Conductive pastes, electronic components, and multilayer ceramic capacitors

Abstract

The present invention provides a conductive paste that sufficiently suppresses the aggregation of conductive powder within the conductive paste and exhibits sufficiently high film surface smoothness after drying. [Solution] A conductive paste comprising conductive powder, ceramic powder, binder resin, and organic solvent, wherein an organic titanate compound having a phosphate group as a functional group is attached to at least a portion of the surface of the conductive powder.

Description

Technical Field

[0001] The present disclosure relates to a conductive paste, an electronic component, and a multilayer ceramic capacitor. In particular, the present disclosure relates to a conductor constituting an electronic component, particularly a conductive paste used to form an internal electrode of a multilayer ceramic capacitor, and an electronic component having a conductor formed using this conductive paste or a multilayer ceramic capacitor provided with an internal electrode.

Background Art

[0002] With the miniaturization and high performance of electronic devices such as mobile phones and digital devices, miniaturization and high capacitance are desired for electronic components including multilayer ceramic capacitors. A multilayer ceramic capacitor has a structure in which a plurality of dielectric layers and a plurality of internal electrode layers are alternately laminated, and by thinning these dielectric layers and internal electrode layers, it is possible to achieve its miniaturization and high capacitance.

[0003] A multilayer ceramic capacitor is manufactured, for example, as follows. First, a conductive paste for an internal electrode is printed on the surface of a dielectric green sheet containing a dielectric powder such as barium titanate (BaTiO3) and a binder resin in a predetermined electrode pattern and dried to form a dry film. Next, a laminate is obtained by laminating the dry film and the green sheet so as to alternately overlap. Next, this laminate is heat-bonded and integrated to form a bonded body. This bonded body is cut, and after performing a debinding treatment in an oxidizing atmosphere or an inert atmosphere, firing is performed to obtain a fired chip. Then, an external electrode paste is applied to both ends of the fired chip, and after firing, nickel plating or the like is applied to the surface of the external electrode to obtain a multilayer ceramic capacitor.

[0004] However, in the firing process to obtain fired chips, there is a considerable mismatch (a temperature difference exists) between the temperature at which dielectric ceramic powder begins to sinter (around 1200°C) and the temperature at which metal powders such as nickel begin to sinter and shrink. As a result, multilayer ceramic capacitors have a problem in that structural defects such as delamination and cracks are prone to occur.

[0005] With the miniaturization and increased capacitance of multilayer ceramic capacitors, for example, thinning of the electrode film to be dense and continuous for conductive paste and internal electrodes using it, and increasing the dielectric constant and thinning the dielectric layer for ceramic dielectric materials and dielectric layers using it have been investigated, and dielectric layers with a thickness of 2.0 μm or less have already been put into practical use. Furthermore, the thickness of the internal electrode layer is required to be 1.0 μm or less.

[0006] Thus, as multilayer ceramic capacitors become smaller and higher in capacitance, the occurrence of structural defects becomes more pronounced as the number of layers increases or as the thickness of the ceramic dielectric layer decreases.

[0007] Furthermore, with the recent trend towards thinner internal electrode layers, conductive powders also tend to have smaller particle sizes. When conductive powder particles are small, the specific surface area of ​​the particle surface increases, which increases the surface activity of the conductive powder (metal powder). This can lead to the powder becoming more prone to aggregation and reduced dispersibility.

[0008] One of the characteristics required to achieve a thin internal electrode layer that is dense and has excellent continuity is that the dried nickel paste film for the internal electrodes does not have any protrusions that penetrate the dielectric green sheet. This is because, as the capacitance increases, the thickness of the dielectric layer decreases, so the smoothness of the dried nickel paste film for the internal electrodes must be improved. In other words, if the thickness of the dielectric green sheet is thinner than the height of the protrusions in the dried conductive paste film for the internal electrodes, the protrusions will penetrate the ceramic green sheet, causing a short circuit between the electrode films, which will reduce the reliability and yield of the capacitor.

[0009] To solve these problems, for example, Japanese Patent Publication No. 2003-249121 proposes a method for controlling the drying rate, expressed as the relative evaporation rate, within an appropriate range in order to suppress unevenness on the surface of the printed coating film.

[0010] Furthermore, the conductive paste used to form the internal electrode layer of a multilayer ceramic capacitor contains conductive powder, ceramic powder, binder resin, and organic solvent. However, to improve the dispersibility of the conductive powder, the conductive paste may also contain a dispersant. In addition, from the viewpoint of improving the dispersibility of the conductive powder, a dispersant may be attached to the surface of the conductive powder. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2003-249121 [Overview of the project] [Problems that the invention aims to solve]

[0012] However, in Japanese Patent Publication No. 2003-249121, the solvent selected for the purpose of controlling the relative evaporation rate was only considered in relation to the solubility with the binder resin used. In conductive pastes using these solvents and binder resins, it may not be possible to control the aggregation of conductive powder (metal powder).

