JP2000252153A - Laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress and prevent the deterioration of insulation properties by setting a ratio of an insulation resistance value of a dielectric, having the maximum insulation resistance value to that of a dielectric, having the minimum insulation resistance value to a specified value or less. SOLUTION: A laminate 2 is comprised of three kinds of dielectrics 6 (A, B, C), which are made of various dielectric materials (A', B', C') differing in temperature property of permittivity and inner electrodes 7 (7a-7d), formed respectively on one surfaces of the dielectrics A, B and C. In this case, for example the dielectric material A' is 0.35PNN-0.65PMN, the dielectric material B' of the dielectric B is 0.95PMN-0.05PT, and the dielectric material C' of the dielectric C is 0.85PMN-0.15PT. (PNN is Pb(Ni1/3 Nb2/3)O3; PMN is Pb(Mg1/3Nb2/3)O3, and PT is PbTiO3). In addition, in the respective dielectrics A, B and C, the ratio of an insulation value of a dielectric having the maximum insulation resistance value to that of a dielectric having the minimum insulation resistance value is set to 10 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional multilayer ceramic capacitor. The capacitor 1 is formed by laminating and firing such that a ceramic sheet serving as a dielectric 6 and a metal layer serving as an internal electrode 7 are alternately exposed, and one end of the internal electrode 7 is alternately exposed on the opposite side surface of the ceramic sheet. Then, the external electrode 3 is formed on each of the opposing side surfaces 4a and 4b where the internal electrodes 6 of the multilayer body 2 are exposed, and is electrically connected to the internal electrode 6. I have.
In addition, 5 is an exterior body.

The dielectric 6 is generally formed of the same dielectric material. However, in order to improve the temperature characteristic of the dielectric constant ε and manufacture a capacitor having a larger capacitance, different types of dielectric materials having different temperature characteristics are used. There is known an invention in which ceramic sheets made of a dielectric material are laminated and integrated. For example, the multilayer ceramic capacitors described in JP-A-48-65446 have a dielectric loss factor (dielectric constant ε).
X tan δ) and laminated with high dielectric ceramic thin plates having different temperature characteristics and firing. Such a capacitor has an advantage that the breakdown voltage can be increased in addition to the improvement of the dielectric constant ε. In this case, considering the temperature characteristics and dielectric loss factor of each ceramic material, the number of laminated layers is adjusted and combined so as to have a predetermined temperature characteristic.

[0004]

In manufacturing a conventional multilayer ceramic capacitor in which ceramic sheets made of different types of ceramic materials are laminated and integrated, the temperature characteristics and the dielectric loss factor of each dielectric material must be sufficiently considered. After the design, and after the manufacture, the inspection process checks whether the characteristics are the expected values or not.

However, in actual use,
Deterioration of characteristics over time is important. In particular, deterioration of insulation characteristics not only loses the function as a multilayer ceramic capacitor, but also may cause fatal problems in peripheral components and equipment. For this reason, various accelerated tests, such as a high humidity load test, a humidity resistance test, and a PCT test, described in JIS C5102 have been performed on multilayer ceramic capacitors. At this time, when considering the deterioration of the insulation characteristics, in the multilayer ceramic capacitor formed by laminating and integrating different kinds of dielectric materials having different temperature characteristics of the dielectric constant as described above, consider the insulating properties of the respective dielectrics. There is a need. However, the evaluation of the insulation properties of the entire multilayer ceramic capacitor has been mostly performed so far, and this has been insufficient. As a result of examining this point in more detail, even if the insulation resistance value of each dielectric has a high value at the beginning, if there is a difference in the insulation resistance value of each dielectric, the insulation resistance value is low. It was found that the reliability was deteriorated in the same manner as described above.

The inventors of the present invention have conducted experiments by changing the insulation resistance value of each dielectric. As a result, when the ratio of the maximum insulation resistance to the minimum insulation resistance is reduced to a certain value or less, deterioration of the insulation characteristics is reduced. It has been found that it can be suppressed or prevented.

[0007]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above-mentioned conventional problems and experimental results. It is an object of the present invention to suppress or reduce the deterioration of the insulation characteristics and to reduce the use for a long period of time. It is an object of the present invention to provide a multilayer ceramic capacitor capable of ensuring the reliability of the multilayer ceramic capacitor.

In order to achieve the above object, the present invention relates to a multilayer ceramic capacitor comprising a plurality of laminated two or more dielectrics having different dielectric constants with different temperature characteristics. The ratio of the insulation resistance value of the dielectric having the minimum insulation resistance value to that of the dielectric material is set to 10 or less.

