JP2008258468A - Laminated ceramic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated ceramic capacitor of high reliability, miniature, and high capacity and its manufacturing method. <P>SOLUTION: An average particle diameter of dielectric particles constituting a dielectric layer 11 is made to be different depending on layer directions of the dielectric layer 11, in which an average particle diameter of dielectric particles 13B located in the vicinity of a circumferential part 12B of an internal electrode layer 12 is made smaller than that of dielectric particles 13A in the vicinity of a central portion 12A of the internal electrode layer 12. Therefore, it is possible to make large the permittivity and electrostatic capacity per unit area. Further, there is reduced an average particle diameter of dielectric particles 13B located in the vicinity of the circumferential part 12B of the internal electrode layer 12 where there easily occur short circuiting and bad reliability so that short circuiting and bad reliability can be restrained, ensuring a high reliability, miniature, high capacitance laminated ceramic capacitor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer ceramic capacitor and a method for manufacturing the same.

  In recent years, there has been a high demand for downsizing of electronic components accompanying the increase in the density of electronic circuits, and the downsizing and increase in capacity of multilayer ceramic capacitors are rapidly progressing. In order to realize this, a method has been adopted in which the dielectric layer per layer in the multilayer ceramic capacitor is thinned. Further, as the thickness of the dielectric layer is reduced, the number of dielectric particles constituting one dielectric layer is decreasing, and the structure of the dielectric particles greatly affects the characteristics of the capacitor. Control of the structure of the particles has become extremely important.

For example, in Patent Document 1, even when the dielectric particles are miniaturized and the multilayer ceramic capacitor is thinned, the average number of particles per layer of the dielectric layer is set to 3 or more and 6 or less. There has been proposed a technique for realizing a multilayer ceramic capacitor that has a good temperature characteristic satisfying the B characteristic while keeping the defect rate low, and also has a good DC bias characteristic. Further, in Patent Document 2, the electrostatic capacity per unit volume is increased by making the average particle size of the dielectric particles constituting the dielectric layer in the direction parallel to the internal electrode layer larger than the thickness of the dielectric layer. A technology for realizing a multilayer ceramic capacitor having a large capacity even when it is large and small is proposed.
JP 2005-129802 A JP 2002-305124 A

  However, when the dielectric particles are miniaturized, the dielectric constant decreases when the dielectric particles are miniaturized, and it becomes difficult to realize a multilayer ceramic capacitor having a large capacitance per unit volume. On the other hand, when the dielectric particles are made larger, the capacitance per unit volume can be increased, but the electrical characteristics such as temperature characteristics deteriorate, and the dielectric layer is made thinner. In some cases, there is a problem that short circuit failure and reliability failure are likely to occur. Therefore, when the dielectric layer is thinned, it has been difficult to suppress short circuit defects and reliability defects and to obtain a high dielectric constant.

  The present invention solves the above-mentioned conventional problems, and suppresses short-circuit failure and reliability failure even when the dielectric layer is thinned and highly laminated, and is a highly reliable, small-sized and high-capacity laminated layer. An object of the present invention is to provide a ceramic capacitor and a manufacturing method thereof.

  In order to achieve the above object, the present invention provides a multilayer ceramic capacitor having an internal electrode layer and a dielectric layer, wherein the average particle size of the dielectric particles constituting the dielectric layer is determined in the layer direction of the dielectric layer. A multilayer ceramic capacitor in which the average particle size of the dielectric particles in the vicinity of the peripheral portion of the internal electrode layer is smaller than the average particle size of the dielectric particles in the vicinity of the central portion of the internal electrode layer. Yes, by increasing the average particle size of the dielectric particles near the center of the internal electrode layer, the dielectric constant is large and the capacitance per unit volume can be increased. The average particle size of the dielectric particles in the vicinity of the peripheral part of the internal electrode layer, which is a part that tends to generate defects, is reduced, so that occurrence of short-circuit failure and reliability failure can be suppressed, and high reliability and small size so The multilayer ceramic capacitor of capacity.

