JP6940398B2 - Capacitor - Google Patents

Description

The present disclosure relates to multilayer capacitors.

A laminated capacitor (hereinafter referred to as a capacitor) includes a capacitor body in which a plurality of layers of ceramic layers and internal electrode layers are alternately laminated, and an external electrode provided on an end surface of the capacitor body. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2003-17356

The capacitor of the present disclosure is a capacitor including a capacitor body in which a plurality of layers of dielectric layers and internal electrode layers are alternately laminated, and the internal electrode layer has a metal portion and the internal electrode layer in the thickness direction. a through hole penetrating in, possess a closed pores present in the internal electrode layers, the cross-section of the internal electrode layer, when measured in the longitudinal direction in which the internal electrode layer extends, the The average value of the length of the through hole in the longitudinal direction is Lop, the average value of the length of the closed hole in the longitudinal direction is Lcp, and the inside electrode layer is within the range of the predetermined length Le in the longitudinal direction. When the total length of the through hole included in the above in the longitudinal direction is Lopt and the total length of the closed hole included in the predetermined length Le is Lcpt, Lcp. Is 0.01 μm or more and 1 μm or less, Lcpt / Le is 2% or more and 20% or less, Lop is 2 μm or more and 20 μm or less, Lopt / Le is 8% or more and 29% or less, (Lcpt + Lopt) / Le is 22% or more and 39% or less, And Lcpt / (Lcpt + Lopt) is 5% or more and 71% or less.

It is a perspective view which shows one Embodiment of a capacitor schematically. FIG. 1 is a cross-sectional view taken along the line ii-ii of FIG. It is a cross-sectional view which enlarged the part A of FIG. FIG. 2 is a cross-sectional view taken along the line iv-iv of FIG. It is a plan perspective view which enlarged the periphery of part A in the iv-iv line cross section of FIG.

In recent years, for example, with the further miniaturization and higher performance of mobile electronic devices, capacitors are required to be smaller and have a higher capacity and to have an improved withstand voltage.

The capacitor of the embodiment has external electrodes 3 on two opposing end faces of the capacitor body 1. The capacitor body 1 has a structure in which the dielectric layer 5 and the internal electrode layer 7 are alternately laminated. In the capacitor main body 1, the number of layers of the dielectric layer 5 and the internal electrode layer 7 is shown to be small, but the present embodiment is not limited to this, and includes a configuration in which the number of layers reaches several hundred layers.

The capacitor of the embodiment has an internal electrode layer 7 together with a metal portion 7a, a through hole 9 penetrating the internal electrode layer 7 in the thickness direction, and a closed hole 11 existing in the internal electrode layer 7.

The through holes 9 and the closed air holes 11 existing in the internal electrode layer 7 will be described with reference to FIGS. 3, 4, and 5. FIG. 3 is an enlarged cross-sectional view of part A of FIG. 2, which is an enlarged view showing a part of the vertical cross section of the capacitor main body 1. In this case, one internal electrode layer 7 is sandwiched between two dielectric layers 5 from above and below. In FIG. 3, the predetermined length Le when the cross section of the internal electrode layer 7 is measured in the longitudinal direction, which is the direction in which the internal electrode layer 7 extends, has one through hole 9 and one closed hole 11, respectively. However, within the range of the actual length Le, a plurality of through holes 9 and a plurality of closed holes 11 are included. FIG. 4 is a cross-sectional view taken along the line iv-iv of FIG. FIG. 4 shows a state in which the laminated dielectric layer 5 and the internal electrode layer 7 are viewed in a plan view. FIG. 5 is an enlarged plan perspective view of the periphery of part A in the iv-iv line cross section of FIG.

In the capacitor of the embodiment, the internal electrode layer 7 has a through hole 9 and a closed air hole 11. The through hole 9 may be filled with a part of the porcelain of the dielectric layer 5. The inside of the closed air hole 11 is empty.

