Composite particles, conductive paste and electronic components

Abstract

To provide a fine composite particle having a high sintering initiation temperature.SOLUTION: A composite particle 12 comprises: a large particle 14; and small particles 16 stuck to the surface of the large particle 14 and having an average particle diameter smaller than that of the large particle 14, in which, provided that the average particle diameter of the large particles 14 is defined as R and the average particle diameter of the small particles 16 is defined as r, R is 30 or more to 300 nm or less, and r is 3 or more to 30 nm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electronic component having an internal electrode layer, and to composite particles used in the electronic component. [Background technology]

[0002] As multilayer ceramic capacitors become thinner, the diameter of nickel particles used in the internal electrode layers is also becoming smaller. However, as the nickel particles become smaller, the sintering start temperature decreases. If such nickel particles are used in the internal electrode layers, they may cause cracks or electrode discontinuities.

[0003] For example, in Patent Document 1, a composite nickel fine powder is formed by a wet, dry or semi-dry supporting method in order to shift the temperature at which rapid thermal shrinkage of nickel fine powder for paste begins to increase.

[0004] Specifically, in the wet support method of Patent Document 1, an aqueous solution containing a water-soluble salt of a metal element or the like is added to a slurry in which metallic nickel particles or the like are dispersed, and then the pH is adjusted with an acid or alkali to fix a metal oxide or the like derived from the water-soluble salt to the surface of the nickel particles. However, with this method, the metal oxide or the like fixed to the surface of the nickel particles may diffuse into the dielectric layer, potentially affecting the composition of the dielectric layer. Furthermore, with this method, it is difficult to control the amount of metal oxide or the like fixed to the surface of the nickel particles and the thickness of the fixed layer. Furthermore, with this method, there is a possibility that the metal oxide or the like may aggregate.

[0005] Furthermore, in the dry and semi-dry deposition methods of Patent Document 1, metallic nickel particles with attached ultrafine particles collide with each other or with other objects to adhere the ultrafine particles to the surface of the nickel particles. However, because the dry and semi-dry deposition methods of Patent Document 1 are dry processes, they suffer from the problem of agglomeration of nickel particles and ultrafine particles. When agglomeration of nickel particles occurs, there are no ultrafine particles between the nickel particles, and sintering of those areas is accelerated. Furthermore, the presence of agglomerated nickel particles in the internal electrode layer hinders the thinning of the internal electrode layer. Furthermore, agglomeration of nickel particles causes abnormal growth of nickel particles into spherical shapes, leading to short circuits. Furthermore, agglomeration of ultrafine particles reduces the number of ultrafine particles that effectively function as co-materials. Furthermore, agglomeration of ultrafine particles itself can become the starting point for internal electrode discontinuities. Furthermore, once agglomeration of ultrafine particles occurs, it is difficult to re-separate them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-282102 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and aims to provide composite particles that are suitable for use as particles for forming electrodes, that are fine, and that have a high sintering initiation temperature. [Means for solving the problem]

[0008] In order to achieve the above object, the composite particle according to the present invention comprises a large particle and a small particle attached to the surface of the large particle and having an average particle size smaller than that of the large particle, The average particle size of the large particles is represented by R, and the average particle size of the small particles is represented by r; The R is 30 nm or more and 300 nm or less, The r is 3 nm or more and 30 nm or less.

[0009] The present inventors have found that by using the composite particles having the above-described configuration, the sintering start temperature is increased even though the composite particles are fine. Furthermore, since the sintering start temperature of the internal electrode layers formed using the conductive paste containing the composite particles is increased, the sintering start temperature of the internal electrode layers can be made closer to the sintering start temperature of the ceramic layers. As a result, cracks in the ceramic layers caused by differences in thermal shrinkage behavior between the internal electrode layers and the ceramic layers can be prevented, and electrode discontinuities in the internal electrode layers can be prevented, making it possible to easily achieve thin layers between the internal electrode layers and the ceramic layers.

[0010] Furthermore, by having R fall within the above range, it becomes easier to achieve thinning of the internal electrode layers. From the above viewpoint, it is preferable that R is smaller than at least 1 / 5 of the thickness of the internal electrode layers.

[0011] When r is within the above range, small particles can be easily dispersed.

[0012] The particle size ratio (r / R) of the large particles to the small particles is preferably 0.01 or more and 0.17 or less.

[0013] When r / R is within the above range, small particles are less likely to fall off from large particles.

[0014] The material of the large particles is preferably conductive.

[0015] The large particles may be made of at least one material selected from nickel, nickel alloys, copper, copper alloys, silver, and silver alloys.

[0016] The small particles are preferably made of an oxide material.

[0017] The material of the small particles may be at least one selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide and zirconium oxide, preferably barium titanate or silicon oxide, more preferably barium titanate.

[0018] By using barium titanate as the material for the small particles, the influence on the composition of the ceramic layers in the laminate can be suppressed.

[0019] It is preferable that the average coverage of the small particles with respect to the large particles is 3% or more and 50% or less.

