JPH02260604A - Lamination type varistor - Google Patents

Abstract

PURPOSE:To improve reliability by a method wherein connection gaps are provided on one edge face of an electrode, non-connection gaps wider than the connection gaps are provided on the other edge face, and the gaps on the top part and the bottom part are formed larger than the gaps on the other electrode. CONSTITUTION:Edge faces 3a of inner electrodes 3 are internally positioned by providing connection gaps alternately on both edge faces 4a and 4b of a sintered body 4. Other edge faces 3b are alternately positioned inner than both edge faces 4a and 4b by providing non-connection gaps (t) which are wider than the gaps T. Each electrode 3 is connected to outer electrode 5 through the intermediary of a lead-out layer 6. The non-connection gaps (t') of the other edge faces 3c of the top part and the bottom part of the inner electrodes 3' and the left and the right edge faces 4a and 4b are made larger than the gaps (t) of the other electrodes 3. To be more precise, the length from one edge face 3a to the other edge face 3c of the electrodes 3' is formed shorter than one half of the length (l) of the sintered body 4. As a result, the degeneration of the inner electrodes due to high humidity and the intrusion of a plating solution can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multilayer varistor that functions as a voltage nonlinear resistor, and in particular can prevent deterioration of varistor characteristics by preventing deterioration of internal electrodes. This invention relates to a structure that reduces stray current and improves reliability of parts.

[Conventional technology]

In general, 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. 6. (For example, see Japanese Patent Publication No. 58-23921.) This multilayer varistor 3° is made by alternately stacking ceramic layers 31 mainly composed of ZnO and internal electrodes 32 and sintering them together. 33 left and right end surfaces 33
a, 33b, and one end surface 32a of each internal electrode 32 is alternately exposed to the left and right end surfaces 33a, 33b of the sintered body 33 and connected to the external electrode 34. It has become.

[Problem that the invention seeks to solve]

By the way, the conventional multilayer varistor 3o described above has a sintered body 3
3, since the structure is such that one end surface 32a of the internal electrode 32 is exposed to the outside, there is a problem that the exposed portion of the internal electrode 32 is easily deteriorated in a humid atmosphere.

In addition, when this type of multilayer varistor 30 is connected to a wiring board by soldering, if the external electrode 34 is baked from the electrode, silver will be melted and incorporated into the solder, resulting in so-called silver cracks. was.

In order to prevent such silver corrosion, a heat-resistant metal layer such as nickel or copper that is difficult to melt by solder is formed on the silver electrode by plating, and the solder adhesion is improved. For this purpose, a solder layer is also formed by plating on a metal layer made of plating. However, if a metal layer or a solder layer is further formed on the surface of the external electrode 34, the plating solution tends to enter through the exposed portion of the internal electrode, resulting in a problem that the varistor characteristics deteriorate.

Therefore, in order to prevent deterioration of the internal electrodes due to the above-mentioned high humidity and penetration of plating solution, the applicant proposed a multilayer varistor as shown in FIG.
No. 49). This laminated varistor 20 has one end surface 21a and the other end surface 21b of an internal electrode 21 buried in a ceramic layer 24 so as not to be exposed to the outside to form a sintered body 22, and both end surfaces of the sintered body 22. 22a, 22b,
A lead-out layer 23 made of a solid solution of AI or the like is formed in the sintered body 22, and one end surface 21a of the internal electrode 21 is electrically led out alternately through the lead-out layer 23. According to this multilayer varistor 20, the internal electrode 21 is connected to the sintered body 2.
Since the exposed portion of the internal electrode 21 is eliminated, deterioration of the internal electrode 21 can be prevented even in a humid atmosphere or during plating solution treatment, and as a result, deterioration of varistor characteristics can be avoided.

By the way, it has been found that although the above-described multilayer varistor 20 can improve moisture resistance and plating resistance, leakage current is likely to occur, and there is a risk of short circuit in some cases. This is because a current flows in a portion other than the earthen floor of the internal electrode 21 for obtaining varistor characteristics.For example, the derivation layer 23 has a structure in which AI or the like is dissolved therein.

The lower part 23a tends to protrude inward, so that the other end surfaces 21b of the uppermost and lowermost internal electrodes 21 and the derivation layer 2
It is thought that the gap between the upper and lower portions 23a of 3 becomes smaller, and leakage current occurs in these parts.

