External electrode paste, external electrode, and method for manufacturing multilayer ceramic electronic component

Abstract

Provided is a technique for improving electrical characteristics of a multilayer ceramic electronic component. The technology disclosed herein provides an external electrode paste used for forming an external electrode of a multilayer ceramic electronic component comprising the external electrode and an internal electrode. This external electrode paste includes a first conductive powder, a second conductive powder, a thermosetting resin, and an organic solvent. The first conductive powder includes copper-containing core particles and a silver-containing coating layer provided on at least a portion of the surface of the core particles. The second conductive powder is a tin powder or a tin-containing alloy powder.

Description

Paste for External Electrodes, External Electrodes, and Method for Manufacturing Multilayer Ceramic Electronic Components

[0001] The present disclosure relates to a paste for external electrodes, an external electrode, and a method for manufacturing a multilayer ceramic electronic component. This application claims priority based on Japanese Patent Application No. 2025-031151 filed on February 28, 2025, the entire content of which is incorporated herein by reference.

[0002] Japanese Patent No. 5400801 discloses a conductive paste for external electrodes of ceramic electronic components containing nickel as a main component in internal electrodes. This conductive paste contains 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 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 a paste formed by mixing an organic solvent as needed. 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 Unexamined Patent Publication 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 arranged on the end surfaces, on the first and second main surfaces, and on the first and second side surfaces, connected to the internal electrode layers. 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.

[0007] Japanese Patent Publication No. 5400801, Japanese Unexamined Patent Publication No. 2013-118357, Japanese Patent Publication No. 7528763, Japanese Patent Publication No. 5390408, Japanese Unexamined Patent Publication No. 2023-64724

[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.

[0010] The technology disclosed herein provides an external electrode paste used for forming the external electrode of a multilayer ceramic electronic component having an external electrode and an internal electrode. This external electrode paste comprises a first conductive powder, a second conductive powder, a thermosetting resin, and an organic solvent. The first conductive powder comprises copper-containing core particles and a silver-containing coating layer provided on at least a portion of the surface of the core particles. The second conductive powder is tin powder or tin-containing alloy powder. With this configuration, the electrical properties of the multilayer ceramic electronic component can be improved.

[0011] The technology disclosed herein provides an external electrode for a multilayer ceramic electronic component. The external electrode includes a cured film of the aforementioned external electrode paste. 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 aforementioned external electrode 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.

[0013] Figure 1 is a schematic cross-sectional view of a multilayer ceramic capacitor 1.

[0014] The embodiments of the technology disclosed herein will now be described. 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] As described in the prior art documents cited above, conductive pastes for forming external electrodes of multilayer ceramic electronic components may contain silver powder and a thermosetting resin. While thermosetting resins can bond the silver powder to the internal electrodes, from the viewpoint of achieving excellent electrical properties in ceramic electronic components, for example, it is desirable to increase the bonding strength between the silver powder and the internal electrodes. The inventors considered that if an alloy phase between silver and a metal (e.g., nickel, copper, etc.) contained in the internal electrodes could be formed by, for example, heat treatment, the bonding strength between the silver powder and the internal electrodes could be increased. However, it is difficult to form an alloy phase between silver and a metal contained in the internal electrodes by heat treatment at temperatures sufficient to cure thermosetting resins. Therefore, the inventors investigated the composition of the paste for external electrodes.

[0016] The technology disclosed herein provides an external electrode paste used for forming the external electrode of a multilayer ceramic electronic component having an external electrode and an internal electrode. This external electrode paste comprises a first conductive powder, a second conductive powder, a thermosetting resin, and an organic solvent. The first conductive powder comprises copper-containing core particles and a silver-containing coating layer provided on at least a portion of the surface of the core particles. The second conductive powder is tin powder or tin-containing alloy powder.

[0017] The first conductive powder and the second conductive powder are components that impart electrical conductivity to the cured film (hereinafter also referred to as the "external electrode") obtained by heat-treating the paste for the external electrode. The first conductive powder and the second conductive powder may contain unavoidable impurities generated during the manufacturing process of the powder particles, etc., in an amount of approximately 2% by mass or less (preferably 1% by mass or less, more preferably 0.5% by mass or less) of the total powder.