[0020] When the total volume of the large particles and the small particles is taken as 100 vol %, the volume of the small particles is preferably 1 vol % or more and 23 vol % or less.

[0021] In the internal electrode layer formed from the conductive paste containing the above-mentioned composite particles, small particles may become co-materials. As described above, in the present invention, the content of small particles that become co-materials is reduced, and even if the co-materials that are not derived from the composite small particles that were previously required are not included or only a small amount is included, the sintering start temperature of the internal electrode layer can be sufficiently shifted to the higher temperature side, thereby reducing the effect of the co-materials on the composition of the ceramic layer. Note that the co-material is a material added to a powder that is easy to sinter in order to delay sintering.

[0022] The conductive paste according to the present invention contains the above composite particles, a binder, and a solvent.

[0023] The electronic component according to the present invention is an electronic component having a ceramic layer and an internal electrode layer, The internal electrode layers are formed from the conductive paste.

[0024] The electronic component according to the present invention is an electronic component having an electrode layer, The electrode layer is formed from the conductive paste. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a composite particle according to one embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory diagram of a method for measuring the average coverage in the present invention. [Figure 4] FIG. 4 is an explanatory diagram of a method for measuring the average coverage in the present invention. [Figure 5] FIG. 5 is an explanatory diagram of a method for measuring the average coverage in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] [ First embodiment: Composite particles ] As shown in FIG. 2, the composite particle 12 according to this embodiment has a large particle 14 and small particles 16 that are attached to the surface of the large particle 14 and have an average particle size smaller than that of the large particle 14.

[0027] <Large particles> Although there are no particular limitations on the large particles 14, they are preferably conductive, and are more preferably at least one selected from Ni, Ni-based alloys, Cu, Cu-based alloys, Ag, and Ag-based alloys, and even more preferably Ni or Ni-based alloys. Note that the large particles 14 may contain trace elements such as C, S, N, and O in amounts of about 1 mass % or less.

[0028] In this embodiment, the large particles 14 may be a plurality of large particles 14 made of the same material, or may be a mixture of a plurality of large particles 14 made of different materials.

[0029] The average particle size (R) of the large particles 14 in this embodiment is 30 nm or more and 300 nm or less, and preferably 30 nm or more and 100 nm or less. In this embodiment, even if the large particles 14 are made relatively fine, the small particles 16 adhere to the surfaces of the large particles 14, so the sintering start temperature can be shifted to a higher temperature.

[0030] Furthermore, when R is within the above range, it becomes easier to achieve thin layers of the internal electrode layers 3. From the above viewpoint, R is preferably smaller than at least ⅕ of the thickness of the internal electrode layers 3.

[0031] When the large particles 14 are composed of large particles 14 made of two or more different materials, the average particle size of the large particles 14 made of one material and the average particle size of the large particles 14 made of another material may be within the above range, but they may also be different.

[0032] The different materials include metals or alloys made of different elements, or metals or alloys made of the same elements but with different compositions.

[0033] <Small particles> The material of the small particles 16 is not particularly limited, but is preferably a material that has the effect of shifting the sintering start temperature of the internal electrode layers 3 to a higher temperature, more preferably an oxide, and even more preferably an insulating material. Specific examples of an insulating oxide material that has the effect of shifting the sintering start temperature of the internal electrode layers 3 to a higher temperature include barium titanate, calcium barium titanate, strontium barium titanate, (Ba 1-x Ca x )(Ti 1-y Zr y )O3, silicon oxide, titanium oxide, zirconium oxide and aluminum oxide, and barium titanate or silicon oxide is preferred, and barium titanate is more preferred.

[0034] By using barium titanate as the material for the small particles, it is possible to suppress the influence on the composition of the ceramic layer 2 in the laminate.

[0035] The small particles 16 in this embodiment preferably have crystallinity. This allows the sintering start temperature of the internal electrode layers 3 to be shifted to a higher temperature. The presence of crystallinity can be confirmed by, for example, a scanning transmission electron microscope (STEM) or an X-ray diffraction method (XRD).

[0036] Furthermore, the small particles 16 in this embodiment are smaller than the large particles 14. The average particle size (r) of the small particles 16 is 3 nm to 30 nm, and preferably 6 nm to 20 nm. When r is within the above range, the small particles are easily dispersed.

[0037] In this embodiment, when the average particle size of the large particles 14 is represented by R and the average particle size of the small particles 16 attached to the large particles 14 is represented by r, (r / R) is preferably 0.01 or more and 0.17 or less, and more preferably 0.03 or more and 0.15 or less. When r / R is within the above range, the small particles 16 are less likely to fall off the large particles 14.

[0038] In this embodiment, the small particles 16 may be a plurality of small particles 16 made of the same material, or a mixture of a plurality of small particles 16 made of different materials.

[0039] When the small particles 16 are composed of small particles 16 made of two or more different materials, the average particle size of the small particles 16 made of one material may be different from the average particle size of the small particles 16 made of another material.