[0013] Furthermore, when using methods such as adding a dispersant to a conductive paste or attaching a dispersant to the surface of conductive powder, as the particle size of the conductive powder decreases, the specific surface area of ​​the conductive powder increases, which inevitably leads to an increase in the proportion of dispersant added or attached. However, increasing the amount of dispersant added can lead to a decrease in the viscosity of the conductive paste, or if sufficient dispersant cannot be added, the viscosity of the conductive paste may change over time after manufacturing.

[0014] This disclosure is proposed in view of the above circumstances and aims to provide a conductive paste that sufficiently suppresses the aggregation of conductive powder in the conductive paste and has sufficiently high film surface smoothness after drying, as well as electronic components and multilayer ceramic capacitors using this paste. [Means for solving the problem]

[0015] A conductive paste according to one aspect of this disclosure is A conductive paste comprising conductive powder, ceramic powder, binder resin, and organic solvent, An organic titanate compound having a phosphate group as a functional group is attached to at least a portion of the surface of the conductive powder. It is characterized by the following:

[0016] Preferably, the organic titanate compound contains at least one of bis(dioctyl pyrophosphate) oxyacetate titanate, isopropyl tris(dioctyl pyrophosphate) titanate, or bis(dioctyl pyrophosphate) ethylene titanate.

[0017] It is preferable that the organotitanate compound is contained in the conductive paste at 0.25 mass% or more and 2.0 mass% or less.

[0018] The binder resin preferably contains ethyl cellulose having a mass average molecular weight of 30,000 or more and 150,000 or less and an ethoxy group content of 45 mass% or more and 50 mass% or less.

[0019] The number average particle diameter of the conductive powder is preferably 0.02 μm or more and 0.4 μm or less.

[0020] The conductive powder preferably contains at least one metal powder selected from Ni, Pd, Pt, Au, Ag, Cu, or an alloy thereof.

[0021] The number average particle diameter of the ceramic powder is preferably 0.01 μm or more and 0.1 μm or less.

[0022] The ceramic powder preferably contains a perovskite-type oxide.

[0023] For the dried film obtained by applying the conductive paste of one aspect of the present disclosure to a glass plate so that the wet film thickness is 10 μm and then drying the glass plate in an oven set at 120 °C for 20 minutes, the roughness is randomly measured at 5 locations in a measurement range of 200 μm × 250 μm using a laser microscope, and it is preferable that the average value of the obtained values is 0.095 μm or less.

[0024] An electronic component of one aspect of the present disclosure is an electronic component including at least a conductor, wherein the conductor is formed using the conductive paste of one aspect of the present disclosure.

[0025] A multilayer ceramic capacitor of one aspect of the present disclosure is a multilayer ceramic capacitor having at least a laminate in which a dielectric layer and an internal electrode layer are laminated, wherein the internal electrode layer is formed using the conductive paste of one aspect of the present disclosure.

Advantages of the Invention

[0026] According to one aspect of the present disclosure, a conductive paste is provided in which aggregation of conductive powder in the conductive paste is sufficiently suppressed, and the film surface smoothness after drying is sufficiently high.

[0027] Therefore, by using the conductive paste of one aspect of the present disclosure, it is possible to further thin the electrode pattern including the conductor of the electronic component or the internal electrode of the multilayer ceramic capacitor, and it is possible to improve the productivity thereof.

Brief Description of the Drawings

[0028] [Figure 1] FIG. 1 is a perspective view (FIG. 1A) and a cross-sectional view (FIG. 1B) showing a multilayer ceramic capacitor as an example of an embodiment of the present disclosure.

Modes for Carrying Out the Invention

[0029] The inventors of the present disclosure have intensively studied to solve the above-described problems. As a result, by attaching an organic titanate compound having a phosphate group as a functional group to at least a part of the surface of the conductive powder, in a conductive paste containing ceramic powder, a binder resin, and an organic solvent, it is possible to maintain high dispersibility of the conductive powder, and it has been found that the smoothness of the unevenness on the surface of the printed coating film and further the smoothness of the film surface after drying can be maintained, and the present disclosure has been completed.

[0030] [Conductive Paste] A conductive paste as an example of an embodiment of the present disclosure includes conductive powder, ceramic powder, a binder resin, and an organic solvent, and an organic titanate compound having a phosphate group as a functional group is attached to at least a part of the surface of the conductive powder.

