Conductive paste and use thereof

Abstract

To provide a conductive paste having a small amount of heat shrinkage in the initial stage of baking in spite of using fine conductive particles.SOLUTION: The conductive paste disclosed herein contains a conductive powder, a dielectric powder, a binder, and an organic solvent. The conductive powder of the conductive paste contains at least first conductive particles having a D50 particle size of 110nm or more and 240nm or less and second conductive particles having a D50 particle size of 20nm or more and 90nm or less. When the total mass of the conductive powder is 100wt%, the content ratio of the second conductive particles is 0. 2wt% or more and 8wt% or less. According to the conductive paste having such a configuration, it is possible to realize an internal electrode layer thinned to a submicron level while suppressing contact failure, interfacial peeling, and the like due to rapid thermal shrinkage at the initial stage of firing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to a conductive paste and a technology using the conductive paste. [Background technology]

[0002] Multi-layer ceramic capacitors (MLCCs) are widely used in various electronic devices due to their small size and high capacitance. These MLCCs have a structure in which multiple dielectric layers containing a dielectric (ceramic material) and internal electrode layers containing a conductive metal are stacked. In the manufacture of MLCCs, a conductive paste containing conductive particles is applied to the surface of a green sheet (dielectric sheet) containing a dielectric, and then the two are simultaneously dried and fired. During this simultaneous firing, the conductive paste tends to thermally shrink before the dielectric sheet. This difference in thermal shrinkage behavior can cause poor contact and interfacial peeling between the internal electrode layer and the dielectric layer. For this reason, dielectric particles are added to the conductive paste for MLCCs. This allows the thermal shrinkage behavior of the dielectric sheet and the conductive paste to be similar. An example of such a conductive paste containing dielectric particles is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-108294 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is difficult to completely uniformly disperse conductive particles in the conductive paste for the internal electrodes. Therefore, even if the conductive paste is applied to the same thickness, there may be areas where almost no conductive particles are present. In this case, there is a risk of the internal electrode layer breaking after firing. For this reason, in the formation of a typical internal electrode layer, the thickness of the conductive paste applied is set so that multiple conductive particles are arranged in the thickness direction. This prevents the internal electrode layer from breaking even if the conductive particles are unevenly distributed in the paste.

[0005] Meanwhile, with the recent trend toward thinner MLCCs, there is a demand for thinner internal electrode layers at the submicron level. To achieve a submicron-level internal electrode layer while arranging a sufficient number of conductive particles in the thickness direction, it is necessary to use extremely small conductive particles of 240 nm or less. However, because small conductive particles easily transmit heat to their interior, they undergo significant thermal shrinkage in the early stages of firing. Therefore, even though dielectric particles are added, thinned internal electrode layers experience significant thermal shrinkage in the early stages of firing, which can lead to poor contact with the dielectric layer or interfacial peeling.

[0006] The technology disclosed herein has been made to solve the above-mentioned problems, and aims to provide technology related to a conductive paste that has little thermal shrinkage in the early stages of firing despite using tiny conductive particles. [Means for solving the problem]

[0007] The conductive paste disclosed herein contains a conductive powder, dielectric particles, a binder, and an organic solvent. The conductive powder in the conductive paste has a cumulative 50% particle diameter (D 50 First conductive particles having a particle diameter of 110 nm or more and 240 nm or less, and D 50 The conductive paste disclosed herein contains at least second conductive particles having a particle diameter of 20 nm or more and 90 nm or less. When the total mass of the conductive powder is taken as 100 wt%, the content of the second conductive particles is 0.2 wt% or more and 8 wt% or less.

[0008] To solve the above-mentioned problems, the present inventors focused on voids that occur in conductive paste immediately before firing. Specifically, in the manufacture of MLCCs, a conductive paste applied to a dielectric sheet is subjected to drying and debinding processes. These low-temperature heating processes remove the organic solvent and binder, resulting in the formation of numerous voids in the conductive paste (precursor film) immediately before firing. When this porous precursor film is fired, the molten conductive particles flow to fill the voids, which can result in a significant volume loss in the early stages of firing. In contrast, the conductive paste disclosed herein contains, in addition to first conductive particles with a size of 110 nm to 240 nm, which are the main conductive component, extremely small second conductive particles with a size of 20 nm to 90 nm. These second conductive particles fill the gaps between the first conductive particles, thereby suppressing the formation of pores in the precursor film, which is one of the causes of thermal shrinkage in the early stages of firing. As a result, a conductive paste with low thermal shrinkage in the early stages of firing can be realized, even when the first conductive particles, the main conductive component, are miniaturized.

