JPH08222468A - Ceramic element and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a ceramic element which is almost free from deterioration in characteristics and excellent in weather resistance and reliability. CONSTITUTION: Ceramic layers 1 and inner electrode layers 2 are alternately laminated into a laminate, an outer electrode 3 is provided in each of the end faces of the laminate, a high-resistance layer 6 formed of silicon metaphosphate and silica powder is formed on the surface of the laminate except its parts where the outer electrodes 3 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic element such as a capacitor and a method for manufacturing the same.

[0002]

2. Description of the Related Art A grain boundary insulating semiconductor ceramic capacitor having both varistor characteristics and capacitor characteristics as a ceramic element will be described as an example.

The grain boundary insulation type semiconductor ceramic capacitor is disclosed in Japanese Patent Application Laid-Open No. 3-1516, etc.
First, as starting _{materials, Sr (1-x) Ba} x to Ti molar ratio of 0.95 ≦ Sr _(1-x) of Ba x /Ti<1.00 become so contained an excess of Ti Sr _{(1 -x)} Ba _x TiO ₃ (where 0 <x ≦ 0.3) is added to Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ ,
_{W 2 O 5, Dy 2 O} 3, Nd 2 O 3, Y 2 O 3, La 2 O 3, Co
At least one kind of O ₂ is 0.05 to 2.0 m
ol%, Mn and Si are converted to MnO ₂ and SiO ₂ , respectively, and the total amount is 0.2 to 5.0 mol%, NaAlO
A mixed powder of a composition containing 0.05 to 4.0 mol% of ₂ is prepared.

Next, the mixed powder is pulverized, mixed and dried, then calcined in air or in a nitrogen atmosphere, further calcined, and then the pulverized powder is dispersed in a solvent together with an organic binder to form a green sheet. To do. After that, as shown in FIG. 3, the internal electrode paste 5 is printed on the green sheet 4 so as to reach the opposite edges alternately (however, not printed on the green sheets of the uppermost layer and the lowermost layer). The green sheet 4 on which the internal electrode paste 5 is printed is laminated, pressed and pressed to obtain a molded body, and then this molded body is calcined in air. After calcination, after firing in a reducing atmosphere or a nitrogen atmosphere, reoxidation is performed in air, and external electrode paste is applied to both ends where the internal electrodes 2 are exposed and baked to form external electrodes 3. Then, plating such as solder is performed on it. In this way, the chip type laminated grain boundary insulation type semiconductor ceramic capacitor as shown in FIG. 2 is manufactured.

[0005]

However, in the multilayer ceramic element obtained by such a manufacturing method, open pores are formed on the surface, so that ions may penetrate into the element during plating or the surface may be exposed. Problems such as deterioration of capacitance and varistor voltage characteristics are often caused by adhesion and change of ceramic composition, or migration of water from element surface causing migration of internal electrodes during current load. It was happening. Therefore, an object of the present invention is to provide a ceramic element excellent in weather resistance and reliability with almost no deterioration in characteristics.

[0006]

To achieve this object, the present invention covers at least open pores on the surface of a ceramic element with a paste in which silicon metaphosphate and silica powder are mixed, and the paste is cured. .

[0007]

With this structure, it is possible to prevent unnecessary ions and water from adhering to and entering the surface and the inside of the ceramic element, and prevent characteristic deterioration such as capacitance and varistor voltage.

[0008]

EXAMPLE A first example of the present invention will be specifically described below.

FIG. 1 is a partially cutaway perspective view of a laminated ceramic element according to an embodiment of the present invention.

First, SrTiO ₃ , CaCO ₃ , and BaCO
₃ , MgCO ₃ , and TiO ₂ are weighed so as to have the composition of the first component shown in No. 1 to No. 16 of (Table 1) and mixed with a ball mill for 20 hours.

[0011]

[Table 1]

Next, after drying, it was baked at 1100 ° C. for 4 hours, pulverized again by a ball mill or the like for 75 hours, and then dried to obtain the first component.

Next, the first component, the second component, and the third component are weighed so as to have the molar ratios shown in Nos. 1 to 16 of (Table 1) and (Table 2), and are then ball milled. After mixing for 20 hours, it is dried and mixed with a butyral resin and an organic solvent such as butyl acetate to prepare a slurry.

