JP3478482B2 - Multilayer ceramic capacitors - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic ceramic capacitor, and more particularly, to a large-sized monolithic ceramic capacitor used in a medium-high pressure range. 2. Description of the Related Art FIG. 3 shows a monolithic ceramic capacitor 1 of interest to the present invention, wherein (1) is a plan view and (2) is a front view. As shown in FIG. 3, a multilayer ceramic capacitor 1 has a rectangular parallelepiped capacitor body 2 defined by a longitudinal dimension L, a width dimension W and a thickness dimension T, and both ends of the capacitor body 2 in the longitudinal direction. And first and second external electrodes 3 and 4 respectively formed on the portion. The capacitor body 2 includes a plurality of dielectric layers 5, which are stacked in a state of extending in parallel with a plane defined by a longitudinal dimension L and a width dimension W of the capacitor body 2, and a specific dielectric layer. And a plurality of sets of internal electrodes 6 facing each other with the layer 5 interposed therebetween. [0005] A plurality of sets of internal electrodes 6 are connected to the first external electrode 3.
And the one electrically connected to the second external electrode 4 are alternately arranged. FIG.
The internal electrode 6 shown by breaking a part of the capacitor body 2 in (1) is electrically connected to the first external electrode 3 as can be seen from the outline shown by the broken line. The internal electrode 6 electrically connected to the second external electrode 4 has a symmetrical form with the illustrated internal electrode 6. Conventionally, such a multilayer ceramic capacitor 1 is designed with a dimensional relationship of L> W and W ≦ 2T with respect to a longitudinal dimension L, a width dimension W and a thickness dimension T of the capacitor body. Was common. [0007] Regarding the multilayer ceramic capacitor 1 as described above, it is desired to increase the capacity and the voltage as recent market needs. [0008] As means for satisfying these demands,
In the multilayer ceramic capacitor 1, for example, it is conceivable to increase the number of stacked internal electrodes 6 and increase the thickness of the dielectric layer 5. However, in the case of using such a means, the multilayer ceramic capacitor 1 is connected to, for example, a rated voltage of 250.
For medium and high pressures of V or more, a thickness of 20 μm
Since the above dielectric layer 5 is required, if it is attempted to obtain a large capacitance of 1 μF or more, the number of laminated internal electrodes 6 becomes very large, and therefore, the dimension T in the thickness direction of the capacitor body 2 becomes very thick. I have to do it. Therefore, in firing for obtaining the capacitor body 2, the sintering property of the ceramic constituting the dielectric layer 5 is poor or unstable, and pores are easily generated in the dielectric layer 5, The sinterability of the electrode 6 deteriorates,
Alternatively, the sintering state tends to vary.
As a result, in the obtained multilayer ceramic capacitor 1, delamination occurs or a breakdown voltage (BDV) occurs.
In addition to the deterioration of the initial characteristics, such as a decrease in the value and the occurrence of cracks due to electrostriction, reliability such as high-temperature life may be reduced. As a means for increasing the capacitance of the multilayer ceramic capacitor 1, it is also conceivable to increase the longitudinal dimension L and the width dimension W of the capacitor body 2, thereby increasing the effective area of the internal electrode 6. Can be However, simply increasing the longitudinal dimension L and the width dimension W of the capacitor body 2 to increase the effective area of the internal electrodes 6 as described above would not be sufficient.
This means that little measures have been taken to improve the BDV of the multilayer ceramic capacitor 1, and when trying to use this multilayer ceramic capacitor 1 for medium and high pressures, problems with BDV and the like will be encountered. SUMMARY OF THE INVENTION It is an object of the present invention to provide a multilayer ceramic capacitor which can solve the above-mentioned problems, particularly, problems relating to BDV. According to the present invention, there is provided a capacitor body having a rectangular parallelepiped shape defined by a longitudinal dimension, a width dimension and a thickness dimension, and a rectangular parallelepiped capacitor body provided on both longitudinal ends of the capacitor body. First and second formed
A plurality of dielectric layers, and a specific dielectric layer, wherein the plurality of dielectric layers are stacked so as to extend in parallel with a plane defined by the longitudinal dimension and the width direction dimension of the capacitor body. And a plurality of sets including a base metal, in which the ones electrically connected to the first external electrode and the ones electrically connected to the second external electrode are alternately arranged. And an internal electrode
Is sintered during firing to obtain a dielectric layer.
