JP2008091441A - Varistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a varistor capable of obtaining desired varistor characteristics by preventing generation of varistor characteristics on a portion other than a portion between internal electrodes. <P>SOLUTION: Li is dispersed on a varistor element body 11 of a stacked chip varistor 1 from its external surface side. A region where Li is dispersed near the external surface of the varistor element body 11 has a very high electric resistance. Accordingly, a varistor voltage of a region between the two terminal electrodes 51 in the varistor element body 11 and a varistor voltage of a region between the two connection conductors 41 in the varistor element body 11 are extremely higher than a varistor voltage of a region between the first and second internal electrodes 23, 33 in the varistor element body 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a varistor, and more particularly, to a varistor including a sintered body mainly composed of ZnO and exhibiting voltage nonlinear characteristics.

As this type of varistor, a sintered body mainly composed of ZnO and exhibiting a voltage non-linear characteristic, a pair of internal electrodes disposed in the sintered body so as to face each other at a predetermined interval, and sintered A device including a pair of terminal electrodes that are arranged on the outer surface of the body and electrically connected to corresponding internal electrodes among a plurality of internal electrodes is known (for example, see Patent Document 1).
JP 2002-246207 A

  It is an object of the present invention to provide a varistor capable of obtaining desired varistor characteristics by suppressing occurrence of voltage non-linear characteristics (hereinafter referred to as varistor characteristics) except in a region between a plurality of internal electrodes. And

  In recent years, with the miniaturization of electronic devices such as DSC (Digital Still Camera), DVC (Digital Video Camera), PDA (Personal Digital Assistant), notebook personal computers or mobile phones, there is a demand for high-density mounting of electronic components such as varistors. Is getting tougher. In order to satisfy the demand for high-density mounting, it is considered that the electronic component package is a ball grid array package (hereinafter simply referred to as a BGA package). The BGA package has a large number of solder bumps arranged in parallel on the back surface thereof. The BGA package is mounted on the mounting substrate by reflowing each solder bump in a state of being superimposed on the corresponding pad of the mounting substrate.

  As a configuration in which the varistor is made to correspond to the BGA package, a configuration in which solder bumps and terminal electrodes are arranged on the back side facing the mounting substrate is conceivable. However, when the solder bumps and terminal electrodes are arranged on the back side facing the mounting substrate, it is difficult to identify the mounting direction of the varistor. If the varistor is mounted with its mounting direction being incorrect, it will not function properly.

  Therefore, the varistor according to the present invention has ZnO as a main component and develops voltage nonlinear characteristics, and has a sintered body having first and second principal surfaces facing each other, and at least some of them face each other. In this way, the plurality of internal electrode pairs having the first and second internal electrodes arranged in the sintered body and the first internal electrodes of the predetermined internal electrode pair among the plurality of internal electrode pairs are electrically connected to each other. A plurality of connection conductors formed on the first main surface so as to be connected to each second internal electrode of the plurality of internal electrode pairs, and electrically connected to the second internal electrode A plurality of terminal electrodes formed on the second main surface, and a varistor voltage higher than a varistor voltage in a region between the plurality of internal electrode pairs in the sintered body is provided between the plurality of connection conductors. The region having the first main surface side is formed with a plurality of terminal currents. Between, wherein the region having a high varistor voltage than the varistor voltage of the region between the plurality of internal electrode pairs in the sintered body is formed from the second major surface side.

  In the varistor according to the present invention, since the plurality of terminal electrodes are formed on the second main surface, the varistor is in a state in which the second main surface is opposed to a mounting component (for example, an electronic component or a mounting substrate). Thus, a configuration corresponding to the BGA package is realized. Since the connection conductor is formed on the first main surface so as to electrically connect the first internal electrodes of the predetermined internal electrode pair among the plurality of internal electrode pairs, the connection conductor is formed at a position corresponding to the connection conductor. There will be a region that functions as a varistor. Therefore, the connection conductor functions as a mark for identifying the mounting direction of the varistor, and the varistor can be mounted appropriately and easily. Further, according to the present invention, it is not necessary to newly provide a mark for identifying the mounting direction of the varistor, and the manufacturing cost of the varistor does not increase.

  By the way, the present inventors made a varistor having a configuration in which a plurality of terminal electrodes are arranged on the second main surface of a sintered body mainly composed of ZnO, and examined the electrical characteristics thereof. In such varistors, a new fact has been found that varistor characteristics occur not only in a region between a plurality of internal electrode pairs but also in a region between a plurality of terminal electrodes.

  The phenomenon that varistor characteristics occur between a plurality of terminal electrodes is considered to be due to the following reason. When a potential difference occurs between the plurality of terminal electrodes, an electric field is generated between the plurality of terminal electrodes. Since the electric lines of force in this electric field pass through the vicinity of the outer surface of the sintered body on which the plurality of terminal electrodes are formed, varistor characteristics occur in the region between the plurality of terminal electrodes in the sintered body.

  The vicinity of the outer surface of the sintered body is more susceptible to the firing atmosphere and heat than the inside of the sintered body, and variations in oxygen diffusion and ZnO crystal growth are likely to occur. Further, in the vicinity of the outer surface of the sintered body, ZnO crystal growth is promoted by heat and oxygen diffusion, and the varistor voltage tends to be lower than in the inside of the sintered body. For this reason, the varistor characteristics generated in the region between the plurality of terminal electrodes in the sintered body have variations and cannot be ignored with respect to the varistor characteristics generated in the region between the plurality of internal electrodes in the sintered body. The varistor characteristics will be affected.

  Usually, in the multilayer chip varistor, each terminal electrode is disposed at the end of the sintered body, and therefore the distance between the terminal electrodes is relatively large. Therefore, varistor characteristics that occur in the region between the plurality of terminal electrodes in the sintered body are unlikely to occur, and even if varistor characteristics occur, the varistor characteristics that occur in the region between the plurality of internal electrodes in the sintered body are ignored. it can.

  However, as described above, due to the demand for downsizing of electronic components, when the varistor is configured to correspond to the BGA package, the interval between the plurality of terminal electrodes arranged on the same outer surface becomes extremely small. End up. For this reason, the influence of the varistor characteristics generated in the region between the plurality of terminal electrodes in the sintered body becomes larger. Note that, for the same reason that varistor characteristics occur in the region between the plurality of terminal electrodes in the sintered body, varistor characteristics also occur in the region between the plurality of connection conductors in the sintered body.

  On the other hand, in the varistor according to the present invention, the varistor voltage in the region between the plurality of connection conductors in the sintered body is higher than the varistor voltage in the region between the plurality of internal electrodes in the sintered body. Therefore, it is difficult for varistor characteristics to occur in the region between the plurality of connecting conductors in the sintered body, and even if varistor characteristics occur in the region, the varistor characteristics occur in the region between the plurality of internal electrodes in the sintered body. Negligible for varistor characteristics. In the varistor according to the present invention, the varistor voltage in the region between the plurality of terminal electrodes in the sintered body is higher than the varistor voltage in the region between the plurality of internal electrodes in the sintered body. Therefore, varistor characteristics hardly occur in the region between the plurality of terminal electrodes in the sintered body, and even if varistor characteristics occur in the region, the varistor characteristics occur in the region between the plurality of internal electrodes in the sintered body. Negligible for varistor characteristics. As a result, the occurrence of varistor characteristics outside the region between the plurality of internal electrodes is suppressed, and desired varistor characteristics can be obtained.