An object of the present invention is to provide a multilayer varistor that can prevent deterioration of varistor characteristics by preventing deterioration of internal electrodes due to high humidity and plating solution, and can further improve reliability of quality by preventing leakage current. There is a particular thing.

[Means for solving problems]

Therefore, the present invention connects a ceramic layer and an internal electrode such that one end surface of the internal electrode is located inward with a connection gap, and the other end surface is located inward with a non-connection gap wider than the connection gap. By alternately stacking the layers to form a laminate, and lowering the resistance of the connection gap portions at both ends of the laminate, one end surface of the internal electrodes is electrically led out alternately to the end surface of the laminate. The multilayer varistor is characterized in that a derivation layer is formed, and the non-connection gap of the internal electrode located in the outer rain layer of the multilayer body is made larger than the non-connection gap of the other internal electrodes.

Here, the connection gap means the distance from one end surface of the internal electrode to the end surface of the laminate, and the non-connection gap means the distance from the other end surface of the internal electrode to the end surface of the laminate.

Also, making the non-connection gap of the internal electrode of the rain layer outer layer larger than the connection gap of other internal electrodes means that one end surface of the internal electrode of the rain layer outer layer is connected to the derivation layer, and its length is set to be larger than that of the other internal electrodes. This means that the length is shorter than the length, and it is preferable that the length does not exceed 1/2 of the length of the laminate.

[Effect]

According to the multilayer varistor according to the present invention, one end surface 2 of the internal electrode is located inside the laminate with a connecting gap and a non-connecting gap, respectively, and is embedded in the laminate, so that the internal electrode The exposed part of the varistor can be completely eliminated, preventing deterioration of the internal electrodes even in a humid atmosphere, and preventing the plating liquid from entering when forming the external electrodes, thereby avoiding deterioration of varistor characteristics. can. In this case, since one end surface of each internal electrode is connected to the lead-out layer, it can be connected to the external electrode via the lead-out layer.

Furthermore, in the present invention, the non-connection gap between the other end surface of the inner electrode of the outermost layer and the end surface of the laminate is made larger than other non-connection gaps, so that the non-connection gap is larger than the other non-connection gaps.

Even if the lower part protrudes inward, there is a sufficient distance between it and the other end surface, and as a result, no current flows through this part, preventing leakage current and reducing power consumption, thermal runaway, etc. problems can be resolved and quality reliability can be improved.

〔Example〕

Embodiments of the present invention will be described below 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, l denotes the laminated varistor of this embodiment, and this varistor 1 has a rectangular parallelepiped shape, and a ZnO ceramic layer 2 that exhibits a varistor function and an internal electrode 3' or 3 made of PT are alternately arranged. External electrodes 5 made of Ag/Pa are formed on the left and right end surfaces 4a and 4b of a sintered body 4 formed by laminating them and firing them together.

Further, one end surface 3a of the internal electrode 3 is alternately positioned inwardly with a connecting gap T adjacent to both end surfaces 4a, 4b of the sintered body 4, and the other end surface 3b is also alternately located. A non-connection gap t, which is wider than the connection gap T, is opened from both end surfaces 4a and 4b of the sintered body 40 and is located inwardly, so that each internal electrode 3 is embedded and enclosed within the sintered body 4. has been done.

Furthermore, a derivation layer 6 made by lowering the resistance of the ceramic layer 2 is formed on the left and right end surfaces 4a and 4b of the sintered body 4, and the derivation layer 6 extends inward from the connection gear 711 portion. The inner electrode 3 has a thickness such that it is connected to one end surface 3a of the internal electrode 3. This derivation layer 6 has the above-mentioned both end surfaces 4a and 4b.
It is formed by applying a paste containing Al as a main component to the portion and heating it to form a solid solution in the ZnO of the sintered body 4, thereby reducing the resistance value of this portion. Further, the outer surface of the derivation layer 6 is connected to the external electrode 5 , so that each of the internal electrodes 3 is electrically connected to the external electrode 5 via the derivation layer 6 .

The non-connection gap (' is the non-connection gap t of the other internal electrode 3) between the other end surface 3C of the uppermost and lowermost internal electrodes 1ii3' and the left and right end surfaces 4a and 4b of the sintered body 4.
It is formed larger.

