JP2010205812A - Laminated ceramic capacitor and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated ceramic capacitor which can have electrostatic capacity close to a design value and also has small variance in electrostatic capacity, and to provide a method of manufacturing the same. <P>SOLUTION: The laminated ceramic capacitor is characterized by employing a step in which a capacitor body 1 is subjected to reoxidation processing after being subjected to barrel polishing by mixing media balls and ceramic particles 11 of 0.2 to 0.8 μm in average particle size together, and characterized in that ceramic particles 11 of 0.2 to 0.8 μm in average particle size stick on an exposed end surface 10 of an internal electrode layer 7, wherein the rate of the total length obtained by summing up particle sizes of the ceramic particles 11 sticking on the exposed end surface 10 of the internal electrode layer 7 is 5 to 20% when the width of the internal electrode layer 7 exposed on an end surface 9 of the capacitor body 1 is 100%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In recent years, with the spread of mobile devices such as mobile phones and the high speed and high frequency of semiconductor elements, which are the main components of personal computers, multilayer ceramic capacitors mounted on such electronic devices are required to be smaller and have higher capacities. Increasingly.

  For this reason, multilayer ceramic capacitors use nickel as the internal electrode layer, and the dielectric layer and internal electrode layer are being made thinner and higher, but recently the dielectric layer and internal electrode layer have been made thinner. The thickness of the dielectric layer is 2 μm or less, and the thickness of the internal electrode layer is less than 1 μm (for example, see Patent Document 1).

  Incidentally, a multilayer ceramic capacitor using nickel as an internal electrode layer is manufactured, for example, by the following process. First, a conductive paste mainly composed of nickel powder is printed on the surface of the ceramic green sheet to form an internal electrode pattern. Next, several hundred layers of ceramic green sheets on which internal electrode patterns are formed are laminated, and then the ceramic green sheets on which the conductive paste is not printed are superposed on the upper and lower surfaces of the ceramic green sheets, which are integrated by pressing and heating. A laminate is formed. Next, the laminate is cut into individual pieces, and then co-fired in a reducing atmosphere in which the partial pressure of oxygen is adjusted using a hydrogen-nitrogen mixed gas to produce a capacitor body that is a sintered body. Finally, a multilayer ceramic capacitor can be obtained by forming an external electrode on the end face where the internal electrode layer of the capacitor body is exposed.

  In the above-described process, the capacitor body obtained after the simultaneous firing is fired in a reducing atmosphere, so that the dielectric layer is in a reduced state and does not exhibit desired dielectric properties. For this reason, the capacitor body after co-firing is usually subjected to re-oxidation treatment in order to develop desired dielectric properties. This re-oxidation treatment is performed at a lower temperature and higher oxygen partial pressure than the conditions during co-firing. (For example, refer to Patent Document 2).

JP 2003-68564 A JP 2005-26351 A

  However, in the multilayer ceramic capacitor as described above in which the dielectric layer and the internal electrode layer are thinned, the internal electrode layer constituting the capacitor body is oxidized from the portion exposed on the end face of the capacitor body to the inside by reoxidation treatment. For this reason, the capacitance of the monolithic ceramic capacitor is lower than the design value, and there is a problem that the variation of the capacitance becomes large especially in the mass production process.

  Accordingly, an object of the present invention is to provide a multilayer ceramic capacitor that can obtain a capacitance close to a design value and has a small variation in capacitance, and a method for manufacturing the same.

  The multilayer ceramic capacitor of the present invention includes a capacitor body in which dielectric layers and internal electrode layers mainly composed of nickel are alternately stacked, and an external electrode provided on an end surface of the capacitor body where the internal electrode layer is exposed. And ceramic particles having an average particle size of 0.2 μm to 0.8 μm are attached to the exposed end face of the internal electrode layer, and are exposed to the end face of the capacitor body. When the width of the internal electrode layer is defined as 100%, the ratio of the total length obtained by adding the particle diameters of the ceramic particles adhering to the end face of the internal electrode layer is 5% to 20%. And

  In the multilayer ceramic capacitor of the present invention, since the ceramic particles having the above average particle diameter adhere to the exposed end surface of the internal electrode layer exposed on the end surface of the capacitor body, the capacitor body is subjected to reoxidation treatment. However, the oxidation of the internal electrode layer can be suppressed. As a result, it is possible to suppress a reduction in the effective area contributing to the capacitance of the internal electrode layer, obtain a capacitance close to the design value, and reduce the variation in capacitance.

  In the multilayer ceramic capacitor of the present invention, it is desirable that the exposed end surface of the internal electrode layer is on the inner side of the end surface of the capacitor body.

  In the multilayer ceramic capacitor of the present invention, the end face of the internal electrode layer exposed at the end face of the capacitor body is on the inner side of the end face of the capacitor body, so that the ceramic particles are likely to enter the recess located at the end face of the internal electrode layer. For this reason, the ratio of the total length which added the particle diameter of the ceramic particle with respect to the width | variety of an internal electrode layer can be enlarged, and the effect of the oxidation suppression of an internal electrode layer can further be heightened. As a result, the obtained multilayer ceramic capacitor can obtain a capacitance closer to the design value, and the variation in capacitance can be further reduced.