[0040] The average particle diameters of the large particles 14 and the small particles 16 according to this embodiment and the coverage ratio of the small particles 16 to the large particles 14 are measured as follows.

[0041] A liquid containing composite particles 12 is dropped onto the stage of a scanning electron microscope (SEM) or STEM and air-dried. Next, an SEM image or the like is taken. Figure 3 shows a schematic diagram of an SEM image. The field of view of an SEM image or the like is not particularly limited, but should be approximately (R × 8) × (R × 6), where R is the average particle size of the large particles 14.

[0042] Next, "large particles 14 with a visible outline" are selected from the SEM image, etc. In Figure 4, the outlines of the "large particles 14 with a visible outline" in Figure 3 are shown in bold, and the outlines of the "small particles 16 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, etc., and which are present in the foreground in the SEM image, etc. Therefore, if even a portion of a large particle 14 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) other large particles 14, that large particle 14 does not qualify as a "large particle 14 with a visible outline."

[0043] The circle-equivalent diameters of the "large particles 14 with a visible outline" confirmed by the above method and the "small particles 16 with a visible outline" attached to the "large particles 14 with a visible outline" are calculated, and the circle-equivalent diameters are used as particle diameters to calculate the average particle diameter (R) of the large particles 14 and the average particle diameter (r) of the small particles 16.

[0044] Furthermore, as shown in FIG. 5, the center of gravity G is determined for each "large particle 14 with a visible outline," and a circle with a radius equal to "0.25 × particle diameter (Ra) of the large particle" is drawn from the center of gravity G, and this circle is designated as a virtual circle 18. Note that the "particle diameter Ra" refers to the particle diameter of each large particle 14, not the average particle diameter R. The total area of ​​the small particles 16 contained in the virtual circle 18 relative to the area of ​​the virtual circle 18 is designated as the coverage rate. The coverage rates are determined for all of the "large particles 14 with a visible outline" shown in FIGS. 3 and 4, and the average value is designated as the average coverage rate.

[0045] In this embodiment, the average coverage of the small particles 16 with respect to the large particles 14 is preferably 3% or more and 50% or less, and more preferably 5% or more and 30% or less.

[0046] Furthermore, the coverage variation, which is indicated by the standard deviation of the coverage, is preferably 0% or more and 20% or less, and more preferably 0% or more and 5% or less. In this embodiment, by attaching the small particles 16 to the large particles 14 by electrostatic adsorption, which will be described later, it is possible to suppress aggregation of the small particles 16, thereby keeping the coverage variation low. The formula for the coverage variation (standard deviation) is as follows:

[0047]

number

[0048] In the above formula, "the number of observed composite particles" represented as n is the number of composite particles 12 having "large particles 14 whose outlines can be confirmed" in the observed field of view.

[0049] In this embodiment, the ratio of the number of composite particles 12 with a coverage rate of 0% to the number of composite particles 12 observed, i.e., the ratio of composite particles 12 with a coverage rate of 0%, is preferably 60% or less, and more preferably 10% or less.

[0050] Furthermore, in this embodiment, when r / R is, for example, approximately 0.07 to 0.09, the number of small particles 16 included in the imaginary circle 18 is preferably 0 to 20, and more preferably 1 to 15. Note that the "small particles 16 included in the imaginary circle 18" does not include small particles 16 that are partially missing.

[0051] In this embodiment, the number of agglomerates of small particles 16 in a visual field of (R×80)×(R×60) is preferably 3 or less, more preferably 1 or less, and even more preferably 0.

[0052] In this embodiment, the content of the small particles 16 relative to the large particles 14 is preferably 1 vol % or more and 23 vol % or less, and more preferably 2 vol % or more and 11 vol % or less.

[0053] [ Second embodiment: Conductive paste ] In this embodiment, the conductive paste contains composite particles 12, a binder, and a solvent. Known binders and solvents can be used.

[0054] In this embodiment, the small particles 16 serve to shift the sintering start temperature of the composite particles 12 to a higher temperature. Because the small particles 16 are attached to the large particles 14, the effect of the co-material can be more efficiently achieved than in conventional conductive pastes that use uncomposite small particles as a co-material. Therefore, the effect of the co-material can be sufficiently achieved even if the content of the small particles 16 combined with the large particles 14 is relatively low, or even if the uncomposite co-material contained in conventional conductive pastes is not included or the content is low. This reduces the impact of the components constituting the co-material on the composition of the ceramic layer 2. Another advantage is that the cost of the co-material can be reduced.

[0055] [ Third embodiment: Multilayer ceramic capacitor ] As one embodiment of the present invention, a multilayer ceramic capacitor 1 will be described. Fig. 1 shows a cross-sectional view of a typical multilayer ceramic capacitor 1.

[0056] The multilayer ceramic capacitor 1 has ceramic layers 2 and internal electrode layers 3 that are substantially parallel to a plane including the X-axis and Y-axis, and a ceramic body 10 in which the ceramic layers 2 and internal electrode layers 3 are alternately stacked along the Z-axis direction.

