JP2007142342A - Multi-layer ceramic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer ceramic capacitor whose sintering performance of ceramic layers of a center functional portion and a protective layer side functional portion in a functional portion can be improved simultaneously and is excellent in the reliability of the insulation and characteristic of a DC bias even if the ceramic layer and an inside electrode layer of the functional portion which composes the capacitor body and contributes to the electrostatic capacity is a thin layer or a high multilayer, and to provide a its manufacturing method. <P>SOLUTION: With a ceramic layer 5 positioned in the center in the direction of the multi-layer of the functional portion 9 as a center ceramic layer 5b, and with the ceramic layer 5 adjacent to the protective layer 11 of the functional portion 9 as a protective layer side ceramic layer 5a, the number of voids of a section of 100 μm<SP>2</SP>in the center ceramic layer 5b is 0-2, a mean particle-diameter D5bb of a ceramic particle 5bb in the center ceramic layer 5b is 0.1 μm-0.5 μm, the number of voids of a section of 100 μm<SP>2</SP>in the protective layer side ceramic layer 5a is 4-6, and a mean particle-diameter D5aa of a ceramic particle 5aa in the protective layer side ceramic layer 5a is 0.15 μm-0.6 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer ceramic capacitor and a method for manufacturing the same, and more particularly, to a small and high capacity multilayer ceramic capacitor obtained by thinning and stacking a ceramic layer and internal electrode layers and a method for manufacturing the same.

  FIG. 6 is a schematic cross-sectional view showing a conventional multilayer ceramic capacitor. In the illustrated multilayer ceramic capacitor, a capacitor body 109 in which ceramic layers 101 and internal electrode layers 103 exhibiting ferroelectricity are alternately stacked is formed, and an external electrode 111 is formed on the end face of the capacitor body 109. Has been.

In recent years, such a multilayer ceramic capacitor has been required to be small in size and high in capacity. For this reason, the ceramic layer 101 and the internal electrode layer 103 have been thinned and multi-layered. As the dielectric powder used as the above, fine dielectric powder having an average particle diameter of 0.4 μm or less has been used (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 11-354370

  However, when a thin-layer, highly-laminated multilayer ceramic capacitor is formed using fine dielectric powder having an average particle size of 0.4 μm or less, the ceramic layer 101 is fine because the ceramic particles are fine even after sintering. Since the relative dielectric constant is low, the multilayer ceramic capacitor has a problem that it is difficult to obtain a desired capacitance.

  On the other hand, when firing at a high temperature to increase the sinterability of the ceramic layer 101 with respect to the above problems, the sinterability of the ceramic layer 101 can be increased and the dielectric constant can be increased. As a result, the average particle size of the ceramic particles 101 in the ceramic layer 101 is increased, and the reliability and DC bias characteristics in the high temperature load test are lowered.

  Therefore, the present invention can improve the sinterability of the ceramic layer even when the ceramic layer and internal electrode layer are thin and highly laminated, and has a good reliability and DC bias characteristics in a high temperature load test. The object is to provide a capacitor.

The multilayer ceramic capacitor of the present invention is composed of a functional part in which ceramic layers having a plurality of ceramic particles and internal electrode layers are alternately laminated, and a protective layer comprising the ceramic layer provided on the upper and lower surfaces of the functional part. In a multilayer ceramic capacitor comprising a capacitor body and a pair of external electrodes provided on opposite end surfaces of the capacitor body,
The ceramic layer disposed in the central portion of the functional unit in the stacking direction is a central ceramic layer, and the ceramic layer adjacent to the protective layer of the functional unit is a protective layer side ceramic layer,
The number of voids in a cross section of 100 μm ² of the central ceramic layer is 0 to 2, the average particle size of ceramic particles in the central ceramic layer is 0.1 μm or more and 0.5 μm or less, and the cross section of the protective layer side ceramic layer is 100 μm The number of voids in ² is 4 to 6, the average particle size of the ceramic particles in the protective layer-side ceramic layer is 0.15 μm or more and 0.6 μm or less, and the average particle size of the ceramic particles in the central ceramic layer Is also small.

