Conductive paste and its applications

Abstract

To provide technology that improves the electrical properties of multilayer ceramic electronic components. [Solution] The present invention discloses a conductive paste, comprising a conductive powder, a thermosetting resin, and an organic solvent. The conductive powder comprises silver-containing powder, tin powder, and tin-containing alloy powder. In another aspect, the present invention discloses an external electrode for a multilayer ceramic electronic component, comprising a cured film of the conductive paste. In yet another aspect, the present invention provides a method for manufacturing a multilayer ceramic electronic component comprising an internal electrode and an external electrode using the conductive paste.

Description

Technical Field

[0001] The present disclosure relates to a conductive paste and use thereof. Background Art

[0002] Japanese Patent No. 5400801 discloses a conductive paste for external electrodes of ceramic electronic components, which contains nickel as a main component of internal electrodes. This conductive paste comprises component (A) to component (D). Component (A) is Ag particles and / or Ag alloy particles having an average particle diameter of 0.2 to 30 µm and a melting point of 700°C or higher. Component (B) is SnAg alloy particles having an average particle diameter of 0.2 to 18 µm and a melting point of 200°C or higher and lower than 700°C. Component (C) is a paste formed by mixing a copper-containing compound selected from the group consisting of copper nitrate, copper cyanide, copper octoate, copper formate, copper acetate, copper oxalate, copper benzoate and copper acetylacetonate; an amino compound; and optionally an organic solvent. Component (D) is a thermosetting resin. The publication describes that such a configuration can provide an external electrode for a multilayer ceramic electronic component having favorable electrical properties (capacitance, tanδ).

[0003] Japanese Patent Laid-Open No. 2013-118357 discloses a ceramic electronic component including a ceramic body and an external electrode disposed on the ceramic body. The external electrode has a first conductive layer and a second conductive layer. The first conductive layer contains a resin, a first metal component, and a second metal component having a higher melting point than the first metal component. The second conductive layer is disposed on the first conductive layer and is formed of a plating film. Alloy particles containing the first metal component and the second metal component protrude from the surface of the first conductive layer toward the second conductive layer side. The publication describes that such a configuration can provide a ceramic electronic component excellent in mechanical durability.

[0004] The multilayer ceramic electronic component disclosed in Japanese Patent Publication No. 7528763 comprises a ceramic body and a pair of external electrodes. The ceramic body includes a plurality of stacked ceramic layers and a plurality of stacked internal electrode layers, and includes a first main surface and a second main surface facing each other in the stacking direction, a first side surface and a second side surface facing each other in the width direction perpendicular to the stacking direction, and a first end surface and a second end surface facing each other in the length direction perpendicular to the stacking direction and the width direction. The pair of external electrodes are connected to the internal electrode layers and are positioned on the end surfaces, the first and second main surfaces, and the first and second side surfaces. Each of the pair of external electrodes includes a base electrode layer connected to the internal electrode layer and a resin external electrode layer stacked on the base electrode layer. The resin external electrode layer contains one or more silane coupling agents from among amine-based, isocyanate-based, epoxy-based, mercapto-based, and ureido-based silane coupling agents. The resin external electrode layer contains a thermosetting resin and metal powder, and the silane coupling agent covers at least a portion of the surface of the metal particles of the metal powder. In the resin external electrode layer, the content of the silane coupling agent relative to the thermosetting resin is 0.1 wt% to 10 wt%. The porosity of the resin external electrode layer is 0.79% to 1.22%. The publication states that this configuration can suppress deterioration of electrical properties.

[0005] Japanese Patent Publication No. 5390408 discloses a thermosetting conductive paste. The thermosetting conductive paste comprises (A) 45 to 85 parts by weight of silver powder having an average particle size of 0.2 to 30 μm, (B) 5 to 35 parts by weight of tin-silver alloy powder having an average particle size of 0.2 to 15 μm, (C) 5 to 25 parts by weight of silver and / or silver-tin alloy fine powder having an average particle size of 15 to 150 nm, and (D) 6 to 18 parts by weight of thermosetting resin. The total of components (A), (B), and (C) is 100 parts by weight. The publication states that this configuration achieves good bonding between internal and external electrodes and good electrical properties.

[0006] Japanese Patent Publication No. 2023-64724 discloses a conductive resin composition comprising (a) tin powder, (b) epoxy resin, (c) organic acid compound, and (d) phenolic curing agent. The publication states that a conductive resin composition having such a configuration exhibits good conductivity and excellent adhesion (bonding strength) to various substrates. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5400801 [Patent Document 2] Japanese Patent Publication No. 2013-118357 [Patent Document 3] Patent No. 7528763 [Patent Document 4] Patent No. 5390408 [Patent Document 5] Japanese Patent Publication No. 2023-64724 [Overview of the project] [Problems that the invention aims to solve]

[0008] Conventionally, multilayer ceramic electronic components sometimes have a structure in which a resin electrode containing conductive powder and resin is layered on the surface of an external electrode to ensure reliability against impacts such as drops and bending. To realize such a structure, a process for forming the external electrode and a process for forming the resin electrode are required, which can lead to an increase in the number of processes and an increase in cost. In this regard, some of the prior art documents mentioned above propose using a resin electrode as the external electrode. However, when a resin electrode is used as the external electrode, a problem may arise, such as poor connection with the internal electrode, resulting in unsatisfactory electrical characteristics.

