Conductive paste for electrode formation

Abstract

A conductive paste for forming an electrode according to the present disclosure contains metal particles, a binder, a metal oxide additive, and a solvent. The metal oxide additive contains a metal oxide in which the temperature, at which the standard Gibbs energy of formation of the metal oxide in the Ellingham diagram is higher than that of carbon dioxide or carbon monoxide, is within the range of 500-1,000ºC.

Description

Technical Field

[0001] The present disclosure relates to a conductive paste for electrode formation.

Background Art

[0002] An example of the prior art is described in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The conductive paste for electrode formation of the present disclosure contains metal particles, a binder, a metal oxide additive, and a solvent, and the metal oxide additive contains a metal oxide in which the temperature at which the standard Gibbs energy is higher than that of carbon dioxide or carbon monoxide in the Ellingham diagram is within the range of 500 to 1000 °C. Furthermore, the metal elements contained in the metal oxide additive are different from any of the metal elements contained in the metal particles. .

Brief Description of the Drawings

[0005] [Figure 1] It is a diagram showing an Ellingham diagram.

Modes for Carrying Out the Invention

[0006] The object, features, and advantages of the present disclosure will become clearer from the following detailed description and drawings.

[0007] The ceramic capacitor having the structure on which the present disclosure is based has a laminated structure in which ceramic layers and internal electrode layers are alternately laminated, for example, as described in Patent Document 1.

[0008] A multilayer ceramic capacitor is obtained by printing an electrode pattern with conductive paste onto the surface of an unfired dielectric tape, stacking multiple such layers, and then firing them.

[0009] With the miniaturization of electronic devices such as smartphones, there is a demand for miniaturization of multilayer ceramic capacitors, and progress is being made in thinning the dielectric layers. In order to maintain the strength of the thinned, unfired dielectric tape, for example, the binder content is increased or the molecular weight is increased. Similarly, in conductive pastes used for electrode formation, the binder content is increased or the molecular weight is increased to enable printing in thin layers, to increase the strength of dielectric tapes printed with conductive paste, and to improve adhesion during lamination.

[0010] In the debinding process, the binder in the conductive paste is burned by heating. However, increasing the binder content or molecular weight necessitates raising the heating temperature or lengthening the burning time to ensure sufficient combustion. This can lead to oversintering or oxidation of the metal particles remaining as electrodes, potentially causing a decrease in the capacitance of the multilayer ceramic capacitor.

[0011] The purpose of this disclosure is to provide a conductive paste for electrode formation that enables miniaturization of multilayer ceramic capacitors.

[0012] The conductive paste for electrode formation described herein will be described in detail below. However, the conductive paste for electrode formation described herein is not limited to the specific embodiments described below.

[0013] The conductive paste for electrode formation in this embodiment contains metal particles, a binder, a metal oxide additive, and a solvent, wherein the metal oxide additive contains a metal oxide whose standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide in the Ellingham diagram, and which is within the range of 500 to 1000°C.

[0014] (metal particles) The metal particles are conductive materials, which are particulate or powdered metal elements. The metal elements may be, for example, metal elements known as electrode materials for multilayer ceramic capacitors. The metal elements may be, for example, base metal elements. Examples of base metal elements include nickel, copper, cobalt, iron, tin, and zinc.

[0015] The metal particles can be in particulate or powder form, and their shape is not particularly limited, but they may be spherical, needle-shaped, or irregularly shaped, for example. The average particle diameter of the metal particles is, for example, 50 to 300 nm, preferably 100 to 250 nm. The average particle diameter is calculated from the captured images using a scanning electron microscope (SEM) to photograph 200 to 300 metal particles and image analysis software (Image J).

[0016] The content of metal particles (solid content) is, for example, 20 to 70% by mass, preferably 30 to 60% by mass, relative to the entire conductive paste for electrode formation.