In order to solve the above-mentioned technical problems, the longitudinal dimension and the width dimension of the capacitor body are each set to be at least four times the thickness dimension. that you,
First, it has one feature. The present invention has been made on the basis of attention to the relationship between the longitudinal dimension, the width dimension, the thickness dimension, and the BDV of the capacitor body, and the longitudinal dimension, the width dimension, and the thickness. When the BDV was evaluated by changing the dimension in various directions, it was found that the BDV was improved by making each of the dimension in the longitudinal direction and the dimension in the width direction at least four times the dimension in the thickness direction as described above. . When the BDV was evaluated by variously changing the length, width and thickness dimensions of the above-described capacitor body, the BDV was further increased by making the width dimension larger than the length dimension. Found to improve. Therefore, in the present invention, the width dimension of the co-down <br/> capacitor body, and to be larger than the longitudinal dimension as the following features. According to the present invention, there is provided a capacitor body in which both a longitudinal dimension and a width dimension are 10 mm or more, or a capacitor layer having a capacitance of 1 μF or more and a dielectric layer between internal electrodes facing each other. The thickness is 20 μm or more,
It is particularly advantageously applied to large multilayer ceramic capacitors, such as those having a rated voltage of 250 V or more. Therefore, in the present invention,
Both the longitudinal dimension and the width dimension are 10 mm
And the capacitance is 1 μF or more and oppose each other.
The thickness of the dielectric layer between the internal electrodes is 20 μm or more.
To have a rated voltage of 250 V or more.
It is a sign. FIG. 1 shows a multilayer ceramic capacitor 11 according to an embodiment of the present invention.
(1) is a partially cutaway plan view, and (2) is a front view. As shown in FIG. 1, a multilayer ceramic capacitor 11 has a rectangular parallelepiped capacitor body 12 defined by a longitudinal dimension L, a width dimension W and a thickness dimension T, and both ends of the capacitor body 12 in the longitudinal direction. And first and second external electrodes 13 and 14 respectively formed on the portion. The capacitor body 12 includes a plurality of dielectric layers 15 stacked in a state of extending in parallel with a plane defined by the longitudinal dimension L and the width dimension W of the capacitor body 12, and a specific dielectric layer 15. It includes a plurality of sets of internal electrodes 16 that face each other with a dielectric layer 15 interposed therebetween. In the plurality of sets of internal electrodes 16, those electrically connected to the first external electrodes 13 and those electrically connected to the second internal electrodes 14 are alternately arranged. The internal electrode 16 illustrated by breaking a part of the capacitor body 12 in 1 (1) is electrically connected to the first external electrode 13 as can be seen from the outline shown by the broken line. . The internal electrode 16 electrically connected to the second external electrode 14 has a symmetrical form with respect to the internal electrode 16 shown in FIG. The description described so far substantially applies to the conventional multilayer ceramic capacitor 1 shown in FIG. As a characteristic configuration of the present invention, in this embodiment, both the longitudinal dimension L and the width dimension W of the capacitor body 12 are four times or more the thickness dimension T. By increasing both the longitudinal dimension L and the width dimension W of the capacitor body 12, the effective area of each internal electrode 16 can be increased. Therefore, it is not necessary to rely on an increase in the number of stacked internal electrodes 16 for increasing the capacitance, and the dimension T in the thickness direction of the capacitor body 12 can be reduced. Therefore, the sinterability of the ceramic constituting the dielectric layer 15 is improved, and uneven sintering and generation of pores can be suppressed. In particular, when the multilayer ceramic capacitor 11 is used at a medium or high voltage of a rated voltage of 250 V or more, the area of each internal electrode 16 is increased,
It has been confirmed that the electric field concentration when a voltage is applied between the internal electrodes 16 facing each other is reduced, and the BDV value is greatly improved. Reducing the number of stacked internal electrodes 16 is also effective in suppressing the occurrence of cracks due to electrostriction, and contributes to an improvement in BDV value. In view of the above, in the present invention, both the longitudinal dimension L and the width dimension W of the capacitor body 12 are set to be four times or more the thickness dimension T. In order to confirm the above, the results of an experiment performed using a specific multilayer ceramic capacitor as a sample are described below. Multilayer ceramic capacitors having the same capacitance and the same rated voltage were prepared by changing the ratio of L: W: T variously as shown in Table 1 below. Then, a DC voltage was applied to the multilayer ceramic capacitor relating to each sample to determine BDV. Table 1 shows the BDV of Sample 1.
