JP2006032404A - Method of manufacturing multilayered ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a multilayered ceramic capacitor by which a reliable multilayered ceramic capacitor can be easily obtained even if a nickel-based internal electrode layer is made thin. <P>SOLUTION: The multilayered ceramic capacitor comprises a dielectric ceramic layer and a ceramic chip wherein the internal electrode layer formed mainly of nickel is formed. The dielectric ceramic layer is formed of barium titanate-based dielectric ceramic which contains, as sub-components, a barium oxide and/or a calcium oxide, a manganese oxide, an rare earth oxide, and a silicon oxide at prescribed ratios. The ceramic chip is reoxidized by being held in an oxidizing atmosphere by the oxygen partial pressure of 6×10<SP>-10</SP>-2×10<SP>-7</SP>MPa at 700-1,050°C for 2-6 hours. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a multilayer ceramic capacitor, and more particularly to a method for manufacturing a multilayer ceramic capacitor using a barium titanate-based dielectric ceramic.

  A multilayer ceramic capacitor has, for example, a structure in which a pair of external electrodes is provided on a multilayer body in which dielectric ceramic layers and internal electrode layers are alternately stacked. As dielectric ceramics used in this multilayer ceramic capacitor, those having various compositions are known. Among them, barium titanate dielectric ceramics have a high dielectric constant.

  Multilayer ceramic capacitors using barium titanate-based dielectric ceramics, for example, are formed by alternately laminating green sheets that become barium titanate-based dielectric ceramic layers by firing and paste layers that become internal electrode layers by firing. After the laminated body is obtained, the laminated body is fired to form a ceramic chip. Thereafter, the surface layer of the entire ceramic chip is removed by polishing, and then external electrodes are formed at predetermined positions.

  As the internal electrode layer of a multilayer ceramic capacitor, a material formed of platinum or palladium has been widely used in the past. However, in order to provide a cheaper multilayer ceramic capacitor, an internal electrode mainly composed of nickel has been used in recent years. An electrode layer (hereinafter, this internal electrode layer is referred to as a “nickel-based internal electrode layer”) is often used.

  When the internal electrode layer of the multilayer ceramic capacitor is a nickel-based internal electrode layer, the firing for obtaining the ceramic chip described above is reducible because the paste layer for forming the internal electrode layer is a nickel-based internal electrode layer. Performed in an atmosphere. At this time, the green sheet is also fired to become a barium titanate-based dielectric ceramic layer. However, since the green sheet is fired in a reducing atmosphere, its electrical characteristics are not desired. In order to obtain a multilayer ceramic capacitor having desired electrical characteristics, it is necessary to reoxidize the barium titanate dielectric ceramic layer while suppressing the oxidation of the nickel internal electrode layer after the production of the ceramic chip. This re-oxidation is difficult to set, and various improvements have been made to the re-oxidation conditions to date.

For example, Patent Document 1 discloses that the oxygen partial pressure in the atmosphere is 10 ⁻⁶ atm or more, particularly 10 ⁻⁵ to 10 ⁻⁴ atm, the treatment temperature is 1100 ° C. or less, particularly 500 to 1000 ° C., and the holding time is 0 to 0. A manufacturing method is described in which annealing (reoxidation) is performed for 20 hours, particularly 6 to 10 hours, to obtain a multilayer ceramic capacitor using a barium titanate dielectric ceramic.

  Patent Document 2 discloses a laminated type using barium titanate-based dielectric ceramics by performing heat treatment (reoxidation) in an atmosphere containing 3% by volume or more of carbon dioxide gas under conditions of 600 to 1100 ° C. A manufacturing method for obtaining a ceramic capacitor is described.

In Patent Document 3, the oxygen partial pressure in the atmosphere is 10 ⁻⁴ to 10 ⁻⁸ atm, more preferably 10 ⁻⁴ to 10 ⁻⁷ atm, and the holding temperature or the maximum temperature is 900 to 1200 ° C., more preferably. Is a manufacturing method of obtaining a multilayer ceramic capacitor using a barium titanate dielectric ceramic by performing heat treatment (reoxidation) at 900 to 1100 ° C. and holding time of 0 to 6 hours, particularly 2 to 5 hours Is described.
JP-A-8-124785 Japanese Patent Laid-Open No. 10-163063 Japanese Patent Laid-Open No. 2000-124058

  However, in recent years, as various electronic devices have been reduced in size and weight, it has become necessary to further improve the characteristics of multilayer ceramic capacitors without increasing their size. As a result, a new problem arises in a multilayer ceramic capacitor having a nickel-based internal electrode layer.

  In other words, in order to increase the capacitance without increasing the size of the multilayer ceramic capacitor, in recent years, the nickel-based internal electrode layer and the dielectric ceramic layer have been made thinner to increase the number of layers. As the electrode layer has become thinner, it has become difficult to obtain a multilayer ceramic capacitor with high reliability and high yield.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multilayer ceramic capacitor in which it is easy to obtain a multilayer ceramic capacitor having high reliability and high yield even when the nickel-based internal electrode layer is thinned. An object of the present invention is to provide a method of manufacturing a ceramic capacitor.

