Multilayer ceramic electronic component and method for manufacturing same

Abstract

A multilayer ceramic electronic component according to one embodiment of the present invention comprises a laminate in which a ceramic layer and an internal electrode containing a metal as a main component are alternately laminated, an element body having a ceramic protection part that covers the surface of the laminate, and an external electrode that is disposed on the surface of the element body and is electrically connected to the internal electrode. The relationship 0.12 ppm ≤ CS ≤ 14.5 ppm is satisfied, where CS is the sulfur concentration in the element body, the sulfur concentration being obtained by dividing a sulfur amount obtained through analysis using a combustion-infrared absorption method for a gas generated in a process for heating, to 1250°C, a powder-form sample obtained by grinding the element body by the mass of the powder-form sample before heating.

Description

Multilayer ceramic electronic component and its manufacturing method

[0001] The present invention relates to a multilayer ceramic electronic component and a method for manufacturing the same.

[0002] Multilayer ceramic electronic components, particularly multilayer ceramic capacitors, are used to control voltage and current in automobiles and healthcare / medical devices. Demand for multilayer ceramic capacitors has been increasing in recent years due to the electrification of automobiles and the growing demand for healthcare / medical devices. Since failures or malfunctions in automobiles and healthcare / medical devices pose a threat to the safety of users, the multilayer ceramic capacitors used in these devices must be highly reliable.

[0003] One of the causes of reduced reliability in multilayer ceramic capacitors is structural defects such as cracks that occur inside the capacitor. Multilayer ceramic capacitors are generally manufactured by printing a paste for internal electrodes on green sheets containing dielectric powder and a binder, laminating and pressing multiple green sheets together, and then degreasing and firing the resulting capacitors. If structural defects such as delamination or cracks occur due to the binder burning suddenly or the internal electrodes shrinking significantly during the degreasing and firing process, these structural defects can become a pathway for moisture and other degrading factors to penetrate, reducing reliability.

[0004] As a method for reducing structural defects in multilayer ceramic capacitors, it has been reported that the catalytic action of nickel, which is an internal electrode material, is suppressed by sulfur, thereby suppressing the rapid combustion of the binder (for example, Patent Documents 1 to 3).

[0005] Patent Document 1 discloses that the nickel paste for the internal electrodes contains a sulfur-containing organic compound.

[0006] Patent Documents 2 and 3 disclose that nickel particles used in paste for internal electrodes contain sulfur.

[0007] In this way, by suppressing the catalytic action of nickel with sulfur, it is possible to suppress the rapid combustion of the binder during degreasing. However, when using an internal electrode paste containing sulfur, it is necessary to take new measures to prevent structural defects caused by gases generated by decomposition or volatilization of sulfur or compounds containing sulfur (for example, Patent Document 3).

[0008] Patent Document 3 discloses that nickel powder generates a gas containing sulfur in a temperature range of 750°C or higher, which is higher than the degreasing temperature, and that the amount of gas generated and the temperature range are controlled.

[0009] JP 2006-24539 A JP 2014-91862 A JP 2017-25400 A

[0010] When a sulfur-containing internal electrode paste is used to suppress structural defects during the manufacture of multilayer ceramic capacitors, sulfur remains in the compact after degreasing, and the sulfur burns during firing, creating a localized reducing atmosphere, which can be problematic. Specifically, the localized reducing atmosphere can cause the ceramic dielectric to become semiconducting or promote the solid solution of the dielectric components, causing abnormal grain growth and significantly reducing reliability.

[0011] Patent Document 3 examines the relationship between the sulfur content in the internal electrode paste and the type and amount of gas generated when the paste is heated, but does not examine the sulfur content in the molded body after degreasing or the laminated sintered body after firing.

[0012] The present invention has been made to solve the above problems, and has as its object to provide a highly reliable multilayer ceramic electronic component.

[0013] The present inventors have conducted various studies to solve the above-mentioned problems, and have found that the above object can be achieved by using an internal electrode paste containing metal particles and sulfur when manufacturing a multilayer ceramic capacitor, and optimizing the heat treatment conditions of the molded body to adjust the temperature at which sulfur compounds start to be generated during firing to 750°C or higher, the temperature at which the amount of generation peaks to 750°C or higher and 1000°C or lower, and the temperature at which generation ends to 1050°C or lower, and by controlling the amount of sulfur in the element constituting the obtained multilayer ceramic capacitor to be within a specific range, thereby completing the present invention.

[0014] That is, a first aspect of the present invention for solving the above-mentioned problems is a laminate in which ceramic layers and internal electrodes mainly composed of metal are alternately laminated, and an element body having a ceramic protective part covering the surface of the laminate, and external electrodes arranged on the surface of the element body and electrically connected to the internal electrodes, wherein the element body is pulverized into a powder sample, and a sulfur amount obtained by analyzing gas generated in the process of heating the powder sample to 1250°C using a combustion-infrared absorption method is divided by the mass of the powder sample before heating to obtain a sulfur concentration C in the element body. Ｓ When set to 0.12 ppm≦C Ｓ The multilayer ceramic electronic component satisfies the condition of ≦14.5 ppm.

