JPH0314219B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a method for manufacturing a ceramic capacitor,
In particular, the present invention relates to a method of manufacturing highly reliable ceramic capacitors that prevent deterioration of insulation resistance at high temperatures.

(Prior Art) In recent years, as electronic components have become smaller and lighter, ceramic capacitors have also been pursued to be smaller and lighter. In particular, with regard to ceramic capacitors, in parallel with the progress of miniaturization, studies are being conducted to increase the capacitance, and as a means of achieving this, attempts are being made to reduce the thickness of the capacitors.

The following improvements can be considered as means for making ceramic capacitors thinner.

A method of forming a thin dielectric ceramic layer using a vacuum thin film forming method such as a sputtering method, a vacuum evaporation method, an ion plating method, or a vapor phase evaporation method.

A method of making the dielectric ceramic layer as thin as possible by microcrystallizing the dielectric ceramic material.

A method of obtaining a grain boundary insulated dielectric ceramic layer by forming an insulating layer at the grain boundaries of a thin semiconductor ceramic layer.

Among the above methods, there is a method in which internal electrodes are formed between a plurality of dielectric ceramic layers to form a laminated ceramic capacitor to further increase the capacitance.

(Problems to be Solved by the Invention) However, after thinning the dielectric ceramic layer by the above method, electrodes for taking out the capacitance can be formed by sputtering, vacuum evaporation, ion plating, or vapor phase evaporation. When a ceramic capacitor is formed by the electroless plating method or the electroless plating method, various troubles occur. What is particularly noticeable is the deterioration of insulation resistance when used at high temperatures.

The biggest cause of this trouble is that the dielectric ceramic is made of metal oxide, and the electrodes are made of metal. That is, according to such a combination,
At the interface where the metal oxide constituting the dielectric ceramic and the metal constituting the electrode come into contact, it is thought that exchange of oxygen occurs as an inevitable phenomenon. This exchange of oxygen is difficult to recognize at room temperature, but as the temperature rises, exchange of oxygen begins to take place.

For example, if the dielectric ceramic is TiO ₂ and the electrode is
Taking a ceramic capacitor made of Cu as an example, at high temperature, for example 150℃,
TiO ₂ and Cu change as follows.

TiO ₂ reduced _{TiO 2} −x Cu oxidized CuO Of course, the insulation resistance (IR) changes significantly, and its value generally decreases by more than two orders of magnitude.

Such a reduction is particularly noticeable when the dielectric ceramic layer is made thinner, and applies to the ceramic capacitor obtained by the above-mentioned improvement means for making the ceramic capacitor thinner.

(Objective of the Invention) Therefore, an object of the present invention is to provide a highly reliable ceramic capacitor that does not cause changes in dielectric constant or deterioration of insulation resistance by having a structure that does not reduce the dielectric ceramic when used at high temperatures. With the goal.

(Structure of the Invention) That is, the present invention provides a method for manufacturing a ceramic capacitor in which an electrode for external connection is formed on the surface of a dielectric ceramic via a tin oxide layer, in which a tin oxide layer is formed by sputtering, ion plating, or vacuum evaporation. The electrodes for external connection are formed by sputtering method, vacuum evaporation method, ion plating method, vapor phase evaporation method,
This is a method for manufacturing a ceramic capacitor, characterized in that it is formed by any of the electroless plating methods.

Here, examples of dielectric ceramics include high dielectric constant ceramics such as barium titanate and strontium titanate, titanium oxide, magnesium titanate, magnesium oxide-titanium oxide, silicon oxide, etc. These include temperature-compensated ceramics, such as semiconductor ceramics, and grain-boundary insulated dielectric ceramics, in which the grain boundaries of semiconductor ceramics are made into insulators.

Further, when the thickness of the dielectric ceramic is 50 μm or less, the effect becomes more pronounced when a tin oxide layer is interposed between the dielectric ceramic and the external connection electrode. In other words, the thickness of the dielectric ceramic is
If the thickness exceeds 50 μm, even if the dielectric ceramic is reduced by the electrode during high-temperature use, the dielectric ceramic has a sufficient thickness, so changes in dielectric constant and deterioration in insulation resistance will not be noticeable. Therefore, the dielectric ceramic of the present invention having a thickness of 50 μm or less is particularly effective. However, there is no problem in applying the present invention to a dielectric ceramic having a thickness exceeding 50 μm, and it is optional to interpose a tin oxide layer between the dielectric ceramic and the external connection electrode.

As a method for forming the tin oxide layer, a thin film forming method such as a sputtering method, an ion plating method, a vacuum evaporation method, a vapor phase evaporation method, etc. is used. When forming a tin oxide layer by sputtering, for example, metal tin can be used as a target and the atmosphere during sputtering can be a mixed gas of argon and oxygen. In addition, when forming a tin oxide layer by vacuum evaporation method,
For example, a tin oxide layer can be formed by heating metallic tin or metallic tin powder and evaporating it in an oxygen-containing atmosphere. Furthermore, in the case of vapor phase deposition, after forming a tin layer, a tin oxide layer can be formed by thermal oxidation.