  In the multilayer ceramic capacitor of the present invention, when the average particle size of the ceramic particles is 0.3 μm to 0.6 μm, and the width of the internal electrode layer exposed on the end face of the capacitor body is 100%, It is desirable that the ratio of the total length obtained by adding the particle diameters of the ceramic particles adhering to the exposed end face of the internal electrode layer is 8% to 15%.

  When the average particle diameter of the ceramic particles adhering to the exposed end face of the internal electrode layer and the ratio thereof are in the above-described range, the capacitance of the obtained multilayer ceramic capacitor can be made closer to the design value. At the same time, variations in capacitance can be further reduced.

  The manufacturing method of the multilayer ceramic capacitor of the present invention is as follows: (a) a ceramic green sheet and internal electrode patterns mainly composed of nickel are alternately stacked, and a capacitor body molded body in which the end surfaces of the internal electrode patterns are exposed on the end surfaces is formed. (B) firing the capacitor body compact in a hydrogen-nitrogen reducing atmosphere to form a capacitor body; (c) forming the capacitor body with a media ball and an average particle size of 0.2 μm; A step of barrel-polishing with ceramic particles of ˜0.8 μm, and (d) an oxygen content higher than that in the reducing atmosphere at a temperature lower than the firing temperature in step (b) of the barrel-polished capacitor body. A step of performing reoxidation treatment under pressure, and (e) an external electrode on the end surface where the end surface of the internal electrode layer of the capacitor body that has been reoxidized is exposed. Forming the step.

  According to the method for producing a multilayer ceramic capacitor of the present invention, the capacitor body obtained after firing is subjected to barrel polishing using a media ball and ceramic particles having an average particle size of 0.2 μm to 0.8 μm. Since minute irregularities can be easily formed on the end face and ceramic particles can be easily attached to the end face of the internal electrode layer exposed on the end face of the capacitor body, the barrel-polished capacitor body is subjected to reoxidation treatment. However, oxidation from the end surface of the internal electrode layer to the inside can be suppressed, and a decrease in the effective area of the internal electrode layer can be suppressed. As a result, it is possible to easily obtain a multilayer ceramic capacitor whose electrostatic capacity is close to the design value and whose variation is small.

  In the method for manufacturing a multilayer ceramic capacitor according to the present invention, it is desirable to perform barrel polishing until the end face of the internal electrode layer is located inside the end face of the capacitor body.

  In the manufacturing method of the multilayer ceramic capacitor of the present invention, if the end of the internal electrode layer is formed so as to be inside the end surface of the capacitor body by controlling the barrel polishing conditions, the ceramic particles easily collect in the recess, The oxidation of the internal electrode layer can be further suppressed in the oxidation treatment. As a result, it is possible to easily obtain a multilayer ceramic capacitor whose electrostatic capacity is closer to the design value and whose variation is smaller.

  In the method for producing a multilayer ceramic capacitor of the present invention, it is desirable to use ceramic particles having an average particle size of 0.3 μm to 0.6 μm.

  In the manufacturing method of the multilayer ceramic capacitor of the present invention, when ceramic particles having an average particle size of 0.3 μm to 0.6 μm are used, the ceramic present on the end surface of the internal electrode layer exposed on the end surface of the capacitor body The particles can be present over a range of 8% to 15% with respect to the width of the internal electrode layer. As a result, it is possible to obtain a multilayer ceramic capacitor whose electrostatic capacity is closer to the design value and whose variation is further smaller.

  According to the multilayer ceramic capacitor of the present invention, fine ceramic particles are attached to the end face of the internal electrode layer exposed at the end face of the capacitor body. Therefore, even if the capacitor body is reoxidized, the internal electrode layer Therefore, the reduction of the effective area contributing to the capacitance of the internal electrode layer can be suppressed. As a result, it is possible to obtain a capacitance close to the design value and to reduce variations in capacitance.

It is a schematic sectional drawing which shows an example of the multilayer ceramic capacitor of this invention. It is the schematic diagram which expanded the end surface of the capacitor | condenser main body when the A section of FIG. 1 is planarly viewed from the direction of the arrow. FIG. 9 is another example of the present invention, and is a schematic diagram showing that the exposed end surface of the internal electrode layer is inside the end surface of the capacitor body.

  FIG. 1 is a schematic cross-sectional view showing an example of the multilayer ceramic capacitor of the present invention.

  In the multilayer ceramic capacitor of the present invention, external electrodes 3 are formed at both ends of the capacitor body 1. The external electrode 3 is formed, for example, by baking Cu or an alloy paste of Cu and Ni.

  The capacitor body 1 is configured by alternately laminating dielectric layers 5 made of dielectric ceramics and internal electrode layers 7. An exposed internal electrode layer 7 is partially joined to the external electrode 3 on the end face 9 of the capacitor body 1. In FIG. 1, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner, but the laminated ceramic capacitor of the present invention has a laminated layer in which the dielectric layer 5 and the internal electrode layer 7 are several hundred layers. It is a body.