[0015] A second aspect of the present invention for solving the above-mentioned problems includes: (A) preparing ceramic powder; (B) mixing the ceramic powder with a binder and forming the mixture into a sheet to obtain a green sheet; (C) forming an internal electrode pattern containing metal and sulfur on the green sheet; (D) stacking a predetermined number of the green sheets on which the internal electrode pattern has been formed, and arranging green sheets for cover layers at both ends in the stacking direction, and then pressing the stacked sheets together to obtain a green laminate; (E) dividing the green laminate into individual pieces to obtain a pre-fired element; and (F) separating the pre-fired element from the binder. (H) heat-treating the pre-fired body after binder removal in a weakly reducing atmosphere at a temperature range of 800°C to 1100°C for 1 hour to 48 hours, and (I) firing the heat-treated pre-fired body to obtain a sintered body, and the method also includes either (G) after (F), applying an external electrode paste to the surface of the pre-fired body after binder removal, or (J) after (I), forming external electrodes on the surface of the sintered body.

[0016] According to the present invention, a highly reliable multilayer ceramic electronic component can be provided.

[0017] FIG. 1 is a schematic diagram (longitudinal cross-sectional view) showing the structure of the multilayer ceramic capacitor according to the first embodiment of the present invention. FIG. 2 is a schematic diagram (width-direction cross-sectional view) showing the structure of the multilayer ceramic capacitor according to the first embodiment of the present invention. FIG. 3 is a schematic diagram (longitudinal cross-sectional view) showing the structure of a first modified example of the multilayer ceramic capacitor according to the first aspect of the present invention. FIG. 4 is a schematic diagram (longitudinal cross-sectional view) showing the structure of a second modified example of the multilayer ceramic capacitor according to the first aspect of the present invention. FIG. 5 is a schematic diagram (overall perspective view) showing the structure of a third modified example of the multilayer ceramic capacitor according to the first aspect of the present invention. FIG. 6 is a Weibull plot created based on HALT results for the multilayer ceramic capacitors according to the examples and comparative examples of the present invention.

[0018] The configuration and effects of the present invention will be described below, along with the technical concept, with reference to the drawings. However, the mechanism of action includes assumptions, and the correctness of such assumptions does not limit the present invention.

[0019] [Multilayer Ceramic Electronic Component] <First Embodiment> FIG. 1 shows a first embodiment of a multilayer ceramic capacitor, which is an embodiment of a multilayer ceramic electronic component according to a first aspect of the present invention. The multilayer ceramic capacitor 100 according to the first embodiment has a rectangular parallelepiped shape and includes a pair of faces perpendicular to each of three mutually orthogonal axes: the L axis, which is the length direction, the W axis, which is the width direction, and the T axis, which is the height direction. The rectangular parallelepiped is not limited to a mathematically defined rectangular parallelepiped; any shape can be recognized as a rectangular parallelepiped when observed as a whole. Therefore, a rectangular parallelepiped in the present disclosure also includes a ceramic capacitor with rounded edges and corners, a ceramic capacitor with curved edges, and a ceramic capacitor with curved faces with a small curvature. The length (L), width (W), and height (T) dimensions of the ceramic capacitor 100 can each independently take any value, and the relative sizes among them are not limited. For example, (L direction dimension) > (W direction dimension) ≥ (T direction dimension), or (W direction dimension) > (L direction dimension), or (T direction dimension) > (W direction dimension).

[0020] The size of the multilayer ceramic capacitor 100 is, for example, 0.25 mm in the L direction, 0.125 mm in the W direction, and 0.125 mm in the T direction, or 0.4 mm in the L direction, 0.2 mm in the W direction, and 0.2 mm in the T direction, or 0.6 mm in the L direction, 0.3 mm in the W direction, and 0.3 mm in the T direction, or 1.0 mm in the L direction, 0.5 mm in the W direction, and 0.5 mm in the T direction, or 3.2 mm in the L direction, 1.6 mm in the W direction, and 1.6 mm in the T direction, or 3.2 mm in the L direction, 2.5 mm in the W direction, and 2.5 mm in the T direction, or 4.5 mm in the L direction, 3.2 mm in the W direction, and 2.5 mm in the T direction. As the size of the multilayer ceramic capacitor 100 increases, the amount of the internal electrodes 22 increases, which increases the likelihood of structural defects caused by the catalytic action of the metal that is its main component, and defects such as semiconductorization of the ceramic layer and abnormal grain growth caused by sulfur added to suppress the catalytic action. Therefore, the effect of suppressing these defects by keeping the sulfur content in the element body 10 within a specific range becomes more pronounced in large-sized multilayer ceramic capacitors 100. Specifically, the effect of suppressing the defects becomes more pronounced in multilayer ceramic capacitors that satisfy any of the following: a length of 3.2 mm or more, a width of 2.5 mm or more, and a height of 2.5 mm or more.

[0021] As shown in the cross-sectional views of FIG. 1 (LT cross section) and FIG. 2 (WT cross section), the multilayer ceramic capacitor 100 according to the first embodiment includes a laminate 20 in which dielectric layers 21 made of dielectric ceramic and internal electrodes 22 mainly composed of metal are alternately stacked in the T direction, and an element body 10 having a protective portion 30 covering the surface of the laminate 20.

