JP7767006B2 - Composite particles, conductive paste and electronic components - Google Patents

Description

The present invention relates to electronic components having internal electrode layers and to composite particles used in electronic components.

As multilayer ceramic capacitors become thinner, the nickel particles used in the internal electrode layers are also becoming smaller in diameter. However, as nickel particles become smaller, the sintering start temperature decreases. Using such nickel particles in the internal electrode layers may cause cracks or electrode breaks.

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

Specifically, in the wet support method described in 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 the pH is then adjusted with an acid or alkali to cause a metal oxide or the like derived from the water-soluble salt to adhere to the surface of the nickel particles. However, with this method, the metal oxide or the like adhered 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 adhered to the surface of the nickel particles and the thickness of the adhered layer. Furthermore, with this method, there is a risk of the metal oxide or the like agglomerating.

Furthermore, in the dry and semi-dry deposition methods of Patent Document 1, metallic nickel particles with attached ultrafine particles are collided with each other or with other objects, thereby adhering 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, there is a problem with the aggregation of nickel particles and ultrafine particles. When nickel particles aggregate, there are no ultrafine particles between the nickel particles, and sintering is promoted at that point. Furthermore, the presence of nickel particle aggregation in the internal electrode layer hinders the thinning of the internal electrode layer. Furthermore, the aggregation of nickel particles causes the nickel to grow abnormally into a spherical shape, which can cause short circuits. Furthermore, the aggregation of ultrafine particles reduces the number of ultrafine particles that effectively function as co-materials. Furthermore, when ultrafine particle aggregation occurs, the aggregation of ultrafine particles itself can become the starting point for internal electrode discontinuities. Another problem is that once ultrafine particles aggregate, they are difficult to re-separate.

Japanese Patent Application Laid-Open No. 2000-282102

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide composite particles that are fine and have a high sintering initiation temperature, and are suitable for use, for example, as particles for forming electrodes.

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.

The inventors have discovered that by using composite particles with the above configuration, the composite particles are fine yet have a high sintering start temperature. Furthermore, because the sintering start temperature of the internal electrode layer formed from the conductive paste containing the composite particles is high, the sintering start temperature of the internal electrode layer can be brought closer to the sintering start temperature of the ceramic layer. As a result, cracks in the ceramic layer caused by differences in thermal shrinkage behavior between the internal electrode layer and the ceramic layer can be prevented, and electrode discontinuities in the internal electrode layer can be prevented, making it easy to achieve thin layers of the internal electrode layer and the ceramic layer.

Furthermore, by having R fall within the above range, it becomes easier to achieve thin internal electrode layers. From the above perspective, it is preferable that R be at least 1/5 of the thickness of the internal electrode layers.

When r falls within the above range, it becomes easier to disperse small particles.

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.

By keeping r/R within the above range, small particles are less likely to fall off from large particles.

It is preferable that the material of the large particles is conductive.

The material of the large particles may be at least one selected from nickel, nickel alloy, copper, copper alloy, silver, and silver alloy.

The material of the small particles is preferably an oxide.

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, and more preferably barium titanate.

By using barium titanate as the material for the small particles, the impact on the composition of the ceramic layers in the laminate can be minimized.

It is preferable that the average coverage ratio of the small particles to the large particles is 3% or more and 50% or less.

When the total volume of the large particles and the small particles is 100 vol%, it is preferable that the volume of the small particles is 1 vol% or more and 23 vol% or less.

In internal electrode layers formed from conductive pastes containing the above-mentioned composite particles, small particles may serve as co-materials. As described above, the present invention reduces the content of small particles that serve as co-materials, and even if it does not contain or contains only small amounts of co-materials that are not derived from the composite small particles that were previously required, it is possible to sufficiently shift the sintering start temperature of the internal electrode layer to the higher temperature side, thereby reducing the effect of co-materials on the composition of the ceramic layer. Note that a co-material is a material added to easily sintered powders to delay sintering.

The conductive paste according to the present invention contains the above-mentioned composite particles, a binder, and a solvent.

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.

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.

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

[ 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 .