The thickness of this tin oxide layer is preferably 2 μm or less. This is because ESR increases when the thickness exceeds 2 μm.

The type of metal used for the external connection electrode is not particularly limited, and commonly used metals such as Ag, Au, Cr, Zr, V, Ni, Zn, Cu,
There are one type or a combination of two or more of Sn, Pb-Sn, Mn, Mo, W, Ti, Pd, Al, etc., and this external connection electrode may have a multilayer structure.
Examples include Cr-Cu and Cr-Ni-Ag.

Further, in the manufacturing method of the present invention, examples of structures of ceramic capacitors to be used include ceramic capacitors made of a single layer of dielectric ceramic, multilayer ceramic capacitors, and the like.
The present invention is also applicable to the case where the various ceramic capacitors described above are of the grain boundary insulation type.

(Example) Hereinafter, this invention will be explained in detail according to an example.

Example 1 Ceramic dielectric raw material powder having the following composition was prepared.

_Nd2Ti2O7 : 63 mol% _{, BaTiO3} : 14 mol _% ,
TiO ₂ : 23 mol% This raw material powder was mixed with polyvinyl alcohol as a binder, a surfactant, a dispersant, and water to prepare a slurry. Next, a ceramic green sheet with a thickness of 35 μm was prepared using this slurry by a doctor blade method.

This ceramic green sheet has a length of 7.0mm,
Cut into 5.0mm wide pieces and place on this sheet.
An Ag-Pd paste containing 70 wt% Ag and 30 wt% Pd was printed. Eleven ceramic green sheets with internal electrodes formed in this way were stacked so that the internal electrodes were exposed at the end faces of the stack. This laminate was fired in air at 1250°C to obtain a sintered unit.
The thickness of each dielectric layer of the obtained laminate was 20 μm.

Next, a tin oxide layer was first formed by sputtering on the end face of this laminated sintered unit where the internal electrodes were exposed.

This tin oxide layer was formed under the following conditions.

Sputtering atmosphere: Argon containing 10% oxygen Pressure: 2 x 10 ^-3 Torr Target: 5 inch diameter, 5 mm thick tin plate Voltage: 500 VD.C. Current: 2.0 A Sputtering time: 5 minutes Tin oxide layer film Thickness: 3500 Å Subsequently, a Ni layer as a solder heat-resistant layer was first formed by sputtering on the tin oxide layer as a first layer of external connection electrode.

This Ni layer was formed under the following conditions.

Sputtering atmosphere: Argon Pressure: 2×10 ^-3 Torr Target: Nickel plate with a diameter of 5 inches and a thickness of 2 mm Voltage: 480VD.C. Current: 2.0A Time: 15 minutes Film thickness: 5000Å Furthermore, a An Ag layer was formed by sputtering as a two-layer external connection electrode.
This Ag layer serves as a solderable layer.

The Ag layer was formed under the following conditions.

Sputtering atmosphere: Argon Pressure: 2×10 ^-3 Torr Target: 5 inches in diameter, 5 mm thick: Ag
Plate Voltage: 540VD.C. Current: 2.0A Time: 6 minutes Film thickness: 1 μm A high temperature accelerated load life test was conducted on the multilayer capacitor obtained through the above process under the following conditions.
In other words, this capacitor is installed in a temperature atmosphere of 150℃, and the voltage is 6 times the rated voltage (50V).
When 300V was applied and the insulation resistance (IR) was measured after 100 hours, it was 10 ¹¹ Ω. By the way, the initial value of the insulation resistance (IR) of this multilayer capacitor is 10 ¹¹ Ω.
It was hot. In addition, when installed in an atmosphere with a temperature of 45°C and a relative temperature of 95%, a rated voltage of 50V was applied, and the insulation resistance (IR) was measured after 500 hours, it was 10 ¹¹ Ω.
No change was observed compared to the initial value.

Comparative Example 1 The Ni layer serving as the external connection electrode of the first layer and the external connection of the second layer were formed under the same conditions as Example 1 without forming a tin oxide layer on the laminated sintered unit obtained in Example 1. A multilayer capacitor was fabricated by forming an Ag layer as an electrode.

When this multilayer capacitor was tested in the same manner as in Example 1, the insulation resistance (IR) decreased to 10 ⁹ Ω after 10 hours, and deteriorated to 10 ⁶ Ω after 25 hours.

Example 2 SrTiO ₃ : 99.3 mol%, Y ₂ O ₃ : 0.3 mol%,
Each component was weighed so that the composition was 0.2 mol% of SiO ₂ and 0.2 mol% of Al ₂ O ₃ , and 10% by weight of an organic binder was added to the weighed raw materials. Mixing and grinding were performed. After granulating this, it was molded at a pressure of 1000 kg/cm ² to obtain a disc-shaped molded product. This molded body was fired at 1350°C for 2 hours. Metal oxides such as Pb and Bi are applied to the surface of the resulting porcelain, and heat treatment is performed at a temperature of 1000 to 1200°C to transform the grain boundaries of the porcelain into insulators, creating a grain-boundary insulated semiconductor porcelain body. did.

