Conductive paste, dried film, internal electrodes, and multilayer ceramic capacitors

Abstract

To provide a conductive paste for forming an internal electrode to be used in a layered ceramic electronic component, the conductive paste being capable of improving adhesion by suppressing a sheet attack and reducing the hardness of a dried film.SOLUTION: Provided is a conductive paste which contains conductive metal powder, ceramic powder, a binder resin, an additive and an organic solvent. The organic solvent contains (A) at least one selected from dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate and isobornyl isobutyrate, and (B) at least one selected from ethylene glycol monobutyl ether acetate and dipropylene glycol methyl ether acetate, and the additive contains a phosphate polyester in an amount of more than 0 mass% and equal to or less than 2.0 mass% relative to the total mass of the conductive paste.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a conductive paste, a dry film thereof, an internal electrode for a multilayer ceramic capacitor formed by firing the dry film, and a multilayer ceramic capacitor having the internal electrode.

Background Art

[0002] With the miniaturization, thinning, and shortening of electronic devices such as mobile phones and digital devices, miniaturization, high capacitance, and high performance are also desired for multilayer ceramic devices such as multilayer ceramic capacitors (hereinafter referred to as MLCCs). The most effective means for achieving these is to reduce the thickness of the internal electrode layer and the dielectric layer and increase the number of layers.

[0003] An MLCC is generally manufactured as follows. First, to form a dielectric layer, a dielectric green sheet (hereinafter also simply referred to as "green sheet") made of a dielectric ceramic powder such as barium titanate (BaTiO3) and an organic binder such as polyvinyl butyral is formed. Also, to form an internal electrode layer, a conductive paste in which conductive metal powder is dispersed in an organic vehicle containing a resin binder is prepared. After printing this conductive paste on the surface of the green sheet in a predetermined pattern, drying for removing the organic solvent is performed to form a dry film serving as the internal electrode. Next, the dry film and the green sheet are heat-pressed and integrated in a multilayer stacked state to form a pressed body. The pressed body is cut, and a de-organic binder treatment is performed at 500°C or lower in an oxidizing atmosphere or an inert atmosphere, and then heat firing is performed at about 1300°C in a reducing atmosphere so that the internal electrode is not oxidized to obtain a fired chip. Next, an external electrode paste is applied to the fired chip, and after firing, nickel plating or the like is applied on the external electrode to complete the MLCC.

[0004] However, in the above firing process, the temperature at which dielectric ceramic powder begins to sinter is around 1200°C, which is a considerable mismatch with the temperature at which sintering and shrinkage with conductive metal powder such as nickel begins. As a result, structural defects such as delamination and cracks are likely to occur. In particular, as miniaturization and high capacity are achieved, the occurrence of structural defects becomes more pronounced as the number of layers increases or as the thickness of the dielectric layer decreases.

[0005] Typically, conductive pastes used in internal electrode layers contain ceramic powders primarily composed of perovskite-type oxides such as barium titanate or strontium zirconate, which have a composition similar to that of the dielectric layer, in order to suppress premature sintering and shrinkage of the dielectric layer. This controls the sintering behavior of the conductive metal powder and prevents a mismatch in the sintering shrinkage behavior between the internal electrode layer and the dielectric layer. It also suppresses the deterioration of electrical properties, such as increased dielectric loss due to structural defects caused by significant differences between the constituent elements of the dielectric layer and the constituent elements of the dielectric powder contained in the electrode paste.

[0006] The conductive paste used in the internal electrode layer is prepared by dispersing conductive metal powder in an organic vehicle containing a binder resin, and adjusting its viscosity with an organic solvent. Generally, ethyl cellulose is used as the binder resin constituting this organic vehicle, and terpineol is generally used as the organic solvent.

[0007] However, when a conductive paste using terpineol as an organic solvent is used in combination with a green sheet that, for example, uses butyral resin as a binder resin, terpineol may remain in the coating during the printing and drying process. In this case, it can cause a dissolving effect on the butyral resin, which is commonly used as a binder resin in green sheets. This dissolving effect of the internal electrode paste on the organic binder in the green sheet is called "sheet attack."

[0008] In multilayer ceramic capacitors, "sheet attack" does not pose a practical problem when the green sheet thickness is relatively thick, such as 10-20 μm. However, when the green sheet thickness is thin, around 5 μm, if this sheet attack occurs, the butyral resin in the green sheet dissolves, causing the green sheet to swell and dissolve. This can lead to problems such as holes forming in the conductive paste printed area during the lamination of dielectric green sheets, or delamination between the dielectric layer and the internal electrode layer during firing.

