JPH09293604A - Manufacture of grain-boundary insulated laminated ceramic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen irregularity in the electrical characteristics of grain-boundary insulated laminated ceramic elements and to make the reproducibility of the characteristics of the elements enhance by a method wherein the elements are uniformly mixed with powder of the same porosity of the same material as the material for the elements of box-shaped sheaths and are filled in a sheath, then a plurality of these sheaths are stacked to be subjected to firing in a reducing atmosphere. SOLUTION: A semiconductivity-material is mixed into a main component, a strontium titanate, a green sheet is molded from powder obtained by drying, calcinating and grinding the mixture and thereafter, the sheet is cut, internal electrodes 2 are respectively printed on the cut sheets and the sheets are laminated. After that, invalid layers 3 are respectively stacked on the upper and lower surfaces of this laminated material to press and pressure bond. Then, this laminated material is cut into the shapes of grain-boundary insulated laminated ceramic elements, decreasing of the elements is conducted, a chamfering of the elements is conducted and external electrodes 4 are respectively applied on the end surfaces of the elements with the same electrode paste as that used for printing the electrodes 2 on the sheets. Then, the elements are uniformly mixed with powdered particles of the same material as that for the elements in box-shaped and porous sheaths having an apparent volume porosity of 50 to 70% to ensheathe and a plurality of sheaths are stacked and are subjected to firing in a reducing atmosphere.

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 grain boundary insulation type multilayer ceramic element used in various electronic devices and the like.

[0002]

2. Description of the Related Art In recent years, semiconductors such as ICs and LSIs have been widely used for electronic devices in order to reduce their size and improve their performance. However, in some cases, semiconductors may malfunction or be destroyed due to abnormal surge current or electrostatic surge noise. Therefore, a high-performance noise absorber has been required to ensure the noise resistance of these electronic devices. Among these requirements, the grain boundary insulation type multilayer ceramic element containing strontium titanate as a main component has good noise absorption, is stable against temperature and frequency, and has a varistor function. Has been expanded.

A conventional grain boundary insulation type laminated ceramic element,
And the manufacturing method thereof will be described with reference to FIG.

FIG. 1 is a grain boundary insulation type multilayer ceramic element, and FIG. 2 is a manufacturing process diagram thereof. In FIG. 1, 1 is a ceramic layer, 2 is an internal electrode, 3 is an ineffective layer, 4 is an inner outer electrode, and 5 is an outer outer electrode.

In the grain boundary insulation type laminated ceramic element having the above structure, the ceramic layers 1 and the internal electrodes 2 are alternately laminated, and the ineffective layer 3 made of the same component as the ceramic layer 1 is laminated on the upper and lower surfaces of the laminated body. Then, after pressure-bonding, the grain boundary insulation type laminated ceramic element piece having a predetermined shape is cut, and then the external electrodes 4 are formed on both exposed end surfaces of the internal electrode 2. next,
After degreasing, the grain boundary insulation type multilayer ceramic elements are randomly packed and fired in a reducing atmosphere. After that, the sintered body is reoxidized, and the external electrode 5 is further connected to the external electrode 4.
To obtain a grain boundary insulation type laminated ceramic element as shown in FIG.

[0006]

However, in the above-mentioned conventional firing method, there is an influence of overlapping of grain boundary insulation type laminated ceramic elements in the sheath and residual oxygen in the sheath, and thus, particularly high-laminated products and large-sized products are obtained. However, it was difficult to control the reduction reaction and the sintering reaction uniformly on the surfaces which were overlapped at the time of firing, and on the surface layer and the central portion of the element, and the element was uneven in the sintered state. Therefore, during the reoxidation treatment of the sintered element, the reoxidation state at the interface of the sintered particles becomes non-uniform, and as a result, the electrical characteristics vary, and the desired electrical characteristics cannot be obtained.

An object of the present invention is to solve the above-mentioned problems of the conventional products, and to provide a method for manufacturing a grain boundary insulation type laminated ceramic element having a small variation in electric characteristics and a high characteristic reproducibility.

[0008]

In order to achieve this object, the present invention has a box shape as a firing sheath used for firing.
In addition, a material having an apparent porosity of 50% to 70% is used, which is further uniformly mixed with a co-dough powder of the same material as the grain boundary insulation type multilayer ceramic element and packed in a sheath, which is stacked in a plurality of stages and placed in a reducing atmosphere. This prevents the elements from overlapping each other and replaces the reducing atmosphere gas with the residual oxygen in the sheath promptly.Furthermore, the reducing atmosphere gas is evenly distributed in the sheath and reduced uniformly. The obtained sintered body can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A method of manufacturing a grain boundary insulating type laminated ceramic element according to claim 1 of the present invention is a method of laminating a plurality of layers in which a ceramic layer containing strontium titanate as a main component and an internal electrode layer are alternately laminated. Then, the grain boundary insulation type laminated ceramic element is cut into a grain boundary insulation type laminated ceramic element piece having a predetermined shape, and then the grain boundary insulation type laminated ceramic element is placed in a box-shaped firing sheath having an open porosity of 50 to 70%. , And evenly mix with the co-dough having the same composition as the device and pack in the sheath, stack the firing sheaths in multiple stages, cover the uppermost sheath with the same material, and fire in a reducing atmosphere. Next, the sintered body is reoxidized, and then external electrodes are formed on both end surfaces, the co-material prevents the elements from overlapping, and the apparent porosity of the sheath is determined by the reducing atmosphere gas and residual oxygen. The inside of the sheath can be replaced promptly, and the reducing atmosphere gas can easily flow into and out of the sheath, so that a uniformly reduced sintered body can be obtained.