In the multilayer ceramic capacitor, when the thickness of the capacitor body in the stacking direction is t ₀ and the thickness of the protective layer is t ₁ , 0.2 ≧ t ₁ / t ₀ ≧ 0.15. desirable.

  The manufacturing method of the multilayer ceramic capacitor of the present invention uses (a) a ceramic green sheet based on a spherical ceramic powder having an average particle diameter DM and a necked ceramic powder having an average particle diameter DL larger than the average particle diameter DM. Forming a ceramic green sheet formed in a step, and (b) forming a pattern sheet SMM in which a plurality of internal electrode patterns are formed on one main surface of the ceramic green sheet containing the ceramic powder having the average particle size DM, Forming a pattern sheet SLL having a plurality of internal electrode patterns formed on one main surface of a ceramic green sheet containing the necked ceramic powder having the average particle diameter DL; and (c) a central portion in the stacking direction of the pattern sheet SMM. In addition, the pattern sheet SLL is the uppermost layer in the stacking direction. And (d) a step of forming a capacitor body in which an inner electrode pattern is exposed on an end surface by cutting and firing the laminate, and (e) the capacitor. Forming an external electrode on an end surface of the main body where the internal electrode pattern is exposed.

  In the multilayer ceramic capacitor of the present invention, the ceramic layer disposed in the central portion in the stacking direction of the functional portion that contributes to the development of capacitance is the central ceramic layer, and the ceramic layer in contact with the protective layer of the functional portion is the protective layer When the side ceramic layer is used, the ceramic powder that is necked as the protective layer side ceramic layer is used, and the spherical ceramic powder is used for the central ceramic layer, so that the average number of voids per unit area in the protective layer side ceramic layer and the central ceramic layer By setting the average number of voids per unit area in the layer, the average particle size of the ceramic particles in the protective layer-side ceramic layer, and the average particle size of the ceramic particles in the central ceramic layer within the above ranges, the ceramic layer and the internal electrode layer Even if the layer is thin or highly stacked, the center in the functional part It is possible to improve sinterability of the preliminary protective layer side ceramic layer at the same time, thereby to obtain a good multilayer ceramic capacitor of reliability and DC bias characteristics at high-temperature load test.

(Construction)
The multilayer ceramic capacitor of the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor of the present invention.

  In the multilayer ceramic capacitor of the present invention, an external electrode 3 is formed on the end face of the capacitor body 1. The capacitor body 1 includes a functional part 9 in which ceramic layers 5 and internal electrode layers 7 are alternately stacked, and a protective layer 11 made of a ceramic layer 5 provided on the upper and lower surfaces of the functional part 9. The external electrode 3 is connected to the end surface of the capacitor body 1 from which the internal electrode layer 7 is derived.

  FIG. 2 shows the present invention for showing the difference between voids and ceramic particles in a central ceramic layer disposed in the center in the stacking direction and a protective layer side ceramic layer adjacent to the protective layer in a thin-layer, highly-laminated multilayer ceramic capacitor. It is a cross-sectional schematic diagram of this multilayer ceramic capacitor.

  According to the present invention, for example, when a thin-layer, highly-laminated multilayer ceramic capacitor is formed using fine dielectric powder having an average particle size of 0.3 μm or less, the ceramic layer 5 and the internal electrode are formed in the multilayer ceramic capacitor. In the functional unit 9 in which the layers 7 are alternately stacked, the ceramic layer 5 disposed in the center of the functional unit 9 in the stacking direction is used as the central ceramic layer 5 b and the ceramic layer 5 in contact with the protective layer 11 of the functional unit 25. When the protective layer side ceramic layer 5a is used, the protective layer side ceramic layer 5a is less sinterable than the central ceramic layer 5b, and therefore many voids V are generated in the protective layer side ceramic layer 5a. I knew that it would be easier to do.

  In addition, since the sinterability of the protective layer side ceramic layer 5b is thus reduced, the average particle size of the ceramic particles 5aa in the protective layer side ceramic layer 5a is also reduced. For this reason, because of the many voids V in the protective layer side ceramic layer 5a and the ceramic particles 5aa in which grain growth is suppressed, such a ceramic layer 5 has a low relative dielectric constant, and the multilayer ceramic capacitor has a desired capacitance. Becomes difficult to obtain. Further, because of many voids V formed in the ceramic layer 5, the reliability in the high temperature load test was also lowered.