The method for manufacturing a multilayer ceramic capacitor of the present invention that achieves the above object is characterized in that the dielectric ceramic layer forming green sheets and the internal electrode layer forming paste layers are fired in a state of being alternately stacked, A preparation step of preparing a ceramic chip in which the green sheet becomes a dielectric ceramic layer and the paste layer is an internal electrode layer mainly composed of nickel, and reoxidation for reoxidizing the dielectric ceramic layer in the ceramic chip And at least one of barium oxide and calcium oxide, manganese oxide, rare earth oxide, and silicon oxide as subcomponents in the preparation step, and an atomic ratio of calcium atoms to titanium atoms Is 0 or 0.001 to 0.12, the total amount of barium and calcium atoms The atomic ratio is 1.001 to 1.12, the atomic ratio of manganese atoms is 0.005 or less, the atomic ratio of the rare earth elements constituting the rare earth oxide is 0.0004 to 0.10, the number of silicon atoms A ceramic chip in which the dielectric ceramic layer is formed of a barium titanate dielectric ceramic having a ratio of 0.001 to 0.12 and an average particle diameter of 0.05 to 0.6 μm is prepared, and the reoxidation is performed In the step, the ceramic chip is held at 700 to 1050 ° C. for 2 to 6 hours in an oxidizing atmosphere having an oxygen partial pressure of 6 × 10 ⁻¹⁰ to 2 × 10 ⁻⁷ MPa.

  Here, the “internal electrode layer mainly composed of nickel (nickel-based internal electrode layer)” in the present invention means an internal electrode layer whose composition excluding inevitably generated oxide is simple nickel, and unavoidable. This is a general term for an internal electrode layer formed of an alloy having an atomic percentage of nickel of 80 at% or more in a composition excluding oxides that are generated.

According to the method for manufacturing a multilayer ceramic capacitor of the present invention, reoxidation of the barium titanate dielectric ceramic layer having the above composition is performed in an oxidizing atmosphere having an oxygen partial pressure of 6 × 10 ⁻¹⁰ to 2 × 10 ⁻⁷ MPa. , By maintaining at 700 to 1050 ° C. for 2 to 6 hours, even when the internal electrode layer mainly composed of nickel (nickel internal electrode layer) is thinned, its oxidation is suppressed and the reliability is high. It becomes easy to obtain a multilayer ceramic capacitor with a high yield.

  In the method for manufacturing a multilayer ceramic capacitor according to the present invention, (1) the dielectric ceramic layer further contains magnesium oxide, vanadium oxide, tungsten oxide, or molybdenum oxide as a subcomponent, and an atom of magnesium atom relative to a titanium atom. The number ratio is 0.03 or less, the atomic ratio of vanadium atoms and the number of tungsten atoms are 0.006 or less, the atomic ratio of molybdenum atoms is 0.003 or less, and the atomic ratio of the vanadium atoms is X, satisfying the formula (X + Y + 2Z) ≦ 0.006 when the atomic ratio of tungsten atoms is Y and the atomic ratio of molybdenum atoms is Z, (2) holding the ceramic chip in the reoxidation step The temperature is 700 to 900 ° C., and (3) the thickness of the internal electrode layer is 0.5 to 2.0 μm. Or (4) edge oxidation that occurs in the internal electrode layer in the reoxidation step when the thickness at which the surface layer of the ceramic chip is removed by polishing after the reoxidation step is n [μm]. It is preferable to make the ratio not more than the value represented by the formula (0.85 + n) /0.132 [%].

  According to the invention of (1), since the subcomponent is further contained in the barium titanate-based dielectric ceramic layer, it becomes easy to obtain a multilayer ceramic capacitor with improved electrical characteristics. According to the invention of (2) above, since the holding temperature of the ceramic chip is set to 700 to 900 ° C. in the reoxidation step, it becomes easy to obtain a long-life multilayer ceramic capacitor. According to the invention of (3) above, since the thickness of the internal electrode layer is 0.5 to 2.0 μm, it is easy to obtain a small multilayer ceramic capacitor having a large electrostatic capacity. According to the invention of (4), since the end oxidation ratio in the internal electrode layer is not more than the above value, it is easy to suppress poor conduction between the internal electrode layer and the external electrode.

  According to the method for manufacturing a multilayer ceramic capacitor of the present invention, it is easy to obtain a highly reliable multilayer ceramic capacitor with a high yield even when the nickel-based internal electrode layer is thinned. It is easy to provide a small multilayer ceramic capacitor having a large size at low cost with high reliability.

  As described above, the method for manufacturing a multilayer ceramic capacitor of the present invention includes a preparation step and a reoxidation step. Hereinafter, these steps will be sequentially described.

<Preparation process>
In the preparation step, the green sheet for forming the dielectric ceramic layer and the paste layer for forming the internal electrode layer are baked in an alternately laminated state so that the green sheet becomes the dielectric ceramic layer and the paste. A ceramic chip having a nickel-based internal electrode layer is prepared.

  As described above, the dielectric ceramic layer in this ceramic chip contains at least one of barium oxide and calcium oxide, manganese oxide, rare earth oxide, and silicon oxide as subcomponents, and calcium with respect to titanium atoms. The atomic ratio of atoms is 0 or 0.001 to 0.12, the atomic ratio of the total amount of barium atoms and calcium atoms is 1.001 to 1.12, the atomic ratio of manganese atoms is 0.005 or less, The atomic ratio of rare earth elements constituting the rare earth oxide is 0.0004 to 0.10, the atomic ratio of silicon atoms is 0.001 to 0.12, and the average particle size is 0.05 to 0.6 μm. It is made of a barium titanate dielectric ceramic.