[0009] Such sheet attack can reduce the dielectric strength and insulation properties of MLCCs, resulting in failure to achieve the desired capacitance or deterioration of load life characteristics. Therefore, to avoid such sheet attack, research has been conducted on materials such as organic solvents used in conductive pastes.

[0010] For example, it has been proposed to use a solvent with relatively low compatibility with butyral resin as the organic solvent used in the conductive paste for the internal electrodes (see, for example, Patent Document 1). Specifically, Patent Document 1 proposes a conductive paste using dihydroterpinyl acetate.

[0011] Furthermore, conventional conductive pastes are manufactured using, for example, cellulosic resins (e.g., ethylcellulose) as a binder resin and organic solvents such as terpineol. However, when the above-mentioned crimped body is manufactured using such a conductive paste, poor adhesion between the internal electrode layer and the dielectric layer can occur, sometimes resulting in delamination.

[0012] For example, Patent Document 2 describes an internal electrode paste containing polyvinyl butyral resin in which, when an anionic surfactant having a carboxyl group (COOH group) is used as an organic additive, the adhesion between the internal electrode layer and the dielectric layer may decrease. To improve adhesion, an internal electrode paste is proposed that contains nickel powder, ceramic powder, ethylcellulose resin, polyvinyl butyral resin, an organic solvent, and an anionic surfactant, wherein the acetal resin is contained in an amount of 1% to 2.5% by mass of the total paste amount. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Patent No. 2976268 [Patent Document 2] Japanese Patent Publication No. 2017-143202 [Overview of the project] [Problems that the invention aims to solve]

[0014] However, in recent years, with the miniaturization of electronic components, the internal electrode layers and dielectric layers of multilayer ceramic capacitors have also become thinner, and the number of layers of internal electrode layers and dielectrics has increased. Conventional technology has not been able to achieve sufficient results, and problems such as insufficient capacitance and delamination between the internal electrode layers and dielectric layers have occurred.

[0015] In view of these circumstances, the present invention aims to provide a conductive paste used in multilayer ceramic devices that can suppress sheet attack and improve the adhesion of a laminate obtained by laminating a dried film and a green sheet, and a multilayer ceramic capacitor formed using the conductive paste. [Means for solving the problem]

[0016] As a result of diligent research and development, the inventors have discovered that by appropriately specifying the type of additive in the conductive paste and its content, in addition to the combination of organic solvents, the hardness of the dried film formed from the conductive paste can be controlled. This has led to the present invention, as it is possible to suppress sheet attack on the thinned green sheet, poor adhesion of the laminate, and delamination.

[0017] In other words, a conductive paste according to one embodiment of the present invention is a conductive paste for a multilayer ceramic device comprising conductive metal powder, ceramic powder, binder resin, additives and an organic solvent, wherein the organic solvent is a mixed solvent obtained by mixing (A) at least one selected from dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate and isobornyl isobutyrate and (B) at least one selected from ethylene glycol monobutyl ether acetate and dipropylene glycol methyl ether acetate, and the additive contains phosphate polyester in an amount greater than 0% by mass and less than or equal to 2.0% by mass of the total amount of the conductive paste.

[0018] Furthermore, it is preferable that the conductive metal powder is one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and their alloys. Furthermore, it is preferable that the ceramic powder is a conductive paste of barium titanate (BaTiO3), which is a perovskite-type oxide. Furthermore, it is preferable that the ceramic powder is a perovskite-type oxide ferroelectric. In addition, the multilayer ceramic device has a dielectric layer formed using a dielectric green sheet and an internal electrode layer formed using the conductive paste, and it is preferable that the dielectric green sheet is of the same type as the ceramic powder.

[0019] Further, the conductive paste preferably has a Vickers hardness of 5 Hv or more and 11 Hv or less when measured under the following conditions in a dried film obtained by applying the conductive paste onto a green sheet containing barium titanate and polyvinyl butyral resin with a WET film thickness of 38 μm and drying it at 75° C. for 20 minutes. [[ID=G2]](Measurement conditions) Measure the Vickers hardness of the surface of the dried film under the condition of a test force of 98 mN using a micro-Vickers hardness tester.

[0020] Also, the internal electrode of the multilayer ceramic capacitor according to an embodiment of the present invention is formed using the dried film for the internal electrode.

[0021] Also, the multilayer ceramic capacitor according to an embodiment of the present invention has an internal electrode. The multilayer ceramic capacitor is a multilayer ceramic capacitor having an internal electrode layer and a dielectric layer formed using a dielectric green sheet, and the thickness of the dielectric green sheet is preferably 2 μm or less.