[0009] In light of these circumstances, the inventors of the present invention wanted to improve the electrical properties of multilayer ceramic electronic components equipped with resin electrodes as external electrodes. [Means for solving the problem]

[0010] The technology disclosed herein provides a conductive paste comprising a conductive powder, a thermosetting resin, and an organic solvent. The conductive powder comprises silver-containing powder, tin powder, and tin-containing alloy powder. Such a configuration can improve the electrical properties of multilayer ceramic electronic components.

[0011] The technology disclosed herein provides an external electrode for a multilayer ceramic electronic component. This external electrode includes a cured film of the conductive paste described above. Such a configuration can improve the electrical properties of the multilayer ceramic electronic component.

[0012] The technology disclosed herein provides a method for manufacturing a multilayer ceramic electronic component comprising an internal electrode and an external electrode. This manufacturing method includes applying a coating of the conductive paste to the internal electrode, drying the coating to form a dried coating, and heat-treating the dried coating. With this configuration, a multilayer ceramic electronic component having excellent electrical properties can be manufactured. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic cross-sectional view of a multilayer ceramic capacitor 1. [Modes for carrying out the invention]

[0014] The embodiments of the technology disclosed herein will be described below. Matters other than those specifically mentioned herein that are necessary for carrying out the technology disclosed herein can be understood based on the technical content taught herein and the common technical knowledge of those skilled in the art. The technology disclosed herein can be carried out based on the content disclosed herein and the common technical knowledge of the art. In this specification and in the claims, A to B (where A and B are arbitrary numbers) means A or greater and B or less, and also includes the case where A is greater and B is less than or equal to A.

[0015] In the manufacturing process of multilayer ceramic electronic components, for example, a heat treatment (sintering) is performed to integrate the dielectric layer and the internal electrode (internal electrode layer), followed by an annealing treatment. By performing the annealing treatment, for example, the dielectric layer can be re-oxidized, thereby improving the performance of the multilayer ceramic electronic component. However, the annealing treatment can cause the metal (e.g., nickel, copper, etc.) contained in the internal electrode to oxidize, resulting in the formation of a metal oxide film. In particular, the metal oxide film is likely to form on the end face portion that is exposed to air. The formation of a metal oxide film is undesirable because it reduces the connectivity between the internal electrode and the external electrode, and consequently leads to a decrease in the electrical properties of the multilayer ceramic electronic component. Therefore, it is necessary to remove the metal oxide film formed on the internal electrode and improve the connectivity between the internal electrode and the external electrode. Accordingly, the inventors investigated the composition of a conductive paste.

[0016] The technology disclosed herein provides for a conductive paste comprising a conductive powder, a thermosetting resin, and an organic solvent. The conductive powder comprises silver-containing powder, tin powder, and tin-containing alloy powder.

[0017] The conductive powder is a component that imparts electrical conductivity to a cured film obtained by heat-treating a conductive paste (hereinafter also referred to as a "conductive film"). The conductive powder may contain unavoidable impurities generated in the production process of the powder particles, generally in an amount of 2% by mass or less (preferably 1% by mass or less, more preferably 0.5% by mass or less) based on the entire mass of each powder.

[0018] The silver-containing powder may, for example, include silver powder. The silver powder may be composed of, for example, particles made of a simple substance of silver (Ag) or particles made of an alloy containing silver. As used herein, an alloy containing silver is an alloy in which the content ratio of silver in the entire alloy is generally 40% by mass or more, for example 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 90% by mass or more, and less than 100% by mass, alternatively 98% by mass or less. Examples of such alloys include AgPd, AgPt, AgCu, and AgSn. The silver-containing alloy is preferably an alloy whose main component is silver. In the present specification, the phrase "P is a main component of Q" means that among the components constituting Q, P is the component having the maximum content with respect to the entire Q.

[0019] Alternatively, the silver-containing powder may include silver-coated copper powder. The silver-coated copper powder may be composed of, for example, silver-coated copper particles including core particles and a silver-containing coating layer provided on at least a part of the surface of the core particles. The core particles may be, for example, particles containing copper. The copper-containing particles may be, for example, particles made of a simple substance of copper (Cu) or particles made of an alloy containing copper. As used herein, an alloy containing copper is an alloy in which the content ratio of copper in the entire alloy is generally 40% by mass or more, for example 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 90% by mass or more, and less than 100% by mass, alternatively 98% by mass or less. Examples of such alloys include CuSn, CuZn, and CuNi.

[0020] The silver-containing coating layer may be, for example, a layer made of silver (Ag) or a layer made of a silver-containing alloy. The silver-containing alloy, in this context, is an alloy in which the silver content of the whole is approximately 40% by mass or more, for example 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, and less than 100% by mass, or 98% by mass or less. Examples of such alloys include AgCu, AgPd, AgPt, AgSn, etc. The silver-containing alloy is preferably an alloy in which silver is the main component.

[0021] The coating layer is provided here on at least a portion of the surface of the core particles. The coverage of the coating layer on the core particle surface is not particularly limited as long as the effects of the disclosed technology are realized. For example, when a conductive paste is used as a material constituting part of a multilayer ceramic electronic component, from the viewpoint of electrical connectivity between the external electrode and the internal electrode, the coverage of the core particle surface is generally 40% or more, for example 50% or more, preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, particularly preferably 90% or more, and may be 95% or more or 97% or more. A higher coverage rate is preferable because a lower coverage rate makes the copper contained in the core particles more susceptible to oxidation. The coverage rate is not particularly limited, but may be, for example, 100% or less, less than 100%, 99.8% or less, 99.5% or less, or 99% or less of the core particle surface.