  Such a ceramic chip may be produced by itself or may be purchased from another manufacturer. In the case of self-manufacture, the above-described green sheet and paste are prepared, and a green chip in which green sheets and paste layers are alternately laminated is obtained using these, and then the green chip is fired. Hereinafter, each of the green sheet for forming the dielectric ceramic layer, the paste for forming the nickel-based internal electrode layer, the green chip, and the firing of the green chip will be described in detail.

(I) a green sheet for forming a dielectric ceramic layer;
A green sheet for forming a dielectric ceramic layer is prepared, for example, by weighing a predetermined amount of a powder of barium titanate and a powder of a subsidiary component or a compound which becomes the subsidiary component by firing, and the powder is used as a resin binder. After mixing with a binder such as a slurry to obtain a slurry, the slurry is obtained by, for example, forming the slurry into a desired shape by a doctor blade method.

Here, specific examples of the compound that becomes barium oxide, calcium oxide, or manganese oxide by firing include nitrate, carbonate, and the like for each of barium, calcium, and manganese. Examples of rare earth oxides include yttrium oxide (Y ₂ O ₃ ), scandium oxide (Sc ₂ O ₃ ), europium oxide (Eu ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), and dysprosium oxide (Dy). ₂ O ₃ ), holmium oxide (Ho ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), thulium oxide (Tm ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), lutetium oxide (Lu ₂ O ₃ ), Terbium oxide (Tb ₄ O ₇ ) can be used, and a compound that becomes the above oxide by firing, such as nitrates and carbonates for each rare earth element, can also be used. Only one kind of rare earth oxide or a compound that becomes a rare earth oxide by firing may be used, or two or more kinds may be used in combination.

  The atomic ratio of each metal element (including silicon atoms) in the slurry is substantially the atomic ratio of each metal element in the barium titanate-based dielectric ceramic layer in the ceramic chip. For example, when an oxide is used as a raw material for each subcomponent, the total amount of barium oxide and calcium oxide is 0.1 to 12 mol, manganese oxide is 0.5 mol or less, and rare earth oxidation with respect to 100 mol of barium titanate. By preparing 0.02-5 mol of the product and 0.1-12 mol of silicon oxide and preparing the above slurry, the barium titanate dielectric ceramic layer having the composition (atomic ratio) described above is finally obtained. It is possible to obtain a green sheet.

  Specific examples of the binder used for preparing the slurry include resin binders such as ethyl cellulose, abietic acid resin, and polyvinyl butyral. In preparing the slurry, additives such as a plasticizer, a dispersant, and a solvent can be added as necessary. Specific examples of the plasticizer include abietic acid derivatives, diethyl succinate, polyethylene glycol, polyalkylene glycol, phthalate ester, dibutyl phthalate, and the like. Specific examples of the dispersant include glycerin, octadecylamine, trichloro, and the like. Examples include acetic acid, oleic acid, octadiene, ethyl oleate, glyceryl monooleate, glyceryl trioleate, glyceryl tristearate, and menseden oil. Specific examples of the solvent include toluene, terpineol, butyl carbitol, methyl ethyl ketone, and the like.

  The slurry is preferably obtained by mixing the above-described raw material powder with other components so that the ratio thereof is about 30 to 60% by mass. At this time, the ratio of the binder is about 1 to 10% by mass, the ratio of the plasticizer is about 0.5 to 5% by mass, the ratio of the dispersant is about 0.01 to 5% by mass, and the remaining amount is the solvent. Is preferred. A green sheet can be obtained by forming this slurry into a desired shape and drying it.

(II) Internal electrode layer forming paste;
The internal electrode layer forming paste is, for example, one or more kinds of metal powder (nickel powder, nickel alloy powder, or nickel powder and a metal other than nickel) that becomes a nickel-based internal electrode by firing. It can be prepared by mixing an organic vehicle with one or a plurality of compound powders that become a nickel-based internal electrode by firing). For example, specific examples of the compound that becomes nickel by firing include nickel carbonate and nitrate.

  The metal powder and the compound powder preferably have a size of about 0.05 to 0.6 μm, and more preferably about 0.2 to 0.5 μm. The shape of the powder is not particularly limited, and various shapes such as a spherical shape and a flake shape can be used.

  The organic vehicle used for preparing the paste contains a binder and a solvent. Examples of the binder include ethyl cellulose, acrylic resin, butyral resin, and examples of the solvent include terpineol, butyl carbitol, and kerosene. Etc. can be used respectively.

  The ratio of the total amount of the metal powder and the compound powder in the paste can be about 40 to 60% by mass, the ratio of the binder can be about 1 to 5% by mass, and the remaining amount. Can be the above-mentioned solvent.

(III) Green chip;
For example, the green chip is formed by laminating a plurality of the above-described green sheets on a supporting substrate formed of a resin film or the like to form a lower-layer exterior sheet, and the paste layer and the above-described green sheet on the exterior sheet. Are alternately and repeatedly formed one by one, and then a plurality of the above-described green sheets are further laminated as an upper-layer exterior sheet to obtain a laminate, and a load is applied to the laminate to apply pressure to each layer and then desired. It is obtained by cutting into a shape and finally removing the supporting substrate. In alternately laminating green sheets and internal electrode forming paste layers, an internal electrode conducting to one external electrode and an internal electrode conducting to another external electrode in the finally obtained multilayer ceramic capacitor These green sheets and paste layers are arranged so as to be alternately positioned via the barium titanate-based dielectric ceramic layers. In many cases, the shape of the green chip is a rectangular parallelepiped, but other shapes may be used as necessary.