[0009] In addition, in an experiment conducted by the inventor, it was confirmed that when the content ratio of the second conductive particles to the total mass of the conductive powder exceeds 8 wt%, the amount of thermal shrinkage in the early stages of firing increases rapidly, even though the precursor film is prevented from becoming porous. For this reason, in the conductive paste disclosed herein, the content ratio of the second conductive particles is limited to 8 wt% or less. Although it is not intended to limit the technology disclosed herein, it is speculated that this rapid increase in the amount of thermal shrinkage is due to the following reasons. First, the second conductive particles are D 50 Because the particles are extremely small, with a particle diameter of 90 nm or less, they are very susceptible to thermal shrinkage. Therefore, when the content ratio of the second conductive particles exceeds a certain amount, the shrinkage-promoting effect of using extremely small conductive particles exceeds the shrinkage-suppressing effect of suppressing the porosity of the precursor film. This is presumably why the amount of thermal shrinkage in the early stages of firing reversed when the content ratio of the second conductive particles was 8 wt%. [Brief explanation of the drawings]

[0010] [Figure 1] 10 is a graph showing the relationship between the content ratio of second conductive particles and the thermal shrinkage rate of Samples 1 to 14. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the technology disclosed herein will be described below with reference to the accompanying drawings. Note that matters other than those specifically mentioned in this specification (for example, the configuration and properties of the conductive paste) that are necessary for implementing the technology disclosed herein (such as the detailed structure of the MLCC) can be implemented based on the contents of this specification and the common general technical knowledge of a person skilled in the art to which the technology disclosed herein belongs.

[0012] [Conductive paste] The conductive paste disclosed herein contains, as its main components, a conductive powder, a dielectric powder, a binder, and an organic solvent. The components of the conductive paste disclosed herein will be described below.

[0013] 1.Conductive powder The conductive powder is a powder material containing inorganic particles (conductive particles) with excellent electrical conductivity. These conductive particles are the main component of the internal electrode layers of MLCCs. Conventional, well-known inorganic particles with the desired conductivity can be used without any particular limitation. Examples of conductive particles include particles of metals such as nickel (Ni), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir), aluminum (Al), and tungsten (W), as well as alloys containing these metals. The conductive powder may be composed of any one of the above-mentioned conductive particles alone or in combination of two or more. Although not particularly limited, it is preferable to use a metal species for the conductive particles that exhibits behavior similar to that of the dielectric layer adjacent to the internal electrode layer. Examples of such metal species include rhodium, platinum, palladium, gold, nickel, and copper. When only the quality (melting point and conductivity) of the conductor film is taken into consideration, noble metals such as platinum and palladium are preferable, but when the balance between quality and material cost is taken into consideration, nickel is particularly preferable.

[0014] When the total mass of the conductive paste is taken as 100 wt%, the total mass of the conductive powder is preferably 30 wt% or more, more preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 45 wt% or more. As the total mass of the conductive powder increases, fewer components (binder, organic solvent, etc.) are removed before firing, which more effectively prevents the precursor film from becoming porous immediately before firing. On the other hand, the upper limit of the total mass of the conductive powder is preferably 70 wt% or less, more preferably 65 wt% or less, even more preferably 60 wt% or less, and particularly preferably 55 wt% or less. This prevents the viscosity of the conductive paste from increasing, contributing to improved MLCC production efficiency.

[0015] The conductive powder disclosed herein is D 50 It contains two types of conductive particles (first conductive particles and second conductive particles) with different particle sizes. By mixing these two types of conductive particles in an appropriate ratio, the amount of thermal shrinkage in the early stages of firing can be reduced, even though the conductive particles are miniaturized. This will be explained in detail below.

[0016] (1) First conductive particles The first conductive particles are D 50 The particle diameter is 240 nm or less. By using such minute first conductive particles as the main component, it is possible to realize an internal electrode layer that is thinned to the submicron level. From the viewpoint of further thinning the internal electrode layer, the D of the first conductive particles 50 The particle size is preferably 220 nm or less, more preferably 200 nm or less, and particularly preferably 180 nm or less.

[0017] On the other hand, the D of the first conductive particle 50 It has been confirmed that when the particle diameter is less than 110 nm, the amount of thermal shrinkage increases rapidly in the early stages of firing, even when the second conductive particles are appropriately added. Although this does not limit the technology disclosed herein, it is speculated that this rapid increase in the amount of thermal shrinkage is due to the first conductive particles, which are the main component of the conductive powder, becoming too small, resulting in the shrinkage-promoting effect of using minute conductive particles becoming dominant. For this reason, in the conductive paste disclosed herein, the D of the first conductive particles 50 The lower limit of the particle diameter is set to 110 nm or more. From the viewpoint of more suitably reducing the amount of thermal shrinkage in the initial stage of firing, the D 50 The particle size is preferably 120 nm or more, more preferably 130 nm or more, even more preferably 140 nm or more, and particularly preferably 150 nm or more.

