JP2000331867A - Laminated capacitor and manufacture of it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated capacitor which comprises a plurality of internal electrodes whose main component is Ni or Ni alloy and is excellent in electric characteristics such as electrostatic capacity temperature change coefficient and high temperature line. SOLUTION: A ceramics sintered body 2 comprising a plurality of internal electrodes 3-8 whose main component is Ni or Ni alloy is comprised in a laminated capacitor 1. Here, in the ceramics sintered body 2, the Ni concentration at a first ceramics sintered body part 1 where the plurality of internal electrodes 3-8 are laminated through a ceramics layer for extracting a capacity is set lower than the Ni concentration at second and third ceramics sintered body parts 2 and 3 positioned in the lamination direction, vertical, of a first ceramics sintered body part B as well as fourth and fifth ceramics sintered body parts 4 and 5 between the first ceramics sintered body part 1 and first and second end surfaces 2a and 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer capacitor having a plurality of internal electrodes arranged in a ceramic sintered body and a method for manufacturing the same, and more particularly, to a multilayer capacitor using Ni or a Ni alloy as the internal electrodes and a method for manufacturing the same. About the method.

[0002]

2. Description of the Related Art Hitherto, multilayer capacitors using dielectric ceramics using Ni or Ni alloy as internal electrodes have been proposed in order to reduce costs. When manufacturing this type of multilayer capacitor, a ceramic laminate in which internal electrodes mainly composed of Ni or a Ni alloy are laminated via unfired ceramic layers is prepared.
Then, a ceramic sintered body is obtained by firing the laminate.

However, when the above-mentioned ceramic laminate is fired in air, Ni is oxidized and its function as an internal electrode is reduced, and in the extreme case, it does not function as an internal electrode. Therefore, when Ni or a Ni alloy is used as the internal electrode, it is necessary to fire the ceramic laminate in a neutral or reducing atmosphere.

However, when the ceramic laminate is fired in a neutral or reducing atmosphere, Ni constituting the internal electrodes diffuses into the ceramic. Also, depending on the amount of Ni diffusion, the electrical characteristics of the finally obtained multilayer capacitor, for example, the temperature dependence of the capacitance may change, or the life at high temperatures may be shortened.

Therefore, in order to suppress the amount of Ni diffusion, a method of coating a Ni powder or a Ni alloy powder used as an internal electrode with glass or controlling the atmosphere during firing has been used. .

[0006]

However, even if the method of suppressing the amount of Ni diffusion is used, Ni or N
When an internal electrode mainly composed of an i-alloy was formed, it was difficult to reduce the variation in the diffusion amount of Ni in the ceramic sintered body. That is, the capacitance temperature change rate tends to change and the high-temperature life tends to decrease.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art and, despite the use of an internal electrode containing Ni or a Ni alloy as a main component, the electric current caused by the diffusion of Ni to the ceramics side. It is an object of the present invention to provide a multilayer capacitor and a method for manufacturing the same, which can effectively suppress the deterioration of mechanical characteristics.

[0008]

A multilayer capacitor according to the present invention is arranged so as to overlap with a ceramic sintered body via a ceramic layer in the ceramic sintered body. A plurality of internal electrodes, which are drawn out to the first or second end face and are mainly composed of Ni or a Ni alloy, and first and second inner faces formed to cover the first and second end faces of the ceramic sintered body. A first ceramic sintered body part, comprising a second external electrode, wherein the plurality of internal electrodes are stacked via a ceramic layer to obtain a capacitance. The second and third ceramic sintered body portions and the ceramic between the first ceramic sintered body portion and the first or second end face are respectively located at upper and lower portions in the stacking direction. When the sintered body portions are the fourth and fifth ceramic sintered body portions, the Ni concentration in the first ceramic sintered body portion is lower than the Ni concentration in the second to fifth ceramic sintered body portions. It is characterized by being low.

