JPH06196352A - Manufacture of layered capacitor - Google Patents

Abstract

PURPOSE:To realize a layered capacitor having satisfactory sintering properties, no deterioration of an insulating resistance and high reliability by dividing baking step into a degreasing zone, a sintering zone and an oxygen lack supplementing zone, specifying O2 partial pressures in the respective zones, and baking it. CONSTITUTION:After paste for an internal electrode 3 is printed on a green sheet 2 to form an unbaked ceramic sheet, they are sequentially laminated, and a green sheet is laminated on and underneath the laminate as a cover sheet 5. Baking of the case of baking an unbaked capacitor material 1 is partitioned as a temperature rising step up to 1000 deg.C, a baking step from the temperature to a highest temperature is partitioned as a sintering zone, and a temperature falling step from the highest temperature to the ambient temperature is partitioned to an oxygen lack supplementing zone. The degreasing zone is set with an atmosphere in which O2 partial pressure is 10<-13>-10<-15>atm, the sintering zone is set with an atmosphere in which O2 partial pressure is 10<-16>-10<-18>atm, and the supplementing zone is set with an atmosphere in which O2 partial pressure is 10<-10>-10<-13>atom.

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 by the following manufacturing sequence.

First, a conductive paste containing nickel particles is printed on one surface of a plurality of long unfired dielectric ceramic sheets to form a sheet-shaped conductive layer for internal electrodes using nickel as an internal electrode. After stacking every other sheet by shifting in the longitudinal direction, press-bonding and cutting at the position where the conductive layer of the shifted sheet is exposed on the cut surface and the position where the conductive layer of the non-shifted sheet is exposed on the cut surface. Then, an unfired capacitor element body composed of laminated chip pieces is prepared. Next, after degreasing the capacitor element body in the air at a temperature of 300 ° C., for example, the capacitor element body is subsequently fired in a reducing atmosphere at a temperature of 1150 to 1300 ° C. to form a capacitor element body (fired). To do.

Then, a conductive paste containing silver (Ag) particles is applied to the exposed end surface of the capacitor body and the peripheral edge portion continuing to the exposed end surface to form a conductive layer for external electrodes. A laminated capacitor is prepared by baking at a temperature of 600 to 900 ° C. in the atmosphere. The outer electrode of the multilayer capacitor thus manufactured is electrically connected to the inner electrode at the end face, and is directly adhered to the end face and the peripheral edge portion of the capacitor body connected to this end face.

As described above, in the multilayer capacitor in which nickel is used for the internal electrodes, the nickel is not oxidized so that it is fired in a weakly reducing atmosphere. However, since degreasing is insufficient in the atmosphere, the degreasing is performed by firing in air at a temperature of 300 ° C.

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 temperatures of 1150 to 13
The temperature rising rate up to 50 ° C. is 100 ° C./hour, the temperature is maintained for 1 to 3 hours after reaching the sintering temperature (maximum temperature), and then the temperature decreasing rate up to normal temperature is 200 ° C./hour.

[0007]

When the unbaked capacitor element body was degreased at a temperature of 300 ° C. in the atmosphere in the manufacture of the above-mentioned conventional multilayer capacitor using nickel as an internal electrode, it is then placed in a batch furnace. If a large amount of the capacitor element body is put in and fired in a reducing atmosphere, degreasing tends to be insufficient, and as a result, the sinterability of the obtained multilayer capacitor is deteriorated and crack defects are likely to occur. In addition, since firing is performed in a reducing atmosphere, even if a reduction resistant material is used for the ceramic material of the capacitor body, oxygen defects are likely to occur in the obtained multilayer capacitor, and as a result, the insulation resistance deteriorates in the high temperature load test. There is a problem that it ends up.

An object of the present invention is to solve the above problems and to provide a method of manufacturing a highly reliable multilayer capacitor which has good sinterability and does not deteriorate in insulation resistance even when subjected to a high temperature load test.