[0031] Hereinafter, each component constituting the conductive paste of this example will be described in detail.

[0032] (conductive powder) The conductive powder is not particularly limited, and any metal powder applicable to the conductive paste application can be used. For example, at least one metal powder selected from Ni, Pd, Pt, Au, Ag, Cu, or alloys thereof can be used as the conductive powder.

[0033] Among these, metal powder made of Ni or a Ni alloy is preferred from the viewpoint of conductivity, corrosion resistance, and cost. As the Ni alloy, for example, an alloy of Ni with at least one element selected from the group consisting of Mn, Cr, Co, Al, Fe, Cu, Zn, Ag, Au, Pt, or Pd can be used. The Ni content in the Ni alloy is, for example, 50% by mass or more, preferably 80% by mass or more. The metal powder made of Ni or a Ni alloy may contain several hundred ppm of sulfur to suppress rapid gas generation due to partial thermal decomposition of the binder resin during the debindering process.

[0034] The number-average particle size of the conductive powder is preferably 0.02 μm or more and 0.4 μm or less, and more preferably 0.05 μm or more and 0.2 μm or less. When the average particle size of the conductive powder is within the above range, it can be suitably used as a conductive paste for the internal electrodes of thin-film multilayer ceramic capacitors, and for example, it is possible to improve the smoothness and density of the dried film.

[0035] The number-average particle size of conductive powder is a value obtained from observation using a scanning electron microscope (SEM). It is the average value obtained by measuring the particle size of multiple particles from an image observed with an SEM at a magnification of 10,000x.

[0036] The conductive powder content is preferably 40% to 65% by mass, and more preferably 45% to 60% by mass, relative to the total conductive paste. When the conductive powder content is within the above range, the conductivity and dispersibility are excellent.

[0037] (Organotitanate compounds) In this example of conductive paste, an organic titanate compound having a phosphate group as a functional group is attached to at least a portion of the surface of the conductive powder.

[0038] Organic titanate compounds, which have a phosphate group as a functional group, have a structure in which an organic functional group containing a phosphate group is bonded to a titanium atom.

[0039] Organic titanate compounds, which possess a phosphate group as a functional group, exhibit unique reactivity with various inorganic and organic substances and are used as modifiers for plastics, metals, glass, coatings, and other materials. In relation to conductive powders, organic titanate compounds with a phosphate group function as modifiers, and their adhesion to the surface of the conductive powder maintains high dispersibility of the conductive powder in the conductive paste, thereby sufficiently suppressing aggregation and achieving high film surface smoothness after drying.

[0040] The organic titanate compound, which has a phosphate group as a functional group, only needs to be attached to at least a portion of the surface of the conductive powder; it does not need to cover the entire surface of the conductive powder. However, the organic titanate compound can also be attached to the entire surface of the conductive powder.

[0041] Furthermore, while applying an organic titanate compound equipped with a phosphate group as a functional group can improve the dispersibility of conductive powders and ceramic powders, it does not sufficiently improve the smoothness of the film surface after drying.

[0042] Organic titanate compounds having a phosphate group as a functional group are not particularly limited as long as they have a phosphate group as a functional group, and known organic titanate compounds can be used. Preferably, such organic titanate compounds include at least one of bis(dioctyl pyrophosphate)oxyacetate titanate, isopropyltris(dioctyl pyrophosphate) titanate, or bis(dioctyl pyrophosphate)ethylene titanate.

[0043] In this case, the organic titanate compound having a phosphate group as a functional group may include at least one of bis(dioctyl pyrophosphate) oxyacetate titanate, isopropyl tris(dioctyl pyrophosphate) titanate, or bis(dioctyl pyrophosphate) ethylene titanate, or any two of these, or all of these.

[0044] The amount of organic titanate compound having a phosphate group as a functional group added to the conductive paste is 0.25% by mass or more and 2.0% by mass or less, preferably 0.3% by mass or more and 1.5% by mass or less, and more preferably 0.5% by mass or more and 1.0% by mass or less. When the organic titanate compound is included within the above range, it is possible to achieve high surface smoothness in the film after drying. However, if the amount of organic titanate compound added exceeds 2.0% by mass, the organic titanate compounds may interact with each other, which may cause aggregation.

[0045] An organic titanate compound having a phosphate group as a functional group can be attached to a portion of the surface of a conductive powder by kneading the organic titanate compound with the conductive powder beforehand prior to the manufacture of the conductive paste. Because the organic titanate compound forms strong chemical bonds, such as covalent or ionic bonds, with the conductive powder and is adsorbed onto the metal surface, the organic titanate compound does not detach from the surface of the conductive powder during the subsequent manufacturing process of the conductive paste.

