JP2844287B2 - Manufacturing method of multilayer 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 method for manufacturing a multilayer capacitor, and more particularly to a method for manufacturing a multilayer capacitor using nickel as an internal electrode.

[0002]

2. Description of the Related Art Conventionally, a multilayer capacitor using nickel as an internal electrode is manufactured in the following manufacturing sequence.

[0003] First, a conductive paste containing nickel particles is printed on one surface of a plurality of long unsintered dielectric ceramic sheets to form a sheet-like conductive layer for internal electrodes using nickel as an internal electrode. After alternately stacking every other sheet in the longitudinal direction, pressing and crimping, cutting at the position where the conductive layer of the shifted sheet is exposed at the cut surface and at the position where the conductive layer of the unshifted sheet is exposed at the cut surface As a result, an unfired capacitor body made of laminated chip pieces is prepared. Next, the capacitor body is degreased at a temperature of 300 ° C. in the atmosphere, for example, and then fired at a temperature of 1150 to 1300 ° C. in a reducing atmosphere to prepare a capacitor body (baked). I do.

Subsequently, a conductive paste containing silver (Ag) particles is applied to an end surface of the capacitor body where the conductive layer is exposed and a peripheral edge portion connected to the end surface to form a conductive layer for an external electrode. It is baked at a temperature of 600 to 900 ° C. in the atmosphere to produce a multilayer capacitor. The external electrode of the multilayer capacitor thus formed is electrically connected to the internal electrode at the end face, and directly adheres to the end face and the peripheral edge of the capacitor body connected thereto.

As described above, in a multilayer capacitor using nickel for the internal electrode, firing is performed in a weakly reducing atmosphere in order to prevent oxidation of nickel. However, since the degreasing becomes insufficient in the above atmosphere, degreasing is performed by firing at a temperature of 300 ° C. in the air.

[0006] The capacitor bodies thus degreased are arranged in a plane on a zirconia setter and fired in a closed batch furnace. When the atmosphere in the furnace was measured at a temperature of 850 ° C., the partial pressure of O ₂ introduced into the furnace was 10 ⁻¹⁶ to 10 ⁻¹⁸ atm.
The mixing ratio of the mixed gas of H ₂ gas, N ₂ gas, CO gas, and CO ₂ gas is adjusted so that The firing profile performed in such an atmosphere is from room temperature to 1150-13.
The rate of temperature rise up to 50 ° C. is 100 ° C./hour, and after reaching the sintering temperature (maximum temperature), the temperature is maintained for 1 to 3 hours, and then the rate of temperature drop to room temperature is 200 ° C./hour.

[0007]

In the above-mentioned conventional production of a multilayer capacitor using nickel as an internal electrode, when an unfired capacitor body is degreased at a temperature of 300 ° C. in the air, it is then placed in a batch furnace. When firing in a reducing atmosphere with a large amount of the capacitor body, the degreasing tends to be insufficient, and as a result, the resulting multilayer capacitor has a problem that the sinterability is reduced and crack failure is likely to occur. In addition, since firing is performed in a reducing atmosphere, even when using a reduction-resistant material as the ceramic material of the capacitor body, the obtained multilayer capacitor tends to have oxygen defects, and as a result, insulation resistance deteriorates in a high temperature load test. Problem.

An object of the present invention is to provide a method for manufacturing a multilayer capacitor which solves such a problem and has high sinterability and which does not deteriorate in insulation resistance even when subjected to a high-temperature load test.

[0009]

According to a method of manufacturing a multilayer capacitor of the present invention, a plurality of unsintered ceramic sheets having a nickel conductive layer for an internal electrode formed thereon are laminated and pressed to form a laminated unsintered capacitor. After firing the element body, in a method of manufacturing a multilayer capacitor in which conductive layers for external electrodes are formed on both end surfaces of the capacitor element body and peripheral edges connected thereto, the firing when firing the unfired capacitor element is performed at a temperature. The process of raising the temperature up to 1000 ° C. is defined as a degreasing zone, the sintering process at the highest temperature thereafter is defined as a sintering zone, and the process of decreasing the temperature from the maximum temperature to room temperature is divided into an oxygen deficiency replenishment zone.
The degreasing zone has an atmosphere with an O ₂ partial pressure of 10 ⁻¹³ to 10 ⁻¹⁵ atm, the sintering zone has an atmosphere with an O ₂ partial pressure of 10 ⁻¹⁶ to 10 ⁻¹⁸ atm, and the oxygen defect replenishment zone has an O ₂ partial pressure of O _2. Partial pressure is 10
^The firing is performed in an atmosphere of ^-10 to 10 ^-13 atm.