  The thickness of each green sheet (excluding the exterior sheet) in this green chip is the size and performance of the multilayer ceramic capacitor to be finally manufactured, and the barium titanate dielectric in this multilayer ceramic capacitor. Depending on the number of laminated layers of the body ceramic layer and the nickel-based internal electrode layer, the thickness can be appropriately selected within a range of about 0.5 to 5 μm. The thickness of each paste layer is the size and performance of the multilayer ceramic capacitor to be finally manufactured, and each of the barium titanate dielectric ceramic layer and the nickel-based internal electrode layer in this multilayer ceramic capacitor. Depending on the number of laminated layers, etc., it can be appropriately selected within a range of about 0.5 to 2.0 μm.

(IV) Green chip firing;
The green chip can be fired by heating at about 1100 to 1350 ° C. for about 1 to 3 hours in a humidified reducing atmosphere. At this time, as the humidified reducing atmosphere, for example, an atmosphere obtained by humidifying a mixed atmosphere of an inert gas (nitrogen gas or the like) and hydrogen gas with a wetter can be used, and its oxygen partial pressure is 6 × 10 ^−16. It is preferable to be about ˜1 × 10 ⁻⁹ MPa. For example, the partial pressure of hydrogen gas in the mixed atmosphere is set to about 0.5 to 10% of the total pressure, and the dew point temperature of the mixed atmosphere is set to about 0 to 50 ° C. It is possible to adjust.

  The temperature rising rate during firing is preferably about 50 to 500 ° C./hour, and more preferably about 200 to 300 ° C./hour. The cooling rate after firing is preferably about 50 to 500 ° C./hour, and more preferably about 200 to 300 ° C./hour.

  When the binder is contained in the green sheet or the paste layer for forming the internal electrode layer, the binder is held by holding the green chip for about 5 to 20 hours at about 180 to 400 ° C. in an air atmosphere or a reducing atmosphere. It is preferable to perform the above-mentioned baking after removing. In this case, the temperature rising rate is preferably about 5 to 300 ° C./hour, more preferably about 10 to 100 ° C./hour.

  By firing the green chip as described above, the green sheet in the green chip becomes a barium titanate-based dielectric ceramic layer having the composition described above, and the paste layer becomes a nickel-based internal electrode layer, thereby obtaining a ceramic chip. It is done. However, the electrical characteristics of the barium titanate-based dielectric ceramics in the ceramic chip obtained in this way are insufficient to be applied to a multilayer ceramic capacitor as it is. Oxidize.

  The reason why the composition and average particle diameter of the barium titanate-based dielectric ceramic layer are defined as described above is as follows.

  Calcium oxide and barium oxide as subcomponents in barium titanate-based dielectric ceramics have a low IR (insulation resistance) deterioration over time and a multilayer ceramic with a small change in capacitance due to a change in ambient temperature. Since it is a useful component for obtaining a capacitor, in the method for manufacturing a multilayer ceramic capacitor of the present invention, the barium titanate-based dielectric ceramic contains at least one of calcium oxide and barium oxide as a subcomponent. .

  When calcium oxide is contained as a subcomponent, the content is preferably adjusted so that the atomic ratio of calcium atoms to titanium atoms is about 0.001 to 0.12. If the atomic ratio is less than 0.001, it is difficult to obtain the effect due to the inclusion of calcium oxide, and if it exceeds 0.12, the capacity of the multilayer ceramic capacitor tends to decrease. The atomic ratio of calcium atoms to titanium atoms is more preferably about 0.001 to 0.05.

  In addition, when barium oxide is contained as an accessory component, the atomic ratio of barium atoms (including barium atoms constituting the main component barium titanate) to titanium atoms is about 1.001 to 1.12. It is preferable to adjust the content so that When the atomic ratio is less than 1.001, it is difficult to obtain the effect of containing barium oxide as a subcomponent, and when it exceeds 1.12, the capacity of the multilayer ceramic capacitor tends to decrease. The ratio of the number of barium atoms to titanium atoms is more preferably about 1.001 to 1.05.

  However, even if the atomic ratio of the total amount of calcium atoms and barium atoms (including barium atoms constituting the main component barium titanate) with respect to titanium atoms exceeds 1.12, the capacitance of the multilayer ceramic capacitor Therefore, the atomic ratio of the total amount is preferably about 1.12 or less. The atomic ratio is more preferably about 1.00 to 1.05.

  Manganese oxide, a minor component, is a useful component for densifying barium titanate-based dielectric ceramic layers, and is useful for obtaining multilayer ceramic capacitors with little deterioration over time in IR (insulation resistance). It is preferable to adjust the content so that the atomic ratio of manganese atoms to titanium atoms is about 0.005 or less. When this atomic ratio exceeds 0.005, the change with time of the capacitance of the multilayer ceramic capacitor when a DC electric field is applied becomes large. The atomic ratio of manganese atoms to titanium atoms is more preferably about 0.01 to 0.4.

  The rare earth oxide is a component useful for improving the high temperature durability of the multilayer ceramic capacitor using the barium titanate dielectric ceramic, and the atomic ratio of the rare earth element (the atomic ratio to the titanium atom) is 0. It is preferable to adjust the content so as to be about .0004 to 0.10. If the atomic ratio is less than 0.0004, the deterioration of IR (insulation resistance) of the multilayer ceramic capacitor with time tends to increase, and if it exceeds 0.10, the sinterability of the barium titanate dielectric ceramic layer and The capacitance of the multilayer ceramic capacitor tends to decrease. The atomic ratio of rare earth elements (atomic ratio to titanium atoms) is more preferably about 0.001 to 0.07.