[0057] 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 2 and the internal electrode layers 3 may be slightly uneven or tilted.

[0058] The internal electrode layers 3 are stacked so that their ends are alternately exposed on the surfaces of two opposing end faces of the ceramic body 10. A pair of external electrodes 4 are formed on both end faces of the ceramic body 10 and connected to the exposed ends of the alternately arranged internal electrode layers 3 to form a capacitor circuit.

[0059] The thickness of the ceramic layer 2 is not particularly limited, but is preferably 2 μm or less per layer, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. The lower limit of the thickness is not particularly limited, but is, for example, about 0.3 μm.

[0060] The number of laminated ceramic layers 2 is not particularly limited, but is preferably 20 or more, and more preferably 50 or more.

[0061] The ceramic layer 2 may be made of, for example, BaTiO3, CaTiO3, SrTiO3, CaZrO3, (K 1-x Na x )Sr2Nb5O 15 , Ba3TiNb4O 15 , (Ba 1-x Ca x )(Ti 1-y Zr y Dielectric ceramics consisting of a main component such as SiO3 can be used. Subcomponents such as Mn compounds, Mg compounds, Cr compounds, Co compounds, Ni compounds, rare earth elements, Si compounds, and Li compounds can also be added to these main components.

[0062] The internal electrode layer 3 according to this embodiment is obtained by firing at least the composite particles 12 shown in FIG.

[0063] In the internal electrode layer 3, the "large particles 14 of the composite particles 12" can be confirmed as a conductive material after firing. Also, the "small particles 16 of the composite particles 12" are co-materials and can be confirmed as an insulating material after firing.

[0064] In this embodiment, when the total mass of the conductive material and insulating material in the internal electrode layer 3 is taken as 100 mass%, the content of the insulating material is 0.4 mass% or more and 20 mass% or less, and preferably 3 mass% or more and 15 mass% or less.

[0065] The upper limit of the thickness of the internal electrode layer 3 according to this embodiment is not particularly limited, but is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. The internal electrode layer 3 according to this embodiment can be made relatively thin because it can suppress electrode discontinuity. The lower limit of the thickness of the internal electrode layer 3 is also not particularly limited, but is 0.3 μm.

[0066] <External electrode> There are no particular limitations on the external electrode conductive material contained in the external electrodes 4, but in this embodiment, inexpensive Ni, Cu, and alloys thereof can be used. The thickness of the external electrodes 4 may be determined appropriately depending on the application, etc., but is usually 10 to 50 μm.

[0067] <Manufacturing method for multilayer ceramic capacitors> Next, an example of a method for manufacturing the multilayer ceramic capacitor 1 shown in FIG. 1 will be described.

[0068] First, in this embodiment, large particles 14 and small particles 16 are prepared, and the small particles 16 are attached to the surfaces of the large particles 14 to produce the composite particles 12 shown in Fig. 2. The method for attaching the small particles 16 to the surfaces of the large particles 14 is not particularly limited, and for example, the small particles 16 may be attached to the surfaces of the large particles 14 by electrostatic adsorption, a mechanochemical method, a method of synthesizing and precipitating the small particles 16 on the surfaces of the large particles 14, or an organic material such as a resin may be used to attach the small particles 16 to the surfaces of the large particles 14.

[0069] In this embodiment, it is preferable to attach the small particles 16 to the surfaces of the large particles 14 by electrostatic adsorption, because electrostatic adsorption allows the small particles 16 to be attached to the surfaces of the large particles 14 with low energy.

[0070] In addition, in the case of electrostatic adsorption, the small particles 16 can be adsorbed to the large particles 14 in a state close to monodispersion.

[0071] Furthermore, in the case of electrostatic adsorption, separately synthesized "highly crystalline material," "highly heat-resistant material," and / or "material with a nearly spherical shape" can be used as the small particles 16, thereby maximizing the effect of the small particles 16 as a co-material. Note that the closer the small particles 16 are to being spherical, the smaller the specific surface area (a perfect sphere is the smallest), and the smaller the surface free energy, which tends to increase the sintering start temperature.

[0072] Furthermore, electrostatic adsorption can reduce aggregation of the small particles 16. Aggregation of the small particles 16 reduces the number of small particles 16 that function effectively as co-materials, which may cause electrode discontinuities.

[0073] Furthermore, since the electrostatic adsorption thickness can be changed by changing the particle size of the small particles 16, it is easy to control the adsorption thickness of the co-material (small particles 16) on the surface of the large particles 14.

[0074] Furthermore, in the case of electrostatic adsorption, the large particles 14 and the small particles 16 are charged with opposite charges before being adsorbed, which has the advantage that it is easy to control the amount of small particles 16 that adhere to the large particles 14.

[0075] For the above reasons, by attaching the small particles 16 to the surfaces of the large particles 14 by electrostatic adsorption, the effect of shifting the sintering start temperature of the composite particles 12 to the higher temperature side can be further enhanced.