[0046] (Ceramic powder) The ceramic powder is not particularly limited, and for example, in the case of a conductive paste for the internal electrodes of a multilayer ceramic capacitor, it is appropriately selected from known ceramic powders depending on the type of multilayer ceramic capacitor to be applied. Examples of ceramic powders include perovskite-type oxides containing Ba and Ti, and barium titanate (BaTiO3) is preferred.

[0047] As the ceramic powder, a ceramic powder mainly composed of barium titanate and containing oxides as minor components may be used. Examples of oxides include oxides of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, or one or more rare earth elements. Alternatively, as the ceramic powder, a perovskite-type oxide ferroelectric ceramic powder may be used in which the Ba or Ti atoms of barium titanate (BaTiO3) are substituted with other atoms, such as Sn, Pb, or Zr.

[0048] In conductive paste for internal electrodes, a ceramic powder with the same composition as the dielectric ceramic powder constituting the green sheet of a multilayer ceramic capacitor can be used as the ceramic powder. This suppresses crack generation due to a mismatch in shrinkage at the interface between the dielectric layer and the internal electrode layer during the sintering process. Examples of such ceramic powders include oxides of ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R(rare earth element)2O3, and TiO2. One type of ceramic powder may be used, or two or more types may be used.

[0049] The number-average particle size of the ceramic powder is, for example, 0.01 μm or more and 0.1 μm or less, preferably in the range of 0.01 μm or more and 0.07 μm or less. Because the average particle size of the ceramic powder is within this range, when used as a conductive paste for internal electrodes, it is possible to form sufficiently fine, thin, and uniform internal electrodes.

[0050] The number-average particle size of ceramic powder is a value obtained from observation using a scanning electron microscope (SEM). It is the average value obtained by measuring the particle size of multiple particles from an image observed with an SEM at a magnification of 50,000x.

[0051] The ceramic powder content is preferably 1 to 30 parts by mass, and more preferably 3 to 30 parts by mass, per 100 parts by mass of conductive powder.

[0052] The ceramic powder content is preferably 1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 20% by mass or less, relative to the entire conductive paste.

[0053] When the ceramic powder content is within the above range, it exhibits excellent conductivity and dispersibility.

[0054] (Binder resin) In the conductive paste of this example, the binder resin contains ethyl cellulose having a mass-average molecular weight of 30,000 to 150,000 and an ethoxy group content of 45% to 50% by mass.

[0055] The inclusion of ethyl cellulose in the binder resin allows for high surface smoothness in the dried film. Furthermore, although there is a firing process in the process of processing the conductive paste into internal electrodes, the residual carbon content after firing does not increase excessively, ensuring sufficient printability.

[0056] Furthermore, if the mass-average molecular weight of ethylcellulose is less than 30,000, it may be difficult to obtain sufficient viscosity for printing. Also, if the mass-average molecular weight of ethylcellulose is greater than 150,000, the resulting conductive paste may become thicker, potentially resulting in poor printability.

[0057] Furthermore, if the ethoxy group content of ethylcellulose is in the range of 45% to 50% by mass, it exhibits excellent compatibility with organic solvents and good solubility, thus enabling high surface smoothness in the dried film. More preferably, the ethoxy group content of ethylcellulose is 47% to 50% by mass.

[0058] As the binder resin, ethylcellulose alone may be used, but other binder resins may also be included. For example, in addition to ethylcellulose, cellulosic resins such as methylcellulose, ethylhydroxyethylcellulose, and nitrocellulose, acrylic resins, and butyral resins such as polyvinyl butyral can be used. One type of these resin may be used, or two or more types may be used.

[0059] Of these, it is preferable to use at least one selected from methylcellulose, ethyl hydroxyethylcellulose, nitrocellulose, or polyvinyl butyral. For example, when the conductive paste is used for the internal electrodes of a multilayer ceramic capacitor, it is preferable to include polyvinyl butyral from the viewpoint of improving the adhesive strength with the green sheet.

[0060] In a binder resin comprising at least one selected from methylcellulose, ethyl hydroxyethylcellulose, nitrocellulose, or polyvinyl butyral, the mass-average molecular weight is preferably, for example, 20,000 or more and 300,000 or less.

[0061] If the mass-average molecular weight is less than 20,000, it becomes difficult to obtain sufficient viscosity for printing. A more preferable lower limit for the mass-average molecular weight is 30,000.

