JPH03209806A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To enhance thermal shock resistance, and to effectively prevent generation of cracks by a method wherein the blending ratio of CeO2 and ZrO2 is differentiated for each dielectric ceramic layer, and the materials are selected so as to obtain a specific composition. CONSTITUTION:The dielectric ceramic layers 8 to 11, which are located on the inner side pinched between inner electrodes 3 to 7, are constituted by the material containing BaTiO3, CeO2 and ZrO2 of 100-x1-y1, z1 and y1mol% in the composition wherein the relation of 6>y1<=x1>0 is realized between x1 and y1. Also, the dielectric ceramic layers 12 and 13, on the outer surface side outside the outermost inner electrodes 3 and 7 among the superposed inner electrodes 3 to 7, are composed of the material containing BaTiO3, CeO2 and ZrO2 of 100-x2-y2, x2 and y2 mol %, in the composition wherein the relation of 6>x2<=y2>0 will be realized between x2 and y2. As a result, thermal shock resistance can be enhanced, the trouble such as cracks and the like are hardly generated, a large capacitance is obtained easily, and an unsatisfactory quality factor and the like hardly take place.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a multilayer ceramic capacitor using a sintered body obtained by integrally firing a dielectric ceramic layer with a plurality of internal electrodes interposed therebetween, and in particular, , relates to a multilayer ceramic capacitor with excellent thermal shock resistance.

[Conventional technology]

In response to the demand for smaller size and higher capacity, multilayer ceramic capacitors have become smaller and smaller in recent years.
Extremely small ones of about mm x 0.8 mm x 0.5 mm have also appeared.

Such small multilayer ceramic capacitors are used in hybrid ICs or as chip components that are directly attached to printed circuit boards.

As demand for small-sized multilayer ceramic capacitors such as those mentioned above increases, automatic insertion methods are becoming more sophisticated. In order to increase the efficiency of automatic insertion, soldering temperatures are currently becoming higher, and temperatures up to 400°
It is no longer rare for soldering to occur at temperatures exceeding ℃.

On the other hand, ceramic materials inherently have excellent thermal shock resistance. However, multilayer ceramic capacitors are constructed using a sintered body obtained by integrally firing dielectric ceramic layers with internal electrodes interposed therebetween. In such a ceramic-metal composite material, the thermal conductivity of the ceramic dielectric layer is lower than that of the internal electrode, so a temperature difference occurs between the dielectric ceramic layer and the internal electrode during soldering.

As a result, tensile stress is applied to the dielectric ceramic layer, which has a low thermal conductivity, and cracks tend to occur at the contact interface between the dielectric ceramic layer and the internal electrode. Generally, this crack is caused by the internal electrode and
This was more likely to occur in areas that were in contact with the outer dielectric ceramic layer than with the outermost inner electrode.

As a method for preventing the above-described rank from occurring, no such method has been proposed in the past for multilayer ceramic capacitors. Slightly, in Special Publication No. 1-13205, Mgz Ti 04 Ca
In a multilayer capacitor made of T i 03 material,
MgzTiO in the dielectric ceramic layer located outside the inner electrode in the outermost layer.

The only structure proposed is a structure in which the mixing ratio of CaT i O2 and the mixing ratio of the dielectric ceramic layer sandwiched between the internal electrodes is different.

[Technical problem to be solved by the invention] However,
In the structure disclosed in Japanese Patent Publication No. 1-13205, M
Since the dielectric constant of the gz TiCL-CaTi03-based material is low, there is a problem in that it is disadvantageous in obtaining a large-capacity capacitor.

Furthermore, it is known that the firing temperature is high, the plating resistance of MgzTiO4 is insufficient, and there are problems such as Q defects.

Therefore, an object of the present invention is to provide a multilayer ceramic capacitor that not only has excellent thermal shock resistance, but also has excellent reliability, which can easily be increased in capacity, and is unlikely to cause Q defects.

[Means for solving technical problems]

As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present application used a B a T i O3 ceramic material with a high dielectric constant, and further developed a dielectric material on the inner side sandwiched between adjacent internal electrodes. The above problem is achieved by making the composition of the ceramic layer different from the composition of the dielectric ceramic layer on the outer surface side located outside the outermost internal electrode and selecting a specific composition. The present inventors have discovered that the present invention can be obtained.

That is, the present invention provides a multilayer ceramic capacitor in which a plurality of internal electrodes are arranged in a sintered body made of dielectric ceramic so as to overlap each other with dielectric ceramic layers interposed therebetween. The ceramic layer contains BaTi0sCeO2 and ZrO□ at 100-xy1%Xl and 71 mol%, respectively, and has a composition in which the relationships 6〉y1≧X, 〉0 are established between Xl and y. On the other hand, the dielectric ceramic layer on the outer surface side of the outermost inner electrode among the overlapping inner electrodes contains BaTiO3, CeO□, and ZrO, respectively, at 100-x.

-y2, x2, It is characterized by a composition different from that of the dielectric ceramic layer on the surface side.

The multilayer ceramic capacitor of the present invention has a dielectric constant of B
Since it is made of aTi○3-based ceramic material, it is suitable for producing smaller, larger-capacity multilayer ceramic capacitors.