[0022] The coverage can be calculated, for example, by using the TEM-EDX method. When the core particles are particles composed of a simple copper substance and the coating layer is a layer composed of a simple silver substance (when the particles are silver-coated copper particles), first, element maps of each of Ag element and Cu element in the cross section of the particle to be measured are obtained based on the TEM-EDX method. Then, each element map is converted into a predetermined bit image (for example, an 8-bit image) using image analysis software (for example, Image-J). Then, the converted element map of Cu element is binarized at a predetermined pixel value (for example, 40 to 80) and subjected to Skeletonize processing. Then, the number of dots at a predetermined pixel value (for example, 255) in the element map of Cu element subjected to such image processing is measured as "area LCu of the Cu core particle". Similarly, the converted Ag element map is binarized at a predetermined pixel value (for example, 40 to 255) and subjected to Skeletonize processing. The number of dots at a predetermined pixel value (for example, 255) in the element map of Ag element subjected to such image processing is measured as "internal area LAg of the Ag coating layer". The measured LCu and LAg are substituted into the following formula (I): Coverage = (LAg / LCu) × 100 ··· (I) to calculate the coverage of the Ag coating layer in a single silver-coated copper particle. The average value of the coverage of the Ag coating layer of any 10 particles close to the average particle diameter among the plurality of particles can be taken as "the coverage of the Ag coating layer". When either the core particles or the coating layer is an alloy, an element map is obtained for each constituent element of the alloy, and the coverage of the coating layer can be calculated by using the above procedure. The coverage may also be a nominal value provided by the manufacturer or the like.

[0023] The mass ratio of the coating layer to the core particles (coating layer:core particles) is not particularly limited and may be, for example, 30:70 to 1:99, 25:75 to 3:97, 20:80 to 5:95, or 15:85 to 7:93, from the viewpoint of realizing the effects of the technology disclosed herein. The mass ratio (coating layer:core particles) can be obtained, for example, by using ICP-AES (inductively coupled plasma emission spectroscopy), XRF (X-ray fluorescence analysis), etc. The mass ratio (coating layer:core particles) may be a nominal value from the manufacturer, etc.

[0024] The average particle size of the silver-containing powder is not particularly limited, but may be approximately 0.1 μm to 20 μm. From the viewpoint of realizing the effects of the technology disclosed herein, the average particle size of the silver-containing powder is, for example, 0.3 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more. From a similar viewpoint, the average particle size of the silver-containing powder is, for example, 15 μm or less, preferably 10 μm or less, and more preferably 5 μm or less. In this specification, "average particle size" refers to the D value corresponding to 50% of the cumulative value from the smallest particle size in the volume-based particle size distribution based on laser diffraction scattering method. 50 It refers to the diameter.

[0025] The shape of the particles constituting the silver-containing powder is not particularly limited, as long as the effects of the technology disclosed herein are realized. The particles constituting the silver-containing powder may be, for example, spherical. With respect to the particles constituting the silver-containing powder, and the particles constituting the tin powder and tin-containing alloy powder described later, "spherical" means that the average aspect ratio is approximately 1 to 1.5, for example 1 to 1.3, preferably 1 to 1.2, more preferably 1 to 1.15, and even more preferably 1 to 1.1. The average aspect ratio can be obtained, for example, by observing the silver-containing powder, tin powder, or tin-containing alloy powder with an SEM, randomly selecting a number of particles (for example 10 to 300) from the obtained observation images, calculating the aspect ratio (ratio of major axis to minor axis) based on the major axis and minor axis of each particle, and obtaining the arithmetic mean.

[0026] In this context, tin powder is composed of particles made up of elemental tin (Sn). The presence of tin powder in the conductive paste allows it to reduce other metal oxides, for example. These other metal oxides are those with a higher standard Gibbs free energy (Gibbs) of formation than tin oxide (SnO). For example, the standard Gibbs free energy of formation for tin oxide (SnO) is -251.82 (kJ / mol), while that of nickel oxide (NiO) is -211.7 (kJ / mol), which is higher than that of tin oxide (SnO). Therefore, the presence of tin powder in the conductive paste allows for the reduction of nickel oxide (NiO) to metallic nickel (Ni) on surfaces coated with the conductive paste, for example. Furthermore, the standard Gibbs free energy of formation for copper oxide (CuO) is -129.5 (kJ / mol), which is higher than that of tin oxide (SnO). Therefore, on surfaces coated with conductive paste, copper oxide (CuO) can also be reduced to metallic copper (Cu). As mentioned above, conductive paste may contain silver (Ag) and copper (Cu) components. However, the standard Gibbs free energy of formation for silver oxide (Ag2O) is -11.22 (kJ / mol), and the standard Gibbs free energy of formation for copper oxide (CuO) is -129.5 (kJ / mol). These are higher than the standard Gibbs free energy of formation for nickel oxide (NiO) and higher than the standard Gibbs free energy of formation for copper oxide (CuO). Therefore, neither the silver (Ag) component nor the copper (Cu) component can reduce nickel oxide (NiO) or copper oxide (CuO).

[0027] The average particle size of the tin powder is not particularly limited, but may be approximately 0.1 μm to 25 μm. From the viewpoint of realizing the effects of the technology disclosed herein, the average particle size of the tin powder is, for example, 0.3 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more. From a similar viewpoint, the average particle size of the tin powder is, for example, 20 μm or less, and preferably 15 μm or less. The shape of the particles constituting the tin powder is not particularly limited, as long as the effects of the technology disclosed herein are realized. The particles constituting the tin powder may be, for example, spherical.

