JPH02302005A - Laminate-type varistor - Google Patents

Abstract

PURPOSE:To prevent a quality of internal electrodes from being changed by a method wherein the internal electrodes are buried completely inside a ceramic layer, the left end face and the right end face of a laminated body are coated with a mixture of metal zinc and zinc oxide, this mixture is oxidized and heat-treated and low-resistance layers from which the internal electrodes are extracted alternately are formed. CONSTITUTION:Individual internal electrodes 3 are buried inside a ceramic layer 2. The internal electrodes 3 are not exposed at peripheral edges of a sintered body 4. As a result, even when the internal electrodes 3 are used in a high-humidity atmosphere, their quality is not changed. Even when the sintered body 4 is immersed in an electrolytic plating liquid, the plating liquid does not creep. As a result, it is possible to prevent a varistor characteristic from being aggravated and to enhance quality. In addition, since low-resistance layers 6 are formed on the left end face and the right end face 4a, 4b of the sintered body 4, the resistance layers 6 are connected to end faces 3a of the internal electrodes 3; the internal electrodes 3 can be connected to external electrodes 5 via the resistance layers 6; the internal electrodes 3 can be extracted even in a state that they have been sealed. The low-resistance layers 6 can be realized when a paste composed of metal zinc and zinc oxide is coated and this paste is heat-treated simultaneously with a baking operation of a laminated body.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a multilayer varistor that functions as a voltage non-linear resistor, and in particular can prevent deterioration of varistor characteristics by preventing deterioration of internal electrodes, and improves the performance of components. It relates to a structure that improves credibility.

[Conventional technology]

Generally, a varistor is a resistive element whose resistance value changes non-linearly depending on the applied voltage. Conventionally, as such a varistor, there is a rectangular parallelepiped-shaped multilayer varistor as shown in FIG. (Refer to Japanese Patent Publication No. 5B-23921), this multilayer varistor 10 is made by alternately stacking and integrally sintering ceramic layers 11 mainly composed of ZnO and internal molds 8i112, and 1 Right end surface 1
External electrodes 14 are formed on 3a and 13b. Further, one end surface 12a of each of the internal electrodes 12 is alternately exposed to left and right end surfaces 13a and 13b of the sintered body 13 and connected to the external electrode 14.

[Problem that the invention seeks to solve]

By the way, the conventional multilayer varistor 10 described above has a sintered body 1
3, since the structure is such that one end surface 12a of the internal electrode 12 is exposed to the outside, the exposed portion of the internal electrode 12 is likely to deteriorate in a high humidity atmosphere, and the external part 12a is easily damaged by plating. When forming the internal electrodes 12, the plating solution tends to enter through the exposed portions of the internal electrodes 12, resulting in deterioration of the varistor characteristics and poor quality reliability.

Here, internal electrode 1 due to the above-mentioned high humidity and invasion of plating solution.
In order to prevent deterioration of the internal electrode 2, one end TjM of the internal electrode 2 must be
It is conceivable to encapsulate 12a in the ceramic layer 11 so as not to expose it to the outside. However, if this is done, the internal electrode 12 cannot be connected to the external electrode 8i14, so it cannot be adopted as is.

The present invention has been made to solve the above-mentioned conventional problems, and can prevent deterioration of varistor characteristics by preventing deterioration of internal electrodes due to high humidity and intrusion of plating fluid, thereby improving quality reliability. The aim is to provide a multilayer varistor that can.

[Means for Solving the Problems] Therefore, the present invention provides a multilayer varistor in which ceramic layers and internal electrodes are alternately stacked to form a multilayer body.
By burying the internal electrodes inside the ceramic layer so as not to expose them to the periphery of the laminate, and applying a mixture of metallic zinc and zinc oxide to both end surfaces of the laminate and subjecting it to oxidation heat treatment. , a low resistance layer is formed from which the internal electrodes are alternately led out.

Here, the low resistance layer is formed by forming a powder made of a mixture of metal zinc and zinc oxide into a paste form, applying this to both end faces of the laminate, and then baking it in air. This can be achieved by forming low-resistance ceramic layers with many oxygen defects on both end faces of the laminate.

[Effect]

According to the multilayer varistor according to the present invention, the internal electrodes are buried in the ceramic layer and the exposed parts of the internal electrodes are completely eliminated, so that deterioration of the internal electrodes can be prevented even in a high temperature atmosphere, and It is possible to prevent the plating solution from entering when forming the external electrodes, thereby avoiding deterioration of varistor characteristics and improving quality reliability.