[0018] In this specification, "D 50The particle size is measured according to the following procedure. First, double-sided tape is attached to a sample stage for SEM observation, and particles to be measured are thinly and sparsely placed on it to fix the particles to the stage. Next, gold is deposited on the stage with the particles fixed, and it is set in a field emission scanning electron microscope (FE-SEM). The particles are then observed at an appropriate magnification (for example, 50,000 to 100,000 times), and several (for example, four) FE-SEM observation images are obtained. Next, image analysis particle size distribution measurement software (Mountec Corporation, Mac-View Ver. 4) is used to extract 400 or more (for example, 1,000) particles that are independent (not overlapping) within the observed image, and image analysis is performed. The area of ​​the extracted particles is then measured. The particle diameter (circle equivalent diameter) is then calculated based on the measured particle area. Next, a number-based particle size distribution is created based on the measurement results of the particle diameters of the extracted particles. The particle diameter of the particles that corresponds to the cumulative 50% by number of particles from the smallest diameter in this particle size distribution is defined as "D 50 particle size”.

[0019] The shape of the first conductive particles is not particularly limited, and can be spherical, plate-like, needle-like, or the like. However, the first conductive particles are preferably spherical particles with an average aspect ratio of 1 to 2 (preferably 1 to 1.5, more preferably 1 to 1.3, even more preferably 1 to 1.2, and particularly preferably 1 to 1.1). As the first conductive particles become more spherical, the second conductive particles are more likely to fill the gaps between the first conductive particles, thereby more effectively preventing the precursor film from becoming porous. Note that the "aspect ratio" in this specification can be calculated as the ratio of the minor axis to the major axis of the fine particles observed in the FE-SEM observation image described above. The arithmetic mean value of the aspect ratios of 100 or more fine particles (e.g., 100 to 1,000 fine particles) can be defined as the "average aspect ratio."

[0020] When the total mass of the conductive powder is taken as 100 wt%, the content of the first conductive particles is preferably 99.8 wt% or less, more preferably 99.5 wt% or less, even more preferably 99 wt% or less, and particularly preferably 98.5 wt% or less. This allows the addition of an amount of second conductive particles that is sufficient to suppress thermal shrinkage in the early stages of sintering. Meanwhile, the lower limit of the content of the first conductive particles is preferably 92 wt% or more, more preferably 93 wt% or more, and even more preferably 94 wt% or more. This prevents the excessive addition of second conductive particles or other conductive particles (third to fifth conductive particles described below). As a result, the shrinkage suppression effect of the technology disclosed herein can be more suitably exhibited.

[0021] (2) Second conductive particles The second conductive particles are D 50 The second conductive particles have a particle diameter of 90 nm or less. In other words, the second conductive particles are smaller than the first conductive particles. The second conductive particles fill the gaps between the first conductive particles. This makes it possible to prevent the precursor film from becoming porous immediately before firing. As a result, the amount of thermal shrinkage in the early stages of firing can be reduced. Note that as the second conductive particles become smaller, the second conductive particles are more likely to fill the gaps between the first conductive particles. From this perspective, the D of the second conductive particles 50 The particle size is preferably 80 nm or less, more preferably 75 nm or less, even more preferably 70 nm or less, and particularly preferably 65 nm or less.

[0022] On the other hand, the second conductive particles are very small particles and therefore tend to shrink easily in the early stage of firing. 50 If the particle diameter is less than 20 nm, this shrinkage at the initial stage of firing becomes more pronounced. In this case, even though the precursor film immediately before firing is prevented from becoming porous, the amount of thermal shrinkage at the initial stage of firing may increase. For this reason, in the conductive paste disclosed herein, the D 50 The lower limit of the particle diameter is set to 20 nm or more. 50The particle size is preferably 30 nm or more, more preferably 35 nm or more, even more preferably 40 nm or more, and particularly preferably 45 nm or more.

[0023] In the conductive paste disclosed herein, the content of the second conductive particles is set to 0.2 wt% or more when the total mass of the conductive powder is 100 wt%. This allows a sufficient amount of the second conductive particles to fill the gaps between the first conductive particles, thereby suppressing the formation of porosity in the precursor film immediately before firing. To more effectively suppress the formation of porosity in the precursor film, the content of the second conductive particles is preferably 0.4 wt% or more, more preferably 0.5 wt% or more, even more preferably 0.8 wt% or more, and particularly preferably 1 wt% or more. Meanwhile, in the conductive paste disclosed herein, the upper limit of the content of the second conductive particles is set to 8 wt% or less. As mentioned above, experimental results have confirmed that when the content of the second conductive particles exceeds 8 wt%, the amount of thermal shrinkage in the early stages of firing increases rapidly, even though the formation of porosity in the precursor film is suppressed. This is presumably because the shrinkage-promoting effect of the extremely small second conductive particles exceeds the shrinkage-suppressing effect of suppressing the formation of porosity in the precursor film. The upper limit of the content of the second conductive particles is preferably 7 wt % or less, and particularly preferably 6 wt % or less.