Advantages of the Invention

[0022] The conductive paste of the present invention can suppress sheet attack and improve the adhesion of the laminate (dried film - green sheet). Further, even when a dried film is formed by screen printing using the conductive paste on a thinned green sheet (for example, with a thickness of 2 μm or less), the multilayer ceramic capacitor formed with the internal electrode of the present invention can suppress sheet attack and very effectively suppress the occurrence of problems such as delamination due to poor adhesion of the laminate.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a perspective view and a cross-sectional view showing a multilayer ceramic capacitor according to an embodiment.

Embodiments for Carrying Out the Invention

[0024] [Conductive paste] The conductive paste of this embodiment comprises conductive metal powder, ceramic powder, binder resin, organic solvent, and additives, and is a conductive paste in which the conductive metal powder and ceramic powder are dispersed in the organic solvent, and can be suitably used in multilayer ceramic devices such as multilayer ceramic capacitors. In this specification, the organic solvent includes an organic solvent for the vehicle contained in the organic vehicle and an organic solvent for the paste used to adjust the viscosity of the conductive paste.

[0025] The conductive paste of this embodiment is a conductive paste that eliminates problems such as sheet attack, poor green sheet peeling, and interlayer delamination during laminate cutting by selecting a suitable amount of additive for a specific organic solvent.

[0026] The conductive paste of this embodiment contains conductive metal powder, ceramic powder, binder resin, additives, and organic solvents, (1) The organic solvent contains (A) at least one selected from dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate and isobornyl isobutyrate, and (B) at least one selected from ethylene glycol monobutyl ether acetate and dipropylene glycol methyl ether acetate. (2) The additive contains polyester phosphate. The following provides a detailed explanation of each component.

[0027] 1. Conductive metal powder The conductive metal powder is not particularly limited, and one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and their alloys can be used as appropriate. Among these, nickel (Ni) powder is optimal when considering conductivity, corrosion resistance, and cost. When using Ni powder, Ni powder containing several hundred ppm of sulfur (S) can be used to suppress the rapid gas generation due to the partial thermal decomposition of the binder resin during the debindering process.

[0028] As MLCCs become smaller, in order to form a thinner and finer internal electrode layer, the particle size of the metal powder is preferably 0.05 to 1.0 μm, and more preferably 0.1 to 0.5 μm, from the viewpoint of improving the smoothness and density of the dried film. If the particle size of the metal powder is less than 0.05 μm, the specific surface area of ​​the particles becomes too large, resulting in excessively high surface activity of the metal powder, which not only adversely affects drying and binder removal characteristics but also makes it difficult to obtain appropriate viscosity characteristics, potentially leading to deterioration of the conductive paste during long-term storage. Furthermore, if the particle size is larger than 1.0 μm, the film formation performance when thinning the paste coating film deteriorates, making it difficult to obtain the desired capacitance, or the smoothness of the dried film becomes insufficient, and the metal powder filling becomes insufficient, making it difficult to secure the desired dried film density. Therefore, it is undesirable as it becomes difficult to form a sufficiently thin and uniform internal electrode.

[0029] The content of conductive metal powder in the conductive paste is preferably 40 to 60% by mass, and more preferably 45 to 55% by mass. If the content is less than 40% by mass, sufficient conductivity cannot be obtained, and if the content exceeds 60% by mass, dispersibility may decrease.

[0030] 2. Ceramic powder The ceramic powder is not particularly limited and can be appropriately selected depending on the type of multilayer ceramic device to be applied. In particular, it is preferable to use a ferroelectric perovskite-type oxide, and more preferably to use barium titanate (BaTiO3, sometimes referred to as BT).

[0031] Furthermore, the ceramic powder can also be made primarily of barium titanate, with oxides (e.g., oxides of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and one or more rare earth elements) as minor components. In addition, perovskite-type oxide ferroelectric ceramic powder can be used, such as barium titanate (BaTiO3) in which the Ba or Ti atoms are substituted with other atoms, such as Sn, Pb, or Zr.

[0032] Furthermore, the ceramic powder in the conductive paste can be the same composition as the dielectric ceramic powder that constitutes the green sheet of the multilayer ceramic device. Examples of dielectric ceramic powders include oxides such as ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R(rare earth element)2O3, TiO2, and Nd2O3. Note that one type of ceramic powder may be used, or two or more types may be used.