[0076] The oxide nanoparticles used as the small particles 16 have hydroxyl groups on their outermost surface, so they are generally highly hydrophilic and disperse well in water or highly polar solvents, such as alcohols and glycols. Although it depends on the manufacturing method and dispersion method, oxide nanoparticles often have a negative surface charge and can be used for compounding. A small amount of additive may be added to stabilize the dispersion.

[0077] The nickel powder used as the large particles 14 has a very weak positive or negative charge, depending on the manufacturing method. By using a polymer electrolyte such as polydiallyldimethylammonium chloride (PDDA) or polyethyleneimine (PEI) to change this to a strong positive charge, it can be combined with the negative oxide nanoparticles (small particles 16).

[0078] When BaTiO3 is used as the small particles 16, they are compounded, for example, by the following method: First, Ni particles (large particles 14) whose surfaces are positively charged are added to an organic solvent to prepare a "dispersion liquid containing Ni particles whose surfaces are positively charged."

[0079] Furthermore, a "dispersion liquid containing BaTiO3 with a negatively charged surface" is also prepared. The reason for using an organic solvent is that if the solvent is water, the surface ions of BaTiO3 will dissolve in the water. Note that alcohols, glycols, ketones, etc. can be used as the solvent for the BaTiO3 solution.

[0080] A "dispersion liquid containing Ni particles with positively charged surfaces" and a "dispersion liquid containing BaTiO3 particles with negatively charged surfaces" are mixed, and the BaTiO3 particles are adsorbed onto the Ni particles by electrostatic adsorption to obtain composite particles 12.

[0081] Next, ceramic green sheets containing ceramic material for forming the ceramic body 10 are prepared.

[0082] Ceramic materials include BaTiO3, CaTiO3, SrTiO3, CaZrO3, (K 1-x Nax )Sr2Nb5O 15 , Ba3TiNb4O 15 , (Ba 1-x Ca x )(Ti 1-y Zr y ) Ceramic materials consisting mainly of O3 can be used.

[0083] Next, a conductive paste is applied onto the ceramic green sheets to form conductive patterns corresponding to the internal electrode layers 3.

[0084] Since the conductive paste according to this embodiment contains composite particles 12, it is preferable to knead the paste relatively gently in order to maintain the structure of the composite particles 12, and it is preferable to knead the paste using a planetary centrifugal mixer.

[0085] The conductive paste can be applied by various printing methods, such as screen printing, but since the conductive paste of this embodiment contains composite particles 12, it is preferable to apply it by screen printing or gravure printing in order to maintain the structure of the composite particles 12.

[0086] A mother laminate is produced by stacking a plurality of ceramic green sheets without a conductive pattern, a ceramic green sheet with a conductive pattern, and a plurality of ceramic green sheets without a conductive pattern in this order and pressing them in the stacking direction.

[0087] The mother laminate is cut to produce a plurality of green ceramic bodies. The mother laminate can be cut by dicing or press cutting. The green ceramic bodies may also be subjected to barrel polishing or the like to round off the edges and corners.

[0088] Before firing, the green chip is subjected to a binder removal treatment. The binder removal conditions are a temperature rise rate of preferably 5 to 300°C / hour, a holding temperature of preferably 180 to 800°C, and a temperature holding time of preferably 0.5 to 24 hours. The binder removal atmosphere is air or a reducing atmosphere.

[0089] The rate of temperature rise during firing is preferably 50 to 500°C / hour, more preferably 200 to 300°C / hour.

[0090] The temperature held during firing is preferably 1200 to 1350°C, more preferably 1220 to 1300°C, and the holding time is preferably 0.5 to 8 hours, more preferably 2 to 3 hours.

[0091] The firing atmosphere is preferably a reducing atmosphere, and the atmospheric gas may be, for example, a humidified mixed gas of N2 and H2.

[0092] The oxygen partial pressure during firing may be determined appropriately depending on the type of conductive material in the conductive paste. When a base metal such as Ni or a Ni alloy is used as the conductive material, the oxygen partial pressure in the firing atmosphere should be 10 -14 ~10 -10 It is preferable to set the oxygen partial pressure to 10 MPa. -14 MPa or more, it becomes easy to prevent the conductive material of the internal electrode layer 3 from abnormal sintering, and it becomes easy to prevent the internal electrode layer 3 from being broken. -10 By setting the pressure to MPa or less, it becomes easier to prevent oxidation of the internal electrode layers 3. The temperature drop rate is preferably 50 to 500° C. / hour.

[0093] After firing in a reducing atmosphere, the ceramic body 10 may be annealed. The oxygen partial pressure in the annealing atmosphere is 10 -9 ~10 -5 The annealing pressure may be 950 to 1150° C., and the annealing time may be 0 to 20 hours. As the atmospheric gas for annealing, for example, humidified N2 gas or the like may be used.

[0094] In the above-mentioned binder removal treatment, firing and annealing, N2 gas or mixed gas can be humidified using a wetter, etc. In this case, the water temperature is preferably about 5 to 75°C.