  In this case, when the ceramic layer 5 and the internal electrode layer 7 are made thin and highly laminated, the sinterability of the protective layer side ceramic layer 5a is lowered from the ceramic layers provided on the upper and lower surfaces of the functional part 9. Since the sinterability of the protective layer 11 is originally lower than that of the central ceramic layer 5b with many ceramic layers sandwiched between the internal electrode layers 9, the protective layer side is affected by the low sinterability of the protective layer 11 side. This is because the sinterability decreases to the ceramic layer 5a.

  On the other hand, in order to improve the sinterability of the protective layer side ceramic layer 21a, the central ceramic layer 5b and the protective layer side ceramic layer 5a are sintered when the firing is performed at a high temperature to improve the sinterability of the protective layer side ceramic layer 21a. However, the average particle size of the ceramic particles 5aa and 5bb in the ceramic layers 5a and 5b at both portions is increased, and reliability and DC bias characteristics in a high temperature load test are deteriorated. Based on these findings, the present invention has been recalled.

That is, in the capacitor main body 1 according to the present invention, the ceramic layer 5 constituting the capacitor main body 1 has voids V as shown in the enlarged view of FIG. When the ceramic layer 5 disposed at the center of the ceramic layer 5 is a central ceramic layer 5b, and the ceramic layer 5 adjacent to the protective layer 11 of the functional unit 9 is a protective layer side ceramic layer 5a, the protective layer side ceramic layer 5a In the relationship between the average number of voids A in the 100 μm ² region of the laminated cross section of the central portion between the external electrodes and the average number of voids B in the 100 μm ² region of the central cross section of the central ceramic layer 5 b between the external electrodes The average number of voids B per unit area of the layer-side ceramic layer 5a is made larger than the average number of voids A per unit area of the central ceramic layer 5b. , B = 4 to 6 carbon atoms, it is important that the A = 0 to 2 amino relationship.

In the present invention, together with the void V in the ceramic layer 5 described above, the average particle diameter D5aa of the ceramic particles 5aa in the protective layer side ceramic layer 5a is made smaller than the average particle diameter D5bb of the ceramic particles 5bb in the central ceramic layer 5b. The average particle diameter D5bb of the ceramic particles 5bb in the region of 100 μm ^{2 in} the laminated section of the central ceramic layer 5b is 0.1 μm or more and 0.5 μm or less, and the laminate of the protective layer side ceramic layer 5a It is important that the average particle diameter D5aa of the ceramic particles 5aa in the region of 100 μm ^{2 in} the cross section is 0.15 μm or more and 0.6 μm or less. In this case, for example, when the thickness of the ceramic layer 5 is 2 μm, the evaluation is performed on a region having a width of 50 μm.

  That is, in the present invention, when the ceramic body 5 is formed by multilayering the ceramic layers 5, the number of voids V in the central ceramic layer 5b and the protective layer side ceramic layer 5a is set to the above relationship, By controlling the size of the ceramic particles 5bb and 5aa together with the void V in the ceramic layer 5b and the protective layer side ceramic layer 5a, the electric field strength between the ceramic particles 5aa and 5bb can be increased. Insulation can be achieved.

  In the present invention, in particular, the number of voids in the central ceramic layer 5b is 4-5, and the average particle diameter D5bb of the ceramic particles 5bb is 0.12 μm or more and 0.15 μm or less, while the number of voids in the protective layer-side ceramic layer 5a. 0 to 1 and the average particle diameter D5aa of the ceramic particles 5aa is 0.18 μm or more and 0.3 μm or less, the capacitance is high, the rate of change in the temperature characteristics of the capacitance is small, and the capacitance The DC bias characteristic is reduced, and the high temperature load (HALT) test is also improved.

  Further, according to the present invention, when the ceramic particles 5aa of the protective layer-side ceramic layer 5a are made smaller than the ceramic particles 5bb of the central ceramic layer 5b, the smaller the average particle diameter in the multilayer ceramic capacitor, the temperature characteristics of the capacitance ( There is an advantage that (temperature dependence) can be reduced.

