysis, and if the concentration in the liquid was 50% or more higher than the original concentration of the small particle components, co-material separation was deemed to have occurred. In other words, the surface layer of the conductive paste was sampled, the concentration of small particle components was measured using ICP analysis, and if the concentration of the small particle components in the paste was 50% or more higher than the concentration of the small particle components in the conductive paste before the conductive paste was left to stand, co-material separation was deemed to have occurred.

[0193] Internal electrode layer thickness variation CV The cross sections of the 10 capacitor samples manufactured as described above were mirror-polished and observed using an SEM. The thickness of the internal electrode layer was measured using the SEM observation, and the "internal electrode layer thickness variation CV" was calculated using the "average thickness of the internal electrode layer" and the "standard deviation of the thickness of the internal electrode layer" using the following formula (9). The results are shown in Table 1B. Internal electrode layer thickness variation CV = (standard deviation of internal electrode layer thickness) / (average value of internal electrode layer thickness) Equation (9)

[0194] Measurement of heat shrinkage start temperature The thermal shrinkage starting temperature of each sample was measured by thermomechanical analysis (TMA) using a Rigaku Thermo Plus EVO2 TMA measuring instrument, and the thermal shrinkage starting temperature was determined by the tangent method.

[0195] In the tangent method, the intersection of the tangent at the inflection point and the baseline is identified, and the temperature (T0) at the intersection is identified as the thermal shrinkage starting temperature, as shown in Fig. 9. The inflection point may be identified, for example, by referring to a DTMA curve obtained by differentiating a TMA curve as shown in Fig. 9, and the maximum value of the DTMA curve may be taken as the inflection point.

[0196] When measuring the thermal shrinkage start temperature or sintering start temperature using TMA, the temperature at which a specified shrinkage rate is reached may be specified as the thermal shrinkage start temperature or sintering start temperature, such as the temperature T1 at a shrinkage rate of 10% shown in Figure 9. However, the shrinkage rate is affected by organic residues and voids in the evaluation sample, and the temperature at the set shrinkage rate (for example, T1 in Figure 9) tends to be higher than the temperature at the intersection specified by the tangent method (for example, T0 in Figure 9). In this experiment, we decided to use the tangent method to reduce the influence of organic residues and voids and more accurately measure the thermal shrinkage start temperature.

[0197] The thermal shrinkage starting temperature of the raw material powder used to form the ceramic layers of the multilayer ceramic capacitor varies depending on the composition of the dielectric composition, but is, for example, 1000°C to 1200°C, which is higher than the thermal shrinkage temperature of metal particles. Therefore, in the evaluation of composite particles in this experiment, those with a higher thermal shrinkage starting temperature were determined to be preferable as electrode materials.

[0198] [Table 1A]

[0199] [Table 1B]

[0200] From sample numbers 1 to 11, 14, and 22 to 25, it was confirmed that when the degree of release was between 0% and 50% (sample numbers 1 to 10, 14, and 22 to 25), the number of days (months) required for co-material separation was longer than when the degree of release was 55% or more (sample number 11).

[0201] Furthermore, it is considered that when the degree of liberation was 0% or more and 50% or less (sample numbers 1 to 10, 14, 22 to 25), the number of days (months) required for co-material separation was longer than when the degree of liberation was 91% (sample number 12), and the internal electrode layer thickness variation CV was reduced, and the thermal shrinkage starting temperature was also increased.

[0202] In sample numbers 1 to 10, 14, and 22 to 25, aggregation of the composite particles is suppressed without subjecting the conductive paste to strong shearing treatment as in sample number 12, so there is no need to subject it to strong shearing treatment, and as a result, small particles are prevented from detaching from the composite particles and becoming free particles.For this reason, it is thought that in sample numbers 1 to 10, 14, and 22 to 25, the number of days (months) required for separation of the composite material was long, the internal electrode layer thickness variation CV was reduced, and the thermal shrinkage starting temperature was also increased.

[0203] From sample numbers 1 to 10, 14, 15, and 22 to 25, it was confirmed that when the cohesion index is less than 1.2 (sample numbers 1 to 10, 14, and 22 to 25), the internal electrode layer thickness variation CV can be reduced compared to when the cohesion index is 1.2 (sample number 15).

[0204] From sample numbers 1 to 10, 14, 16, and 22 to 25, it was confirmed that when the cohesion index is less than 1.2 (sample numbers 1 to 10, 14, and 22 to 25), the internal electrode layer thickness variation CV can be reduced compared to when the cohesion index is 2.00 (sample number 16).

[0205] Compared to sample number 16, it is believed that sample numbers 1 to 10, 14, and 22 to 25 were able to suppress aggregation of composite particles in the first place, and therefore were able to reduce the internal electrode thickness variation CV. [Explanation of symbols]

[0206] 2... Multilayer ceramic capacitors 4... Element body 10 … Internal electrode layer 20...ceramic layer 6 … External electrode 11...Conductive paste 110 ... Internal electrode pattern layer (paste dried film) 110a ... coating interface of internal electrode pattern layer (paste dried film) 12 … Composite particles 14...Large particles 14a … outermost surface of large particles 14b: Imaginary circle showing a depth of 2 nm from the outermost surface of a large particle to the center of the large particle 16a … small particles 16b … free particles 18... Virtual circle 19… Binder et al.

Claims

1. A conductive paste in which composite particles are dispersed in a binder and a solvent, The composite particles have large particles and small particles attached to the surfaces of the large particles and having an average particle size smaller than that of the large particles, the degree of liberation of free particles dispersed in the conductive paste and having an average particle size smaller than that of the large particles is 0% or more and 50% or less; The liberation degree is defined by the following formula (1): Freedom (%) = 100 × MF / (MF + MS) (1) MF is the total mass of free particles; MS is the total mass of the small particles; the composite particles in the conductive paste have an aggregation index of less than 1.2; The aggregation index is defined by the following formula (2): Coagulation index = average value of Ra / DL (2) DL is the particle size of the large particle, The Ra is the smoothness of the coating film of the conductive paste.

2. the large particles are metal particles; 2. The conductive paste according to claim 1, wherein the main component of the metal particles is nickel, copper, silver, palladium, or at least one selected from these metal elements.

3. 2. The conductive paste according to claim 1, wherein the average coverage of the small particles attached to the surfaces of the large particles is 3% or more and 60% or less.

4. 2. The conductive paste according to claim 1, wherein the small particles and / or free particles are at least one selected from the group consisting of barium titanate, silicon oxide, titanium oxide, aluminum oxide, zinc oxide, praseodymium oxide, cobalt oxide, chromium oxide, bismuth oxide, boron oxide, calcium oxide, magnesium oxide, strontium oxide, bismuth ferrite, bismuth titanate, potassium sodium niobate, bismuth sodium titanate, potassium bismuth titanate, Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, and zirconium oxide.

5. 2. The conductive paste according to claim 1, wherein the viscosity of the conductive paste is 0.5 Pa·s to 30 Pa·s (100 rpm).

6. 2. The conductive paste according to claim 1, wherein the concentration of the large particles in the conductive paste is 20% by mass to 60% by mass.

7. An electronic component having an electrode layer formed using the conductive paste according to any one of claims 1 to 6.

Images