Method for manufacturing conductive paste and method for manufacturing multilayer ceramic capacitors

Abstract

To form an internal electrode pattern on a ceramic green sheet while preventing a sheet attack phenomenon, in which an organic binder in the ceramic green sheet swells or dissolves, and preventing a short-circuit defect of the resultant multilayer ceramic capacitor.SOLUTION: A method for manufacturing a conductive paste includes: a step of forming a first mixture including a metal powder, a dispersant and a hydrophobic solvent; a step of forming a second mixture including a hydrophilic binder and a hydrophilic solvent; and a step of forming a third mixture by mixing the first and second mixtures.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for producing a conductive paste and a method for producing a multilayer ceramic capacitor.

Background Art

[0002] The present invention relates to a method for producing a conductive paste and a method for producing a multilayer ceramic capacitor. In particular, the present invention relates to a conductive paste that is directly formed on a ceramic green sheet for forming an internal electrode of a multilayer ceramic capacitor.

[0003] At present, a multilayer ceramic capacitor is formed by cross-laminating ceramic green sheets and internal electrode patterns formed using a conductive paste. The ceramic green sheet mainly contains ceramic powder typified by barium titanate (BaTiO3) or the like and an organic binder as main components.

[0004] Conventionally, a conductive paste in which metal powder is dispersed in a vehicle obtained by dissolving an organic binder in a hydrophobic organic solvent has been used.

[0005] Therefore, as shown in FIG. 1, when a conventional conductive paste is formed, dried, and formed on a ceramic green sheet 10 on which first and second internal electrode patterns 21 and 22 have already been laminated, the "sheet attack" phenomenon, in which the organic solvent in the conductive paste swells or dissolves the organic binder in the ceramic green sheet 10, occurs.

[0006] Such a sheet attack phenomenon causes problems such as lowering the insulation of the dielectric layer of the final product, i.e., the multilayer ceramic capacitor, and increasing the incidence of short circuits.

[0007] To solve these problems, Patent Document 1 discloses a conductive paste composed of a metal powder, an organic binder made of a resin such as ethylcellulose, and a solvent such as dihydroterpineol.

[0008] However, when using dihydroterpineol as a solvent, if the solvent content is insufficient, the viscosity of the conductive paste increases, which significantly reduces its workability.

[0009] Furthermore, while Patent Document 2 discloses a conductive paste containing a metal component, a water-soluble resin, and water, it has the problem that the entire surface of the metal powder must be modified to be hydrophilic. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] JP 1997-017687 A [Patent Document 2] JP 1999-233388 A [Overview of the project] [Problems that the invention aims to solve]

[0011] One of the several objectives of the present invention is to prevent the sheet attack phenomenon, which causes swelling or dissolution of the organic binder in the ceramic green sheet when forming an internal electrode pattern on the ceramic green sheet, thereby preventing short-circuit defects in the resulting multilayer ceramic capacitor.

[0012] However, the objectives of the present invention are not limited to those described above and can be more easily understood in the process of describing specific embodiments of the present invention. [Means for solving the problem]

[0013] One embodiment of the present invention provides a method for producing a conductive paste, comprising the steps of: forming a first mixture containing metal powder, a dispersant, and a hydrophobic solvent; forming a second mixture containing a hydrophilic binder and a hydrophilic solvent; and mixing the first and second mixtures to form a third mixture.

[0014] Another embodiment of the present invention provides a method for manufacturing a multilayer ceramic capacitor, comprising the steps of: providing a ceramic green sheet; forming a conductive paste on the ceramic green sheet; stacking the ceramic green sheets on which the conductive paste is formed to form a ceramic laminate; firing the ceramic laminate; and forming external electrodes on the outside of the ceramic laminate, wherein the conductive paste comprises a first mixture containing metal powder, a dispersant, and a hydrophobic solvent, and a second mixture containing a hydrophilic binder and a hydrophilic solvent, and the first mixture is dispersed in the second mixture to form an emulsion. [Effects of the Invention]

[0015] By providing a method for manufacturing a conductive paste and a multilayer ceramic capacitor according to embodiments of the present invention, the sheet attack phenomenon does not occur when forming an internal electrode pattern on a ceramic green sheet, thereby preventing a decrease in the insulating properties of the dielectric layer of the resulting multilayer ceramic capacitor and reducing the short-circuit failure rate. [Brief explanation of the drawing]