[0022] The element body 10 has lead portions 11 (11a, 11b) on a surface parallel to the stacking direction (T direction) from which the internal electrodes 22 (22a, 22b) are drawn every other layer. That is, the element body 10 has a lead portion 11a from which the internal electrode 22a is drawn in the L direction and a lead portion 11b from which the internal electrode 22b is drawn in the L direction. In the multilayer ceramic capacitor 100 shown in FIG. 1 , a pair of lead portions 11a and 11b are formed on substantially the entire opposing surfaces perpendicular to the L direction of the element body 10. However, the arrangement of the lead portions in the multilayer ceramic capacitor according to the first aspect of the present invention is not limited to this. The lead portions may be formed only in a portion of a surface parallel to the stacking direction, or may be formed only in one surface, or multiple pairs may be formed. Furthermore, the lead portions may not only directly draw the internal electrodes, but also draw connecting conductors that electrically connect internal electrodes of the same polarity to each other, as in a second modified example described below.

[0023] A protective portion 30 is arranged on the surface of the element body 10 other than the draw-out portion, covering the surface of the laminate 20. The protective portion 30 includes a cover portion 31 arranged on a surface perpendicular to the T direction and a side margin portion 32 arranged on a surface perpendicular to the W direction.

[0024] The multilayer ceramic capacitor 100 according to the first embodiment includes external electrodes 40a and 40b that are disposed on the surface of the element body 10 and electrically connect the internal electrodes 22a and 22b that are led out to the lead portions 11a and 11b, respectively.

[0025] Hereinafter, each component constituting the multilayer ceramic capacitor 100 according to the first embodiment will be described in detail.

[0026] (Dielectric Layer) The dielectric layer 21 is made of a dielectric ceramic. The composition of the dielectric ceramic is not particularly limited as long as it forms a dense dielectric ceramic by co-firing with the internal electrodes 22 described later, and may be appropriately selected depending on the properties required for the multilayer ceramic capacitor. Examples of the composition of the dielectric ceramic include barium titanate (BaTiO ３ ) as the main component, strontium titanate (SrTiO ３) as the main component, and Ba having a perovskite structure １－ｘ－ｙ Ca ｘ Sr ｙ Ti １－ｚ Zr ｚ O ３ Examples of the dielectric ceramic include those having the above-mentioned main component as a main component. The dielectric ceramic may contain an additive element in addition to the main component. Examples of the additive element include at least one selected from Mo, Nb, Ta, W, Mg, Mn, V, Cr, rare earth elements (Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), and Co, Ni, Li, B, Na, K, and Si. The additive element may be contained as a single element or in the form of a compound such as an oxide, nitride, or carbide. Furthermore, the additive element may exist in a solid solution state in the main component, or may form a different phase from the elements constituting the main component or other additive elements.

[0027] The average particle size of the dielectric layers 21 is preferably 0.5 μm or less. When the average particle size is within this range, the reliability of the multilayer ceramic capacitor 100 is particularly high. The average particle size is more preferably 0.3 μm or less.

[0028] Here, the average particle diameter of the dielectric layer 21 is determined by the following procedure. First, the multilayer ceramic capacitor 100 is cut along a plane parallel to the lamination direction passing through the vicinity of the center in the L direction to obtain a cut surface on which the internal electrodes 22 (22a, 22b) are exposed. Next, the cut multilayer ceramic capacitor 100 is embedded in resin so that the cut surface is exposed, and the resin is hardened. Next, the cut surface exposed on the surface of the hardened resin is mirror-polished. Next, carbon is vapor-deposited on the polished cut surface to impart conductivity, and a measurement sample is obtained. Next, the obtained measurement sample is observed using a scanning electron microscope (SEM) at a magnification that allows approximately 60 to 200 dielectric particles to fit in the field of view, and 4 to 6 photographs are taken at different observation points. Next, the photographs are processed to calculate the circle-equivalent diameter of each particle. Next, the obtained circle-equivalent diameter r of each individual particle is calculated. ｉ From the calculated number of particles n, the average particle diameter r is calculated using the following formula (1). ａｖｇis calculated, and this is used as the average grain size r ａｖｇ Let's say.

[0029]

[0030] (Internal Electrode) The internal electrodes 22 (22a, 22b) are primarily composed of a metal. The type of metal is not particularly limited, and nickel (Ni), copper (Cu), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), and alloys thereof can be used. Among these, nickel (Ni) is preferred as the primary component because of its high heat resistance, which allows for the formation of a dense dielectric layer 21 at elevated firing temperatures, and its relatively low cost. Here, the term "primary component element" as used herein refers to the element with the highest content, expressed in atomic percent (atomic %). Each of these metals may catalytically induce rapid combustion of the binder during firing in the manufacture of the multilayer ceramic capacitor 100. However, the catalytic action of each of these metals can be suppressed by using sulfur in combination with the metals when forming the internal electrode pattern.

[0031] The internal electrodes 22 (22a, 22b) may contain, in addition to metal, dielectric particles having the same composition as the dielectric ceramic that constitutes the dielectric layer 21, or a glass component.

[0032] (Protective portion) The protective portion 30 includes a cover portion 31 arranged on a surface perpendicular to the T direction of the laminate 20 and a side margin portion 32 arranged on a surface perpendicular to the W direction, and has the function of protecting the dielectric layer 21 and the internal electrode 22.

[0033] There are no limitations on the material of the protective part 30, as long as it has high electrical insulation and low permeability to deterioration factors such as moisture. From the viewpoints of making shrinkage during firing uniform when manufacturing the multilayer ceramic capacitor 100 and mitigating internal stress within the multilayer ceramic capacitor 100, it is preferable that the main component of the protective part 30 be the same as that of the dielectric ceramic that forms the dielectric layer 21.