[0018] The first conductive powder comprises core particles and a coating layer, as described above. The core particles are, in this case, copper-containing particles. The copper-containing particles may be, for example, particles made of pure copper (Cu), or particles made of a copper-containing alloy. The copper-containing alloy is, in this case, an alloy in which the copper 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 CuSn, CuZn, CuNi, etc. It is preferable that the copper-containing alloy is an alloy in which the main component is copper. In this specification, "P is the main component of Q" means that among the components constituting Q, P has the highest content relative to the whole of Q.

[0019] The coating layer here contains silver. The 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 here 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 the main component is silver.

[0020] 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, from the viewpoint of electrical connectivity between the external electrode and the internal electrode, the coverage is approximately 40% or more of the core particle surface, 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 lower coverage rate makes the copper contained in the core particles more susceptible to oxidation, so a higher coverage rate is preferable. On the other hand, the coverage rate may be, for example, 100% or less of the core particle surface, less than 100%, 99.8% or less, 99.5% or less, or 99% or less.

[0021] The coverage rate can be calculated, for example, by using the TEM-EDX method. When the core particle is made of elemental copper and the coating layer is made of elemental silver (in the case of silver-coated copper particles), first, elemental maps of Ag and Cu elements in the cross-section of the particle to be measured are obtained based on the TEM-EDX method. Next, each elemental 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 Cu elemental map is binarized with predetermined pixel values ​​(for example, 40 to 80) and subjected to Skeletonize processing. The number of dots at a predetermined pixel value (for example, 255) in the Cu elemental map after such image processing is measured as the "area of ​​the Cu core particle LCu". Similarly, the converted Ag elemental map is binarized with predetermined pixel values ​​(for example, 40 to 255) and subjected to Skeletonize processing. The number of dots at a predetermined pixel value (e.g., 255) in the elemental map of the Ag element after such image processing is measured as the "internal area of ​​the Ag coating layer LAg". By substituting the measured LCu and LAg into the following formula (I): Coverage = (LAg / LCu) × 100 ... (I), the coverage of the Ag coating layer in a single silver-coated copper particle is calculated. The average value of the Ag coating layer coverage of any 10 particles close to the average particle size from among multiple particles can be used as the "Ag coating layer coverage". If either the core particle or the coating layer is an alloy, the elemental map can be obtained for each constituent element of the alloy, and the coverage of the coating layer can be calculated using the procedure described above. The coverage may be the nominal value of the manufacturer, etc.

[0022] 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.

[0023] The average particle size of the first conductive 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 first conductive 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 first conductive 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.

[0024] The shape of the particles constituting the first conductive powder is not particularly limited, as long as the effects of the technology disclosed herein are realized. The particles constituting the first conductive powder may be, for example, spherical. With respect to the particles constituting the first conductive powder and the particles constituting the second conductive 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 first conductive powder or the second conductive powder with an SEM, randomly selecting a plurality 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 thereof.

[0025] The second conductive powder, in this case, includes at least one of tin powder and tin-containing alloy powder. The tin powder is composed of particles consisting of, for example, elemental tin (Sn). The tin-containing alloy powder is composed of particles consisting of, for example, tin-containing alloy. By including the second conductive powder in the external electrode paste, the tin that has been liquefied by heat treatment in the external electrode manufacturing process can form an alloy phase with silver and the metal contained in the internal electrode. This increases the bonding strength between the external electrode and the internal electrode. From this viewpoint, it is preferable that the melting point of the tin-containing alloy is below the heat treatment temperature 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 even more preferable that the melting point of the tin-containing alloy is less than or equal to the melting point of tin.

[0026] 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.

[0027] 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 entire 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 entire tin-containing alloy may be less than 100% by mass, or 98% by mass or less.

[0028] The average particle size of the second conductive 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 second conductive 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 second conductive powder is, for example, 20 μm or less, and preferably 15 μm or less.

[0029] The shape of the particles constituting the second conductive powder is not particularly limited, as long as the effects of the technology disclosed herein are realized. The particles constituting the second conductive powder may be, for example, spherical.