[0028] The tin-containing alloy powder is composed of particles made of, for example, a tin-containing alloy. By including the tin-containing alloy powder in the conductive paste, an alloy phase can be formed between each metal component in the tin-containing alloy powder, which has been liquefied by, for example, heat treatment, and other metal components (for example, nickel or copper components contained in the internal electrodes). This can improve the connectivity between the conductive film and the parts containing other metal components.

[0029] From the viewpoint of more efficiently forming the alloy phase described above, it is preferable that the melting point of the tin-containing alloy constituting the tin-containing alloy powder is below the heat treatment temperature used when manufacturing the external electrode (for example, 400°C or below). The melting point of the tin-containing alloy may be higher than the melting point of tin, or it may be below the melting point of tin. The melting point of the tin-containing alloy may be close to the melting point of tin. Although not particularly limited, the difference between the melting point of the tin-containing alloy and the melting point of tin is preferably 10°C or more, and more preferably 15°C or more. The difference between the melting point of the tin-containing alloy and the melting point of tin is, for example, less than 120°C, preferably 110°C or less, and more preferably 100°C or less. It is more preferable that the melting point of the tin-containing alloy is below the melting point of tin.

[0030] Tin-containing alloys, for example, contain a tin component and at least one other metallic component. Examples of other metallic components include zinc (Zn), copper (Cu), nickel (Ni), silver (Ag), indium (In), and bismuth (Bi). Examples of tin-containing alloys include SnZn alloys, SnCu alloys, SnNi alloys, SnAg alloys, SnIn alloys, SnBi alloys, InSnAg alloys, SnBiAg alloys, and SnAgCu alloys.

[0031] The tin (tin component) content in the tin-containing alloy is not particularly limited, as long as the effects of the technology disclosed herein are achieved. From the viewpoint of better achieving the effects of the technology disclosed herein, the tin content relative to the total tin-containing alloy is, for example, 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, and the higher the amount, the better. Although not particularly limited, the tin content relative to the total tin-containing alloy may be less than 100% by mass, or 98% by mass or less.

[0032] The average particle size of the tin-containing alloy powder is not particularly limited, but may be approximately 0.1 μm to 25 μm. From the viewpoint of realizing the effects of the technology disclosed herein, the average particle size of the tin-containing alloy powder is, for example, 0.3 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more. From a similar viewpoint, the average particle size of the tin-containing alloy powder is, for example, 20 μm or less, preferably 15 μm or less, and more preferably 10 μm or less.

[0033] The shape of the particles constituting the tin-containing alloy powder is not particularly limited, as long as the effects of the technology disclosed herein are realized. The particles constituting the tin-containing alloy powder may be, for example, spherical.

[0034] In conductive powders, for example, from the viewpoint of improving conductivity in conductive films, it is preferable that silver-containing powder be the main component. The content of silver-containing powder when the total conductive powder is considered to be 100% by mass is generally 40% by mass or more, for example 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more. From the viewpoint of favorably realizing the effects of including tin powder, including the effects of including tin-containing alloy powder, etc., the content of silver-containing powder when the total conductive powder is considered to be 100% by mass is, for example 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less.

[0035] For example, from the viewpoint of favorably realizing the effects of including tin powder and tin-containing alloy powder, the mass ratio of tin powder to tin-containing alloy powder (tin powder:tin-containing alloy powder) is, for example, 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40.

[0036] When the entire conductive paste is considered as 100% by mass, the content of conductive powder is, for example, 60% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more, from the viewpoint of forming a conductive film of appropriate thickness. On the other hand, for example, from the viewpoint of making the conductive paste easier to apply, when the entire conductive paste is considered as 100% by mass, the content of conductive powder is preferably 95% by mass or less, and more preferably 90% by mass or less.

[0037] A thermosetting resin is a resin component that hardens through polymerization reactions, crosslinking reactions, etc., by heat treatment. The thermosetting resin can be any thermosetting resin used in this type of application without particular limitations. Examples of thermosetting resins include acrylic resins, epoxy resins, phenolic resins, polyimide resins, unsaturated polyester resins, urea resins, melamine resins, urethane resins, and imide resins. The thermosetting resin may be a single type or a combination of two or more types. In a conductive paste, when the conductive powder is 100 parts by mass, the thermosetting resin may be present in an amount of, for example, 0.5 to 20 parts by mass, preferably 1 to 15 parts by mass, more preferably 2 to 12 parts by mass, and even more preferably 3 to 10 parts by mass. The content of thermosetting resin when the entire conductive paste is considered as 100% by mass is, for example, 0.5% to 20% by mass, preferably 1% to 15% by mass, more preferably 2% to 12% by mass, and even more preferably 3% to 10% by mass.

[0038] While not particularly limited, epoxy resins are preferably used as thermosetting resins from the viewpoint of improving the strength of the conductive film. Here, epoxy resin refers to a resin having epoxy groups in its molecule, and may also contain other functional groups. By heat-treating the epoxy resin at a predetermined temperature (for example, 200°C or higher), a crosslinked network in which epoxy groups are bonded to each other can be formed. Examples of epoxy resins include naphthalene-type epoxy resins, biphenyl-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, novolac-type epoxy resins, resol-type epoxy resins, polyfunctional phenol-based epoxy resins, and dicyclopentadiene-type epoxy resins.