  Silicon oxide is a useful component for improving the sinterability of the barium titanate-based dielectric ceramic layer, so that the atomic ratio of silicon atoms to titanium atoms is about 0.001 to 0.12. It is preferable to adjust the content. If the atomic ratio is less than 0.001, it is difficult to obtain the effect of containing silicon oxide, and if it exceeds 0.12, the IR (insulation resistance) of the multilayer ceramic capacitor tends to be lowered. The atomic ratio of silicon atoms to titanium atoms is more preferably about 0.02 to 0.06.

  If necessary, magnesium oxide, vanadium oxide, tungsten oxide, molybdenum oxide and the like can be contained in addition to the above-described subcomponents.

  Magnesium oxide is a useful component for reducing the change with time of the capacitance of the multilayer ceramic capacitor. When magnesium oxide is contained, the content is preferably adjusted so that the atomic ratio of magnesium atoms to titanium atoms is about 0.03 or less. If this atomic ratio exceeds 0.03, the capacity of the multilayer ceramic capacitor tends to decrease. The ratio of the number of magnesium atoms to titanium atoms is more preferably about 0.005 to 0.02.

  Vanadium oxide, tungsten oxide, and molybdenum oxide are useful components for reducing the time-dependent change of the capacitance of the multilayer ceramic capacitor under a DC electric field and improving the dielectric breakdown voltage of the multilayer ceramic capacitor. . When these components are contained, the atomic ratio of vanadium atom, tungsten atom, and molybdenum atom to titanium atom is X, the atomic ratio of vanadium atom is Y, the atomic ratio of tungsten atom is Y, the atomic number of molybdenum atom When the ratio is represented by Z, it is preferable that the value of the formula (X + Y + 2Z) is selected to be about 0.006 or less. If the atomic ratio represented by the above formula exceeds 0.006, the IR (insulation resistance) of the multilayer ceramic capacitor tends to decrease. The atomic ratio is more preferably about 0.0001 to 0.005.

  The average particle size of the sintered barium titanate dielectric ceramic layer is preferably about 0.1 to 0.6 μm. When this average particle size is smaller than 0.1 μm, the relative dielectric constant is lowered, and the capacity of the multilayer ceramic capacitor is easily lowered. If the average particle size is larger than 0.6 μm, the number of particles of the barium titanate dielectric ceramic interposed between the adjacent nickel internal electrode layers is reduced. Therefore, the IR of the multilayer ceramic capacitor is reduced. (Insulation resistance) Life is likely to decrease.

<Reoxidation process>
In the re-oxidation step, the above-described ceramic chip is held in an oxidizing atmosphere having an oxygen partial pressure of 6 × 10 ⁻¹⁰ to 2 × 10 ⁻⁷ MPa at 700 to 1050 ° C. for 2 to 6 hours to obtain titanic acid in the ceramic chip. Reoxidize the barium dielectric ceramic layer.

If the oxygen partial pressure at this time is higher than 2 × 10 ⁻⁷ MPa, oxidation of the nickel-based internal electrode layer in the ceramic chip proceeds and the electrical characteristics thereof are liable to deteriorate, and from 6 × 10 ⁻¹⁰ MPa. However, if the pressure is low, the barium titanate-based dielectric ceramic layer is not sufficiently re-oxidized, and its electrical characteristics tend to be insufficient for use in a multilayer ceramic capacitor.

  In addition, when the holding temperature in the reoxidation process is less than 700 ° C., the oxidation of the nickel-based internal electrode layer can be suppressed, but the reoxidation of the barium titanate-based dielectric ceramic layer becomes insufficient, and the electrical characteristics are laminated. It tends to be insufficient for use in ceramic capacitors. On the other hand, when the holding temperature exceeds 1050 ° C., it becomes easy to sufficiently reoxidize the barium titanate dielectric ceramic layer, but on the other hand, the oxidation of the nickel-based internal electrode layer proceeds and the electrical connection with the external electrode is improved. It becomes difficult to plan. Similarly, if the holding time is less than 2 hours, re-oxidation of the barium titanate dielectric ceramic layer tends to be insufficient, and if it exceeds 6 hours, oxidation of the nickel-based internal electrode layer tends to proceed.

When the oxygen partial pressure in the oxidizing atmosphere is about 6 × 10 ⁻¹⁰ to 2 × 10 ⁻⁷ MPa, the holding temperature is about 700 to 900 ° C., and the holding time is about 2 to 6 hours, the nickel internal electrode layer is reduced to 0. Even when the barium titanate-based dielectric ceramic layer is thinned to about 1.0-5.0 μm, the yield of highly reliable multilayer ceramic capacitors is high. Easy to get under.

  The heating rate and cooling rate in the reoxidation step are each preferably about 50 to 500 ° C./hour, and more preferably about 100 to 300 ° C./hour.

  By performing the reoxidation process in this manner, it becomes possible to sufficiently reoxidize the barium titanate dielectric ceramic layer while suppressing the oxidation of the nickel internal electrode layer.