[0062] If the mass-average molecular weight is 30,000 or higher, sufficient printability can be ensured without increasing the residual carbon content. On the other hand, if the mass-average molecular weight exceeds 300,000, the resulting conductive paste may become thicker, potentially worsening its printability. If the mass-average molecular weight is 300,000 or less, a conductive paste with excellent printability can be obtained while ensuring compatibility with ethylcellulose. The preferred upper limit for the mass-average molecular weight of binder resins other than ethylcellulose depends on factors such as the mixing ratio with ethylcellulose, but setting it to 300,000 or less makes it possible to reduce residual carbon after firing.

[0063] When the binder resin includes a resin other than ethylcellulose, it is preferable that the mass ratio of ethylcellulose to the other resin be 30-70:70-30.

[0064] The binder resin content is preferably 1 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of conductive powder.

[0065] The binder resin content is preferably 0.5% to 10% by mass, and more preferably 1% to 6% by mass, relative to the total conductive paste.

[0066] When the binder resin content is within the above range, it exhibits excellent conductivity and dispersibility.

[0067] (Organic solvents) The organic solvent has the function of dissolving the binder resin and adjusting the viscosity of the conductive paste. Preferably, the boiling point of the organic solvent is above 100°C. If the boiling point of the organic solvent is below 100°C, there is a risk that the organic solvent will evaporate during the manufacturing of the conductive paste.

[0068] The organic solvent is not particularly limited, and any known organic solvent capable of dissolving the binder resin can be used. Examples of organic solvents include acetate-based solvents such as dihydroterpinyl acetate, isobornyl acetate, isobornyl propinate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, and dipropylene glycol methyl ether acetate; terpene-based solvents such as terpineol and dihydroterpineol; and saturated aliphatic hydrocarbon-based solvents such as tridecane, nonane, and cyclohexane.

[0069] Furthermore, one type of organic solvent may be used, or two or more types may be used.

[0070] The content of the organic solvent (amount added during preparation) is not particularly limited and can be arbitrarily selected depending on the viscosity required for the conductive paste.

[0071] For example, the content of the organic solvent is preferably 40 parts by mass or more and 100 parts by mass or less, and more preferably 65 parts by mass or more and 95 parts by mass or less, per 100 parts by mass of conductive powder.

[0072] The content of the organic solvent is preferably 20% by mass or more and 60% by mass or less, and more preferably 35% by mass or more and 55% by mass or less, relative to the entire conductive paste.

[0073] When the content of the organic solvent is within the above range, it exhibits excellent conductivity and dispersibility.

[0074] (Dispersant) In the conductive paste of this example, the dispersant is an optional component. If a dispersant is added further, it is added to the organic vehicle together with the conductive powder and dielectric ceramic powder. The dispersant has the function of maintaining the dispersion state of the conductive powder in the conductive paste composition and suppressing changes in the viscosity of the conductive paste composition over time.

[0075] In the conductive paste of this example, the type of dispersant is not particularly limited. For example, cationic dispersants, anionic dispersants, nonionic dispersants, amphoteric surfactants, polymeric dispersants, etc., can be used. Among these, the use of anionic dispersants is preferred.

[0076] Examples of anionic dispersants include carboxylic acid-based dispersants, phosphate-based dispersants, and phosphate-based dispersants. These dispersants can be used individually or in combination of two or more. Anionic dispersants have a high adsorption capacity to the surface of conductive powders, and therefore contribute to improving the dispersibility of inorganic components through their surface modification effect. While they do not achieve the same effect as attaching organic titanate compounds with phosphate groups as functional groups to conductive powders, they do have the function of improving the surface smoothness of the coating film and improving the density of the internal electrode layer.

[0077] The dispersant content is preferably 0.01 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of conductive powder, and more preferably 0.2 parts by mass or more and 1.0 part by mass or less. If the dispersant content is less than 0.01 parts by mass per 100 parts by mass of conductive powder, it tends to be difficult to obtain sufficient dispersibility. On the other hand, if it exceeds 2.0 parts by mass, problems such as poor drying properties and a decrease in the density of the internal electrode layer may occur.

[0078] (Other additives) In this example, to adjust the viscosity or impart appropriate viscosity, additional organic solvents or binder resins different from those described above may be added to the conductive paste, depending on the purpose. It is preferable to use organic solvents or binder resins with known compositions applicable to conductive pastes as these additional organic solvents or binder resins. In this case, it is preferable that they be added within the range of the organic solvent or binder resin content in the conductive paste composition. Furthermore, if necessary, known additives applicable to the conductive paste composition, such as defoamers, plasticizers, thickeners, and chelating agents, may also be added.