  The dielectric layer 5 is composed of crystal particles in which magnesium oxide, rare earth element (RE) oxide, manganese oxide, and the like are dissolved in barium titanate, and a grain boundary phase mainly composed of silicon oxide. Made of body porcelain. The types of dielectric ceramics are not limited to those described above, and other dielectric ceramics can be used. The thickness is desirably 2 μm or less, particularly 1 μm or less. As a result, the multilayer ceramic capacitor can be reduced in size and capacity. In addition, when the thickness of the dielectric layer 5 is 0.4 μm or more, it is possible to reduce the variation in capacitance and stabilize the capacitance-temperature characteristic.

  The material for forming the internal electrode layer 7 is preferably a base metal such as nickel (Ni) or copper (Cu) from the viewpoint that the manufacturing cost can be suppressed even when the number of layers is increased, and is the same as that of the dielectric layer 5 in the present invention. In particular, nickel (Ni) is more preferable in that firing can be performed. The thickness of the internal electrode layer 7 is preferably 0.5 to 2 μm.

  FIG. 2 is an enlarged schematic view of the end surface of the capacitor body when the portion A of FIG. 1 is viewed in plan from the direction of the arrow. Here, a straight line drawn in the width direction of the internal electrode layer 7 indicates a partial width W of the internal electrode layer 7. Further, D1, D2 and D3 shown in FIG. 2 indicate the particle diameters of the ceramic particles 11 existing on the end face 10 of the internal electrode layer 7. The ratio of the ceramic particles 11 present on the internal electrode layer 7 is obtained from the formula {(D1 + D2 + D3 +... Dn) / W} × 100 (%). However, n is an integer. This can be measured over the entire width of the end face 10 of the internal electrode layer 7 and calculated as an average value thereof.

  In the multilayer ceramic capacitor of the present invention, ceramic particles 11 having an average particle size of 0.2 μm to 0.8 μm are attached to the end surface 10 of the internal electrode layer 7 exposed from the end surface 9 of the capacitor body 1. Further, the ratio of the ceramic particles 11 adhering to the exposed end face 10 of the internal electrode layer 7 is as shown in FIG. 2 when the width of the end 10 of the exposed internal electrode layer 7 is 100%. It is important that the ratio of the total length obtained by adding the particle diameters (D1 + D2 + D3 +... Dn) of the ceramic particles 11 is 5% to 20%.

  When the average particle diameter of the ceramic particles 11 adhering to the exposed end face 10 of the internal electrode layer 7 and the ratio thereof are within the above-described range, the end face 10 where the internal electrode layer 7 is exposed even if the capacitor body 1 is subjected to reoxidation treatment. 1 to the interior 10A (in FIG. 1, near the A portion and in FIG. 2 near the end face 10 of the internal electrode layer 7), the oxidation is suppressed, so that the effective area of the internal electrode layer 7 is reduced. Can be suppressed. For this reason, it is possible to obtain a capacitance of 90% or more with respect to the design value of the multilayer ceramic capacitor, and it is possible to reduce the variation (CV) of the capacitance to 5% or less.

  On the other hand, when the average particle size of the ceramic particles 11 is smaller than 0.2 μm, the ceramic particles 11 are likely to adhere to the exposed end surface 10 of the internal electrode layer 7, and the width of the internal electrode layer 7 at the end surface 10. Since the ratio of the ceramic particles 11 in the width direction of the end face 10 of the internal electrode layer 7 to W exceeds 20%, the connection area between the external electrode 3 and the internal electrode layer 7 becomes small, and the multilayer ceramic capacitor The capacitance is lower than the design value.

  On the other hand, when the average particle diameter of the ceramic particles 11 is larger than 0.8 μm, the ceramic particles 11 are difficult to adhere to the exposed end surface 10 of the internal electrode layer 7, and thus the width W of the end surface 10 of the internal electrode layer 7. On the other hand, the proportion of the ceramic particles 11 in the end face 10 of the internal electrode layer 7 is lower than 5%. For this reason, the internal electrode layer 7 is likely to be oxidized from the end face 10 to the inside 10A. In this case, the effective area is greatly reduced, the capacitance is lower than the design value, and the capacitance variation (CV) is also large. Become.

  Therefore, the average particle diameter of the ceramic particles 11 adhering to the exposed end face 10 of the internal electrode layer 7 is set to 0.2 μm to 0.8 μm, and the internal electrode layer 7 with respect to the width W at the end face 10 of the internal electrode layer 7. The ratio of the ceramic particles 11 to the end face 10 is preferably 5% to 20%, in particular, the average particle diameter of the ceramic particles 11 is 0.3 μm to 0.6 μm, and the width of the end face 10 of the internal electrode layer 7. The ratio of the ceramic particles 11 occupying the end face 10 of the internal electrode layer 7 to W is desirably 8% to 15%. In this case, the capacitance can be close to the design value, and the variation in capacitance (CV) can be further reduced.