[0033] The particle size of the ceramic powder is preferably in the range of 0.01 μm to 0.5 μm, and more preferably in the range of 0.01 μm to 0.3 μm. A particle size within this range allows for the formation of sufficiently fine, thin, and uniform internal electrodes. If the particle size of the ceramic powder is less than 0.01 μm, the specific surface area of ​​the particles becomes too large, resulting in excessively high surface activity of the ceramic powder. This not only negatively affects drying and binder removal characteristics but also makes it difficult to obtain appropriate viscosity characteristics, potentially leading to deterioration of the conductive paste during long-term storage. On the other hand, if the particle size is greater than 0.5 μm, the film-forming properties when thinning the conductive paste coating film deteriorate, making it difficult to obtain the desired capacitance or resulting in insufficient smoothness in the dried film. Furthermore, insufficient packing of the ceramic powder may result in an inability to secure the desired dried film density.

[0034] The particle size of the ceramic powder is determined from observation using a scanning electron microscope (SEM). Specifically, it is the average value (SEM average particle size) obtained by measuring the particle size of multiple individual particles from images observed with an SEM at a magnification of 50,000x.

[0035] The ceramic powder content is, for example, 1% to 20% by mass, preferably 3% to 10% by mass, relative to the total conductive paste. When the ceramic powder content is within the above range, the dispersibility and sinterability are excellent.

[0036] 3. Binder resin The binder resin is not particularly limited, and can be any cellulosic resin such as methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, or nitrocellulose, as well as acrylic resins, butyral resins, or other resins that dissolve in organic solvents. Among these, cellulosic resins and butyral resins are preferred as binder resins, with cellulosic resins being more preferred. Ethylcellulose is preferred among the cellulosic resins. Furthermore, the molecular weight of the binder resin is preferably around 20,000 to 200,000.

[0037] If the binder resin contains a cellulose-based resin (e.g., ethylcellulose), the content of the cellulose-based resin may be 30% by mass or more, 60% by mass or more, 70% by mass or more, or 100% by mass, relative to the total binder resin.

[0038] Furthermore, it is known that including a specific amount of butyral resin as a binder resin improves the adhesion strength between the green sheet and the dried film (see, for example, paragraphs

[0005] to

[0008] of Patent Document 2). However, in the conductive paste of this embodiment, as will be described later, by including phosphate polyester as an additive, the adhesion strength between the green sheet and the dried film can be sufficiently improved even when butyral resin is not included or is present in a small amount.

[0039] When the binder resin contains butyral resin, the butyral resin content may be 70% by mass or less, 40% by mass or less, or 30% by mass or less, relative to the total binder resin. The lower limit of the butyral resin is not particularly limited, but may be 5% by mass or more, or 10% by mass or more, relative to the total binder resin. When the conductive paste according to this embodiment contains butyral resin within the above range, the adhesion can be further improved.

[0040] The binder resin content is preferably 0.5% to 10% by mass, and more preferably 1% to 7% by mass, relative to the total conductive paste. When the binder resin content is within the above range, the conductivity and dispersibility are excellent.

[0041] 4. Organic solvents Organic solvents can dissolve binder resins as components of organic vehicles. Furthermore, organic solvents can disperse conductive metal powders, ceramic powders, and organic vehicles to adjust the overall viscosity of the conductive paste, enabling it to be printed in a predetermined pattern.

[0042] Furthermore, the organic solvent preferably comprises at least one acetate-based solvent (A) selected from dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, and isobornyl isobutyrate, and at least one acetate-based solvent (B) selected from ethylene glycol monobutyl ether acetate and dipropylene glycol methyl ether acetate, and more preferably a mixed solvent obtained by mixing acetate-based solvent (A) and acetate-based solvent (B). Isobornyl acetate (IBA) is preferred as acetate-based solvent (A), and ethylene glycol monobutyl ether acetate (EGBA) is preferred as acetate-based solvent (B). Using such a mixed solvent makes it easier to adjust the viscosity characteristics of the conductive paste and increases the drying speed of the conductive paste. Furthermore, by using this mixed solvent in combination with a phosphate polyester (additive), as described later, adhesion can be further improved.

[0043] The acetate solvent (A) is preferably contained in an amount of 50% to 90% by mass, more preferably 60% to 80% by mass, relative to 100% by mass of the organic solvent. The acetate solvent (B) is preferably contained in an amount of 10% to 50% by mass, more preferably 20% to 40% by mass, relative to 100% by mass of the organic solvent.

[0044] In addition to being used to adjust the viscosity of the conductive paste, organic solvents are also used to adjust the organic vehicle. For adjusting the organic vehicle, it is preferable to use the same type of organic solvent used for adjusting the viscosity of the conductive paste, for example, acetate-based solvent (A) or acetate-based solvent (B), because it improves compatibility with the organic vehicle.