According to a second aspect of the present invention, a box-shaped first sheath having an apparent porosity of 50 to 70%, in which a grain boundary insulating type laminated ceramic element is inserted, and no element is inserted,
A plurality of second sheaths, each having a box shape with a cutout opening provided in a part of its side surface and having an apparent porosity of 50 to 70%, are alternately stacked and fired in a reducing atmosphere. Substitution of residual oxygen and inflow and outflow of reducing gas are facilitated from the four side surfaces and the upper and lower surfaces of the entered sheath, and the atmosphere in the sheath filled with the elements becomes more uniform.

According to a third aspect of the present invention, the co-dough used has the same composition as that of the element to be fired, and is a powder which is previously sintered in a reducing atmosphere into a granular powder,
This prevents overlapping of the grain boundary insulation type multilayer ceramic elements to be fired, and because the reduced powder does not affect the firing elements, it is easy for the reducing gas to come into contact with the individual elements. Therefore, the entire element can be uniformly reduced and sintered.

By using the above-mentioned manufacturing method, when the sintered element is reoxidized, the adsorption reaction of oxygen to the particle interfaces in the element is uniformly carried out, and it is possible to obtain an electric property regardless of whether it is a highly laminated product or a large shaped product. It is possible to provide a grain boundary insulation type multilayer ceramic element in which variations in characteristics are reduced and which are highly reproducible in characteristics.

(Embodiment 1) An embodiment of the present invention will be described below.

Since the drawings and the names of the components used are basically the same as those of the conventional product, the same components are used and the description thereof is simplified.

First, 97.1 mol% of strontium titanate, which is the main component, contains 0.5 mol% of niobium oxide as a semiconducting substance, 0.5 mol% of tantalum oxide, and 0.4 mol% of manganese oxide as a sintering aid. 1.0 mol% of silicon and 0.5 mol% of sodium silicate (Na ₂ SiO ₃ ) as an oxidation promoter were weighed out, and according to the process shown in FIG. 2, compounding (6), mixing (7) and drying ( 8) After that, calcination (9) at a temperature of 1100 ° C. and crushing (1)
Perform 0). The obtained powder is mixed with an organic solvent and a binder to prepare a slurry (11). Then, after forming a 25 μm thick green sheet by the doctor blade method, it is cut (12) into a predetermined size. The internal electrode 2 is printed (13) on the cut green sheet by using an electrode paste whose main component is nickel oxide. A plurality of layers are laminated to form a laminated body, and when the laminated body is cut into a grain boundary insulation type laminated ceramic element shape, the internal electrode 2
The internal electrodes 2 are printed and laminated (14) so that the electrodes are alternately exposed on different end faces of the device. After that, the ineffective layers 3 are stacked on the upper surface and the lower surface of the laminated body and pressure-bonded. Next, the laminated body is cut (15) into a grain boundary insulation type laminated ceramic element shape and degreased (16). After degreasing, the element is chamfered, and the external electrode 4 is applied (17) to the element end face with the same electrode paste as the internal electrode 2, and then the box-shaped porous sheath having an apparent porosity of 50 to 70% is used. The element is uniformly mixed with powder particles of the same material and packed in a sheath (18), and a plurality of these are stacked and a lid of the same material as the box-shaped sheath is placed on the top of the stack and inserted into a firing furnace at 1200 ° C. The reducing atmosphere firing (19) was performed while flowing a fixed amount of a mixed gas of nitrogen and hydrogen for the reducing atmosphere at the temperature. In this case, the inflowing reducing gas diffuses into the sheath through the pores of the sheath, is easily replaced with the residual oxygen in the sheath, and acts evenly on the entire element during firing through the space of the co-dough uniformly mixed with the element. To do. This realizes uniform sintering and reduction reaction of the entire device. Then, the sintered element is subjected to reoxidation treatment (20) in air at a temperature of 850 ° C., and then the external electrode 5 containing silver as a main component is applied (21) on the external electrode 4 and baked to obtain a finished product. did. As its electrical characteristics, the varistor voltage (V
_{0.1 mA} ) and the electrostatic capacitance (C _{1 KHz} ) at a frequency of 1 _KHz were measured. The results are shown in (Table 1) together with the finished product manufactured by the conventional method.