  Preferably, in the region having a varistor voltage higher than the varistor voltage in the region between the plurality of internal electrode pairs in the sintered body located between the plurality of connection conductors, the alkali metal is diffused from the first main surface side. The region having a varistor voltage higher than the varistor voltage in the region between the plurality of internal electrode pairs in the sintered body, which is formed between the plurality of terminal electrodes, diffuses alkali metal from the second main surface side. Is formed. In this case, the region between the plurality of connection conductors in the sintered body and the region between the plurality of terminal electrodes in the sintered body are substantially electrically insulated. Thus, the varistor voltage in the region between the plurality of connecting conductors in the sintered body and the varistor voltage in the region between the plurality of terminal electrodes in the sintered body are changed to the varistor voltage in the region between the plurality of internal electrodes in the sintered body. Can be made higher than that.

  In addition, the varistor according to the present invention has ZnO as a main component and develops voltage non-linear characteristics, and has a sintered body having first and second main surfaces facing each other, and at least some of them face each other. In this way, a plurality of internal electrode pairs having first and second internal electrodes arranged in the sintered body, a plurality of internal conductors arranged in the sintered body, and the first internal electrode and the internal in the internal electrode pair A plurality of connection conductors formed on the first main surface so as to be electrically connected to the conductor, and a first formed on the second main surface so as to be electrically connected to the second internal electrode. Terminal electrodes and a second terminal electrode formed on the second main surface so as to be electrically connected to the internal conductor, and a plurality of internal electrodes in the sintered body between the plurality of connection conductors. A region having a varistor voltage higher than the varistor voltage in the region between the pair is the first main surface. Between the first terminal electrode and the second terminal electrode, a region having a varistor voltage higher than the varistor voltage in the region between the plurality of internal electrode pairs in the sintered body is the second terminal electrode. It is formed from the main surface side.

  In the varistor according to the present invention, since the first and second terminal electrodes are formed on the second main surface, the second main surface is made to face a mounting component (for example, an electronic component or a mounting substrate). The varistor can be mounted in a state, and a configuration corresponding to the BGA package is realized. In the varistor according to the present invention, since the connection conductor is formed on the first main surface so as to electrically connect the first internal electrode and the internal conductor in the internal electrode pair, it corresponds to the connection conductor. A region functioning as a varistor will be present at the position. Therefore, the connection conductor functions as a mark for identifying the mounting direction of the varistor, and the varistor can be mounted appropriately and easily. Further, according to the present invention, it is not necessary to newly provide a mark for identifying the mounting direction of the varistor, and the manufacturing cost of the varistor does not increase.

  Furthermore, in the varistor according to the present invention, the varistor voltage in the region between the plurality of connection conductors in the sintered body is higher than the varistor voltage in the region between the plurality of internal electrodes in the sintered body. Therefore, it is difficult for varistor characteristics to occur in the region between the plurality of connecting conductors in the sintered body, and even if varistor characteristics occur in the region, the varistor characteristics occur in the region between the plurality of internal electrodes in the sintered body. Negligible for varistor characteristics. In the varistor according to the present invention, the varistor voltage in the region between the first terminal electrode and the second terminal electrode in the sintered body is larger than the varistor voltage in the region between the plurality of internal electrodes in the sintered body. Get higher. Therefore, varistor characteristics hardly occur in a region between the first terminal electrode and the second terminal electrode in the sintered body, and even if varistor characteristics occur in the region, the varistor characteristics are The varistor characteristics generated in the region between the plurality of internal electrodes can be ignored. As a result, the occurrence of varistor characteristics outside the region between the plurality of internal electrodes is suppressed, and desired varistor characteristics can be obtained.

  Preferably, in the region having a varistor voltage higher than the varistor voltage in the region between the plurality of internal electrode pairs in the sintered body located between the plurality of connection conductors, the alkali metal is diffused from the first main surface side. The region having a varistor voltage higher than the varistor voltage of the region between the plurality of internal electrode pairs in the sintered body, which is formed between the first terminal electrode and the second terminal electrode. It is formed by diffusing alkali metal from the main surface side. In this case, the region between the plurality of connection conductors in the sintered body and the region between the first terminal electrode and the second terminal electrode in the sintered body are substantially electrically insulated. Become. Thereby, the varistor voltage in the region between the connection conductors in the sintered body and the varistor voltage in the region between the first terminal electrode and the second terminal electrode in the sintered body It can be easily made higher than the varistor voltage in the region between the internal electrodes.

  Preferably, the alkali metal is Li. Li has a relatively small ionic radius and is liable to be dissolved in ZnO crystals. For this reason, it is ensured that the region between the plurality of connecting conductors in the sintered body, the region between the plurality of terminal electrodes in the sintered body, or between the first terminal electrode and the second terminal electrode in the sintered body. The region can be substantially electrically isolated.

  Preferably, the sintered body contains a rare earth metal as an auxiliary component for developing varistor characteristics. When the rare earth metal is included, the sintered body becomes a densified structure. For this reason, the alkali metal hardly diffuses from the one outer surface of the sintered body to a deep portion, and does not reach the region between the plurality of internal electrodes in the sintered body. As a result, it is possible to prevent the diffused alkali metal from affecting the varistor characteristics generated in the region between the plurality of internal electrodes in the sintered body. More preferably, the rare earth metal is Pr.

  According to the present invention, it is possible to provide a varistor capable of suppressing desired varistor characteristics from being generated outside the region between the plurality of internal electrodes and obtaining desired varistor characteristics.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

(First embodiment)
The configuration of the multilayer chip varistor 1 according to the first embodiment will be described with reference to FIGS. FIG. 1 is a perspective view showing the multilayer chip varistor according to the first embodiment as viewed from the first main surface side of the varistor element body. FIG. 2 is a perspective view showing the multilayer chip varistor according to the first embodiment, as viewed from the second main surface side of the varistor element body. FIG. 3 is a diagram for explaining a cross-sectional configuration along the line III-III in FIG. 1. FIG. 4 is a diagram for explaining a cross-sectional configuration along the line IV-IV in FIG. 3. FIG. 5 is a diagram for explaining a cross-sectional configuration along the line V-V in FIG. 4.

  As shown in FIGS. 1 to 5, the multilayer chip varistor 1 includes a varistor element body 11, a plurality (two in the present embodiment) of connection conductors 41, and a plurality (four in the present embodiment). ) Terminal electrode 51.

  The varistor element body 11 has a substantially rectangular plate shape. For example, the varistor element body 11 is set to have a length of about 1 mm, a width of about 1 mm, and a thickness of about 0.5 mm. The varistor element body 11 has a first main surface 13 and a second main surface 15 that face each other. The first main surface 13 and the second main surface 15 have a square shape. That is, the varistor element body 11 has a square shape when viewed from a direction perpendicular to the first main surface 13 and the second main surface 15.

  The varistor element body 11 is a sintered body that exhibits varistor characteristics, and is configured as a laminated body in which a plurality of varistor layers are laminated. In the actual multilayer chip varistor 1, the plurality of varistor layers are integrated so that the boundary between them cannot be visually recognized. The varistor layer contains ZnO (zinc oxide) as a main component and also includes rare earth metal elements, Co, group IIIb elements (B, Al, Ga, In), Si, Cr, Mo, alkali metal elements (K, K) as subcomponents. Rb, Cs) and simple earth metals such as alkaline earth metal elements (Mg, Ca, Sr, Ba) and element bodies containing these oxides. In the present embodiment, the varistor layer contains Pr, Co, Cr, Ca, Si, K, Al, and the like as subcomponents.