  On the other hand, when the average number of voids in the protective layer side ceramic layer 5a and the average number of voids in the central ceramic layer 5b are out of the scope of the present invention, a large number of formed in the protective layer side ceramic layer 5a. The capacitance decreases due to voids, and the reliability of the high temperature load (HALT test) becomes inferior.

  Further, if the average particle diameter D5aa of the ceramic particles 5aa in the protective layer side ceramic layer 5a and the average particle diameter D5bb of the ceramic particles 5bb in the central ceramic layer 5b are out of the range of the present invention, the change in the DC bias characteristic of the capacitance is changed. It is large and the high temperature load reliability is inferior.

When the central ceramic layer 5b is sandwiched between the internal electrode layers 7, the average number of voids in the sandwiched central ceramic layer 5b is used. In addition, the measurement of voids and average particle diameter is performed by measuring a plurality of locations in the range of 100 μm ² with respect to the cross section of the ceramic layer to be observed and averaging.

  Here, the void V in the protective layer side ceramic layer 5a and the central ceramic layer 5b according to the present invention has a diameter of 1/10 or more of the thickness of the protective layer side ceramic layer 5a and the central ceramic layer 5b.

  In the multilayer ceramic capacitor of the present invention, the number of voids V and the difference in the size of the ceramic particles 5aa and 5bb between the central ceramic layer 5b and the protective layer side ceramic layer 5a are controlled as described above. Further, it is more suitable for those having 100 or more layers.

  The thickness of the ceramic layer 5 is preferably 0.5 μm or more and 3 μm or less from the viewpoint of ensuring insulation and increasing the capacity.

Moreover, in the functional part 9 of the capacitor body 1 according to the present invention, when the thickness t _{0 in the} stacking direction is 1, the thickness t ₁ (= t ₂ + t ₂ ′) in the same direction of the protective layer 11 aligned vertically. Is a ratio of 0.15 or more, that is, 0.2 ≧ t ₁ / t ₀ ≧ 0.15. In the present invention, by increasing the thickness of the protective layer 11, the multilayer ceramic capacitor has a high mechanical strength, and its usefulness as a mounting component increases. In addition, in the case of the multilayer ceramic capacitor having the above structure in which the sinterability of the protective layer 11 greatly affects, there is an effect that the reliability and DC bias characteristics in the high temperature load test can be further improved. The thickness of the protective layer 11 is preferably such that t ₁ / t ₀ does not exceed 0.2 in that a higher capacitance can be obtained in the standard dimension of the multilayer ceramic capacitor.

  The ceramic particles 5aa and 5bb according to the present invention are mainly composed of barium titanate and contain additives such as Ca, Mg, rare earth elements, Mn, etc. to improve insulation, reduction resistance, temperature characteristics, and dielectric constant. Further, as a barium titanate-based dielectric, when Ba is A mole and Ti is B mole, grain growth can be suppressed when the A / B ratio is 1.003 or more. For this reason, it is preferable that the ceramic layer 5 is formed of ceramic particles 5aa and 5bb having an A / B ratio of 1.003 or more.

  Further, the internal electrode layer 7 is desirably 0.3 μm or more and 1.5 μm or less from the viewpoint of reducing a step on the ceramic layer 5 and ensuring an effective area while enabling high lamination.

  In the present invention, the target portions of the average particle diameters D5aa and D5bb of the ceramic particles 5aa and 5bb of the protective layer side ceramic layer 5a and the central ceramic layer 5b of the functional unit 9 are within the capacitor body 1 in terms of the potential. The electrode layers 7 are present in the range of the electrodes forming a capacity in which the electrode layers 7 are alternately stacked.

  The internal electrode layer 7 is preferably Ni, Cu or an alloy thereof in terms of cost reduction. However, Ni is mainly used in that the ceramic layer 5 is made of a barium titanate-based dielectric material and can be simultaneously fired therewith. What is made into a component is more preferable.

(Manufacturing method)
Next, a method for producing the multilayer ceramic capacitor of the present invention will be described. FIG. 3 is a schematic view showing a process for manufacturing the multilayer ceramic capacitor of the present invention. The multilayer ceramic capacitor of the present invention comprises the following steps.

