JPH08236386A - Laminated ceramic capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE: To enhance a laminated ceramic capacitor in mechanical strength by a method wherein a residual compressive stress acting on a ceramic crystal and calculated through an X-ray residual stress measurement method is specified. CONSTITUTION: Dielectric layers and inner electrodes of Pd or Pd-Ag are alternately laminated into a laminate of integral structure, and the laminate is burned in an oxidizing atmosphere. The burned laminate is worked into a burned body of prescribed shape, and the burned body of prescribed shape is thermally treated at a temperature above 600 deg.C but below a sintering temperature in an oxidizing atmosphere. After a thermal treatment, a terminal electrode is provided on each of the ends of the burned body for the formation of a laminated ceramic capacitor. At this point, a residual compressive stress acting on a ceramic crystal and calculated by an X-ray residual compressive measurement method is set below 50MPa. By this setup, a laminated ceramic capacitor excellent in flexural strength can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic ceramic capacitor and a method of manufacturing the same, and particularly as an on-vehicle capacitor used under severe conditions, a highly reliable monolithic ceramic capacitor having excellent mechanical strength and a method of manufacturing the same. Related to the improvement of.

[0002]

2. Description of the Related Art In recent years, chip type monolithic ceramic capacitors have been used in large quantities as electronic parts.
In such a laminated ceramic capacitor, dielectric layers made of barium titanate, neodymium titanate or the like and internal electrode layers made of palladium-silver, nickel or the like are alternately laminated. In some cases, dielectric layers are formed above and below the laminated body. A protective layer of the same quality as that of (1) and (2) is adhered and laminated to form a single layer, which is then fired at a predetermined temperature for densification to produce a capacitor porcelain, and then terminal electrodes are baked on both ends of the porcelain.

Further, the fired porcelain may be processed before forming the terminal electrodes. For example, the end faces forming the terminal electrodes are polished, or the porcelain is barrel-polished to smooth the corners of the porcelain.
Incidentally, the polishing of the above-mentioned corners is for preventing chipping during handling in the subsequent steps.

On the other hand, as a ceramic capacitor, an on-vehicle capacitor used outdoors, for example, is directly affected by the temperature due to seasonal changes and is exposed to low or high temperatures in the vehicle, so that it is repeated from low temperature to high temperature. It is necessary to have durability against thermal shock, and for that purpose, high strength is required.

[0005]

However, the dielectric porcelain used in the conventional capacitor has a strength of 200 MPa or less and a fracture toughness value of 1 MPa · m ^1/2, which is as small as that of glass, and the production of the capacitor is therefore difficult. Microcracks are likely to occur in the material during the process, and in particular, when the fired product is processed as described above, the cracks are inevitable. In addition, the strength of these microcracks decreases, and in particular, they do not have sufficient strength to withstand repeated thermal shock from low temperature to high temperature, such as in automobiles. As a capacitor used under severe conditions, its reliability was extremely low.

As a countermeasure against such generation of microcracks, according to Japanese Patent Application Laid-Open No. 3-235314, the laminated compacts are once calcined, then barrel-polished and processed, and then the calcining temperature is higher than the calcining temperature. It has also been proposed to repair microcracks and the like generated during processing by firing at a high temperature to densify.

However, according to this method, many microcracks are introduced in the barrel mill (polishing) because the density and strength of the ceramics are insufficient after the calcination, and the crack tips are not formed even in the subsequent firing. Although it was annealed, there was a problem that large cracks remained.

[0008]

The inventors of the present invention have made earnest studies from the viewpoint of improving the mechanical strength of a monolithic ceramic capacitor. As a result, the compressive residual stress acting on the ceramic crystal of the dielectric layer is As a result of measurement by line residual stress measurement, it was found that a mechanical strength of the monolithic ceramic capacitor can be greatly improved when it is 50 MPa or less, and the present invention has been completed. In addition, in order to keep the compressive residual stress acting on the ceramic crystal that constitutes the capacitor to 50 MPa or less as a result of the X-ray residual stress measurement, the porcelain must be completely dense before processing. It was found that it is effective to heat the material at a predetermined temperature in an oxidizing atmosphere after processing, and the present invention has been completed.

That is, the monolithic ceramic capacitor of the present invention is a monolithic ceramic capacitor in which dielectric ceramic layers and internal electrode layers made of Pd or Pd-Ag are alternately laminated and terminal electrodes are provided at both ends. The compressive residual stress acting on the ceramic crystal calculated by X-ray residual stress measurement is 50 MPa or less.

The method of manufacturing a monolithic ceramic capacitor according to the present invention includes a plurality of dielectric layers and Pd or Pd-A.
The step of firing a formed body in which a plurality of internal electrode layers of g are alternately laminated and integrated in an oxidizing atmosphere, the step of processing the fired product into a predetermined shape, and the fired product after processing
The method is characterized by comprising a step of performing heat treatment in an oxidizing atmosphere at a temperature of not less than ° C and not more than a firing temperature, and a step of forming terminal electrodes at both ends of the fired product after the heat treatment.

