JP3008575B2 - Varistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a varistor functioning as a voltage non-linear resistor, and more particularly to a varistor capable of improving surge withstand without increasing the number of internal electrodes and the area of the electrodes, thereby reducing material costs and applications. Related to a structure that can be enlarged.

[0002]

2. Description of the Related Art A varistor whose resistance value varies nonlinearly in accordance with an applied voltage is used as a surge absorbing element for preventing an abnormal voltage from being applied. Conventionally, as an example of such a varistor, there is a laminated varistor as shown in FIG. 4 (for example, see Japanese Patent Publication No. 58-23921).
The varistor 20 includes a ceramic layer 21 and an internal electrode 2.
2 are alternately laminated and integrally sintered, and external electrodes 24 are formed on the left and right end surfaces 23a and 23b of the sintered body 23. Also, one end faces 22a of the internal electrodes 22 are alternately led out to the left and right end faces 23a and 23b of the sintered body 23, and the one end faces 22a are connected to the external electrodes 24. Such a multilayer varistor 2
In the case of No. 0, an improvement in surge withstand is required to obtain more excellent characteristics, and for that purpose, it is effective to increase the number of laminated internal electrodes 22 and the electrode area. For example,
In order to obtain a surge withstand capacity of about 100 A, about 10 to 20 internal electrodes 22 are laminated.

However, in the above-mentioned conventional multilayer varistor, a noble metal such as Ag or Pd is often used for the internal electrode. Therefore, there is a problem that the material cost increases as the number of layers and the electrode area increase. Further, when the number of stacked internal electrodes is increased, the capacitance is also increased. Therefore, the internal electrodes cannot be used for a high-frequency signal line, and there is a problem that the application is limited.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and it is possible to improve the surge withstand without increasing the number of laminated internal electrodes and the electrode area. It is an object of the present invention to provide a varistor that can be used for a signal line.

[0005]

Means for Solving the Problems The inventors of the present invention have examined the situation in which a conventional varistor is destroyed when a surge current of an actual value or more is applied to the conventional varistor. It was found that it was concentrated on the outer peripheral portion of the electrode. From this, the present inventors have conceived that the surge resistance can be improved if the surge current concentrated on the outer peripheral edge portion of the internal electrode can be dispersed, and the present invention has been made. Therefore, the present invention embeds a pair of internal electrodes facing each other with a ceramic layer in between inside a ceramic sintered body,
In a varistor formed by connecting only one end face of each of the internal electrodes to external electrodes formed on the left and right end faces of the sintered body,
The thickness of the ceramic layer at the outer peripheral edge of the internal electrode is 1.05 times or more the thickness at the center. Here, the ratio of the inter-electrode distance is set to 1.05 times or more because if it is less than this, the effect of improving the surge withstand capacity cannot be obtained so much. On the other hand,
If it exceeds 1.5 times, the surge resistance can be improved, but cracks are likely to occur during delamination or firing, so it is preferably about 1.05 to 1.5 times. Further, the varistor of the present invention also includes a varistor having a structure in which a plurality of pairs of internal electrodes facing each other with a ceramic layer interposed therebetween are embedded in a sintered body.

[0006]

According to the varistor according to the present invention, the thickness of the ceramic layer at the outer peripheral portion of the internal electrode is increased, so that the surge current is uniformly dispersed over substantially the entire surface without being concentrated at the outer peripheral portion of the internal electrode. It will be. as a result,
The surge withstand capability can be improved without increasing the number of internal electrodes or increasing the electrode area, which in turn reduces the amount of precious metal used to reduce material costs, and reduces the capacitance to use for high-frequency signal lines. Can be used, and the applications can be expanded.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and 2 are views for explaining a varistor according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a varistor according to the present embodiment. The varistor 1 is composed of a rectangular parallelepiped ceramic sintered body 2 having a pair of internal electrodes 4 and 4 opposed to each other with a semiconductor ceramic layer 3 exhibiting a function as a voltage non-linear resistor interposed therebetween. At the same time, ceramic layers 5a and 5b as dummy are disposed on the upper and lower surfaces of each of the internal electrodes 4, respectively, and are integrally sintered. One end face 4a of each internal electrode 4
Are alternately exposed on the left and right end faces 2a and 2b of the sintered body 2, and the remaining end faces are located inside the ceramic layer 3 and sealed in the sintered body 2. External electrodes 6 are formed on the left and right end faces 2a and 2b of the sintered body 2, and one end faces 4a of the internal electrodes 4 are connected to the external electrodes 6.