  First, in the step (a), a ceramic green sheet 31 formed using a necked ceramic powder having an average particle diameter DL larger than the average particle diameter DM together with a ceramic green sheet 31 containing spherical ceramic powder having an average particle diameter DM. 32.

  FIG. 4 is a schematic view showing a necked ceramic powder according to the present invention. The necked ceramic powder NP is a state in which spherical ceramic powders are partially sintered and connected.

  The necked ceramic powder NP can be obtained by sintering the spherical ceramic powder once prepared weakly at a temperature lower than the sintering temperature, and crushing and sieving it. The neck Ne is smaller than the maximum diameter of the individual ceramic powders, and it is desirable to maintain the shape of the spherical ceramic powder like a snowman in terms of enhancing the reactivity of the necked ceramic powder NP. The average particle diameter of the necked ceramic powder NP is an equivalent circle diameter determined by image processing (MAC-VIEW) of an electron micrograph. Note that the spherical ceramic powder is a powder dispersed individually, and includes all rounded surfaces.

  Next, in step (b), a plurality of ceramic green sheets 31 containing spherical ceramic powder having an average particle diameter of DM and ceramic green sheets 32 containing necked ceramic powder having an average particle diameter of DL are provided on one main surface of each. This is a step of forming the internal electrode pattern 33.

  Here, in some cases, in order to reduce the step of the internal electrode pattern, a ceramic pattern is formed around the internal electrode pattern 33 as described below (step (b ')). That is, a pattern sheet SMM is formed around the internal electrode pattern 33 of the ceramic green sheet 31 containing the ceramic powder having an average particle size DM, in which the ceramic pattern 35a containing the same ceramic powder as that used for the ceramic green sheet 31 is formed. . At the same time, a pattern sheet SLL in which the ceramic pattern 35b is formed so as to include the ceramic powder NP that is also necked is formed on the ceramic green sheet 32 that includes the ceramic powder NP that is necked with the average particle diameter DL.

  Next, step (c) is a step in which the pattern sheet SMM is laminated at the center in the laminating direction and the pattern sheet SLL is laminated on the uppermost lower layer side in the laminating direction and heated under pressure to form a laminate.

  Next, step (d) is a step of forming the capacitor main body 1 with the internal electrode pattern 33 exposed at the end face after firing the laminate and firing. In addition, (e) of a figure shows the state of a side margin direction and an end margin direction.

  Next, the external electrode 39 is formed on the end surface of the obtained capacitor main body 37.

  Here, the average particle diameter DM of the spherical ceramic powder is 0.1 μm or more in terms of ensuring the relative dielectric constant of the ceramic powder, suppressing grain growth, and forming a thinner and denser ceramic green sheet. 0.5 μm or less, particularly 0.12 to 0.15 μm is desirable.

  On the other hand, the average particle diameter DL of the necked ceramic powder NP is 0.15 to 0.6 μm, particularly in that high strength can be obtained with respect to the thermal shock test while suppressing excessive deformation and improving sinterability. 0.18 to 0.3 μm is desirable.

  When the ceramic powder according to the present invention is a barium titanate-based powder, if the lattice constant ratio c / a is 1.005 or more, the void ratio is reduced while suppressing the grain growth of the necked ceramic powder NP, and the density is increased. The ceramic layer can be easily formed.

  In the present invention, the formation of voids V can be suppressed when the ceramic powder is sintered by using the necked ceramic powder NP having a large average particle size for the ceramic green sheet 32 located on the protective layer 11 side. As a result, the reliability and DC bias characteristics of the multilayer ceramic capacitor can be improved.

  The thickness of the ceramic green sheets 31 and 32 is preferably 1 μm or more and 4 μm or less in terms of high capacity.

  In addition, the pressure heating in the production method of the present invention is such that the amount of the binder used for the ceramic green sheets 31 and 32 is an added amount such that the ceramic green sheets 31 and 32 have adhesive strength, and is more than the glass transition point of the binder. High adhesion is achieved by carrying out the process at a high temperature.

  The firing temperature can be optimized depending on the average particle diameter of the ceramic powder used and the composition and amount of the additive, whereby a high-density sintered body can be obtained.