  CV is obtained by dividing the standard deviation (σ) when the capacitance is measured by the average value (x), and is a value representing the variation of the measured value. In addition, the state in which the internal electrode layer 7 is oxidized refers to a case where a blackened state is observed in the secondary electron image when the multilayer ceramic capacitor is subjected to cross-sectional polishing and observed with a scanning electron microscope, and is not oxidized. Means a state showing gray or silver in the same analysis. Furthermore, the design value of a multilayer ceramic capacitor is a type determined based on a certain standard, and the dielectric constant of the dielectric ceramic constituting the dielectric layer at room temperature, the effective area of the internal electrode layer, and the dielectric layer and the internal Capacitance derived from the number of electrode layers stacked.

  FIG. 3 is another example of the present invention, and is a schematic diagram showing that the exposed end face of the internal electrode layer is inside the end face of the capacitor body.

  In the multilayer ceramic capacitor of the present invention, it is desirable that the exposed end face 10 of the internal electrode layer 7 be inside the end face 9 of the capacitor body 1. In such a structure, since the exposed end face 10 of the internal electrode layer 7 is inside the end face 9 of the capacitor body 1, the recess 10 </ b> B is formed, and thus the ceramic particles 11 are easily collected in the recess 10 </ b> B. As a result, even if the ceramic particles 11 having an average particle diameter of 0.2 μm to 0.8 μm are used, the exposed end face 10 of the internal electrode layer 7 is substantially on the same surface as the end face 9 of the capacitor body 1 as shown in FIG. Even in some cases, the capacitance of the multilayer ceramic capacitor can be made closer to the design value, and the variation (CV) can be further reduced. In this case, the depth of the concave portion 10B is 0.2 to 0.2 because the ceramic particles 11 having an average particle diameter of 0.2 μm or more are likely to be collected and the effective area of the internal electrode layer 7 is hardly reduced. It is desirable that the thickness is 0.5 μm. Here, the end surface 10 of the internal electrode layer 7 being inside the end surface 9 of the capacitor body 1 means a case where the end surface 10 of the internal electrode layer 7 is 0.1 μm or more inside from the end surface 9 of the capacitor body 1.

  By the way, as the ceramic particles 11 attached to the exposed end face 10 of the internal electrode layer 7, alumina, zirconia, aluminum nitride, and mixed particles thereof are preferable. This is because it is difficult to react with the components of the internal electrode layer 7 and the external electrode 3 even in the temperature and atmosphere when the capacitor body 1 is reoxidized and when the external electrode 3 is formed on the end face 9 of the capacitor body 1. . In particular, alumina is preferable in that it has high oxidation resistance and reduction resistance and is thermally stable.

  Here, the ratio of the ceramic particles 11 present on the end face 10 of the internal electrode layer 7 exposed on the end face 9 of the capacitor body 1 is determined as follows.

  First, a multilayer ceramic capacitor is polished parallel to the laminated surface of the internal electrode layer 7 to prepare a sample in which the internal electrode layer 7 and the ceramic particles 11 are exposed. In this polishing, first, rough polishing is performed using # 1000 to # 2000 polishing paper. Next, after polishing using a hard buff coated with a diamond paste having a particle size of 0.1 to 3 μm, a final polishing is further performed using a soft buff.

  Next, this sample is analyzed by a scanning electron microscope equipped with an energy dispersive analyzer (EDS). In this analysis, first, particles that exist in the vicinity of the interface between the internal electrode layer 7 and the external electrode 3 and can be confirmed to be approximately spherical are searched by observation using a scanning electron microscope. Here, the term “approximately spherical” means that the ratio of the longest diameter to the shortest diameter (longest diameter / shortest diameter) of the ceramic particles 11 obtained from an image observed with a scanning electron microscope is 1.3 or less.

  Next, it is confirmed that the particles are ceramic particles 11 used for barrel polishing from X-ray data of EDS obtained by applying an electron beam to particles confirmed by scanning electron microscope observation. At this time, the target ceramic particle 11 is a particle whose component showing the strongest peak in the X-ray data is the same component as the ceramic particle 11 used for barrel polishing.

  The particle diameter (D1, D2, D3... Dn) of each ceramic particle 11 is measured as the maximum diameter in the direction parallel to the internal electrode layer 7 as shown in FIG. Ask. The width of the internal electrode layer 7 is the entire width W of the internal electrode layer 7 formed on the capacitor body 1 which is a sample prepared by polishing. In this case, the region to be analyzed is a substantially central portion in the stacking direction of the capacitor body 1. A region having a width of 5 to 20 μm as one section, and a region having a similar area in the same sample over the entire width W of the internal electrode layer 7 formed in the capacitor body 1 It is. Specifically, the internal electrode obtained by applying the data of the particle diameter of each ceramic particle 11 and the width of the internal electrode layer 7 obtained as described above to the formula {(D1 + D2 + D3 +... Dn) / W} × 100 (%). The ratio of the ceramic particles 11 to the width W of the layer 7 is determined. In addition, such an analysis is similarly performed about 2-5 multilayer ceramic capacitors, and the average value of the ratio of the ceramic particle | grains 11 calculated | required from each sample is calculated | required.