  In the present embodiment, Pr is used as the rare earth metal. Pr is a material for expressing varistor characteristics. The reason for using Pr is that voltage non-linearity is excellent and characteristic variation during mass production is small.

  In the present embodiment, Ca is used as the alkaline earth metal element. Ca becomes a material for controlling the sinterability of the ZnO-based varistor material and improving the moisture resistance. The reason for using Ca is to improve voltage nonlinearity.

  Although content of ZnO in a varistor layer is not specifically limited, When the whole material which comprises a varistor layer is 100 mass%, it is 99.8-69.0 mass% normally. The thickness of the varistor layer is, for example, about 5 to 60 μm.

  In the varistor element body 11, alkali metal is diffused from the outer surface side, and high resistance in the vicinity of the outer surface of the varistor element body 11 is achieved. When the alkali metal is diffused from the outer surface side of the varistor element body 11, the diffused alkali metal is dissolved in the ZnO crystal. As a result, ZnO, which exhibits properties as an n-type semiconductor, has donors reduced by alkali metal and increases electrical resistance. It is also considered that the electrical resistance is increased by the presence of an alkali metal at the grain boundary of ZnO. In this embodiment, Li is used as the alkali metal diffused in the varistor element body 11.

  In the varistor element body 11, a plurality of (in this embodiment, two layers) first internal electrode layers 21 and second internal electrode layers 31 are disposed. The first internal electrode layer 21 and the second internal electrode layer 31 are arranged so that at least one varistor layer is interposed between them.

  Each first internal electrode layer 21 includes a plurality of (in the present embodiment, two) first internal electrodes 23 as shown in FIGS. 3 to 5. Each first internal electrode 23 has a substantially rectangular shape. One first internal electrode 23 is opposed to one second internal electrode 33, which will be described later, with at least a part thereof sandwiching the varistor layer. The first internal electrodes 23 included in the same first internal electrode layer 21 have a predetermined interval from a side surface parallel to the stacking direction of the varistor layers (hereinafter simply referred to as “stacking direction”) and are electrically connected to each other. Are located at predetermined intervals so as to be electrically insulated. Each first internal electrode 23 is drawn out to the first main surface 13 so that one end thereof faces the first main surface 13.

  As shown in FIGS. 3 to 5, each second internal electrode layer 31 includes a plurality (two in the present embodiment) of second internal electrodes 33. Each second internal electrode 33 has a substantially rectangular shape. One second internal electrode 33 faces at least a part of the first internal electrode 23 across the varistor layer. Similar to the first internal electrode 23, the second internal electrodes 33 included in the same second internal electrode layer 31 have a predetermined interval from the side surface parallel to the stacking direction and are electrically insulated from each other. In this way, they are located at predetermined intervals. Each second internal electrode 33 is drawn out to the second main surface 15 so that one end thereof faces the second main surface 15.

  As described above, the first internal electrode 23 and the second internal electrode 33 are arranged in the varistor element body 11 so that at least some of them face each other. Thereby, in the multilayer chip varistor 1, a plurality of (internal) pairs of internal electrodes including the first and second internal electrodes 23 and 33 disposed in the varistor element body 11 so that at least some of them are opposed to each other are provided. In the embodiment, four) are provided.

  The first internal electrode 23 and the second internal electrode 33 include a conductive material. Although it does not specifically limit as a electrically conductive material contained in the 1st internal electrode 23 and the 2nd internal electrode 33, It is preferable to consist of Pd, an Ag-Pd alloy, or Ag. The thickness of the first internal electrode 23 and the second internal electrode 33 is, for example, about 0.5 to 5 μm.

  The first main surface 13 and the second main surface 15 extend in a direction parallel to the stacking direction and perpendicular to the first and second inner electrodes 23 and 33. The stacking direction is a direction parallel to the facing direction of the first internal electrode 23 and the second internal electrode 33, and is a direction perpendicular to the first and second internal electrodes 23 and 33.

  As shown in FIGS. 3 and 5, each of the connection conductors 41 includes the first inner electrode 23 included in the two internal electrode pairs positioned in the stacking direction among the four internal electrode pairs. It arrange | positions on the 1st main surface 13 so that the part pulled out by 1 main surface 13 may be covered. A portion of the first internal electrode 23 drawn out to the first main surface 13 is physically and electrically connected to the corresponding connection conductor 41. As a result, the connection conductor 41 electrically connects the first internal electrodes 23 included in the two internal electrode pairs positioned side by side in the stacking direction.

  Each connection conductor 41 has a substantially rectangular shape (in this embodiment, a substantially rectangular shape). For example, the connecting conductor 41 has a long side length of about 0.8 mm, a short side length of about 0.4 mm, and a thickness of about 2 μm. The long side direction of the connection conductor 41 is parallel to the stacking direction.

  The connection conductor 41 includes Pt. The connection conductor 41 is formed by baking a conductive paste as will be described later. As the conductive paste, a mixture of metal powder containing Pt particles as a main component and glass frit, an organic binder, and an organic solvent is used.

  As shown in FIGS. 2 and 4, each terminal electrode 51 is provided on the second main surface 15 in correspondence with each second internal electrode 33, and has n rows and n columns (parameter n is equal to n). 2 is an even number of 2 or more). In the present embodiment, the terminal electrodes 51 are two-dimensionally arranged in 2 rows and 2 columns. The terminal electrode 51 has a substantially rectangular shape (in the present embodiment, a substantially square shape). In the terminal electrode 51, for example, the length of each side is set to about 0.4 mm, and the thickness is set to about 2 μm.

  As shown in FIGS. 3 and 5, each terminal electrode 51 is formed on the second main surface 15 so as to cover a portion drawn out to the second main surface 15 of the corresponding second internal electrode 33. Has been placed. The portion of the second internal electrode 33 that is drawn out to the second main surface 15 is physically and electrically connected to the corresponding terminal electrode 51. As a result, the terminal electrode 51 is electrically connected to the corresponding second internal electrode 33.

  The terminal electrode 51 contains Pt. The terminal electrode 51 is formed by baking a conductive paste as will be described later. As the conductive paste, a mixture of metal powder containing Pt particles as a main component and glass frit, an organic binder, and an organic solvent is used. Each terminal electrode 51 is provided with a solder bump 53.

  As described above, the first internal electrode 23 and the second internal electrode 33 are positioned so that at least some of them face each other and overlap each other when viewed from the stacking direction. Therefore, a region that overlaps the first internal electrode 23 and the second internal electrode 33 in the varistor layer, that is, a region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11 is a varistor. It functions as a region that develops characteristics.

  In the multilayer chip varistor 1 having the above-described configuration, as shown in FIG. 6, two sets of two varistors B connected in series are included. Each varistor B is composed of a first internal electrode 23, a second internal electrode 33, and a region overlapping the first and second internal electrodes 23, 33 in the varistor layer.