When the internal electrode layer 7 has a through hole 9 and a closed hole 11, the internal electrode layer 7 has only the through hole 9 as much as the ratio of the through hole 9 and the closed hole 11 combined. It is possible to suppress a decrease in the effective area of the internal electrode layer 7 as compared with the case of having. As a result, it is possible to suppress a decrease in the capacitance of the capacitor. The capacitance can be set to a value closer to the design value. In addition, the withstand voltage can be increased for the following reasons.

When a voltage is applied to the capacitor, as shown in FIG. 4, electrons e ⁻ are charged to the entire internal electrode layer 7. In this case, the electron e ⁻ has a negative charge. Therefore, the electrons e ⁻ repel each other in the internal electrode layer 7. In this case, the region 15 (air or a part of the porcelain portion of the dielectric layer 5) other than the internal electrode layer 7 (metal portion 7a) has an electron e ⁻ concentration as compared with the metal portion 7a of the internal electrode layer 7. Is low.

When a sufficiently high voltage is applied to the capacitor, the electron e ⁻ cannot move any further in the internal electrode layer 7. Therefore, when the internal electrode layer 7 does not have the through hole 9 and the air-closing hole 11, and the entire surface is composed of the metal portion 7a, the electron e ⁻ is formed in the corner portion 7d and the edge portion in the internal electrode layer 7. It tends to be unevenly distributed in 7e.

On the other hand, as shown in FIG. 5, when the region 15 other than the metal portion 7a such as the through hole 9 and the closed air hole 11 exists in the plane of the internal electrode layer 7, the corner portion originally exists in the internal electrode layer 7. ^{The electrons e −} that were unevenly distributed in the 7d and the edge portion 7e are now distributed in the vicinity (reference numeral 7c) of the through hole 9 and the closed air hole 11. ^{That is, the uneven distribution of the electrons e −} existing in the internal electrode layer 7 ^{is alleviated, and the density of the electrons e −} in the corner portion 7d and the edge portion 7e of the internal electrode layer 7 becomes low. In other words, the electric flux density at the corner portion 7d and the edge portion 7e of the internal electrode layer 7 can be reduced. As a result, the starting point of the electric line of force generated by the portion having a high density of the electric flux (a bundle of electric lines of force) can be dispersed in the plane of the internal electrode layer 7. As a result, as can be seen from the relational expression of the electric flux density D / ε (relative permittivity) = E (electric field strength), the corner portion 7d and the edge of the internal electrode layer 7 due to the local decrease in the electric field density. The electric field strength in the part 7e can be lowered. As a result, the electric field strength locally generated in the capacitor is lowered, and the decrease in withstand voltage can be suppressed.

In this case, as the applied capacitor, the thickness of the dielectric layer 5 is 0.4 μm or more and 6 μm or less, the thickness of the internal electrode layer 7 is 0.8 μm or more and 2 μm or less, and the dielectric layer 5 and the internal electrode layer 7 are used. A small and highly laminated capacitor having 200 or more layers when one pair is formed is suitable.

Further, when the cross section of the internal electrode layer 7 is measured in the longitudinal direction, which is the direction in which the internal electrode layer 7 extends, Le has a predetermined length including the metal portion 7a, the through hole 9, and the air closure hole 11. And. Let Lo be the average value of the lengths of the through holes 9 in the longitudinal direction. Let Lcp be the average value of the lengths of the closed holes 11 in the longitudinal direction. The total length of the through holes 9 included in the range of the predetermined length Le in the longitudinal direction of the internal electrode layer 7 in the longitudinal direction is Lot, and the longitudinal direction of the air-closing holes 11 included in the range of the predetermined length Le. Let Lcpt be the total length of. At this time, the average diameter (Lop) of the through holes 9 existing in the internal electrode layer 7 is 2 μm or more and 20 μm or less, the ratio (Lop / Le) of the through holes 9 is 8% or more and 29% or less, and the average diameter of the closed pores 11 (Lop). Lcp) is 0.01 μm or more and 1 μm or less, the ratio of closed holes 11 (Lcpt / Le) is 2% or more and 20% or less, and the combined ratio of through holes 9 and closed holes 11 (Lcpt + Lopt) / Le is 22% or more 39. % Or less, the ratio of the closed pores 11 to the combined ratio of the through holes 9 and the closed pores 11 Lcpt / (Lcpt + Lopt) is preferably 5% or more and 71% or less. At this time, the coverage of the internal electrode layer 7 is preferably 70% or more and 92% or less. In this case, the coverage of the internal electrode layer 7 is a value obtained as (Le-Lopt) / Le.