<Large particles>
Although there are no particular limitations on the large particles 14, they are preferably conductive, 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. The large particles 14 may also contain trace elements such as C, S, N, and O in amounts of about 1% by mass or less.

Furthermore, in this embodiment, multiple large particles 14 made of the same material may be used as the large particles 14, or multiple large particles 14 made of different materials may be mixed together.

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.

Furthermore, by having R fall within the above range, it becomes easier to achieve a thinner internal electrode layer 3. From the above perspective, it is preferable that R be at least 1/5 of the thickness of the internal electrode layer 3.

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 need only be within the above range, but they may also be different.

Examples of different materials include metals or alloys made up of different elements, or metals or alloys made up of the same elements but with different compositions.

<Small particles>
The material of the small particles 16 is not particularly limited, but is preferably a material having 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 insulating. Specific examples of the oxide and insulating material having the effect of shifting the sintering start temperature of the internal electrode layers 3 to a higher temperature include at least one selected from barium titanate, calcium barium titanate, strontium barium titanate, (Ba _1-x Ca _x )(Ti _1-y Zr _y )O ₃ , silicon oxide, titanium oxide, zirconium oxide, and aluminum oxide, and barium titanate or silicon oxide is preferred, and barium titanate is more preferred.

By using barium titanate as the material for the small particles, the impact on the composition of ceramic layer 2 in the laminate can be minimized.

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

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

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.

Furthermore, in this embodiment, the small particles 16 may be a mixture of multiple small particles 16 made of the same material, or a mixture of multiple small particles 16 made of different materials.

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.

The average particle size of the large particles 14 and small particles 16 and the coverage ratio of the small particles 16 to the large particles 14 in this embodiment are measured as follows:

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 when the average particle size of the large particles 14 is represented as R, it should be approximately (R x 8) x (R x 6).

Next, "large particles 14 with a visible outline" are selected from the SEM image, etc. Figure 4 shows the outlines of the "large particles 14 with a visible outline" in Figure 3 with a thick line, and also shows the outlines of the "small particles 16 with a visible outline" attached to the "large particles 14 with a visible outline" with a thick line. Note that a "large particle 14 with a visible outline" refers to a large particle 14 whose entire outline is included in the SEM image, etc., and which is 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 that 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."

The circle-equivalent diameters of the "large particles 14 with visible outlines" confirmed by the above method and the "small particles 16 with visible outlines" attached to the "large particles 14 with visible outlines" 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.

Furthermore, as shown in Figure 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 x the particle diameter (Ra) of the large particle" is drawn from the center of gravity G, and this circle is designated as the imaginary 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 coverage rate is the sum of the area of the small particles 16 contained in the imaginary circle 18 relative to the area of the imaginary circle 18. The coverage rates are determined for all of the "large particles 14 with a visible outline" shown in Figures 3 and 4, and the average value is designated as the average coverage rate.

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

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 coverage variation (standard deviation) is as follows:

Note that the "number of observed composite particles" represented as n in the above formula is the number of composite particles 12 that have "large particles 14 with visible outlines" in the observed field of view.

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.

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

In this embodiment, the number of agglomerations of small particles 16 in a field of view of (R x 80) x (R x 60) is preferably 3 or less, more preferably 1 or less, and even more preferably 0.

In this embodiment, the content of small particles 16 relative to 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.

[ 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.

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, they can function as a co-material more efficiently than conventional conductive pastes that use uncomposite small particles as a co-material. Therefore, even if the content of 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 its content is reduced, the co-material effect can be fully achieved. This reduces the impact of the components that make up the co-material on the composition of the ceramic layer 2. Another advantage is that the cost of the co-material can be reduced.

[ Third Embodiment: Multilayer Ceramic Capacitor ]
As one embodiment of the present invention, a multilayer ceramic capacitor 1 will be described. FIG.

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.

Here, "substantially parallel" means that most of the parts are parallel, but there may be some parts that are not parallel, and the ceramic layers 2 and internal electrode layers 3 may be slightly uneven or tilted.

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 are connected to the exposed ends of the alternately arranged internal electrode layers 3 to form a capacitor circuit.

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, approximately 0.3 μm.