The present invention will be described in detail below. In the present invention, P
In a laminated ceramic capacitor having an internal electrode layer made of d or Pd-Ag, the compressive residual stress acting on the ceramic crystal calculated by X-ray residual stress measurement needs to be 50 MPa or less. This is because the compressive residual stress acting on the ceramic crystal is 50 MPa.
If it is larger than the above value, the processing damage is large, the strength is lowered, and the reliability is poor. When the compressive residual stress is 20 MPa or less, almost no processing damage remains and the reliability is excellent, which is particularly desirable.

It is known that ceramics are generally more susceptible to processing damage than metals, and that when they are subjected to processing damage, residual stress acts on the porcelain surface. Further, the larger the processing failure is, the larger the residual compressive stress is, and similarly the strength is lowered. An X-ray residual stress measuring method is used as a measuring method of such a residual stress of ceramics. The X-ray residual stress measurement method utilizes that, when a force is applied to a material, the interatomic distance of the crystal expands or contracts in proportion to the magnitude of the stress within the elastic limit,
The stress is calculated by measuring the change in the crystal plane spacing d by the X-ray diffraction method. From the Bragg diffraction condition, the following is shown using the X-ray wavelength λ, the crystal plane spacing d, and the diffraction angle θ.

N · λ = 2d sin θ Therefore, the strain amount ε is shown as follows using the variation amount δd of the crystal plane spacing and the variation amount δθ of the diffraction angle.

Ε = δd / d = −cot θ · δθ That is, the amount of strain can be calculated from the amount of change δθ in the X-ray diffraction angle, and the angle ψ between the normal to the sample plane and the normal to the crystal plane can be changed. From the relationship between sin2ψ and 2θ, the residual stress σ is shown as follows.

Σ = E / (1 + ν) · δε (ψ) / δsin2ψ = −Ecotθ / 2 (1 + ν) · δ2θ / δsin2ψ Here, E and ν are Young's modulus and Poisson's ratio, respectively.

More specifically, in order to minimize the influence of the terminal electrode, a micropart X-ray stress measuring device has a collimator diameter of 1 mm and a parallel tilt method is used. The characteristic X-ray is an X-ray. A Cr-Kα ray having a small penetration depth of is used.

The dielectric layer of the monolithic ceramic capacitor according to the present invention is made of a known dielectric ceramic, for example, barium titanate (BaTi).
O ₃ ) type, lead type (PbZrTiO ₃ type, PbFeNb)
System, PbFe-based relaxor material system.

These dielectric layers are formed by adding a dispersant, a plasticizer, and a binder to the dielectric composition and mixing them, and then forming the mixture into a sheet by the doctor blade method, and then forming an inner layer made of palladium or palladium-silver. Apply the electrode paste to the surface of the sheet-shaped molded body, stack a predetermined number of this,
Further, a protective layer of the same quality as the dielectric layer is adhered to the upper and lower sides of this laminated body to produce a laminated molded body.

Then, after cutting this laminated molded body into a chip shape, the raw chips are heat-treated in an oxidizing atmosphere such as the air to thermally decompose the organic binder, and then fired at a predetermined temperature in the oxidizing atmosphere. To do. The firing is appropriately controlled depending on the type of dielectric ceramic used, but the conditions are set so that the internal electrodes can be fired simultaneously. The firing temperature is about 900 to 1400 ° C.

Next, the produced chip-shaped fired product is barrel-milled for a predetermined time using alumina abrasive grains or the like, and polished and finished until the corner portion of the chip has an R shape with a radius of about 50 to 150 μm.

Then, the burned material subjected to the polishing process is processed to 600
Heat treatment is performed in an oxidizing atmosphere at a temperature of ℃ or higher and lower than the firing temperature. The heat treatment temperature at this time was limited to the above range by 600
If less than ℃, because the cracks remain without annealing effect of cracks, the heat treatment temperature is higher than the firing temperature, the surface of the fired product is etched, causing surface roughness and causing grain growth of the crystal of the porcelain, and This is because the strength is lowered and the porcelain characteristics change. In particular, from 800 ° C or higher, the firing temperature is 20
A range up to 0 ° C. lower is preferred. Further, the reason why the atmosphere is limited to the oxidizing atmosphere is that the annealing effect of cracks is small in an inert gas such as nitrogen gas or argon gas, and the porcelain characteristics change in the reducing atmosphere. The oxidizing atmosphere has an oxygen partial pressure of 0.2 to 1.0.
A bar having a higher oxygen partial pressure than that in the atmosphere is most preferable.