In the present invention, if there is a difference between the insulation resistance values of the respective dielectrics forming the multilayer ceramic capacitor, the current flowing through the capacitor flows to layers having low resistance values. If this difference exceeds 10 in the ratio of the insulation resistance value, the insulation characteristics deteriorate with time, and the reliability in long-term use is reduced. Therefore, even if the insulation resistance value of the entire multilayer ceramic capacitor is high, and even if each dielectric has a high insulation resistance value, long-term reliability may not be ensured in some cases. On the other hand, when the ratio between the maximum and minimum insulation resistance values is 10 or less, deterioration of insulation characteristics is suppressed, and long-term reliability can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a sectional view showing an embodiment of the multilayer ceramic capacitor according to the present invention. Components equivalent to those shown in the section of the related art are denoted by the same reference numerals. In FIG. 1, a multilayer ceramic capacitor 1 includes a multilayer body 2 and both end edges of the multilayer body 2 in the surface direction, that is, an internal electrode extraction surface 4.
The laminated body 2 includes a pair of external electrodes 3 provided on the a and 4b, respectively, and an exterior body 5 for protecting the front and back surfaces of the multilayer body 2 respectively.

The laminate 2 includes three types of dielectrics 6 (A, B, C) formed of different dielectric materials (A ', B', C ') having different temperature characteristics of dielectric constant. , And internal electrodes 7 (7a to 7d) formed on one surface of each of the dielectrics A, B, and C, respectively. As the dielectric material A 'of the dielectric A, for example, 0.35 PNN-0.6
5PMN is used, and as the dielectric material B 'of the dielectric B, for example, 0.95PMN-0.05PT is used,
As the dielectric material C ′ of the dielectric C, for example, 0.85P
MN-0.15PT is used. PNN is Pb (Ni
_1/3 Nb _2/3 ) O ₃ , PMN is Pb (Mg _1/3 N)
b _2/3 ) O ₃ and PT are PbTiO ₃ . Each of the dielectrics A, B, and C is formed such that the ratio of the insulation resistance between the dielectric having the maximum insulation resistance and the dielectric having the minimum insulation resistance is 10 or less. In this case, since the specific resistance values of the dielectric materials A ′, B ′, and C ′ are different, by adjusting the film thickness of the dielectric materials A, B, and C as shown in FIG. The ratio between the value and the minimum value is set to 10 or less. Specifically, the thickness is set to be larger for a dielectric material having a smaller insulation resistance value.

The insulation resistance value IR of each of the dielectrics A, B, and C
(Ω) is a value obtained by multiplying the specific resistance value ρ (Ωcm) of the material by the distance L (cm) between the electrodes and dividing by the electrode area S (cm ² ).

IR = (ρ × L) / S (1)

The thickness of each of the dielectrics A, B, and C is calculated from the specific resistance of the dielectric material based on the above equation (1) so that the ratio between the maximum value and the minimum value of the insulation resistance does not exceed 10. To design. After the thickness of each of the dielectrics A, B, and C is determined, a combination of the number of layers of each of the dielectrics A, B, and C is determined to obtain a predetermined temperature characteristic.

The internal electrode 7 is a conductive film made of a noble metal such as palladium or silver-palladium alloy (or a base metal material such as Ni or Cu) and is formed to a thickness of about 1 to 3 μm. The internal electrodes 7 a to 7 d are alternately arranged with respect to the left and right external electrodes 3, that is, one end edges of the odd-numbered internal electrodes 7 a and 7 c from the bottom are exposed to one internal electrode extraction surface 4 a of the laminate 2. One end edges of the even-numbered internal electrodes 7b and 7d are exposed on the other internal electrode extraction surface 4b, and are electrically connected to the left and right external electrodes 3 respectively.

The external electrode 3 is formed of three layers: a base conductor film layer 8, a conductive resin layer 9, and a surface plating layer 10.

The underlying conductor film layer 8 is formed of silver or a silver-palladium alloy and glass particles. Conductive resin layer 9
Is formed of an organic solvent containing copper or copper alloy particles. The average particle size of the copper or copper alloy particles is about 10 μm. As the organic solvent, for example, a resol-based phenol resin is used. The surface plating layer 10 is formed by electroplating.

The package 5 is formed of the same dielectric material (A '), (B') or (C ') as the dielectric A, B or C or a dielectric material completely different from these. I have.

In such a multilayer ceramic capacitor 1, of the dielectrics A, B, C formed of different dielectric materials (A ', B', C ') having different temperature characteristics of the dielectric constant ε, respectively. Since the ratio between the dielectric having the maximum insulation resistance and the dielectric having the minimum insulation resistance is set to 10 or less, the deterioration over time of the insulation properties of the dielectric is suppressed or reduced. Can be prevented.
Therefore, reliability in long-term use can be ensured.