  The present invention also includes a step of forming a laminate by alternately laminating a ceramic raw sheet containing dielectric powder and a conductive paste film containing conductive metal powder and dielectric powder serving as internal electrodes. The dielectric powder contained in the conductive paste film has a different weight per unit area in the surface direction of the conductive paste film, and the unit of the dielectric powder contained in the peripheral portion of the conductive paste film A method of manufacturing a multilayer ceramic capacitor in which the weight per area is less than the weight per unit area of the dielectric powder contained in the central portion of the conductive paste film, thereby including in the conductive paste film Since the dielectric powder acts as a component that promotes grain growth of the dielectric layer, the dielectric powder in the central portion of the internal electrode layer is increased because the dielectric powder in the central portion of the conductive paste film is increased. It is possible to increase the average particle size of the child, it is possible dielectric constant to increase the capacitance per large unit volume. Further, since the dielectric powder in the peripheral portion of the conductive paste film is reduced, the growth of dielectric particles in the vicinity of the peripheral portion of the internal electrode layer can be suppressed and the average particle size can be reduced. Therefore, it is possible to suppress occurrence of short-circuit failure and reliability failure, and it is possible to easily manufacture a highly reliable, small and high-capacity multilayer ceramic capacitor with high productivity.

  According to the multilayer ceramic capacitor of the present invention, the dielectric constant is large and the capacitance per unit volume can be increased, and the occurrence of short-circuit failure and reliability failure can be suppressed. And it becomes a small and high capacity multilayer ceramic capacitor.

  Further, according to the method for manufacturing a multilayer ceramic capacitor of the present invention, the average particle size of the dielectric particles in the vicinity of the central portion of the internal electrode layer can be increased, the dielectric constant is large, and the capacitance per unit volume is increased. In addition, it is possible to suppress the growth of dielectric particles in the vicinity of the peripheral portion of the internal electrode layer and to reduce the average particle size. Therefore, it is possible to suppress occurrence of short-circuit failure and reliability failure, and it is possible to easily manufacture a highly reliable, small and high-capacity multilayer ceramic capacitor with high productivity.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention. FIGS. 2 and 3 are enlarged cross-sectional views of main parts of the dielectric layer shown in FIG. FIG. 3 is an enlarged cross-sectional view of the dielectric layer near the central portion of the electrode layer, and FIG. 3 is an enlarged cross-sectional view of the dielectric layer near the peripheral portion of the internal electrode layer.

  As shown in FIGS. 1, 2, and 3, the multilayer ceramic capacitor 10 according to one embodiment of the present invention has an average particle size of dielectric particles constituting the dielectric layer 11 in the layer direction of the dielectric layer 11. The average particle size of the dielectric particles 13B in the vicinity of the peripheral portion 12B of the internal electrode layer 12 is made smaller than the average particle size of the dielectric particles 13A in the vicinity of the central portion 12A of the internal electrode layer 12. ing.

  As described above, the multilayer ceramic capacitor 10 according to the present embodiment has a large dielectric constant and a high electrostatic capacity per unit volume by increasing the average particle diameter of the dielectric particles 13A in the vicinity of the central portion 12A of the internal electrode layer 12. Since the capacity can be increased and the average particle size of the dielectric particles 13B in the vicinity of the peripheral portion 12B of the internal electrode layer 12 which is a portion where short-circuit failure and reliability failure are likely to occur is reduced. The occurrence of defects and reliability failures can be suppressed, and a highly reliable, small and high capacity multilayer ceramic capacitor can be obtained.

(Example)
Next, a method for manufacturing a multilayer ceramic capacitor according to an embodiment of the present invention will be described in detail below based on examples, together with evaluation results of initial characteristics and reliability of the multilayer ceramic capacitor according to the embodiment of the present invention.

