JPH03220711A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To provide a large electric capacity per unit volume and to prevent a delamination, a crack during manufacturing steps by forming a protective layer which does not contribute to the capacity and an active layer which contributes to an electric capacity in a dielectric ceramic layer, and dividing the active layer into two or more layers by the protective layer having a thickness of 100mum or larger. CONSTITUTION:In a laminated ceramic capacity in which dielectric ceramic layers and inner electrodes are alternately laminated, protective layers 1, 3, 5 which do not contribute to an electric capacity and active layers 2, 4 which contribute to an electric capacity are formed in the ceramic layer, and the layers 2, 4 are divided into two or more parts by a plurality of the layers 3 each having 100mum of larger of thickness. In this case, stresses are alleviated by the layers 1, 5 in a state that the number of the inner electrodes is not so many, but many inner electrodes can be laminated as a whole. Thus, the capacity per unit volume can be increased; delamination, and crack during manufacturing steps are eliminated to enhance its reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multilayer ceramic capacitor, and particularly to a highly reliable multilayer ceramic capacitor.

[Conventional technology] In recent years, the demand for smaller and lighter equipment has increased, and as the density of electronic circuits and the density of electronic components mounted on circuit boards has increased, capacitors have also become smaller and have higher capacitance. .

In order to meet this requirement, it is effective to increase the dielectric constant of the dielectric material, improve the electrode effective area ratio, and make the dielectric layer thinner. Among these, thinning the dielectric layer, that is, shortening the distance between internal electrodes, can increase the number of internal electrode layers.
After all, it is most effective because the capacity per unit volume increases in inverse proportion to the square of the distance, and various attempts have been made to improve the green sheet production process, improve the equipment, and increase functionality.

[Problems to be Solved by the Invention] Figure 3 shows the structure of a typical multilayer ceramic chip capacitor, with Figure 3 (a) being a perspective view and Figure 3 (b) showing the connection of a pair of internal electrodes to the bottom surface of the element. A projection view, (C) a cross-sectional view in the length direction of the element, and (d) a cross-sectional view in the width direction of the element.

As shown in the figure, in the multilayer ceramic capacitor, dielectric ceramics 11 and internal electrodes 12 are alternately laminated on a lower protective layer 5, and an upper protective layer 1 is formed at the top. Each internal electrode 2a, 2b is an external electrode 10a, 10
b.

In order to shorten the distance between internal electrodes, it is necessary to reduce the thickness of the green sheet that becomes the dielectric ceramic 11. However, when the thickness of the green sheet becomes 2071 m or less, it is difficult to manufacture capacitors for devices with conventional structures due to the reasons described below. ,
Inconveniences such as peeling and cracking occur. That is,
The internal electrodes are formed by mixing noble metal powder such as silver palladium with an organic binder and an organic solvent to form paste 1 and screen printing on a green sheet. It is difficult to do so. Therefore, 50 to 100 such green sheets
When laminating, thermocompression bonding, or integrally bonding, the difference in thickness is accumulated between the part where the internal electrode is formed and the surrounding part where the internal electrode is not formed, and a large stress concentration occurs at the end of the internal electrode. . This stress concentration during thermal decomposition or sintering of the binder causes delamination and cracks.

Such a problem occurs when the thickness of the green sheet is so thin that the coating thickness of the internal electrode cannot be ignored relative to the thickness of the green sheet. Further, even in such a case, when the number of internal electrodes is small, such as 10 to 20, the stress described above is relaxed in the upper and lower protective layer portions, and the above-mentioned inconvenience does not occur.

In this case, the difference in thickness of 2 to 3 meters per green sea sheet is at most 20 to 60 legs for the entire element, and usually in the protective film part where there are more than 100 legs on one side and more than 200 legs in total on the top and bottom. This is because this difference in thickness is absorbed.

The present invention has been made in view of the conventional circumstances as described above, and has a short distance between internal electrodes and a large number of laminated layers, so it has a large capacity per unit volume and is free from defects such as delamination and tartar. The purpose is to provide a multilayer ceramic capacitor with excellent reliability.

[Means for Solving the Problems] The present invention provides a multilayer ceramic capacitor in which dielectric ceramic layers and internal electrodes are alternately laminated, in which the dielectric ceramic layers do not contribute to the capacitance and the protective layer contributes to the capacitance. A multilayer ceramic capacitor comprising an active layer, the active layer being divided into two or more parts by one or more protective layers having a thickness of 100 yen or more.

[Function] When a large number of green sheets with internal electrodes are laminated as a dielectric ceramic layer, stress is generated due to the difference in thickness between areas where internal electrodes are formed and areas where they are not formed, as described above. Concentration occurs, causing delamination and cracks.