As will be described later, the capacitor of the embodiment has an average diameter (Lop) of through holes 9 existing in the internal electrode layer 7 described above, a ratio of through holes 9 (Lop / Le), and an average diameter of closed pores 11 (Lcp). , The ratio of the closed holes 11 (Lcpt / Le), the ratio of the closed holes 11 to the combined ratio of the through holes 9 and the closed holes 11 (Lcpt / (Lcpt + Lopt), the combined ratio of the through holes 9 and the closed holes 11 (Lcpt / (Lcpt + Lopt)) By limiting the coverage of Lcpt + Lopt) / Le and the internal electrode layer 7, the withstand voltage and capacitance can be increased, and the rate of occurrence of cracks and the like can be reduced.

Hereinafter, how to obtain the length and ratio of the through hole 9 and the closed air hole 11 will be described with reference to FIG. First, a region corresponding to part A shown in FIG. 2 is extracted from the cross section of the capacitor body 1. In this case, the region to be extracted includes a plurality of through holes 9 and closed holes 11 together with the metal portion 7a, respectively. The region to be extracted shall be a range in which the boundary does not include the through hole 9 and the closed air hole 11. The boundary of the region should be in contact with the through hole 9 or the closed air hole 11 other than the region. Let Le be the total length of the extracted predetermined range, Lo be the length of the through hole 9, and Lcp be the length of the closed air hole 11. The total length of the plurality of through holes 9 included in the range of the predetermined length Le is defined as Lopt, and the total length of the closed pores 11 is defined as Lcpt. In this case, when the length Lop of the through hole 9 and the length Lcp of the closed hole 11 are obtained, the position is set so as to pass through the central portion of the closed hole 11 in the thickness direction of the internal electrode layer 7. The lengths of the through holes 9 and the closed holes 11 included in the extracted region are measured, and the average value is calculated for each. The ratio of the through holes 9 is obtained from Lopt / Le using the total Lopt of the lengths of the through holes 9. The ratio of the closed pores 11 is determined from Lcpt / Le using the length Lcpt of the closed pores 11. The combined ratio of the ratio of the through holes 9 and the ratio of the closed air holes 11 is obtained from (Lcpt + Lopt) / Le. The ratio of the closed pores 11 to the combined ratio (Lcpt + Lopt) of the ratio of the through holes 9 and the ratio of the closed pores 11 is obtained from Lcpt / (Lcpt + Lopt). In addition, each of the above-mentioned values may be obtained from the average value of a plurality of regions corresponding to part A extracted.

As the dielectric layer 5 constituting the capacitor of the embodiment, a dielectric porcelain containing mainly crystal particles 9 containing barium titanate as a main component is preferable. Further, for the internal electrode layer 7, silver, palladium or an alloy thereof, or nickel, copper, tungsten, molybdenum or a composite material thereof is suitable.

Next, a method of manufacturing the capacitor of the embodiment will be described. This capacitor uses fine metal powder as the metal powder for forming the conductor pattern for the internal electrode layer, and controls the degreasing conditions and firing conditions of the molded body, which is the main body of the capacitor, as described later. It is manufactured by the conventional manufacturing method of. In this case, the hydrogen concentration and the holding temperature are the main conditions in the degreasing conditions. Among the firing conditions, the hydrogen concentration and the rate of temperature rise are the main conditions.