  The oxidation of the nickel-based internal electrode layer in the re-oxidation process mainly occurs on the end face side exposed on the side surface of the ceramic chip. Oxidation may occur intermittently from the end face toward the inside. When the thickness of the nickel-based internal electrode layer is set to about 0.5 to 2.0 μm and the re-oxidation process is performed under the above-described conditions, the inventors have formed a nickel-based internal electrode layer in the re-oxidation process. It has been found that when the ratio of the generated end oxidation is not more than the value represented by the formula (0.85 + n) /0.132, poor conduction between the nickel-based internal electrode layer and the external electrode is suppressed.

  Here, n in the above formula means a thickness (unit: μm) at which the surface layer of the ceramic chip is removed by polishing after the reoxidation step. When manufacturing a multilayer ceramic capacitor, the surface layer is usually polished and removed by a method such as barrel polishing over the entire ceramic chip that has gone through the reoxidation process, and then external electrodes are formed at predetermined locations. The The above n is the thickness removed at this time. However, n may be 0 (zero).

  Further, the “ratio of end oxidation occurring in the nickel-based internal electrode layer” in the present invention means a ratio obtained as follows. First, as shown in FIG. 1A, a vertical cross section corresponding to a surface obtained by cutting the ceramic chip 10 along the surface 15 is taken. This vertical cross section can be obtained, for example, by polishing the ceramic chip 10 in a predetermined direction. The surface 15 is a surface orthogonal to the region (for example, the side surface 10A) that is finally completely covered by the external electrode in the surface of the ceramic chip 10, and the position thereof is arbitrarily selected. Next, as shown in FIG. 1 (b), each of the nickel-based interiors included in one field of view when this vertical cross section is magnified 100 to 1000 times with a reflection microscope, an electron beam microanalyzer (EPMA) or the like. For the electrode layer 3 (however, one end of which is exposed in the above-described region (for example, the side surface 10A)), the above-described region (side surface 10A) and the space S in plan view between the region and the region are parallel. The total extension of the oxidized region generated in the section between the virtual plane VP which is 20 μm is obtained.

  Here, the above-mentioned “total extension of the oxidized region” means the total extension of the width of the oxidized region in the direction D perpendicular to the virtual plane VP, and its unit is [μm]. When the oxidation regions are intermittently distributed in the section, the width in the direction D is obtained for each of these oxidation regions, and the sum is defined as the total extension.

  The percentage of the total extension occupying the space S (20 μm) is “the ratio of end oxidation in the nickel-based internal electrode layer 3 (unit:%)”. In an actual ceramic chip, each side surface is not necessarily a flat surface, but when determining the rate of end oxidation in the nickel-based internal electrode layer 3, each side surface is assumed to be a flat surface. Reference numeral 5 in FIG. 1B indicates a barium titanate-based dielectric ceramic layer.

  If the thickness of the nickel-based internal electrode layer 3 is about 0.5 to 2.0 μm, in many cases, the oxidized region generated in the above section is not limited to the surface layer of the nickel-based internal electrode layer 3 and is thick. If the above ratio is not more than the value represented by the formula (0.85 + n) /0.132, conduction with the external electrode is performed somewhere in the nickel-based internal electrode layer 3. As a result, it is considered that poor conduction with the external electrode is suppressed. The above ratio is the oxygen partial pressure, holding temperature, or holding time in the atmosphere in the reoxidation step depending on the thickness of the nickel-based internal electrode layer 3 and the composition of the barium titanate-based dielectric ceramic layer 5, etc. Control is possible by selecting appropriately within the range.

  For example, the target multilayer ceramic capacitor is obtained by polishing and removing a surface layer of a ceramic chip (hereinafter referred to as “capacitor chip”) obtained through the above-described reoxidation process by a method such as barrel polishing, if necessary. After smoothing, it can be obtained by forming external electrodes at predetermined locations. The external electrode can be formed, for example, by baking a paste for forming an external electrode at a predetermined location, or by applying an external electrode material such as an In-Ga alloy to the predetermined location.

  When a paste is used in forming the external electrode, this paste is, for example, a powder of a desired conductive material or a powder of a compound that becomes a desired conductive material by baking, an organic vehicle, and a glass powder. Can be prepared.

  The shape of the powder of the conductive material or the shape of the powder of the compound is not limited to a specific shape, and may be various shapes such as a spherical shape and a flake shape. The size of these powders is preferably about 0.5 to 5 μm, and more preferably about 1 to 3 μm. The organic vehicle contains a binder and a solvent, and as the binder, for example, ethyl cellulose, acrylic resin, butyral resin, etc. are used, and as the solvent, for example, terpineol, butyl carbitol, kerosene, or the like is used. . As said glass powder, it is preferable to use a thing with a softening point of about 500-900 degreeC.

  The content of the conductive material powder in the paste used for forming the external electrode or the compound powder that becomes a desired conductive material by baking can be about 40 to 60% by mass. The binder content can be about 1 to 5% by mass, and the glass powder content is preferably about 1 to 10% by mass. The remaining amount is the solvent content.

  When an external electrode is formed by baking a paste, this baking can be performed under the following conditions, for example. That is, baking can be performed by heat treatment at 600 to 800 ° C. for about 10 minutes to 1 hour in a nitrogen gas atmosphere or a mixed gas atmosphere of humidified nitrogen gas and hydrogen gas. The humidification of the nitrogen gas or the mixed gas can be performed using, for example, a wetter. In this case, the water temperature is preferably about 10 to 30 ° C.