  As described above, the long side direction of the connection conductor 41 is substantially parallel to the stacking direction, that is, the connection conductor 41 is arranged to extend in the stacking direction. One terminal electrode 51 and the other terminal electrode 51 of two varistors B connected in series are juxtaposed in the stacking direction. Therefore, two varistors B connected in series exist between the pair of terminal electrodes 51 that are juxtaposed in the long side direction of the connection conductor 41.

  Subsequently, a manufacturing process of the multilayer chip varistor 1 having the above-described configuration will be described with reference to FIGS. FIG. 7 is a flowchart for explaining the manufacturing process of the multilayer chip varistor according to the first embodiment. FIG. 8 is a view for explaining the manufacturing process of the multilayer chip varistor according to the first embodiment.

  First, after weighing ZnO, which is a main component constituting the varistor layer, and trace additives such as Pr, Co, Cr, Ca, Si, K, and Al metals or oxides so as to have a predetermined ratio. The varistor material is adjusted by mixing the components (step S101). Then, an organic binder, an organic solvent, an organic plasticizer, etc. are added to this varistor material, and it mixes and grinds for about 20 hours using a ball mill etc., A slurry is obtained.

  The slurry is applied onto a film made of, for example, polyethylene terephthalate by a known method such as a doctor blade method, and then dried to form a film having a thickness of about 30 μm. The film thus obtained is peeled from the film to obtain a green sheet (step S103).

  Next, a plurality of electrode portions (numbers corresponding to the number of divided chips described later) corresponding to the first internal electrodes 23 are formed on the green sheet (step S105). Similarly, a plurality of electrode portions corresponding to the second internal electrode 33 (a number corresponding to the number of divided chips described later) are formed on different green sheets (step S105). The electrode portions corresponding to the first and second internal electrodes 23 and 33 are printed by a printing method such as screen printing with a conductive paste in which a metal powder mainly composed of Pd particles, an organic binder, and an organic solvent is mixed. It is formed by drying.

  Next, a sheet laminate is formed by stacking each green sheet on which electrode portions are formed and a green sheet on which electrode portions are not formed in a predetermined order (step S107). The sheet laminate thus obtained is cut into, for example, chips, to obtain a plurality of divided green bodies LS1 (see FIG. 8) (step S109). In the obtained green body LS1, a green sheet GS1 in which an electrode portion EL1 corresponding to the first internal electrode 23 is formed, a green sheet GS2 in which an electrode portion EL2 corresponding to the second internal electrode 33 is formed, A green sheet GS3 on which the electrode portions EL1 and EL2 are not formed is sequentially laminated. In addition, you may laminate | stack the green sheet GS3 in which electrode part EL1, EL2 is not formed in each part as needed.

  Next, the green body LS1 is subjected to heat treatment at 180 to 400 ° C. for about 0.5 to 24 hours to remove the binder, and then further fired at 850 to 1400 ° C. for about 0.5 to 8 hours. (Step S111) to obtain the varistor element body 11. By this firing, the green sheets GS1 to GS3 in the green body LS1 become varistor layers. The electrode portion EL <b> 1 becomes the first internal electrode 23. The electrode portion EL <b> 2 becomes the second internal electrode 33.

  Next, Li is diffused from the outer surface of the varistor element body 11 (step S113). Here, first, a Li compound is attached to the surface of the obtained varistor element body 11. A sealed rotating pot can be used for adhesion of the Li compound. Although it does not specifically limit as a Li compound, Li is a compound in which Li can be diffused from the outer surface of the varistor element body 11 by heat treatment, and Li oxide, hydroxide, chloride, nitrate, borate, Carbonates and oxalates are used.

  Then, the varistor element body 11 to which the Li compound is adhered is heat-treated in an electric furnace at a predetermined temperature and time. As a result, Li diffuses from the outer surface of the varistor element body 11 into the varistor element body 11 from the Li compound. A preferable heat treatment temperature is 700 to 1100 ° C., and the heat treatment atmosphere is air. The heat treatment time (holding time) is preferably 10 minutes to 4 hours.

  Next, the connection conductor 41 and the terminal electrode 51 are formed on the outer surface of the varistor element body 11 (step S115). Here, a conductive paste is printed on the first main surface 13 of the varistor element body 11 so as to be in contact with the corresponding first internal electrode 23 by a screen printing method, and then dried, thereby connecting conductors 41. A conductor portion corresponding to is formed. In addition, the conductive paste is printed on the second main surface 15 of the varistor element body 11 so as to be in contact with the corresponding second internal electrode 33 by a screen printing method, and then dried, whereby the terminal electrode 51 is formed. Corresponding electrode portions are formed. Then, the formed electrode portion (conductive paste) is baked at 500 to 1100 ° C. according to the electrode material to obtain the varistor element body 11 in which the connection conductor 41 and the terminal electrode 51 are formed. As described above, the conductive paste for the connection conductor 41 and the terminal electrode 51 may be a mixture of a metal powder containing Pt particles as a main component and a glass frit, an organic binder, and an organic solvent. The glass frit used for the conductive paste for the connection conductor 41 and the terminal electrode 51 contains at least one or more of B, Bi, Al, Si, Sr, Ba, Pr, Zn and the like.

  Through the process described above, the multilayer chip varistor 1 is obtained. In addition, about the formation method of the solder bump 53, the existing formation method can be utilized and description here is abbreviate | omitted.

  As a method for forming the sheet laminate, a method for manufacturing an aggregate substrate described in the specification of Japanese Patent Application No. 2005-201963, which is a prior application of the present application, may be used. In this case, the conductive paste for the connection conductor 41 and the terminal electrode 51 can be applied without dividing and baking the sheet laminate (aggregate substrate) into a plurality of green bodies LS2.

  As described above, according to the first embodiment, since the plurality of terminal electrodes 51 are arranged on the second main surface 15 of the varistor element body 11, the second main surface 15 is mounted on a mounting component (for example, The multilayer chip varistor 1 can be mounted in a state of being opposed to an electronic component, a mounting substrate, etc., and a configuration corresponding to the BGA package is realized. Since the connection conductor 41 is disposed on the first main surface 15 so as to electrically connect the first internal electrodes 23 included in the two internal electrode pairs positioned side by side in the stacking direction, In the element body 11, a region functioning as the varistor B exists at a position corresponding to the connection conductor 41. Therefore, the connection conductor 41 functions as a mark for identifying the mounting direction of the multilayer chip varistor 1, and the multilayer chip varistor 1 can be mounted appropriately and easily.

  When the varistor element body 11 is square when viewed from the direction perpendicular to the first and second main surfaces 13 and 15, the mounting direction of the multilayer chip varistor 1 is based on the outer shape of the varistor element body 11. Is particularly effective because it is difficult to identify.

  Further, according to the present embodiment, it is not necessary to newly provide a mark for identifying the mounting direction of the multilayer chip varistor 1 on the varistor element body 11, and the manufacturing cost of the multilayer chip varistor 1 does not increase.

  By the way, in the multilayer chip varistor 1, since Li is diffused from the outer surface of the varistor element body 11, as shown in FIG. 9, the region 11a in the vicinity of the outer surface of the varistor element body 11 is diffused. , The electrical resistance is extremely high, and it is in a substantially electrically insulated state. That is, the region between the two adjacent terminal electrodes 51 in the varistor element body 11 is substantially electrically insulated, and varistor characteristics are unlikely to occur in the region. Therefore, the varistor voltage in the region between two adjacent terminal electrodes 51 in the varistor element body 11 is larger than the varistor voltage in the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. Is also extremely high.