Furthermore, in the present invention, since the internal electrodes are connected to the low resistance layers formed on both end surfaces of the laminate, by forming the external electrodes on the outer surfaces of the low resistance layers, the internal electrodes can be connected to the external electrodes. It can be derived as follows.

Furthermore, the low resistance layer can be easily manufactured by simply applying a mixed paste of metal zinc and zinc oxide to the surface area of the laminate and heating and baking it in air.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 to 3 are diagrams for explaining a multilayer varistor according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes the multilayer varistor of this embodiment. This varistor 1 has a rectangular parallelepiped shape, and has ceramic layers 2 mainly composed of ZnO and internal electrodes 3 made of PT laminated alternately. External poles 5 made of Ag/Pd are formed on the left and right end faces 4a, 4b of a sintered body 4 formed by integrally firing the above. Further, the periphery of each internal electrode 3 is located inside the ceramic layer 2, that is, the internal electrode 3 is located inside the ceramic layer 2.
is embedded and enclosed within the sintered body 4. In this case, one end surface 3a of each of the internal electrodes 3 is alternately located close to the left and right end surfaces 4a and 4b of the sintered body 4,
The other end surface 3b is on the left side of the sintered body 4.

It is located a little apart from the right end faces 4a and 4b.

A low resistance layer 6 is formed on the left and right end surfaces 4a and 4b of the sintered body 4, and the low resistance layer 6 has a thickness that reaches one end surface 3a of each internal electrode 3. There is. This low resistance layer 6 is formed by applying a paste made of a mixture of metallic zinc and zinc oxide to the left and right end surfaces 4a and 4b of the sintered body 4, and heat-treating it in air. It is something that Further, the outer surface of the low resistance layer 6 is connected to the external electrode 5, and thereby the internal electrode 3 is connected to the external electrode 5 via the low resistance layer 6.

Next, a method for manufacturing the multilayer varistor 1 of this embodiment will be described.

■ First, Z n O (95.0 moi%), Co0 (
1゜0Ilo1%)+M n O(1, Omoj!%
), S bz O* (2,0-01%L Cr t
Bz Os , S fox , and PbO are added to the ceramic material made by mixing O3 (1-01101%).

Add 10 wt% of glass powder consisting of ZnO as a raw material, mix it with an organic binder, and form a green sheet by the doctor blade method.Next, as shown in Figure 3, the green sheet is shaped into a rectangular shape. A large number of ceramic layers 2 are formed by cutting.

(2) On the upper surface of each ceramic layer 2, a paste made of a mixture of PT and vehicle is printed to form internal electrodes 3. In this case, each end surface of the internal electrode 3 is located inside the ceramic layer 2, and one end surface 3 of the internal electrode 3 is
A is formed so that the end face 3b is close to the end face of the ceramic layer 2, and the other end face 3b is a little apart.

(2) Then, the ceramic layers 2 are laminated in sequence so that the internal electrodes 3 and the ceramic layers 2 are alternately overlapped, and the one end surfaces 3a of the internal electrodes 3 are alternately located, and then the upper and lower surfaces of this laminate are stacked. A ceramic layer 7 as a dummy is layered on top of the dummy ceramic layer 7, and this is pressed and bonded with a press to form a laminate.

As a result, each internal electrode 3 is completely embedded and encapsulated within the laminate.

(2) Next, a vehicle is added to a mixed powder containing zinc metal and zinc oxide in a ratio of 1:4 to create a paste. Then, apply this paste to the left and right end surfaces of the laminate, that is, the side surfaces facing one end surface 3a of the internal electrode 3, to a thickness of 50 μm.
Apply so that it becomes m.

■ Heat and bake the above laminate in air at 1200°C,
A sintered body 4 is obtained. Then, by this heat treatment, Zn, ZnO,
Further, due to the reaction of 08 in the air, a low resistance layer 6 in an oxygen-deficient state is formed, and the low resistance layer 6 is connected to one end surface 3a of the internal mold 8i3.

■Finally, the left and right end surfaces 4a of the sintered body 4.

A mask is formed to cover the outer surface except for 4b, and in this state electrolytic plating treatment is performed to form the external electrode 5 on the outer surface of the low resistance layer 6. The external electrode 5 may be formed by applying a paste mainly composed of Ag and adding Pd to the sintered body 4 and then baking the paste. In this way, the multilayer varistor 1 of this example is manufactured.