  Next, a method for producing the multilayer ceramic capacitor of the present invention will be described.

In the step (a), first, a dielectric ceramic material for forming the dielectric layer 5 is prepared. For example, with respect to 100 mol of barium titanate powder, 0.2 to 0.8 mol of MgO powder, 0.3 to 0.8 mol of oxide powder of rare earth element, and 0.1 to 0.00 of MnCO ₃ powder. It mix | blends in the ratio of 5 mol, Furthermore, glass powder is added as a sintering aid in the range which can maintain a desired dielectric property as needed, and raw material powder is obtained. The addition amount of the glass powder is preferably 0.5 to 2 parts by mass when the barium titanate powder is 100 parts by mass.

  Next, a ceramic slurry is prepared by adding a dedicated organic vehicle to the raw material powder, and then a ceramic green sheet is formed using a sheet forming method such as a doctor blade method or a die coater method. In this case, the thickness of the ceramic green sheet is preferably 0.5 to 3 μm because the dielectric layer 5 has a thin layer for increasing the capacity and ensures high insulation.

  Next, a rectangular internal electrode pattern is printed with a thickness of 1 to 3 μm on the main surface of the obtained ceramic green sheet. The conductor paste used as the internal electrode pattern is preferably composed mainly of Ni.

  Next, stack the desired number of ceramic green sheets with internal electrode patterns, and stack multiple ceramic green sheets without internal electrode patterns on the top and bottom so that the upper and lower layers are the same number. Form the body. In this case, the internal electrode pattern in the sheet laminate is shifted by a half pattern in the longitudinal direction.

  Next, the sheet laminate is cut into a lattice shape to form a capacitor body molded body in which the end portions of the internal electrode patterns are exposed.

In step (b), the capacitor body molded body is degreased, and then in a hydrogen-nitrogen mixed gas (oxygen partial pressure: 1 × 10 ⁻⁷ Pa to 1 × 10 ⁻⁹ Pa) at 1100 ° C. to 1200 ° C. By firing at a temperature for 1 to 4 hours, the capacitor body 1 in which the dielectric layer 5 and the internal electrode layer 7 are integrally sintered is produced.

  The capacitor main body 1 manufactured in this manner has a degree that the internal electrode layer 7 can be slightly confirmed from the end face 9, and in this state, it is difficult to make sufficient electrical connection with the external electrode 3.

  Therefore, barrel polishing is performed on the capacitor body 1 immediately after firing under predetermined conditions so that the internal electrode layer 7 is sufficiently exposed to the end face 9 of the capacitor body 1 so that electrical connection with the external electrode 3 can be sufficiently performed. To do.

  In the step (c), first, the capacitor body 1 obtained by firing is placed in a ball mill in which media balls and ceramic particles 11 are mixed, and barrel polishing is performed. A media ball used for barrel polishing is preferably an alumina or zirconia ceramic ball having a diameter of 2 mm to 10 mm. In addition, as conditions for barrel polishing, a range including a specific example to be described later is appropriate, and when a mill container used for barrel polishing has an internal volume of 300 ml to 1000 ml, the amount of media balls is 80 to 150 g, It is preferable that the number of samples of the capacitor body 1 as a sample is 100 to 300, the rotational speed of barrel polishing is 80 to 200 rpm, and the time for barrel polishing is 3 to 10 hours.

  The ceramic particles 11 to be mixed with the media ball are preferably alumina, zirconia, aluminum nitride and mixed particles thereof as described above, and more preferably alumina.

  It is important to use ceramic particles 11 having an average particle size of 0.2 μm to 0.8 μm. When the average particle diameter of the ceramic particles 11 is 0.2 μm to 0.8 μm, irregularities are formed on the end face 9 of the capacitor body 1 after barrel polishing and the end face 10 of the internal electrode layer 7 exposed at the end face 9. Therefore, the ceramic particles 11 are easily attached. For this reason, even if the capacitor body 1 is subjected to a reoxidation treatment, oxidation inside the end surface 10 of the internal electrode layer 7 can be suppressed. As a result, the effective area of the internal electrode layer 7 is increased, a capacitance close to the design value can be obtained, and a multilayer ceramic capacitor having a small variation in capacitance can be easily obtained.

  On the other hand, when the average particle diameter of the ceramic particles 11 is smaller than 0.2 μm, the amount of the ceramic particles 11 attached to the exposed end face 10 of the internal electrode layer 7 increases, and the end face of the internal electrode layer 7 is increased. Since the ratio of the ceramic particles 11 occupying the end face of the internal electrode layer 7 with respect to the width W of 10 exceeds 20%, the contact area between the external electrode 3 and the internal electrode layer 7 is reduced, and the static electricity of the multilayer ceramic capacitor is reduced. The electric capacity becomes lower than the design value. Further, when the average particle diameter of the ceramic particles 11 is larger than 0.8 μm, the ceramic particles 11 hardly adhere to the end face 10 of the internal electrode layer 7. Thus, it becomes lower than 5% of the ceramic particles 11 occupying the end face 10 of the internal electrode layer 7. For this reason, the internal electrode layer 7 is easily oxidized from the exposed end face 10 to the inside 10A, and the effective area is reduced. Therefore, the capacitance is lower than the design value and the variation in capacitance (CV) is also increased.