[0016] [Figure 1] This is a cross-sectional view showing that the first and second internal electrode patterns were formed on a ceramic green sheet by printing a conventional conductive paste. [Figure 2] This is a process flowchart illustrating the manufacturing process of a conductive paste according to one embodiment of the present invention. [Figure 3] This is a schematic diagram illustrating the manufacturing process of a conductive paste according to one embodiment of the present invention. [Figure 4]It is an enlarged view showing the region P in FIG. 3. [Figure 5] It is a photograph obtained by analyzing a dried coating film of the conductive paste according to an embodiment of the present invention with an optical microscope. [Figure 6] It is a perspective view of a multilayer ceramic capacitor comprising a conductive paste manufactured according to an embodiment of the present invention. [Figure 7] It is a cross-sectional view of the multilayer ceramic capacitor of FIG. 6 taken along line A-A'. [Figure 8] It is a process flow chart showing a manufacturing process of a multilayer ceramic capacitor according to an embodiment of the present invention. [Figure 9] It is a cross-sectional view showing a ceramic green sheet on which a conductive paste is formed. DETAILED DESCRIPTION OF EMBODIMENTS

[0017] Hereinafter, embodiments of the present invention will be described with reference to specific embodiments and the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to a person skilled in the art. Accordingly, the shape and size of elements in the drawings may be scaled up or down (or emphasized or simplified) for clearer explanation, and elements denoted by the same reference numerals in the drawings are the same element.

[0018] In order to clearly describe the present invention in the drawings, portions unrelated to the description are omitted. Since the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, the present invention is not necessarily limited to what is illustrated. Constituent elements having the same function within the scope of the same concept will be described using the same reference numerals. Furthermore, throughout the specification, when a certain component is referred to as "comprising", unless specifically stated otherwise, this does not mean that other components are excluded, but means that other components can be additionally included.

[0019] In the drawings, the X direction may be defined as the second direction, the Y direction as the third direction, and the Z direction as the first direction or the lamination direction.

[0020] [Method for Producing Conductive Paste] Hereinafter, a method for producing a conductive paste according to an embodiment of the present invention will be described in detail with reference to FIGS. 2 to 5.

[0021] Referring to FIG. 2, the method for producing a conductive paste according to an embodiment of the present invention comprises: a step (S1) of forming a first mixture (110) comprising a metal powder (101), a dispersant (102) and a hydrophobic solvent (103); a step (S2) of forming a second mixture (210) comprising a hydrophilic binder (201) and a hydrophilic solvent (202); and a step (S3) of mixing the first mixture (110) and the second mixture (210) to form a third mixture (310).

[0022] Hereinafter, the production process of the conductive paste according to the present embodiment will be described in detail for each step.

[0023] Referring to FIG. 3, a first mixture (110) comprising a metal powder (101), a dispersant (102) and a hydrophobic solvent (103) may be formed (S1).

[0024] The metal powder (101) is sufficient as long as it has conductivity, and is not particularly limited. For example, the metal powder (101) may be one or more selected from the group consisting of Ni, Cu, Au, Ag, Pd, Pt and alloys thereof.

[0025] As the dispersant (102), for example, nonionic surfactants, cationic surfactants, anionic surfactants and the like can be used, and these can be used alone or in combination of two or more.

[0026] As will be described later, the dispersant (102) contained in the first mixture is adsorbed on the interface between the first mixture (110) and the second mixture (210). In this case, the hydrophobic groups of the dispersant (102) are adsorbed on the first mixture (110) side, and the hydrophilic groups are adsorbed on the second mixture (210) side.

[0027] When the dispersant 102 is adsorbed to the interface between the first mixture 110 and the second mixture 210, the third mixture 310 can be more stably maintained in the form of an oil-in-water emulsion.

[0028] The hydrophobic solvent 103 is not particularly limited as long as it exhibits hydrophobicity, but examples of usable solvents include acetate 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 solvents such as terpineol and dihydroterpineol; hydrocarbon solvents such as tridecane, nonane, and cyclohexane; and organic solvents such as carboxylate and ester solvents.

[0029] However, the composition of the first mixture 110 is not limited to this, and may further include various additives, such as ceramic co-materials.

[0030] Referring to Figure 3, the first mixture 110 exists in a form in which the metal powder 101 and dispersant 102 are uniformly dispersed in the hydrophobic solvent 103.

[0031] Next, a second mixture 210 containing a hydrophilic binder 201 and a hydrophilic solvent 202 can be formed (S2).