[0024] Similarly to the first conductive particles, the shape of the second conductive particles is not particularly limited and may be spherical, plate-like, needle-like, or the like. However, the second conductive particles are preferably spherical particles with an average aspect ratio of 1 to 2 (preferably 1 to 1.5, more preferably 1 to 1.3, even more preferably 1 to 1.2, and particularly preferably 1 to 1.1). As the second conductive particles become closer to a spherical shape, the second conductive particles are more likely to fill the gaps between the first conductive particles, which effectively prevents the precursor film from becoming porous.

[0025] (3) Other conductive particles As described above, the conductive powder disclosed herein includes first conductive particles and second conductive particles. However, the above description is not intended to limit the particles in the conductive powder to only the first conductive particles and the second conductive particles. In other words, the conductive powder may contain particles of a D different from the first conductive particles and the second conductive particles, as long as the effect of the technology disclosed herein is not significantly impaired. 50 The conductive particles may have a particle size of D 50 Third conductive particles with a particle size of less than 20 nm, D 50 Fourth conductive particles with a particle diameter of more than 90 nm and less than 110 nm, D 50 and fifth conductive particles having a particle diameter of more than 240 nm. However, from the viewpoint of not impairing the thermal shrinkage suppression effect of the technology disclosed herein, the total content ratio of the other conductive particles (third to fifth conductive particles) is preferably 1 wt% or less, more preferably 0.5 wt% or less, even more preferably 0.1 wt% or less, and particularly preferably 0.01 wt% or less, when the total mass of the conductive powder is taken as 100 wt%.

[0026] 2. Dielectric powder The dielectric powder is a powder material containing the same type of ceramic particles (dielectric particles) as the constituent material of the dielectric layer. This dielectric powder functions to adjust the thermal shrinkage rate of the conductive paste and prevent cracks in the internal electrode layer. The dielectric powder also contributes to suppressing thermal shrinkage in the early stages of firing. Regarding the components of the dielectric powder, one type may be used alone or two or more types may be used in combination from among conventionally known dielectric powders, taking into consideration their relationship with the constituent material of the dielectric layer. Examples of materials for the dielectric powder include metal oxides such as barium titanate (BaTiO), strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, zirconium titanate, zinc titanate, barium magnesium niobate, calcium zirconate (CaZrO), strontium zirconate (SrZrO), titanium dioxide (rutile), titanium pentoxide, hafnium oxide, zirconium oxide, aluminum oxide, forsterite, niobium oxide, and barium neodymium titanate. Although not intending to limit the technology disclosed herein, a ceramic material with a relative dielectric constant of 100 or more (preferably 1000 or more, for example, approximately 1000 to 20000) is suitable for the dielectric layer of an MLCC. Therefore, a ceramic powder with a similar relative dielectric constant can be suitably used for the dielectric powder of the conductive paste. Examples of such ceramic powder include barium titanate, strontium titanate, strontium zirconate, and calcium zirconate.

[0027] In addition, the D of the dielectric particles 50 The particle diameter is preferably about the same as that of the second conductive particles. This allows the dielectric particles to fill the gaps between the first conductive particles, more effectively preventing the precursor film from becoming porous. 50 The particle diameter is preferably smaller than that of the first conductive particles. 50 The particle diameter is D of the first conductive particle 50 The diameter is preferably 50% or less of the particle diameter, more preferably 40% or less, more preferably 35% or less, and particularly preferably 30% or less. This allows the dielectric particles to be more easily filled into the gaps between the first conductive particles. In addition, the D of the dielectric particles 50The particle diameter is the D 50 It may be 4% or more of the particle diameter, preferably 6% or more, more preferably 8% or more, even more preferably 10% or more, and particularly preferably 15% or more.

[0028] The specific D of the dielectric particles 50 The particle diameter may be 5 nm or more, or 10 nm or more. 50 The lower limit of the particle diameter is preferably 15 nm or more, more preferably 20 nm or more, further preferably 30 nm or more, and particularly preferably 40 nm or more. 50 The upper limit of the particle diameter may be 150 nm or less, 120 nm or less, or 100 nm or less. 50 The upper limit of the particle size is preferably 90 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, and particularly preferably 60 nm or less.

[0029] In addition, the D of the dielectric particles 50 The particle diameter is the D 50 As with the particle diameter, it can be measured based on SEM observation images of the conductive paste. However, if the sizes of the dielectric particles and the second conductive particles are similar, the D of the dielectric particles and the second conductive particles can be determined based on element mapping based on the SEM observation image. 50 It is preferable to measure the particle diameter. Specifically, if element mapping of the main metal element (e.g., barium (Ba)) of the dielectric particles is obtained, the dispersed position of the dielectric particles in the SEM observation image can be determined. This allows the D 50 Even if the particle diameters are similar, the D 50 Particle size can be measured accurately.