Further, the method for manufacturing a multilayer capacitor according to the present invention is the method for manufacturing a multilayer capacitor according to claim 1, wherein a plurality of internal electrodes mainly composed of Ni or a Ni alloy are provided via a ceramic layer. A step of preparing a laminated unfired ceramic laminate, charging the ceramic laminate in a box, and adding Ni or a Ni alloy at a ratio of 2% by weight or more of the weight of the ceramic laminate charged in the box. The method is characterized by comprising a step of firing the ceramic laminate in the coexistence to obtain a ceramic sintered body, and a step of forming external electrodes on a pair of end surfaces of the ceramic sintered body.

In the method for manufacturing a multilayer capacitor according to the present invention, Ni or a Ni alloy coexists in the box during firing, but the coexistence method is not particularly limited. That is, a Ni or Ni alloy layer may be formed on the inner surface of the box, or Ni or a Ni alloy may be arranged as a separate member around the stacked body put into the box.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of a multilayer capacitor according to the present invention and a method for manufacturing the same will be described with reference to the drawings.

As described above, conventionally, various methods have been employed in order to suppress the amount of Ni in the internal electrodes diffused into the ceramics during firing of the ceramic laminate. That is, conventionally, attention has been paid only to suppressing the diffusion of Ni to the ceramics side, and the distribution of Ni in the sintered ceramic body after firing has not been particularly studied.

The present inventors have studied the distribution of Ni in a conventional ceramic sintered body having an internal electrode containing Ni or a Ni alloy as a main component. The distribution of Ni in ceramics in this conventional multilayer capacitor will be described with reference to FIG. FIG. 2 shows a conventional multilayer capacitor 31.
FIG. In the multilayer capacitor 31, internal electrodes 33 to 38 are arranged in a ceramic sintered body 32 so as to overlap with each other via ceramics. External electrodes 39 and 40 are formed so as to cover the end faces 32a and 32b of the ceramic sintered body 32, respectively.
The internal electrodes 33 to 38 are mainly made of Ni or a Ni alloy.

In the ceramic sintered body 32,
In the portion where the internal electrodes 33 to 38 overlap with the ceramic layer interposed therebetween, that is, the Ni concentration of the ceramic sintered body portion is N in the ceramic sintered body portion which is the outer layer.
i concentration and ceramic sintered body portion and end faces 32a, 32
b, the Ni concentration in the portion of the ceramic sintered body was higher. That is, when firing, Ni
Is diffused from the internal electrodes 33 to 38 toward the ceramic, so that the Ni concentration is highest in the sintered body portion where the internal electrodes 33 to 38 overlap, and is higher than the Ni concentration in the other sintered body parts. Had become.

On the other hand, the inventor of the present invention can control the electrical characteristics of the multilayer capacitor, such as the rate of change in capacitance temperature, The inventors have found that the life or insulation resistance can be improved, and have accomplished the present invention. That is, the present invention has been confirmed by experiments of the present inventors.

FIG. 1 is a longitudinal sectional view showing an embodiment of the multilayer capacitor according to the present invention. In the multilayer capacitor 1, a ceramic sintered body 2 made of dielectric ceramics is used. As the dielectric ceramics constituting the ceramic sintered body 2, any suitable dielectric ceramics conventionally used for multilayer capacitors can be used, and there is no particular limitation. For example, barium titanate-based ceramics or the like can be used. Can be.

In the ceramic sintered body 2, internal electrodes 3 to 8 are arranged so as to overlap with each other via a ceramic layer. The internal electrodes 3, 5, 7 are drawn out to the end face 2 a of the ceramic sintered body 2. Internal electrodes 4, 6, 8
Is drawn out to an end face 2b opposite to the end face 2a.

The internal electrodes 3 to 8 are mainly composed of Ni or a Ni alloy. For an internal electrode mainly composed of Ni or Ni alloy, a method of applying a conductive paste on a ceramic green sheet and baking it when firing ceramics, forming a thin film such as vapor deposition, sputtering or plating of Ni or Ni alloy on the ceramic green sheet It can be formed by an appropriate method such as a method of applying by a method.