In this case, in the step of degreasing and firing the molded body to be the capacitor body, degreasing is performed at a relatively low temperature. In addition, degreasing adopts the condition of holding for a predetermined time. By adopting the condition that degreasing is performed at a relatively low temperature and held for a predetermined time, the organic component contained in the conductor paste in the internal electrode layer 7 before the firing temperature reaches the maximum temperature is adopted. (Carbon) is intentionally left. The remaining organic component can form a neck between the metal powders. In addition, firing is performed under conditions where the rate of temperature rise is high. In the firing, in the temperature region where the internal electrode layer 7 is sintered, the hydrogen concentration is set to be lower than the condition for manufacturing a conventional capacitor. By firing under these conditions, in the temperature range where the internal electrode layer 7 is sintered, the organic component (carbon) remaining after degreasing is vaporized in the internal electrode layer 7, and the pores are closed in the internal electrode layer 7. 11 can be formed. Under the above conditions, the metal powders constituting the conductor pattern are locally gathered and sintered, so that the through holes 9 are formed at the same time. The average diameter and abundance ratio of the through holes 9 and the closed air holes 11 can be changed according to the above-mentioned degreasing conditions and firing conditions.

Hereinafter, as an example of the capacitor, a monolithic ceramic capacitor was specifically manufactured and the dielectric characteristics were evaluated. First, as raw material powder, 0.5 atoms of barium titanate powder having a purity of 99.9% and a molar ratio of Ba / Ti of 1.005 and calcium having a molar ratio of (Ba + Ca) / Ti of 1.005. Barium titanate powder containing% was prepared, and the following components were added thereto to prepare a dielectric powder. Composition of the dielectric powder is against barium powder 100 moles _titanate, V 2 _{O 5} powder with 0.05 mol, 0.7 mol of MgO powder, the oxide powder of a rare earth element _(Dy 2 _{O 3)} 0 .4 mol, MnCO ₃ powder is 0.2 mol, and sintering aid (SiO ₂ = 55, BaO = 20, CaO = 15, Li ₂ O = 10 (mol%) glass powder) is added as a raw material powder ( 1 part by mass was added to 100 parts by mass of barium titanate powder or barium titanate powder containing calcium).

Next, the obtained dielectric powder was put into a mixed solvent of polyvinyl butyral resin and toluene and alcohol, and wet-mixed using a zirconia ball having a diameter of 0.5 mm to prepare a ceramic rally, and a doctor blade method was performed. To prepare a ceramic green sheet having an average thickness of 6 μm.

Next, a plurality of conductor pastes containing nickel (Ni) as a main component were formed on the upper surface of the ceramic green sheet so as to form a rectangular internal electrode pattern. As the conductor paste for forming the internal electrode pattern, nickel powder having an average particle size of 0.15 μm or more and 0.2 μm or less was used as shown in Table 1. A material obtained by adding 10 parts by mass of barium titanate powder as a co-material to 100 parts by mass of this nickel was used.

Next, 300 ceramic green sheets on which the internal electrode pattern was printed were laminated, and 20 ceramic green sheets on which the internal electrode pattern was not printed were laminated on the upper and lower surfaces thereof, and the temperature was 60 ° C. and the pressure was increased using a press machine. A ^{laminated body was produced by bringing them into close contact with each other under the conditions of 10 7} Pa and 10 minutes, and then the laminated body was cut to a predetermined size to form a capacitor main body molded body.

Next, the raw molded body to be the capacitor body was degreased and fired under the conditions shown in Table 1 to prepare the capacitor body. A batch firing furnace was used for this firing.

Next, the produced capacitor body was subjected to a reoxidation treatment. The conditions for the reoxidation treatment were set to a maximum temperature of 1000 ° C. and a holding time of 5 hours in a nitrogen atmosphere.