  When the planar shape of the capacitor chip is rectangular, one external electrode is formed so as to cover the entire side surface, for example, on each side surface located at both ends in the long axis direction when viewed in plan. Of course, in addition to the structure in which the external electrodes are provided at both ends in the long axis direction, a structure in which external electrodes are provided at both ends in the short axis direction, or a structure in which 3 or more external electrodes are provided instead of 2 terminals. However, a multilayer ceramic capacitor can be obtained. A multilayer ceramic capacitor can be obtained by forming the external electrodes in this way. If necessary, a pad layer can be formed on each external electrode by a method such as plating.

<Example 1 to Example 8>
(Preparation process);
First, barium titanate (BaTiO ₃ ) powder, barium oxide (BaO) powder, calcium oxide (CaO) powder, manganese oxide (MnO) powder, yttrium oxide (Y ₂ O ₃ ) powder, silicon oxide (SiO ₂ ) powder, Magnesium oxide (MgO) powder and vanadium oxide (V ₂ O ₃ ) powder were prepared. The average particle diameter of the barium titanate powder is about 0.3 μm.

  Next, each powder is mixed with 1.8 mol of barium oxide, 1.2 mol of calcium oxide, 0.2 mol of manganese oxide, 2.5 mol of yttrium oxide and 100 mol of barium titanate. Weighed and mixed so that silicon was 3.0 mol, magnesium oxide was 0.1 mol, and vanadium oxide was 0.03 mol.

  To 100 parts by weight of the resulting mixture, 4.8 parts by weight of acrylic resin, 10 parts by weight of toluene, 70 parts by weight of ethyl acetate, 6 parts by weight of mineral spirits, and 4 parts by weight of acetone are added and mixed. A green sheet forming paste was obtained.

  Separately, 100 parts by weight of nickel powder having an average particle size of 0.5 μm, 40 parts by weight of an organic vehicle (8 parts by weight of ethyl cellulose dissolved in 92 parts by weight of butyl carbitol), butyl carbitol 10 parts by weight of each were added and mixed to obtain a nickel internal electrode layer forming paste (hereinafter referred to as “internal electrode layer forming paste”).

  Next, a green sheet forming paste was applied to one side of the polyethylene terephthalate film to a thickness of 2.5 μm by the doctor blade method and then dried to form a green sheet. Similarly, a total of 48 green sheets were laminated on one side of a polyethylene terephthalate film to form a lower exterior sheet. Next, a desired number of paste layers for forming an internal electrode layer having a thickness of 1.5 μm formed on a green sheet having a thickness of 2.5 μm are stacked on the lower exterior sheet, and then a further 48 layers of green An upper exterior sheet was formed by laminating sheets to obtain a laminate.

A load of 1500 kg / cm ² was applied to this laminate to crimp each layer, and then a predetermined number of green chips were cut out. Each green chip has 340 internal electrode layer forming paste layers.

  Next, each green chip was heated to 260 ° C. in air and held at this temperature for 8 hours to remove the binder contained in each of the green sheet and the internal electrode layer forming paste layer. The heating rate was 25 ° C./hour.

Thereafter, each green chip was baked by being held at 1275 ° C. for 2 hours in a mixed atmosphere of nitrogen gas and hydrogen gas. At this time, the firing atmosphere (mixed atmosphere) was humidified by a wetter so that the dew point temperature was 20 ° C., and the oxygen partial pressure was 1.0 × 10 ⁻⁵ Pa. The temperature rising rate was 200 ° C./hour, and the cooling rate was 200 ° C./hour.

  By this firing, the green sheet in each green chip becomes a dielectric layer made of a barium titanate ceramic, and the internal electrode layer forming paste layer becomes a nickel internal electrode layer. A predetermined number of ceramic chips having a rectangular parallelepiped shape of 2 × 1.2 mm were obtained.

(Reoxidation process);
The ceramic chip obtained in the preparation step was reoxidized by holding it in a nitrogen gas atmosphere for a predetermined time. The holding temperature at this time is changed for each example within the range of 700 to 1050 ° C. as shown in Table 1 below, and the holding time is also within the range of 2 to 6 hours as shown in Table 1. Changed to. The reoxidation atmosphere (nitrogen gas atmosphere) is humidified by a wetter so that the dew point temperature is 20 ° C. in any of the examples, and the oxygen partial pressure is a value shown in Table 1 below. In addition, the heating rate and the cooling rate were 200 ° C./hour in each example.

  By performing the re-oxidation process in this way, a plurality of ceramic chips were obtained for each example. Among these ceramic chips, one randomly extracted for each example was used as a sample in “Evaluation 1” described later. The remaining ceramic chip is barrel-polished to form a capacitor chip, and then an external electrode is formed of an indium (In) -gallium (Ga) alloy on each of a pair of side surfaces facing each other to form a multilayer ceramic capacitor. Samples of “Evaluation 2” or “Evaluation 3” described later were used.

  When the ceramic chip was barrel-polished to obtain a capacitor chip, the surface layer of each ceramic chip was removed over an average thickness of about 0.4 μm.

<Comparative Examples 1 to 4>
A ceramic chip for each comparative example was obtained in the same manner as in Example 1 or Example 6 except that the holding temperature in the reoxidation step was 600 ° C., 1100 ° C., or 1200 ° C., which is a temperature outside the limited range of the present invention. A capacitor chip and a multilayer ceramic capacitor were respectively produced. Table 1 shows the holding temperature, holding time, and oxygen partial pressure in the reoxidation step in each comparative example.

<Evaluation 1>
The ratio of the end oxidation generated in the nickel internal electrode layer in one ceramic chip randomly extracted for each example and each comparative example is already shown in FIG. 1 (a) and FIG. 1 (b). Obtained by the method described. The results are also shown in Table 1.