[0030] In the paste for external electrodes, the mass ratio (first conductive powder:second conductive powder) of the first conductive powder to the second conductive powder is not particularly limited as long as the effects of the technology disclosed herein are realized. The mass ratio (first conductive powder:second conductive powder) is, for example, 90:10 to 40:60, and preferably 90:10 to 50:50.

[0031] When the entire external electrode paste is considered to be 100% by mass, the total content ratio of the first conductive powder and the second 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 an external electrode of appropriate thickness. On the other hand, for example, from the viewpoint of making the external electrode paste easier to apply, the total content ratio of the first conductive powder and the second conductive powder when the entire external electrode paste is considered to be 100% by mass is preferably 95% by mass or less, and more preferably 90% by mass or less.

[0032] A thermosetting resin is a resin component that hardens through polymerization reactions, crosslinking reactions, etc., by heat treatment. The thermosetting resin may 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 the external electrode paste, when the total amount of the first conductive powder and the second 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 external electrode 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.

[0033] While not particularly limited, epoxy resins are preferably used as thermosetting resins from the viewpoint of improving the strength of the external electrodes. 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.

[0034] The external electrode 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 external electrode paste contains epoxy resin as the thermosetting resin, examples of curing agents include phenolic curing agents, amine curing agents, acid anhydride curing agents, polymercaptan curing agents, polyaminoamide curing agents, isocyanate curing agents, blocked isocyanate curing agents, imidazole curing agents, etc. The curing agent may be a single type or a combination of two or more types. In the external electrode paste, when the total amount of thermosetting resin is 100 parts by mass, the curing agent is preferably contained in an amount of, for example, 10 to 50 parts by mass, preferably 30 to 40 parts by mass.

[0035] The paste for the external electrode may further contain a curing accelerator from the viewpoint of efficiently thermosetting the thermosetting resin. Examples of curing accelerators include guanidine-based curing accelerators, amine-based curing accelerators, and imidazole-based curing accelerators. In the paste for the external electrode, 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.

[0036] The organic solvent is, for example, a component that disperses the first conductive powder and the second conductive powder and dissolves the thermosetting resin. Preferably, the organic solvent is removed, for example, during a drying process in the process of forming the external electrode. As the organic solvent, any organic solvent used in conductive pastes used in this type of application can be used without particular limitation. 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 ethylene 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, when the entire external electrode paste is considered to be 100% by mass, the content of the organic solvent should be set to, for example, 0.5% to 20% by mass, preferably 1% to 10% by mass.

[0037] The external electrode paste may contain various additive components in addition to the above-mentioned constituent components. Conventional known additive components used in this type of application may be used. Examples of additive components include inorganic fillers (excluding the first conductive powder and the second conductive powder mentioned above), dispersants, surfactants, viscosity modifiers, defoamers, plasticizers, antioxidants, and pigments. When the entire external electrode paste is considered as 100% by mass, the content of the additive components 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.

[0038] The external electrode 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.

[0039] When the first conductive powder, the second conductive powder, the resin component, and the organic solvent are mixed, copper ions are released from the core particles of the first conductive powder due to the influence of acidic components remaining in the resin component and surface treatment agents of the first and second conductive powders. When the external electrode paste disclosed herein is applied to the internal electrode, the copper ions in the paste come into contact with the surface of the internal electrode, and the copper ions are reduced, causing copper to precipitate. Subsequently, when heat treatment is performed to cure the thermosetting resin contained in the external electrode paste, the second conductive powder melts, causing tin to become liquid. At this stage, an alloy is formed between the tin that has become liquid, the copper that was previously precipitated, the silver contained in the coating layer of the first conductive powder, and the metal (e.g., nickel, copper, etc.) contained in the internal electrode. This improves the bonding between the conductive component contained in the external electrode paste and the metal contained in the internal electrode, and also improves the bonding strength between the external electrode and the internal electrode. Therefore, by using the external electrode paste disclosed herein, excellent electrical properties can be achieved in multilayer ceramic electronic components. Furthermore, from another perspective, in the manufacturing process of multilayer ceramic electronic components, if a metal oxide film (e.g., nickel oxide film, copper oxide film, etc.) forms on the internal electrodes, the second conductive powder can promote the removal of such metal oxide films. This can contribute to improving the bonding strength between the external and internal electrodes, and consequently to achieving superior electrical properties.