The thickness t of the ceramic layer 3 at the outer peripheral edge 7a of the internal electrode 4 is larger than the thickness t 'at the central portion 7b of the internal electrode 4. 'Is set to 1.05 or more. Thus, the outer peripheral edge 7a of each of the internal electrodes 4 has a structure curved outward.

Next, a method of manufacturing the varistor 1 according to this embodiment will be described. First, ZnO (95.0 mol%), CoO
(1.0 mol%), MnO (1.0 mol%), Sb ₂ O ₃ (2.0 mol%)
1%) and Cr ₂ O ₃ (1.0 mol%), and 10 wt% of glass powder composed of B ₂ O ₃ , SiO ₂ , PbO and ZnO is added to a ceramic material to prepare a raw material. An organic binder and alcohol are added to the raw materials and mixed to form a slurry, a grease sheet having a predetermined thickness is formed from the slurry by a doctor blade method, and then the green sheet is cut into a rectangular shape to form a number of ceramic sheets. I do. Thus, the semiconductor ceramic layer 3 functioning as a voltage non-linear resistor and the ceramic layers 5a and 5b as dummy are formed.

Next, an electrode paste is prepared by mixing Pt with a vehicle, and this paste is printed on the upper surface of the semiconductor ceramic layer 3 to form the internal electrodes 4. The electrode paste is also printed on the upper surface of the uppermost dummy ceramic layer 5b to form the internal electrodes 4. In this case, one end face 4a of each internal electrode 4 is
It is formed so as to be located at the outer edge of 5b and the remaining end face is located inside the ceramic layers 3, 5b.

Then, a ceramic paste 8 formed by mixing a vehicle with the same material as the ceramic sheet is printed on the central portion 7b of the upper surface of the internal electrode 4 of the ceramic layer 3 so as to have a predetermined thickness. Thus, only the outer peripheral edge 7a of the upper internal electrode 4 is exposed. Next, the ceramic paste 8 is printed on the outer peripheral portion 7a of the upper surface of the internal electrode 4 of the dummy ceramic layer 5b so as to have a predetermined thickness. Thus, only the central portion 7b of the lower internal electrode 4 is exposed. Here, the thickness of each of the ceramic pastes 8 is such that the above-described layer thickness t of the outer peripheral edge portion 7a is equal to the thickness of the central portion 7b.
Is appropriately set so as to be 1.05 times or more of the layer thickness t ′ of the above. In addition, instead of printing the above ceramic paste 8,
A ceramic sheet having a predetermined thickness and shape may be separately formed, and the sheets may be stacked.

Next, a dummy ceramic layer 5b is overlaid on the lower surface of the ceramic layer 3. In this case, the internal electrodes 4 are opposed to each other with the ceramic layer 3 interposed therebetween, and one end surface 4a of each internal electrode 4 is alternately positioned on the left and right outer edges of the ceramic layer 3. A dummy ceramic layer 5a on the upper surface of the substrate. Next, a pressure is applied by a press in the laminating direction and pressure is applied to form a laminated body. Thus, the outer peripheral edge 7a of each of the internal electrodes 3 is curved outward, and the layer thickness t at the outer peripheral edge 7a is at least 1.05 times thicker than the layer thickness t 'at the central portion 7b.