[0030] Furthermore, when the total mass of the conductive particles is taken as 100 wt%, the content of the dielectric powder may be 2 wt% or more, preferably 4 wt% or more, more preferably 6 wt% or more, even more preferably 8 wt% or more, and particularly preferably 10 wt% or more. This allows the effects of the dielectric powder (such as crack suppression effect) to be optimally exhibited. On the other hand, the upper limit of the content of the dielectric powder may be 20 wt% or less, preferably 18 wt% or less, more preferably 16 wt% or less, even more preferably 15 wt% or less, and particularly preferably 14 wt% or less. This prevents a decrease in the electrical conductivity of the internal electrode layers.

[0031] As described above, the conductive paste disclosed herein contains at least three types of inorganic particles: first conductive particles, second conductive particles, and dielectric particles. Therefore, when the particle size distribution of the inorganic powder in the conductive paste is measured, peaks originating from the first conductive particles, the second conductive particles, and the dielectric particles are confirmed. Specifically, in the particle size distribution of the inorganic powder in the conductive paste, a first peak originating from the first conductive particles is confirmed at a position of 110 nm or more and 240 nm or less. Furthermore, a second peak originating from the second conductive particles is confirmed at a position of 20 nm or more and 90 nm or less. Finally, a third peak originating from the dielectric particles is confirmed at a position of 5 nm or more and 150 nm or less. Note that the D of the second conductive particles and the dielectric particles is 50 When the particle diameters are similar, the second peak derived from the second conductive particles and the third peak derived from the dielectric particles may overlap. In this case, as described above, by performing element mapping on the SEM observation image, the second peak derived from the second conductive particles and the third peak derived from the dielectric particles can be separated.

[0032] 3. Binder The binder is a component that adjusts the viscosity (fluidity) of the conductive paste and imparts adhesiveness to the conductive film, thereby adhering the conductive powders to each other and to the substrate. The binder is typically a component that disappears upon firing. In other words, the binder is a compound that burns off when the conductive film is fired. The binder may have a decomposition temperature that is lower than the firing temperature of the conductive film, for example, approximately 500°C or lower.

[0033] The type of binder is not particularly limited, and one type alone or two or more types in combination can be used from among conventionally known organic compounds used for this type of application, depending on, for example, the application of the conductive paste and the type of substrate used. The binder is typically a thermoplastic resin. However, it may also be a thermosetting resin. Examples of binders include organic polymer compounds such as cellulose-based resins, polyvinyl acetal-based resins, polyvinyl alcohol-based resins, acrylic resins, urethane-based resins, epoxy-based resins, phenol-based resins, rosin-based resins, polyester-based resins, and ethylene-based resins. Among these, a cellulose-based resin is preferred from the viewpoint of improving burn-through properties during firing and the surface smoothness of the electrode layer. Furthermore, in a conductive paste containing fine conductive powder or dielectric powder as described above, a polyvinyl acetal-based resin is preferably included from the viewpoint of improving the integrity of the conductor film and the adhesion between the conductor film and the substrate. For example, a combination of a cellulose-based resin and a polyvinyl acetal-based resin is preferred.

[0034] Cellulose-based resins include linear polymers (cellulose) containing β-glucose as a repeating unit and all of their derivatives. Examples of cellulose-based resins include methyl cellulose (MC), ethyl cellulose (EC), hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, and nitrocellulose. MC and EC are particularly preferred. Polyvinyl acetal-based resins include polymers having structural units in which consecutive vinyl alcohol structural units are acetalized with an aldehyde compound, and which may contain one or more of unreacted vinyl alcohol structural units and vinyl acetate structural units, which are the unsaponified portions of polyvinyl alcohol-based resins, as well as all of their derivatives (such as modified products). Polyvinyl acetal-based resins have superior adhesiveness and flexibility compared to, for example, cellulose-based resins. Examples of polyvinyl acetal-based resins include polyvinyl butyral resins (PVB), which have a structure in which polyvinyl alcohol is acetalized with butanol.

[0035] Furthermore, when the content of conductive particles is taken as 100 wt%, the content of the binder is preferably 10 wt% or less, more preferably 8 wt% or less, even more preferably 7 wt% or less, and particularly preferably 6 wt% or less. This can suppress an increase in firing residue. On the other hand, the lower limit of the binder content is preferably 1 wt% or more, more preferably 2 wt% or more, and particularly preferably 3 wt% or more. This allows the effects of the binder (such as improved fixation and shape stability) to be optimally exhibited.