[0032] The binder is an organic component that contributes to improving the bonding between the ceramic green sheet and the particles contained in the conductive paste. The hydrophilic binder 201 is not particularly limited as long as it exhibits hydrophilicity, but for example, polyvinyl alcohol, cellulose, or water-soluble acrylic resin can be used.

[0033] The hydrophilic binder 201 does not affect the metal powder 111 and other particles in the first mixture 110, and acts as a matrix that allows the aggregate of metal powder to disperse during the drying of the conductive paste.

[0034] The hydrophilic solvent 202 is not particularly limited, as long as it can dissolve the hydrophilic binder 201, but for example, water or dimethyl sulfoxide can be used.

[0035] Referring to Figure 3, the second mixture 210 exists in a form in which the hydrophilic binder 201 is dispersed in the hydrophilic solvent 202.

[0036] Next, the first mixture 110 and the second mixture 210 can be mixed to form the third mixture 310 (S3).

[0037] A method for producing a conductive paste according to one embodiment of the present invention may further include the step of stirring the third mixture 310.

[0038] Referring to Figure 3, the stirred third mixture 301 can exist in the form of an emulsion. An emulsion is a substance in which other liquid particles that are not dissolved in a given liquid are dispersed in that liquid as colloidal particles or larger particles.

[0039] According to one embodiment of the present invention, the volume ratio of the first mixture 110 to the second mixture 210 may be 1 or less. When the volume ratio of the first mixture 110 to the second mixture 210 is 1 or less, the third mixture 310 can exist in the form of an oil-in-water emulsion in which the hydrophobic first mixture 110 is dispersed in the hydrophilic second mixture 210 in the form of spherical particles.

[0040] Referring to Figure 3, the diameter of the particles of the first mixture 110 dispersed in the second mixture 210 may preferably be 0.1 to 100 μm. When the diameter of the particles of the first mixture 110 is 0.1 to 100 μm, the first mixture 110 can be dispersed in the second mixture 210 as particles of a certain size to form a uniform emulsion.

[0041] Conventional conductive pastes were manufactured by dispersing metal powder in a hydrophobic organic solvent such as a binder. In this case, when printing the conductive paste onto a ceramic green sheet to form internal electrodes, there was a problem in that the organic solvent contained in the conductive paste and the organic binder contained in the ceramic green sheet were mutually compatible, causing the conductive paste to dissolve or swell the already laminated ceramic green sheet.

[0042] As described later, when forming a conductive paste manufactured by one embodiment of the present invention on a ceramic green sheet, the conductive paste in the third mixture 310 state is formed on the already laminated ceramic green sheet.

[0043] In other words, the hydrophilic second mixture 210 is present on the ceramic green sheet, but they are not compatible with each other. Furthermore, since the first mixture 110 exists in the form of spherical particles dispersed within the second mixture 210, the first mixture 110 is not present on the ceramic green sheet. Therefore, the hydrophobic solvent 103 of the first mixture 110 does not swell or dissolve the organic binder in the laminated ceramic green sheet.

[0044] Even during the drying process of the conductive paste formed on the ceramic green sheet, the dispersant 102 in the first mixture 110 allows the third mixture 310 to maintain its emulsion form. Ultimately, only the hydrophobic solvent 103 and the hydrophilic solvent 202 are removed during the drying process, and the dried conductive paste has a form in which aggregates of metal powder are uniformly and densely dispersed within a matrix consisting of a hydrophilic binder 201.

[0045] Therefore, even when multiple ceramic green sheets with conductive paste formed on them are stacked during the manufacturing process of a multilayer ceramic capacitor, the sheet attack phenomenon against already stacked ceramic green sheets will not occur.

[0046] Referring to Figure 4, the dispersant 102 contained in the first mixture is adsorbed at the interface between the first mixture 110 and the second mixture 210. In this case, the hydrophobic group 102a of the dispersant is adsorbed on the first mixture side, and the hydrophilic group 102b is adsorbed on the second mixture side. When the dispersant is adsorbed at the interface between the first mixture 110 and the second mixture 210, the oil-in-water emulsion can be maintained more stably.

[0047] The content of the dispersant 102 in the first mixture 110 may preferably be 0.01 wt% or more.

[0048] When the content of the dispersant 102 in the first mixture 110 is 0.01 wt% or more, the oil-in-water emulsion can be maintained more stably. That is, the oil-in-water emulsion can be maintained even during multiple lamination processes, and the sheet attack phenomenon on already laminated ceramic green sheets can be suppressed.