The relative value of the BDV of each sample when is set to 1.00 is shown. [Table 1] In Table 1, a tendency that BDV is generally improved as the ratio of L and / or W to T is increased, particularly, as can be seen by comparing Sample 7 with Sample 5 or 6, Both L and W are 4 of T
More than double the BDV
Has improved dramatically. From this, samples 7 to 13
It can be seen that a high BDV value can be obtained by setting both L and W at least four times T as shown in FIG. The effect of improving the BDV by increasing the longitudinal dimension L and the width dimension W as described above is due to the effect of a large-sized laminate in which both the longitudinal dimension L and the width dimension W are 10 mm or more. This is particularly noticeable for ceramic capacitors. Similarly, such an effect is obtained when the capacitance is 1 μF or more, and the thickness of the dielectric layer between the internal electrodes facing each other is 20 μm or more.
This is more prominent in the case of a multilayer ceramic capacitor having a rated voltage of 250 V or more. When the internal electrode contains a base metal such as nickel or copper, sintering is performed in a reducing atmosphere. In such a reducing atmosphere, sufficient sinterability of the internal electrode may be obtained. Generally difficult. In this regard, in this embodiment, since the number of stacked internal electrodes 16 can be reduced and the dimension T in the thickness direction of the capacitor body 12 can be reduced, sufficient sinterability of the internal electrodes can be maintained even by firing in a reducing atmosphere. It becomes easy to obtain. Another feature of this embodiment is that the width dimension W of the capacitor body 12 is larger than the longitudinal dimension L. This dimensional relationship is
This is effective in improving V. Referring to Table 1 above, for example, a comparison between Samples 8 and 9, Samples 10 and 11
As can be understood from the comparison between Samples 12 and 13 or between Samples 12 and 13, Samples 9, 11, and 13 each having L <W are samples 8 each having L> W. , 10 and 12 show higher BDV values. This tendency is shown in FIG. 2 as shown in FIG. In FIG. 2, the horizontal axis indicates the ratio of L: W, and the vertical axis indicates BDV. As can be seen from FIG. 2, by making W larger than L, the BDV can be greatly improved as compared with the case where L is larger than W or the case where L and W are equal. As described above, by making the width dimension W larger than the longitudinal dimension L, the sinterability of the internal electrode 16 during firing is further improved, and the adhesion to the dielectric layer 15 is also improved. As a result, it has been confirmed that the rate of occurrence of cracks due to delamination or electrostriction can be significantly reduced. This is because the organic component such as resin or varnish contained in the paste for forming the internal electrode 16 at the time of firing passes through the inside of the internal electrode 16 and is to be joined to the external electrode 13 or 14 on the end face of the capacitor body 12. It is considered that such organic components are more easily removed by making the width dimension W larger than the longitudinal dimension L. Further, as described above, when the internal electrode 16 contains a base metal such as nickel or copper, firing is performed in a reducing atmosphere. Because organic components are more easily removed
It is easier to obtain sufficient sinterability in the internal electrodes 16. As described above, according to the present invention, since both the longitudinal dimension and the width dimension of the capacitor body are four times or more the thickness dimension, the effective area of the internal electrode is reduced. And the concentration of the electric field between the internal electrodes when a voltage is applied is reduced. Further, since the dimension in the thickness direction of the capacitor body can be reduced, it is easy to obtain a uniform sintered body by firing, the leakage current is small, and the high-temperature reliability of the multilayer ceramic capacitor can be improved. From the above, it is possible to obtain a high BDV value in the multilayer ceramic capacitor, and to reduce the size of the capacitor body in the thickness direction. It can be achieved effectively. Further, according to the present invention, the width dimension of the capacitor main body is larger than the longitudinal dimension
Thus, since the sinterability of the internal electrode is stabilized, the BDV can be further improved, and the variation in the BDV value can be reduced. Further, since the sinterability of the internal electrodes is stabilized, the occurrence of cracks due to delamination or electrostriction can be suppressed more effectively, and a multilayer ceramic capacitor can be manufactured with stable quality. . According to the present invention, both the longitudinal dimension and the width dimension of the capacitor body are 10 mm.
