JP2009289992A - Method for manufacturing varistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily manufacturing a varistor wherein the size of an external electrode and a resistor is sufficiently made very small while maintaining successful varistor characteristics. <P>SOLUTION: The method has processes of: forming a plurality of external electrode pairs 30 constituted of external electrodes 32, 34 opposite to each other on one surface 10a of a varistor element 10; forming the resistor on one surface 10a of the varistor element 10 so that the plurality of external electrodes 30 are connected to each other, and the external electrodes 32 and the external electrodes 34 are connected to each other; and forming a connector 20 by removing the resistor formed on an area between the adjacent external electrode pairs 30 by irradiation of a laser beam. The varistor element 10 contains ZnO as a principle component, and contains Ca oxide, Si oxide and oxide of rare earth metal as assistant components, the ratio X of the Ca oxide expressed in terms of a Ca atom to the whole principal component is 2-80 atom%, the ratio Y of the Si oxide expressed in terms of a Si atom is 1-40 atom%, and the varistor element satisfies 1≤X/Y<3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a varistor.

  Varistors are used to protect various control devices, communication devices, and their components from external surges (abnormal voltages) such as static electricity and noise.

  When both the varistor and the resistor are mounted, if the varistor and the resistor are mounted in series, two elements are separately mounted on the printed circuit board, so that a large mounting space is required. For this reason, it becomes difficult to cope with so-called high-density mounting in which each element is mounted in the smallest possible space. Therefore, in order to realize high-density mounting, a varistor in which a varistor element and a resistor are integrated has been proposed (for example, Patent Document 1).

As described above, in the varistor in which the varistor element body and the resistor are integrated, by adjusting the composition of the varistor element body and the composition of the external electrode, the varistor element body and the external electrode are maintained while maintaining good varistor characteristics. Attempts have been made to improve the bond strength.
JP 2006-287029 A

  In a varistor as in Patent Document 1, external electrodes and resistors provided on one surface of a varistor element body are formed by printing and baking pastes for forming external electrodes and resistors, respectively. Recently, as the number of circuits of these external electrodes increases, the shapes of the external electrodes and resistors are reduced, and the space between adjacent external electrodes and resistors is also reduced. For this reason, in the manufacturing method which performs printing and baking as described above, a more precise printing technique is required as the width of the external electrodes and resistors and the interval between adjacent external electrodes and resistors become smaller.

  On the other hand, electronic circuits are required to be further miniaturized, and varistors are also required to have a finer structure in addition to having good varistor characteristics. However, when the structure is miniaturized, it is difficult to produce a shape with excellent lineability by the conventional resistor forming method using printing technology. There is concern about the decline. For this reason, even when forming a fine structure in which the width of the external electrode or resistor and the interval between adjacent external electrodes are 100 μm or less, there is provided a method capable of forming the resistor between the external electrodes with sufficient reliability. There is a need to establish.

  The present invention has been made in view of the above circumstances, and provides a varistor manufacturing method capable of easily manufacturing a varistor in which the size of external electrodes and resistors is sufficiently miniaturized while maintaining good varistor characteristics. The purpose is to provide.

In order to achieve the above object, in the present invention, an external electrode pair consisting of a first external electrode and a second external electrode provided to face the first external electrode on one surface of a varistor element body, A plurality of external electrode forming steps formed so as to be arranged in a predetermined direction are connected to each other, and the first external electrode and the second external electrode in the external electrode pair are connected to each other. As described above, a resistor forming step for forming a resistor on one surface of the varistor element body, and a portion of the resistor formed in a region between the adjacent external electrode pairs is removed by laser light irradiation. And a removing step of forming a connection body having a first external electrode, a second external electrode, and a resistor that connects the first external electrode and the second external electrode, and a varistor element body. Contains zinc oxide as the main component As a calcium oxide, silicon oxide, and rare earth metal oxide, and the ratio X of calcium oxide in the calcium oxide to the whole main component is 2 to 80 atomic%. Provided is a varistor manufacturing method in which the atomic conversion ratio Y is 1 to 40 atomic% and the ratio of X to Y (X / Y) satisfies the following formula (1).
1 ≦ X / Y <3 (1)

  According to the varistor manufacturing method of the present invention, even if the size and interval of the external electrodes and resistors are miniaturized, the varistor has excellent surface insulation resistance and sufficiently suppresses variations in resistance values between the external electrodes. That is, a varistor having good varistor characteristics can be easily manufactured. The reason why such an effect is obtained is as follows. According to the varistor manufacturing method of the present invention, a pair of external electrodes formed on a varistor element body having a large initial surface insulation resistance, that is, a resistor that connects a first external electrode and a second external electrode is applied to a laser beam. It is formed by irradiating. Here, by using the varistor element body having the above-described composition, the surface insulation resistance of the varistor element body can be maintained at a sufficiently high level even if the varistor element body is somewhat altered by laser irradiation. For this reason, even if the width and interval of the external electrodes are miniaturized, it is possible to form a resistor excellent in lineability while maintaining good varistor characteristics.