Next, the laminated body is heated and fired in air at 1200 ° C. for a predetermined time to obtain a sintered body 2. Then, a paste made of Ag / Pb is applied to the left and right end surfaces 2a, 2b of the sintered body 2, and then baked to form the external electrodes 6. Thus, the varistor 1 according to the present embodiment is manufactured.

As described above, according to the varistor 1 of the present embodiment, the layer thickness t of the ceramic layer 3 at the outer peripheral edge 7a of the internal electrode 4 is made 1.05 times or more larger than the layer thickness t 'at the central portion 7b. In addition, the surge current is uniformly distributed over substantially the entire surface of the internal electrode 4, and as a result, the surge withstand capability can be improved without increasing the number of internal electrodes and the electrode area as in the conventional multilayer varistor. As a result, the amount of expensive precious metal used can be reduced to reduce the material cost, and the capacitance can be reduced so that it can be used for high-frequency signal lines.

[0015]

[Table 1]

Table 1 shows the results of tests performed to confirm the effect of improving the surge withstand capability of the varistor of this embodiment. In this test, the layer thickness ratio t / t ′ of each of the examples was set to 1.05.
8 / 1.5 times with various peak values
A surge current of 20 μs was applied to measure the surge withstand capability.
For comparison, the above ratio is 1 times (layer thickness is the same),
And a 1.02-fold comparative sample was prepared, and the same measurement was performed for this. As is clear from the table, in the case of the comparative sample having the same layer thickness (first column), breakdown occurred at 120 A, and surge current was concentrated on the outer peripheral edge of the internal electrode. In addition, a comparative sample having a layer thickness ratio of 1.02 times (second
Column), the surge withstand capability is slightly improved to 130 A, but a satisfactory value has not been obtained. On the contrary,
The sample of the present example (the third to sixth samples) having a layer thickness ratio of 1.05 to 1.5 times
Column), the breakdown was at 200 to 210 A in each case, and it can be seen that the surge withstand capability was greatly improved. On the other hand, when the above ratio is 1.5 times or more, the surge withstand capacity is improved, but delamination and the like are liable to occur.
A range of 1.05 to 1.5 times is desirable.

FIG. 3 is a diagram for explaining a modification of the above embodiment. In the drawing, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. The varistor 10 includes a semiconductor ceramic layer 3 that functions as a voltage nonlinear resistor in the sintered body 2.
And two pairs of internal electrodes 4 opposed to each other are embedded. Then, the outer peripheral edge portion 7a of each internal electrode 4
Is greater than the layer thickness t 'of the central portion 7b by 1.05 times or more. In this modification, a larger surge withstand can be obtained by increasing the number of internal electrodes 4.

[0018]

As described above, according to the varistor according to the present invention, the thickness of the ceramic layer at the outer peripheral portion of the internal electrode is set to 1.05 times or more the thickness of the central portion. There is an effect that the surge withstand capacity can be improved without increasing the size of the electrode or the area of the electrode, and thus, the material cost can be reduced and the application can be expanded.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a varistor according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view for explaining a method of manufacturing the varistor of the embodiment.

FIG. 3 is a sectional view showing a modification of the varistor of the embodiment.

FIG. 4 is a sectional view showing a conventional varistor.

[Explanation of symbols]

 Reference Signs List 1, 1 Varistor 2 Sintered body 2a, 2b End face of sintered body 3 Ceramic layer 4 Internal electrode 4a, one end face of internal electrode 6 External electrode 7a Outer peripheral edge of internal electrode 7b Central part t Layer thickness of outer peripheral edge t ´ Central layer thickness

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-14501 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01C ^7/ 02-7/22

Claims (1)

(57) [Claims] 1. A pair of internal electrodes facing each other across a ceramic layer exhibiting a voltage non-linear characteristic is embedded in a ceramic sintered body, and only one end face of each of the internal electrodes is placed on the left side of the sintered body. A varistor alternately connected to external electrodes formed on the right end surface, wherein the thickness of the ceramic layer at the outer peripheral edge of the internal electrode is at least 1.05 times the thickness at the center. Barista.