[0039] The conductive paste may further contain a curing agent from the viewpoint of efficiently thermosetting the thermosetting resin. The curing agent is, in this case, an organic compound having a reactive group that reacts with the thermosetting resin. For example, when the conductive paste contains an epoxy resin as the thermosetting resin, preferred curing agents include, for example, phenolic curing agents, amine curing agents, acid anhydride curing agents, polymercaptan curing agents, polyaminoamide curing agents, isocyanate curing agents, blocked isocyanate curing agents, and imidazole curing agents. The curing agent may be a single type or a combination of two or more types. In the conductive paste, when the total amount of thermosetting resin is 100 parts by mass, it is preferable that the curing agent be contained in, for example, 10 to 50 parts by mass, preferably 30 to 40 parts by mass.

[0040] The conductive paste may also contain a curing accelerator from the viewpoint of efficiently curing the thermosetting resin. Examples of curing accelerators include guanidine-based curing accelerators, amine-based curing accelerators, and imidazole-based curing accelerators. In the conductive paste, when the total amount of thermosetting resin is 100 parts by mass, the curing accelerator is preferably contained in an amount of 0.5 to 4 parts by mass, preferably 1 to 3 parts by mass.

[0041] The organic solvent is, for example, a component that disperses the conductive powder and dissolves the thermosetting resin. It is preferable that the organic solvent is removed, for example, during a drying process in the process of forming a conductive film. The organic solvent used in conductive pastes for this type of application is not particularly limited. Examples of organic solvents include glycol ether solvents such as ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (cellosolve), diethylene glycol monoethyl ether (ethyl carbitol), diethylene glycol monobutyl ether (butyl carbitol), dipropylene glycol methyl ether, and propylene glycol phenyl ether; glycol solvents such as ethylene glycol, propylene glycol, and diethylene glycol; and ethylene glycol monoethyl ether acetate (cellosolve acetate). Examples include acetate solvents such as diethylene glycol monobutyl ether acetate, dipropylene glycol methyl ether acetate, cyclohexyl acetate, propylene glycol 1-monomethyl ether 2-acetate, 3-methoxybutyl acetate, and ethylene glycol monobutyl ether acetate; ketone solvents such as isophorone, cyclohexanone, and diacetone alcohol; alcohol solvents such as terpineol, dihydroterpineol, dihydroterpinylpropionate, benzyl alcohol, 1-phenoxy-2-propanol, and 3-methyl-3-methoxybutanol; ester solvents; and hydrocarbon solvents such as toluene, xylene, n-hexane, cyclohexane, n-hexane, and mineral spirits. The organic solvent may be used alone or in combination of two or more types. While not particularly limited, the content of the organic solvent should be set to, for example, 0.5% to 20% by mass, preferably 1% to 10% by mass, when the entire conductive paste is considered to be 100% by mass.

[0042] The conductive paste may contain various additives in addition to the components described above. Conventional known additives used in this type of application may be used. Examples of additives include inorganic fillers (excluding the conductive powders described above), dispersants, surfactants, viscosity modifiers, defoamers, plasticizers, antioxidants, and pigments. When the entire conductive paste is considered as 100% by mass, the content of the additives is generally 5% by mass or less, for example, 3% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less.

[0043] The conductive paste disclosed herein can improve the electrical properties of multilayer ceramic electronic components. In this regard, the inventors have considered the following mechanism. However, the mechanism by which the effects of the disclosed technology are obtained is not intended to be limited to the following.

[0044] The conductive paste disclosed herein contains, as conductive powder, silver-containing powder, tin powder, and tin-containing alloy powder. The silver-containing powder can, for example, improve the conductivity of the conductive film. The tin powder can, for example, remove metal oxide films in the internal electrodes by reduction due to its relatively low standard Gibbs free energy of formation of tin oxide (SnO). The tin powder has a low melting point and is easily converted into a liquid phase by heat treatment. For this reason, the inclusion of tin powder in the conductive paste is preferable for more efficient removal of metal oxide films. Furthermore, the tin powder can contribute to improving the connectivity between the internal electrodes and the conductive film (external electrodes) by forming an alloy phase with the metal components contained in the internal electrodes.

[0045] The tin-containing alloy powder contains tin and other metallic components. Therefore, by including the tin-containing alloy powder, the alloy phase can be enriched with other metallic components in addition to the tin. This increases the variety of metallic components in the alloy phase, making it easier to form the alloy phase stably and improving the connectivity between the internal electrode and the conductive film (external electrode). For this reason, using the conductive paste disclosed herein makes it possible to achieve excellent electrical properties in multilayer ceramic electronic components.

[0046] The silver-containing powder may contain at least one of silver powder and silver-coated copper powder. The silver-coated copper powder may comprise copper-containing core particles and a silver-containing coating layer provided on at least a portion of the surface of the core particles. By including silver powder in the silver-containing powder, the conductivity of the conductive film can be better improved. When the silver-containing powder contains silver-coated copper powder, when the conductive paste is applied to the internal electrode, for example, the silver component ensures conductivity, and copper ions are released from the core particles, causing copper to precipitate on the surface of the internal electrode. Since copper can participate in the formation of the alloy phase described above, the variety of metallic components included in the alloy phase can be increased. This can better improve the connectivity between the internal electrode and the conductive film (external electrode).