[0040] The mass ratio of the first conductive powder to the second conductive powder (first conductive powder:second conductive powder) may be 90:10 to 40:60. This allows for better realization of the effects of the technology disclosed herein.

[0041] The thermosetting resin may also contain epoxy resin. This allows for desirable strength to be imparted to the external electrodes, for example, improving the impact resistance of multilayer ceramic electronic components.

[0042] The thermosetting resin may comprise a resin having a phenolic hydroxyl group, or a phenolic resin. As described above, when copper ions released from the core particles of the first conductive powder migrate to the surface of the internal electrode and copper is precipitated, for example, the precipitated copper and oxygen in the air or the like can cause an oxidative polymerization reaction of the thermosetting resin having a phenolic hydroxyl group. A reaction product generated by the oxidative polymerization reaction can be deposited, for example, in the form of a film on the surface of the internal electrode. Since such a reaction product is different from a cured product of the thermosetting resin, it can cause cracking of the external electrode or peeling of the external electrode from the internal electrode. However, since the external electrode paste disclosed herein contains the second conductive powder, the precipitated copper is used for forming the above-described alloy. This can suppress the oxidative polymerization reaction of the thermosetting resin, and consequently can suppress the occurrence of cracks, peeling, and the like in the external electrode.

[0043] The melting point of the tin-containing alloy constituting the tin-containing alloy powder may be not higher than the heat treatment temperature in the external electrode manufacturing process (for example, not higher than 400°C). This makes it easier for the tin-containing alloy to be brought into a liquid phase state by heat treatment. Therefore, the effects of the technology disclosed herein can be better achieved.

[0044] The tin-containing alloy may comprise a tin component and other metal components. The other metal component may be at least one selected from the group consisting of zinc (Zn), copper (Cu), nickel (Ni), silver (Ag), indium (In), and bismuth (Bi). This facilitates lowering the melting point of the tin-containing alloy and also facilitates forming an alloy phase with the metal contained in the internal electrode more easily.

[0045] The external electrode paste disclosed herein is used for manufacturing a multilayer ceramic electronic component including an external electrode and an internal electrode. Hereinafter, a method for manufacturing a multilayer ceramic capacitor (MLCC), which is an example of a multilayer ceramic electronic component, will be described. It should be noted that the term "internal electrode layer" in the following description may be read as "internal electrode" as appropriate.

[0046] The manufacturing method disclosed herein comprises: providing a coating film of an external electrode paste on an internal electrode; drying the coating film to provide a dried film of the coating film; and performing heat treatment on the dried film. In this embodiment, the manufacturing method includes a preparation step, an application step, and a heat treatment step.

[0047] In the preparation step, for example, an external electrode paste is prepared. First, a first conductive powder, a second conductive powder, a thermosetting resin, an organic solvent, and, as necessary, a curing agent, a curing accelerator, and additives are prepared. Each material is as described above. Next, the respective materials are mixed using a mixing device to prepare the external electrode paste. As the mixing device, any mixing device used for this type of application can be used without particular limitation. Mixing conditions may be appropriately set.

[0048] In the application step, for example, the external electrode paste prepared in the preparation step is applied to the internal electrode of an MLCC main body having an internal electrode (see reference numeral "10" in FIG. 1 described later). Thereby, a coating film of the external electrode paste can be provided. As a means for applying the external electrode paste, any conventionally known method used for this type of application may be employed. For example, various printing methods such as screen printing, gravure printing, offset printing, and inkjet printing; doctor blade method; spray method; dip coating method; and the like are preferably used.

[0049] In the drying step, for example, after the application step, the organic solvent contained in the external electrode paste is volatilized to dry the coating film. Thereby, a dried film of the external electrode paste can be provided. As an apparatus for drying the coating film, any drying apparatus used for this type of application can be used without particular limitation. Drying conditions may be appropriately set.