  In addition, a region between the two connection conductors 41 in the varistor element body 11 is substantially electrically insulated, and varistor characteristics hardly occur in the region. For this reason, the varistor voltage in the region between the two connection conductors 41 in the varistor element body 11 is much higher than the varistor voltage in the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. Get higher.

  As described above, in the multilayer chip varistor 1, varistor characteristics are hardly generated in the region between the two adjacent terminal electrodes 51 in the varistor element body 11 and the region between the two connection conductors 41 in the varistor element body 11. Even if varistor characteristics occur in the region between the two adjacent terminal electrodes 51 in the varistor element body 11 and in the region between the two connection conductors 41 in the varistor element body 11, the varistor characteristics are different in the varistor element body 11. The varistor characteristics generated in the region between the first internal electrode 23 and the second internal electrode 33 can be ignored. As a result, the varistor characteristics are suppressed from occurring in a region other than the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11, and the multilayer chip varistor 1 is desired. Varistor characteristics can be obtained.

  Attention is paid to one terminal electrode 51 and the other terminal electrode 51 of two varistors B connected in series. Varistor characteristics generated in a region between two adjacent terminal electrodes 51 in the varistor element body 11 have variations. For this reason, when Li is not diffused in the varistor element body 11, the varistor characteristics of the varistor B also vary due to the influence of this variation. However, as Li is diffused in the varistor element body 11, as described above, it is difficult for varistor characteristics to occur in the region between the two adjacent terminal electrodes 51 in the varistor element body 11, so that variations do not easily occur. . Therefore, the varistor characteristics of the varistor B do not vary.

  When a surge voltage such as ESD (Electrostatic Discharge) is applied to one set of two varistors B connected in series among two sets of varistors B connected in series, one set A potential difference also occurs between the terminal electrodes 51 of the two varistors B connected in series and the terminal electrodes 51 of the two varistors B connected in series in the other set. For this reason, an electric field is generated between these terminal electrodes 51. Similarly, an electric field is generated between the connection conductors 41.

  Attention is paid to the terminal electrodes 51 of two varistors B connected in series in one set and the terminal electrodes 51 of two varistors B connected in series in the other set. Varistor characteristics generated in a region between two adjacent terminal electrodes 51 in the varistor element body 11 have variations, and in a region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. The resulting varistor characteristics cannot be ignored. For this reason, when Li is not diffused in the varistor element body 11, a varistor characteristic occurs in the region between the two terminal electrodes 51 in the varistor element body 11, and two varistors connected in series in one set. Crosstalk occurs between B and the two varistors B connected in series in the other set. However, since Li is diffused into the varistor element body 11, as described above, the varistor characteristics hardly occur in the region between the two terminal electrodes 51 in the varistor element body 11. It does not occur.

  Attention is paid to the connection conductors 41. Varistor characteristics generated in the region between the two connection conductors 41 in the varistor element body 11 have variations, and varistors generated in the area between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. It cannot be ignored for characteristics. For this reason, when Li is not diffused in the varistor element body 11, a varistor characteristic occurs in a region between the two connection conductors 41 in the varistor element body 11, and the two varistors B connected in series in one set Crosstalk occurs between two varistors B connected in series in the other set. However, when Li is diffused into the varistor element body 11, as described above, the varistor characteristic is unlikely to occur in the region between the two connection conductors 41 in the varistor element body 11, and thus the crosstalk occurs. There is no.

  As a result, the varistor B (multilayer chip varistor 1) can obtain desired varistor characteristics.

  In the first embodiment, as described above, since varistor characteristics are unlikely to occur in the region between the two adjacent terminal electrodes 51 in the varistor element body 11 and the region between the two connection conductors 41 in the varistor element body 11, The tolerance of the die chip varistor 1 against ESD, so-called ESD tolerance, is also increased. In addition, since the electric resistance of the region 11 a in which Li in the vicinity of the outer surface of the varistor element body 11 is diffused is extremely high, the leakage current between two adjacent terminal electrodes 51 in the varistor element body 11 and the two in the varistor element body 11. Leakage current between the two connection conductors 41 is less likely to occur, and the leakage current of the multilayer chip varistor 1 is reduced.

  In the first embodiment, the region having a varistor voltage higher than the varistor voltage in the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11 is the outer surface (first main surface). 13 and the second main surface 15) are formed by diffusing Li from the side. As a result, the varistor voltage in the region between the two adjacent terminal electrodes 51 in the varistor element body 11 and the varistor voltage in the region between the two connection conductors 41 in the varistor element body 11 are converted into the first varistor voltage in the varistor element body 11. The varistor voltage in the region between the internal electrode 23 and the second internal electrode 33 can be easily increased.

  In the first embodiment, Li is diffused into the varistor element body 11 as an alkali metal. Li has a relatively small ionic radius and is liable to be dissolved in ZnO crystals. For this reason, the area | region between the two adjacent terminal electrodes 51 in the varistor element | base_body 11 can be reliably made into the state electrically insulated.

  In the first embodiment, the varistor element body 11 includes a rare earth metal, particularly Pr, as an auxiliary component for expressing varistor characteristics. When the rare earth metal is included, the varistor element body 11 becomes a dense structure. For this reason, Li hardly diffuses from the outer surface of the varistor element body 11 to a deep part, and does not reach the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. . As a result, it is possible to prevent the diffused Li from affecting the varistor characteristics generated in the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. .

  Further, in the first embodiment, the varistor element body 11 includes Pr and Ca, and the conductive paste for the connection conductor 41 and the terminal electrode 51 includes Pt. The connection conductor 41 and the terminal are provided on the varistor element body 11. The connection conductor 41 and the terminal electrode 51 are formed by applying and baking a conductive paste for the electrode 51. Thereby, the joint strength of the varistor element body 11, the connection conductor 41, and the terminal electrode 51 can be improved.

  The effect of improving the bonding strength between the varistor element body 11, the connection conductor 41, and the terminal electrode 51 is considered to be caused by the following phenomenon when baking the conductive paste. When the conductive paste is baked on the varistor element body 11, Pr and Ca contained in the varistor element body 11 move near the surface of the varistor element body 11, that is, near the interface between the varistor element body 11 and the conductive paste. And Pr and Ca which moved to the interface vicinity of the varistor element | base_body 11 and an electrically conductive paste, and Pt contained in an electrically conductive paste mutually diffuse. When Pr, Ca, and Pt are interdiffused, a compound of Pr and Pt and a compound of Ca and Pt are formed in the vicinity (including the interface) between the varistor element body 11, the connection conductor 41, and the terminal electrode 51. May be. These compounds cause an anchor effect, and the bonding strength between the varistor element body 11, the connection conductor 41, and the terminal electrode 51 is improved.

  The terminal electrode 51 containing Pt is suitable mainly when the multilayer chip varistor 1 is mounted on an external substrate or the like by solder reflow, and can improve solder erosion resistance and solderability.