[0017] (Binder) The binder may be a known resin component used in conductive paste for electrode formation. The binder is an important resin component for miniaturizing multilayer ceramic capacitors, and it is preferable to increase its content in the conductive paste for electrode formation compared to conventional methods and to use a high-molecular-weight resin. In order to thin the electrode layer in a multilayer ceramic capacitor, it is necessary to reduce the printing thickness of the conductive paste for electrode formation. By using a high-content, high-molecular-weight binder, the viscosity of the conductive paste for electrode formation can be increased, enabling thin-layer printing. Furthermore, by using a high-content, high-molecular-weight binder, the strength of the dielectric tape on which the conductive paste for electrode formation is printed can be increased.

[0018] Examples of the binder include celluloses such as ethyl cellulose and nitrocellulose, acrylic resins, phenolic resins, alkyd resins, styrene resins, rosin esters, polyvinyl butyral, etc. From the perspective of thinning, preferably, ethyl cellulose and polyvinyl butyral having a relatively high molecular weight are mentioned. The binder may be used alone or in combination of two or more.

[0019] The content of the binder varies depending on the type of resin component used, but generally it is 0.5% by mass or more and 20% by mass or less with respect to the metal particles. When ethyl cellulose is used as the binder, its content is preferably, for example, 2.5% by mass or more and 10% by mass or less with respect to the metal particles. When polyvinyl butyral is used as the binder, its content is preferably, for example, 0.5% by mass or more and 10% by mass or less with respect to the metal particles.

[0020] (Metal oxide additive) The metal oxide additive is an additive for promoting the oxidation reaction of the binder in the conductive paste for electrode formation. The metal oxide additive contains a metal oxide. The metal oxide is a metal oxide whose temperature at which the standard formation Gibbs energy is higher than that of carbon dioxide or carbon monoxide in the Ellingham diagram is within the range of 500 to 1000 °C. The binder in the conductive paste for electrode formation is burned by heating in the debinding process of the manufacturing process of the multilayer ceramic capacitor. In the combustion reaction, the resin component of the binder is oxidized to generate carbon dioxide (carbon monoxide) and water. Carbon dioxide (carbon monoxide) and water are gasified and desorbed. By promoting the generation reaction of carbon dioxide (carbon monoxide), for example, even a binder with a high content or a high molecular weight binder can be debound in a relatively short time and at a relatively low temperature.

[0021] In an Ellingham diagram, when a metal oxide having a standard Gibbs free energy of formation higher than that of carbon dioxide or carbon monoxide is present in a conductive paste for electrode formation, carbon in the resin component of the binder is oxidized to generate carbon dioxide (carbon monoxide), and the metal oxide is reduced to a metal element. In the debinding process, the carbon dioxide (carbon monoxide) generated by oxidation desorbs from the conductive paste for electrode formation, and the metal element generated by reduction remains in the conductive paste for electrode formation. The remaining metal element becomes a conductive material of the electrode layer together with the above-mentioned metal particles.

[0022] In the Ellingham diagram, the metal oxide only needs to have a temperature range of 500 to 1000 °C in which the standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide. That is, it is not necessary for the standard Gibbs free energy of formation to be higher than that of carbon dioxide or carbon monoxide throughout the range of 500 to 1000 °C. If the debinding process is carried out under the heating temperature condition in which the standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide within the range of 500 to 1000 °C, the oxidation promoting effect of the binder can be obtained. When the heating temperature condition of the debinding process is determined in advance by other factors, a metal oxide having a standard Gibbs free energy of formation higher than that of carbon dioxide or carbon monoxide is selected at that temperature condition, and this may be contained in the conductive paste for electrode formation as a metal oxide additive. One type of metal oxide may be used, or two or more types may be mixed and used.

