JP2008270328A - Laminated varistor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated varistor that has high reliability that can withstand under a severe usage environment, such as an electronic device for vehicle, and to provide its manufacturing method. <P>SOLUTION: The laminated varistor is provided with a sintere 11 that is formed, by alternatively laminating a varistor layer 12 and an internal electrode 13 and sintering the laminated body and a pair of external electrodes, wherein the internal electrode 13 is alternatively connected with at least both end faces of the sintere 11. The pair of external electrodes is formed of two layers, having different quantities of glass, and the glass content of an inside first external electrode 14 connected to the internal electrode is 5 wt.% or lower (includes zero). The glass content of a second external electrode 15, formed outside on the first external electrode 14, is 10 wt.% to 30 wt.%, thereby preventing infiltration of water content from the outside and obtaining a high-reliability laminated varistor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer varistor used for protecting various electronic devices and in-vehicle electronic devices from malfunction caused by abnormal voltage or noise, and a method for manufacturing the same.

  In recent years, zinc oxide has been used for the purpose of protecting various electronic devices and in-vehicle electronic devices from abnormal voltage due to lightning surge voltage, static electricity, etc., and preventing electronic devices and electronic devices from malfunctioning due to noise generated in the circuit. Many laminated varistors having a main component have been used.

  FIG. 2 is a partially cutaway perspective view of a general laminated varistor 21, in which ceramic layers 22 and internal electrodes 23 made of a varistor material are alternately laminated and sintered to form a sintered body. Are laminated so that their end faces are alternately exposed at opposite end faces of the sintered body, and are alternately connected to a pair of external electrodes 24 formed at both end faces of the sintered body.

As prior art document information related to the invention of the present application, for example, Patent Document 1 is known.
JP 2000-277306 A

  The ceramic layer 22 constituting the laminated varistor 21 mainly composed of zinc oxide is not an insulator but a semiconductor ceramic. Therefore, when moisture, acid, or alkaline liquid infiltrates into the sintered body, the characteristics are as follows. Easy to deteriorate.

  For this reason, it is important to prevent moisture and the like from entering the sintered body.

  In particular, electronic components used in in-vehicle electronic devices are required to withstand more severe usage environments, and further prevent such moisture, acid, and alkaline liquids from entering the sintered body. It is necessary to ensure high reliability.

  Accordingly, an object of the present invention is to provide a highly reliable multilayer varistor that can withstand harsh usage environments such as in-vehicle electronic devices and a method for manufacturing the same.

  In order to achieve this object, the laminated varistor of the present invention comprises a sintered body obtained by sintering a laminated body in which varistor layers and internal electrodes are alternately laminated, and the internal electrodes are provided on at least both end faces of the sintered body. A pair of external electrodes provided in an alternately connected state, and the pair of external electrodes is composed of two layers having different glass amounts. Of the two layers of external electrodes, the inner electrodes connected to the internal electrodes The glass content of the first external electrode is 5% by weight or less (including 0), and the glass content of the second external electrode formed outside on the first external electrode is 10% by weight or more. And a manufacturing method thereof.

  According to the present invention, the glass content of the inner first external electrode in contact with the internal electrode is reduced to 5% by weight or less so that the first external electrode is densely formed to prevent the intrusion of moisture and the like from the outside. In addition, the glass content of the second external electrode and the first external electrode are increased by increasing the glass content of the second external electrode formed outside the first external electrode to 10 wt% to 30 wt%. The Zn component of the sintered body in the vicinity of the terminal portion of the metal reacts to form a glass layer near the surface inside the sintered body facing the terminal portion of the external electrode. Is prevented from entering the sintered body, and a highly reliable laminated varistor can be obtained.

  Hereinafter, a laminated varistor of the present invention and a manufacturing method thereof will be described with reference to an embodiment and drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view of the multilayer varistor according to the first embodiment. The varistor layers 12 and the internal electrodes 13 are alternately laminated and then sintered to form a sintered body 11, and the internal electrodes 13 are alternately paired. The first external electrode 14 is connected.

  A second external electrode 15 having a glass content higher than that of the first external electrode 14 is provided on the first external electrode 14.

  Here, since the first external electrode 14 is directly bonded to the internal electrode 13, it is necessary to be dense.