[0034] (Element) The element 10 having the dielectric layer 21, the internal electrode 22, and the protective portion 30 is crushed into a powder sample, and the powder sample is heated to 1250°C. The sulfur concentration C is calculated by dividing the amount of sulfur obtained by analyzing the gas generated by the combustion-infrared absorption method by the mass of the powder sample before heating. Ｓ However, 0.12 ppm≦C Ｓ ≦14.5 ppm. Ｓ When the value of C is within the above range, the multilayer ceramic capacitor 100 becomes highly reliable. This is presumably due to the following mechanism. Ｓ corresponds to the sulfur concentration in the element body 10. Ｓ The fact that the content of sulfur is 0.12 ppm or more indirectly indicates that a sufficient amount of sulfur is contained to suppress the rapid combustion of the binder caused by the catalytic action of the metal that is the main component of the internal electrodes during firing in the manufacture of the multilayer ceramic capacitor 100. As a result of the action of sulfur suppressing the rapid combustion of the binder and the contraction of the internal electrodes, the element body 10 has fewer structural defects, and the multilayer ceramic capacitor 100 has high reliability. Ｓ The fact that the sulfur content is 14.5 ppm or less indirectly indicates that the sulfur present during degreasing in the production of the multilayer ceramic capacitor 100 was sufficiently removed before firing, and that the generation of a local reducing atmosphere due to sulfur was suppressed during firing. As a result, the semiconductivity and abnormal grain growth of the dielectric layer 21 are suppressed, resulting in a highly reliable multilayer ceramic capacitor 100. Note that, in this disclosure, "sulfur" refers to elemental sulfur unless otherwise specified. Therefore, when an element body or internal electrode is described as "containing sulfur," this refers not only to cases where the element body or internal electrode contains elemental sulfur, but also to cases where the element body or internal electrode contains an organic or inorganic compound containing sulfur as a constituent element.

[0035] Here, C ＳThe value of is determined by the following procedure. First, the external electrodes 40 (40a, 40b) and the like present on the surface of the element body 10 of the multilayer ceramic capacitor 100 are scraped off with waterproof abrasive paper (#500) to obtain the element body 10. Next, the obtained element body 10 is ground using a mortar and pestle to obtain a powdered sample. Next, a predetermined mass of the obtained powdered sample is heated to 1250°C in a high-frequency induction heating furnace, and the amount of sulfur obtained by analyzing the generated gas using a combustion-infrared absorption method is divided by the mass of the powdered sample before heating to obtain the value C. Ｓ Let's say.

[0036] The total amount of metal contained in the element body 10 is preferably 15 mg or more. In an element body 10 with a high metal content, the catalytic activity of the metal is enhanced, which makes the above-mentioned rapid combustion of the binder and large shrinkage of the internal electrodes more likely to occur during degreasing. Furthermore, a high metal content in the element body 10 is synonymous with a large size of the element body 10. In such a large-sized element body 10, if an internal electrode pattern containing sulfur is formed to suppress the catalytic activity, the sulfur is less likely to escape from the center during firing, and sulfur is likely to remain in the element body 10. Therefore, the sulfur in the element body 10 is likely to cause semiconductorization and abnormal grain growth of the dielectric layer 21. For these reasons, as described below, by setting the sulfur content of the element body 10 within a specific range, the effect of suppressing structural defects and defects such as semiconductorization and abnormal grain growth of the dielectric layer is more pronounced.

[0037] When the multilayer ceramic capacitor 100 is manufactured by oneself, the total amount of metal contained in the element body 10 can be calculated based on the composition and amount of the internal electrode paste used during manufacturing. On the other hand, when the multilayer ceramic capacitor 100 is obtained as a finished product, the total amount of metal in the element body 10 is determined by the following procedure. Ｓ A powder sample is obtained in the same manner as in the determination procedure of C. ＳThe mass of the obtained powdered sample may be measured and used as the element mass. The obtained powdered sample is then immersed in an acid solution to dissolve the metal. The type and concentration of the acid solution used may be any that can dissolve the metal that is the main component of the internal electrodes 22 (22a, 22b) without dissolving the dielectric layer 21 (dielectric ceramic) contained in the element body 10. As an example, when the main component of the dielectric layer is barium titanate and the main component of the internal electrodes is nickel, dilute nitric acid can be used. The acid solution containing the powdered sample is then filtered, and the solid content is washed and dried. The mass of the obtained solid content is then measured and used as the dielectric mass. The value obtained by subtracting the dielectric mass from the element mass is used as the total amount of metal contained in the element body 10.

[0038] (External Electrodes) The external electrodes 40 (40a, 40b) are arranged on the surface of the element body 10 and are electrically connected to the internal electrodes 22 (22a, 22b) led out to the lead portions 11 (11a, 11b). As described above, in the multilayer ceramic capacitor according to the first aspect, the arrangement of the lead portions is not limited to that shown in FIG. 1 , and therefore, it goes without saying that the arrangement of the external electrodes is also not limited to this.

[0039] The material of the external electrodes 40 (40a, 40b) is not limited as long as it is conductive. Examples of the material include metals such as nickel (Ni), copper (Cu), tin (Sn), palladium (Pd), platinum (Pt), silver (Ag), and gold (Au), alloys containing any of these as a main component, and conductive resins. The external electrodes 40 (40a, 40b) may be formed by laminating multiple conductive materials on the surfaces of the lead portions 11 (11a, 11b). In the multilayer ceramic capacitor 100 according to the first embodiment shown in FIG. 1 , the entire external electrode 40 has a laminated structure in which a Cu layer 42, a Ni layer 43, and a Sn layer 44 are formed in this order on the surface of a base layer 41 made of Ni.