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

The ceramic layer 2 may be made of a dielectric ceramic whose main component is, for example, BaTiO ₃ , CaTiO ₃ , SrTiO ₃ , CaZrO ₃ , (K _1-x Na _x )Sr ₂ Nb ₅ O ₁₅ , Ba ₃ TiNb ₄ O ₁₅ , (Ba _1-x Ca _x )(Ti _{1-y Zry} ) O _3. Alternatively, a material obtained by adding a subcomponent such as a Mn compound, a Mg compound, a Cr compound, a Co compound, a Ni compound, a rare earth element, a Si compound, or a Li compound to these main components may be used.

The internal electrode layer 3 according to this embodiment is obtained by firing at least the composite particles 12 shown in Figure 2.

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

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.

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.

<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.

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

In this embodiment, large particles 14 and small particles 16 are first 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. For example, the small particles 16 may be attached to the surfaces of the large particles 14 by electrostatic adsorption, by a mechanochemical method, by a method of synthesizing and precipitating the small particles 16 on the surfaces of the large particles 14, or by using an organic material such as a resin to attach the small particles 16 to the surfaces of the large particles 14.

In this embodiment, it is preferable to attach the small particles 16 to the surfaces of the large particles 14 by electrostatic adsorption. This is because electrostatic adsorption makes it possible to attach the small particles 16 to the surfaces of the large particles 14 with low energy.

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.

Furthermore, in the case of electrostatic adsorption, separately synthesized "highly crystalline materials," "highly heat-resistant materials," and/or "nearly spherical materials" can be used as the small particles 16, thereby maximizing the effect of the small particles 16 as a co-material. Furthermore, the closer the small particles 16 are to being spherical, the smaller their specific surface area (a perfect sphere is the smallest), and the smaller the surface free energy, the higher the sintering initiation temperature tends to be.

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

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.

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

For the reasons stated above, attaching small particles 16 to the surfaces of large particles 14 by electrostatic adsorption can further enhance the effect of shifting the sintering start temperature of composite particles 12 to a higher temperature.

The oxide nanoparticles used as small particles 16 have hydroxyl groups on their outermost surface, making them generally highly hydrophilic and dispersible in water and highly polar solvents, such as alcohols and glycols. While this depends on the manufacturing method and dispersion method, oxide nanoparticles often have a negative surface charge, making them suitable for use in composites. A small amount of additive may be added to stabilize the dispersion.

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 composited with negative oxide nanoparticles (small particles 16).

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."

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.

A "dispersion liquid containing Ni particles whose surfaces are positively charged" and a "dispersion liquid containing _BaTiO3 particles whose surfaces are negatively charged" are mixed, and the _BaTiO3 particles are electrostatically adsorbed onto the Ni particles to obtain composite particles 12.

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

As the ceramic material, ceramic materials consisting mainly of BaTiO ₃ , CaTiO ₃ , SrTiO ₃ , CaZrO ₃ , (K _1-x Na _x )Sr ₂ Nb ₅ O ₁₅ , Ba ₃ TiNb ₄ O ₁₅ , (Ba _1-x Ca _x )(Ti _{1-y Zry} )O ₃ or the like can be used.

Next, a conductive paste is applied to the ceramic green sheet to form a conductive pattern corresponding to the internal electrode layer 3.

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

The conductive paste can be applied by various printing methods, such as screen printing. However, since the conductive paste according to 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.

A mother laminate is produced by stacking multiple ceramic green sheets without conductive patterns, a ceramic green sheet with conductive patterns, and multiple ceramic green sheets without conductive patterns in this order, and pressing them in the stacking direction.

By cutting the mother laminate, multiple green ceramic bodies are produced. The mother laminate can be cut by dicing or cutting. Furthermore, the green ceramic bodies may be subjected to barrel polishing or other methods to round the edges and corners.

Before firing, the green chip is subjected to a binder removal process. 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.

The heating rate during firing is preferably 50 to 500°C/hour, more preferably 200 to 300°C/hour.

The firing temperature is preferably 1200 to 1350°C, more preferably 1220 to 1300°C, and the firing time is preferably 0.5 to 8 hours, more preferably 2 to 3 hours.