[0023] Figure 1 shows the Ellingham diagram. In the Ellingham diagram, metal oxides whose standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide at temperatures within the range of 500-1000°C include, for example, CuO (copper(II) oxide), Cu2O (copper(I) oxide), NiO (nickel(II) oxide), CoO (cobalt(II) oxide), Co3O4 (cobalt(II, III) oxide), FeO (iron(II) oxide), Fe2O3 (iron(III) oxide), SnO (tin(II) oxide), SnO2 (tin(IV) oxide), and ZnO (zinc oxide). CuO, Cu2O, NiO, CoO, and Co3O4 have standard Gibbs free energy of formation higher than that of carbon dioxide or carbon monoxide throughout the entire range of 500-1000°C. For FeO and Fe2O3, within the 500-1000°C range, the standard Gibbs free energy of formation is lower than that of carbon dioxide and carbon monoxide between 500 and 700°C, and higher between 700 and 1000°C. For Fe2O3, within the 500-1000°C range, the standard Gibbs free energy of formation is lower than that of carbon dioxide and carbon monoxide between 500 and 600°C, and higher between 600 and 1000°C. For SnO and SnO2, within the 500-1000°C range, the standard Gibbs free energy of formation is lower than that of carbon dioxide and carbon monoxide between 500 and 600°C, and higher between 600 and 1000°C. For ZnO, within the 500-1000°C range, the standard Gibbs free energy of formation is lower than that of carbon dioxide and carbon monoxide between 500 and 950°C, and higher between 950 and 1000°C.

[0024] The content of the metal oxide additive varies depending on the type of metal oxide and binder used, but is typically 0.005 to 5 mol% as oxide relative to the metal particles, preferably 0.01 to 0.5 mol%. If the content exceeds 5 mol%, the metal oxide and metal particles form an alloy, resulting in a lower sintering temperature compared to the metal particles. This decrease in sintering temperature can lead to oversintering of the electrodes during the debindering and firing processes. If the content is less than 0.005 mol%, a sufficient accelerating effect may not be obtained.

[0025] Furthermore, since CuO has the highest standard Gibbs free energy of formation, its oxidation-promoting effect can be excessive, potentially causing cracks in multilayer ceramic capacitors. Therefore, for example, at heating temperatures below 700°C, CoO is preferred over CuO. At heating temperatures of 700°C or higher, FeO and SnO are preferred.

[0026] (solvent) The solvent can disperse or dissolve the above-mentioned metal particles, binder, and metal oxide additive, and does not affect the dielectric tape. Examples include terpineols such as α-terpineol, cyclohexanone, diethylene glycol monobutyl ether acetate, and dihydroterpineol acetate. One solvent may be used, or two or more solvents may be mixed and used.

[0027] The solvent content varies depending on the type of component, but is 30% by mass or more and 80% by mass or less relative to the conductive paste for electrode formation, preferably 40% by mass or more and 70% by mass or less.

[0028] (Other additives) The conductive paste for electrode formation according to this disclosure may contain additives in addition to the above-mentioned components. Examples of additives include dispersants, viscosity modifiers, plasticizers, and adhesion promoters.

[0029] In the manufacturing of multilayer ceramic capacitors, using the conductive paste for electrode formation of this disclosure promotes the combustion (oxidation) of the binder in the binder removal process, allowing the use of binders with high content and high molecular weight, and enabling the thinning of the electrode layer and dielectric layer, thereby miniaturizing the multilayer ceramic capacitor.

[0030] The binder removal process described herein involves heat-treating a laminate, in which unfired dielectric tape and electrode patterns formed by the above-mentioned conductive paste for electrode formation are alternately layered, in a reducing atmosphere at 500 to 1000°C. Since the combustion (oxidation) of the binder is promoted, even when using a high-content, high-molecular-weight binder for the purpose of thinning the layer, the binder removal process can be performed at the same heating temperature and time as conventional methods. Furthermore, when using a normal binder, the binder removal process can be performed at a lower heating temperature and for a shorter heating time than conventional methods.

[0031] Other embodiments of the conductive paste for electrode formation further contain a dielectric material in addition to metal particles, a binder, a metal oxide additive, and a solvent.

[0032] (Dielectric materials) The dielectric material may be, for example, the material that constitutes the dielectric layer in a multilayer ceramic capacitor. A multilayer ceramic capacitor is obtained by debinding a laminate in which unfired dielectric tape and electrode patterns made of the above-mentioned conductive paste for electrode formation are alternately stacked, and then firing it. The dielectric tape and the electrode patterns have different shrinkage rates during firing, and if the difference in shrinkage rates is large, cracks and delamination may occur in the multilayer ceramic capacitor, which may reduce the yield. By incorporating the dielectric material that constitutes the dielectric layer into the conductive paste for electrode formation in advance, the difference in shrinkage rates between the dielectric tape and the electrode patterns can be reduced, and the decrease in yield can be suppressed.