That is, one end surface 3 of the uppermost and lowermost internal electrodes 3'
The length from a to the other end surface 3C is shorter than 172, which is the length l of the sintered body 4.

Next, a method for manufacturing the multilayer varistor I of this example will be described.

■ First, Z n O (95, Omoj%), Coo (
1゜0moj%), MnO (1.0mol
%), S bx 0s (2,0moj!
%), Crl o2 (1, Om
oj! %) in a ceramic material made by mixing B
, O,, SiOx, PbO, and ZnO are added as a raw material in 1O-[%, and an organic binder is mixed with this to form a green sheet by a doctor blade method. This green sheet is cut into rectangular shapes of a predetermined size to form a large number of rectangular ceramic layers 2.

■Next, as shown in Figure 3, each of the above ceramics N2
Internal electrodes 3' and 3 are formed by printing a paste made of a mixture of PT and vehicle on the upper surface of the electrode. In this case, one end surface 3a of each of the internal electrodes 3', 3 is located inward from the left and right end surfaces 2a, 2b of the ceramic layer 2 alternately with connection gaps T opened, and The other end surfaces 3b of the internal electrodes 3 other than the internal molds 8i3' located therein are alternately located inside with non-connection gaps opened from the left and right end surfaces 2a and 2b of the ceramic layer 2.

And the internal electrodes 3' located at the top and bottom
The other end surface 3c is formed so as to be located approximately in the center with a non-connection gap t' opened from the left and right end surfaces 2a and 2b of the ceramic layer 2, respectively.

(2) Next, the ceramic layer 2 and the internal electrodes 3' or 3 are alternately overlapped, and the one end surface 3a of the internal electrode 3'3 is
are stacked one after another so that they are alternately located on the left and right sides, and then a dummy ceramic sheet 8 is placed on top of this laminate, 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) Then, the above laminate is heated and fired in air at 1200°C for 3 hours to obtain a sintered body 4. Next, this sintered body 4 is obtained.
A paste containing AI as a main component is applied to the left and right end surfaces 4a and 4b of the substrate, and the paste is heat-treated at 1000° C. for 1 hour. Through this heat treatment, AjlO2 is dissolved in ZnO on both end surfaces 4a and 4b of the sintered body 4, and the end surfaces 4a and
The resistance value of the portion 4b decreases to form a derivation layer 6, and the derivation layer 6 and one end surface 3a of each internal electrode 3 are connected. Here, as the metal forming the derivation layer 6, A
In addition to 1, Ga, Gd, Y, etc. can be used.

(2) Finally, a paste consisting mainly of Ag with addition of Pd is applied to the outer surface of the derivation layer 6, and this is baked to form the external electrode 5. In this way, the multilayer varistor 1 of this example is manufactured.

Next, the effects of this embodiment will be explained.

According to this embodiment, each internal electrode 3 is encapsulated within the ceramic layer 2 so that the internal electrode 3 is not exposed.
Even when used in a high humidity atmosphere, the internal electrodes 3 will not change in quality, and even if the sintered body 4 is immersed in an electrolytic plating solution, the plating solution will not penetrate, so the varistor characteristics can be improved. Deterioration can be prevented. Furthermore, in this embodiment, the derivation layer 6
and each internal electrode 3 are electrically connected and connected to the external electrode 5 via the derivation layer 6, so that the internal electrode 3 can be led out to the outside while being sealed inside. Moreover, this derivation layer 6 can be realized by simply applying a paste such as AN and heating it.
Easy to manufacture.

Further, according to this embodiment, the uppermost and lowermost internal electrodes 3
``Other end surface 3C and both end surfaces 4a of the sintered body 4.

4b is made larger than the non-connection gap t of the other internal electrodes 3, that is, the other end surface 3C
Since the distance between the derivation layer 6 and the external electrode 5 is sufficient, current will not flow to any part other than the earthen floor of the internal electrode 3 for obtaining varistor characteristics, and as a result, leakage current can be prevented. Furthermore, problems such as power consumption and thermal runaway can be resolved, and quality reliability can be improved.

The table shows the results of characteristic tests conducted to confirm the effects of this example.