[0049] [Example of experiment] A first mixture was formed containing 27.68 wt% Ni powder, 0.5 wt% of an existing surfactant (ED116, an amine-based dispersant), and hexyl acetate as a solvent. A second mixture was formed containing 5 wt% polyvinyl alcohol as a binder and water as a solvent.

[0050] The first and second mixtures were mixed in a volume ratio of 1:5 to form a third mixture, which was then stirred to produce a conductive paste in emulsion form.

[0051] The conductive paste manufactured above was coated onto a PET film with a blade, and then dried with hot air at 60°C to evaporate all the solvents present in the first and second mixtures, forming a dry coating of conductive paste. This coating was then observed with an optical microscope (OM).

[0052] Referring to Figure 5, all solvents in the first and second mixtures are removed. That is, the hydrophilic binder remains present after drying, forming a hydrophilic dried coating.

[0053] Furthermore, the dispersant remains even during the drying process, maintaining the emulsion's form. Therefore, it can be confirmed that the Ni powder exists in the form of spherical Ni aggregates uniformly and densely dispersed within the hydrophilic binder.

[0054] [Manufacturing method for multilayer ceramic capacitors] A conductive paste manufactured according to one embodiment of the present invention can be used for the purpose of manufacturing internal electrodes in multilayer ceramic capacitors.

[0055] Figure 6 is a perspective view of a multilayer ceramic capacitor 400 containing a conductive paste according to an embodiment of the present invention, and Figure 7 is a cross-sectional view of the multilayer ceramic capacitor 400 of Figure 6 cut along the line A-A'.

[0056] Referring to Figures 6 and 7, the ceramic body 410 includes a plurality of dielectric layers 411 and first and second internal electrodes 421 and 422 formed on the dielectric layers 411. The ceramic body may be formed by stacking a plurality of dielectric layers 411 on which the first and second internal electrodes 421 and 422 are formed. The first and second internal electrodes 421 and 422 may be arranged to face each other with a dielectric layer 411 in between. The first and second internal electrodes may be formed from a conductive paste manufactured according to an embodiment of the present invention.

[0057] First and second external electrodes 431 and 432 are formed on the outside of the ceramic body 410, and are electrically connected to the first and second internal electrodes 421 and 422, respectively. Specifically, the first and second external electrodes 431 and 432 can be formed by applying another conductive paste to the outer surface of the ceramic body 410 so as to electrically connect to the first and second internal electrodes 421 and 422, respectively, and then sintering it.

[0058] Figure 8 is a process flowchart of the manufacturing process of a multilayer ceramic capacitor 400 according to an embodiment of the present invention.

[0059] Referring to Figure 8, the method for manufacturing a multilayer ceramic capacitor includes the steps of: providing a ceramic green sheet (P1); forming a conductive paste on the ceramic green sheet (P2); stacking the ceramic green sheets on which the conductive paste is formed to form a ceramic laminate (P3); firing the ceramic laminate (P4); and forming external electrodes on the outside of the ceramic laminate (P5). The conductive paste comprises a first mixture containing metal powder, a dispersant, and a hydrophobic solvent, and a second mixture containing a hydrophilic binder and a hydrophilic solvent, and is characterized in that the first mixture is dispersed in the second mixture in an emulsion.

[0060] The manufacturing process of a multilayer ceramic capacitor according to an embodiment of the present invention will be described in detail step by step below.

[0061] First, a slurry containing ceramic powder such as barium titanate (BaTiO3) and an organic binder is applied to a carrier film and dried to form a ceramic green sheet (P1).

[0062] Next, a conductive paste is formed on the ceramic green sheet (P2). The conductive paste is characterized by comprising a first mixture containing metal powder, a dispersant and a hydrophobic solvent, and a second mixture containing a hydrophilic binder and a hydrophilic solvent, wherein the first mixture is dispersed within the second mixture.

[0063] The method for forming the conductive paste is not particularly limited, but methods such as screen printing or gravure printing can be used.

[0064] Next, the ceramic green sheets on which the conductive paste is formed are stacked to form a ceramic laminate (P3), and external electrodes are formed on the outside of the laminate (P4). The step of forming the external electrodes can be carried out using an external electrode paste. The application of the external electrode paste can be done by dipping the laminate into the external electrode paste, but is not limited to this.

[0065] Figure 9 shows a conductive paste according to an embodiment of the present invention formed on a ceramic green sheet 111 that has already been laminated.