[0095] The debinding treatment, firing and annealing may be carried out consecutively or independently.

[0096] The ceramic body 10 obtained as described above is subjected to end surface polishing by, for example, barrel polishing or sandblasting, and then external electrode paste is applied and fired to form the external electrodes 4. Then, if necessary, a coating layer is formed on the surface of the external electrodes 4 by plating or the like. The external electrode paste contains known binders and solvents in addition to external electrode conductive particles that constitute the external electrode conductive material after firing.

[0097] The multilayer ceramic capacitor 1 of this embodiment manufactured in this manner is mounted on a printed circuit board by soldering or the like, and is used in various electronic devices.

[0098] The internal electrode layers 3 of the multilayer ceramic capacitor 1 according to this embodiment are formed from a conductive paste containing the composite particles 12 according to this embodiment. Since the composite particles 12 according to this embodiment are fine, the demand for thinner layers of the multilayer ceramic capacitor 1 can be met.

[0099] Furthermore, the small particles 16 have the effect of shifting the sintering start temperature of the composite particles 12 to a higher temperature, and the composite particles 12 according to this embodiment have a configuration in which the small particles 16 are attached to the surfaces of the large particles 14. According to the conductive paste including the composite particles 12 according to this embodiment, the sintering start temperature of the composite particles 12 can be efficiently shifted to a higher temperature, and can be made closer to the sintering start temperature of the ceramic layers 2. As a result, cracks in the ceramic layers 2 due to differences in thermal shrinkage behavior between the internal electrode layers 3 and the ceramic layers 2 can be prevented, and electrode discontinuities in the internal electrode layers 3 can be prevented.

[0100] Furthermore, as described above, according to the composite particles 12 of this embodiment, the sintering start temperature of the internal electrode layers 3 can be efficiently shifted to a higher temperature side, so that the content of the co-material can be reduced compared to conventional conductive pastes, thereby reducing the influence of the co-material on the ceramic layers 2.

[0101] 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.

[0102] The electronic component of the present invention is not limited to a multilayer ceramic capacitor, but can be applied to other electronic components, such as all electronic components in which ceramic layers are laminated via internal electrode layers, including bandpass filters, inductors, multilayer three-terminal filters, piezoelectric elements, PTC thermistors, NTC thermistors, and varistors.

[0103] For example, the internal electrode layer 3 may be obtained by firing the composite particles 12 together with conductive particles other than the composite particles 12. The material of the conductive particles is not particularly limited, but Ni, a Ni-based alloy, Cu, a Cu-based alloy, or the like can be used.

[0104] In the conductive paste used in this case, when the total content of the composite particles 12 and the conductive particles is 100 mass%, it is preferable that the composite particles 12 be contained in an amount of 20 mass% or more and 60 mass% or less, and more preferably 25 mass% or more and 45 mass% or less.

[0105] Furthermore, the internal electrode layer 3 may contain a co-material not derived from the small particles 16. The co-material not derived from the small particles 16 is added to the conductive paste as a co-material alone, not as part of the composite particles 12. The average particle size of the co-material not derived from the small particles 16 is not particularly limited, and may be larger than the average particle size of the small particles 16, preferably 0.003 μm or more and 0.100 μm or less. The material of the co-material not derived from the small particles 16 is not particularly limited, but it is preferable to use the material that constitutes the ceramic layer 2 in order to reduce the effect on the composition of the ceramic layer 2.

[0106] Furthermore, the external electrodes 4 may be formed not by firing a paste but by using a resin containing the composite particles 12. In other words, the external electrodes 4 may be resin electrodes containing the composite particles 12. [Example]

[0107] The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited to these examples.

[0108] <Sample numbers 2 to 5, 11, and 12> Ni particles were prepared as the large particles 14 constituting the composite particles 12, and SiO2 particles were prepared as the small particles 16, and the SiO2 particles were attached to the Ni particles by electrostatic adsorption.

[0109] Specifically, the procedure was as follows. First, Ni particles were mixed with an aqueous solution of PDDA to positively charge the Ni particles. SiO2 particles, which were originally negatively charged, were added to the aqueous solution containing the positively charged Ni particles, and the Ni particles and SiO2 particles were composited by electrostatic adsorption. The composite particles were then dried to obtain the composite particles. The volume of the small particles relative to the total volume of the large and small particles in the composite particles was as shown in Table 1.

[0110] The obtained dried film of composite particles was scraped off by flat milling, and the cross section was observed under SEM to count the number of small particle agglomerates in a field of view of (R × 80) × (R × 60). The number of small particle agglomerates was 0 for samples 2 to 5, 11, and 12.