  For this reason, the average particle diameter of the ceramic particles 11 to be used is preferably 0.2 μm to 0.8 μm. When the ceramic particles 11 having an average particle diameter in this range are used for barrel polishing, a multilayer ceramic capacitor is produced. The ratio of the ceramic particles 11 in the end face 10 of the internal electrode layer 7 to the width W of the end face 10 of the internal electrode layer 7 can be 5% to 20%.

  In the method for producing a multilayer ceramic capacitor according to the present invention, the average particle size of the ceramic particles 11 used is 0 because the ratio of the capacitance to the design value can be maintained high and the variation in capacitance (CV) can be further reduced. It is desirable that it is 3 μm to 0.6 μm.

  Furthermore, in the method for manufacturing a multilayer ceramic capacitor according to the present invention, it is desirable to perform barrel polishing until the exposed end surface 10 of the internal electrode layer 7 is located inside the end surface 9 of the capacitor body 1. When the capacitor body 1 is barrel-polished, by using ceramic particles having an average particle diameter of 0.2 μm to 0.8 μm, the concave portion 10B can be easily formed in the portion of the end surface 9 of the capacitor body 1 where the internal electrode layer 7 is exposed. Can be formed. In this case, the depth of the recess 10B can be adjusted by adjusting the polishing time. If the end face 10 where the internal electrode layer 7 is exposed is controlled to be inside the end face 9 of the capacitor body 1 by controlling the barrel polishing conditions, the ceramic particles 11 are likely to collect in the recesses 10B and are reoxidized. The effect of suppressing oxidation of the internal electrode layer 7 in the treatment can be further enhanced.

  Although the size of the capacitor body 1 used in the manufacturing method of the present invention is not limited, it is a small size of 0402 type (the area of the plane parallel to the internal electrode layer 7 is 0.4 mm × 0.2 mm) to 21 type (the same area is 2 mm × 1 mm). This is suitable for a size multilayer ceramic capacitor.

  The dielectric layer 5 constituting the capacitor body 1 is preferably composed of a dielectric ceramic containing 90% to 99% by mass of barium titanate in terms of mass ratio because irregularities are easily formed on the surface after barrel polishing. .

  The internal electrode layer 7 also preferably has a purity of 98% or more except for the dielectric powder contained as a co-material because the irregularities are easily formed after barrel polishing.

In the step (d), next, the barrel-polished capacitor body 1 is at a temperature lower than the firing temperature in the step (b) (900 to 1050 ° C.) and higher in oxygen partial pressure than the firing reducing atmosphere. Re-oxidation treatment is performed at an oxygen partial pressure of 10 ⁻⁴ Pa to 10 ⁻⁶ Pa. The retention time at the highest temperature in the reoxidation treatment is preferably 4 to 10 hours because the dielectric properties such as the relative dielectric constant are improved.

  According to the manufacturing method of the present invention, the capacitor body 1 obtained after firing is subjected to barrel polishing under the above-described conditions, thereby attaching the ceramic particles 11 to the end surface 10 of the internal electrode layer 7 exposed on the end surface 9 of the capacitor body 1. Can be made. For this reason, even if the capacitor body 1 is subjected to a reoxidation treatment, oxidation from the end 10 of the internal electrode layer 7 to the inner side 10A can be suppressed.

  Next, in the step (e), the external electrode 3 is formed on the end face 9 where the internal electrode layer 7 of the capacitor body 1 reoxidized in the step (d) is exposed.

  As the material of the external electrode 3, Cu or an alloy of Cu and Ni is preferably used, and a conductor paste prepared by mixing a small amount of glass powder with such metal powder is used. The glass powder is preferably glass in which another additive component is added to silicon oxide to lower the melting point, and is preferably one that does not easily react with the ceramic particles 11 attached to the end face 9 of the capacitor body 1 after barrel polishing. As a result, baking at a temperature lower than the temperature at which the capacitor body 1 is manufactured can be performed, and oxidation of the internal electrode layer 3 can be prevented even when the external electrode 3 is formed.

  In this case, the conditions for forming the external electrode 3 are preferably a maximum temperature of 700 to 850 ° C. and an oxygen partial pressure of 0.1 to 50 Pa.

  In the manufacturing method of the present invention, as described above, the ceramic particles 11 are also adhered to the end surface 10 of the internal electrode layer 7 exposed to the end surface 9 of the capacitor body 1 after the reoxidation treatment. Even if the external electrode 3 is formed under the above conditions, oxidation from the end 10 of the internal electrode layer 7 to the inner side 10A can be suppressed. A plating film may be formed on the surface of the external electrode 3 in order to improve mountability.