(Second Embodiment)
Next, the configuration of the multilayer chip varistor 2 according to the second embodiment will be described with reference to FIGS. FIG. 10 is a perspective view showing the multilayer chip varistor according to the second embodiment as viewed from the first main surface side of the varistor element body. FIG. 11 is a perspective view showing the multilayer chip varistor according to the second embodiment as viewed from the second main surface side of the varistor element body. FIG. 12 is a diagram for explaining a cross-sectional configuration along the line XII-XII in FIG. 10. 13 is a cross-sectional view for explaining a cross-sectional configuration along the line XIII-XIII in FIG. 14 is a cross-sectional view for explaining a cross-sectional configuration along the line XIIII-XIIII in FIG.

  As shown in FIGS. 10 to 14, the multilayer chip varistor 2 includes a varistor element body 11, a plurality (two in this embodiment) of connection conductors 41, and a plurality of (four in this embodiment). Terminal electrode 51 is provided. In the varistor element body 11, Li is diffused from the outer surface side.

  The varistor element body 11 is provided with a plurality (four layers in this embodiment) of conductor layers 120A to 120D. At least one varistor layer is disposed between the conductor layer 120A and the conductor layer 120B, and at least one varistor layer is disposed between the conductor layer 120C and the conductor layer 120D. It is arranged in.

  As shown in FIGS. 12 to 14, the conductor layer 120 </ b> A and the conductor layer 120 </ b> C each include one first internal electrode 121 and one internal conductor 125. In the conductor layer 120A and the conductor layer 120C, the first inner electrode 121 and the inner conductor 125 have a predetermined interval from the side surfaces parallel to the stacking direction, respectively, and have a predetermined interval so as to be electrically insulated from each other. It is arranged.

  On the other hand, each of the conductor layer 120B and the conductor layer 120D includes one second internal electrode 123 and one internal conductor 125, as shown in FIGS. In the conductor layer 120B and the conductor layer 120D, the second internal electrode 123 and the internal conductor 125 have a predetermined interval from the side surfaces parallel to the stacking direction, respectively, and have a predetermined interval so as to be electrically insulated from each other. It is arranged.

  The first internal electrode 121 of the conductor layer 120A, the second internal electrode 123 of the conductor layer 120B, and the internal conductors 125 of the conductor layers 120C and 120D are arranged on the varistor layer so as to overlap when viewed from the stacking direction. Is arranged. Also, each of the inner conductors 125 of the conductor layers 120A and 120B, the first inner electrode 121 of the conductor layer 120C, and the second inner electrode 123 of the conductor layer 120D are arranged on the varistor layer so as to overlap when viewed from the stacking direction. Is arranged. Therefore, an internal electrode pair 131 and an internal conductor pair 132, which will be described later, are positioned side by side in the stacking direction in the varistor element body 11, and are positioned in a direction substantially perpendicular to the stacking direction.

  Each first internal electrode 121 has a substantially rectangular shape. Each first internal electrode 121 is drawn out to the first main surface 13 such that one end thereof faces the first main surface 13. The first internal electrode 121 in the conductor layer 120A is at least partially opposed to the second internal electrode 123 in the conductor layer 120B with the varistor layer interposed therebetween. The first internal electrode 121 in the conductor layer 120C is at least partially opposed to the second internal electrode 123 in the conductor layer 120D with the varistor layer interposed therebetween.

  Each second internal electrode 123 has a substantially rectangular shape. Each second internal electrode 123 is drawn out to the second main surface 15 such that one end thereof faces the second main surface 15. The second internal electrode 123 in the conductor layer 120B is at least partially opposed to the first internal electrode 121 in the conductor layer 120A with the varistor layer interposed therebetween, and the second internal electrode 123 in the conductor layer 120D is At least part of the varistor layer is opposed to the first internal electrode 121 in the conductor layer 120C.

  As described above, the first internal electrode 121 and the second internal electrode 123 are arranged in the varistor element body 11 so that at least some of them face each other. Thereby, in the multilayer chip varistor 2, a plurality of internal electrode pairs 131 including the first and second internal electrodes 121 and 123 arranged in the varistor element body 11 so that at least some of them are opposed to each other are provided. (Two in this embodiment) will be provided. Therefore, a region where the first internal electrode 121 and the second internal electrode 123 overlap in the varistor layer, that is, a region between the first internal electrode 121 and the second internal electrode 123 in the varistor element body 11. However, it functions as a region that develops varistor characteristics.

  Each inner conductor 125 has a substantially rectangular shape. Each inner conductor 125 is drawn out to the first main surface 13 so that one end thereof faces the first main surface 13, and the second main surface so that the other end faces the second main surface 15. 15 is drawn. In the present embodiment, the varistor elements 11 are arranged in the varistor element body 11 so that the inner conductors 125 in the conductor layers 120A and 20B face each other, and the varistors so that the inner conductors 125 in the conductor layers 120C and 120D face each other. It is arranged in the element body 11. As a result, the multilayer chip varistor 2 is provided with a plurality (two in this embodiment) of a pair of internal conductors 125 (internal conductor pairs 132) disposed in the varistor element body 11.

  The first and second internal electrodes 121 and 123 and the internal conductor 125 include a conductive material. The conductive material contained in the first and second internal electrodes 121 and 123 and the internal conductor 125 is not particularly limited, but is preferably made of Pd or an Ag—Pd alloy. The thicknesses of the first and second internal electrodes 121 and 123 and the internal conductor 125 can be set to about 0.5 to 5 μm, for example.

  Here, the first main surface 13 and the second main surface 15 are in a direction along the stacking direction (a parallel direction in the present embodiment), and the first and second inner electrodes 121 and 123 and the inner conductor 125. Extends in the direction intersecting (in the present embodiment, the direction orthogonal). The stacking direction is a direction parallel to the opposing direction of the first internal electrode 121 and the second internal electrode 123 (the opposing direction of the internal conductors 125), and the first and second internal electrodes 121 and 123 are parallel to each other. In addition, the direction is orthogonal to the inner conductor 125.

  As shown in FIGS. 12 and 14, each connection conductor 41 is connected to the internal electrode pair 131 among the internal electrode pair 131 and the internal electrode pair 132 arranged in the stacking direction in the varistor element body 11. Each of the internal conductors 125 included in the first internal electrode 121 and the internal electrode pair 132 included is arranged on the first main surface 13 so as to cover each part drawn out to the first main surface 13. . Each portion led out to the first main surface 13 of the first inner electrode 121 and each inner conductor 125 is physically and electrically connected to the corresponding connecting conductor 41. As a result, each connection conductor 41 electrically connects the first internal electrode 121 and each internal conductor 125 positioned side by side in the stacking direction.

  In the present embodiment, the terminal electrode 51 has two first terminal electrodes 151 and two second terminal electrodes 152.

  As shown in FIGS. 12 and 14, each first terminal electrode 151 has a second second electrode so as to cover a portion drawn out to the second main surface 15 of the corresponding second inner electrode 123. Each is arranged on the main surface 15. A portion of the second internal electrode 123 drawn to the second main surface 15 is physically and electrically connected to the corresponding first terminal electrode 151. Thus, the first terminal electrode 151 is electrically connected to the corresponding second internal electrode 123, respectively.

  On the other hand, as shown in FIGS. 12 and 14, each second terminal electrode 152 covers a portion drawn out to the second main surface 15 of each internal conductor 125 included in the corresponding internal conductor pair 132. Further, they are arranged on the second main surface 15 respectively. The portion of the inner conductor 125 that is led out to the second main surface 15 is physically and electrically connected to the corresponding second terminal electrode 152. As a result, the second terminal electrode 152 is electrically connected to each internal conductor 125 included in the corresponding internal conductor pair 132.