[0022]

The durability of the monolithic ceramic capacitor under thermal shock due to repeated low temperature and high temperature is almost determined by the mechanical strength characteristics of the porcelain. Therefore, in order to increase the durability against thermal shock, it is necessary to increase the bending strength of the porcelain itself.

According to the present invention, a molded body of a laminated ceramic capacitor is fired in an oxidizing atmosphere and further polished, and then the fired product is subjected to 6-hour heating in an oxidizing atmosphere.
By heat-treating at a temperature of 00 ° C or higher and lower than the firing temperature, the microcracks generated in the manufacturing process and polishing process are annealed, and the compressive residual stress acting on the ceramic crystal by X-ray residual stress measurement is 50 MPa or less. Next to
As a result, the mechanical strength of the porcelain can be increased. As a result, the mechanical strength does not deteriorate even when thermal shock is applied due to repeated low temperature and high temperature, and it is possible to provide excellent reliability as a capacitor used under severe conditions including in-vehicle use. .

[0024]

Example A porcelain pot containing dielectric material powder containing barium titanate as a main component, niobium oxide (Nb ₂ O ₅ ) of 1.5 mol% and a mineralizer, alumina balls, water and a dispersant. And then rotated for 20 hours to obtain a slurry. An organic binder and a plasticizer were added to the obtained slurry and mixed, and a 25 μm thick dielectric green sheet was obtained by the doctor blade method.

On this green sheet, as an internal electrode, a palladium-silver paste having a ratio of palladium to silver of 9: 1 was printed, 30 layers of these were stacked, and further, a green layer on which silver-palladium paste was not printed was printed on the top and bottom of this laminate. Ten sheets were laminated as the protective layer. Then, these were thermocompression bonded and then cut into a predetermined size of a capacitor. This thermocompression-bonded molded product was placed on a zirconia plate and fired at 1300 ° C. in the atmosphere to finally obtain 3.2 ×.
A sintered body for a chip capacitor having a thickness of 1.6 mm and a thickness of about 1 mm was obtained. Barrel polishing was performed so that the corners of this sintered body had a width of 90 μm.

Then, the sintered body was heat-treated under the conditions shown in Table 1 in an oxidizing atmosphere having an oxygen partial pressure shown in Table 1. The compressive residual stress acting on the ceramic crystal after heat treatment was determined by X-ray residual stress measurement. X-ray residual stress measurement uses a micrometer X-ray stress measuring device with a collimator diameter of 1 mm and a parallel tilt method in order to minimize the influence of the terminal electrode. C with shallow penetration depth
The r-Kα ray was used.

Further, in order to clarify the heat treatment effect, J
According to ISR1601, a 3-point bending strength test with a lower span of 2 mm was performed. The measurement results are shown in Table 1.

[0028]

[Table 1]

According to the results shown in Table 1, the sample No. 1 not subjected to the heat treatment and the sample No. 1 having the heat treatment temperature of less than 600 ° C.
2. Furthermore, sample No. 1 whose heat treatment temperature is equal to firing temperature
In No. 3, the residual compressive stress of the ceramic particles was 56 MPa or more, and the bending strength was 190 MPa or less, which was low. In contrast to these comparative examples, all of the other samples according to the present invention have a residual compressive stress of ceramic particles of 50 MPa or less and a high bending strength of 240 MPa or more, and among them, those treated at 800 ° C to 1100 ° C. It is found that the ceramic particles have a residual compressive stress of 37 MPa or less and a high bending strength of 320 MPa or more, and have very good characteristics. Further, it can be seen that the higher the oxygen partial pressure than the samples No. 7 to 10, the higher the strength.

[0030]

As described in detail above, according to the present invention,
It is possible to obtain a monolithic ceramic capacitor excellent in transverse strength, and as a capacitor for use in a vehicle or the like to which a repeated thermal shock of low temperature and high temperature is given, for example,
As a capacitor for an electronic device mounted on an automobile, a construction machine for construction, etc., its reliability can be improved and the range of use of the capacitor can be further expanded.

Claims (2)

[Claims] 1. A dielectric ceramic layer and Pd or Pd-
A monolithic ceramic capacitor, which is formed by alternately laminating internal electrode layers made of Ag and has terminal electrodes at both ends, wherein a compressive residual stress acting on a ceramic crystal calculated by X-ray residual stress measurement is 50 MPa. A monolithic ceramic capacitor characterized in that: 2. A plurality of dielectric layers and Pd or Pd-Ag.
A plurality of internal electrode layers alternately laminated to form a body, which is integrally fired in an oxidizing atmosphere; a step of processing the fired product into a predetermined shape;
A method for manufacturing a monolithic ceramic capacitor comprising the steps of heat treatment in an oxidizing atmosphere lower than the firing temperature and the step of forming terminal electrodes on both ends of the fired article after the heat treatment.