[0066] When a conductive paste according to an embodiment of the present invention is formed on a ceramic green sheet, the hydrophilic second mixture 210' is present on the ceramic green sheet 111, but the second mixture 210' and the organic binder in the ceramic green sheet 111 are not compatible with each other.

[0067] Furthermore, since the first mixture 110' exists in the form of spherical particles dispersed within the second mixture 210', the first mixture 110' does not exist on the ceramic green sheet 111. Therefore, the hydrophobic solvent 103' of the first mixture 110' does not swell or dissolve the organic binder in the laminated ceramic green sheet 111.

[0068] Even during the drying process of the conductive paste formed on the ceramic green sheet, the dispersant 102' in the first mixture 110' allows the conductive paste to maintain its emulsion form.

[0069] Ultimately, only the hydrophobic solvent 103' and the hydrophilic solvent 202' are removed during the drying process, and the dried conductive paste has a form in which aggregates of metal powder 101' are uniformly and densely dispersed within a matrix consisting of a hydrophilic binder 201'.

[0070] Therefore, even if multiple ceramic green sheets with conductive paste formed on them are stacked during the manufacturing process of a multilayer ceramic capacitor, a sheet attack phenomenon does not occur against the already stacked ceramic green sheets.

[0071] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those with ordinary skill in the art that various modifications and variations are possible without departing from the technical matters of the present invention as described in the claims. [Explanation of Symbols]

[0072] 11, 111: Ceramic Green Sheet 21: First internal electrode pattern 22: Second internal electrode pattern 101, 101': Metal powder 102, 102': Dispersant 102a: Hydrophobic group of dispersant 102b: Hydrophilic group of dispersant 103, 103': Hydrophobic solvents 110, 110': 1st mixture 201, 201': Hydrophilic binder 202, 202': Hydrophilic solvent 210, 210': second mixture 310, 310': 3rd mixture 400: Multilayer ceramic capacitor 410: Ceramic body 411: Dielectric layer 421: 1st internal electrode 422:Second internal electrode 431: 1st external electrode 432: 2nd external electrode

Claims

1. A step of forming a first mixture containing metal powder, a dispersant and a hydrophobic solvent, A step of forming a second mixture containing a hydrophilic binder and a hydrophilic solvent, A method for producing a conductive paste, comprising the step of mixing the first and second mixtures to form a third mixture which is an emulsion in which the first mixture is dispersed within the second mixture.

2. A method for producing a conductive paste according to claim 1, further comprising the step of stirring the third mixture.

3. A method for producing a conductive paste according to claim 1 or 2, wherein the volume ratio of the first mixture to the second mixture is 1 or less.

4. A method for producing a conductive paste according to any one of claims 1 to 3, wherein the diameter of the particles of the first mixture is 0.1 to 100 μm.

5. A method for producing a conductive paste according to any one of claims 1 to 4, wherein the content of the dispersant in the first mixture is 0.01 wt% or more.

6. The method for producing a conductive paste according to any one of claims 1 to 5, wherein the metal powder is one or more selected from the group consisting of Ni, Cu, Au, Ag, Pd, Pt and alloys thereof.

7. The stage of installing the ceramic green sheet, The steps include forming a conductive paste on the ceramic green sheet, The steps include: forming a ceramic laminate by stacking ceramic green sheets on which the conductive paste has been formed; The steps include firing the aforementioned ceramic laminate and The step includes forming an external electrode on the outside of the ceramic laminate, A method for manufacturing a multilayer ceramic capacitor, wherein the conductive paste comprises a first mixture containing metal powder, a dispersant, and a hydrophobic solvent, and a second mixture containing a hydrophilic binder and a hydrophilic solvent, wherein the first mixture is dispersed in the second mixture in an emulsion.

8. The method for manufacturing a multilayer ceramic capacitor according to claim 7, wherein the volume ratio of the first mixture to the second mixture is 1 or less.

9. A method for manufacturing a multilayer ceramic capacitor according to claim 7 or 8, wherein the diameter of the particles of the first mixture is 0.1 to 100 μm.

10. A method for manufacturing a multilayer ceramic capacitor according to any one of claims 7 to 9, wherein the content of the dispersant in the first mixture is 0.01 wt% or more.

11. The method for manufacturing a multilayer ceramic capacitor according to any one of claims 7 to 10, wherein the metal powder is one or more selected from the group consisting of Ni, Cu, Au, Ag, Pd, Pt and alloys thereof.

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