Next, the effects of this embodiment will be explained.

According to the multilayer varistor 1 of this embodiment, each internal electrode 3 is buried in the ceramic layer 2 so that the internal electrode 3 is not exposed to the periphery of the sintered body 4, so that it can be used in a high humidity atmosphere. The internal electrodes 3 will not change in quality even after use, and even if the sintered body 4 is immersed in an electrolytic plating solution, the plating solution will not enter, so deterioration of varistor characteristics can be prevented and quality can be improved. You can improve.

Also, in this embodiment, the left side of the sintered body 4. Right end surface 4a, 4b
Since the low resistance layer 6 is formed in the portion, the resistance layer 6 is connected to one end surface 3a of the internal electrode 3, and the internal electrode 3 and the external electrode 5 can be connected via the resistance layer 6. It can be taken out to the outside even when it is sealed. Moreover, this low resistance layer 6 is coated with a paste consisting of metallic zinc and zinc oxide,
Since this can be achieved by simply performing a heat treatment at the same time as the firing of the laminate, manufacturing is easy and the cost does not increase at all.

FIGS. 4 and 5 are characteristic diagrams showing the results of a moisture resistance test conducted to confirm the effects of this example.

In this test, the laminated varistors produced by the manufacturing method of this example were left in an atmosphere with a temperature of 60°C and a relative humidity of 90% for 1000 hours, and then VIIIA and Vo.

The rate of change of 1o was investigated. For comparison, a similar test was also conducted on a conventional multilayer varistor in which the end faces of the internal electrodes were exposed on the left and right end faces of the sintered body.

Figure 4 shows the relationship between the rate of change of vll and elapsed time,
Figure 5 shows the relationship between the rate of change of Vo and +ma and the elapsed time. In Figure 5, curve A (solid line) is the sample of this example, and the curve JIB.
(Dashed line) indicates the conventional sample.

As is clear from the figure, although there is not much difference in the rate of change of Vl+sA between the two (curves A and B),
■. , +aA, the conventional sample B has a change of -25%, while the sample A of this example has an improved change of -19%, which shows that the moisture resistance has improved. .

Further, although the sample of this example was subjected to plating treatment to form external electrodes, no deterioration of characteristics due to this was observed at all, and it was found that intrusion of plating solution was prevented.

〔Effect of the invention〕

As described above, according to the multilayer varistor of the present invention, the internal electrodes are completely buried in the ceramic layer, and
By applying a mixture of metallic zinc and zinc oxide to the left and right end surfaces of the laminate and subjecting it to an oxidation heat treatment, a low resistance layer from which the internal electrodes are alternately led out was formed, so that it could withstand high humidity and plating solution. This has the effect of preventing deterioration of the internal electrodes due to intrusion, avoiding deterioration of varistor characteristics, and improving reliability of quality.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining a multilayer varistor according to an embodiment of the present invention, in which FIG. 1 is a sectional view thereof, FIG. 2 is a perspective view thereof, and FIG. 3 is an exploded perspective view thereof. Figure, 4th
5 and 5 are characteristic diagrams showing the effects of this embodiment, respectively.
FIG. 6 is a sectional view showing a conventional multilayer varistor. In the figure, 1 is a multilayer varistor, 2 is a ceramic layer,
3 is an internal electrode, 3a is one end of the internal electrode, 4 is a sintered body (laminate), and 6 is a low resistance layer. Patent Applicant Murata Manufacturing Co., Ltd. Agent Patent Attorney Tsutomu Figure 1 Figure 2 Figure 3 Figure 4 Specific Gravity Time (h) Gravity Time (h) Figure 6゛10

Claims (1)

[Claims] (1) A laminate is formed by alternately laminating ceramic layers that exhibit a varistor function and internal electrodes, and one end of each internal electrode is led out to the end surface of the laminate, which functions as a voltage nonlinear resistor. In the multilayer varistor, the internal electrodes are buried inside the ceramic layer so as not to be exposed to the periphery of the multilayer body, and a mixture of metallic zinc and zinc oxide is added to both ends of the multilayer body. A multilayer varistor, characterized in that a low resistance layer is formed by oxidation heat treatment, and one end of the internal electrode is alternately guided to an end surface of the multilayer body by the low resistance layer.