[0111] Composite particles other than the composite particles that formed a dried film and were prepared for counting the number of agglomerates were added to ethanol at a ratio of 0.5% by mass and mixed using a vortex mixer for 1 minute. The mixture was left to stand for 1 to 2 hours to allow the composite particles to settle. The supernatant was removed by decantation, and ethanol was added again and mixed. The resulting composite particle-containing liquid was dropped onto an SEM stage, air-dried, and observed under SEM. The average particle size R of the large particles, the average particle size r of the small particles 16, and the average coverage ratio of the small particles to the large particles were measured. The average particle size R and average particle size r are shown in Table 1. The average coverage ratio for samples 2 to 5, 11, and 12 was between 3% and 50%.

[0112] Next, a conductive paste was prepared. Ethyl cellulose was used as the binder for the conductive paste, and terpineol was used as the solvent. 45 parts by mass of the composite particles obtained, 45 parts by mass of the binder, and 52 parts by mass of the solvent were mixed to obtain a conductive paste.

[0113] A conductive paste was applied onto the dielectric sheet to obtain a sample chip.

[0114] Next, the obtained sample chip was subjected to a binder removal treatment and firing under the following conditions to obtain an electrode layer.

[0115] The binder removal treatment conditions were as follows: temperature rise rate: 25°C / hour, holding temperature: 260°C, temperature holding time: 8 hours, atmosphere: air.

[0116] The firing conditions were a temperature increase rate of 200°C / hour, a holding temperature of 1200 to 1350°C, and a holding time of 1 hour. The temperature decrease rate was 200°C / hour. The atmospheric gas was a humidified N2+H2 mixed gas, with an oxygen partial pressure of 10. -12 The pressure was adjusted to MPa.

[0117] In addition, for the firing process, the sintering start temperature and the degree of thermal shrinkage of the electrode layer were measured by thermomechanical analysis (TMA). The TMA measuring device used was a Thermo plus EVO2 manufactured by Rigaku Corporation. The results are shown in Table 1. The degree of thermal shrinkage is a value when the thickness of the internal electrode layer at 1300°C is set to 100% when the large particles are Ni, as shown in Table 1 and Tables 2 to 4 described later, and when the large particles are Ag, the thickness of the internal electrode layer at 700°C is set to 100% as shown in Table 5 described later. The sintering start temperature is the temperature when the degree of thermal shrinkage has reached 10%.

[0118] <Sample Nos. 21 and 22> After firing, the conductive paste was subjected to TMA measurement in the same manner as each sample in Table 1, except that Ni particles having the average particle size R shown in Table 1 were used instead of composite particles. The results are shown in Table 2.

[0119] <Sample Nos. 31 to 33> The small particles 16 were measured by TMA in the same manner as the samples in Table 1, except that BaTiO3 particles were used instead of SiO2 particles and composite particles were prepared by the following method. The results are shown in Table 3.

[0120] First, Ni particles (large particles 14) were mixed with an aqueous solution of PDDA to positively charge the surfaces of the Ni particles. The solvent of the aqueous solution containing the Ni particles with positively charged surfaces was replaced from water to an organic solvent to prepare a "dispersion containing Ni particles with positively charged surfaces." A "dispersion containing BaTiO3 with negatively charged surfaces" was also prepared.

[0121] A dispersion containing Ni particles with a positively charged surface was mixed with a dispersion containing BaTiO3 particles with a negatively charged surface, and the BaTiO3 particles were electrostatically adsorbed onto the Ni particles to obtain composite particles. The organic solvent containing the composite particles was dropped onto the SEM stage, air-dried, and observed using an SEM. The results are shown in Table 3. Samples 31 to 33 had an average coverage of 3% or more and 50% or less, and the number of small particle agglomerates was zero.

[0122] <Sample Nos. 41 to 43> Except for replacing the material of the small particles with SiO2 particles and using particles of the material listed in Table 4, measurements were performed by TMA in the same manner as for each sample in Table 1. The results are shown in Table 1. In addition, for sample numbers 41 to 43, the average coverage was 3% or more and 50% or less, and the number of small particle agglomerations was zero.

[0123] <Sample No. 52> The samples were measured by TMA in the same manner as in Table 1, except that the material of the large particles was changed to Ni particles and particles of the material shown in Table 5 were used. The results are shown in Table 5. Note that for sample number 52, the average coverage was 3% or more and 50% or less, and the number of small particle agglomerates was 0.

[0124] <Sample Nos. 71-78> Furthermore, the sintering initiation temperature was measured by TMA in the same manner as for each sample in Table 1, except that the variation in coverage, the number of composite particles with a coverage of 0%, the proportion of composite particles with a coverage of 0%, the number of small particles contained in the imaginary circle, and the presence or absence of aggregation of small particles were measured. The results are shown in Tables 6 and 7.

[0125] <Multilayer ceramic capacitors> Using the composite particles of sample number 5, a multilayer ceramic capacitor was produced as follows.

[0126] A conductive paste for forming the internal electrode layers was prepared. Ethyl cellulose was used as the binder for the conductive paste, and terpineol was used as the solvent. 45% by mass of the obtained composite particles, 3% by mass of the binder, and 52% by mass of the solvent were mixed to obtain a conductive paste.