Ri der above, in the electrostatic capacitance 1μF or more, a thickness of the dielectric layer between the internal electrodes 20μm or more, which are opposite to each other, since have a higher voltage rating 250V, described above
Such effects according to the present invention appear more remarkably. Further, according to the present invention, since the internal electrode contains a base metal, the internal electrode is fired in a reducing atmosphere, so that the sinterability of the internal electrode tends to be unstable. To reduce the thickness dimension of the capacitor body,
Since the number of stacked internal electrodes can be reduced or the widthwise dimension in which the internal electrodes are exposed can be increased, it is easy to obtain stable sinterability in the internal electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a multilayer ceramic capacitor 11 according to an embodiment of the present invention, wherein (1) is a partially cutaway plan view, and (2) is a front view. . FIG. 2 is a diagram showing a tendency of a change in a BDV value when a ratio between a longitudinal dimension L and a width dimension W in the multilayer ceramic capacitor 11 shown in FIG. 1 is changed. FIGS. 3A and 3B show a conventional multilayer ceramic capacitor 1 of interest to the present invention, wherein FIG. 3A is a partially cutaway plan view and FIG. 3B is a front view. [Description of Signs] 11 Multilayer ceramic capacitor 12 Capacitor main body 13 First external electrode 14 Second external electrode 15 Dielectric layer 16 Internal electrode L Longitudinal dimension W Width dimension T Thickness dimension

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Morinaki Nobushige               2-26-10 Tenjin, Nagaokakyo-shi, Kyoto, Japan               Murata Manufacturing Co., Ltd. (72) Inventor Takeshi Azumi               2-26-10 Tenjin, Nagaokakyo-shi, Kyoto, Japan               Murata Manufacturing Co., Ltd. (72) Inventor Yasuhiko Kubota               2-26-10 Tenjin, Nagaokakyo-shi, Kyoto, Japan               Murata Manufacturing Co., Ltd. (72) Inventor Yoshihiro Komura               2-26-10 Tenjin, Nagaokakyo-shi, Kyoto, Japan               Murata Manufacturing Co., Ltd.                (56) References JP-A-59-188113 (JP, A)                 JP-A-4-18813 (JP, A)

Claims (1)

(57) Claims 1. A rectangular parallelepiped capacitor body defined by a longitudinal dimension, a width dimension, and a thickness dimension, and formed on both longitudinal ends of the capacitor body. A plurality of dielectric layers, the first and second external electrodes being stacked so as to extend in parallel with a plane defined by a longitudinal dimension and a width dimension of the capacitor body. The ones that face each other via the specific dielectric layer and are electrically connected to the first external electrode and the ones that are electrically connected to the second external electrode are arranged alternately. Yes , low
A plurality of sets of internal electrodes including a metal , wherein the internal electrodes are formed when firing to obtain the dielectric layer.
There are those which are sintered, in the laminated ceramic capacitor, a longitudinal dimension and a width dimension of the capacitor body are all state, and are more than four times the thickness dimension, the width dimension of the capacitor body, From longitudinal dimension
Is larger, longitudinal dimension and a width dimension of the capacitor body
Are each 10 mm or more, the capacitance is 1 μF or more, and the internal electrodes facing each other
Wherein the thickness of the dielectric layer is 20 μm or more,
A multilayer ceramic capacitor having a rated voltage of 250 V or more .