[0050] The heat treatment process involves, for example, heat treatment of the MLCC body and the dried film of the external electrode paste after the drying process. This hardens the thermosetting resin contained in the external electrode paste, and the external electrodes are formed. 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 external electrode paste, etc. The heat treatment temperature should be set to, for example, the temperature at which the thermosetting resin contained in the external electrode 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.

[0051] 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.

[0052] 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 laminated. The dielectric layers 20 and internal electrode layers 30 may include, without particular limitation, structures, materials, etc., of conventionally known MLCCs. Although not particularly limited, the internal electrode layers 30 may contain nickel or copper.

[0053] As shown in Figure 1, the MLCC 1 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 external electrode paste disclosed herein. Although not shown, the surface of the external electrodes 40 (in this case, the surface opposite to the main body 10) may be provided with a metal plating layer (e.g., a nickel plating layer, a tin plating layer, etc.).

[0054] The multilayer ceramic electronic components using the external electrode paste disclosed herein are not limited to the MLCC described above. The multilayer ceramic electronic components may be, for example, multilayer inductors, multilayer piezoelectric elements (multilayer varistors), etc.

[0055] The following describes test examples related to the technology disclosed herein, but it is not intended to limit the technology disclosed herein to these test examples.

[0056] [Test 1] <Preparation of Paste for External Electrode> -Example 1- A first metal powder, a second metal powder, a thermosetting resin, a curing agent, a curing accelerator, and an organic solvent were prepared. Here, the first metal powder was a spherical silver-coated copper powder with an average particle size of 2.5 μm. 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%. The second metal powder was a spherical tin powder with an average particle size of 2.5 μm. Microtrac's "MT3300EX" was used to measure the average particle size of each metal powder. The thermosetting resin consisted of a first resin (bisphenol F type epoxy resin with an epoxy equivalent of 170 g / eq) and a second resin (novolacphenol type epoxy resin with an epoxy equivalent of 182 g / eq). The curing agent was a phenolic curing agent (novolacphenol 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.

[0057] The prepared first metal powder, second metal powder, thermosetting resin, additive, and organic solvent were mixed using a mixing device to produce the paste of this example. Here, the mass ratio of the total first metal powder to the total second metal powder to the total resin components (metal powder:resin components) was 86:8. Here, the total resin components refer to the sum of the thermosetting resin, curing agent, and curing accelerator. The mass ratio of the first metal powder to the second metal powder (first metal powder:second metal powder) was 70:30. 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.

[0058] -Example 2- The second metal powder was not used. Therefore, the ratio (first metal powder:second metal powder) was 100:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 1.

[0059] -Example 3- As the first metal powder, a spherical silver 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 1.

[0060] -Example 4- The second metal powder was not used. Therefore, the ratio (first metal powder:second metal powder) was 100:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 3.

[0061] <Formation of Test Multilayer Ceramic Capacitors> First, a 1005-size multilayer ceramic capacitor body (capacitance: 22 nF) was prepared, and the paste for each example was applied to the exposed portion of the internal electrodes on the end face of the multilayer ceramic capacitor body. The paste was applied using the dip-coat method. Next, a drying treatment was performed in a hot-air dryer to volatilize the organic solvent in the paste and form a dry film of paste. The drying conditions were 130°C for 30 minutes. Next, a heat treatment was performed in a belt furnace to heat-cur the resin in the dry film and form the external electrodes. The heat treatment conditions were air atmosphere, 300°C for 30 minutes. Next, the external electrodes were Ni-plated, followed by Sn-plated. In this way, test multilayer ceramic capacitors for each example were fabricated.

[0062] <Measurement of Cap Value> The initial capacitance (Cap value) of the multilayer ceramic capacitors used for testing in each example was measured. The measurement conditions were room temperature, frequency 1 kHz, and voltage 1 V. The measurement device used was the "LCR HiTester 3532-50" manufactured by HIOKI E.E. CORPORATION. The number of samples for each example was 15 (n=15). The minimum (Min), maximum (Max), and average (Ave) 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 itself (22 nF), the better the electrical characteristics can be said to be.