First and second external electrodes 9 and 10 are formed so as to cover the end surfaces 2a and 2b of the ceramic sintered body 2, respectively. The external electrodes 9 and 10 can be formed by an appropriate method such as application and baking of a conductive paste, plating, vapor deposition, or sputtering. Further, two or more of these methods may be used in combination. That is, the external electrodes 9,
10 may have a structure in which a plurality of metal films are stacked.
The metal material constituting the external electrodes 9 and 10 is not particularly limited, and is arbitrary such as Cu, Ni, Ag, Sn, and Ag-Pd.

The multilayer capacitor 1 is characterized in that, in the ceramic sintered body 2, the Ni concentration in the first ceramic sintered body portion where the internal electrodes 3 to 8 overlap with the ceramic layer interposed therebetween is the first ceramic sintered body. Outer layers positioned above and below the body portion in the stacking direction, that is, the second and third ceramic sintered body portions, and the fourth and fifth ceramic sintered portions between the first ceramic sintered body portion and the end faces 2a and 2b. That is, the concentration of each Ni is lower than that of each Ni in the consolidation portion.

In the multilayer capacitor according to the present invention, since the Ni concentration distribution is set as described above, as will be clear from the specific examples described later, the electric characteristics such as the temperature change rate of the capacitance and the high-temperature life are determined. Deterioration of the mechanical characteristics can be suppressed.

It is to be noted that the ordinary sintering method cannot realize the Ni concentration distribution as described above. That is,
Since Ni diffuses from the internal electrodes 3 to 8 to the ceramics side during firing, a simple firing of the ceramic laminate has the same concentration distribution as that of the conventional multilayer capacitor 31.

In the present invention, in order to reduce the Ni concentration in the first ceramic sintered body portion, the ceramic laminate is put into the box and the Ni or Ni alloy is put into the box during firing. Coexist at a ratio of 2 to 3% by weight of the weight. By sintering in the presence of Ni or a Ni alloy as described above, the above-described Ni concentration distribution is realized.

The method for coexisting Ni or a Ni alloy in the box is to form a Ni or Ni alloy layer on the inner surface of the box, or to separate Ni or Ni alloy in the box separately from the ceramic laminate. It can be performed by an appropriate method such as a method in which an alloy powder or a lump is arranged.

Next, specific experimental examples will be described.
Experimental Example 1 A ceramic slurry containing BaTiO ₃ as a main component was prepared. This ceramic slurry was formed into a sheet to obtain a rectangular ceramic green sheet. Ni powder 4 is placed on the upper surface of this rectangular ceramic green sheet.
A conductive paste containing 5.0% by weight, 5.0% by weight of an organic vehicle, and a solvent was screen-printed to a thickness of 1.2 μm after drying to form internal electrodes. A plurality of ceramic green sheets on which the internal electrodes are formed in this way are laminated such that the internal electrode lead portions are alternately arranged in opposite directions, and a plurality of plain ceramic green sheets are laminated on the upper and lower sides in the thickness direction. To obtain a ceramic laminate.

In order to obtain the above ceramic laminate, the number of laminated internal electrodes is 150, the thickness of the ceramic layer between the internal electrodes after firing is 5 μm, and the thickness of the second and third ceramic sintered bodies is respectively 100 μm, 4th
The length L of the fifth sintered body was set to 200 μm. In addition, as shown in FIG. 1, the length L refers to the distance between the first and second end surfaces 2a and 2b and the inner ends of the fourth and fifth sintered bodies. I do. In this case, the inner end of the fourth sintered body portion is the tip position of the internal electrodes 4, 6, 8 on the side not drawn out to the end face 2a. The external dimensions of the ceramic sintered body 2 are 1.9 mm.
The above ceramic laminate was configured to have a size of × 1.2 mm × 1.2 mm.