[0045] Furthermore, the conductive paste may contain organic solvents other than those mentioned above. Other organic solvents added for purposes such as adjusting the viscosity of the conductive paste are not particularly limited, and commonly used organic solvents can be used as long as they do not degrade the properties of the conductive paste.

[0046] The total content of the organic solvent contained in the conductive paste can be, for example, 10% by mass or more and 50% by mass or less, preferably 20% by mass or more and 40% by mass or less, relative to the total amount of the conductive paste.

[0047] 5. Additives (Polyester phosphate) The conductive paste of this embodiment contains a phosphate polyester as an additive. A phosphate polyester is a copolymer having a phosphate group and an ester structure. The molecular weight of the phosphate polyester is not particularly limited, but is preferably 250 to 3000, more preferably 1000 to 3000, and even more preferably 1500 to 2500. The acid value of the phosphate polyester is not particularly limited, but may be, for example, 10 mg KOH / g to about 300 mg KOH / g, 50 mg KOH / g to 200 mg KOH / g, or 100 mg KOH / g to 150 mg KOH / g.

[0048] The presence of polyester phosphate in the conductive paste helps to prevent aggregation of conductive powders. Furthermore, by combining it with the specific organic solvent mentioned above and including polyphosphate ester, the dried film has appropriate flexibility, resulting in improved adhesion to the green sheet and preventing delamination when the crimped body is cut to a predetermined chip size.

[0049] The polyester phosphate is contained in the total amount of the conductive paste in an amount greater than 0% by mass and less than or equal to 2.0% by mass, preferably between 0.05% by mass and less than or equal to 1.0% by mass, and more preferably between 0.1% by mass and less than or equal to 0.5% by mass.

[0050] (Other additives) In the present invention, various additives other than polyester phosphate can be further incorporated to improve properties such as the dispersibility of the conductive powder and the viscosity of the conductive paste. Examples of commercially available additives include surfactants, chelating agents, dispersants, defoamers, plasticizers, and viscosity modifiers. The timing of adding these additives is not particularly limited, but for example, the printing properties of the conductive paste can be adjusted by incorporating and kneading them into an organic vehicle.

[0051] The additive may include, for example, a dispersant. Examples of dispersants include acidic dispersants, basic dispersants, nonionic dispersants, and amphoteric surfactants. Examples of acidic dispersants include carboxylic acid dispersants, and examples of basic dispersants include amine dispersants. Furthermore, the conductive paste does not necessarily have to contain the above-mentioned dispersants as additives. While the above-mentioned dispersants can improve the dispersibility of conductive powders and ceramic powders in the conductive paste, they do not have, or have very little effect, on controlling the plasticity of the dried film and improving adhesion, as is the case with the phosphate polyester used in this embodiment.

[0052] 6. Manufacturing method and properties of conductive paste The conductive paste of this embodiment can be manufactured by preparing the above-mentioned components and stirring and kneading them in a mixer. Alternatively, the binder resin can be dissolved in an organic solvent for the vehicle to prepare an organic vehicle, and the conductive metal powder, ceramic powder, organic vehicle, and dispersant can be added to the organic solvent for the paste, and the mixture can be stirred and kneaded in a mixer to produce the conductive paste.

[0053] The conductive paste of this embodiment preferably has a Vickers hardness of 5 Hv to 11 Hv, and more preferably 7 Hv to 9 Hv, as measured under the following conditions. When the Vickers hardness is within the above range, the resulting dried film can have appropriate flexibility and higher adhesion.

[0054] (Measurement conditions) A conductive paste is applied to a green sheet containing barium titanate and polyvinyl butyral resin to a wet film thickness of 38 μm, and then dried at 75°C for 20 minutes to obtain a dry film. The surface of the obtained dry film is measured at five or more points using a micro Vickers hardness tester under a test force of 98 mN, and the average value obtained is taken as the Vickers hardness of the conductive paste (dry film).

[0055] [Multilayer ceramic capacitors] Hereinafter, embodiments of the multilayer ceramic capacitor of the present invention will be described with reference to the drawings. In the drawings, schematic representations and changes in scale may be made as appropriate. Furthermore, the position and orientation of components will be described with reference to the XYZ Cartesian coordinate system shown in Figure 1 and other figures as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal directions, and the Z direction is vertical (up and down direction).

[0056] Figures 1A and 1B show a multilayer ceramic capacitor 1. The multilayer ceramic capacitor 1 comprises a ceramic laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and an external electrode 20.