The composition of the dielectric ceramic layer on the inner side and the composition of the dielectric ceramic layer on the outer surface side are different as described above and are selected to have a specific composition, so the thermal shock resistance is improved. is enhanced. That is, in the present invention, Cc, 2 and Z r in each dielectric ceramic layer
By varying the blending ratio of O2 as described above and selecting a specific composition, thermal shock resistance is enhanced, especially for the internal electrodes and the dielectric material located outside the outermost internal electrode. The generation of cracks due to heat between the ceramic layer and the ceramic layer is effectively prevented.

In the present invention, in the composition including the inner dielectric ceramic layer, the blending ratio of CeO□ and ZrO2 is
and y8 mol% and are blended so that the above relationship is established for the following reason. That is, as will be clear from the examples described later, in the inner dielectric ceramic layer, ZrO is the same as CeO□, or
This is because by containing more than □, the heat resistance 1i impact resistance is improved. However, the content of ZrCh is 6
If the amount exceeds mol%, the effect of improving thermal shock resistance cannot be obtained, and furthermore, in terms of electrical properties, the capacitance temperature change rate etc. are adversely affected, making it impractical, and sintering properties are also reduced. Therefore, the content of ZrO2 is set to be less than 6 mol%.

The blending ratio of CeO□ in the dielectric ceramic layer on the inner side is the same as the blending ratio of ZrO□ above, or
It will be less than the blending ratio of rO□. That is, y1≧
As long as x1 holds true, the blending ratio of CeO7 is arbitrary.

On the other hand, in the present invention, in the dielectric ceramic layer on the outer surface side, Ce0z is the same as ZrO, or
It is contained in a larger amount than rO□. That is, χ2≧y2. This means that CeO□ is the same as ZrO2 or Z
This is because thermal shock resistance can be improved by containing more than rO□.

However, the content of CeO□ mixed in the outer dielectric ceramic layer is less than 6 mol%. this is,
This is because if CeO□ is contained in an amount of 6 mol % or more, sinterability decreases and the effect of improving thermal shock resistance cannot be obtained. In addition, the content 5i y t of ZrO□ is CeO
It is optional as long as it is the same as the content 11xz of CeO2 or less than the content X2 of CeO.

-Japan- The material constituting the multilayer ceramic capacitor of the present invention is mainly composed of BaTiO3, and contains C in the above-mentioned specific proportion.
Any material may be used as long as it contains at least eOz and ZrO2, and therefore a sintering aid such as SiO□ may be further mixed therein.

〔Effect of the invention〕

In the present invention, the composition of the inner dielectric ceramic layer sandwiched between the internal electrodes is different from the composition of the outer dielectric ceramic layer, and the composition of each dielectric ceramic layer is set to the above-described specific composition. Since it contains CeO□ and ZrO2 in proportion, the thermal shock resistance can be effectively improved. Therefore, even if soldering is performed at a high temperature of over 400° C., accidents such as cranking are unlikely to occur.

Therefore, it can be efficiently and automatically inserted into a printed circuit board, etc., and the reliability of the electronic device in which it is incorporated can be improved.

〔Example〕

Hereinafter, non-limiting examples of the present invention will be described.

BaTi0. and at least Ce as a subcomponent.
A composition obtained by adding 0.1% by weight of MnO as a sintering aid to 100 parts by weight of a dielectric composition containing O□ and ZrO is thoroughly mixed, and a binder is added to prepare a slurry. After defoaming, a ceramic green sheet was formed by a doctor blade method.

A plurality of types of ceramic green sheets as described above were prepared with different amounts of CeO2 and ZrO□ added as subcomponents.

A conductive paste for forming internal electrodes is printed on one main surface of the prepared ceramic green sheet, and an appropriate number of ceramic green sheets printed with conductive paste and, if necessary, ceramic green sheets without conductive paste printed are laminated, The obtained laminate was pressed in the thickness direction and then fired to obtain the sintered body 2 shown in FIG. 1. Inside this sintered body 2, internal electrodes 3 to 7 are arranged so as to overlap with each other via internal dielectric ceramic layers 8 to 11. Reference numeral 12.13 indicates a dielectric ceramic layer on the outer surface side, that is, a dielectric ceramic layer located outside the outermost internal electrode 3.7. Also, 1, 11.
Reference numeral 15 indicates an external electrode mainly made of Ag, and reference numerals 16 and 17 indicate solder plating layers formed to improve solderability.

A plurality of types of multilayer ceramic capacitors having the structure shown in FIG. 1 were manufactured using the several types of ceramic green sheets described above as appropriate.

The multilayer ceramic capacitor 1 shown in FIG.
Thermal shock resistance of multilayer ceramic capacitors constructed using materials with varying amounts of Oz and ZrO2 was investigated. First, the contents of CeO□ and ZrO7 in the inner dielectric ceramic layers 8 to 11 sandwiched between the internal electrodes 3 to 7 were constant at 3 mol% each, and the composition of the outer surface side was changed. Mink capacitors were prepared and evaluated for thermal shock resistance. The results are shown in FIG. In FIG. 2, the horizontal axis shows the heat 11·i impact temperature ΔT, and the vertical axis shows the bending strength after heat +1i impact.