The firing atmosphere is preferably a reducing atmosphere, and the atmospheric gas may be, for example, a humidified mixed gas of N ₂ and H ₂ .

In addition, the oxygen partial pressure during firing may be appropriately determined depending on the type of conductive material in the conductive paste, but 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 is preferably 10 ^-14 to 10 ^-10 MPa. By setting the oxygen partial pressure to 10 ^-14 MPa or more, it becomes easier to prevent abnormal sintering of the conductive material of the internal electrode layers 3, and it becomes easier to prevent the internal electrode layers 3 from being broken. In addition, by setting the oxygen partial pressure to 10 ^-10 MPa or less, it becomes easier to prevent oxidation of the internal electrode layers 3. The temperature decreasing rate is preferably 50 to 500°C/hour.

After firing in a reducing atmosphere, the ceramic body 10 may be annealed. The oxygen partial pressure in the annealing atmosphere may be ^10-9 to ^10-5 MPa, the annealing temperature may be 950 to 1150°C, and the annealing time may be 0 to 20 hours. The annealing atmosphere gas may be, for example, humidified _N2 gas.

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.

Binder removal, firing, and annealing may be performed consecutively or independently.

The ceramic body 10 obtained as described above has its end surfaces polished, for example by barrel polishing or sandblasting, and is then coated with external electrode paste and fired to form the external electrodes 4. If necessary, a coating layer is then formed on the surface of the external electrodes 4 by plating or other methods. 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.

The multilayer ceramic capacitor 1 of this embodiment manufactured in this manner is mounted on a printed circuit board by soldering or other means and used in various electronic devices, etc.

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. Because the composite particles 12 according to this embodiment are fine, they can meet the demand for thinner layers in the multilayer ceramic capacitor 1.

The small particles 16 also have the effect of shifting the sintering start temperature of the composite particles 12 to a higher temperature, and the composite particles 12 of this embodiment are configured such that the small particles 16 are attached to the surfaces of the large particles 14. The conductive paste containing the composite particles 12 of this embodiment can efficiently shift the sintering start temperature of the composite particles 12 to a higher temperature, bringing it closer to the sintering start temperature of the ceramic layer 2. As a result, cracks in the ceramic layer 2 due to differences in thermal contraction behavior between the internal electrode layer 3 and the ceramic layer 2 can be prevented, and electrode discontinuities in the internal electrode layer 3 can also be prevented.

Furthermore, as described above, the composite particles 12 according to this embodiment can efficiently shift the sintering start temperature of the internal electrode layer 3 to a higher temperature, thereby reducing the content of the co-material compared to conventional conductive pastes. This reduces the effect of the co-material on the ceramic layer 2.

The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment and can be modified in various ways without departing from the spirit of the present invention.

The electronic component of the present invention is not limited to multilayer ceramic capacitors and can be applied to other electronic components. Examples of other electronic components include all electronic components in which ceramic layers are stacked via internal electrode layers, such as bandpass filters, inductors, multilayer three-terminal filters, piezoelectric elements, PTC thermistors, NTC thermistors, and varistors.

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

In this case, the conductive paste used preferably contains 20% by mass or more and 60% by mass or less of composite particles 12, and more preferably 25% by mass or more and 45% by mass or less, when the total content of composite particles 12 and conductive particles is 100% by mass.

The internal electrode layer 3 may also contain a co-material that is not derived from the small particles 16. The co-material that is not derived from the small particles 16 is added to the conductive paste as a co-material alone, rather than as part of the composite particles 12. The average particle size of the co-material that is 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 that is 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.

Furthermore, when forming the external electrode 4, instead of forming it by firing a paste, the external electrode 4 may be formed from a resin containing composite particles 12. In other words, the external electrode 4 may be a resin electrode containing composite particles 12.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

<Sample Nos. 2 to 5, 11, and 12>
Ni particles were prepared as the large particles 14 constituting the composite particles 12, and SiO ₂ particles were prepared as the small particles 16, and the SiO ₂ particles were attached to the Ni particles by electrostatic adsorption.