[0057] The following describes a method for manufacturing a multilayer ceramic capacitor using the conductive paste described above. First, a conductive paste is printed onto a ceramic green sheet and dried to form a dried film. Multiple green sheets, each having this dried film on its upper surface, are laminated by pressing to obtain a laminate. The laminate is then fired to integrate it, thereby creating a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. Subsequently, a pair of external electrodes 20 are formed at both ends of the ceramic laminate 10 to manufacture a multilayer ceramic capacitor 1. A more detailed explanation follows below.

[0058] First, an unfired ceramic sheet, known as a green sheet, is prepared. This green sheet can be made, for example, by adding a binder resin such as polyvinyl butyral and a solvent such as terpineol to a predetermined ceramic raw material powder such as barium titanate, creating a dielectric layer paste. This paste is then applied in a sheet-like manner to a support film such as a PET film, dried, and the solvent removed.

[0059] The thickness of the green sheet is not particularly limited, but from the viewpoint of miniaturizing multilayer ceramic capacitors, it is preferably 0.3 μm or less, and may also be 0.2 μm or less. The lower limit of the thickness of the green sheet is, for example, 0.05 μm or more. The conductive paste of this embodiment can suppress sheet attack and improve adhesion even when a thinned green sheet is used.

[0060] Next, a conductive paste is printed and applied to one side of a green sheet, and then dried to form a dried film on one side of the green sheet. Multiple such sheets are prepared. The method for printing the conductive paste is not particularly limited, and known methods such as screen printing and gravure printing can be used, but screen printing is preferably used for printing the conductive paste in this embodiment. The thickness of the dried film formed from the conductive paste may be 1.5 μm or less, or 1 μm or less, from the viewpoint of thinning the internal electrode layer 11. The lower limit of the thickness of the dried film is not particularly limited, but for example, it is about 0.5 μm or more.

[0061] Furthermore, the dried film of this embodiment preferably has a Vickers hardness of 5 Hv to 11 Hv, and more preferably 7 Hv to 10 Hv. When the Vickers hardness is within the above range, the dried film has appropriate flexibility, and the adhesion between the dried film and the green sheet is further improved. The Vickers hardness is the average value obtained by measuring the Vickers hardness of the surface of the dried film at 5 or more points using a micro-Vickers hardness tester under a test force of 98 mN, as described in the examples below.

[0062] Next, the green sheets are peeled off the support film, and the green sheets and the dried film formed on one side of them are laminated alternately. Then, a laminate is obtained by heating and pressurizing. Alternatively, protective ceramic green sheets without conductive paste can be placed on both sides of the laminate.

[0063] Next, the laminate is cut to a predetermined size to form green chips, and then the green chips are subjected to a debinder treatment and fired in a reducing atmosphere to produce a laminated ceramic fired body (ceramic laminate 10). The atmosphere used for the debinder treatment is preferably air or an N2 gas atmosphere. The temperature used for the debinder treatment is, for example, 200°C to 400°C. Furthermore, the holding time at the above temperature during the debinder treatment is preferably 0.5 hours to 24 hours. The firing is performed in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layer, and the firing temperature of the laminate is, for example, 1000°C to 1350°C, with a holding time at the temperature of 0.5 hours to 8 hours.

[0064] By firing the green chips, the organic binder in the ceramic green sheet is completely removed, and the ceramic raw material powder is fired to form a ceramic dielectric layer 12. In addition, the organic vehicle in the dried film is removed, and nickel powder or nickel-based alloy powder is sintered or melted and integrated to form an internal electrode layer 11, and a multilayer ceramic fired body is formed in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Furthermore, from the viewpoint of incorporating oxygen into the dielectric layer to improve reliability and suppressing re-oxidation of the internal electrode, the multilayer ceramic fired body may be subjected to annealing treatment after firing.

[0065] Then, a multilayer ceramic capacitor 1 is manufactured by providing a pair of external electrodes 20 to the fabricated multilayer ceramic firing body. For example, the external electrodes 20 comprise an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Suitable materials for the external electrodes 20 include, for example, copper, nickel, or alloys thereof. Electronic components other than multilayer ceramic capacitors can also be used. [Examples]

[0066] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited in any way by the examples.

[0067] [Properties of conductive paste] The properties of the dried film obtained from the conductive paste were evaluated under the following conditions.

[0068] (1) Seat attack properties A conductive paste was printed onto the surface of a 2 μm thick green sheet (containing barium titanate (BT) and polyvinyl butyral) to a wet film thickness of 38 μm. The sheet was dried at 75°C for 20 minutes to obtain a sheet (dried film sheet) with a dried film formed on the green sheet. Immediately after the formation of the dried film sheet, the back surface of the dried film sheet was observed under a microscope. If the swelling phenomenon characteristic of sheet attack was not observed, it was evaluated as ○ (good sheet attack properties); if it was observed, it was evaluated as × (poor sheet attack properties).