First, ceramic raw material powder containing barium titanate with an average particle size of about 0.2 μm as the main component and added with rare earth oxides and additives such as SiO ₂ , MgO, MnO ₂ is mixed and calcined. And dielectric powder having an average particle size of about 0.2 μm was prepared.

  This dielectric powder was mixed with a binder such as polyvinyl butyral resin or acrylic resin, a plasticizer such as phthalate ester, and a solvent such as butyl acetate to obtain a ceramic slurry. The ceramic slurry was applied on a polyethylene terephthalate (hereinafter referred to as PET) film using a method such as a doctor blade and dried to prepare a ceramic raw sheet. At this time, a ceramic raw sheet having a thickness after drying of about 2 μm was prepared.

  On the other hand, a conductive paste film serving as an internal electrode was formed on a PET film and prepared. A conductive paste film to be an internal electrode was prepared as follows.

  First, metallic nickel powder is used as a conductive metal powder to be an internal electrode, and this is used as a main component. Barium titanate having an average particle diameter of about 0.05 μm as a dielectric powder is 20 wt% with respect to the weight of the metallic nickel powder. The nickel paste was prepared by mixing with a binder such as polyvinyl butyral resin, a plasticizer such as phthalate ester, and a solvent such as butyl acetate.

  Using this nickel paste, a conductive paste film was prepared by applying and drying the PET film in a pattern to be an internal electrode by a gravure printing method. Note that the pattern of the conductive paste film that becomes the internal electrode is a rectangular pattern that is vertically and horizontally so that individual multilayer ceramic capacitors can be obtained when the dimensions, shape, and position are cut and separated in a later step. It was set as the pattern which arranged many pieces.

  Then, as shown in FIG. 4, the conductive paste film of one rectangular pattern at this time has a cross-sectional shape that is thick at the central portion and thin at the peripheral portion. FIG. 4 shows the cross-sectional shape in the short direction of one rectangular pattern, that is, the cross-sectional shape in the direction of the cross-section shown in FIG. 1 when used as the internal electrode of the multilayer ceramic capacitor. However, the cross-sectional shape in the longitudinal direction of the rectangular pattern is similarly thick at the central portion and thin at the peripheral portion.

  Using the ceramic raw sheet and the conductive paste film prepared above, these were alternately laminated to produce a laminate having 300 conductive paste films, and this laminate was fired 1.6 mm after firing. It cut | disconnected and isolate | separated by the predetermined dimension so that it might become a * 0.8mm dimension, and it was set as the individual laminated body green chip. This multilayer green chip was fired to form external electrodes, and a multilayer ceramic capacitor of this example was produced.

  On the other hand, for comparison, the above-mentioned nickel paste was used and applied to a pattern to be an internal electrode on a PET film by a screen printing method and dried to form a conductive paste film of a comparative example different from the above. And prepared. Also at this time, the pattern of the conductive paste film that becomes the internal electrode is a rectangular pattern so that when the dimensions, shape, and position are cut and separated in a later step, a single piece multilayer ceramic capacitor is obtained. It was set as the pattern which arranged many in length and breadth. At this time, as shown in FIG. 5, the conductive paste film having one rectangular pattern had a cross-sectional shape having substantially the same thickness in both the central portion and the peripheral portion. FIG. 5 shows the cross-sectional shape in the short direction of one rectangular pattern, that is, the cross-sectional shape in the direction that becomes the cross-section shown in FIG. 1 when used as the internal electrode of the multilayer ceramic capacitor. However, the cross-sectional shape in the longitudinal direction of the rectangular pattern was also the shape having substantially the same thickness in both the central portion and the peripheral portion.

  Using the same ceramic raw sheet as in the above example and the conductive paste film in the above comparative example, these were alternately laminated to produce a laminate having 300 conductive paste films. The laminated body was cut and separated at a predetermined size so as to have a size of 1.6 mm × 0.8 mm after firing to obtain a piece-by-piece laminated body green chip. This multilayer green chip was fired to form external electrodes, and a multilayer ceramic capacitor of a comparative example was produced.