Specifically, the procedure was as follows. First, Ni particles were mixed with an aqueous solution of PDDA to positively charge the Ni particles. Originally negatively charged _SiO2 particles 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 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.

The resulting dried film of composite particles was scraped off using flat milling, and the cross section was observed using an SEM. The number of small particle agglomerates was counted within a field of view of (R x 80) x (R x 60). Samples 2 to 5, 11, and 12 showed zero small particle agglomerates.

Composite particles other than those that formed into 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 with a vortex mixer for 1 minute. The mixture was left to stand for 1-2 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 with an 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 were as shown in Table 1. For sample numbers 2-5, 11, and 12, the average coverage ratio was 3% or more and 50% or less.

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 weight of the resulting composite particles, 45 parts by weight of the binder, and 52 parts by weight of the solvent were mixed to obtain a conductive paste.

Conductive paste was applied to the dielectric sheet to obtain a sample chip.

The resulting sample chip was then subjected to binder removal and firing under the following conditions to obtain an electrode layer.

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

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, and the oxygen partial pressure was set to ^10-12 MPa.

The sintering start temperature and degree of thermal shrinkage of the electrode layer during the firing process were measured using 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 calculated based on the thickness of the internal electrode layer at 1300°C being 100% when the large particles are Ni, as shown in Table 1 and Tables 2 to 4 described below, and the thickness of the internal electrode layer at 700°C being 100% when the large particles are Ag, as shown in Table 5 described below. The sintering start temperature is the temperature at which the degree of thermal shrinkage reaches 10%.

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

<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.

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 with 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.

A "dispersion containing Ni particles with positively charged surfaces" and a "dispersion containing _BaTiO3 particles with negatively charged surfaces" were mixed, 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 an SEM stage, air-dried, and observed with an SEM. The results are shown in Table 3. For sample numbers 31 to 33, the average coverage was 3% or more and 50% or less, and the number of small particle agglomerates was zero.

<Sample Nos. 41 to 43>
The TMA measurements were performed in the same manner as for each sample in Table 1, except that the material of the small particles was changed to _SiO2 particles and particles of the material shown in Table 4 were used. 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 0.

<Sample No. 52>
The TMA measurements were performed in the same manner as for each sample 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 agglomerations of small particles was zero.

<Sample Nos. 71 to 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.

<Multilayer ceramic capacitors>
Using the composite particles of Sample No. 5, a multilayer ceramic capacitor was produced as follows.

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 weight of the resulting composite particles, 3% by weight of binder, and 52% by weight of solvent were mixed to obtain a conductive paste.

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

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

Multiple green ceramic bodies were produced by cutting the mother laminate.

The resulting green chip was then subjected to binder removal, firing, and annealing under the following conditions to obtain a laminated ceramic fired body (ceramic element).

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 N ₂ +H ₂ mixed gas.

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, and the oxygen partial pressure was set to ^10-12 MPa.

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 N ₂ gas (oxygen partial pressure: 10 ⁻⁷ MPa).

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

Next, the end faces of the obtained ceramic body were polished by sandblasting, and 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 x 0.5 mm x 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.

Tables 1 to 5 confirm that samples containing small particles (sample numbers 2 to 5, 11, 12, 31 to 33, 41 to 43, and 52) have a higher sintering start temperature and thermal shrinkage progresses more slowly than samples not containing small particles (sample numbers 21 and 22).

1... Multilayer ceramic capacitor 2... Ceramic layer (dielectric layer)
3... Internal electrode layer 4... External electrode 10... Ceramic body 12... Composite particle 14... Large particle 16... Small particle 18... Imaginary circle

Claims (9)

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 . The composite particles described in claim 1, wherein the particle size ratio (r/R) between the large particles and the small particles is 0.01 or more and 0.17 or less. 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. 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. 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,
The composite particle according to any one of claims 1 to 4 , wherein the imaginary circle has a center of gravity of the large particle whose outline can be confirmed, and a radius of the circle whose length is 0.25 multiplied by the particle diameter of the large particle. A conductive paste comprising the composite particles according to any one of claims 1 to 5 , a binder, and a solvent. 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. 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 . 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 .