[0040] <Modification (1)> A first modification of the multilayer ceramic capacitor according to the first embodiment is a multilayer ceramic capacitor 200 in which external electrodes 40 (40 a, 40 b) are arranged in an L-shape in cross section on the surface of the element body 10, as shown in Fig. 3. The multilayer ceramic capacitor 200 having such a structure has the advantage that it can be made low-profile, since the external electrodes 40 do not extend around the upper cover layer.

[0041] <Modification (2)> A second modification of the multilayer ceramic capacitor according to the first embodiment is a multilayer ceramic capacitor 300 in which the connection conductors 23 (23a, 23b) that electrically connect internal electrodes 22 (22a, 22b) of the same polarity formed inside the element body 10 are drawn out to one cover portion 31 to form drawn-out portions 11 (11a, 11b), as shown in Fig. 4. The multilayer ceramic capacitor 300 having such a structure has the advantage that it can be made smaller, since there are no external electrodes 40 (40a, 40b) in the L direction and the W direction.

[0042] <Modification (3)> A third modification of the multilayer ceramic capacitor according to the first embodiment is a multilayer ceramic capacitor 400 in which external electrodes 40 are arranged at four locations, as shown in Fig. 5. Even in a multilayer ceramic capacitor having such a structure, the effect of the present invention, i.e., improved reliability, can be obtained by setting the amount of sulfur contained in the element body within a specific range.

[0043] [Method for Manufacturing Multilayer Ceramic Electronic Component] Second Embodiment Next, a method for manufacturing a multilayer ceramic electronic component according to a second aspect of the present invention will be described below as a second embodiment, taking as an example the case of manufacturing the multilayer ceramic capacitor according to the first embodiment.

[0044] (A) Preparation of Dielectric Porcelain Composition Powder) First, a powder of the dielectric porcelain composition is prepared. Commercially available powder of the dielectric porcelain composition can be used as appropriate. When the dielectric porcelain composition is produced in-house, various raw material powders containing the constituent elements thereof are mixed in a predetermined ratio and pre-fired (calcined). When the various raw material powders are mixed in a predetermined ratio, various additives such as the above-mentioned additive elements and sintering aids may be further added, and these various additives may be further added to the powder after calcination.

[0045] (B) Preparation of Green Sheet Next, the powder of the dielectric ceramic composition described above is mixed with a binder and a dispersion medium to prepare a slurry, and the slurry is formed into a sheet to obtain a green sheet.

[0046] The binder used is one that can maintain the shape of the green sheet and volatilizes without leaving carbon or other residues during the binder removal process prior to firing. Examples of binders that can be used include polyvinyl alcohol, polyvinyl butyral, cellulose, urethane, and vinyl acetate binders. The amount of binder used is not particularly limited, but since it is removed in a later process, it is preferable to keep it as small as possible within a range that achieves the desired moldability and shape retention in order to reduce raw material costs.

[0047] The dispersion medium used is one that does not cause aggregation of the calcined powder and binder and can be easily removed by volatilization or the like after forming into a green sheet, as described below. Examples of the dispersion medium that can be used include water and alcohol-based solvents.

[0048] Components for adjusting the properties of the slurry, such as dispersants, plasticizers, and thickeners, may be added to the slurry.

[0049] The method for mixing the mixed powder with the binder and the dispersion medium is not particularly limited as long as the components are mixed uniformly while preventing the inclusion of impurities. One example is ball mill mixing.

[0050] The prepared slurry can be formed into a sheet to obtain a green sheet by a commonly used method such as a doctor blade method or a die coating method.

[0051] (C) Formation of Internal Electrode Pattern Next, the formation of an internal electrode pattern containing metal and sulfur on the green sheet can be performed by a method of printing or applying an internal electrode paste containing each of the components onto the green sheet in a predetermined pattern, or by a method of forming a film containing each of the components onto the green sheet in a predetermined pattern by vapor deposition or sputtering. By making the internal electrode pattern contain sulfur, the catalytic action of the metal is suppressed, and the formation of structural defects caused by the rapid combustion of the binder during binder removal, which will be described later, can be suppressed.

[0052] When forming an internal electrode pattern using an internal electrode paste, the internal electrode paste used is obtained by mixing metal particles, elemental sulfur or a sulfur-containing compound, and a vehicle in a triple roll mill. The internal electrode paste may contain glass frit and dielectric ceramic composition powder in addition to the above-mentioned components.

[0053] The amount of sulfur in the internal electrode paste is preferably 0.01 mass % or more and 1.0 mass % or less, and more preferably 0.05 mass % or more and 0.5 mass % or less, in terms of elemental conversion relative to the mass of the metal particles, in order to effectively suppress the catalytic action of the metal while suppressing the conversion of the dielectric layer to semiconductor.

[0054] The type and amount of binder and solvent contained in the vehicle to be used are not limited, and may be selected appropriately taking into consideration the viscosity of the internal electrode paste, ease of handling, compatibility with the green sheet, and the like.

[0055] The internal electrode paste can be printed on the green sheet using, for example, a screen mask on which a predetermined internal electrode pattern is formed. When printing, spaces that will become side margins when the multilayer ceramic capacitor is completed may be left.

