JP2000277367A - Multilayer ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of structural defects such as delamination, and improve the temperature characteristic of a capacitor by reducing residual stresses. SOLUTION: A multilayer ceramic capacitor comprises a capacitor body 1, formed by laminating dielectric layers 3 and internal electrode layers 4 where the layer 3 alternates with the layer 4, with external electrodes 2 arranged on both sides of the body 1. Each layer 3 has a plurality of projections 7 arranged at prescribed intervals which project in the direction of lamination. In this case, a projection height h of the projections 7 in the direction of lamination is in the range of 0.5 to 1.0 μm.

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 comprising alternately laminated dielectric layers and internal electrode layers.

[0002]

2. Description of the Related Art Conventionally, a multilayer ceramic capacitor has a capacitor body formed by alternately laminating dielectric layers and internal electrode layers, and exposing a part of the internal electrode layers alternately to opposing side surfaces of the laminate. External electrodes were formed on both ends of the main body.

[0003] A general method of manufacturing such a multilayer ceramic capacitor is as follows. First, for example, a ceramic slurry in which dielectric ceramic powder is dispersed in an organic binder is formed into a sheet to form a ceramic green sheet, and screen printing is performed. An internal electrode pattern is printed on the ceramic green sheet with a conductive paste by a method or the like.

Then, a plurality of ceramic green sheets on which the internal electrode patterns are printed are laminated, and a plurality of ceramic green sheets on which the internal electrode patterns are not printed are laminated on both sides of the laminate. The laminated molded body thus obtained is cut into chips so that the internal electrode layers are exposed at the end faces, and is fired.

[0005] Then, the sintered laminate is polished to expose an internal electrode layer on its end face, a conductive paste is applied to this end face, and this is baked to form an external electrode. I was making chip capacitors.

As shown in FIG. 5, the capacitor body 11 is formed by alternately stacking dielectric layers 12 and internal electrode layers 13.

Further, as another method of manufacturing a multilayer ceramic capacitor, there is a manufacturing method in which a conductive paste is applied in advance to an end portion of a ceramic laminate before firing, and the laminate and the conductive paste are simultaneously fired. .

[0008] Further, a method for obtaining a laminate is not only a so-called sheet method using ceramic green sheets, but also a method using a ceramic green sheet.
A so-called printing method in which a ceramic paste and a conductive paste are alternately printed is also employed.

In such a multilayer ceramic capacitor, a desired capacitance can be obtained by the above-described lamination method.

[0010]

However, in the above-mentioned conventional multilayer ceramic capacitor, the internal stress generated due to the difference in the firing shrinkage and the thermal expansion coefficient between the internal electrode layer and the dielectric layer is large, and as the number of stacked layers increases, There has been a problem that internal stress is increased, structural defects such as delamination are likely to occur, and temperature characteristics of capacitance are deteriorated.

That is, the internal electrode layer is made of metal, and the dielectric layer is made of ceramics. At the firing stage, the internal electrode layer tends to shrink earlier than the dielectric layer. The skin portion of the dielectric layer receives compressive stress due to the contraction of the electrode layer.

In the cooling step after sintering, the internal electrode layer tends to shrink earlier than the dielectric layer because the coefficient of thermal expansion of the internal electrode layer is larger than that of the dielectric layer. The skin portion of the dielectric layer receives compressive stress due to the contraction of the electrode layer.

In the conventional multilayer ceramic capacitor, as shown in FIG. 5, since the dielectric layer 12 is flat, the compression generated on the surface of the dielectric layer 12 (boundary portion with the internal electrode layer 13). Stress is superimposed and remains, and such a residual stress increases as the number of layers increases, causing a problem that a structural defect is generated or a temperature characteristic of capacitance is deteriorated.

An object of the present invention is to provide a multilayer ceramic capacitor capable of suppressing the occurrence of structural defects such as delamination and improving the temperature characteristics of capacitance by reducing residual stress.

[0015]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventor has found that when a plurality of projecting deformation regions are formed in a dielectric layer of a multilayer ceramic capacitor, a part of the internal stress is reduced in the deformation regions. It has been found that it has been released and the residual stress of the multilayer ceramic capacitor can be reduced, and the present invention has been achieved.

That is, the multilayer ceramic capacitor of the present invention is a multilayer ceramic capacitor in which external electrodes are provided at both ends of a capacitor body in which dielectric layers and internal electrode layers are alternately stacked, wherein the dielectric layers are A plurality of protrusions projecting in the stacking direction are formed at predetermined intervals.

Here, the height h of the protrusion in the stacking direction of the protrusion is h.
Is desirably 0.5 to 10.0 μm. Also,
It is desirable that the plurality of protrusions be formed at intervals x of 10 to 300 μm.