[0079] (viscosity) The conductive paste in this example preferably has a viscosity of 18 Pa·s or less 24 hours (1 day) after manufacturing, more preferably 15 Pa·s or less, even more preferably 10 Pa·s or less, and particularly preferably 5 Pa·s or less. When the viscosity of the conductive paste is within the above range, it becomes possible to apply the conductive paste to a variety of printing methods.

[0080] The viscosity of conductive paste can be measured, for example, using a rheometer. In this case, in the shear rate dependence (flow curve) measurement, the rotation speed is 4 sec. -1 It is preferable to measure under these conditions.

[0081] (Surface smoothness of the dried film) In this example, the conductive paste is applied to a glass plate to a wet film thickness of 10 μm, and then the glass plate is placed in an oven set to 120°C and dried for 20 minutes. The roughness of the dried film is then measured repeatedly at five random locations within a measurement range of 200 μm × 250 μm using a laser microscope, and it is preferable that the average value of the obtained values ​​(average roughness) is 0.095 μm or less. By exhibiting such surface smoothness in the dried film of the conductive paste, it becomes possible to further thin the electrode patterns, including conductors in electronic components or internal electrodes in multilayer ceramic capacitors.

[0082] The average value (average roughness) is more preferably 0.090 μm or less, and even more preferably 0.086 μm or less.

[0083] (Method for manufacturing conductive paste) In the method for producing the conductive paste described in this example, first, an organic titanate compound having a phosphate group as a functional group is attached to the surface of the conductive powder. As described above, the organic titanate compound is added to the conductive powder in advance and kneaded to obtain a kneaded product.

[0084] The subsequent steps are not particularly limited, and known methods can be used.

[0085] A conductive paste can be manufactured, for example, by preparing a mixture of conductive powder and an organic titanate compound having a phosphate group as a functional group, ceramic powder, and an organic vehicle, and if a dispersant is to be added, further preparing the dispersant, and then stirring and kneading these components using a three-roll mill, ball mill, mixer, etc.

[0086] Alternatively, a conductive paste can be prepared by dissolving the binder resin in an organic solvent for the vehicle to create an organic vehicle, adding a mixture of conductive powder and an organic titanate compound having a phosphate group as a functional group, ceramic powder, and the organic vehicle to an organic solvent for the paste, adding a dispersant if necessary, and then stirring and kneading in a mixer.

[0087] [Multilayer ceramic capacitor (electronic component)] An example of a conductive paste according to one embodiment of the present disclosure can be suitably applied to the formation of conductors in electronic components, particularly the internal electrode layer of a multilayer ceramic capacitor having at least a laminate in which a dielectric layer and an internal electrode layer are stacked.

[0088] Examples of conductors in electronic components include electrodes that make up passive components such as resistors, inductors, and capacitors; wiring and electrodes in ceramic substrates, printed circuit boards, solar cells, and touch panels; and conductive adhesives used when mounting electronic components onto substrates.

[0089] The conductive paste in this example is particularly suitable for forming the internal electrode layer of a multilayer ceramic capacitor. Therefore, the structure and manufacturing method of a multilayer ceramic capacitor will be described below with reference to the drawings. In the drawings, schematic representations and changes in scale may be used as appropriate. The position and orientation of components will be described with reference to the XYZ Cartesian coordinate system shown in Figure 2, etc., as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up and down).

[0090] Figure 1 (Figures 1A and 1B) schematically shows the structure of the 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.

[0091] (1) To manufacture a multilayer ceramic capacitor 1 with such a structure using the conductive paste of this example, first, the conductive paste is printed onto a dielectric layer made of a ceramic green sheet, dried, and a dried film is formed.

[0092] More specifically, an unfired ceramic sheet, known as a ceramic green sheet, is prepared. Examples of this ceramic green sheet include a dielectric layer paste obtained by adding an organic binder such as polyvinyl butyral and a solvent such as terpineol to a predetermined ceramic raw material powder, such as barium titanate. This paste is then applied in a sheet-like manner to a support film such as a PET film, dried, and the solvent removed. The thickness of the dielectric layer made from the ceramic green sheet is not particularly limited, but from the viewpoint of miniaturizing multilayer ceramic capacitors, it is preferably between 0.05 μm and 3 μm.

[0093] Next, several sheets of this ceramic green sheet are prepared by printing (coating) the conductive paste of this example onto one side of the sheet using a known method such as screen printing, drying it, and forming a dried film. It is preferable that the thickness of the conductive paste (dried film) after printing be 1 μm or less after drying, from the viewpoint of thinning the internal electrode layer 11.