[0036] 4. Organic Solvents The organic solvent is a liquid medium for dispersing the inorganic powder. The organic solvent is a solvent that evaporates when heated. The type of solvent is not particularly limited, and one type alone or two or more types in appropriate combination can be used from among conventionally known solvents depending on, for example, the use of the conductive paste or the type of substrate on which the conductive film is formed. Examples include alcohol-based solvents having an -OH group, ether-based solvents having an ether bond (RO-R'), ester-based solvents having an ester bond (RC(=O)-O-R'), and hydrocarbon-based solvents composed of carbon atoms and hydrogen atoms.

[0037] Furthermore, without limiting the technology disclosed herein, when the total mass of the conductive paste is 100 wt%, the proportion of the organic solvent is preferably 70 wt% or less, more preferably 65 wt% or less, and particularly preferably 60 wt% or less. This reduces the amount of components removed before firing, thereby more effectively preventing the precursor film from becoming porous. Meanwhile, the lower limit of the organic solvent content is preferably 25 wt% or more, more preferably 30 wt% or more, more preferably 35 wt% or more, and particularly preferably 40 wt% or more. This can impart appropriate fluidity to the paste and improve workability during film formation.

[0038] 5. Other additives The conductive paste may contain various additives to the extent that they do not significantly impair the effects of the technology disclosed herein, such as dispersants, sintering inhibitors, thickeners, plasticizers, pH adjusters, stabilizers, leveling agents, antifoaming agents, antioxidants, preservatives, and colorants (pigments, dyes).

[0039] For example, dispersants suppress the aggregation of inorganic particles (conductive particles, dielectric particles) and prevent the generation of coarse particles. Specifically, dispersants adsorb to the surfaces of inorganic particles and stabilize the solid-liquid interface between the inorganic particles and the organic solvent. This inhibits contact between the inorganic particles and prevents the generation of coarse particles due to aggregation. Examples of such dispersants include anionic dispersants such as carboxylic acid-based dispersants, phosphate-based dispersants, and sulfonic acid-based dispersants. The amount of dispersant added, based on the total mass of the conductive paste as 100 wt%, is preferably 0.01 wt% or more, more preferably 0.05 wt% or more, and particularly preferably 0.1 wt% or more. This effectively prevents the aggregation of inorganic particles. On the other hand, the upper limit of the amount of dispersant added is preferably 3 wt% or less, more preferably 2 wt% or less, and particularly preferably 1 wt% or less. Because the dispersant is also an organic component that is removed before firing, reducing the amount added can prevent the precursor film from becoming porous.

[0040] The components of the conductive paste disclosed herein have been described above. This conductive paste contains first conductive particles of 110 nm to 240 nm and second conductive particles of 20 nm to 90 nm. This allows the second conductive particles to fill the gaps between the first conductive particles, thereby preventing the conductive paste (precursor film) from becoming porous immediately before firing. The content of the second conductive particles in this conductive paste is set to 0.2 wt% to 8 wt%. This effectively prevents the precursor film from becoming porous, thereby suppressing the shrinkage-inhibiting effect caused by the use of extremely small conductive particles. Therefore, the conductive paste disclosed herein can achieve internal electrode layers that are thinned to the submicron level while preventing contact failure and interfacial peeling due to rapid thermal shrinkage during the initial firing stage.

[0041] [Preparation of conductive paste] The method for preparing the conductive paste disclosed herein is not particularly limited, and conventionally known methods can be appropriately adopted. For example, the conductive paste can be prepared by weighing out the first conductive particles, second conductive particles, dielectric particles, binder, organic solvent, and other additives to a predetermined content ratio (mass ratio) and stirring and mixing them homogeneously. A suitable preparation procedure for the conductive paste disclosed herein is as follows: First, organic components such as an organic solvent and a binder are mixed to prepare a vehicle. Next, the vehicle, the first conductive particles, the second conductive particles, and the dielectric powder are mixed and stirred. An inorganic powder slurry in which an inorganic powder is dispersed in a dispersion medium such as an organic solvent may be prepared in advance, and the slurry may then be mixed with the vehicle. The inorganic powder slurries may be prepared separately for the first conductive particles, the second conductive particles, and the dielectric powder. Alternatively, an inorganic powder slurry may be prepared by mixing the respective powders. The mixing and stirring device used for the preparation may be a conventionally known device without particular limitation. Examples of such stirring and dispersing devices include a ball mill, a bead mill, a roll mill, a magnetic stirrer, a planetary mixer, a disperser, a high-pressure disperser, and a mortar.