[0034] 1000 pieces of the ceramic laminate obtained as described above are put into a box made of alumina and coated with ZrO ₂ , and the area around the area where the ceramic laminate is arranged in the box is placed. Ni
A metal mass was placed. With respect to this Ni metal lump, a plurality of Ni metal lumps were dispersed and arranged so as to be 5% by weight when the weight of the ceramic laminate put in the box was 100% by weight.

Thereafter, firing was performed at a temperature of 1300 ° C. in a reducing atmosphere of N ₂ + 3% by volume H ₂ + H ₂ O. In this way, a ceramic sintered body is obtained, a Cu paste is applied to both end surfaces of the obtained ceramic sintered body, baked, and a Ni plating layer and a Sn plating layer are sequentially formed on the surface of the Cu layer. Thereby, the first and second external electrodes were formed, and a multilayer capacitor was obtained.

As described above, a multilayer capacitor of Sample 4 shown in Table 1 below was obtained. In addition, the proportion of the Ni metal lump added during firing was 1% by weight (sample 2) and 3% by weight, based on the total weight of the ceramic laminate 100% put into the box.
Each of the multilayer capacitors of Sample Nos. 2, 3, and 5 was obtained in the same manner as described above except that (Sample 3) and 7% by weight (Sample 5) were used.

For comparison, a multilayer capacitor of Sample 1 was obtained in the same manner as described above except that the Ni metal lump was not put into the box during firing. For each of the multilayer capacitors of Samples 1 to 5 obtained as described above, the rate of change in capacitance with temperature was measured. The results are shown in Table 1 below. Further, with respect to each multilayer capacitor, a voltage of 64 V was applied at a temperature of 150 ° C., an accelerated life test was performed, and a high-temperature life was evaluated. The results are shown in Table 1 below.

[0031]

[Table 1]

As is clear from Table 1, it can be seen that as the amount of the Ni mass put into the box increases, the rate of change in capacitance with temperature decreases and the high temperature life (MTTF) improves.

In particular, it can be seen that when the addition ratio of the Ni metal lump is 3% by weight or more and 5% by weight or less, the capacitance temperature change rate can be more effectively improved. Further, it can be seen that the high-temperature life can be effectively improved by setting the Ni metal lump to 3% by weight or more.

Next, the structure of each of the above multilayer capacitors is represented by W
Using a DX (wavelength dispersive X-ray microanalyzer)
analyzed. Each of the first ceramic sintered body portion, the second, third ceramic sintered body portion, and the fourth and fifth ceramic sintered body portions in the ceramic sintered body of each multilayer capacitor is 100 μm × 10
The surface analysis of the Ni element was performed in the vertical cross section region of 0 μm. As a result, after confirming that Ni is substantially uniformly dispersed in each region and that Ni is not unevenly distributed in each region, the Ni concentration in each region is calculated as W
The number of counts detected by the detector of DX was measured.
The average count is shown in Table 2 below.

[0035]

[Table 2]

The average count number in Table 2 corresponds to the Ni concentration in each region. As is clear from Table 2,
1% by weight of the multilayer capacitor of sample number 1 and Ni metal lump
It can be seen that in the multilayer capacitor of Sample No. 2 which was baked while coexisting in the ratio of 1, the Ni concentration was high in the first ceramic sintered body portion, that is, in the region that greatly affected the characteristics.

On the other hand, in the multilayer capacitors of Sample Nos. 3 to 5, N
i concentration is low, the second and third ceramic sintered body portions,
It can be seen that the Ni concentration is lower than the Ni concentration in the fourth and fifth ceramic sintered bodies.

Therefore, as is clear from the comparison of the evaluation results of the multilayer capacitors of Sample Nos. 1 and 2 and the multilayer capacitors of Sample Nos. 3 to 5, the Ni concentration in the first ceramic sintered body portion was reduced by the other ceramics. It can be seen that, by making the Ni concentration lower than that of the binder portion, a multilayer capacitor having excellent capacitance temperature change rate and high-temperature life characteristics can be obtained.