  Here, as described above, the internal electrode pair 131 and the internal conductor pair 132 are positioned side by side in the stacking direction in the varistor element body 11 and are aligned in a direction substantially perpendicular to the stacking direction. Therefore, the second terminal electrically connected to the first terminal electrode 151 electrically connected to the second internal electrode 123 included in the internal electrode pair 131 and the respective internal conductors 125 included in the internal conductor pair 132. The terminal electrodes 152 are also arranged on the second main surface 15 so as to be positioned side by side in the stacking direction and aligned in a direction substantially perpendicular to the stacking direction. That is, the first and second terminal electrodes 151 and 152 are arranged alternately in the row direction and the column direction.

  In the multilayer chip varistor 2 having the above-described configuration, as shown in FIG. 15, two sets of varistors B that connect the first terminal electrode 151 and the second terminal electrode 152 are included. Each varistor B is composed of a first internal electrode 121, a second internal electrode 123, and a region where the first and second internal electrodes 121 and 123 overlap in the varistor layer. The connection conductor 41 extends in a direction substantially parallel to the stacking direction, and the first and second terminal electrodes 151 and 152 that are electrically connected to the varistor B are juxtaposed in the stacking direction. Each varistor B exists between the pair of first and second terminal electrodes 151 and 152 that are juxtaposed in the long side direction of the connection conductor 41.

  Since the multilayer chip varistor 2 having the above-described configuration can be manufactured in the same procedure as the multilayer chip varistor 1, the description of the manufacturing process of the multilayer chip varistor 2 is omitted.

  As described above, in the second embodiment, the plurality of first and second terminal electrodes 151 and 152 are arranged on the second main surface 15 of the varistor element body 11. Therefore, the multilayer chip varistor 2 can be mounted with the second main surface 15 facing a mounting component (for example, an electronic component or a mounting substrate), and a configuration corresponding to the BGA package is realized. It will be. Further, in the present embodiment, the connection conductor 41 is included in the internal electrode pair 131 among the internal electrode pair 131 and the internal conductor pair 132 arranged in the stacking direction in the varistor element body 11. Arranged on first main surface 13 so as to electrically connect internal electrode 121 and each internal conductor 125 included in internal conductor pair 132. Therefore, the varistor element body 11 has a region functioning as the varistor B at a position corresponding to the connection conductor 41. Therefore, the connection conductor 41 is a mark for identifying the mounting direction of the multilayer chip varistor 2. Thus, the multilayer chip varistor 2 can be mounted appropriately and easily.

  Incidentally, in the multilayer chip varistor 2, as described above, Li is diffused from the outer surface of the varistor element body 11, so that the region near the outer surface of the varistor element body 11 has an extremely high electric resistance and is substantially reduced. Is electrically insulated. That is, the region between the two adjacent terminal electrodes 151 and 152 in the varistor element body 11 is substantially electrically insulated, and varistor characteristics are unlikely to occur in the region. For this reason, the varistor voltage in the region between the two adjacent terminal electrodes 151 and 152 in the varistor element body 11 is the varistor in the region between the first internal electrode 121 and the second internal electrode 123 in the varistor element body 11. Extremely higher than voltage. The varistor voltage in the region between the two connection conductors 41 in the varistor element body 11 is also extremely higher than the varistor voltage in the region between the first internal electrode 23 and the second internal electrode 33 in the varistor element body 11. Become.

  As described above, in the multilayer chip varistor 2, varistor characteristics are hardly generated in the region between the two adjacent terminal electrodes 151 and 152 in the varistor element body 11 and the region between the two connection conductors 41 in the varistor element body 11. Even if varistor characteristics occur in the region between the two adjacent terminal electrodes 151 and 152 in the varistor element body 11 and in the region between the two connection conductors 41 in the varistor element body 11, the varistor characteristics are as follows. 11 is negligible for the varistor characteristics generated in the region between the first internal electrode 121 and the second internal electrode 123. As a result, the varistor characteristics are suppressed from occurring in a region other than the region between the first internal electrode 121 and the second internal electrode 123 in the varistor element body 11, and the multilayer chip varistor 2 is desired. Varistor characteristics can be obtained.

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  In the present embodiment, Li is used as the alkali metal diffused in the varistor element body 11, but the present invention is not limited to this, and Na, K, Rb, or Cs may be used.

  In the present embodiment, Li is diffused from the entire outer surface of the varistor element body 11. However, the present invention is not limited to this, and the outer electrode (connection conductor 41 and terminal electrodes 51, 151, 152) formed outside is not limited to this. Li may be diffused only from the surfaces (the first main surface 13 and the second main surface 15). Further, Li may be diffused only from a region between two adjacent external electrodes on the outer surface of the varistor element body 11.

  In the present embodiment, the external electrodes (the connection conductor 41 and the terminal electrodes 51, 151, and 152) are formed by a printing method (a conductive paste is applied and baked), but the present invention is not limited thereto. The external electrodes (connection conductor 41 and terminal electrodes 51, 151, 152) may be formed by a plating method, particularly a vacuum plating method (vacuum deposition method, sputtering method, ion plating method, etc.).

  In the present embodiment, Li is diffused in the varistor element body 11 before forming the external electrodes (the connection conductor 41 and the terminal electrodes 51, 151, and 152). However, the present invention is not limited to this. Li may be diffused into the varistor element body 11 after the external electrodes (the connection conductor 41 and the terminal electrodes 51, 151, 152) are formed.

  In this embodiment, a glass layer is formed on the terminal electrodes 51, 151, and 152, and the terminal electrodes 51, 151, and 152 and the solder bump 53 may be connected via the glass layer. . In this case, the glass layer is formed so that at least a part of the terminal electrodes 51, 151, 152 is exposed. In the glass layer, a plurality of through holes reaching the terminal electrodes 51, 151, and 152 are formed at the edge on the side where the terminal electrodes 51, 151, and 152 are exposed. The solder bump 53 is located so as to cover the exposed portions of the terminal electrodes 51, 151, and 152 and the edge of the glass layer, and is connected to the terminal electrodes 51, 151, and 152 through a plurality of through holes. By connecting the solder pump 53 to the terminal electrodes 51, 151, and 152 in this way, it is possible to improve the bonding strength between the terminal electrodes 51, 151, 152 and the solder pump 53.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

In this example, a multilayer chip varistor having the same configuration as that of the multilayer chip varistor 1 according to the first embodiment is manufactured, and one terminal electrode 51 and the other terminal electrode 51 of two varistors B connected in series are formed. varistor voltage between (hereinafter, referred to as the varistor voltage V _{1 LINE)} and the terminal electrode of the two varistors B connected in series in the terminal electrode 51 and the other set of two varistors B connected in series in one set The varistor voltage with respect to 51 (hereinafter referred to as varistor voltage _V2line ) was measured. As the varistor voltage V _1line and the varistor voltage V _2line , a varistor voltage V _1mA (unit: V) when a current of 1 mA was passed was measured.