[0069] (2) Dry film hardness A conductive paste was applied to a 4.5 μm thick green sheet (containing barium titanate (BT) and polyvinyl butyral) to a wet film thickness of 38 μm, and dried at 75°C for 20 minutes to obtain a dried film sheet. The Vickers hardness of the surface of the dried film sheet formed in this way was measured at n=5 points using a micro Vickers hardness tester (HMV-G21DT) manufactured by Shimadzu Corporation under a test force of 98 mN, and the average value was calculated.

[0070] (3) Adhesion A conductive paste (sample) was applied to the surface of a pre-prepared green sheet containing barium titanate and polyvinyl butyral to form a conductive paste film with a wet thickness of 38 μm. The resulting green sheet and the conductive paste film formed on its surface for internal electrodes were dried at 75°C for 20 minutes to obtain a sheet with a dried film formed on the green sheet (dried film sheet). The dried film sheet and another green sheet were stacked so that the side with the conductive paste applied (the side with the dried film) was sandwiched between the green sheets, and then pressed at 40°C and 20 MPa for 20 seconds to create a laminate (for evaluation).

[0071] After cutting the obtained laminate into 1 cm squares, both sides of the laminate were set in jigs on a tensile testing machine (Shimadzu Corporation, AGS-50NX) using tape, and then a tensile test was performed. At a test speed of 20 mm / min, if delamination occurred at the interface between the green sheet and the conductive paste dry film when tension was applied, it was evaluated as "×", and if tension could be maintained without delamination until the tape peeled off, it was evaluated as "〇".

[0072] [Materials used] (conductive metal powder) Nickel powder (particle size 0.2 μm) was used as the conductive metal powder.

[0073] (Ceramic powder) Barium titanate (BT) was used as the ceramic powder.

[0074] (Organic Vehicle) Organic vehicles 1 and organic vehicle 2 were used. Organic vehicle 1 was prepared by mixing ethyl cellulose (EC) as a binder resin and isobornyl acetate as an organic solvent in a predetermined ratio (resin:organic solvent = 20:80, by weight) and heating and mixing at 60°C. Organic vehicle 2 was prepared by mixing polyvinyl butyral (PVB) as a binder resin and isobornyl acetate as an organic solvent in a predetermined ratio (resin:organic solvent = 15:85, by weight), and heating and mixing at 60°C.

[0075] Furthermore, organic vehicles 1' and 2' were prepared by replacing the organic solvent in organic vehicles 1 and 2 with terpineol (TPO).

[0076] (Organic solvents) Organic solvent 1 was isobornyl acetate (acetate-based solvent (A)), and organic solvent 2 was ethylene glycol monobutyl ether acetate (acetate-based solvent (B)).

[0077] (Additives) The additive used was a phosphate polyester with a molecular weight between 250 and 3000.

[0078] (Example 1) As shown in Table 1, a conductive paste was prepared by dissolving 51.0% by mass of nickel powder (Ni) with a particle size of 0.2 μm as a conductive metal powder, 7.7% by mass of barium titanate (BT) with a particle size of 0.05 μm as a ceramic powder, 10.1% by mass of the aforementioned organic vehicle 1, 4.3% by mass of organic vehicle 2, and 0.1% by mass of polyester phosphate in a mixed solvent of 21.4% by mass of organic solvent 1 and 5.4% by mass of organic solvent 2.

[0079] (Example 2) As shown in Table 1, a conductive paste was prepared by dissolving 51.0% by mass of nickel powder (Ni) with a particle size of 0.2 μm as a conductive metal powder, 7.7% by mass of barium titanate (BT) with a particle size of 0.05 μm as a ceramic powder, 10.1% by mass of the aforementioned organic vehicle 1, 4.3% by mass of organic vehicle 2, and 0.3% by mass of polyester phosphate in 21.2% by mass of organic solvent 1 and 5.4% by mass of organic solvent 2.

[0080] (Example 3) As shown in Table 1, a conductive paste was prepared by dissolving 51.0% by mass of nickel powder (Ni) with a particle size of 0.2 μm as a conductive metal powder, 7.7% by mass of barium titanate (BT) with a particle size of 0.05 μm as a ceramic powder, 10.1% by mass of the aforementioned organic vehicle 1, 4.3% by mass of organic vehicle 2, and 0.5% by mass of polyester phosphate in 21.0% by mass of organic solvent 1 and 5.4% by mass of organic solvent 2.