(Experimental Example 2) In the same manner as in Experimental Example 1, a ceramic laminate was prepared. Upon firing, a Ni metal paste was applied to the inner surface of the box used in Experimental Example 1 and dried.
The amount of the Ni metal paste is converted into Ni,
The results are shown in Table 3 below. That is, assuming that the total amount of the ceramic laminate put into the box is 100% by weight, the weight is set to 2% by weight (sample number 7), 4% by weight (sample number 8) and 6% by weight (sample number 9). . In sample No. 6, for the purpose of comparison, no Ni paste was applied to the box.

Experimental Example 1 was placed on the box prepared as described above.
The ceramic laminate was charged in the same manner as in Example 1, and fired in the same atmosphere and temperature as in Experimental Example 1 to obtain a ceramic sintered body.
External electrodes were formed in the same manner as in Example 1 to obtain a multilayer capacitor.

With respect to the multilayer capacitors of Sample Nos. 6 to 9 obtained as described above, the capacitance temperature change rate and the accelerated life test were performed in the same manner as in Example 1. The results are shown in Table 3 below.

[0042]

[Table 3]

As is clear from Table 3, the inner surface of the box
It can be seen that even when Ni is co-fired with the ceramic laminate by applying the paste, the capacitance temperature change rate and the high-temperature life are improved as the Ni addition ratio increases.

The multilayer capacitors obtained in Sample Nos. 6 to 9 were also subjected to WDX in the same manner as in Experimental Example 1.
, The Ni concentration of each ceramic sintered body was measured. Table 4 shows the results.

[0045]

[Table 4]

As is apparent from Table 4, there is a correlation between the ratio of coexisting Ni and the dispersibility of Ni in the ceramic sintered body. Further, in Sample Nos. 7 to 9 in which the rate of change in capacitance temperature and the high temperature life were improved, the first
It can be seen that the Ni concentration in the ceramic sintered body portion is lower than the Ni concentration in other ceramic sintered body portions.

Further, as is clear from Table 3, when Ni is added, if the addition ratio of Ni is 2% by weight or more, the capacitance temperature change rate and the high-temperature life can be improved.

Therefore, from the results of Experimental Examples 1 and 2, when sintering Ni in the coexistence with the ceramic laminate, Ni is present in an amount of 2 wt% or more with respect to 100 wt% of the total weight of the ceramic laminate. It can be seen that when firing is performed, a multilayer capacitor having good electrical characteristics can be obtained.

The upper limit of the amount of coexisting Ni is not particularly limited in order to improve the temperature change rate of the capacitance and the high temperature life. However, as the amount of Ni introduced into the box increases, the amount of the ceramic laminate introduced is more limited. Therefore, a comprehensive judgment may be made in consideration of productivity and the like. In consideration of the above productivity, even if Ni is made to coexist, it is usually preferable that the addition ratio is 3% by weight or less based on 100% by weight of the total weight of the ceramic laminate.

In Experimental Examples 1 and 2, a Ni metal lump and a Ni paste were used, but NiO powder may be used.
That is, when firing the ceramic laminate in a reducing atmosphere, the form of adding Ni is not particularly limited as long as a Ni atmosphere can be formed near the ceramic laminate. In addition, the measurement of the Ni concentration in the ceramic sintered body may be performed using an energy dispersive X-ray microanalyzer (EDX) or the like in addition to the WDX.

[0051]

As described above, in the multilayer capacitor according to the present invention, the Ni concentration in the first ceramic sintered body portion from which the plurality of internal electrodes are stacked via the ceramic layer and the capacitance is taken out constitutes the outer layer. From the Ni concentration of the second and third ceramic sintered body portions and the fourth and fifth ceramic sintered body portions between the first ceramic sintered body portion and the first or second end face. Is also low, so N
In a multilayer capacitor having a plurality of internal electrodes mainly composed of an i or Ni alloy, it is possible to improve electrical characteristics such as a temperature change rate of a capacitance and a high temperature life. Therefore, it is possible to provide a multilayer capacitor that uses inexpensive internal electrodes containing Ni or a Ni alloy as a main component and has good electrical characteristics.