[0018]

In the multilayer ceramic capacitor of the present invention, since the internal electrode layer is made of metal and the dielectric layer is made of ceramic, the internal electrode layer shrinks during the firing step and the cooling step after sintering. However, in the multilayer ceramic capacitor of the present invention, a plurality of protrusions protruding in the laminating direction are formed at predetermined intervals on the dielectric layer. The compressive stress generated in the skin portion is dispersed in each direction at the protrusion, and the residual stress decreases. Thereby, structural defects such as delamination are suppressed, and the temperature characteristics of capacitance can be further improved.

The height h of the protrusion in the stacking direction of the protrusions is set to 0.5 to 10.0 μm, or the plurality of protrusions are formed at an interval x of 10 to 300 μm so that the residual Stress can be more effectively reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a multilayer ceramic capacitor according to the present invention is formed by forming external electrodes 2 at both ends of a capacitor main body 1.
Is formed by alternately stacking dielectric layers 3 and internal electrode layers 4 as shown in FIG.

As shown in FIGS. 2 to 4, a plurality of protrusions 7 protruding in the laminating direction are formed on the dielectric layer 3 at predetermined intervals x. The protruding portion 7 has a hemispherical shape, and the protruding height h of the protruding portion 7 in the laminating direction is 0.
The maximum width L of the protrusion 7 in the dielectric layer plane direction is 5 to 100 μm. The plurality of protrusions 7 are provided on the dielectric layer 3 by 10 to 30.
It is formed with an interval x of 0 μm.

Here, the protruding height h of the protruding portion 7 in the laminating direction is set to 0.5 to 10.0 μm because the internal stress can be sufficiently reduced in this range. That is, when the protrusion height h is 0.5 μm or less, the internal stress is not sufficiently relaxed, and the effect of improving the rate of change in temperature characteristics of capacitance is small. On the other hand, if it exceeds 10.0 μm, short-circuit failure due to breakage of the green sheet is likely to occur. The height h of the protrusion 7 in the stacking direction is 2.
Desirably, it is 0 to 5.0 μm.

Further, the plurality of protrusions 7 are
When the interval X is smaller than 10 μm, a short failure due to breakage of the green sheet easily occurs. On the other hand, when the interval X exceeds 300 μm, the internal stress is not sufficiently relaxed, and This is because the rate of change in the temperature characteristic of the capacitance tends to increase. The interval x is 20 to 1
Desirably, it is 00 μm.

Further, the maximum width L of the protrusion 7 in the dielectric layer plane direction is set to 5 to 100 μm because the maximum width L is 5 μm.
If it is smaller than this, short-circuit failure due to breakage of the green sheet is likely to occur, and if it exceeds 100 μm, the internal stress is not sufficiently relaxed, and the rate of temperature characteristic change of capacitance tends to increase. Maximum width L is 10-50μ
m is desirable.

In the multilayer ceramic capacitor of the present invention, for example, first, a green sheet to be a dielectric layer is prepared. The green sheet contains, for example, barium titanate as a main component, yttrium oxide, a dielectric powder to which manganese carbonate and magnesium oxide are added, water and a dispersant, and after mixing and grinding in a ball mill, an organic binder is mixed. The obtained slurry is formed into a tape having a predetermined thickness.

As a material of the dielectric layer, barium titanate is used as a main component, and 0.5 to 8 mole parts of magnesium oxide and 0.05 to 0.5 manganese carbonate are added to 100 mole parts of the main component. Molar parts, yttrium oxide 0.3 ~
It is desirable to use those containing 4 mol parts in terms of improving properties such as dielectric constant.

As the conductor paste, for example, a paste obtained by adding an organic plasticizer to nickel powder is prepared.

Then, a conductive paste of nickel is applied to the upper surface of the green sheet of the dielectric layer by, for example, a screen printing method. Next, the first indenter having regular convex portions (hemispherical shape) and the second indenter having concave portions corresponding to the convex portions of the first indenter sandwich the green sheet coated with the conductive paste. Then, protrusions are formed on the surface of the green sheet at predetermined intervals. Next, the green sheets on which the protrusions are formed are stacked so that the protrusions overlap.

Then, after cutting the obtained laminated molded body into predetermined dimensions, it is baked at an oxygen partial pressure of 3 × 10 ^{−8 to} 3 × 10 ⁻³ Pa at a temperature of 1150 to 1300 ° C. for 0.5 to 3 hours. Next, an oxygen partial pressure of 1 × 10 ⁻² to 2 × 10 ⁴ Pa and a temperature of 900
Heat treatment at 1150 ° C. for 1 to 5 hours.

Next, a paste in which an organic plasticizer is added to copper powder is prepared, and the paste is baked on a sintered body so as to be alternately electrically connected to the internal electrode layers, thereby preparing a multilayer ceramic capacitor. .

In the above example, a protruding portion is formed on the green sheet by the first indenter having a regular convex portion and the second indenter having a concave portion corresponding to the convex portion of the first indenter. However, any method may be adopted as long as the protrusion can be formed.