[0033] Since the dielectric material only needs to have a small difference in shrinkage rate compared to the dielectric tape, various materials used in known dielectric layers can be used. Examples of dielectric materials include strontium titanate powder, barium titanate powder, barium strontium titanate powder, and barium in which an alkaline earth element such as calcium or strontium is dissolved. 1-x Ca x TiO3 (X=0.01~0.1) powder, Ba 1-x Sr xTiO3 (X=0.01~0.1) powder, or a barium titanate site in which calcium is solid-dissolved and zirconium is solid-dissolved in the titanium site. 1-x Ca x Ti 1-y Examples include ZryO3 (X=0.01~0.1, y=0.05~0.5) powder. Preferably, the dielectric material is the same dielectric material (common material) as the dielectric material constituting the dielectric layer in a multilayer ceramic capacitor manufactured using a conductive paste for electrode formation. If the dielectric material constituting the dielectric layer is, for example, barium titanate, then the dielectric material to be included in the conductive paste for electrode formation may also be barium titanate powder.

[0034] The dielectric material content varies depending on the type of dielectric material used, but is generally 0.5% by mass or more and 40% by mass or less relative to the metal particles, preferably 5% by mass or more and 20% by mass or less.

[0035] A method for manufacturing conductive paste for electrode formation will be described below. The manufacturing method shown below is just one example, and conductive paste for electrode formation may be manufactured by other methods.

[0036] A metal slurry is prepared by adding a solvent and a dispersant to metal particles and subjecting them to a dispersion treatment. A binder is added to the metal slurry to adjust it to a predetermined solid content concentration and viscosity. Separately from the metal slurry, an accelerator slurry is prepared by adding a solvent and a dispersant to a metal oxide additive and subjecting it to a dispersion treatment. A binder is added to the accelerator slurry to adjust it to a predetermined solid content concentration and viscosity. The metal slurry and the accelerator slurry are mixed and adjusted to a predetermined solid content concentration and viscosity to obtain a conductive paste for electrode formation.

[0037] If the conductive paste for electrode formation contains a dielectric material, the dielectric material should be added to the accelerator slurry beforehand.

[0038] A method for manufacturing multilayer ceramic capacitors will be described below. The manufacturing method shown below is just one example, and multilayer ceramic capacitors may be manufactured by other methods as long as the conductive paste for electrode formation of this disclosure is used.

[0039] A dielectric slurry containing ceramic powder, additives, and a dispersant is prepared. A binder is added to the dielectric slurry to adjust it to a predetermined solid content concentration and viscosity. The dielectric slurry is formed on a carrier film to produce a dielectric tape. An electrode pattern is printed on the dielectric tape using the conductive paste for electrode formation of this disclosure to produce a patterned dielectric film. The patterned dielectric films are laminated and pressed to obtain a laminate. The laminate is cut into individual pieces and subjected to a debindering treatment in a reducing atmosphere. After the debindering treatment, it is fired in a reducing atmosphere. The capacitor body obtained after firing is subjected to re-oxidation treatment and barrel polishing treatment as needed. External electrodes are formed on the capacitor body and the surface of the external electrodes is plated to obtain a multilayer ceramic capacitor.

[0040] (Examples) Conductive pastes for electrode formation were prepared containing the following metal oxides as additives: CuO (Example 1), Co3O4 (Example 2), Fe2O3 (Example 3), SnO2 (Example 4), and ZnO (Example 5). The composition of the conductive paste for electrode formation in Example 1 is as follows. As a comparative example, a conductive paste for electrode formation without metal oxide additives was prepared.