[0056] (D) Preparation of green laminate Next, a predetermined number of green sheets on which the internal electrode patterns have been formed are stacked and the green sheets are pressure-bonded together to obtain a green laminate. The stacking and pressure-bonding may be performed by a conventional method, and a method such as pressing the stacked green sheets together in the stacking direction while heating them and thermo-compressing them by the action of a binder can be used.

[0057] During lamination and compression bonding, green sheets that will become cover portions when the multilayer ceramic capacitor is completed are added to both ends in the lamination direction. In this case, the green sheets to be added may have the same composition as the green sheets on which the internal electrode patterns are printed, or a different composition. From the viewpoint of making the shrinkage rate during firing uniform, it is preferable that the composition of the green sheets to be added is the same as or similar to the green sheets on which the above-mentioned internal electrode precursors are arranged.

[0058] (E) Preparation of Pre-fired Element Next, the green laminate is singulated into individual element shapes to obtain pre-fired elements. For singulation, a commonly used means such as a dicing saw or a laser cutting machine can be used. After singulating the green laminate to form a surface on which the internal electrode precursor is exposed, the surface may be coated with a material for forming a side margin portion to obtain a pre-fired element.

[0059] (F) Removal of Binder Next, the obtained pre-fired body is heated to volatilize and remove the binder. The heating conditions may be appropriately set in consideration of the volatilization temperature and content of the binder. For example, nitrogen (N ２ ) atmosphere at a temperature of 200°C to 500°C for 5 to 20 hours.

[0060] (G) Application of External Electrode Paste Next, if necessary, external electrode paste is applied to the surface of the pre-fired element body from which the binder has been removed, so as to cover the lead portions. If external electrode paste is not applied to the pre-fired element body at this stage, external electrodes are formed by (J) described below.

[0061] The external electrode paste used is obtained by mixing metal particles and ceramic particles having the same composition as the dielectric ceramic composition contained in the pre-fired element body together with a vehicle in a triple roll mill. The external electrode paste may contain glass frit in addition to the above-mentioned components.

[0062] There are no limitations on the type and amount of binder and solvent contained in the vehicle used, and they may be selected appropriately taking into consideration the viscosity of the external electrode paste, ease of handling, and the like.

[0063] Examples of methods for applying the external electrode paste include immersing (dipping) a portion of the pre-fired element body in a bath of the external electrode paste, or applying the external electrode paste to the surface of the pre-fired element body.

[0064] (H) Pre-firing heat treatment) Next, the pre-firing element body from which the binder has been removed and to which external electrode paste has been applied as necessary is subjected to a pre-firing heat treatment for 1 to 48 hours in a weakly reducing atmosphere at a temperature range of 800°C to 1100°C prior to firing. By such a pre-firing heat treatment in which the element body is maintained at a relatively high temperature for a long period of time in a weakly reducing atmosphere, sulfur contained in the internal electrode pattern is volatilized and removed from the pre-firing element body, and its concentration is sufficiently reduced. As a result, the formation of a localized reducing atmosphere due to residual sulfur is suppressed during firing, which is performed subsequent to the pre-firing heat treatment.

[0065] The weak reducing atmosphere used in the pre-firing heat treatment is hydrogen (H ２ ) at a concentration of 0.01% by volume or more and 0.3% by volume or less, and the balance is nitrogen (N ２ ) a nitrogen-hydrogen mixed atmosphere is exemplified.

[0066] (I) Firing of Pre-Firing Body) Next, the body after the pre-firing heat treatment is heated to a predetermined temperature and fired. When setting the firing conditions, it is preferable to take into consideration the sinterability of the dielectric ceramic composition, and the heat resistance and oxidation resistance of the metal contained in the internal electrode paste. Furthermore, when an external electrode paste is applied to the surface of the pre-firing body prior to firing, it is also preferable to take into consideration the heat resistance and oxidation resistance of the metal contained therein. Examples of firing conditions include the addition of nitrogen (N ２ ) and hydrogen (H ２ ) and water vapor (H ２ The firing is carried out in a reducing atmosphere containing a mixture of nitrogen (N O ) at a temperature of 1100°C to 1400°C for 10 minutes to 2 hours. ２ ) A reoxidation treatment may be performed in a gas atmosphere or a low-oxygen atmosphere at a temperature of 600°C to 1000°C.

[0067] (J) Formation of External Electrodes If the sintered body obtained by firing does not have external electrodes without performing the above (G), external electrodes are formed on the surface of the sintered body. Examples of methods for forming external electrodes include a method in which a conductive paste is applied by printing, dipping, or coating and then baked, vapor deposition, and sputtering.

[0068] The sintered body thus obtained may be used as a multilayer ceramic capacitor as is, or may be used as a multilayer ceramic capacitor after forming a conductive layer on the surface of the external electrodes by means of plating, vapor deposition, etc. The multilayer ceramic capacitor thus obtained has a structure shown in Figures 1, 2, 3, or 5.

[0069] <Modification (1) of the Second Embodiment> In the second embodiment, in order to form a connecting conductor pattern inside the element body, through holes may be formed in the green sheet prior to the formation of the internal electrode pattern. Punching, laser processing, or the like can be used as a method for forming the through holes in the green sheet. By forming the internal electrode pattern on the green sheet with the through holes formed therein, or by filling the through holes with a conductor separately from the internal electrode pattern, a green sheet with a conductor penetrating in the thickness direction can be obtained.