[0047] The melting point of the tin-containing alloy constituting the tin-containing alloy powder may be below the heat treatment temperature in the manufacturing process of the external electrode (for example, below 400°C). This makes it easier to bring the tin-containing alloy into a liquid state through heat treatment. Therefore, the effects of the technology disclosed herein can be better realized.

[0048] The difference between the melting point of the tin-containing alloy and the melting point of tin may be 10°C or more. This allows for better realization of the effects described above.

[0049] The thermosetting resin may also be an epoxy resin. This allows for the imparting of desirable strength to the conductive film, thereby improving, for example, the impact resistance of multilayer ceramic electronic components.

[0050] The conductive paste disclosed herein may be used to form the external electrode of a multilayer ceramic electronic component comprising an external electrode and an internal electrode. This makes it possible to manufacture a multilayer ceramic electronic component with excellent electrical properties. Below, a method for manufacturing a multilayer ceramic capacitor (MLCC), which is an example of a multilayer ceramic electronic component, will be described. In the following description, the term "internal electrode layer" may be read as "internal electrode" as appropriate.

[0051] The manufacturing method disclosed herein includes applying a conductive paste coating to an internal electrode, drying the coating to form a dried coating, and heat-treating the dried coating. In this embodiment, the manufacturing method includes a preparation step, a coating step, and a heat treatment step.

[0052] In the preparation step, for example, the conductive paste disclosed herein is prepared. First, silver-containing powder, tin powder, tin-containing alloy powder, thermosetting resin, organic solvent, and, if necessary, a curing agent, curing accelerator, and additives are prepared. Each material is as described above. Next, each material is mixed using a mixing device to prepare the conductive paste. Any mixing device used for this type of application can be used without particular limitation. The mixing conditions may be set as appropriate.

[0053] In the coating process, for example, the conductive paste prepared in the preparation process is applied to the internal electrodes of the MLCC body (see reference numeral "10" in Figure 1, described later), which is equipped with internal electrodes. This creates a coating film of conductive paste. As for the means of applying the conductive paste, any conventionally known method used in this type of application may be employed, but for example, various printing methods such as screen printing, gravure printing, offset printing, and inkjet printing; doctor blade method; spray method; dip coating method; etc. are preferably used.

[0054] The drying process, for example, involves volatilizing the organic solvent contained in the conductive paste after the coating process to dry the coating film. This allows a dry film of conductive paste to be formed. Any drying apparatus used for this type of application can be used without particular limitations as the device for drying the coating film. The drying conditions should be set as appropriate.

[0055] The heat treatment process involves, for example, heat treatment of the MLCC body and the dried film of the conductive paste after the drying process. This hardens the thermosetting resin contained in the conductive paste, creating a conductive film (external electrode). The conditions for the heat treatment are not particularly limited and can be set appropriately depending on the application of the electronic component, the type of thermosetting resin contained in the conductive paste, etc. The heat treatment temperature should be set to, for example, the temperature at which the thermosetting resin contained in the conductive paste hardens. The heat treatment temperature can be set to, for example, 150°C to 400°C. The heat treatment time should be set to, for example, 15 minutes to 3 hours. The atmosphere during the heat treatment should be, for example, an air atmosphere, or an inert atmosphere such as a nitrogen atmosphere or a noble gas atmosphere.

[0056] The manufacturing method for multilayer ceramic electronic components disclosed herein is not limited to the embodiments described above. For example, this manufacturing method may include any additional steps besides those described above.

[0057] Figure 1 is a schematic cross-sectional view of a multilayer ceramic capacitor 1. As shown in Figure 1, the multilayer ceramic capacitor (MLCC) 1 comprises a body 10 in which dielectric layers 20 and internal electrode layers 30 are alternately and integrally stacked. The dielectric layers 20 and internal electrode layers 30 may include structures, materials, etc., of conventionally known MLCCs without particular limitations. Although not particularly limited, the internal electrode layers 30 may contain nickel or copper.

[0058] As shown in Figure 1, the MLCC1 is provided with a pair of external electrodes 40 on the side of the main body 10. In this embodiment, the external electrodes 40 include a cured film of the conductive paste disclosed herein. Therefore, the external electrodes 40 contain a resin. This resin is a cured product of a thermosetting resin contained in the conductive paste. Although not shown, a metal plating layer (e.g., a nickel plating layer, a tin plating layer, etc.) may be provided on the surface of the external electrodes 40 (in this case, the surface opposite to the main body 10).

[0059] The multilayer ceramic electronic components using the conductive paste disclosed herein are not limited to the MLCCs described above. The multilayer ceramic electronic components may also be, for example, multilayer inductors, multilayer piezoelectric elements (multilayer varistors), etc.

[0060] The following describes examples of tests relating to the technology disclosed herein, but it is not intended to limit the technology disclosed herein to these examples.

[0061] [Test 1] <Preparation of conductive paste> -Example 1- We prepared silver-containing powder, tin powder, tin-containing alloy powder, a thermosetting resin, a curing agent, a curing accelerator, and an organic solvent as conductive powders. Here, the silver-containing powder was silver powder A, which was spherical and had an average particle size of 2 μm. Silver powder A was produced by a dry process. The tin powder was spherical and had an average particle size of 2.5 μm. The tin-containing alloy powder was spherical and had an average particle size of 3.9 μm (SnAgCu powder). The SnAgCu powder contained 96.5% by mass of Sn, 3% by mass of Ag, and 0.5% by mass of Cu, and had a melting point of 217°C. Microtrac's "MT3300EX" was used to measure the average particle size of the conductive powders. The thermosetting resins were a first resin (bisphenol F type epoxy resin with an epoxy equivalent of 170 g / eq) and a second resin (novolac phenol type epoxy resin with an epoxy equivalent of 182 g / eq). The curing agent was a phenolic curing agent (novolac phenol curing agent with a phenolic hydroxyl group equivalent of 104 g / eq). The curing accelerator was 2-phenyl-4-methyl-5-hydroxymethylimidazole. The organic solvent was diethylene glycol monobutyl ether.