[0041] Metal particles: Nickel powder (average particle size 200nm) 500g Binder: Polyvinyl butyral 25g Metal oxide additive: CuO 3.39g Dielectric material: Barium titanate powder (average particle size 20 nm) 50 g Solvent: Dihydroterpineol acetate 500g

[0042] The metal particles constitute 40% by mass of the total paste, the binder constitutes 5% by mass relative to the metal particles, the metal oxide additive (CuO) constitutes 0.5 mol% relative to the metal particles, the dielectric material constitutes 10% by mass relative to the metal particles, and the solvent constitutes 100% by mass relative to the metal particles. In addition, the metal oxide additives in Examples 2 to 5 were also added in an amount of 0.5 mol% relative to the metal particles.

[0043] Multilayer ceramic capacitors were fabricated using barium titanate as the dielectric material, employing each of the prepared conductive pastes for electrode formation. For each conductive paste, the heating temperature during the binder removal process was set to 600°C, 800°C, and 950°C. All other conditions in the manufacturing process of the multilayer ceramic capacitors were kept the same.

[0044] Each multilayer ceramic capacitor was weighed to 0.5g, 1.5g of a combustion aid (Cu) was added, and the mixture was heated to 1200°C using a high-frequency heating device. The amount of carbon in the generated gas was measured using a carbon analyzer. The amount of carbon measured here represents the amount of carbon remaining in the multilayer ceramic capacitor, and is due to the binder that remained without being burned (oxidized) during the debindering process. The measurement results for the residual carbon amount [mass%] are shown in Table 1.

[0045] [Table 1]

[0046] When CuO (Example 1) and Co3O4 (Example 2) were used as metal oxide additives, the amount of residual carbon was lower than that of the comparative examples, regardless of whether the debindering temperature was 600°C, 800°C, or 950°C. When Fe2O3 (Example 3) and SnO2 (Example 4) were used, the amount of residual carbon was almost the same as that of the comparative examples at a debindering temperature of 600°C, but was lower than that of the comparative examples at 800°C and 950°C. Fe2O3 and SnO2 showed no effect at 600°C because their standard Gibbs free energy of formation is lower than that of carbon dioxide and carbon monoxide at 500-700°C in the Ellingham diagram, but showed an effect at 800°C and 950°C because their standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide at 700-1000°C. ZnO showed an effect at 950°C because its standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide at 950-1000°C.

[0047] The following embodiments are possible with respect to this disclosure.

[0048] The conductive paste for electrode formation of the present disclosure comprises metal particles, a binder, a metal oxide additive, and a solvent, wherein the metal oxide additive includes a metal oxide whose standard Gibbs free energy of formation is higher than that of carbon dioxide or carbon monoxide in the Ellingham diagram, and which is within the range of 500 to 1000°C.

[0049] According to the conductive paste for electrode formation of this disclosure, the metal oxide additive promotes the combustion of the binder resin, so a binder for thinning can be used, making it possible to miniaturize multilayer ceramic capacitors.

Claims

1. It contains metal particles, a binder, a metal oxide additive, and a solvent. The aforementioned metal oxide additive is Co ３ O ４ (Cobalt(II,III) oxide), FeO (Iron(II) oxide), SnO (Tin(II) oxide), SnO ２ A conductive paste for forming internal electrodes in multilayer ceramic capacitors, comprising at least one selected from tin(IV) oxide and zinc oxide (ZnO).

2. The conductive paste for electrode formation according to claim 1, wherein the metal oxide additive comprises two or more metal oxides.

3. The conductive paste for electrode formation according to claim 1, wherein the content of the metal oxide additive is 0.005 to 5 mol% as an oxide relative to the metal particles.

4. The conductive paste for electrode formation according to claim 1, further comprising a dielectric material.

5. The conductive paste for electrode formation according to claim 1, wherein Ni powder is used as the metal particles.

6. The conductive paste for electrode formation according to claim 1, wherein the metal particles constitute 20 to 70% by mass of the entire conductive paste for electrode formation.

7. The conductive paste for electrode formation according to claim 1, wherein the binder is present in an amount of 0.5% by mass or more and 20% by mass or less relative to the metal particles.

8. A method for removing binder in the manufacturing of ceramic capacitors, A binder removal method comprising heating a laminate in which unfired dielectric tape and an electrode pattern formed by a conductive paste for electrode formation according to any one of claims 1 to 7 are alternately stacked, in a reducing atmosphere at 500 to 1000°C.

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