[0010]

The firing process for firing an unfired capacitor body is divided into a degreasing zone, a sintering zone, and an oxygen defect replenishment zone. In each zone, firing is performed with an O ₂ partial pressure in a specific range of atmosphere. By doing so, it is possible to produce an excellent multilayer capacitor having no crack failure and less deterioration of insulation resistance in a high-temperature load test. At that time, the O ₂ partial pressure in the degreasing zone was set to 10 ⁻¹³ to 10 ⁻¹⁵ atm. In this range, oxygen is sufficiently supplied, and degreasing proceeds quickly. If the O ₂ partial pressure is too low in the degreasing zone, the replenishment of oxygen becomes insufficient and the degreasing tends to be delayed, and if the O ₂ partial pressure is too high, the internal electrodes will oxidize and expand. It is. The reason why the O ₂ partial pressure is set to 10 ⁻¹⁶ to 10 ⁻¹⁸ atm in the sintering zone is that in this range, the ceramic can be sintered without oxidizing the Ni internal electrode. If the O ₂ partial pressure in the sintering zone is lower than the above range, oxygen vacancies increase, insulation resistance deteriorates, and
This is because if the O ₂ partial pressure is too high, the Ni internal electrode will undergo oxidative expansion and cracks will occur. The reason that the O ₂ partial pressure is set to 10 ⁻¹⁰ to 10 ⁻¹³ atm in the oxygen defect replenishment zone is that oxygen is sufficiently supplied in this range, so that oxygen defects generated at the time of firing can be compensated. Not compensate reliably oxygen defects of the capacitor body when the O ₂ partial pressure in the oxygen defects replenishment zone is too low than the range replenishment of oxygen becomes poor, and when the O ₂ partial pressure is too high than the above range internal This is because the electrode expands with oxygen. Incidentally, the raised an O ₂ partial pressure compared to debinding zone with an oxygen deficiency supplementation zone because less oxidation effect of nickel of the internal electrodes.

[0011]

EXAMPLES Specific examples of the present invention will be described together with comparative examples.

First, as a dielectric material for a capacitor, a slurry was prepared by adding an appropriate amount of a binder to the composition shown in the embodiment proposed by the present applicant in Japanese Patent Publication No. 60-20851, and having a thickness of 18 μm. A green sheet made of an unfired dielectric ceramic material is prepared and has a purity of 98.
An internal electrode paste prepared by kneading 0% nickel (Ni) powder, a ceramic material, and a binder was prepared.

Next, an internal electrode paste is printed on a green sheet (unfired dielectric ceramic material) according to a conventional method to form an unfired ceramic sheet, and 50 layers of the unfired ceramic sheet are sequentially formed according to the conventional method. After laminating, 5 layers of the green sheet (unfired dielectric ceramic material) are laminated as a cover sheet on each of the upper and lower sides of the laminate, and then cut into a size of 3.2 mm × 1.6 mm to form a laminate of chip pieces. The unfired capacitor element was prepared.
Subsequently, the unfired capacitor body is placed in the air at a temperature of 30 ° C.
A sample capacitor was prepared by holding at 0 ° C. for 15 hours to perform a degreasing process.

The thus prepared sample capacitors were arranged in a plane on a zirconia setter, and fired in a closed batch furnace to obtain a capacitor body (fired). The partial pressure of O ₂ in each zone when the firing process was performed on the sample capacitor was adjusted to be the partial pressure shown in Table 1.

The firing profile in the batch furnace was as follows. The rate of temperature rise in the degreasing zone from normal temperature to 1000 ° C. was 100 ° C./hour, and O ₂
The partial pressure was 10 ^-13 to 10 ^-15 atm in the examples of the present invention, and the comparative examples were out of the above range or 10 ^-16 atm, 10 ^-17 atm, 10
^-18 atm. The heating rate in the sintering zone from a temperature of 1000 ° C. to a temperature of 1150 to 1350 ° C. is 100 ° C./hour,
The O ₂ partial pressure in the atmosphere of the zone is 10 ^{−16 in the} embodiment of the present invention.
^-10 atm to ^10-18 atm.
^-16 atm, 10 ^-17 atm, or 10 ^-18 atm. The temperature drop rate in the oxygen deficiency replenishment zone from the sintering temperature (1150-1350 ° C.) to room temperature was 200 ° C./hour, and the O ₂ partial pressure in the atmosphere in the zone was 10 ⁻¹⁰ to 10 ^{−13 in the} examples of the present invention. atm, and Comparative Examples were out of the above range or 10 ^-16 atm, 10 ^-17 atm, or 10 ^-18 atm.

Incidentally, the O ₂ partial pressure in each zone is determined by using a zirconia sensor set in a furnace at a temperature of 850 ° C.
The amount of O ₂ in the mixed gas introduced into the furnace was measured, and this value was defined as the O ₂ partial pressure. Adjustment of the O ₂ partial pressure in each zone is performed by mixing a nitrogen gas (N ₂ ), a hydrogen gas (H ₂ ), a carbon monoxide gas (CO), and a carbon dioxide gas (CO ₂ ) introduced into the furnace. Was adjusted by adjusting the mixing ratio. The mixing ratio of these gases may be appropriately set depending on the ceramic material constituting the capacitor body, the amount of nickel serving as the conductive material for the internal electrode, and the sintering temperature. Generally, nitrogen gas is 95.0 to 99.9%: Hydrogen gas 0.1-4.0%
And carbon monoxide gas to be added is 250 to 1
About 0000 ppm, carbon dioxide gas is 200-500
It is about 0 ppm.