[0009]

A method of manufacturing a multilayer capacitor according to the present invention is a multilayer unbaked capacitor in which a plurality of unbaked ceramic sheets having a nickel conductive layer for an internal electrode are stacked and pressure-bonded. In the method for manufacturing a multilayer capacitor in which conductive layers for external electrodes are formed on both end faces of the capacitor element body and the peripheral edge portions continuing to the element element body after firing, the firing temperature when firing the unfired capacitor element body is The temperature increasing process 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 temperature decreasing process after the highest temperature to normal temperature is divided into an oxygen defect supplementing zone,
The degreasing zone had an O ₂ partial pressure of 10 ⁻¹³ to 10 ⁻¹⁵ atm, the sintering zone had an O ₂ partial pressure of 10 ⁻¹⁶ to 10 ⁻¹⁸ atm, and the oxygen defect supplementing zone had an O ₂ atmosphere. Partial pressure is 10
^The feature is that the firing is performed in an atmosphere of ^-10 to ^{-10 -13} atm.

[0010]

The firing process when firing an unfired capacitor element body is divided into a degreasing zone, a sintering zone, and an oxygen defect supplementing zone, and firing is performed with an O ₂ partial pressure in each zone as an atmosphere in a specific range. By doing so, it is possible to produce an excellent multilayer capacitor which is free from crack defects and whose insulation resistance is less deteriorated 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, because deoxidation proceeds quickly because oxygen is sufficiently supplied in this range. If the O ₂ partial pressure in the degreasing zone is lower than the above range, oxygen replenishment will be poor and degreasing will be delayed, and if the O ₂ partial pressure is higher than the above range, the internal electrodes will undergo oxidative expansion. Is. Further, the O ₂ partial pressure in the sintering zone is set to 10 ⁻¹⁶ to 10 ⁻¹⁸ atm, which makes it possible to sinter the ceramic without oxidizing the Ni internal electrode. If the O ₂ partial pressure in the sintering zone is too lower than the above range, oxygen defects become large and the insulation resistance deteriorates.
This is because if the O ₂ partial pressure is higher than the above range, the Ni internal electrode expands due to oxidation and cracks occur. Further, the O ₂ partial pressure in the oxygen defect replenishing zone is set to 10 ⁻¹⁰ to 10 ⁻¹³ atm so that oxygen is sufficiently supplied in this range so that oxygen defects generated during firing can be compensated. If the O ₂ partial pressure in the oxygen defect replenishing zone is too lower than the above range, the oxygen replenishment will be poor, and oxygen defects in the capacitor body cannot be reliably compensated. If the O ₂ partial pressure is too high, This is because the electrode expands with oxygen. The O ₂ partial pressure in the oxygen defect supplementing zone can be increased as compared with that in the degreasing zone because the effect of oxidation of nickel on the internal electrodes is small.

[0011]

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

First, as a dielectric material for a capacitor, an appropriate amount of a binder was added to the composition shown in the example proposed by the applicant in Japanese Patent Publication No. 60-20851 to prepare a slurry having a thickness of 18 μm. A green sheet made of an unfired dielectric ceramic material is prepared, and 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 the green sheet (unfired dielectric ceramic material) by a conventional method to prepare an unfired ceramic sheet, and then 50 layers of this unfired ceramic sheet are sequentially processed by the conventional method. After stacking, stacking 5 layers of the green sheet (unfired dielectric ceramic material) as a cover sheet on each of the upper and lower sides of the stack, cut into a size of 3.2 mm × 1.6 mm, and stacking chip pieces. A non-fired capacitor element body was prepared.
Then, the unfired capacitor element was placed in the atmosphere at a temperature of 30
A sample capacitor was prepared by performing a degreasing process by holding it at 0 ° C. for 15 hours.

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

The firing profile in the batch furnace was as follows. The temperature rising rate in the degreasing zone from room temperature to 1000 ° C. was 100 ° C./hour, and O _{2 in} the atmosphere of the zone was set.
The partial pressure is 10 ^-13 to 10 ^-15 atm in the embodiment of the present invention, and the comparative example is outside the above range or 10 ^-16 atm, 10 ^-17 atm, 10
^-18 atm. The temperature rising rate in the sintering zone from the temperature of 1000 ° C. to the 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} present embodiment.
10 ^-18 atm, and the comparative example is outside the above range or 10
^-16 atm, 10 ^-17 atm, or 10 ^-18 atm. The temperature decreasing rate in the oxygen defect replenishing zone from the sintering temperature (1150 to 1350 ° C.) to room temperature is 200 ° C./hour, and the O ₂ partial pressure in the atmosphere of the zone is 10 ⁻¹⁰ to 10 ^{−13 in the} present embodiment. Atm, the comparative example was set to a value other than the above range or 10 ^-16 atm, 10 ^-17 atm, or 10 ^-18 atm.