[0094] (2) A plurality of dielectric layers having a dried film on the upper surface are laminated by compression to obtain a laminate, and then the laminate is fired to integrate them, thereby producing a ceramic laminate 10 in which the internal electrode layer 11 and dielectric layer 12 are alternately laminated.

[0095] More specifically, the ceramic green sheet is peeled from the support film, and then the dielectric layer made of the ceramic green sheet and the dried film formed on one side thereof are laminated alternately. After that, a laminate is obtained by heating and pressurizing. In addition, a configuration in which protective ceramic green sheets without conductive paste are further arranged on both sides of the laminate is also possible.

[0096] 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 the 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, it is preferable to maintain this temperature for 0.5 hours to 24 hours during the debinder treatment.

[0097] The firing process is carried out in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layer. The firing temperature of the laminate is, for example, between 1000°C and 1350°C, and the holding time during firing is, for example, between 0.5 hours and 8 hours.

[0098] By firing the green chips, the organic binder in the 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 the conductive powder (for example, nickel powder or nickel-based alloy powder) is sintered or melted and integrated to form internal electrodes, thus forming a laminated ceramic fired body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked.

[0099] Furthermore, annealing treatment may be applied to the multilayer ceramic sintered body after firing, from the viewpoint of incorporating oxygen into the dielectric layer to improve reliability and suppressing re-oxidation of the internal electrodes.

[0100] (3) Subsequently, a multilayer ceramic capacitor 1 is manufactured by forming a pair of external electrodes 20 on both ends of the ceramic laminate 10.

[0101] For example, the external electrode 20 comprises 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 electrode 20 include, for example, copper, nickel, or alloys thereof. [Examples]

[0102] The present disclosure will be described in further detail below based on examples and comparative examples, but the present disclosure is not limited in any way by the examples.

[0103] [Evaluation Method] (Evaluation of the viscosity of conductive paste) The viscosity of the conductive paste 24 hours after manufacturing was measured using a rheometer (Anton Paar, Rheometer MCR501) and the flow curve was measured at a shear rate of 4 seconds. -1 The value was defined as the viscosity of the conductive paste.

[0104] (Evaluation of the smoothness of a conductive paste-dried film) Using an applicator, conductive paste was applied to a glass plate to a wet film thickness of 10 μm. The glass plate was then placed in an oven set to 120°C and dried for 20 minutes to obtain a dried conductive paste film. The roughness of the dried film was measured at five random locations within a measurement range of 200 μm × 250 μm using a laser microscope (Keyence Corporation, VK-X3000). The average value of the obtained values ​​was used as the average roughness of the conductive paste dried film and as an indicator of its smoothness.

[0105] [Example 1] Nickel (Ni) powder (manufactured by Sumitomo Metal Mining Co., Ltd., number average particle size 0.2 μm) was added at a concentration of 50% by mass, and bis(dioctyl pyrophosphate) oxyacetate titanate (manufactured by Ajinomoto Fine Techno Co., Ltd., PrenAct 138S) was added at a concentration of 0.5% by mass. These materials were placed in a container and kneaded with a spatula to obtain a mixture.

[0106] To this mixture, 3.8% by mass of barium titanate (BaTiO3) powder (number average particle size 0.06 μm), 3% by mass of binder resin from an organic vehicle consisting of ethyl cellulose resin (weight average molecular weight: 160,000, ethoxy group content: 48% by mass) and polyvinyl butyral resin (weight average molecular weight: 170,000) (mixing ratio of ethyl cellulose resin to polyvinyl butyral resin is 1:1), and 100% by mass of organic solvent from an organic vehicle consisting of terpineol and cyclohexane (mixing ratio of terpineol to cyclohexane is 7:3) were added. These materials were then mixed in a three-roll mill to produce a conductive paste.

[0107] The viscosity of the obtained conductive paste and the average roughness of the dried conductive paste film were measured 24 hours after preparation. The types of organic titanate compounds are shown in Table 1, and the viscosity and average roughness obtained from the measurements are shown in Table 2. The same procedure was followed for Examples 2-9 and Comparative Examples 1 and 2.

[0108] [Example 2] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that isopropyl tris(dioctyl pyrophosphate) titanate (PlenAct 38S, manufactured by Ajinomoto Fine Techno Co., Ltd.) was used as the organic titanate compound.

[0109] [Example 3] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that bis(dioctyl pyrophosphate)ethylene titanate (PlenAct 238S, manufactured by Ajinomoto Fine Techno Co., Ltd.) was used as the organic titanate compound.

[0110] [Examples 4-6] Conductive pastes for Examples 4-6 were prepared and evaluated in the same manner as in Examples 1-3, except that dihydroterpineol was used as the organic solvent.