  According to the manufacturing method of the present invention, the distance between adjacent resistors can be narrowed as compared with a method in which a pair of external electrodes are individually connected by resistors in conventional screen printing. As a result, the width of the resistor can be increased, and even if the connection body is miniaturized, the occurrence of microcracks is suppressed, and the resistance value of the resistor can be easily adjusted, that is, trimming by laser light can be easily performed. it can. Therefore, it is possible to obtain a varistor in which variation in resistance value between the external electrodes is sufficiently suppressed.

  In the present invention, it is preferable to further include a trimming step of trimming a part of the resistor in the connection body formed in the removing step with a laser beam.

  Thereby, it is possible to obtain a varistor in which variation in resistance value between the external electrodes is further suppressed.

  Further, in the present invention, it is preferable to repeat the laser beam irradiation a plurality of times.

  In such a manufacturing method, the irradiation amount per unit area of the varistor element body of the laser light can be reduced per time as compared with the method of removing the resistor by the laser light irradiation only once. This can prevent the surface of the varistor element from being altered or damaged. Further, it is possible to sufficiently remove the resistor formed in the region between adjacent connection bodies. Therefore, a varistor having a more excellent surface insulation resistance can be manufactured.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the varistor which can manufacture easily the varistor in which the size of the external electrode or the resistor was fully refined | miniaturized can be provided, maintaining a favorable varistor characteristic.

  In the following, preferred embodiments of the present invention will be described with reference to the drawings as the case may be.

  In the varistor manufacturing method of the present embodiment, the first external electrode and the first external electrode are formed on the surface (hereinafter referred to as “main surface”) from which the lead wire of the internal electrode provided inside the varistor element body is exposed. An external electrode forming step of forming a plurality of external electrode pairs composed of a second external electrode provided so as to face one external electrode so as to be arranged in one direction, and all of the external electrodes provided on the one surface A resistor forming step of forming a resistor on one surface of the varistor element body so that the external electrodes are connected, and a resistor formed in a region between adjacent external electrode pairs are removed by laser light irradiation. A removal step of forming a connection body that insulates adjacent external electrode pairs and includes a first external electrode, a second external electrode, and a resistor that connects the first external electrode and the second external electrode. And in the connection body formed in the removal step And a trimming step of trimming a portion of the antibody with a laser beam. Details of each step will be described below.

(External electrode formation process)
FIG. 1 is a process diagram showing an external electrode forming process in the varistor manufacturing method of the present embodiment. In the external electrode forming step, a plurality of external electrode pairs 30 including the first external electrode 32 and the second external electrode 34 facing each other are formed at predetermined positions on the main surface 10a of the varistor element body 10. The plurality of external electrode pairs 30 are arranged at a predetermined interval L. The first external electrode 32 and the second external electrode 34 are respectively arranged at positions corresponding to the lead lines of the internal electrodes of the varistor element body 10, and the main surface 10 a is opposed to each other with a predetermined interval S. It is provided above.

  In order to form the external electrode pair 30, first, a conductive paste is prepared. As the conductive paste, a known paste can be used. For example, a mixture of metal powder such as metal oxide, Ag particles and Pd particles, glass frit, organic binder and organic solvent is used.

  Next, a conductive paste is printed at a predetermined position on one main surface 10a of the varistor element body 10 by a screen printing method. At this time, the conductive paste is printed at a position corresponding to a lead line of an internal electrode (not shown) arranged inside the varistor element body 10.

  After the conductive paste is printed, it is dried and baked at 500 to 850 ° C. to form the external electrode pair 30. As a result, on the main surface 10a of the varistor element body 10, external electrode pairs 30 having a width T arranged at a predetermined interval L in one direction are obtained. That is, the external electrode pair 30 includes a first external electrode 32 and a second external electrode 34 arranged at a predetermined interval S so as to face each other.

(Resistance forming process)
FIG. 2 is a process diagram showing a resistor forming process in the varistor manufacturing method of this embodiment. In the resistor forming step, the resistor 60 is formed so as to connect all of the plurality of first external electrodes 32 and the plurality of second external electrodes 34 formed on the main surface 10a.