[0127] To prepare the ceramic element 10 for the multilayer ceramic capacitor, a conductive paste was applied to a ceramic green sheet containing BaTiO3 as the main component, and a conductive pattern corresponding to the internal electrode layer 3 was formed.

[0128] A mother laminate was produced by stacking multiple ceramic green sheets without a conductive pattern, a ceramic green sheet with a conductive pattern, and multiple ceramic green sheets without a conductive pattern in this order and pressing them in the stacking direction.

[0129] The mother laminate was cut to produce a plurality of green ceramic bodies.

[0130] Next, the obtained green chip was subjected to a binder removal treatment, firing, and annealing under the following conditions to obtain a fired laminated ceramic body (ceramic element body).

[0131] The binder removal treatment conditions were as follows: temperature rise rate: 25°C / hour, holding temperature: 500°C, temperature holding time: 8 hours, atmosphere: humidified N2+H2 mixed gas.

[0132] The firing conditions were a temperature increase rate of 200°C / hour, a holding temperature of 1200 to 1350°C, and a holding time of 1 hour. The temperature decrease rate was 200°C / hour. The atmospheric gas was a humidified N2+H2 mixed gas, with an oxygen partial pressure of 10. -12 The pressure was adjusted to MPa.

[0133] The annealing conditions were as follows: temperature rise rate: 200°C / hour, holding temperature: 1000°C, temperature holding time: 2 hours, temperature drop rate: 200°C / hour, atmospheric gas: humidified N2 gas (oxygen partial pressure: 10 -7 MPa).

[0134] A wetter was used to humidify the atmospheric gas during firing and annealing.

[0135] Next, the end faces of the obtained ceramic body were polished by sandblasting, and then Cu was applied as external electrodes to obtain the multilayer ceramic capacitor sample shown in Figure 1. The size of the obtained capacitor sample was 1.0 mm × 0.5 mm × 0.5 mm, with a dielectric layer thickness of 3.0 μm, an internal electrode layer thickness of 1.5 μm, and four dielectric layers sandwiched between the internal electrode layers.

[0136] [Table 1]

[0137] [Table 2]

[0138] [Table 3]

[0139] [Table 4]

[0140] [Table 5]

[0141] [Table 6]

[0142] [Table 7]

[0143] From Tables 1 to 5, it was confirmed that when small particles were included (sample numbers 2 to 5, 11, 12, 31 to 33, 41 to 43, 52), the sintering start temperature was higher and thermal shrinkage proceeded more slowly than when small particles were not included (sample numbers 21 and 22). [Explanation of symbols]

[0144] 1. Multilayer ceramic capacitor 2... Ceramic layer (dielectric layer) 3… Internal electrode layer 4… External electrode 10... Ceramic body 12… Composite particles 14...Large particles 16…Small particles 18... Virtual circle

Claims

1. The method comprises: a large particle; and a small particle attached to the surface of the large particle and having an average particle size smaller than that of the large particle, The average particle size of the large particles is represented by R, and the average particle size of the small particles is represented by r; The R is 30 nm or more and 300 nm or less, The r is 3 nm or more and 30 nm or less, the large particles are made of at least one material selected from nickel, nickel alloys, silver, and silver alloys; the small particles are made of at least one material selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide, and zirconium oxide; an average coverage ratio of the small particles to the large particles is 3.0% or more and 47.5% or less; Composite particles, wherein the variation in coverage, represented by the standard deviation of the coverage of the small particles relative to the large particles, is 0% or more and 20% or less.

2. 2. The composite particle according to claim 1, wherein the particle size ratio (r / R) of the large particle to the small particle is 0.01 or more and 0.17 or less.

3. When the total volume of the large particles and the small particles is 100 vol%, 3. The composite particle according to claim 1, wherein the volume of the small particles is 1 vol % or more and 23 vol % or less.

4. 4. The composite particles according to claim 1, wherein the proportion of the composite particles in which the coverage of the small particles with respect to the large particles is 0% is 60% or less.

5. the particle size ratio (r / R) of the large particles to the small particles is 0.07 to 0.09; The number of small particles 16 included in the imaginary circle 18 is 0 to 20, A composite particle according to any one of claims 1 to 4, wherein the virtual circle has its center of gravity at the center of gravity of the large particle whose outline can be confirmed, and has a radius whose length is 0.25 multiplied by the particle diameter of the large particle.

6. A conductive paste comprising the composite particles according to any one of claims 1 to 5, a binder, and a solvent.

7. the number of agglomerations of the small particles in a predetermined field of view is 0; 7. The conductive paste according to claim 6, wherein the predetermined field of view is a rectangle having one side whose length is 80 times the particle diameter of the large particle and another adjacent side whose length is 60 times the particle diameter of the large particle.

8. An electronic component having a ceramic layer and an internal electrode layer, An electronic component, wherein the internal electrode layers are formed from the conductive paste according to claim 6 or 7.

9. An electronic component having an electrode layer, An electronic component, wherein the electrode layer is formed from the conductive paste according to claim 6 or 7.

Images