Using this semiconductor ceramic body, a tin oxide layer, a first layer of external connection electrodes, and a second layer of external connection electrodes were formed on the surface of the semiconductor ceramic body in the same manner as in Example 1, and a grain boundary insulated semiconductor ceramic body was formed. Created a capacitor.

This capacitor was subjected to the high temperature accelerated load life test described in Example 1. As a result, while the initial value of insulation resistance (IR) was 10 ¹⁰ Ω,
After 100 hours, it was 10 ¹⁰ Ω, confirming that there was almost no deterioration in insulation resistance (IR).

Comparative Example 2 Using the grain boundary insulated semiconductor ceramic body obtained in Example 2, external connection of the first layer was made under the same conditions as Example 1 without forming a tin oxide layer on the surface of this ceramic body. A grain boundary insulated semiconductor porcelain capacitor was fabricated by forming a Ni layer serving as a secondary electrode and an Ag layer serving as a second external connection electrode.

When this capacitor was tested in the same manner as in Example 1, the insulation resistance (IR) was
The resistance decreased to 10 ⁷ Ω, and after 25 hours, it deteriorated to 10 ⁵ Ω.

Example 3 On an alumina substrate, an Ag layer and a Ni layer were used as the lower electrode.
The layers were formed sequentially in the same manner as in Example 1, and the tin oxide layer was also formed in the same manner as in Example 1.

Next, a SiO ₂ film, which is a dielectric ceramic, is deposited on the tin oxide layer using high-frequency sputtering.
It was formed to a thickness of Å.

Note that the conditions for forming the SiO ₂ film by high frequency sputtering method are as follows.

Sputtering atmosphere: Algon containing 5% oxygen Pressure: 5×10 ^-3 Torr Target: quartz plate with diameter of 5 inches and thickness of 5 mm Input power: 500 W Time: 100 minutes SiO ₂ film thickness: 5000 Å After that, Example 1: Tin oxide layer on SiO ₂ film
was formed by the same method as above, and then Ni
A thin film capacitor made of SiO ₂ was produced by sequentially forming layers and Ag layers in the same manner as in Example 1.

The high temperature accelerated load life test described in Example 1 was conducted on this capacitor. As a result, the initial value of insulation resistance (IR) was 10 ¹³ Ω, but
After hours it was 10 ¹³ Ω.

Comparative Example 3 In producing the thin film capacitor according to Example 3, a thin film capacitor was produced by carrying out the method described in Example 3 except for forming the tin oxide layer.

When this capacitor was tested in the same manner as in Example 1, the insulation resistance was reduced to 10 ⁸ Ω.

(Effects) As described above, according to the ceramic capacitor obtained by the manufacturing method of the present invention, since the tin oxide layer is interposed between the dielectric ceramic and the external connection electrode, the electrode As a result, deterioration of electrical properties, particularly insulation resistance, can be prevented.

Claims (1)

[Claims] 1. A method for manufacturing a ceramic capacitor in which an electrode for external connection is formed on the surface of a dielectric ceramic via a tin oxide layer, wherein the tin oxide layer is formed by a sputtering method, an ion plating method, a vacuum evaporation method, or an air vapor deposition method. A ceramic capacitor characterized in that it is formed by any one of phase evaporation methods, and the external connection electrodes are formed by any one of sputtering method, vacuum evaporation method, ion plating method, vapor phase evaporation method, and electroless plating method. manufacturing method. 2. Forming a first external connection electrode on a substrate, forming a dielectric ceramic on the first external connection electrode via a tin oxide layer, and forming a tin oxide layer on the dielectric ceramic. In a method of manufacturing a ceramic capacitor in which a second external connection electrode is formed through a tin oxide layer, a tin oxide layer is formed by one of sputtering, ion plating, vacuum evaporation, or vapor phase evaporation, 2. The method of manufacturing a ceramic capacitor according to claim 1, wherein the ceramic capacitor is formed by any one of a sputtering method, a vacuum evaporation method, an ion plating method, a vapor phase evaporation method, and an electroless plating method. 3. A laminated dielectric ceramic element body consisting of a plurality of layers of dielectric ceramic and a plurality of internal electrodes arranged in a laminated state with each other via the dielectric ceramic to form a capacitance, A method for manufacturing a multilayer ceramic capacitor in which a pair of external connection electrodes for taking out capacitance connected to a predetermined one of the internal electrodes is formed via a tin oxide layer, comprising: sputtering the tin oxide layer. , ion plating method, vacuum evaporation method, or vapor phase evaporation method, and external connection electrodes are formed by sputtering method, vacuum evaporation method, ion plating method, , vapor phase evaporation method, or electroless plating method. A method of manufacturing a ceramic capacitor according to claim 1, wherein the ceramic capacitor is formed by: 4. The method of manufacturing a ceramic capacitor according to claims 1 to 3, wherein the dielectric ceramic has a thickness of 50 μm or less. 5. The method of manufacturing a ceramic capacitor according to claims 1 to 3, wherein the tin oxide layer has a thickness of 2 μm or less.