In order to form the resistor 60, first, a resistance paste is prepared. A well-known thing can be used for a resistance paste. For example, glass powder mixed with a commercially available organic binder and organic solvent is used. As the glass powder, a mixture of RuO ₂ and glass such as Al ₂ O ₃ —B ₂ O ₃ —SiO ₂ can be used. As the Sn-based resistance paste, a mixture of SnO ₂ and glass such as Al ₂ O ₃ —B ₂ O ₃ —SiO ₂ can be used. As the La-based resistance paste, a mixture of LaB ₆ and glass such as Al ₂ O ₃ —B ₂ O ₃ —SiO ₂ can be used.

  The organic binder used for the resistance paste is not particularly limited, and can be appropriately selected from various binders such as ethyl cellulose and polyvinyl butyral. The organic solvent can be appropriately selected from various organic solvents such as terpineol, butyl carbitol, acetone and toluene. There is no restriction | limiting in particular in the compounding ratio of resistance paste, For example, 1-20 mass parts of said organic binders, and 1-40 mass parts of said organic solvents can be mix | blended with respect to 100 mass parts of total amounts of a metal and an oxide powder. . These blending ratios can be appropriately changed in order to adjust the fluidity of the resistance paste.

  Next, the resistance paste is printed by a screen printing method so as to span the plurality of first external electrodes 32 and the plurality of second external electrodes 34. After the resistance paste is printed, the resistor 60 is formed by drying and baking at 800 to 900 ° C., for example. The resistor 60 includes a region between the first external electrode 32 and the second external electrode 34, an end of the first external electrode 32 on the second external electrode 34 side, and the second external electrode 34. It is formed so as to cover the end on the first external electrode 32 side. Thus, the plurality of external electrode pairs 30 provided on the main surface 10 a are connected by the resistor 60.

  According to the varistor manufacturing method of this embodiment, the size of the resistor 60 to be formed is sufficiently larger than the case of forming the resistor by printing the resistor paste so as to individually connect one external electrode pair 30. Can be large. For this reason, in the resistor formation process of this embodiment, the high positional accuracy is not required in the screen printing of the resistance paste. Therefore, the varistor manufacturing method of the present embodiment allows the width T of the first external electrode 32 and the second external electrode 34 and the distance L between adjacent external electrode pairs 30 to be small (for example, 100 μm or less). A varistor in which variation in resistance value between the first external electrode 32 and the second external electrode 34 is sufficiently reduced can be obtained.

(Removal process)
FIG. 3 is a process diagram showing a resistor removal process in the varistor manufacturing method of the present embodiment. In the removing step, a part of the resistor 60 is removed by irradiating the resistor in the region between the adjacent external electrode pairs 30 of the resistor 60 with laser light.

  In the present embodiment, a part of the resistor 60 formed on the main surface 10a of the varistor element body 10 is removed by irradiation with laser light. Specifically, the laser light is irradiated in order from the laser light irradiation line 40 on the left side in FIG. 3 along the laser light irradiation line 40 in FIG. A part of the resistor 60 is cut off. As a result, a connection body composed of a resistor and a pair of external electrodes connected by the resistor can be formed.

  A commercially available laser beam irradiation device can be used as the laser beam oscillation device. The light source of the laser light is not particularly limited, and various solid lasers, liquid lasers, and gas lasers can be used. Of these, YAG laser or YVO4 laser can be preferably used. Also, the output of the laser beam can be appropriately adjusted according to the material and thickness of the resistor to be formed.

  FIG. 4 is a top view showing an example of a varistor obtained by the manufacturing method of the present invention. That is, FIG. 4 is a top view of the varistor after a part of the resistor 60 formed in a region between the adjacent external electrode pairs 30 is removed. The varistor 100 includes a varistor element body 10, a pair of external electrodes 32 and 34 formed on the main surface 10 a of the varistor element body 10, and a resistor 62 that connects the pair of external electrodes 32 and 34. A plurality of connecting bodies 20 and resistors 64 formed so as to be scattered in a region between adjacent connecting bodies 20 are provided.

  FIG. 5 is a partially enlarged view showing a region A on the surface of the varistor 100 shown in FIG. 4 in an enlarged manner. As described above, by removing a part of the resistor 60 in the region between the external electrode pair 30, the connection body 20 including the resistor 62 and the external electrode pair 30 connected by the resistor 62 is formed. . The first external electrode 32 and the second external electrode 34 in the connection body 20 are electrically connected by a resistor 62.

  If the adjacent connection bodies 20 are electrically insulated from each other, as shown in FIG. 5, the resistors 64 may be scattered in the region P between the adjacent connection bodies 20. Since the resistors 64 are formed so as not to electrically connect the adjacent connecting bodies 20 (resistors 62), the adjacent connecting bodies 20 are electrically connected to each other on the main surface 10a of the varistor element body 10. Is insulated.