First, barium titanate powder, MgO powder, Y ₂ O ₃ powder and MnCO ₃ powder were prepared as raw material powders. These various powders when formed into a powdered barium amount of 100 moles titanate, 0.5 mol of MgO _powder, Y 2 _{O 3} powder was 0.5 mol per mol 1 mol, MnCO ₃ powder, further, the glass powder ( A dielectric powder was prepared by adding 1 part by mass of SiO ₂ = 55, BaO = 20, CaO = 15, Li ₂ O = 10 (mol%) to 100 parts by mass of barium titanate powder.

  This dielectric powder was wet mixed using a zirconia ball having a diameter of 5 mm and a mixed solvent composed of toluene and alcohol as a solvent.

  Next, the wet-mixed powder is put into a mixed solvent of polyvinyl butyral resin and toluene and alcohol, and wet-mixed using zirconia balls having a diameter of 5 mm to prepare a ceramic slurry, and the thickness is 2 by the doctor blade method. A 5 μm ceramic green sheet was produced.

  Next, a plurality of rectangular internal electrode patterns mainly composed of Ni were formed on the upper surface of the ceramic green sheet. The conductor paste for forming the internal electrode pattern was obtained by adding 15 parts by mass of barium titanate (BT) powder to 100 parts by mass of Ni powder having an average particle size of 0.3 μm.

Next, 200 ceramic green sheets on which internal electrode patterns were printed were laminated, and 20 ceramic green sheets on which the internal electrode patterns were not printed were laminated on the upper and lower surfaces, respectively, using a press machine at a temperature of 60 ° C. and pressure The laminated body was produced by closely adhering under the conditions of 10 ⁷ Pa and 10 minutes, and then the laminated body was cut into a predetermined size to form a capacitor body molded body.

Next, after debinding the capacitor body molded body in the air, the capacitor body was baked at 1140 ° C. for 2 hours in a hydrogen-nitrogen mixed gas atmosphere at an oxygen partial pressure of 10 ⁻⁸ Pa. Produced. The size of the manufactured capacitor body was equivalent to 1005 type, 0.95 × 0.48 × 0.48 mm ³ , the thickness of the dielectric layer was 1 μm, and the thickness of one internal electrode layer was 1 μm. . The design value of the capacitance obtained with this capacitor body is 2.2 μF.

  Next, the produced capacitor body was barrel-polished. For the barrel polishing, a polypot having an internal volume of 500 mL was used, alumina balls having an average particle diameter of 5 mm were used as media balls, and the amount was 100 g. Ceramic particles having different average particle diameters were prepared, and the amount added was 40 g. Pure water was used as the solvent for barrel polishing. Pure water was filled with polypot when barrel polishing.

  In barrel polishing, the number of samples of the capacitor body of the above size is 200, the rotational speed of barrel polishing is 100 rpm, and the time is Sample No. For Samples 1 to 13, sample No. 14 was 8 hours. Sample No. of the capacitor body thus obtained was obtained. In each of Nos. 1 to 13, the exposed end face of the internal electrode layer is located about 0.4 μm inside the end face of the capacitor body. In No. 14, the end portion of the internal electrode layer was at a position about 0.05 μm inside the end surface of the capacitor body.

Subsequently, the produced capacitor body was oxidized in a nitrogen atmosphere (oxygen partial pressure: 10 ⁻⁶ Pa) at 1000 ° C. for 5 hours.

Next, a conductor paste containing Cu as a main component is applied to both ends of the capacitor body after barrel polishing, and baked under conditions of a temperature of 800 ° C., an oxygen partial pressure of 1 Pa, and a maximum temperature holding time of 0.2 hours. Went. Conductor paste used contains a small amount of glass (SiO ₂ : 60% by mass, Al ₂ O ₃ : 20% by mass, B ₂ O ₃ : 20% by mass) with respect to 100 parts by mass of Cu powder (99% purity). It was. Thereafter, Ni plating and Sn plating were sequentially performed on the surface of the external electrode by barrel plating to produce a multilayer ceramic capacitor.

  Next, the following evaluation was performed on these multilayer ceramic capacitors. The capacitance was measured at a temperature of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms, and an average value, a ratio to a design value, and variation (CV) were obtained. The number of samples was 20.

  The ratio of the ceramic particles present at the end of the internal electrode layer exposed at the end face of the capacitor body was determined by the following method.

  First, a sample of the multilayer ceramic capacitor was polished to the vicinity of the central portion in the stacking direction parallel to the stacking surface of the internal electrode layer to prepare a sample in which the internal electrode layer and ceramic particles were exposed. In this polishing, first, rough polishing was performed using # 1000 to # 2000 polishing paper. Next, after polishing using a hard buff to which a diamond paste having a particle size of 0.1 to 3 μm was applied, finish polishing was further performed using a soft buff.