Regarding the varistor material, 99.9% purity ZnO (97.725 mol%), Pr (0.5 mol%), Co (1.5 mol%), Al (0.005 mol%), K ( 0.05 mol%), Cr (0.1 mol%), Ca (0.1 mol%) and Si (0.02 mol%) were added. Regarding the Li diffusion treatment, the obtained varistor element body 11 was mixed with Li ₂ CO ₃ powder (average particle size: 3 μm) in a sealed rotating pot, and 1 μg of Li ₂ CO ₃ powder per piece was mixed. Attached. The amount of Li ₂ CO ₃ powder introduced into the sealed rotating pot was in the range of 0.01 μg to 10 mg per piece. The heat treatment temperature was 900 ° C., and the heat treatment time was 10 minutes.

The multilayer chip varistor was designed so that the distance D _i1 between the first internal electrode 23 and the second internal electrode 33 was set to 40 μm, and a varistor voltage V _{1 mA of} 54 V was obtained. Interval _{D e2} between spacing _{D e1} and two connecting conductors 41 between the two terminal electrodes 51, 20μm, 40μm, 80μm, 120μm , a multilayer chip varistor respectively set to 160 .mu.m, when subjected to Li diffusion process In each case, five samples were prepared and the varistor voltage V _1line and varistor voltage V _{2line of} each sample were measured. The measurement results are shown in FIG. In FIG. 16, “-” indicates that the measurement device (KEITHLEY2400 SOURCE METER) used has exceeded the measurable range (up to 200V), and the varistor voltage _V2line could not be measured properly. ing.

In the measurement results shown in FIG. 16, in the multilayer chip varistor without Li diffusion, the CV (coefficient of variation) is greater than 5%, and the varistor voltage V _1line varies greatly with _respect to each design value. On the other hand, in the multilayer chip varistor subjected to the Li diffusion process, the CV is 5% or less, and the variation of the varistor voltage V _1line with respect to the design value is extremely small. The reason why the criterion is 5% is that a varistor element suitable for circuit design and practical use with a stable ESD protection level can be supplied.

In the multilayer chip varistor that does not _perform the Li diffusion treatment, the varistor voltage _V2line could be measured. As a result, varistor characteristics are generated in a region between the terminal electrodes 51 of two varistors B connected in series in one set and the terminal electrodes 51 of two varistors B connected in series in the other set. Can understand. On the other hand, in the multilayer chip varistor subjected to the Li diffusion treatment, the varistor voltage V _2line exceeded the measurable range and could not be measured. As a result, varistor characteristics are substantially generated in a region between the terminal electrodes 51 of two varistors B connected in series in one set and the terminal electrodes 51 of two varistors B connected in series in the other set. I can understand that.

  From the above, the effectiveness of the present invention was confirmed.

1 is a perspective view showing a multilayer chip varistor according to a first embodiment. 1 is a perspective view showing a multilayer chip varistor according to a first embodiment. It is a figure for demonstrating the cross-sectional structure along the III-III line | wire of FIG. It is a figure for demonstrating the cross-sectional structure along the IV-IV line of FIG. It is a figure for demonstrating the cross-sectional structure along the VV line of FIG. It is a figure for demonstrating the equivalent circuit of the multilayer chip varistor which concerns on 1st Embodiment. It is a flowchart for demonstrating the manufacturing process of the multilayer chip varistor which concerns on 1st Embodiment. It is a figure for demonstrating the manufacturing process of the multilayer chip varistor which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the structure of the multilayer chip varistor concerning 1st Embodiment. It is a perspective view which shows the multilayer chip varistor concerning 2nd Embodiment. It is a perspective view which shows the multilayer chip varistor concerning 2nd Embodiment. It is a figure for demonstrating the cross-sectional structure along the XII-XII line | wire of FIG. It is sectional drawing for demonstrating the cross-sectional structure along the XIII-XIII line | wire of FIG. It is sectional drawing for demonstrating the cross-sectional structure along the XIIII-XIIII line of FIG. It is a figure for demonstrating the equivalent circuit of the multilayer chip varistor which concerns on 2nd Embodiment. It is a graph which shows the measurement result of the varistor voltage in an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Stack type chip varistor, 11 ... Varistor element | base_body, 11a ... Area | region where Li was diffused, 13 ... 1st main surface, 15 ... 2nd main surface, 23 ... 1st internal electrode, 33 ... 2nd internal electrode, 41 ... connection conductor, 51 ... terminal electrode, 121 ... 1st internal electrode, 123 ... 2nd internal electrode, 151 ... 1st terminal electrode, 152 ... 2nd terminal electrode.

Claims (7)

A sintered body having ZnO as a main component and voltage non-linear characteristics, and having first and second main surfaces facing each other;
A plurality of internal electrode pairs having first and second internal electrodes disposed in the sintered body so that at least some of them face each other;
A plurality of connection conductors formed on the first main surface so as to electrically connect first internal electrodes of a predetermined internal electrode pair of the plurality of internal electrode pairs;
A plurality of terminal electrodes provided corresponding to the second internal electrodes of the plurality of internal electrode pairs and formed on the second main surface so as to be electrically connected to the second internal electrodes; ,
With
Between the plurality of connection conductors, a region having a varistor voltage higher than a varistor voltage of a region between the plurality of internal electrode pairs in the sintered body is formed from the first main surface side,
A region having a varistor voltage higher than a varistor voltage in a region between the plurality of internal electrode pairs in the sintered body is formed between the plurality of terminal electrodes from the second main surface side. A varistor. The alkali metal diffuses from the first main surface side in the region having a varistor voltage higher than the varistor voltage of the region between the plurality of internal electrode pairs in the sintered body, which is located between the plurality of connection conductors. Formed by
In the region having a varistor voltage higher than the varistor voltage of the region between the plurality of internal electrode pairs in the sintered body located between the plurality of terminal electrodes, alkali metal diffuses from the second main surface side. The varistor according to claim 1, wherein the varistor is formed. A sintered body having ZnO as a main component and voltage non-linear characteristics, and having first and second main surfaces facing each other;
A plurality of internal electrode pairs having first and second internal electrodes disposed in the sintered body so that at least some of them face each other;
A plurality of internal conductors disposed in the sintered body;
A plurality of connection conductors formed on the first main surface so as to electrically connect the first internal electrode and the internal conductor in the internal electrode pair;
A first terminal electrode formed on the second main surface so as to be electrically connected to the second internal electrode;
A second terminal electrode formed on the second main surface so as to be electrically connected to the inner conductor;
Between the plurality of connection conductors, a region having a varistor voltage higher than a varistor voltage of a region between the plurality of internal electrode pairs in the sintered body is formed from the first main surface side,
A region having a varistor voltage higher than a varistor voltage in a region between the plurality of internal electrode pairs in the sintered body is between the first terminal electrode and the second terminal electrode. A varistor formed from the surface side. The alkali metal diffuses from the first main surface side in the region having a varistor voltage higher than the varistor voltage of the region between the plurality of internal electrode pairs in the sintered body, which is located between the plurality of connection conductors. Formed by
The region having a varistor voltage higher than a varistor voltage of the region between the plurality of internal electrode pairs in the sintered body, which is located between the first terminal electrode and the second terminal electrode, 4. The varistor according to claim 3, wherein the varistor is formed by diffusing an alkali metal from the main surface side of 2.   The varistor according to claim 2, wherein the alkali metal is Li.   6. The varistor according to claim 2, wherein the sintered body includes a rare earth metal as an auxiliary component for developing varistor characteristics.   The varistor according to claim 6, wherein the rare earth metal is Pr.

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