In the above example, the protruding portion 7 has a hemispherical shape. However, in the present invention, if the protruding portion 7 protrudes in the stacking direction, for example, a conical shape, a quadrangular pyramid shape, etc. Shape may be used.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a dielectric material containing barium titanate as a main component, 1 mole portion of yttrium oxide, 2 mole portions of magnesium oxide, and 0.1 mole portion of manganese carbonate with respect to 100 mole portions of the main component. Water and a dispersant were added to the powder, mixed and pulverized by a ball mill using ZrO ₂ balls, and then an organic binder was mixed. The resulting slurry was formed into a 13 μm-thick tape.

On the other hand, as an internal electrode, a paste prepared by adding an organic plasticizer to nickel powder was prepared, and formed on the tape by a screen printing method. Next, a first indenter having a regular hemispherical protrusion having a diameter of 20 μm at intervals of 100 μm, and a second indenter having a recess corresponding to the protrusion of the first indenter.
The tape coated with the conductive paste was sandwiched by the indenter, and a hemispherical protrusion was formed on the tape surface.

Next, the tape having the protruding portions was laminated so that the protruding portions were overlapped.

At this time, a laminated molded body was formed such that the protrusions overlapped over each layer.

For the purpose of comparison, a laminated molded article in which tapes having no projections were laminated was also prepared.

After cutting the obtained molded body, the oxygen partial pressure was set to 1
Baking at × 10 ⁻⁶ Pa and a temperature of 1260 ° C. for 2 hours,
Heat treatment was performed at an oxygen partial pressure of 1 × 10 Pa and a temperature of 1000 ° C. for 1 hour. Next, a copper paste was applied to both end surfaces of the sintered body for 800 minutes.
C. to form an external electrode that is electrically connected to the internal electrode. The thickness of the dielectric layer is 9 μm, and the number of effective dielectric layers is 100.
A multilayer capacitor having a layer, outer dimensions of 2 mm × 1.2 mm × 1.2 mm, and an effective electrode area of 0.78 mm ² was obtained. In addition, the height h of the protrusions in the stacking direction, the maximum width L in the plane direction of the dielectric layer, and the distance x between the plurality of protrusions were variously changed to manufacture a multilayer capacitor.

Next, these samples were transferred to an LCR meter 42
The capacitance was measured at + 25 ° C. and + 125 ° C. using 84A at a frequency of 1.0 kHz and an input signal level of 1.0 Vrms. In addition, the occurrence of delamination was observed by appearance inspection. The results are shown in Table 1.

[0040]

[Table 1]

As shown in Table 1, in the case of the comparative example in which the dielectric layer was formed in a planar shape, that is, in which the protrusion was not formed (Sample No. 1), 125 ° C. with respect to the capacitance of + 25 ° C.
The rate of change of the capacitance was -16% on average, whereas the rate of change of the temperature of the capacitance was small at -14% or less in the sample of the present invention. Furthermore, in the sample of the comparative example, delamination occurred in three out of 300 samples, whereas no delamination occurred in the sample of the present invention.

[0042]

The multilayer ceramic capacitor of the present invention has the following features.
Since a plurality of protrusions protruding in the stacking direction are formed at predetermined intervals on the dielectric layer, the compressive stress generated in the skin portion of the dielectric layer is dispersed in the protrusions in each direction, and the residual stress is reduced. Thereby, structural defects such as delamination are suppressed, and the temperature characteristics of capacitance can be further improved.

The height h of the protrusions in the stacking direction is 0.5 to 10.0 μm, or a plurality of protrusions are formed at intervals x of 10 to 300 μm. The residual stress can be reduced more effectively.

[Brief description of the drawings]

FIG. 1 is a side view showing a multilayer ceramic capacitor of the present invention.

FIG. 2 is a sectional view of the capacitor body of FIG. 1;

FIG. 3 is a cross-sectional view of FIG.

FIG. 4 is a perspective view showing a protruding portion and its vicinity.

FIG. 5 is a sectional view of a capacitor body of a conventional multilayer ceramic capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Capacitor main body 2 ... External electrode 3 ... Dielectric layer 4 ... Internal electrode layer 7 ... Protrusion

Claims (3)

[Claims] 1. A multilayer ceramic capacitor in which external electrodes are provided at both ends of a capacitor body in which dielectric layers and internal electrode layers are alternately laminated. A multilayer ceramic capacitor, wherein the protrusions are formed at predetermined intervals. 2. The projection height h of the projection in the stacking direction is 0.5.
The multilayer ceramic capacitor according to claim 1, wherein the thickness of the multilayer ceramic capacitor is in the range of ~ 10.0m. 3. The multilayer ceramic capacitor according to claim 1, wherein the plurality of protrusions are formed at intervals x of 10 to 300 μm.