  Further, in the present invention, as described above, the protective layer side ceramic layer 5a is sintered as compared with the spherical ceramic powder used for the central ceramic layer 5b located in the central portion in the stacking direction of the functional unit 9 constituting the capacitor body 1. Since ceramic powder having high cohesiveness is used, even if a low-sintering protective layer 11 having no internal electrode layer 7 is adjacent, the influence can be reduced and the protective layer-side ceramic layer 5a can be made dense. . In addition, by using the necked ceramic powder NP, the average particle size of the sintered ceramic particles can be controlled to an appropriate size. Therefore, in addition to the characteristics of DC bias characteristics, reliability such as high temperature load life test (HALT) is also available. Can also be increased.

  The necked ceramic powder NP according to the present invention is particularly suitable for a multilayer ceramic capacitor having 100 or more layers so that the sinterability of the ceramic layer 5 is greatly different between the central portion in the stacking direction and the protective layer side. is there.

  The multilayer ceramic capacitor according to the present invention was produced as follows. Here, spherical and necked BT (barium titanate) was used as the barium titanate powder. The powder had an A / B ratio of 1 and 1.003 when barium was A mol and titanium was B mol. The lattice constant ratio c / a between the two powders was 1.008 for spherical ceramic powder and 1.006 for necked ceramic powder.

  FIG. 5 is a firing shrinkage curve of a shaped body of spherical barium titanate powder having an average particle diameter of 0.1 μm and necked ceramic powder having an average particle diameter of 0.15 μm. The ceramic powder thus necked has a higher shrinkage rate in the final sintering stage.

As the additive, MgO, Y ₂ O ₃ , or MnO having an average particle diameter of 0.5 μm was used. These addition amounts were both 0.5 mol per 100 mol of barium titanate powder. In addition, 1.2 parts by mass of glass powder composed of SiO ₂ 50 mol%, Li ₂ O 10 mol%, BaO 20 mol%, and CaO 20 mol% was added to 100 parts by mass of the barium titanate powder. . The average particle size of the glass powder was also 0.5 μm. The average particle diameters of the spherical ceramic powder and the necked ceramic powder used are shown in Table 1.

Next, a mixed powder obtained by adding the above MgO, Y ₂ O ₃ , MnO (added as MnCO ₃ ) to each of the DM and DL barium titanate-based powders using zirconia balls having a diameter of 5 mm is used as a solvent. As a mixed solvent of toluene and alcohol was added and wet mixed.

  Next, a mixed solvent of polyvinyl butyral resin and toluene / alcohol is added to each wet-mixed powder (average particle size DM, DL), and wet mixed using zirconia balls having a diameter of 5 mm to prepare a ceramic slurry. A ceramic green sheet having a thickness of 3 μm was prepared by a blade method.

  Next, a plurality of rectangular internal electrode patterns mainly composed of Ni powder having an average particle diameter of 0.2 μm were formed on the upper surfaces of the ceramic green sheets having the average particle diameters DM and DL. Form ceramic pattern using ceramic slurry containing barium titanate powder with mean particle size DM or DL so that the same ceramic powder is applied around the internal electrode pattern of ceramic green sheet printed with internal electrode pattern did. The ceramic pattern had substantially the same thickness as the internal electrode pattern.

Next, pattern sheets SMM and SML in which the internal electrode pattern and the ceramic pattern are formed on the ceramic green sheet having the average particle diameter of DM or DL are collectively laminated so as to have the layer configuration shown in Table 1 and then pressed. A matrix laminate was formed by heating, and then the matrix laminate was cut to produce a capacitor body molded body. The number of functional parts stacked was 100, and the protective layer was formed by stacking ceramic green sheets having an average particle diameter of DM and a thickness of 3 μm on the upper and lower layers so as to have respective thickness ratios. The pressure heating conditions were a temperature of 60 ° C., a pressure of 10 ⁷ Pa, and a time of 10 minutes.