[0070] When green sheets having conductors penetrating therethrough in the thickness direction are stacked to form a green laminate, the conductors in the through holes are connected in the stacking direction and connected to internal electrode patterns formed on green sheets adjacent in the stacking direction, thereby forming precursors of connecting conductors. In this case, by forming through holes filled with conductors in one of the green sheets for the cover layer as well, part of the precursor of the connecting conductor is exposed on the surface of the cover layer.

[0071] <Variation (2) of the Second Embodiment> In the second embodiment, holes through which the internal electrode patterns are drawn out to the wall surfaces may be formed in the thickness direction (stacking direction) of the green laminate obtained by stacking and pressing green sheets, and a conductor may be filled in the holes to form precursors of connecting conductors.

[0072] The multilayer ceramic capacitor obtained by each of the modifications of the second embodiment has the structure shown in FIG.

[0073] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0074] Example 1 (Preparation of Internal Electrode Paste) A conductive paste containing nickel powder and 0.1 mass % of sulfur relative to the nickel powder (hereinafter simply referred to as "internal electrode paste 1") was prepared as an internal electrode paste.

[0075] (Preparation of Green Sheet) Pre-fired barium titanate (BaTiO ３ ) powder (average particle size 0.2 μm) was prepared. Furthermore, powders of oxides of Mn, Ho, Si, etc. were prepared as trace additive components. A polyvinyl butyral binder and an alcohol-based solvent were added to these powders, and the mixture was mixed in a wet ball mill. The resulting mixed slurry was molded with a doctor blade to obtain a green sheet.

[0076] (Fabrication of Multilayer Ceramic Capacitor) The internal electrode paste 1 was screen-printed on the obtained green sheet to form an electrode pattern, and then 600 layers of the green sheet were stacked. 20 green sheets without the internal electrode paste printed on each of the top and bottom surfaces were stacked to form a cover, and then thermocompression bonded to obtain a laminate. This laminate was then divided into individual pieces and heated to 300°C in a nitrogen atmosphere to remove the binder. The lead-out surface of this laminated chip was immersed in a conductive paste containing nickel to form a precursor for the external electrode. The laminate after the formation of the precursor for the external electrode was then heated in a weakly reducing atmosphere of N ２ -0.06% by volume H ２ The chips were subjected to a pre-sintering heat treatment in which they were held at 800°C for 48 hours in a nitrogen atmosphere, followed by sintering at 1200°C for 2 hours in a so-called reducing-steam atmosphere in which water vapor was introduced into a reducing gas containing hydrogen in nitrogen, to obtain the multilayer ceramic capacitor of Example 1. The obtained multilayer ceramic capacitor had a rectangular shape with a surface perpendicular to the stacking direction of the multilayer chip measuring 3.2 mm x 2.5 mm, and the dielectric layer was 2.5 μm thick. The total amount of nickel contained in the element body of the obtained multilayer ceramic capacitor was 17.4 mg.

[0077] Reference Example 1 In order to examine the influence of the amount of sulfur contained in the internal electrode pattern on the reliability of the multilayer ceramic capacitor, a multilayer ceramic capacitor according to Reference Example 1 was obtained in the same manner as in Example 1, except that a conductive paste containing nickel powder and 0.2 mass % of sulfur relative to the nickel powder (hereinafter simply referred to as "internal electrode paste 2") was used as the internal electrode paste.

[0078] Example 2 A multilayer ceramic capacitor according to Example 2 was obtained in the same manner as in Example 1, except that the temperature and time of the pre-firing heat treatment were changed to 900° C. and 12 hours, respectively.

[0079] [Comparative Examples 1 and 2] A multilayer ceramic capacitor according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the temperature and time of the pre-sintering heat treatment were changed to 200°C and 4 hours, respectively. Also, a multilayer ceramic capacitor according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the temperature and time of the pre-sintering heat treatment were changed to 1100°C and 6 hours, respectively.

[0080] [Examples 3 and 4] A multilayer ceramic capacitor according to Example 3 was obtained in the same manner as in Comparative Example 1, except that, when producing the multilayer ceramic capacitor, the number of laminations of green sheets on which internal electrode paste 1 was printed was 155. The total amount of nickel contained in the element body of the multilayer ceramic capacitor according to Example 3 was 0.190 mg. Furthermore, a multilayer ceramic capacitor according to Example 4 was obtained in the same manner as in Comparative Example 2, except that, when producing the multilayer ceramic capacitor, the number of laminations of green sheets on which internal electrode paste 1 was printed was 1060. The total amount of nickel contained in the element body of the multilayer ceramic capacitor according to Example 4 was 40.0 mg.

[0081] [Evaluation of multilayer ceramic capacitors] Ｓ For each of the multilayer ceramic capacitors according to Examples 1 to 4, Reference Example 1, and Comparative Examples 1 and 2, the C of the element body was measured by the above-mentioned method. Ｓ The results are shown in Table 1.

[0082] (Reliability) For each of the obtained multilayer ceramic capacitors (n=50), the time to failure was measured using a Highly Accelerated Limit Test (HALT). The measurement was performed by applying a DC electric field of 18 V / μm to each sample in a constant temperature bath at 150°C and measuring the time to failure, when the leakage current became 10 times the minimum leakage current. A Weibull plot was created from the obtained measurement results. Those exhibiting a single slope were judged as passing, and those exhibiting two or more slopes were judged as failing. The results are shown in Table 1. FIG. 6 shows a Weibull plot created based on the measurement results of each of the multilayer ceramic capacitors according to Examples 1 and 2 and Comparative Examples 1 and 2.