In this test, the laminated varistor produced by the manufacturing method of this example was left in an atmosphere with a temperature of 60° C. and a relative humidity of 90% for 1000 hours, and then V, , and ■. 1□
The rate of change was investigated. Also, the leakage current μA is 6 of VlaA.
Measured at 0% voltage. For comparison, a conventional multilayer varistor (with the structure shown in Fig. 6) in which the end faces of the internal electrodes are exposed on the surface of the sintered body, and a conventional multilayer varistor in which the internal electrodes are buried in the sintered body and all internal A similar test was also conducted on a comparative multilayer varistor (having the structure shown in FIG. 5) having electrodes of the same length.

As is clear from the table, in the case of the conventional sample (column 2) in which the end face of the internal electrode is exposed, the leakage current is not so large, but the VlaA r Va,t exhibits moisture resistance.
am (7) The rate of change is -8%, -23%, and the varistor characteristics are deteriorated. In addition, in the case of the comparative sample (column 3) in which the internal electrode is embedded in the sintered body, VlaA
+Vo, +*a (7) The rate of change was -4°6%, indicating that the moisture resistance was improved compared to the conventional sample. However, the leakage current is as large as 0.95 μA. On the other hand, in the sample of this example (column 1), VIIIA + vl + aA (D change rate is -4
, -6%, the moisture resistance is improved like the above comparative sample, and the leakage current is also 0.13 μA.
It can be seen that this is an improvement over the conventional sample and comparative sample.

Furthermore, although a metal layer was applied to the external electrode of the sample of this example by plating, no deterioration of the characteristics was observed at all due to this.

FIG. 4 shows a modification of the above embodiment, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts.

This multilayer varistor l connects the left and right outer end surfaces 9a of the uppermost and lowermost internal electrodes 9 to the lead-out layer 6, and provides a gap between the inner end surfaces 9b of the inner electrodes 9 to connect the internal electrodes 9 to the two. This is an example in which a larger non-connection gap t' is formed between the inner end surface 9b and the left and right end surfaces 4a and 4b of the sintered body 4 on the opposite side. In this case as well, deterioration of the internal electrodes can be prevented and leakage current can be prevented, and the same effects as in the above embodiment can be obtained. Moreover, according to this structure, printing and lamination work of internal electrodes can be facilitated.

〔Effect of the invention〕

As described above, according to the multilayer varistor according to the present invention,
One end surface of the internal electrode is positioned inward with a connection gap, the other end surface is positioned inward with a non-connection gap wider than the connection gap, and one end surface of the internal electrode is alternately placed on both ends of the laminate. In addition to forming a lead-out layer that electrically leads to This has the effect of preventing electrode deterioration and deterioration of varistor characteristics, as well as preventing leakage current and improving quality reliability.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining a multilayer varistor according to an embodiment of the present invention, and FIG. 1 is a diagram showing the I of FIG.
-1 line sectional view, FIG. 2 is a perspective view thereof, FIG. 3 is a plan view of the exploded state, FIG. 4 is a sectional view showing a modification of the above embodiment, and FIG. 5 is a process of establishing the present invention. 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 another internal electrode, 3' and 9 are the topmost electrodes. The lowermost (outermost layer) internal electrode, 3a and 9a are one end surface of the internal electrode, 3b is the other end surface, 3c and 9b are the other end surfaces of the uppermost and lowermost internal electrodes, 4 is a sintered body (laminated body) , 4a, 4
b is the left and right end surfaces of the sintered body, 6 is a lead-out layer, T is a connection gap, t is a non-connection gap, and t' is a non-connection gap between the uppermost and lowermost internal electrodes.

Claims (1)

[Claims] (1) A ceramic layer that exhibits a varistor function and an internal electrode are arranged such that one end surface of the internal electrode is located inward from the end surface of the ceramic layer with a connection gap, and the other end surface is a non-connection gap that is wider than the connection gap. By forming a laminate by alternately stacking the inner electrodes so that they are open and positioned inward, and by lowering the resistance of the connection gap portions at both ends of the laminate, one of the internal electrodes is formed on both end surfaces of the laminate. It is characterized by forming lead-out layers that electrically lead out the end faces alternately, and further making the non-connection gaps of the internal electrodes located at both outermost layers of the laminate larger than the non-connection gaps of the other internal electrodes. Laminated varistor.