  If the first external electrode 14 is a porous electrode, when moisture from the outside enters, the moisture penetrates into the sintered body 11 through the interface between the internal electrode 13 and the varistor layer 12, and the laminated varistor. This leads to deterioration of the characteristics.

  In order to make the first external electrode 14 dense, it is desirable that the glass frit or ceramic powder other than the metal component is not contained or is contained in a small amount.

  Therefore, it is preferable that the first external electrode 14 has a composition as close to pure metal as possible, and the glass content with respect to the metal amount is preferably suppressed to 5% by weight or less.

  When the glass content exceeds 5% by weight, the metal and the glass cannot be completely compatible with each other, which may cause pores and increase the possibility of moisture entering the internal electrode 13 through the first external electrode 14. .

  Further, since the first external electrode 14 is in direct contact with the end face of the varistor layer 12, if the glass content increases beyond 5% by weight, the glass diffuses into the varistor layer 12 and the varistor voltage decreases. This is not preferable because it leads to a decrease in characteristics.

  The second external electrode 15 formed on the first external electrode 14 does not come into direct contact with the end face of the varistor layer 12 or the internal electrode 13, so that the denseness is not so required.

  Rather, by making the glass content of the second external electrode 15 larger than the glass content of the first external electrode 14, the glass contained in the second external electrode 15 becomes a dense first external electrode. 14, and reacts with the varistor layer 12 at the terminal portion 16 of the first external electrode 14, so that Zn near the surface of the inside of the sintered body facing this terminal portion 16 is formed from Zn which is a component of glass and the sintered body. The glass layer 17 is formed, and it has been confirmed that this glass layer can prevent intrusion of moisture and the like from the terminal portion of the external electrode.

  In the first external electrode 14 in which the ceramic varistor layer 12 is low in glass having high adhesion, the adhesion to the sintered body 11 tends to decrease at the terminal end 16, and moisture is baked through the terminal end 16. There is a possibility of entering the interface of the internal electrode 13 inside the bonded body 11.

  The end portion 16 is shown in two places in the upper and lower portions in FIG. 1, but refers to all portions where the end portion of the first external electrode 14 is in contact with the sintered body.

  As described above, in the multilayer varistor of the present embodiment, the first external electrode 14 that is directly bonded to the internal electrode 13 is made dense to prevent water intrusion, and the water intrusion from the terminal portion 16 is also terminated. This is prevented by forming the glass layer 17 in the vicinity of the portion 16.

  With this configuration, a highly reliable laminated varistor can be obtained.

  Next, the manufacturing method of the laminated varistor according to the embodiment of the present invention will be described.

  First, a ceramic slurry is prepared by mixing a varistor powder mainly composed of ZnO and made of additives such as oxides of Bi and Sb, a polyvinyl butyral resin as an organic material, a solvent, a plasticizer, a dispersant, and the like. A green sheet to be the ceramic layer 12 is produced by firing using a doctor blade method or the like.

  On the other hand, an electrode paste is prepared by mixing a metal powder made of Ag and a vehicle made of a solvent, a resin, a plasticizer, or the like as an organic material, and this electrode paste is applied on a green sheet by a screen printing method to form an internal electrode. A conductor layer to be 13 is formed.

  Next, after stacking 17 green sheets on which the conductor layer is formed, one or more green sheets not coated with electrode paste are stacked on the upper and lower layers to form upper and lower protective layers. A body green block (not shown) was prepared.

  Next, this laminate green block is cut into dimensions of 6.6 mm in length, 5.8 mm in width, and 3.3 mm in thickness, and a substantially rectangular parallelepiped laminate (not shown) that becomes a sintered body 11 by firing. Produced. At this time, the both end surfaces of the laminate were structured such that one end of the conductor layer was alternately exposed every other layer across the green sheet.

  After debinding the laminate, the laminate was fired at a temperature of 800 ° C. to 950 ° C. to obtain a sintered body 11 having a length of 5.7 mm, a width of 5.0 mm, and a thickness of 2.7 mm.

  The sintered body 11 is barrel-polished to chamfer corners, and a conductor layer is formed using an electrode paste containing borosilicate glass in an amount of 5% by weight or less with respect to a metal component on a pair of both end faces. Formed and baked to form the first external electrode 14.