  Next, the multilayer ceramic capacitor of the present example obtained above and the multilayer ceramic capacitor of the comparative example were evaluated. As the evaluation, the average particle diameter of the dielectric particles of the dielectric layer, the capacitance, the short-circuit defect rate, and the deterioration of the insulation resistance after the high-temperature load test were evaluated as a reliability test. The evaluation results are shown in (Table 1).

  As a method for measuring the average particle diameter of the dielectric particles, the obtained multilayer ceramic capacitor is cut along a plane (surface shown in FIG. 1) that is perpendicular to the internal electrode and parallel to the end face on which the external electrode is formed. The surface is polished, subjected to chemical etching, and then observed with a scanning electron microscope (SEM). The diameter is calculated by converting the cross-sectional area of the dielectric particles into the area of a circle, and 1.5 times the diameter. Was the particle size. In addition, as an observation measurement, each of ten multilayer ceramic capacitors was used as a sample, and five 10000-times SEM photographs were taken for each of the dielectric layers near the central portion and the peripheral portion of the internal electrode layer. The average value was obtained by measuring the size of each of 10 dielectric particles. In the above description, the dielectric layer in the vicinity of the peripheral portion of the internal electrode layer refers to the dielectric layers in both regions up to 10% of the length of the internal electrode layer from both ends of the internal electrode layer on the cut surface. Pointing.

  The capacitance was measured with a digital LCR meter in a constant temperature bath at 20 ° C. at a measurement frequency of 1 kHz and a measurement voltage of 1.0 Vrms, and evaluated as an average value of 100 samples excluding short-circuit defects. The short-circuit defect rate was determined by measuring the resistance value of 100 capacitor samples and setting the resistance value of 10Ω or less as a short-circuit defect.

  The high temperature load test as a reliability test was evaluated as follows. A resistance value after applying a rated voltage of 6.3 V for 1 minute was measured using an insulation resistance meter, and 100 resistance values of 100 MΩ or more were selected as non-defective products, and the average value of these samples was used as the initial value. Each of these 100 samples was left for 1000 hours with a rated voltage of 6.3 V applied in a constant temperature bath at 85 ° C., then taken out, and after applying a rated voltage of 6.3 V for 1 minute using an insulation resistance meter. The resistance value was measured, and the average value of these was taken as the post-test value. In addition, those having a resistance value of 2 MΩ or less were regarded as poor insulation resistance degradation.

  As shown in (Table 1), the average particle diameter of the dielectric particles of the dielectric layer 11 of the multilayer ceramic capacitor 10 of this example differs in the layer direction of the dielectric layer 11, and the peripheral portion of the internal electrode layer 12 The average particle size of the dielectric particles 13B near 12B is 0.30 μm, the average particle size of the dielectric particles 13A near the central portion 12A of the internal electrode layer 12 is 0.39 μm, and the dielectric particles near the peripheral portion The average particle size of 13B is smaller than the average particle size of the dielectric particles 13A in the vicinity of the central portion, and is one-third of the average particle size of the dielectric particles 13A in the vicinity of the central portion.

  In the multilayer ceramic capacitor 10 of this embodiment, the average particle size of the dielectric particles 13B in the vicinity of the peripheral portion of the internal electrode layer 12 of the dielectric layer 11 is smaller than the average particle size of the dielectric particles 13A in the vicinity of the central portion. The reason is as follows. Since the dielectric powder of barium titanate having an average particle diameter of about 0.05 μm contained in the conductive paste film works as a component for promoting the grain growth of the dielectric layer, the conductive paste film is thickened in the central portion and included in the dielectric paste. Since the weight per unit area of the body powder is increased, the average particle size of the dielectric particles in the vicinity of the central portion of the internal electrode layer can be increased, and the conductive paste film is thinned and included in the peripheral portion. Since the weight per unit area of the dielectric powder is reduced, the growth of dielectric particles in the vicinity of the peripheral portion of the internal electrode layer can be suppressed and the average particle size can be reduced. As a method of changing the weight per unit area of the dielectric powder contained in the conductive paste film between the central portion and the peripheral portion, in addition to the method of changing the thickness as described above, the central portion of the conductive paste film It is also possible to use a method in which the addition amount of the dielectric powder is changed between the portion and the peripheral portion.