Next, the capacitor body molded body was subjected to binder removal treatment at 300 ° C./h in the air at a temperature increase rate of 10 ° C./h, and the temperature increase rate from 500 ° C. was 300 ° C./h. 1170 ° C. (calcined at an oxygen partial pressure of 10 ⁻⁶ Pa for 2 hours, subsequently cooled to 1000 ° C. at a temperature lowering rate of 300 ° C./h, and reoxidized at 1000 ° C. for 7.5 hours in a nitrogen atmosphere. The capacitor body was manufactured by cooling at a temperature drop rate of / h, the size of the capacitor body was 2 × 1 mm ² and the thickness was 0.7 to 0.8 mm, and the thickness of the dielectric layer was 2.5 μm. Met.

  Next, the fired capacitor body was barrel-polished, and then an external electrode paste containing Cu powder and glass was applied to both ends of the capacitor body and baked at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer ceramic capacitor.

  Next, the following evaluation was performed on these multilayer ceramic capacitors.

  The thickness ratio of the protective layer to the total thickness of the capacitor body is obtained by polishing the cross-section in the stacking direction of the obtained multilayer ceramic capacitor, and the thickness of the capacitor body and the thickness of the protective layer positioned above and below the capacitor electrode portion The total thickness) ratio was measured. The number of samples was 10 each.

The average particle size of the ceramic particles in the ceramic layer was measured using the following method. First, the external electrode surface of the multilayer ceramic capacitor was buried in a resin and polished to the center of the porcelain using abrasive paper. Next, chemical etching was performed using a solution (HCl = 0.09%, HF = 0.04%) at 25 ° C. for 5 seconds to expose the grain boundaries. The central part in the stacking direction of the polished surface where the grain boundary is exposed and the protective side are photographed with an electron microscope (SEM), the area of the cross section of the ceramic particle is measured for a region of 100 μm ² , and the diameter is determined from the contour of the obtained ceramic particle. Calculated and averaged.

  Here, the central ceramic layer was measured and averaged at 10 locations for each of the central layer ± 2 layers, and the protective layer side ceramic layer was measured at 10 locations for the upper and lower 2 layers of the ceramic layers. In addition, the observation location was made into the center part between external electrodes. The number of ceramic particles used for the particle size calculation was n = 100.

  The number of voids in the ceramic layer was also determined by taking an electron micrograph of the same region where the ceramic particles were observed and counting directly from the photograph. The number of measurements was also the same.

  The capacitance was measured using an LCR meter at room temperature (25 ° C.) under the conditions of AC 1 V and measurement frequency 1 kHz.

  For the temperature characteristics of capacitance, the capacitance is measured using an LCR meter at temperatures of −55 and 85 ° C. under the conditions of AC1V and measurement frequency of 1 kHz, and the rate of change is obtained based on the capacitance at 25 ° C. It was.

  The DC bias characteristics of the capacitance were measured with respect to the obtained multilayer ceramic capacitor at DC voltages of 3.15 V and 6.3 V, and the respective capacitances measured at high voltage and low voltage were measured at low voltage. The rate of decrease in capacitance at a high voltage relative to the capacitance was evaluated. The number of samples was 30 each.

  The HALT (high temperature load reliability) test was performed with a DC voltage of 22 V applied at 125 ° C., and a sample having a leakage current exceeding 10 mA was regarded as defective. The measurement time was 1000 hours, and one or more defects were considered defective. The number of samples was 100 each.

The mechanical strength of the multilayer ceramic capacitor was evaluated by generating a crack by pressing a cylinder having a diameter of 1 mm against the capacitor sample at a pressure of 2 × 10 ⁵ Pa using a load test apparatus. The sample after the test was observed using a stereomicroscope, and a sample with a crack on the sample surface was regarded as having a crack. The number of samples was 10 each.

It should be noted that a layer that contributes to capacity when the thickness ratio t ₁ / t _{0 of} the protective layer exceeds the standard dimension for a sample that exceeds 0.2, or when the outer dimensions are the same as those of the sample according to the present invention described above. The number decreased and the capacitance decreased.

  From the results of Tables 1 and 2, Sample No. using a spherical ceramic powder for the ceramic layer of the central functional part of the capacitor body and a ceramic powder necked for the protective layer side functional part. 2 to 12, the capacitance is 0.3 μF or more, the capacitance temperature characteristic is within −15%, the DC bias characteristic is −30% or less, there is no defect in high temperature load reliability (HALT), and the strength There were no cracks in the test.