[0063] <Measurement of D-value> The dielectric loss (D-value) of the multilayer ceramic capacitors used for testing in each example was measured. The measurement conditions were room temperature, frequency 1 kHz, and voltage 1 V. The measuring device used was the "LCR HiTester 3532-50" manufactured by HIOKI E.E. CORPORATION. The number of samples for each example was 15 (n=15). The minimum (Min), maximum (Max), and average (Ave) Cap values ​​measured in each example are shown in the corresponding column in the table. Note that a smaller D-value indicates better electrical characteristics.

[0064]

[0065] As shown in Table 1, in the multilayer ceramic capacitor of Example 1, the Cap value (average value) was closest to 22 nF, and the D value was the smallest. The paste in Example 1 contained silver-coated copper powder, tin powder, thermosetting resin, and an organic solvent. From this, it was found that by using an external electrode paste with such a configuration, a multilayer ceramic electronic component (in this case, a multilayer ceramic capacitor) with excellent electrical characteristics can be realized.

[0066] [Test 2] - Example 5 - The ratio (first metal powder: second metal powder) was 50:50. 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 15 (n=15). The results are shown in the corresponding column of Table 2.

[0067] -Example 6- The ratio (first metal powder:second metal powder) was 90:10. 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 15 (n=15). The results are shown in the corresponding column of Table 2.

[0068]

[0069] Table 2 shows the results for Example 1 and Example 2 for reference. From the results shown in Table 2, it was found that the electrical characteristics of the multilayer ceramic capacitor can be improved by changing the ratio of silver-coated copper powder to tin powder.

[0070] [Test 3] - Example 7 - As the second metal powder, spherical tin powder with an average particle size of 10 μm was used. The mass ratio of the total of the first and second metal powders to the resin component (metal powder:resin component) was 82:8. The mass ratio of the first metal powder to the second metal powder (first metal powder:second metal powder) was 70:30. 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. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 1. Next, external electrodes were attached to the multilayer ceramic capacitor body using the materials and procedure described above, and this was used as the test multilayer ceramic capacitor for this example. That is, in this example, neither Ni plating nor Sn plating was performed on the external electrodes. Then, the Cap value and D value were calculated for the test multilayer ceramic capacitor for this example. The number of samples in this example was 15 (n=15). The results are shown in the corresponding column in Table 3.

[0071] -Example 8- As the second metal powder, spherical tin 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 7. Next, the test multilayer ceramic capacitor for this example was prepared using the same materials and procedure as in Example 7, and the Cap value and D value were calculated. The number of samples in this example was 15 (n=15). The results are shown in the corresponding column of Table 3.

[0072] -Example 9- As the second metal powder, a spherical tin alloy powder (SnAgCu powder) with an average particle size of 3.9 μm was used. The SnAgCu powder contained 96.5 mass% Sn component, 3 mass% Ag component, and 0.5 mass% Cu component. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 7. Next, the test multilayer ceramic capacitor for this example was prepared using the same materials and procedure as in Example 7, and the Cap value and D value were calculated. The number of samples in this example was 15 (n=15). The results are shown in the corresponding column of Table 3.

[0073] -Example 10- As the second metal powder, a spherical tin alloy powder (SnBiAg powder) with an average particle size of 3.4 μm was used. The SnBiAg powder contained 48.4 mass% Sn, 51 mass% Bi, and 0.6 mass% Ag. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 7. Next, the test multilayer ceramic capacitor for this example was prepared using the same materials and procedure as in Example 7, and the Cap value and D value were calculated. The number of samples in this example was 15 (n=15). The results are shown in the corresponding column of Table 3.

[0074]

[0075] As shown in Table 3, the results from Examples 7 and 8 show that the electrical characteristics of multilayer ceramic capacitors can be improved even when using tin powders with different average particle sizes. Furthermore, the results from Examples 9 and 10 show that the electrical characteristics of multilayer ceramic capacitors can also be improved when using tin-containing alloy powder instead of tin powder.

[0076] [Test 4 (Reference Example)] - Example 11 - As the first metal powder, spherical 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 1. Next, the multilayer ceramic capacitor for this example was prepared using the same materials and procedure as in Example 7, and the Cap value and D value were calculated. The number of samples in this example was 15 (n=15). The results are shown in the corresponding column of Table 4.