  On the other hand, in the comparative example, the amount of dielectric powder contained in the conductive paste film in the central portion and the peripheral portion with substantially the same thickness is made substantially the same, so the dielectric particles of the dielectric layer of the multilayer ceramic capacitor of the comparative example The average particle size of the dielectric layer does not vary in the layer direction of the dielectric layer, and the average particle size is 0.37 μm in the vicinity of the peripheral portion and the central portion of the internal electrode layer.

  As is clear from the evaluation results shown in (Table 1), the multilayer ceramic capacitor of this example has a capacitance almost the same as that of the multilayer ceramic capacitor of the comparative example. Compared with the multilayer ceramic capacitor, it is found that the short-circuit defect and the deterioration of the insulation resistance after the high temperature load test are extremely small, and according to this example, a highly reliable multilayer ceramic capacitor can be obtained with a high yield. This is considered to be due to the following reason.

  The short circuit failure can be considered as follows. In the comparative example, since the conductive paste film in the peripheral portion is thick, when producing a laminate by laminating and pressing the ceramic raw sheet and the conductive paste film, the conductive paste film is caused by a large step due to the presence or absence of the conductive paste film. The pressing force is likely to concentrate on the peripheral part of the ceramic, and the ceramic raw sheet is deformed in this part in the direction of thinning, and the conductive paste films are close to each other. The dielectric particles in the vicinity of the peripheral portion of the internal electrode layer, which is this portion, grow and grow in size when fired, and move the metallic nickel powder of the conductive paste existing around the dielectric particles to make it close The metallic nickel powder between the conductive paste films is connected to cause a short circuit failure. On the other hand, in this embodiment, since the conductive paste film in the peripheral portion is thin, the level difference due to the presence or absence of the conductive paste film is small, and the deformation of the ceramic raw sheet in the peripheral portion of the conductive paste film is small. It is difficult for films to be close to each other. The dielectric particles in the vicinity of the peripheral portion of the internal electrode layer, which is this portion, do not grow so much during firing and the particle size is small, so that the metal nickel powder of the conductive paste existing around the dielectric particles can move. In addition, since there is no connection with the metallic nickel powder of the conductive paste film of the adjacent layer, the occurrence of short-circuit defects can be reduced.

  Moreover, the deterioration of the insulation resistance after the high temperature load test is considered as follows. In general, in a ceramic capacitor, distortion is generated in ceramic dielectric particles by applying a voltage, and the amount of distortion increases as the dielectric constant of the dielectric particles increases (so-called electrostriction phenomenon). In the multilayer ceramic capacitor, the dielectric layer in which the internal electrode layer exists causes distortion in the direction extending in the thickness direction of the dielectric layer due to the application of voltage, but in the surrounding dielectric ceramic portion without the internal electrode layer, Does not cause distortion. For this reason, in the boundary portion with or without the internal electrode layer, a minute crack is likely to occur in the dielectric layer due to the stress due to the presence or absence of the strain, and the insulation resistance is likely to deteriorate. As described above, the amount of strain due to electrostriction increases as the dielectric constant increases. Therefore, as the particle size of the dielectric particles increases and the dielectric constant increases, fine cracks are more likely to occur in the dielectric layer. It is easy to bring about deterioration.

  For the above reason, in the comparative example, since the average particle size of the dielectric particles in the vicinity of the peripheral portion of the internal electrode layer that is in the vicinity of the boundary portion with or without the internal electrode layer is large and the dielectric constant is large, It is considered that cracks occurred and the insulation resistance deteriorated, resulting in 2 out of 100 defective insulation resistance deteriorations. On the other hand, in this example, since the average particle diameter of the dielectric particles in the vicinity of the peripheral portion of the internal electrode layer is small, it is considered that the dielectric layer is not cracked and the insulation resistance is not deteriorated. .