[0111] [Example 7] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that the amount of organic titanate compound added was changed to 1.0% by mass.

[0112] [Example 8] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that the amount of organic titanate compound added was changed to 2.0% by mass.

[0113] [Example 9] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that a mixture of bis(dioctyl pyrophosphate) oxyacetate titanate and isopropyl tris(dioctyl pyrophosphate) titanate (0.25% by mass of each) was used as the organic titanate compound.

[0114] [Example 10] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that nickel (Ni) powder (manufactured by Sumitomo Metal Mining Co., Ltd., number average particle size 0.1 μm) was used as the conductive powder.

[0115] [Comparative Example 1] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that titanium(IV) tetrabutoxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), which is a butyl titanate represented by the following chemical formula (1), was used as the organic titanate compound.

[0116] [ka]

[0117] [Comparative Example 2] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that titanium(IV) isopropoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the organic titanate compound.

[0118] [Comparative Example 3] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that methyl methacrylate (Fujifilm Wako Pure Chemical Industries, Ltd., mass-average molecular weight: 6000) was used as the binder resin.

[0119] [Comparative Example 4] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that it was formulated with 50% by mass of nickel (Ni) powder, 3.8% by mass of barium titanate (BaTiO3) powder, 0.5% by mass of 3-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., KBM-503) as a dispersant, a total of 3% by mass of binder resin in an organic vehicle consisting of ethyl cellulose resin and polyvinyl butyral resin, and 100% by mass of organic solvent in an organic vehicle consisting of terpineol and cyclohexane.

[0120] [Table 1]

[0121] [Table 2]

[0122] (Evaluation results) In all of the conductive pastes of Examples 1 to 10, in which the specific organic titanate compound in this example is attached to at least a portion of the surface of the conductive powder, the viscosity of the conductive paste after 24 hours of preparation is 18 Pa·s or less, and the average roughness of the dried conductive paste film is 0.095 μm or less. Therefore, it is understood that this disclosure provides a conductive paste with sufficiently high film surface smoothness after drying.

[0123] On the other hand, the conductive pastes of Comparative Examples 1 to 4 had a viscosity greater than 19 Pa·s 24 hours after manufacturing, and an average roughness greater than 0.095 μm of the dried conductive paste film. Therefore, it is understood that they do not possess sufficient characteristics for further thinning of electrode patterns, including conductors in electronic components or internal electrodes in multilayer ceramic capacitors. [Explanation of Symbols]

[0124] 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 comprising conductive powder, ceramic powder, binder resin, and organic solvent, An organic titanate compound having a phosphate group as a functional group is attached to at least a portion of the surface of the conductive powder. Conductive paste.

2. The conductive paste according to claim 1, wherein the organic titanate compound comprises at least one of bis(dioctyl pyrophosphate) oxyacetate titanate, isopropyl tris(dioctyl pyrophosphate) titanate, or bis(dioctyl pyrophosphate) ethylene titanate.

3. The conductive paste according to claim 1, wherein the organic titanate compound is contained in the conductive paste in an amount of 0.25% by mass or more and 2.0% by mass or less.

4. The conductive paste according to claim 1, wherein the binder resin contains ethyl cellulose having a mass-average molecular weight of 30,000 or more and 150,000 or less, and an ethoxy group content of 45% by mass or more and 50% by mass or less.

5. The conductive paste according to claim 1, wherein the number-average particle size of the conductive powder is 0.02 μm or more and 0.4 μm or less.

6. The conductive paste according to claim 1, wherein the conductive powder comprises at least one metal powder selected from Ni, Pd, Pt, Au, Ag, Cu, or alloys thereof.

7. The conductive paste according to claim 1, wherein the number-average particle size of the ceramic powder is 0.01 μm or more and 0.1 μm or less.

8. The conductive paste according to claim 1, wherein the ceramic powder comprises a perovskite-type oxide.

9. The conductive paste according to claim 1, wherein the paste is applied to a glass plate to a wet thickness of 10 μm, and the glass plate is dried in an oven set to 120°C for 20 minutes to obtain a dried film, and the roughness of the dried film is repeatedly measured at five random locations within a measurement range of 200 μm × 250 μm using a laser microscope, and the average value of the obtained values ​​is 0.095 μm or less.

10. An electronic component comprising at least a conductor, wherein the conductor is formed using a conductive paste according to any one of claims 1 to 9.

11. A multilayer ceramic capacitor having at least a laminate in which a dielectric layer and an internal electrode layer are stacked, wherein the internal electrode layer is formed using a conductive paste according to any one of claims 1 to 9.

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