[0081] (Comparative Example 1) As shown in Table 1, a conductive paste was prepared by dissolving 51.0% by mass of nickel powder (Ni) with a particle size of 0.2 μm as a conductive metal powder, 7.7% by mass of barium titanate (BT) with a particle size of 0.05 μm as a ceramic powder, 10.1% by mass of the aforementioned organic vehicle 1, and 4.3% by mass of organic vehicle 2 in 21.5% by mass of organic solvent 1 and 5.4% by mass of organic solvent 2.

[0082] (Comparative Example 2) As shown in Table 1, a conductive paste was prepared by dissolving 51.0% by mass of nickel powder (Ni) with a particle size of 0.2 μm as a conductive metal powder, 7.7% by mass of barium titanate (BT) with a particle size of 0.05 μm as a ceramic powder, 10.1% by mass of the aforementioned organic vehicle 1', 4.3% by mass of organic vehicle 2', and 0.5% by mass of polyester phosphate in 26.4% by mass of terpineol.

[0083] Table 1 shows the component compositions of Examples 1-3 and Comparative Examples 1-2, and Table 2 shows the evaluation results.

[0084] [Table 1]

[0085] [Table 2]

[0086] (Evaluation results) As is clear from Tables 1 and 2, in Examples 1 to 3 using the conductive paste of this embodiment, there was no sheet attack, the film hardness was low, and the adhesion was improved.

[0087] On the other hand, in Comparative Example 1, which does not contain polyester phosphate, no sheet attack phenomenon was observed, but the film hardness was high and the adhesion was low. Furthermore, in Comparative Example 2, which uses an organic solvent other than that of this embodiment, although the film hardness is relatively low because it contains polyester phosphate, sheet attack occurred and the adhesion was reduced.

[0088] From the above, it can be seen that the conductive paste of this embodiment, by using a specific organic solvent and containing a specific amount of polyester phosphate, can prevent sheet attack and improve adhesion, representing a significant improvement over conventional products. [Industrial applicability]

[0089] The conductive paste of the present invention can suppress problems such as delamination due to poor adhesion of the laminate in the manufacturing process of multilayer ceramic capacitors using thin-film green sheets, and can be suitably used as a raw material for internal electrodes of multilayer ceramic capacitors, which are chip components of electronic devices such as mobile phones and digital devices. [Explanation of symbols]

[0090] 1. Multilayer ceramic capacitor 10 Ceramic Laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 Plating layer

Claims

1. A conductive paste for multilayer ceramic devices comprising conductive metal powder, ceramic powder, binder resin, additives and organic solvent, The organic solvent comprises (A) at least one selected from dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate and isobornyl isobutyrate, and (B) at least one selected from ethylene glycol monobutyl ether acetate and dipropylene glycol methyl ether acetate. A conductive paste wherein the additive contains polyester phosphate in an amount greater than 0% by mass and less than or equal to 2.0% by mass of the total amount of the conductive paste.

2. The conductive paste according to claim 1, wherein the conductive metal powder consists of one metal powder selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof.

3. The ceramic powder is a perovskite-type oxide, barium titanate (BaTiO ３ The conductive paste according to claim 1, wherein the conductive paste is as described in claim 1.

4. The conductive paste according to claim 1, wherein the ceramic powder is a perovskite-type oxide ferroelectric.

5. The conductive paste according to claim 1, wherein the multilayer ceramic device has a dielectric layer formed using a dielectric green sheet and an internal electrode layer formed using the conductive paste, and the dielectric ceramic powder contained in the dielectric green sheet and the ceramic powder contained in the conductive paste are powders of the same composition.

6. The conductive paste according to claim 1, wherein the conductive paste is applied to a green sheet containing barium titanate and polyvinyl butyral resin to a wet film thickness of 38 μm, and dried at 75°C for 20 minutes, and the dried film obtained has a Vickers hardness of 5 Hv or more and 11 Hv or less, as measured under the following conditions. (Measurement conditions) The Vickers hardness of the surface of the dried film is measured using a micro-Vickers hardness tester under a test force of 98 mN.

7. A dried film for the internal electrodes of a multilayer ceramic capacitor formed using the conductive paste described in claim 1.

8. Internal electrode of a multilayer ceramic capacitor using the dried film for internal electrodes described in claim 7.

9. A multilayer ceramic capacitor having internal electrodes as described in claim 8.

10. A multilayer ceramic capacitor having an internal electrode layer as described in claim 8 and a dielectric layer formed using a dielectric green sheet, wherein the thickness of the dielectric green sheet is 3 μm or less, as described in claim 9.

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