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

Nickel (Ni) powder having a purity of 98.0%, a ceramic material, and a binder are provided on the end face where the conductive layer of the capacitor element body thus fired is exposed and the peripheral edge portion connected to the end face. After coating the external electrode paste prepared by kneading to form the external electrode conductive layer, the external electrode is formed by baking at a temperature of 900 ° C. in a nitrogen atmosphere, and the O ₂ partial pressure in each zone is varied. Different multilayer capacitors were created.

FIG. 1 shows a multilayer capacitor manufactured by the above method. In the drawings, reference numeral 1 denotes a capacitor element body internally laminated with ceramic layers 2 and having internal electrodes 3 exposed at alternately facing end surfaces. Reference numeral 4 denotes a peripheral edge portion of a capacitor element body 1 continuous to the end surface and an upper and lower covers. It is an external electrode continuously formed on the end surface of the sheet 5.

Soldering was performed on each of the laminated capacitors having different O ₂ partial pressures produced by the above method, and cracks were observed on each of the laminated capacitors (100 samples). An impedance analyzer (model 4278A) manufactured by Hewlett-Packard Company. The electrostatic capacity (20 samples) was measured by a thermostatic bath (model BV-220) manufactured by TABAI and a constant voltage power supply manufactured by Tokyo Seiden Co., Ltd., and a high temperature load test (200 samples) was performed. The cracks were observed with a metallographic microscope. The measurement conditions with the impedance analyzer were a frequency of 1 kHz and a signal voltage of 1V. Further, in the high temperature load test, a failure of 20 V1 MΩ or less up to 1000 hours was examined while loading 32 V at a temperature of 85 ° C. The results obtained are shown in Table 1.

[0020]

[Table 1]

In the sample numbers in Table 1, the unmarked O ₂ partial pressure in each zone is the capacitor element body within the scope of the present invention, and the marked * indicates the O ₂ partial pressure in each zone. It 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 O ₂ partial pressure range of 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 that does not deteriorate and is satisfactory as a multilayer capacitor (capacitance value: 1110 to 1220 nF)
It turns out that it has. On the other hand, a multilayer capacitor obtained by firing outside the O ₂ partial pressure range of each zone of the present invention (indicated by * in Table 1), for example, sample numbers 1, 10, 26, 32 in Table 1 above Etc. has a large or small electrostatic capacity as a multilayer capacitor, further cracking, deterioration of insulation resistance, or whether cracking occurs despite having a predetermined electrostatic capacity, In addition, it is not suitable for practical use because it cannot withstand a high temperature load test and its insulation resistance deteriorates.

[0023]

As described above, according to the present invention, the firing process of the capacitor element body is divided into a degreasing zone, a sintering zone, and an oxygen defect supplementing zone, and O ₂ during firing in each zone is divided.
Since the partial pressure is controlled within a specific range, degreasing can be performed quickly, and it is possible to compensate for the lack of sintering due to the residual C during firing, and there is no crack.
Further, oxygen defects can be compensated for, and even if a high temperature load test is performed, insulation resistance is not deteriorated and a highly reliable multilayer capacitor can be manufactured very easily.

[Brief description of drawings]

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

[Explanation of symbols]

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

Claims (1)

[Claims] 1. A laminated unfired capacitor element body obtained by laminating a plurality of unfired ceramic sheets having nickel conductive layers for internal electrodes formed thereon and press-bonding them together, In the method for manufacturing a multilayer capacitor in which a conductive layer for an external electrode is formed on a peripheral edge portion continuous with it, firing when firing an unfired capacitor element body is performed by using a heating process up to a temperature of 1000 ° C. as a degreasing zone, and thereafter. The sintering process at the highest temperature is used as the sintering zone, and the temperature decreasing process from the highest temperature to normal temperature is divided into the oxygen defect supplement zone,
The degreasing zone had an O ₂ partial pressure of 10 ⁻¹³ to 10 ⁻¹⁵ atm, the sintering zone had an O ₂ partial pressure of 10 ⁻¹⁶ to 10 ⁻¹⁸ atm, and the oxygen defect supplementing zone had an O ₂ atmosphere. Partial pressure is 10
^A method of manufacturing a multilayer capacitor, which comprises firing in an atmosphere of ^-10 to 10 ^-13 atm.