(Embodiment) Next, as an embodiment, a required number of dielectrics A, B and C formed by three kinds of dielectric materials (A ', B' and C ') having different temperature characteristics are laminated. A method for manufacturing a multilayer ceramic capacitor will be briefly described.
FIG. 2 shows the temperature characteristics of the dielectrics A, B, and C. Table 1 shows the specific resistance, the thickness of the dielectric, and the number of stacked layers.

[0021]

[Table 1]

First, each dielectric material (A ', B', C ')
Each time, a polyvinyl butyral resin 10, toluene 15 and isopropyl alcohol 15 are added to the dielectric material 100 and kneaded in a ball mill for 24 hours, then applied on a silicon-processed PET film and dried to form a ceramic sheet. At this time, the thickness of each ceramic sheet is the thickness described in Table 1 calculated from the specific resistance value of each of the dielectrics A, B, and C. In addition, in order to set the JIS temperature characteristic standard of the capacitor formed of such a ceramic sheet to the B characteristic, in this embodiment, the number of laminated ceramic sheets of different materials is set to the number shown in Table 1.

Next, three dielectric layers which do not include the internal electrodes serving as the outer package 5 are stacked. In this case, in the present embodiment, the dielectric layer is formed of the dielectric material (A '), but is formed of the dielectric material (B') or (C ') or a completely different dielectric material. You may.

Next, a 60 μm thick green sheet made of a dielectric material (A ′) in which a conductor film serving as an internal electrode 7 is formed by screen printing on a dielectric layer serving as an exterior body 5 Twenty layers are stacked so that the films are alternated. Next, a 30 μm-thick green sheet made of a dielectric material (B ′) formed by screen printing and having a conductive film serving as the internal electrode 7 formed on the stacked green sheets is formed on the green sheet so that the conductive films alternate. The layers are laminated.
Further, 10 layers of 30 μm thick green sheets made of a dielectric material (C ′) on which a conductor film serving as the internal electrode 7 is formed by screen printing are laminated thereon so that the conductor films alternate. Finally, three dielectric layers that do not include the internal electrodes serving as the exterior body 5 are superimposed thereon and integrated by thermocompression bonding. This is cut into a predetermined size to produce a green chip (unfired laminate). Then, the green chip was fired at a predetermined temperature and integrated to form a laminate 2, and then external electrodes 3 were formed to produce a multilayer ceramic capacitor 1.

On the other hand, a capacitor in which each of the dielectrics A, B and C had a thickness of 30 μm and was laminated in layers of 10 was prepared in the same manner as in the embodiment as a comparative example. The temperature characteristics of both the example and the comparative example satisfied the B characteristic of the temperature characteristic standard of JIS. This is reflow-soldered to a substrate made of glass epoxy resin, and 50 ° C at 60 ° C. and 90% RH.
A voltage of V was applied to perform a moisture resistance load test. The results are shown in FIGS. 3 (a) and 3 (b). As is apparent from this figure, the insulation of the capacitor of the comparative example decreased with time, whereas the insulation of the capacitor of the example did not show any abnormality.

In the above-described embodiment, an example is shown in which the external electrode 3 is formed in a three-layer structure. However, the present invention is not limited to this, and one or two or four or more layers may be used. The dielectric 6 is made of three types of dielectric materials (A ′, B ′,
Although it was formed by C ′), it may be any two or more types.

[0027]

As described above, according to the multilayer ceramic capacitor of the present invention, it is possible to suppress or prevent the insulation characteristics of the dielectric from deteriorating over time. Therefore, the insulation characteristics and reliability of the capacitor can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a multilayer ceramic capacitor according to the present invention.

FIG. 2 is a diagram illustrating temperature characteristics of capacitance.

FIGS. 3A and 3B are diagrams showing a change in insulation resistance value in a moisture resistance load test.

FIG. 4 is a sectional view of a conventional multilayer ceramic capacitor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor, 2 ... laminated body, 3 ... external electrode, 5 ... exterior body, 6 (A, B, C) ... dielectric, 7, 7
a to 7d: internal electrode, 8: base conductor film layer, 9: conductive resin layer, 10: surface plating layer.

Continued on the front page F-term (reference) 4G031 AA03 AA11 AA14 AA23 AA32 BA09 CA03 CA07 5E001 AB03 AC09 AC10 AD00 AE00 AE03 AF00 AF06 AH01 AH05 AH06 AH09 AJ02 5E082 AA01 AB03 BC35 EE04 EE23 EG26 GG26 FG26 GG26 JJ05 JJ12 JJ21 JJ23 LL02 LL03 MM22 MM24 PP02

Claims (1)

[Claims] 1. A multilayer ceramic capacitor comprising two or more dielectrics having different dielectric constants having different temperature characteristics, wherein a dielectric having a maximum insulation resistance and a dielectric having a minimum insulation resistance are provided. A multilayer ceramic capacitor wherein the ratio of the insulation resistance of the body is set to 10 or less.