[0042] [Conductive paste applications] As described above, the conductive paste disclosed herein is used in the manufacture of MLCCs. In the manufacture of this MLCC, first, a green sheet (dielectric sheet) containing a dielectric is arranged. Next, a conductive paste is applied to the surface of this dielectric sheet. The method for applying the conductive paste can be any conventionally known method without any particular limitations. Examples of application methods include printing methods such as screen printing, gravure printing, offset printing, and inkjet printing, as well as spray coating and dip coating. In the manufacture of MLCCs, a laminate is produced by repeatedly arranging dielectric sheets and applying the conductive paste. This laminate is then dried and fired to produce a laminated chip in which multiple dielectric layers and internal electrode layers are alternately stacked. An external electrode paste is applied to the side of this laminated chip and then fired again to produce an MLCC.

[0043] [Test example] Test examples relating to the technology disclosed herein will be described below, but the following description is not intended to limit the technology disclosed herein to those shown in the test examples.

[0044] 1. Conductive Paste Preparation (1) Samples 1 to 14 In this test, a conductive paste containing first conductive particles, second conductive particles, dielectric powder, a binder, and an organic solvent was prepared. 50 Nickel powder with a particle diameter of 160 nm was prepared. 50 Nickel powder with a particle diameter of 50 nm was prepared. 50 Barium titanate powder with a particle diameter of 50 nm was prepared. A mixture of cellulose resin and polyvinyl butyral resin was prepared as the binder. Dihydroterpineol was prepared as the organic solvent. To prepare the conductive paste, a vehicle was prepared by mixing organic components such as an organic solvent and a binder. Next, the vehicle, first conductive particles, second conductive particles, and dielectric powder were mixed and stirred to prepare the conductive paste. At this time, the mixing ratio of the conductive powder, dielectric powder, binder, and organic solvent was set to 50:4:3:43. In Samples 1 to 14, the mixing ratio of the first conductive particles and the second conductive particles was changed as shown in Table 1.

[0045] (2) Sample 15 In sample 15, the D of the first conductive particles 50 The particle diameter was changed to 100 nm, and the D 50 A conductive paste was prepared under the same conditions as Sample 9, except that the particle size was changed to 20 nm.

[0046] 2.Evaluation Test (1) Dry density measurement In this test, a dry film was prepared and its dry density was measured. The dry density was measured using the following procedure. The prepared sample for each example was applied to a PET substrate using an applicator to a thickness of approximately 250 μm, and then dried at 110°C for approximately 15 minutes to form a dry coating film. This dry coating film was then cut into disks with a diameter of 20 mm to prepare five measurement samples for each example. The mass, radius, and thickness of the measurement samples were then measured, and the dry density of the dry coating film was calculated using the following formula. (Dry density) = (mass) / {π × (radius) × (thickness)}

[0047] The mass and radius were measured once for each measurement sample. The thickness was measured at three points for each measurement sample using a digital electronic micrometer (K351C, manufactured by Anritsu Corporation), and the average value was used. The dry density was the arithmetic mean value of the values ​​obtained for five measurement samples. The measurement results are shown in Table 1.

[0048] (2) Measurement of thermal shrinkage rate at the beginning of firing In this test, the dried film of each sample was heated under conditions that simulated the initial firing stage of MLCC manufacturing. Specifically, the sample was first applied to a PET film to form a coating. This application was performed using an applicator with a 250 μm gap. The coating was then dried at 110°C for approximately 15 minutes. The dried coating was then punched out with a 20 mm diameter die to obtain a disk-shaped dried film. The dried film was then fired on a ceramic plate. The firing conditions were as follows: first, the binder was removed by heating to 600°C for 20 minutes in a nitrogen gas atmosphere; then, the gas in the heating furnace was replaced with 1% hydrogen gas, and the temperature was increased to 1000°C at a rate of 200°C / h. This heating temperature was then maintained for 10 minutes to simulate the initial firing stage of MLCC manufacturing. The diameter ratio of the dried film before and after firing and the thermal shrinkage (%) of each sample at the initial firing stage were measured. The measurement results are shown in Table 1. Also, D 50 For Samples 1 to 14, which have the same particle diameter, the relationship between the content (%) of the second conductive particles and the thermal shrinkage (%) is shown in FIG.

[0049] [Table 1]

[0050] Comparison of Sample 1 and Samples 2 to 14 in Table 1 and Figure 1 confirmed that adding second conductive particles improved the dry density after solvent removal. Furthermore, as shown in Samples 2 to 14, a trend was confirmed in which the dry density after solvent removal improved as the content ratio of second conductive particles to the total amount of conductive powder increased. This confirmed that adding second conductive particles can effectively suppress porosity in the dried film. Furthermore, when the dried films were actually fired, Samples 2 to 12 had a lower thermal shrinkage rate at the initial stage of firing compared to Sample 1. On the other hand, Samples 13 to 14 showed a rapid increase in thermal shrinkage rate at the initial stage of firing, despite suppressing porosity in the dried film. This indicates that the shrinkage suppression effect of adding second conductive particles is reversed at a content of 8 wt%. This is presumably because, when the content ratio of extremely small second conductive particles exceeds 8 wt%, the shrinkage-promoting effect due to the miniaturization of conductive particles exceeds the shrinkage suppression effect due to the suppression of porosity.