  From the above results, in the multilayer ceramic capacitor of the present invention, the average particle size of the dielectric particles near the peripheral portion of the internal electrode layer is smaller than the average particle size of the dielectric particles near the central portion of the internal electrode layer. A multilayer ceramic capacitor that has a large dielectric constant and a large capacitance per unit volume by increasing the average particle size of the dielectric particles in the vicinity of the center portion of the internal electrode layer. The average particle size of the dielectric particles in the vicinity of the peripheral part of the internal electrode layer, where defects and reliability defects are likely to occur, is reduced, so that the occurrence of reliability defects such as short-circuit defects and insulation resistance deterioration defects is suppressed. It can be seen that the multilayer ceramic capacitor has a high reliability, a small size and a high capacity.

  The above effect can be obtained by reducing the average particle size of the dielectric particles in the vicinity of the peripheral portion of the internal electrode layer as compared with the average particle size of the dielectric particles in the vicinity of the central portion of the internal electrode layer. By making the average particle size of the dielectric particles in the vicinity of the peripheral portion of the internal electrode layer 1/3 or less of the average particle size of the dielectric particles in the vicinity of the central portion, the above-described more remarkable effect can be obtained.

  The multilayer ceramic capacitor and the method for manufacturing the same according to the present invention have a large dielectric constant and can increase the capacitance per unit volume, and can suppress the occurrence of short-circuit defects and reliability defects. Even in the case of layering and increasing the number of layers, a highly reliable multilayer ceramic capacitor can be manufactured with a high yield, and is particularly useful as a small-sized and high-capacity multilayer ceramic capacitor and a method for manufacturing the same.

Schematic cross-sectional view of a multilayer ceramic capacitor in an embodiment Enlarged sectional view of the dielectric layer near the center of the internal electrode layer of the same multilayer ceramic capacitor Enlarged sectional view of the dielectric layer near the periphery of the internal electrode layer of the same multilayer ceramic capacitor The figure which shows the cross-sectional shape of the electrically conductive paste film | membrane in embodiment The figure which shows the cross-sectional shape of the electrically conductive paste film | membrane in a comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Multilayer ceramic capacitor 11 Dielectric layer 12 Internal electrode layer 12A Central part of internal electrode layer 12B Peripheral part of internal electrode layer 13A, 13B Dielectric particle

Claims (4)

A multilayer ceramic capacitor having an internal electrode layer and a dielectric layer, wherein the average particle diameter of the dielectric particles constituting the dielectric layer is made different in the layer direction of the dielectric layer. A multilayer ceramic capacitor in which an average particle size of dielectric particles in the vicinity of a peripheral portion is smaller than an average particle size of dielectric particles in the vicinity of a central portion of the internal electrode layer. A multilayer ceramic capacitor in which an average particle size of dielectric particles in the vicinity of the peripheral portion of the internal electrode layer is set to 1/3 or less of an average particle size of dielectric particles in the vicinity of the central portion. A step of forming a laminate by alternately laminating a ceramic raw sheet containing dielectric powder, and a conductive paste film containing conductive metal powder and dielectric powder serving as internal electrodes, the conductive paste film The weight per unit area of the dielectric powder contained in the conductive paste film is different in the surface direction of the conductive paste film, the weight per unit area of the dielectric powder contained in the peripheral portion of the conductive paste film, A method for manufacturing a multilayer ceramic capacitor, wherein the dielectric powder contained in the central portion of the conductive paste film is less than the weight per unit area. By reducing the thickness of the peripheral portion of the conductive paste film compared to the thickness of the central portion, the weight per unit area of the dielectric powder contained in the peripheral portion of the conductive paste film 4. The method for manufacturing a multilayer ceramic capacitor according to claim 3, wherein the dielectric powder contained in the central portion of the paste film is less than the weight per unit area of the dielectric powder.

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