<Evaluation 2>
With respect to each of the multilayer ceramic capacitors obtained in each Example and each Comparative Example, the insulation resistance when the ambient temperature is 20 ° C .; hereinafter abbreviated as “R _i 20”. A), insulation resistance when the ambient temperature and 0.99 ° C. (hereinafter, abbreviated as _"R i 0.99".) Is _obtained, the ratio of the logarithm of _R i 20 with respect to _{R i 150 (log (R i} 20 / R _i 150)) was calculated. The results are also shown in Table 1. A multilayer ceramic capacitor having a smaller value has less deterioration in insulation resistance even when used at high temperatures.

<Evaluation 3>
For each of the multilayer ceramic capacitors obtained in each Example and Comparative Examples 3 to 4, a high temperature accelerated life test (HALT) was performed under the conditions of an atmospheric temperature of 160 ° C. and an applied voltage of 12.6 V. Based on the result, mean time to failure (MTTF) was obtained. The results are also shown in Table 1. A multilayer ceramic capacitor having a larger value has a longer life.

As is clear from the log (R _i 20 / R _i 150) value and MTTF value shown in Table 1, each multilayer ceramic obtained in Examples 1 to 8 and Comparative Examples 3 to 4 was used. The capacitor is highly reliable because it has a small variation in electrical characteristics with respect to changes in environmental temperature and has a long lifetime. In particular, each multilayer ceramic capacitor of Examples 1 to 6 in which the holding temperature in the reoxidation process is 700 to 900 ° C. has high reliability.

On the other hand, each multilayer ceramic capacitor of Comparative Examples 1 and 2 in which the holding temperature in the reoxidation process is 600 ° C., which is a temperature outside the limit range of the present invention, is log (R _i 150 / R _i 20). As is clear from the large value, the fluctuation of the electrical characteristics with respect to the change of the environmental temperature is large. This is considered to be due to insufficient reoxidation of the barium titanate dielectric ceramic layer in the reoxidation step.

  In addition, each multilayer ceramic capacitor obtained in Comparative Examples 3 to 4 was likely to have a capacitance smaller than the design value. This is considered to be due to the fact that the end oxidation ratio of the nickel internal electrode layer is high, so that poor conduction between the nickel internal electrode layer and the external electrode was likely to occur.

FIG. 1A is a perspective view for explaining how to determine the rate of end oxidation of a nickel-based internal electrode layer in a ceramic chip. FIG. 1B is a diagram of the nickel-based internal electrode layer in a ceramic chip. It is sectional drawing for demonstrating how to obtain | require the ratio of edge part oxidation.

Explanation of symbols

3. Nickel internal electrode layer (internal electrode layer mainly composed of nickel)
5 ... Barium titanate dielectric ceramic layer 10 ... Ceramic chip

Claims (5)

The green sheet for forming the dielectric ceramic layer and the paste layer for forming the internal electrode layer are fired in an alternately laminated state, so that the green sheet becomes a dielectric ceramic layer and the paste layer is mainly composed of nickel. Including a preparation step of preparing a ceramic chip as an internal electrode layer and a reoxidation step of reoxidizing the dielectric ceramic layer in the ceramic chip,
In the preparation step, at least one of barium oxide and calcium oxide, manganese oxide, rare earth oxide, and silicon oxide is contained as an accessory component, and the atomic ratio of calcium atoms to titanium atoms is 0 or 0.00. 001 to 0.12, the atomic ratio of the total amount of barium atoms and calcium atoms is 1.001 to 1.12, the atomic ratio of manganese atoms is 0.005 or less, and the rare earth element atoms constituting the rare earth oxide The dielectric is formed by a barium titanate-based dielectric ceramic having a number ratio of 0.0004 to 0.10, an atomic ratio of silicon atoms of 0.001 to 0.12, and an average particle diameter of 0.05 to 0.6 μm. Prepare a ceramic chip with a body ceramic layer formed,
In the re-oxidation step, the ceramic chip is held at 700 to 1050 ° C. for 2 to 6 hours in an oxidizing atmosphere having an oxygen partial pressure of 6 × 10 ⁻¹⁰ to 2 × 10 ⁻⁷ MPa. Capacitor manufacturing method.   The dielectric ceramic layer further contains magnesium oxide, vanadium oxide, tungsten oxide, or molybdenum oxide as subcomponents, the atomic ratio of magnesium atoms to titanium atoms is 0.03 or less, the atomic ratio of vanadium atoms and tungsten The number of atoms is 0.006 or less, the atomic ratio of molybdenum atoms is 0.003 or less, the atomic ratio of vanadium atoms is X, the atomic ratio of tungsten atoms is Y, and molybdenum atoms are atoms. 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein when the number ratio is expressed by Z, the formula (X + Y + 2Z) ≦ 0.006 is satisfied.   The method for manufacturing a multilayer ceramic capacitor according to claim 1 or 2, wherein the holding temperature of the ceramic chip is set to 700 to 900 ° C in the reoxidation step.   The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein the thickness of the internal electrode layer is 0.5 to 2.0 μm. When the thickness at which the surface layer of the ceramic chip is removed by polishing after the re-oxidation step is n [μm], the ratio of edge oxidation that occurs in the internal electrode layer in the re-oxidation step is expressed by the formula (0.85 + n ) /0.132 [%] or less, the method for producing a multilayer ceramic capacitor according to claim 1.

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