In addition, the characteristics (a) to (d) shown in FIG. 2 indicate that the dielectric ceramic layer 1.2.13 on the outer surface side is
On the other hand, the characteristics of each laminated ceramic capacitor composed of a composition in which CeC)z and ZrO2 are blended in the proportions shown in Table 1 below are shown.

As is clear from Table 1 and FIG. 2, when the multilayer ceramic capacitor of conventional product (a) is subjected to a thermal shock of 300° C. or higher, the strength deteriorates significantly as cracks develop.

On the other hand, (b) and (
It can be seen that in the multilayer ceramic capacitor C), there is almost no deterioration in strength even when subjected to a thermal shock of 500"C.

However, as shown in (d), when the blending ratio of CeC2 reaches 6 mol %, it can be seen that the heat gj impact resistance decreases again. This is because when CeO2 is contained in a large amount of 6 mol%, the sinterability is significantly reduced.

Although it is not clear from the results shown in FIG. 2, according to the inventor's experiments, it is possible to obtain the effect of the present invention when the amount of CeO7 added is smaller than the amount of ZrO2 added. could not.

Therefore, from the characteristics shown in FIGS. 2(a) to (d), the composition constituting the outer dielectric ceramic layer is as follows, when the content ratios of Ce0z and ZrO2 are set to X2 and y2 mol%, respectively. It can be seen that it is necessary to have a composition that satisfies the relationship: 6>χ2≧y2>0.

Next, the amounts of CeO□ and ZrO2 added in the dielectric ceramic layer on the outer surface side were changed to 4 mol% and 2 mol%, respectively.
Thermal shock resistance was studied when the contents of CeOz and ZrO in the inner dielectric ceramic layer sandwiched between the internal electrodes were varied. The results are shown in Figure 3. In No. 3, each characteristic indicated by (a) to (d) is as follows:
Table 2 shows the thermal shock resistance of each multilayer ceramic capacitor when the content of CeO2 and ZrO2 in the inner dielectric ceramic layer is as shown in Table 2 below.

As is clear from Table 2 and Figure 3, it can be seen that excellent thermal shock resistance can be achieved with the exception of the multilayer ceramic capacitor (a). In the multilayer ceramic capacitor (a),
Although 6 mol % of ZrO2 is added to the inner dielectric ceramic layer, the thermal shock resistance is insufficient. Not only that, but when 6 mol% of ZrO□ is added,
In terms of electrical properties, the capacitance temperature change rate, etc. deteriorates, making it impractical, and there is also the problem that sinterability deteriorates and it is impossible to obtain a dense sintered body.
Contrary to the proportions shown in the table, it has been confirmed that the effects of the present invention cannot be obtained when CeO□ is contained in a larger amount than ZrO2.

Therefore, from the characteristics shown in FIGS. 3(a) to 3(d), the composition of the inner dielectric ceramic layer is as follows: , 6>y+≧χ1>0.

From the above results, the dielectric ceramic N12 on the outer surface side.
In the inner dielectric ceramic layers 8 to 11, it is necessary that the CeO2 content 11x2 is the same as the ZrO2 content y2 or larger than the ZrO□ content y2. It is necessary that the content y1 is greater than the CeO□ content 1 or the ZrO2 content yl, and the composition of the inner dielectric ceramic layer is different from the composition of the outer dielectric ceramic layer. It turns out that this is necessary.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a multilayer ceramic capacitor to which the present invention is applied, and FIG. 2 is a diagram showing the deflection against thermal shock temperature when the contents of CeO2 and ZrO2 in the dielectric ceramic layer on the outer surface side are varied. Figure 3 shows the strength relationship between CeO□ and ZrO□ in the inner dielectric ceramic layer.
FIG. 3 is a diagram showing the relationship between bending strength and thermal shock temperature when the content is changed. In the figure, 1 is a multilayer ceramic capacitor, 2 is a sintered body, 3 to 7 are internal electrodes, 8 to 11 are inner dielectric ceramic layers, and 12 and 13 are outer surface dielectric ceramic layers.

Claims (1)

[Claims] A sintered body made of a dielectric ceramic mainly composed of BaTiO_3 and containing at least CeO_2 and ZrO_2 as subcomponents; In the multilayer ceramic capacitor, the inner dielectric ceramic layer sandwiched between the internal electrodes contains 100-x_1-y_1, x_1 and y_1 mol% of BaTiO_3, CeO_2 and ZrO_2, respectively, and x_1 and y_1, 6>y_1≧x_
The dielectric ceramic layer on the outer surface side, which is located outside the outermost internal electrode among the overlapping internal electrodes, is made of BaTiO_3.
, CeO_2 and ZrO_2 at 100-x
_2-y_2, contains x_2 and y_2 mol%, and is composed of a composition that satisfies the relationship 6>x_2≧y_2 between x_2 and y_2, and the composition of the inner dielectric ceramic layer and the outer surface side A multilayer ceramic capacitor characterized in that the composition of the dielectric ceramic layer is different from that of the dielectric ceramic layer.