In the present invention, the dielectric ceramic layer that forms the internal electrode and contributes to the capacitance, that is, the active layer, is divided into two or more parts with a thickness of 100/! A protective layer of m or more is provided. In this way, even if the number of internal electrodes is not so large, stress can be relaxed by the upper and lower protective layers, and a large number of internal electrodes can be laminated as a whole. Therefore, a highly reliable multilayer ceramic capacitor with a large capacitance per unit volume and no delamination or cracking during the manufacturing process can be obtained.

[Example] Examples of the present invention will be described in detail below.

Magnesium lead tungstate (Pb (11/2 to M)
Wl/2) 03), Nickel lead niobate (
Pb(N! 173 N b273 > 03 >
A pre-fired powder of a three-component dielectric material consisting of lead titanate (PbTi03) was mixed with an organic binder, an organic solvent, and an organic plasticizer to prepare a slurry. This slurry was coated on a polyester base film by a doctor blade method. A green sheet with a thickness of 15 mm was prepared by casting and drying.Then, it was peeled off from the polyester base film.
It was cut into a predetermined shape. A part of the obtained cut green sheet is coated with silver palladium paste 1 to 1 as an internal electrode material.
was screen printed with a thickness of 3 feet.

Using these green sheets, they were laminated in a predetermined number and order as shown in Table 1 and integrated by thermocompression bonding to produce a total of four types of molded bodies, two types of Examples and two types of Comparative Examples. Each of the obtained green sheet shaped bodies was cut into chip shapes using a dicing saw to obtain raw chips.

FIG. 1 is a cross-sectional view in the width direction of a raw chip for a multilayer ceramic capacitor according to an embodiment of the present invention manufactured in this manner. In the figure, FIG. 1(a) corresponds to Example 1,
The active layer is divided into an upper active layer 2 and a lower active layer 4, and an intermediate protective layer 3 is formed between them. Also, Figure 1 (
b) corresponds to Example 2, in which the active layer is divided into an upper active layer 2, an intermediate active layer 7, and a lower active layer 4, with intermediate protective layers 3a and 3b formed therebetween.

FIG. 2 shows a cross-sectional view in the width direction of a raw chip for a multilayer ceramic capacitor of a comparative example, which was also produced for comparison. Figure 2 (a) is Comparative Example 1, Figure 2 (b) is Comparative Example 2.
The case is shown below.

These raw chips were treated in air at 600° C. for 8 hours to thermally decompose and remove the organic binder, and the number of chips with delamination was counted by visual inspection. next,
The sintered chips obtained by firing in air at 950° C. for 1 hour were cut, and the inside was observed to determine the number of cracks. Table -
1 shows the observation results. In multilayer ceramic capacitors with a conventional structure, when the number of internal electrodes increases, there is a high probability that delamination and cracks will occur during the binder pyrolysis process or firing process, and if there is a crank inside, the withstand voltage will decrease. It is known that characteristic defects such as a decrease in resistance and short circuits occur during moisture resistance tests. In contrast, the structure of the present invention provides one or more thicknesses of 1
It can be seen that when a protective layer of 001IIn or more is provided between the active layers, the stress inside the laminate due to the cumulative thickness of the internal electrodes is effectively alleviated, and no delamination or cracks occur at all. .

(Margins below) [Effects of the Invention] As explained above, the multilayer ceramic capacitor of the present invention has a large capacitance per unit volume, and no delamination or cracks occur during the manufacturing process.
There are no manufacturing problems and high reliability can be expected.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view in the width direction of an example of a raw chip for a multilayer ceramic capacitor according to the present invention, FIG. 2 is a cross-sectional view in the width direction of an example of a raw chip for a multilayer ceramic capacitor manufactured for comparison, and FIG. A perspective view (a) of a typical multilayer ceramic chip capacitor, a projection view (b) of a pair of internal electrodes onto the bottom surface of the element, a longitudinal cross-sectional view (C), and a cross-sectional view (d) in the width direction are shown, respectively. 1... Upper protective layer 2... Upper active layer 3.3a
, 3b... Intermediate protective layer 4... Lower active layer 5... Lower protective layer 7...
Intermediate active layer 9...active layer 10a, 10b...
...External electrode 0 11...Dielectric ceramic 2a 2b...Internal electrode

Claims (1)

[Claims] (1) In a multilayer ceramic capacitor formed by alternately laminating dielectric ceramic layers and internal electrodes, the dielectric ceramic layer consists of a protective layer that does not contribute to capacitance and an active layer that contributes to capacitance, and the active layer A multilayer ceramic capacitor characterized by being divided into two or more parts by one or more protective layers having a thickness of 100 μm or more.