  Next, this sample was analyzed by a scanning electron microscope equipped with an energy dispersive analyzer (EDS). In this analysis, the following analysis was performed using a scanning electron microscope over the entire width from the end in the width direction of the internal electrode layer. First, particles that could be confirmed to be approximately spherical were searched for with a scanning electron microscope having a width of one section of about 5 μm. Here, as the roughly spherical ceramic particles, those having a ratio of the longest diameter to the shortest diameter (longest diameter / shortest diameter) of 1.3 or less of the ceramic particles determined from an image observed with a scanning electron microscope were selected.

  Next, an electron beam is applied to the particles confirmed by scanning electron microscope observation, and the particles showing the strongest peak from the X-ray data of EDS obtained are the same as the ceramic particles used for barrel polishing. did.

  Next, the particle diameter (D1, D2, D3,... Dn) of each ceramic particle is measured as the maximum diameter in the direction parallel to the internal electrode layer as shown in FIG. Asked.

  Next, the data of the particle diameter and the width of the internal electrode layer obtained as described above is applied to the formula {(D1 + D2 + D3 +... Dn) / W} × 100 (%) to obtain the width of the internal electrode layer. The ratio of ceramic particles to W was determined. This analysis was performed two times for each sample in the example, and the average value was obtained.

  As is apparent from the results in Table 1, the average particle diameter of the ceramic particles adhering to the exposed end face of the internal electrode layer is 0.2 μm to 0.8 μm, and the width W of the internal electrode layer is 100%. When the sample number of the present invention is 5% to 20%, the ratio of the total length of the ceramic particles plus the particle diameter is 5% to 20%. In 2-9 and 11-14, the ratio of the capacitance to the design value was 91% or more, and the variation in capacitance was 4% or less, which was close to the design value.

  Further, among these samples, when the samples prepared by changing only the barrel polishing time were compared, the sample in which the exposed end face of the internal electrode layer was positioned about 0.4 μm from the end face of the capacitor body. (No. 5) has a higher ratio of the capacitance to the design value than the sample (No. 14) in which the exposed end face of the internal electrode layer is about 0.05 μm inside the end face of the capacitor body, Also, the variation was small.

  Further, the sample No. 1 in which the average particle diameter of the ceramic particles is 0.3 μm to 0.6 μm and the adhesion amount of the ceramic particles is 8% to 15%. In 3 to 5, the ratio of the capacitance to the design value was 95% or more, and the variation was 3% or less.

  In these samples, even when the secondary electron image was observed with a scanning electron microscope, a portion that turned black from the end to the inside of the internal electrode layer was hardly seen.

  On the other hand, in the samples outside the scope of the present invention (Sample Nos. 1, 7 and 10), the ratio of the capacitance to the design value is as low as 86% or less, or the variation in capacitance is as large as 10% or more. It was.

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 End face of capacitor body 10 End face where internal electrode layer is exposed 11 Ceramic particles

Claims (6)

  A multilayer ceramic capacitor comprising: a capacitor body in which dielectric layers and internal electrode layers mainly composed of nickel are alternately stacked; and an external electrode provided on an end surface of the capacitor body where the internal electrode layer is exposed. The ceramic electrode having an average particle size of 0.2 μm to 0.8 μm is attached to the exposed end face of the internal electrode layer, and the width of the internal electrode layer exposed to the end face of the capacitor body is set to 100. %, The ratio of the total length obtained by adding the particle diameters of the ceramic particles adhering to the exposed end face of the internal electrode layer is 5% to 20%.   2. The multilayer ceramic capacitor according to claim 1, wherein the exposed end surface of the internal electrode layer is on the inner side of the end surface of the capacitor body.   When the average particle diameter of the ceramic particles is 0.3 μm to 0.6 μm and the width of the internal electrode layer exposed at the end face of the capacitor body is 100%, the exposed end face of the internal electrode layer 3. The multilayer ceramic capacitor according to claim 1, wherein a ratio of a total length obtained by adding a particle diameter of the ceramic particles adhering to is 8% to 15%. (A) forming a capacitor body molded body in which ceramic green sheets and internal electrode patterns mainly composed of nickel are alternately laminated, and end surfaces of the internal electrode patterns are exposed on the end surfaces;
(B) firing the capacitor body molded body in a hydrogen-nitrogen reducing atmosphere to form a capacitor body;
(C) barrel-polishing the capacitor body using media balls and ceramic particles having an average particle size of 0.2 μm to 0.8 μm;
(D) re-oxidizing the barrel-polished capacitor body at an oxygen partial pressure lower than the firing temperature in the step (b) and higher than the reducing atmosphere;
And (e) forming an external electrode on an end face where the end face of the internal electrode layer of the capacitor body subjected to the reoxidation treatment is exposed.   The method for producing a multilayer ceramic capacitor according to claim 4, wherein barrel polishing is performed until an end face of the internal electrode layer is positioned inside an end face of the capacitor body. 6. The method for producing a multilayer ceramic capacitor according to claim 4, wherein the ceramic particles have an average particle size of 0.3 to 0.6 [mu] m.

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