[0077] -Example 12- The second metal powder was not used. Therefore, the ratio (first metal powder:second metal powder) was 100:0. Otherwise, the paste for this example was prepared using the same materials and procedure as in Example 11. Next, the test multilayer ceramic capacitor for this example was prepared using the same materials and procedure as in Example 7, and the Cap value and D value were calculated. The number of samples in this example was 15 (n=15). The results are shown in the corresponding column of Table 4.

[0078]

[0079] As shown in Table 4, the results from Examples 11 and 12 show that when the first metal powder is copper powder, it is not possible to improve the electrical characteristics of the multilayer ceramic capacitor.

[0080] The technologies disclosed herein may include the following items: Item 1: An external electrode paste used for forming the external electrode of a multilayer ceramic electronic component having an external electrode and an internal electrode, comprising: a first conductive 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; a second conductive powder comprising at least one of tin powder and tin-containing alloy powder; a thermosetting resin; and an organic solvent. Item 2: The external electrode paste according to Item 1, wherein the mass ratio of the first conductive powder to the second conductive powder (first conductive powder:second conductive powder) is 90:10 to 40:60. Item 3: The external electrode paste according to Item 1 or 2, wherein the thermosetting resin comprises an epoxy resin. Item 4: The external electrode paste according to any one of Items 1 to 3, wherein the melting point of the tin-containing alloy constituting the tin-containing alloy powder is 400°C or less. Item 5: The external electrode paste according to any one of Items 1 to 4, wherein the tin-containing alloy comprises a tin component; and another metallic component which is at least one of zinc (Zn), copper (Cu), nickel (Ni), silver (Ag), indium (In), and bismuth (Bi). Item 6: The external electrode paste according to any one of Items 1 to 5, wherein the multilayer ceramic electronic component comprises the internal electrode which comprises nickel or copper. Item 7: The external electrode paste according to any one of Items 1 to 6, wherein the external electrode comprises a resin, the resin being a cured product of the thermosetting resin. Item 8: An external electrode for a multilayer ceramic electronic component, comprising a cured film of the external electrode paste according to any one of Items 1 to 7. Item 9: A method for manufacturing a multilayer ceramic electronic component comprising an internal electrode and an external electrode, comprising: applying a coating film of an external electrode paste described in any one of Items 1 to 7 to the internal electrode; drying the coating film to provide a dried coating film; and performing heat treatment on the dried coating film.

[0081] 1 Multilayer ceramic capacitor (MLCC) 10 Multilayer chip 20 Dielectric layer 30 Internal electrode layer 40 External electrode

Claims

1. An external electrode paste used for forming the external electrode of a multilayer ceramic electronic component having an external electrode and an internal electrode, comprising: a first conductive 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; a second conductive powder comprising at least one of tin powder and tin-containing alloy powder; a thermosetting resin; and an organic solvent.

2. The paste for external electrodes according to claim 1, wherein the mass ratio of the first conductive powder to the second conductive powder (first conductive powder:second conductive powder) is 90:10 to 40:

60.

3. The external electrode paste according to claim 1, wherein the thermosetting resin comprises an epoxy resin.

4. The external electrode paste according to claim 1, wherein the melting point of the tin-containing alloy constituting the tin-containing alloy powder is 400°C or lower.

5. The external electrode paste according to claim 4, wherein the tin-containing alloy comprises a tin component; and another metallic component which is at least one of zinc (Zn), copper (Cu), nickel (Ni), silver (Ag), indium (In), and bismuth (Bi).

6. The external electrode paste according to claim 1, wherein the multilayer ceramic electronic component comprises the internal electrode containing nickel or copper.

7. The external electrode paste according to claim 1, wherein the external electrode contains a resin, and the resin is a cured product of the thermosetting resin.

8. An external electrode for a multilayer ceramic electronic component, comprising a cured film of the external electrode paste described in any one of claims 1 to 7.

9. A method for manufacturing a multilayer ceramic electronic component comprising an internal electrode and an external electrode, comprising: applying a coating film of an external electrode paste according to any one of claims 1 to 7 to the internal electrode; drying the coating film to provide a dried coating film; and performing heat treatment on the dried coating film.

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