  Thereafter, a conductive layer is formed on the first external electrode 14 by using an electrode paste containing 5 to 20% by weight of borosilicate glass and having a larger amount of glass than the electrode paste used for the first external electrode 14. Were formed and baked to form the second external electrode 15, thereby preparing samples Nos. 2 to 6.

  In addition, as a comparative example, the second external electrode 15 is not formed and the first external electrode 14 is formed using an electrode paste not containing glass (sample number 1), and the glass content is the present embodiment. Samples outside the range (sample number 2) were produced, and each was laminated and fired in the same manner as in this embodiment to produce a laminated varistor of a comparative example.

  By the EPMA (electron beam microanalysis) analysis of the cross sections of sample numbers 2 to 7, it was confirmed that a glass layer mainly composed of Si and Zn was formed.

  A reliability test was performed by applying a rated voltage (16 V) to the multilayer varistor according to the first embodiment and the multilayer varistor of the comparative example in high temperature and high humidity of 85 ° C. and 85%.

The varistor voltage V _{1 mA} of the sample after the test is measured, and the change rate of 10% or more compared with the varistor voltage before the test is counted as the number of defects (Table 1).

  In Table 1, the sample number with an asterisk (*) indicates that it is out of the scope of the present embodiment.

  As shown in (Table 1), in Sample No. 1 in which the second external electrode 15 was not provided, moisture entered from the vicinity of the terminal portion of the external electrode, and 17 out of 30 defects were observed.

  In addition, although the second external electrode 15 was formed, in the sample number 2 whose glass content is outside the range of the present embodiment, 6 out of 30 defects were similarly observed.

  In the sample number 7 in which the glass content of the second external electrode 15 is 35% by weight outside the range of the present embodiment, the change rate of the varistor voltage did not exceed 10% in the reliability test. The glass floated on the surface of the external electrode 15, resulting in poor electrical contact with the external terminal for varistor voltage measurement.

  For this reason, the varistor voltage was measured by removing the glass on the surface of the second external electrode so as to ensure electrical contact with the external terminal, but the solderability was significantly impaired.

  As is apparent from the above results, the glass content of the inner first external electrode 14 connected to the internal electrode out of the two layers of external electrodes according to the present embodiment is 5% by weight or less, and The glass content of the second external electrode 15 formed outside on the first external electrode 14 is 10% by weight to 30% by weight, thereby preventing deterioration of characteristics due to moisture intrusion from the outside. It can be seen that a highly functional laminated varistor can be obtained.

  The multilayer varistor of the present invention is a dense external electrode in which the glass content of the first external electrode directly bonded to the internal electrode is reduced, and further includes a large amount of glass formed on the first external electrode. The glass layer for preventing moisture intrusion is formed inside the sintered body near the wraparound terminal portion of the external electrode by the external electrode 2 and can maintain high reliability even in high temperature and high humidity. This is useful for laminated varistors used in electronic devices for electronic devices and various electronic devices.

Sectional drawing of the laminated varistor in Embodiment 1 of this invention Partial cutaway perspective view of a typical laminated varistor

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Sintered body 12 Varistor layer 13 Internal electrode 14 1st external electrode 15 2nd external electrode 16 Termination part 17 Glass layer 21 Multilayer varistor 22 Ceramic layer 23 Internal electrode 24 External electrode

Claims (2)

A sintered body obtained by sintering a laminate in which varistor layers and internal electrodes are alternately laminated, and a pair of external electrodes provided in a state in which the internal electrodes are alternately connected at least at both end faces of the sintered body. And the pair of external electrodes is composed of two layers having different glass amounts, and the glass content of the inner first external electrode connected to the internal electrode among the external electrodes composed of the two layers is 5% by weight or less ( And a glass content of the second external electrode formed outside on the first external electrode is 10% by weight to 30% by weight. Laminating step for alternately laminating varistor layers and internal electrodes to obtain a laminated body, firing step for firing the laminated body to obtain a sintered body, and external electrodes for forming external electrodes on both end faces of the sintered body A method of manufacturing a laminated varistor including a forming step, wherein the electrode forming step forms a first external electrode having a glass content of 5% by weight or less (including 0) on both end faces of the sintered body, A method for producing a laminated varistor, comprising forming a second external electrode having a glass content of 10 wt% to 30 wt% on a first external electrode.

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