[0083]

[0084] From the above results, the sulfur concentration C Ｓ However, 0.12 ppm≦C Ｓ It can be seen that the multilayer ceramic capacitors according to the examples that satisfy the condition of C≦14.5 ppm have high reliability. Ｓ It is clear that the inventions according to the comparative examples in which the value of is outside the aforementioned range have low reliability. As a result of SEM observation to determine the average particle size of the multilayer ceramic capacitor according to comparative example 2, it was confirmed that cracks existed at the boundary between the cover portion and the internal electrode. From this fact, it is presumed that in the multilayer ceramic capacitor according to comparative example 2, as a result of excessive removal of sulfur in the heat treatment before firing, the amount of sulfur contained in the internal electrodes during firing was extremely low, and the catalytic action of nickel was insufficiently suppressed.

[0085] Furthermore, since the multilayer ceramic capacitor according to Reference Example 1 was excellent in reliability, similar to that according to Example 1, it is estimated that even when an internal electrode pattern having a high sulfur content is formed, the sulfur concentration in the element body can be sufficiently reduced by performing a pre-firing heat treatment under predetermined conditions.

[0086] This specification also discloses the following techniques.

[0087] (Note 1) An element body having a laminate in which ceramic layers and internal electrodes mainly composed of metal are alternately stacked, a ceramic protective part covering the surface of the laminate, and external electrodes arranged on the surface of the element body and electrically connected to the internal electrodes, wherein the element body is crushed into a powder sample, and a sulfur amount obtained by analyzing the gas generated in the process of heating the powder sample to 1250°C using a combustion-infrared absorption method is divided by the mass of the powder sample before heating to obtain a sulfur concentration C in the element body. Ｓ When set as above, 0.12 ppm≦C Ｓ A multilayer ceramic electronic component that satisfies the following criteria: ≦14.5 ppm.

[0088] (Appendix 2) The multilayer ceramic electronic component according to (Appendix 1), wherein the total amount of the metal contained in the element body is 15 mg or more.

[0089] (Supplementary Note 3) The method includes: (A) preparing ceramic powder; (B) mixing the ceramic powder with a binder and forming the mixture into a sheet to obtain a green sheet; (C) forming an internal electrode pattern containing metal and sulfur on the green sheet; (D) stacking a predetermined number of green sheets on which the internal electrode pattern has been formed, arranging green sheets for cover layers at both ends in the stacking direction, and then pressing the stacked sheets together to obtain a green laminate; (E) dividing the green laminate into individual pieces to obtain a pre-fired body; (F) removing the binder from the pre-fired body; (H) heat-treating the pre-fired body after binder removal in a weakly reducing atmosphere at a temperature range of 800°C to 1100°C for 1 hour to 48 hours; and (I) firing the pre-fired body after the heat treatment to obtain a sintered body; and (G) after (F), applying an external electrode paste to the surface of the pre-fired body after binder removal; or (J) forming external electrodes on the surfaces of the sintered body after (I).

[0090] The present invention provides a highly reliable multilayer ceramic electronic component, which is useful in that it can be applied to products that require high reliability, such as automobiles and health and medical devices.

[0091] 100, 200, 300, 400 Multilayer ceramic capacitor 10 Body 11 (11a, 11b) Lead portion 20 Laminate 21 Dielectric layer 22 (22a, 22b) Internal electrode 23 (23a, 23b) Connecting conductor 30 Protective portion 31 Cover portion 32 Side margin portion 40 (40a, 40b) External electrode 41 Underlayer 42 Cu layer 43 Ni layer 44 Sn layer

Claims

1. A ceramic laminate and an internal electrode mainly composed of metal are alternately laminated in a laminated body, and a ceramic protective part covering the surface of the laminate is provided. An external electrode is disposed on the surface of the body and electrically connected to the internal electrode. The sulfur concentration in the body is determined by dividing the amount of sulfur obtained by analyzing the gas generated in the process of heating a powdered sample obtained by crushing the body to 1250°C using a combustion-infrared absorption method by the mass of the powdered sample before heating. Ｓ When set, 0.12 ppm≦C Ｓ A multilayer ceramic electronic component that satisfies the following criteria: ≦14.5 ppm.

2. The multilayer ceramic electronic component according to claim 1, wherein the total amount of said metals contained in said element body is 15 mg or more.

3. (A) preparing ceramic powder; (B) mixing the ceramic powder with a binder and forming the mixture into a sheet to obtain a green sheet; (C) forming an internal electrode pattern containing metal and sulfur on the green sheet; (D) stacking a predetermined number of green sheets on which the internal electrode pattern has been formed, arranging green sheets for cover layers at both ends in the stacking direction, and then pressing the stacked green sheets together to obtain a green laminate; (E) singulating the green laminate to obtain a pre-fired body; (F) removing the binder from the pre-fired body; (H) subjecting the pre-fired body after the binder removal to a heat treatment in a weak reducing atmosphere at a temperature range of 800°C to 1100°C for 1 hour to 48 hours; and (I) firing the pre-fired body after the heat treatment to obtain a sintered body; and (G) after (F), applying an external electrode paste to the surface of the pre-fired body after the binder removal; or 3. The method for producing a multilayer ceramic electronic component according to claim 1, further comprising: (J) forming external electrodes on the surfaces of the sintered body after (I).

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