The capacitor body obtained after firing had a length of 3.2 mm, a width of 1.6 mm, and a thickness of 1.6 mm. The average thickness of the dielectric layer was 5 μm. The average thickness of the internal electrode layer is shown in Table 2. The effective area of the internal electrode layer per layer was 1.78 mm ² . Here, the effective area is the area of the overlapping portion of the internal electrode layers formed alternately in the stacking direction so as to be exposed on different end faces of the capacitor body.

Next, after barrel polishing the capacitor body, 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 an external electrode. Then, using an electrolytic barrel machine, the surface of the external electrode 3 was sequentially Ni-plated and Sn-plated to prepare a multilayer ceramic capacitor.

Next, the following evaluation was performed on the produced multilayer ceramic capacitor.

As described above, the evaluation of the through holes and the closed pores in the internal electrode layer was performed by the method shown in FIG. The lengths of the closed air holes and the through holes and their ratios were measured by extracting the region corresponding to the part A shown in FIG. 2 from the cross section of the condenser from the vertical cross section of the condenser. The number of extracted portions was the middle region in the capacitor stacking direction and three locations from the central portion in the width direction. In this case, each extracted region contained 3 to 10 through holes and closed pores, respectively. The total length of each extracted region was Le, the length of the through hole was Lop, and the length of the closed pore was Lcp. The total length of the through holes was defined as Lopt, and the total length of the closed pores was defined as Lcpt. In this case, when determining the length Lop of the through hole and the length Lcp of the closed pore, the position passing through the central portion of the closed hole was measured in the thickness direction of the internal electrode layer. The ratio of through holes was determined from Lopt / Le. The ratio of closed pores was determined from Lcpt / Le. The combined ratio of the ratio of through holes and the ratio of closed pores was obtained from (Lcpt + Lopt) / Le. The ratio of the closed pores to the combined ratio of the ratio of the through holes and the ratio of the closed pores was obtained from Lcpt / (Lcpt + Lopt). Table 2 shows the length Lop of the through hole, the length Lcp of the closed pore, and each ratio obtained from these as an average value.

The crack occurrence rate was determined by visually inspecting 500 capacitors at random after the reoxidation treatment.

The capacitance was measured at room temperature (25 ° C.) using an LCR meter at a temperature of 25 ° C., a frequency of 1.0 kHz, and an AC voltage of 1.0 Vrms.

The withstand voltage was measured with the boost speed as 5 V / sec. The number of samples was 30, and the average value was calculated.

Samples 3 to 13 prepared by using nickel powder having an average particle size of 0.15 μm or more and 0.19 μm or less as the conductor paste for the internal electrode layer and setting the rate of temperature rise during firing to 300 ° C./h or more and 1000 ° C./h or less. In all the samples, closed pores were observed in the internal electrode layer. These samples had a capacitance of 4.5 μF or more and 5.1 μF or less. Further, the withstand voltage was 381 V or more and 451 V. The crack occurrence rate was 3 out of 500 or less.

In these samples, the average diameter (Lop) of through-holes existing in the internal electrode layer is 2 μm or more and 20 μm or less, the ratio of through-holes (Lopt / Le) is 8% or more and 29% or less, and the average diameter of closed pores (Lcp). Is 0.01 μm or more and 1 μm or less, the ratio of closed pores (Lcpt / Le) is 2% or more and 20% or less, the combined ratio of through holes and closed pores (Lopt + Lcpt) / Le is 22% or more and 39% or less, through holes. The ratio of the closed pores to the combined ratio of the closed pores and the closed pores Lcpt / (Lcpt / Lcot) was 5% or more and 71% or less. The coverage of the internal electrode layer was 70% or more and 92% or less.

Among these samples, sample No. 4 to 6 and 9 to 13 have a withstand voltage of 400 V or more and 451 V.
It was as follows. In these samples, the average diameter of the closed pores (Lcp) was 0.5 μm or more and 1 μm or less, and the combined ratio of the through holes and the closed pores (Lopt + Lcpt) / Le was 28% or more and 39% or less.