[0016]

[Table 1]

As is clear from (Table 1), the product of the present invention has much smaller variations in both varistor voltage and electrostatic capacitance than those produced by the conventional method. This is because the element uniformly reacts with the reducing gas by the firing method in which the element is uniformly mixed with the co-dough using a porous sheath, and oxygen is generated at the grain boundary interface of the sintered element in the subsequent reoxidation treatment. It seems to indicate that the adsorption was carried out homogeneously. On the other hand, in the conventional method, it is considered that the replacement of residual oxygen in the firing sheath was insufficient and that the sufficient sintering and reduction reaction were not performed because the surfaces of the elements were overlapped.

(Embodiment 2) As in Embodiment 1, a first firing sheath in which an element is packed in a sheath and a second firing sheath in which a notch portion is provided in a part of the side surface are alternately formed. A plurality of them were stacked and inserted into a furnace, and fired in a reducing atmosphere under the same conditions as in the first embodiment. Then, the reoxidation treatment of the sintered element and the external electrode 5 were formed. The evaluation results of the electrical performance of the obtained sintered element are shown in (Table 1).

As is clear from (Table 1), the second embodiment
It can be seen that the product of the present invention has a smaller variation in electrical performance than that of the first embodiment. This means that by inserting empty sheaths with notches on the side surface at every other stage, it is possible to replace residual oxygen and reduce the reducing gas in the sheaths packed with elements, rather than stacking the sheaths packed with elements. Since the inflow and outflow are performed from the upper and lower surfaces in addition to the four side surfaces of the sheath, it shows that the sintering and reduction reactions of the element were further homogenized.

In the second embodiment, the empty sheath having a notch in a part of the side surface is used. However, if a space through which the reducing gas can freely pass is provided on the upper and lower surfaces of the sheath in which the element is clogged, other empty sheaths are provided. The same effect can be obtained by using the means.

In the first and second embodiments, the box-shaped sheath is used. In the case of a plate-shaped sheath, the reducing gas and the radiant heat of the furnace act directly on the packed sheath to reduce the element This is to prevent unevenness in the sintering and reduction reaction between the surface layer portion and the inside, resulting in variations in the electrical performance of the element. Furthermore, the apparent porosity of the baked sheath is 50% ~
70% means that the reducing gas and thermal radiation of the furnace in the case of using the sheath having the cutout opening on the side surface are prevented from directly acting on the element to be fired, and the reducing gas is prevented from entering the sheath. This is to obtain open pores that do not hinder the inflow and outflow, and to obtain mechanical strength that can withstand the load when the fired sheaths are stacked in multiple stages.

Further, the reason why the reduced co-material is uniformly mixed with the element to fill the sheath is for the reason shown in the first embodiment.

[0023]

As described above, when the firing of the present invention is performed, a box-shaped firing sheath is used and a porous sheath having an apparent porosity of 50% to 70% is used. By mixing and packing in a mixture, stacking them in multiple stages and firing in a reducing atmosphere, the element can be sintered and the reduction reaction can be homogenized, and as a result, regardless of whether it is a highly laminated product or a large-sized product. In addition, it is possible to provide a grain boundary insulation type monolithic ceramic element which has a uniform oxygen adsorption reaction to the element grain boundaries in the reoxidation treatment of the sintered element and has little variation in electrical characteristics and high characteristic reproducibility. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a grain boundary insulation type monolithic ceramic element according to an embodiment of the present invention.

[Fig. 2] Manufacturing process drawing of the same grain boundary insulation type ceramic component

[Explanation of symbols]

 1 Ceramic Layer 2 Internal Electrode 3 Ineffective Layer 4 Inner External Electrode 5 Outer External Electrode

Claims (3)

[Claims] 1. A laminated body obtained by alternately laminating a plurality of ceramic layers containing strontium titanate as a main component and internal electrode layers is cut into a grain boundary insulation type laminated ceramic element having a predetermined shape, and then one surface is opened. Using a fired sheath having a box shape and an apparent porosity of 50 to 70%, a grain boundary insulation type multilayer ceramic element is uniformly mixed with a co-dough having the same composition as that of the element and packed into a sheath. A plurality of layers are stacked, the uppermost sheath is covered with the same material and fired in a reducing atmosphere, then the sintered body is reoxidized, and then external electrodes are provided on both end faces of the grain boundary insulation type multilayer ceramic element. A method for manufacturing a grain boundary insulation type multilayer ceramic element, which is characterized by being formed. 2. A grain-boundary insulation-type laminated ceramic device comprising a box-shaped first firing sheath having a grain-boundary insulation-type laminated ceramic element sheathed therein and having an apparent porosity of 50 to 70%, and a cutout opening provided on a side surface thereof. Box-like with no ceramic elements and apparent porosity of 5
2. The method for manufacturing a grain boundary insulation type monolithic ceramic element according to claim 1, wherein a plurality of layers of 0 to 70% of the second sheath are alternately stacked and fired in a reducing atmosphere. 3. The co-dough is a granular powder which has the same composition as the grain boundary insulating type laminated ceramic element to be fired and which has been previously sintered in a reducing atmosphere into a granular powder. A method for manufacturing the grain boundary insulation type monolithic ceramic element as described in 1.