  In particular, in the sample having a thick protective layer, no crack was generated in the strength test. Further, Sample No. using a necked ceramic powder having an average particle size of 0.18 to 0.3 μm as the ceramic layer of the protection side functional part. 3 to 5, the capacitance is 0.4 μF or more, the capacitance temperature characteristic is within −7.01%, the capacitance DC bias characteristic is −9% or less, and high temperature load reliability (HALT). No cracks were found in the strength test.

  On the other hand, in samples using spherical ceramic powder for all ceramic layers or samples in which the average particle size and void ratio are not within the scope of the present invention, the capacitance is low or the DC bias characteristics of the capacitance Is large, or a defect in high-temperature load reliability was observed.

It is a cross-sectional schematic diagram of the multilayer ceramic capacitor of the present invention. For a thin-layer, highly-laminated multilayer ceramic capacitor, the multilayer ceramic of the present invention is used to show the difference between voids and ceramic particles in the central ceramic layer disposed in the center in the stacking direction and the protective layer-side ceramic layer adjacent to the protective layer 27 It is a cross-sectional schematic diagram of a capacitor. It is process drawing which shows the manufacturing method of the multilayer ceramic capacitor of this invention. It is a schematic diagram which shows the necked ceramic powder which concerns on this invention. 2 is a firing shrinkage curve of a shaped body of spherical barium titanate powder having an average particle diameter of 0.1 μm and necked ceramic powder having an average particle diameter of 0.15 μm according to the present invention. It is a cross-sectional schematic diagram which shows the conventional multilayer ceramic capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor main body 3 External electrode 5 Ceramic layer 5a Protective layer side ceramic layer 5b Central ceramic layer 5aa, 5bb Ceramic particle 7 Internal electrode layer 9 Function part 11 Protective layer t0 Protective layer thickness 31 Ceramic green sheet 33 Internal electrode pattern NP Ceramic powder

Claims (3)

A capacitor body comprising a functional part in which ceramic layers having a plurality of ceramic particles and internal electrode layers are alternately laminated, and a protective layer comprising the ceramic layer provided on the upper and lower surfaces of the functional part, and In a multilayer ceramic capacitor comprising a pair of external electrodes provided on opposite end faces,
The ceramic layer disposed in the central portion of the functional unit in the stacking direction is a central ceramic layer, and the ceramic layer adjacent to the protective layer of the functional unit is a protective layer side ceramic layer,
The number of voids in a cross section of 100 μm ² of the central ceramic layer is 0 to 2, the average particle size of ceramic particles in the central ceramic layer is 0.1 μm or more and 0.5 μm or less, and the cross section of the protective layer side ceramic layer is 100 μm The number of voids in ² is 4 to 6, the average particle size of the ceramic particles in the protective layer-side ceramic layer is 0.15 μm or more and 0.6 μm or less, and the average particle size of the ceramic particles in the central ceramic layer Multilayer ceramic capacitors characterized by being small. Wherein _{t 0} the stacking direction of the thickness of the capacitor body, the thickness of the protective layer is taken as _{t 1, 0.2 ≧ t 1 /} t 0 ≧ 0.15 a multilayer ceramic capacitor according to claim 1, wherein. (A) A ceramic green sheet formed using a necked ceramic powder having an average particle diameter DL larger than the average particle diameter DM is formed together with a ceramic green sheet based on a spherical ceramic powder having an average particle diameter DM. And (b) forming a pattern sheet SMM having a plurality of internal electrode patterns formed on one main surface of a ceramic green sheet containing the ceramic powder having the average particle size DM, and necking the ceramic powder having the average particle size DL Forming a pattern sheet SLL in which a plurality of internal electrode patterns are formed on one main surface of a ceramic green sheet including: (c) the pattern sheet SMM in the center of the stacking direction and the pattern sheet SLL in the stacking direction Laminating on the uppermost layer side and pressurizing and heating to form a laminate (D) forming the capacitor body with the internal electrode pattern exposed on the end face by firing after cutting the laminate, and (e) forming the external electrode on the end face with the internal electrode pattern exposed on the capacitor body. And a process for producing a multilayer ceramic capacitor.

Images