[0062] The prepared conductive powder, thermosetting resin, curing agent, curing accelerator, and organic solvent were mixed using a mixing device to create the paste for this example. The mass ratio of silver-containing powder, tin powder, and tin-containing alloy powder (silver-containing powder:tin powder:tin-containing alloy powder) was 70:15:15. The mass percentage of each component when the entire paste is considered as 100% by mass is shown in the corresponding column in the table.

[0063] -Example 2- As the tin-containing alloy powder, a spherical tin alloy powder (SnBiAg powder) with an average particle size of 3.4 μm was used. The SnBiAg powder contained 48% by mass of Sn, 51% by mass of Bi, and 1% by mass of Ag, and had a melting point of 138°C. Otherwise, the paste of this example was prepared using the same materials and procedure as in Example 1.

[0064] -Example 3- Neither tin powder nor tin-containing alloy powder was used. Therefore, the ratio (silver-containing powder:tin powder:tin-containing alloy powder) was 100:0:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 1.

[0065] -Example 4- Tin-containing alloy powder was not used. The ratio (silver-containing powder:tin powder:tin-containing alloy powder) was 70:30:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 1.

[0066] -Example 5- The silver-containing powder was silver powder B, which was spherical and had an average particle size of 2 μm. Silver powder B was produced by a wet process. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 1.

[0067] -Example 6- The silver-containing powder was silver powder B, which was spherical and had an average particle size of 2 μm. Silver powder B was produced by a wet process. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 2.

[0068] -Example 7- The silver-containing powder was silver powder B, which was spherical and had an average particle size of 2 μm. Silver powder B was produced by a wet process. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 3.

[0069] -Example 8- The silver-containing powder was silver powder B, which was spherical and had an average particle size of 2 μm. Silver powder B was produced by a wet process. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 4.

[0070] <Formation of test multilayer ceramic capacitors> First, a 1005-size multilayer ceramic capacitor body (capacitance: 22 nF) was prepared, and the paste of each example was applied to the portion where the internal electrode is exposed on the end face of the multilayer ceramic capacitor body. Dip coating was used as the paste application method. Next, a drying treatment was performed in a hot-air dryer to volatilize the organic solvent in the paste, thereby forming a dried paste film. The drying treatment conditions were 130° C. for 30 minutes. Next, a heat treatment was performed in a belt furnace to thermally cure the resin in the dried film, thereby forming external electrodes. The heat treatment conditions were an air atmosphere, 300° C., and 30 minutes. Next, the external electrodes were plated with Ni, followed by Sn plating. Thereby, test multilayer ceramic capacitors for each example were produced.

[0071] <Measurement of Cap Value> The initial capacitance (Cap value) of the test multilayer ceramic capacitor of each example was measured. The measurement conditions were room temperature, a frequency of 1 kHz, and a voltage of 1 V. As the measurement device, "LCR HiTester 3532-50" manufactured by Hioki E.E. Corporation was used. The number of samples for each example was 10 (n=10). The minimum value (Min), maximum value (Max), and average value (Ave) of the Cap values measured in each example are shown in the corresponding columns in the table. Note that the closer the Cap value is to the capacitance of the multilayer ceramic capacitor body (22 nF), the more excellent the electrical characteristics are.

[0072] <Measurement of D Value> The dielectric loss value (D value) of the test multilayer ceramic capacitor of each example was measured. The measurement conditions were room temperature, a frequency of 1 kHz, and a voltage of 1 V. As the measurement device, "LCR HiTester 3532-50" manufactured by Hioki E.E. Corporation was used. The number of samples for each example was 10 (n=10). The minimum value (Min), maximum value (Max), and average value (Ave) of the D values measured in each example are shown in the corresponding columns in the table. Note that the smaller the D value is, the more excellent the electrical characteristics are.

[0073]

Table 1

[0074] As shown in Table 1, in Examples 1 and 2, and Examples 5 and 6, the Cap value (average value) of the multilayer ceramic capacitor was closest to 22nF, and the D value was the smallest. Examples 1 and 2, and Examples 5 and 6 contained silver-containing powder (silver powder), tin powder, tin-containing alloy powder, thermosetting resin, and an organic solvent. From this, it was found that by using a conductive paste with this configuration, a multilayer ceramic electronic component (in this case, a multilayer ceramic capacitor) with excellent electrical properties can be realized. In Examples 1 and 2, as described above, silver powder A, which was produced by the dry method, was used. In Examples 5 and 6, as described above, silver powder B, which was produced by the wet method, was used. From this, it was found that the effect of achieving excellent electrical properties in a multilayer ceramic electronic component does not depend on the method of producing the silver powder.

