JP2716342B2 - Chip type multilayer ceramic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip type multilayer ceramic capacitor, and more particularly to a structure for preventing cracks.

[0002]

2. Description of the Related Art As shown in FIG. 4 (a), a conventional chip-type multilayer ceramic capacitor comprises a plurality of dielectric sheets having conductive internal electrodes formed thereon such that internal electrode extraction portions are opposed to each other. After alternately laminating and laminating dielectric sheets to be protective layers on the upper and lower sides of the laminated ceramic element and integrating them, an external electrode 3 is provided on a surface of the obtained multilayer ceramic element 1 from which internal electrodes 2 facing each other are taken out. I was

Further, in order to reduce stress during mounting, the surface of the above-mentioned chip-type multilayer ceramic capacitor on which external electrodes are formed is covered with a metal cap-shaped member as shown in FIG.
A plurality of chip-type multilayer ceramic capacitors with metal caps and a dielectric sheet having conductive internal electrodes formed thereon as shown in JP-A-3-136308 are alternately arranged such that internal electrode extraction portions face each other. A chip-type multilayer ceramic capacitor is proposed in which a layer having a different coefficient of thermal expansion is provided outside of a laminated ceramic element in which a dielectric sheet serving as a protective layer is laminated above and below the laminated ceramic element, and the laminated ceramic element is integrally fired. It had been.

[0004]

The conventional chip-type multilayer ceramic capacitor has a difference in the coefficient of thermal expansion between the substrate and the ceramic material when it is fixed to the substrate by mounting or when subjected to a rapid temperature change while being fixed. This causes thermal stress near the interface between the external electrode and the multilayer ceramic element.However, unlike a metal material, a ceramic material hardly relieves stress due to elasticity and the like, and tends to cause brittle fracture due to stress concentration. When the stress is concentrated near the interface between the external electrode and the multilayer ceramic element and exceeds the critical fracture stress, cracks occur and the insulation resistance is deteriorated.

Further, the conventional chip-type multilayer ceramic capacitor with a metal cap has a problem that the operation of attaching the metal cap is difficult to be automated and the metal cap itself is expensive. Also, a plurality of dielectric sheets on which conductive internal electrodes are adhered and formed as disclosed in JP-A-3-136308 are alternately laminated such that the internal electrode take-out portions are opposed to each other. In a chip-type multilayer ceramic capacitor in which layers with different coefficients of thermal expansion are provided outside the multilayer ceramic element obtained by laminating body sheets and integrated, the different ceramic materials with different coefficients of thermal expansion are integrally fired. Therefore, delamination called delamination is likely to occur during the firing. In addition, the laminated structure with the same coefficient of thermal expansion makes the critical fracture stress higher than that of the above-mentioned conventional chip-type multilayer ceramic capacitors, but since it is integrally fired, cracks will occur if the critical fracture stress is exceeded, and the insulation resistance will be inferior. There was a problem.

[0006]

According to the present invention, there is provided a chip-type multilayer ceramic capacitor in which a plurality of dielectric sheets having conductive internal electrodes formed thereon are alternately laminated such that internal electrode extraction portions face each other. In a chip-type multilayer ceramic capacitor in which external electrodes are provided on opposing internal electrode extraction surfaces of a laminated ceramic element in which a dielectric sheet serving as a protective layer is laminated and integrated on the top and bottom, at least a thin plate is mounted on the mounting surface side It has a structure characterized by being stacked and held.

[0007] As the lap protection means, it is preferable to use the above-mentioned structure in which a part of the external electrode is shared and held, or the structure is held by an adhesive.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a chip type multilayer ceramic capacitor according to an embodiment of the present invention. FIG. 2 shows FIG.
FIG.

Hereinafter, a manufacturing method will be described.