The thus obtained fired capacitor body has an exposed end surface of the conductive layer and a peripheral edge portion connected to the end surface, which is coated with nickel (Ni) powder having a purity of 98.0%, a ceramic material, and a binder. After forming a conductive layer for external electrodes by applying a paste for external electrodes formed by kneading, the external electrodes are formed by baking at a temperature of 900 ° C. in a nitrogen atmosphere, and the partial pressure of O ₂ in each zone is various. Different multilayer capacitors were made.

FIG. 1 shows a multilayer capacitor produced by the above method. In the drawings, reference numeral 1 denotes a capacitor body having internal electrodes 3 laminated inside via ceramic layers 2 and alternately exposed to opposite end faces, and 4 denotes a peripheral edge of the capacitor body 1 connected to the end face and upper and lower covers. The external electrodes are formed continuously on the end face of the sheet 5.

Solder to each of the multilayer capacitors having different O ₂ partial pressures prepared by the above method, crack observation of each multilayer capacitor (100 samples), an impedance analyzer (Model 4278A) manufactured by Hewlett-Hackard Company. (20 samples), and a high-temperature load test (200 samples) was performed using a constant temperature bath (model BV-220) manufactured by TABAI and a constant voltage power supply manufactured by Tokyo Seiden Co., Ltd. In addition, the crack observation was performed by the metallographic observation. The measurement conditions of the impedance analyzer were a frequency of 1 kHz and a signal voltage of 1 V. In the high-temperature load test, a failure of 20 V 1 MΩ or less was examined for up to 1000 hours while applying 32 V at a temperature of 85 ° C. Table 1 shows the obtained results.

[0020]

[Table 1]

In the sample numbers shown in Table 1, the blanks indicate that the O ₂ partial pressure in each zone is within the scope of the present invention, and the asterisks indicate the O ₂ partial pressure in each zone. This is a capacitor body outside the scope of the present invention.

As is clear from Table 1, the multilayer capacitor obtained by firing within the range of the partial pressure of O ₂ in each zone of the present invention has no appearance cracks, and has a high insulation resistance even when subjected to a high-temperature load test. Capacitance without deterioration and satisfying as a multilayer capacitor (capacitance value is 1101 to 1220 nF)
It can be seen that this has On the other hand, a multilayer capacitor obtained by firing outside the O ₂ partial pressure range (indicated by * in Table 1) of each zone of the present invention, for example, sample numbers 1, 10, 26, and 32 in Table 1 above Etc., whether the capacitance as a multilayer capacitor is large or small, furthermore, cracks are generated, insulation resistance is deteriorated, or cracks are generated despite having a predetermined capacitance, In addition, it cannot withstand a high temperature load test and its insulation resistance deteriorates, which is not suitable for practical use.

[0023]

[Effect of the Invention] When according to the present invention as described above, divides the firing process of the capacitor element body degreasing zone, sintering zone, the oxygen defects replenishment zone, O ₂ during the firing of each zone
Since the partial pressure is controlled in a specific range, degreasing can be performed promptly, so that insufficient sintering due to residual C during firing can be compensated, and there is no crack.
In addition, it is possible to compensate for oxygen vacancies, and to produce a highly reliable multilayer capacitor without deterioration of insulation resistance even when a high-temperature load test is performed.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a multilayer capacitor manufactured according to an embodiment of the present invention;

[Explanation of symbols]

1 capacitor body, 3 internal electrode, 4
External electrodes.

Claims (1)

(57) [Claims] An unfired ceramic sheet on which a nickel conductive layer for an internal electrode is formed is laminated and pressed, and a laminated unfired capacitor element is fired. In a method for manufacturing a multilayer capacitor in which a conductive layer for an external electrode is formed on a peripheral edge portion connected thereto, the firing when firing the unfired capacitor element is performed by raising the temperature up to 1000 ° C. as a degreasing zone, and thereafter. The sintering process at the highest temperature is the sintering zone, and the cooling process from the highest temperature to the normal temperature is divided into the oxygen deficiency replenishment zone,
The degreasing zone has an atmosphere with an O ₂ partial pressure of 10 ⁻¹³ to 10 ⁻¹⁵ atm, the sintering zone has an atmosphere with an O ₂ partial pressure of 10 ⁻¹⁶ to 10 ⁻¹⁸ atm, and the oxygen defect replenishment zone has an O ₂ partial pressure of O _2. Partial pressure is 10
^A method for manufacturing a multilayer capacitor, comprising firing in an atmosphere of ^-10 to 10 ^-13 atm.