In the method for manufacturing a multilayer capacitor according to the present invention, a ceramic laminate having an internal electrode containing Ni or a Ni alloy as a main component is charged into a box and fired.
2% by weight of Ni or Ni alloy based on the weight of the ceramic laminate
Since they coexist at the above ratio, a multilayer capacitor having a Ni concentration distribution according to the present invention can be provided. Therefore, it is possible to provide a multilayer capacitor having excellent electrical characteristics such as a capacitance temperature change rate and a high-temperature life.

In addition, as described above, Ni is used for firing.
Alternatively, since it is only necessary to allow a Ni alloy to coexist, a multilayer capacitor that is inexpensive and has excellent electrical characteristics can be provided without significantly increasing the number of steps.

When Ni or a Ni alloy coexists in the box, if a Ni or Ni alloy layer is formed on the inner surface of the box, the space in the box can be effectively used, and more ceramic laminates can be used. The body can be fired.

Further, N around the laminate put in the box
When placing i or Ni alloy, use the same box,
The ceramic laminate can be fired many times, and the addition ratio of Ni or Ni alloy can be easily adjusted according to the amount of the ceramic laminate to be charged.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view for explaining a multilayer capacitor according to one embodiment of the present invention.

FIG. 2 is a longitudinal sectional view for explaining a Ni concentration distribution in a ceramic sintered body in a conventional multilayer capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laminated capacitor 2 ... Ceramic sintered compact 2a, 2b ... 1st, 2nd end surface 3-8 ... Internal electrode 9, 10 ... 1st, 2nd external electrode ... 1st ceramic sintered compact part, ... second and third ceramic sintered body portions ... fourth and fifth ceramic sintered body portions

Claims (4)

[Claims] 1. A ceramic sintered body, disposed in the ceramic sintered body so as to overlap with a ceramic layer interposed therebetween, and drawn to a first or second end face of the ceramic sintered body. Ni
Or a plurality of internal electrodes mainly composed of a Ni alloy, and first and second external electrodes formed so as to cover first and second end faces of the ceramic sintered body. The first ceramic sintered body portion, in which the electrodes are laminated via the ceramic layer and the capacitance is taken out, is the first ceramic sintered body portion, and the ceramic sintered body portions located above and below the first ceramic sintered body portion in the laminating direction. The second and third ceramic sintered body portions, and the ceramic sintered body portion between the first ceramic sintered body portion and the first or second end face are replaced with fourth and fifth ceramic sintered body portions, respectively. The multilayer capacitor according to claim 1, wherein the Ni concentration in the first ceramic sintered body portion is lower than the Ni concentration in the second to fifth ceramic sintered body portions. 2. The method for manufacturing a multilayer capacitor according to claim 1, wherein an unfired ceramic laminate in which a plurality of internal electrodes mainly composed of Ni or a Ni alloy are laminated via a ceramic layer is provided. And charging the ceramic laminate into a box, Ni or Ni
A step of firing the ceramic laminate by causing the alloy to coexist at a ratio of 2% by weight or more of the weight of the ceramic laminate placed in the housing to obtain a ceramic sintered body; and a pair of end faces of the ceramic sintered body. Forming an external electrode on the multilayer capacitor. 3. The method for producing a multilayer capacitor according to claim 2, wherein a Ni or Ni alloy layer is formed on an inner surface of the box when Ni or a Ni alloy coexists in the box. 4. The method for manufacturing a multilayer capacitor according to claim 2, wherein, when Ni or a Ni alloy coexists in the box, Ni or a Ni alloy is arranged around the ceramic laminated body in the box. .