A slurry obtained by mixing a dielectric ceramic powder having a chemical formula of ABO3 (A and B are metal elements and O is oxygen) and having a perovskite crystal structure with an organic binder is formed by a tape casting method. An internal electrode 2 made of silver / palladium is formed on the formed and dried dielectric sheet, and the internal electrodes 2 are stacked so that their take-out portions face each other. Further, a dielectric sheet serving as a protective layer is laminated and integrated above and below. Then, after performing the thermocompression bonding and the binder removal, the multilayer ceramic element 1 is obtained by sintering. Next, a heat-resistant thin plate 9 made of the same ceramic material as the above-mentioned dielectric ceramic is disposed on the lower surface or both surfaces thereof, and the external electrodes 3 mainly composed of silver are formed on the surface from which the internal electrodes 2 are taken out. Obtain a ceramic capacitor. The chip-type multilayer ceramic capacitor thus obtained is affected by a sudden temperature change when or when the conventional chip-type multilayer ceramic capacitor is fixed to the substrate 7 by mounting as shown in FIG. In addition, since the coefficient of thermal expansion of the ceramic material is one order of magnitude smaller than that of the substrate material and the external electrode 3, a crack 10 generated by thermal stress generated between the external electrode 3 and the multilayer ceramic element causes a gap between the multilayer ceramic element 1 and the thin plate 9. 11 can be escaped.
By preventing the crack 10 from entering the inside of the multilayer ceramic element 1, the insulation resistance of the multilayer ceramic capacitor can be prevented from being deteriorated.

This effect is supported, in particular, by temperature cycling tests. Table 1 shows a comparison of the life characteristics in the temperature cycle test between this embodiment and a conventional chip-type multilayer ceramic capacitor. Test conditions (JIS C
5102) is shown below.

Minimum operating temperature: −55 ° C. Maximum operating temperature: 125 ° C. Number of cycles: 1000 times Failure criterion: Degradation of two or more digits from the initial value of insulation resistance Number of samples: 100 Board material: Aluminum

[0014]

[Table 1]

As is clear from the above description, by providing the gap 11 without the thin plate being in close contact with the capacitor body, a chip-type multilayer ceramic capacitor having excellent ability with respect to the temperature cycle can be obtained.

Embodiment 2 shown in FIG. 3 is a second embodiment of the present invention, in which a thin plate 9 of ceramic, plastic or the like is fixed with an adhesive 6. The chip-type multilayer ceramic capacitor of the present embodiment shows the same value as that of the first embodiment in the life characteristics in the temperature cycle test.

[0017]

As described above, the present invention has a structure in which thin plates are provided in a chip-type multilayer ceramic capacitor without being closely attached to each other, so that a conventional chip-type multilayer ceramic capacitor is fixed to a substrate by mounting. When it is affected by a sudden temperature change in the fixed state, the thermal expansion of the ceramic material is smaller than that of the substrate material and the external electrode by one order of magnitude, so that the thermal expansion occurs between the external electrode and the multilayer ceramic element. The thin plate is provided to prevent the deterioration of the insulation resistance due to the cracks and to prevent the cracks from escaping into the gap 11 to prevent the deterioration of the insulation resistance.

If the material of the thin plate is the same as the ceramic material of the multilayer ceramic capacitor body,
This is preferable in that a large cost increase is suppressed. From the viewpoint of preventing cracks, a material having a thermal expansion coefficient intermediate between that of the mounting substrate and the capacitor body is preferable.

Further, the present invention has an effect that a conventional chip-type multilayer ceramic capacitor manufacturing line can be effectively used as it is and an inexpensive multilayer ceramic capacitor can be supplied.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is a sectional view of FIG.

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4A is a cross-sectional view of a conventional chip-type multilayer ceramic capacitor. (B) is a sectional view of a conventional multilayer ceramic capacitor with a metal cap.

FIG. 5 is a cross-sectional view of a conventional chip-type multilayer ceramic capacitor mounted on a substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multilayer ceramic element 2 Internal electrode 3 External electrode 4 Conductive adhesive 5 Metal cap 6 Adhesive 7 Substrate 8 Solder 9 Thin plate 10 Crack 11 Gap

Claims (3)

(57) [Claims] 1. A plurality of dielectric sheets on which conductive internal electrodes are adhered and formed are alternately laminated such that internal electrode take-out portions are opposed to each other, and dielectric sheets serving as protective layers are laminated on and under the dielectric sheets. in facing the chip-type monolithic ceramic capacitor formed by providing an external electrode to the internal electrode extraction surface of the integral laminated ceramic device, are held stacked without contact sheet is to at least the mounting surface side, the
The thickness of the thin plate is the thickness of the multilayer ceramic element in the stacking direction.
The thinner plate and the length of the thin plate
The external electrode is the same as the length of the
The chip-type multilayer ceramic capacitor is also provided at both ends of the chip. 2. The chip-type multilayer ceramic capacitor according to claim 1, wherein the chip-type multilayer ceramic capacitor and the thin plate have a structure held by a part of the external electrode. 3. The chip-type multilayer ceramic capacitor according to claim 1, wherein said chip-type multilayer ceramic capacitor and said thin plate have a structure held by an adhesive.