[0014]

[Table 2]

Using this slurry, a raw sheet having a thickness of 50 μm is formed by a doctor blade method or the like, dried, and cut into a predetermined size. Next, the inner electrode paste 5 is not printed on the green sheets 4 which are the uppermost layer and the lowermost layer, and Ag-P is formed on the other green sheets 4 as shown in FIG.
The internal electrode paste 5 made of d is screen-printed so that one reaches the edge, and 30 layers are laminated so that the internal electrode paste 5 reaches the edge where the internal electrode paste 5 is alternately opposed. Then, pressure and pressure are applied to cut into a predetermined size.

[0016] Then, degreased at 700 ° C. in air, further after calcination at 1150 ° C. in air, coating the external electrode paste comprising NiO on both end surfaces to expose the internal electrodes 2, for example, N ₂ : H ₂ = 10: 1 in a reducing atmosphere
Bake at 250 ° C for 3 hours, and then in air at 900 ° C for 2 hours.
Reoxidize for hours. After that, an external electrode paste made of Ag—Pt is applied to both end surfaces of the exposed Ni external electrode, and the external electrode 3 is baked in air at 850 ° C. for 10 minutes to form the external electrode 3, and the multilayer ceramic as shown in FIG. Get the element.
Next, a silica paste in which SiO ₂ having an average particle diameter of about 0.5 μm and silicon metaphosphate is sufficiently mixed is applied to the surface of the device.

Thereafter, heat treatment is performed at 350 ° C. for about 60 minutes to form the high resistance layer 6 on the surface of the element other than the portion where the external electrode 3 is formed.

After that, for example, Ni plating is performed on the external electrodes 3 and solder plating is further performed. The characteristics of the element thus obtained and the results of the humidity and mid-load test are shown in (Table 3).

[0019]

[Table 3]

V _{0.1 mA} is a voltage applied to both ends of the device when a direct current of 0.1 _mA is applied. Further, the shape of the multilayer ceramic element shown in this embodiment is usually 212.
It is a size called 5.

Further, (Table 4) shows the rate of change in capacitance and the rate of change in varistor voltage after a voltage test in humidity.

[0022]

[Table 4]

The types of plating are shown only for some metals, but any type of metal may be used, and the method may be acidic plating, basic plating, or electrolytic plating. Either plating or electroless plating may be used.

Further, Ag-P is used as a material for the internal electrodes 2.
Some examples such as d are shown, but Ag, Pd, Pt, Ni, C
It may be one or more kinds of metals, alloys or oxides of u, Zn and In.

In this example, the high resistance layer was formed so as to have a thickness of about 4 μm except the portion where the external electrode 3 was formed on the surface of the device.

In this embodiment, a laminated ceramic element is shown as an example, but the same effect can be obtained with a ceramic element having another shape such as a disk type.

[0027]

As described above, according to the present invention, since the pores on the surface of the ceramic element are filled with silica to seal the pores, moisture and unnecessary ions can be prevented from entering the inside of the ceramic element.

Further, since a mixture of silicon metaphosphate and silica powder has solvent resistance, acid resistance, alkali resistance and heat resistance, silica is the main component on the surface of the ceramic element excluding the electrode forming portion. By forming a high-resistance layer that protects the sealed part, it is possible to reinforce the part that has been stopped and also to attach unnecessary ions and water to the surface of the ceramic element,
It is possible to further prevent intrusion into the interior. Then, it is possible to prevent the ceramic element from being damaged during plating or soldering. Further, since the internal electrodes do not cause migration when a current is loaded, it is possible to prevent deterioration of characteristics such as capacitance and varistor voltage.

Further, since the present invention is easy in terms of process, the practical effect is extremely large.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a multilayer ceramic element according to an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of a multilayer ceramic element according to an embodiment of the present invention.

FIG. 3 is an exploded perspective view of a ceramic element according to an embodiment of the present invention.

[Explanation of symbols]

 1 Ceramic layer 3 External electrode 6 High resistance layer

Claims (2)

[Claims] 1. A ceramic element comprising: a ceramic element; and a hardened paste of silicon metaphosphate and silica powder embedded in at least open pores on the surface of the ceramic element. 2. A method of manufacturing a ceramic element in which at least open pores on the surface of the ceramic element are covered with a paste in which silicon metaphosphate and silica powder are mixed and then the paste is cured.