[0075] [Exam 2] -Example 9- As the silver-containing powder, a spherical silver-coated copper powder with an average particle size of 2.5 μm was used. The silver-coated copper powder consisted of copper particles as core particles and a silver coating layer on the surface of the core particles. The mass ratio of silver to copper (silver:copper) in the silver-coated copper powder was 10:90. The coverage rate of the silver coating layer in the silver-coated copper powder was 98% or more and less than 100%. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 1. Next, a test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0076] -Example 10- As the silver-containing powder, a spherical silver-coated copper powder with an average particle size of 2.5 μm was used. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 2. Next, a test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0077] -Example 11- Neither tin powder nor tin-containing alloy powder was used. Therefore, the ratio (silver-containing powder:tin powder:tin-containing alloy powder) was 100:0:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 9. Next, a test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0078] -Example 12- Tin-containing alloy powder was not used. Therefore, the ratio (silver-containing powder:tin powder:tin-containing alloy powder) was 70:30:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 9. Next, a test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0079] -Example 13- Tin powder was not used. Therefore, the ratio (silver-containing powder:tin powder:tin-containing alloy powder) was 70:0:30. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 9. Next, a test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0080] -Example 14- Tin powder was not used. Therefore, the ratio (silver-containing powder:tin powder:tin-containing alloy powder) was 70:0:30. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 10. Next, a test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0081] -Example 15- As the tin-containing alloy powder, spherical tin alloy powder (SnBi powder) with an average particle size of 3.0 μm was used. The SnBi powder in this example contained 42 mass% Sn and 58 mass% Bi, and had a melting point of 139°C. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 9. Next, the test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0082] -Example 16- As the tin-containing alloy powder, spherical tin alloy powder (SnBi powder) with an average particle size of 3.1 μm was used. The SnBi powder in this example contained 72 mass% Sn and 28 mass% Bi, and had a melting point of 139°C. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 9. Next, the test multilayer ceramic capacitor for this example was prepared using the materials and procedure described above, and the Cap value and D value were calculated. The number of samples in this example was 10 (n=10). The results are shown in the corresponding column of Table 2.

[0083] [Table 2]

[0084] As shown in Table 2, the results from Examples 9 and 10, and Examples 15 and 16, indicate that the electrical characteristics of multilayer ceramic capacitors can be improved even when silver-coated copper powder is used as the silver-containing powder.

[0085] The technologies disclosed herein may include the following: Section 1: It is a conductive paste, A conductive powder containing silver-containing powder, tin powder, and tin-containing alloy powder, Thermosetting resin and Organic solvents and including, Conductive paste. Section 2: The aforementioned silver-containing powder is Silver powder; and, Silver-coated copper powder comprising copper-containing core particles and a silver-containing coating layer provided on at least a portion of the surface of the core particles; Including at least one of the following: The conductive paste of item 1. Section 3: The melting point of the tin-containing alloy constituting the aforementioned tin-containing alloy powder is 400°C or lower. A conductive paste as described in item 1 or 2. Section 4: The difference between the melting point of the tin-containing alloy and the melting point of tin is 10°C or more. A conductive paste as described in any one of items 1 to 3. Section 5: The thermosetting resin includes an epoxy resin. A conductive paste as described in any one of items 1 to 4. Item 6: Used for forming the external electrode of a multilayer ceramic electronic component having an external electrode and an internal electrode, A conductive paste as described in any one of items 1 to 5. Section 7: The internal electrode contains nickel or copper. A conductive paste as described in any one of items 1 to 6. Section 8: The external electrode contains resin, The resin is a cured product of the thermosetting resin. A conductive paste as described in any one of items 1 to 7. Section 9: External electrodes for multilayer ceramic electronic components, A hardened film of a conductive paste described in any one of items 1 to 8, external electrode. Section 10: A method for manufacturing a multilayer ceramic electronic component comprising an internal electrode and an external electrode, The internal electrode is provided with a coating of the conductive paste described in any one of items 1 to 8, The coating film is dried, and a dried film of the coating film is provided. The aforementioned dried film is subjected to heat treatment, A manufacturing method that includes this. [Explanation of Symbols]

[0086] 1. Multilayer ceramic capacitor (MLCC) 10 stacked chips 20 Dielectric layer 30 Internal electrode layer 40 External electrode

Claims

1. It is a conductive paste, A conductive powder containing silver-containing powder, tin powder, and tin-containing alloy powder, Thermosetting resin and Organic solvents and including, Conductive paste.

2. The aforementioned silver-containing powder is Silver powder; and, Silver-coated copper powder comprising copper-containing core particles and a silver-containing coating layer provided on at least a portion of the surface of the core particles; Including at least one of the following: The conductive paste according to claim 1.

3. The melting point of the tin-containing alloy constituting the aforementioned tin-containing alloy powder is 400°C or lower. The conductive paste according to claim 1.

4. The difference between the melting point of the tin-containing alloy and the melting point of tin is 10°C or more. The conductive paste according to claim 3.

5. The thermosetting resin includes an epoxy resin. The conductive paste according to claim 1.

6. Used for forming the external electrode of a multilayer ceramic electronic component having an external electrode and an internal electrode, The conductive paste according to claim 1.

7. The internal electrode contains nickel or copper. The conductive paste according to claim 6.

8. The external electrode contains resin, The resin is a cured product of the thermosetting resin. The conductive paste according to claim 6.

9. External electrodes for multilayer ceramic electronic components, A hardened film of a conductive paste according to any one of claims 1 to 8, external electrode.

10. A method for manufacturing a multilayer ceramic electronic component comprising an internal electrode and an external electrode, The internal electrode is provided with a coating of the conductive paste described in any one of claims 1 to 8, The coating film is dried, and a dried film of the coating film is provided. The aforementioned dried film is subjected to heat treatment, A manufacturing method that includes this.

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