Furthermore, among these samples, sample No. In 4 to 6 and 9 to 12, the withstand voltage was 402 V or more and 451 V or less, and no crack was observed. In these samples, the ratio of closed pores Lcpt / Le was 2% or more and 16% or less, the average diameter of through holes (Lop) was 3 μm or more and 20 μm or less, and the ratio of through holes Lopt / Le was 15% or more and 29% or less. rice field. The coverage of the internal electrode layer was 70% or more and 85% or less.

Furthermore, among these samples, sample No. 4, 5 and 9 had a withstand voltage of 430 V or more and 451 V or less. In these samples, the average diameter of the through-holes (Lop) is 12 μm or more and 15 μm or less, the ratio of through-holes Lopt / Le is 19% or more and 20% or less, the average diameter of the closed pores is 0.6 μm or more and 1 μm or less, and the closed pores. Ratio Lcpt / Le is 10% or more and 16% or less. The ratio of the through hole and the closed air hole (Lpp + Lcp) is 30% or more and 35% or less, and the ratio of the closed air hole to the total ratio of the through hole and the closed air hole (Lcp / Lco) is 34% or more and 46% or less. rice field. The coverage of the internal electrode layer was 80% or more and 81% or less.

On the other hand, samples 1 and 2 prepared by using nickel powder having an average particle size of 0.2 μm as the conductor paste for the internal electrode layer and setting the rate of temperature rise during firing to 100 ° C./h are included in the internal electrode layer. No closed pores were observed. These samples had a capacitance of 4.5-4.7 μF, but a withstand voltage of 365 V. In addition, the crack occurrence rate was 1 in 500.

1 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Capacitor body 3 ・ ・ ・ ・ ・ ・ ・ ・ External electrode 5 ・ ・ ・ ・ ・ ・ ・ ・ Dielectric layer 7 ・ ・ ・ ・ ・ ・ ・ ・・ Internal electrode layer 7a ・ ・ ・ ・ ・ ・ ・ ・ ・ Metal part 9 ・ ・ ・ ・ ・ ・ ・ ・ Through hole 11 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Closed hole

Claims (4)

A capacitor having a capacitor body in which a plurality of layers of a dielectric layer and an internal electrode layer are alternately laminated.
The internal electrode layers, and organic metal portion, and a through hole penetrating the inner electrode layer in the thickness direction, and a closed pores present in the internal electrode layers,
When the cross section of the internal electrode layer is measured in the longitudinal direction, which is the direction in which the internal electrode layer extends,
The average value of the lengths of the through holes in the longitudinal direction was defined as Lop.
Let Lcp be the average value of the lengths of the closed pores in the longitudinal direction.
The total length of the through hole in the longitudinal direction included in the range of the predetermined length Le in the longitudinal direction of the internal electrode layer is defined as Lot.
When the total length of the closed pores in the longitudinal direction included in the predetermined length Le range is Lcpt,
Lcp is 0.01 μm or more and 1 μm or less, Lcpt / Le is 2% or more and 20% or less,
Lop is 2 μm or more and 20 μm or less, Lopt / Le is 8% or more and 29% or less,
(Lcpt + Lopt) / Le is 22% or more and 39% or less,
And Lcpt / (Lcpt + Lopt) is 5% or more and 71% or less.
Capacitor. The capacitor according to claim 1, wherein the Lcp is 0.5 μm or more and 1 μm or less, and (Lcpt + Lopt) / Le is 28% or more and 39% or less. The capacitor according to claim 2, wherein Lcpt / Le is 2% or more and 16% or less, Lop is 3 μm or more and 20 μm or less, and Lopt / Le is 15% or more and 29% or less. Lcp is 0.6 μm or more and 1 μm or less, Lcpt / Le is 10% or more and 16% or less,
Lop is 12 μm or more and 15 μm or less, Lopt / Le is 19% or more and 20% or less,
The capacitor according to claim 3, wherein (Lopt + Lcpt) / Le is 30% or more and 35% or less, and Lcpt / (Lcpt + Lopt) is 34% or more and 46% or less.

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