[0051] Furthermore, in Sample 15, the thermal shrinkage rate increased in the early stage of firing, even though the content ratio of the second conductive particles was set to 5 wt%, similar to Sample 9. This indicates that the D 50 It is presumed that when the particle diameter is 100 nm or less, the shrinkage-promoting effect due to the miniaturization of the conductive particles becomes dominant.

[0052] The technology disclosed herein has been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technology disclosed herein encompasses the aspects described in items 1 to 8 below.

[0053] <Item 1> A conductive paste comprising a conductive powder, a dielectric powder, a binder, and an organic solvent, The conductive powder is The cumulative 50% particle diameter (D 50 First conductive particles having a particle diameter of 110 nm or more and 240 nm or less; The above D 50 second conductive particles having a particle diameter of 20 nm or more and 90 nm or less; Contains at least The conductive paste has a content ratio of the second conductive particles of 0.2 wt % or more and 8 wt % or less when the total mass of the conductive powder is 100 wt %.

[0054] <Item 2> Item 2. The conductive paste according to item 1, wherein the total mass of the conductive powder is 30 wt% or more and 70 wt% or less when the total mass of the conductive paste is 100 wt%.

[0055] <Item 3> 3. The conductive paste according to item 1 or 2, wherein the content of the first conductive particles is 92 wt% or more and 99.8 wt% or less when the total mass of the conductive powder is 100 wt%.

[0056] <Item 4> D of the dielectric powder 50 4. The conductive paste according to any one of items 1 to 3, wherein the particle diameter is 20 nm or more and 90 nm or less.

[0057] <Item 5> 5. The conductive paste according to any one of items 1 to 4, wherein the content of the dielectric powder is 2 wt % or more and 20 wt % or less when the total mass of the conductive powder is taken as 100 wt %.

[0058] <Item 6> 6. The conductive paste according to any one of items 1 to 5, wherein the conductive powder is a powder containing nickel particles.

[0059] <Item 7> 7. The conductive paste according to any one of items 1 to 6, wherein the dielectric powder is a powder containing barium titanate particles.

[0060] <Item 8> A dry film comprising a conductive powder, a dielectric powder, and a binder, The conductive powder is The cumulative 50% particle diameter (D 50 First conductive particles having a particle diameter of 110 nm or more and 240 nm or less; The above D 50 second conductive particles having a particle diameter of 20 nm or more and 90 nm or less; Contains at least The dry film has a content ratio of the second conductive particles of 0.2 wt % or more and 8 wt % or less when the total mass of the conductive powder is 100 wt %.

Claims

1. A conductive paste comprising a conductive powder, a dielectric powder, a binder, and an organic solvent, The conductive powder is The cumulative 50% particle diameter (D ５０ first conductive particles having a particle diameter of 110 nm or more and 240 nm or less; The above D ５０ second conductive particles having a particle diameter of 20 nm or more and 90 nm or less; Contains at least A conductive paste in which the content ratio of the second conductive particles is 0.2 wt % or more and 8 wt % or less when the total mass of the conductive powder is 100 wt %.

2. 2. The conductive paste according to claim 1, wherein the total mass of the conductive powder is 30 wt % or more and 70 wt % or less when the total mass of the conductive paste is 100 wt %.

3. The conductive paste according to claim 1 or 2, wherein a content ratio of the first conductive particles is 92 wt % or more and 99.8 wt % or less when the total mass of the conductive powder is 100 wt %.

4. D of the dielectric powder ５０ The conductive paste according to claim 1 or 2, wherein the particle diameter is 20 nm or more and 90 nm or less.

5. 3. The conductive paste according to claim 1, wherein the content of said dielectric powder is 2 wt % or more and 20 wt % or less when the total mass of said conductive powder is taken as 100 wt %.

6. The conductive paste according to claim 1 or 2, wherein the conductive powder is a powder containing nickel particles.

7. The conductive paste according to claim 1 or 2, wherein the dielectric powder is a powder containing barium titanate particles.

8. A dry film comprising a conductive powder, a dielectric powder, and a binder, The conductive powder is The cumulative 50% particle diameter (D ５０ first conductive particles having a particle diameter of 110 nm or more and 240 nm or less; The above D ５０ second conductive particles having a particle diameter of 20 nm or more and 90 nm or less; Contains at least A dry film in which the content ratio of the second conductive particles is 0.2 wt % or more and 8 wt % or less when the total mass of the conductive powder is 100 wt %.

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