When the portion formed in the region between the adjacent connecting bodies 20 is removed from the resistor 60 by irradiating the laser light, the main surface 10a of the varistor element body 10 is directly irradiated with the laser light. There is a tendency that the surface of the varistor element body 10 is scraped or a deteriorated layer is formed. In order to obtain a varistor 100 having a sufficiently high surface insulation resistance, it is preferable to sufficiently suppress the alteration of the varistor element body associated with laser light irradiation. For this reason, it is preferable to reduce the irradiation amount of the laser light per unit area of the main surface 10a as much as possible within a range in which the insulation properties between the adjacent connection bodies 20 can be maintained. The irradiation amount of the laser light can be set to 0.1 to 5.0 kJ / cm ² , for example.

  In the removing step, the laser beam is irradiated along the laser beam irradiation line 40 shown in FIG. 3, but this laser beam irradiation is preferably repeated a plurality of times. Thereby, the amount of laser irradiation per one time is reduced, and alteration and damage of the varistor element body 10 can be further reduced.

  In the case where the laser light irradiation is repeated a plurality of times, it is preferable that the second and subsequent laser light irradiation amounts per unit area be smaller than the first laser light irradiation amount. In such a method, the first laser light irradiation is mainly performed to scrape off part of the resistor 60 in the region P, and the second and subsequent laser light irradiations are generated by the previous irradiation. This can be done to remove uncut parts or debris generated by shaving. Therefore, alteration and damage of the varistor element body 10 can be further reduced.

  In the present embodiment, the resistor 62 connecting the pair of external electrodes is formed by processing a large-sized resistor 60 formed by screen printing by laser light irradiation. For this reason, it is not necessary to form the resistor 62 which connects each pair of external electrodes 30 by a screen printing method. Therefore, even when the distance L between the adjacent external electrodes and the width T of the first external electrode 32 and the second external electrode 34 become a small size of, for example, 100 μm or less, the resistor 62 having excellent line characteristics is formed. can do. Therefore, even when the size and interval of the first external electrode 32, the second external electrode 34, and the resistor 62 are reduced, variation in resistance value in the connection body 20 can be reduced.

  Even when the interval between adjacent connecting members 20 is small (for example, 100 μm or less), since the spot diameter of the laser beam is sufficiently small (25 to 50 μm), the adjacent connecting members can be reliably insulated. For this reason, the dispersion | variation in the resistance value of the adjacent connection body 20 can fully be reduced.

(Trimming process)
FIG. 6 is a process diagram showing a trimming process in the varistor manufacturing method of the present embodiment. In the trimming step, a part of the resistor 62 that connects the first external electrode 32 and the second external electrode 34 is trimmed to adjust the resistance value of the connection body 20. That is, a part of the resistor 62 is irradiated with laser light, and a part of the resistor 62 is removed by trimming to form the trimming portion 50.

  In the varistor manufacturing method in this embodiment, the resistor 62 is formed by laser light irradiation. For this reason, compared with the case where the resistor 62 is formed by the screen printing method, the width R of the resistor 62 can be made sufficiently large. Therefore, generation of microcracks due to trimming can be sufficiently suppressed. In addition, the trimming of the resistor 62 can be easily performed, and variation in the resistance value of the connection body 20 can be further reduced.

  As described above, in the conventional varistor manufacturing method, the resistor 62 connecting the pair of external electrodes is formed by the screen printing method. In such a manufacturing method, due to the printing accuracy of the resistance paste, it is necessary to maintain the interval between the adjacent resistors at a certain size or more in order to prevent short circuit between the adjacent connectors. For this reason, the width R of the resistor cannot be increased, the alignment of trimming is difficult, and the resistance value of the connection body cannot be finely adjusted. In addition, there is a problem that microcracks are easily generated in the resistor during trimming. By adopting the varistor manufacturing method according to the present embodiment, such a problem can be solved.

  The laser beam used for trimming the resistor 62 and its light source can be the same as those used in the resistor removing step described above. The frequency, irradiation intensity, and irradiation amount of the laser can be arbitrarily adjusted according to the material and thickness of the resistor 62.

  FIG. 7 is a scanning electron micrograph (1000 ×) showing a cross section taken along line VII-VII in the varistor of FIG. 6. As shown in FIG. 7, a resistor is formed on one surface of the varistor element body. Resistors constituting the connection body are formed on both ends of the photograph in FIG. In addition, as shown in FIG. 7, the dotted | punctate resistor may be formed in the area | region (on the main surface of a varistor element | base_body) between adjacent connection bodies (resistor).

In the varistor manufacturing method of this embodiment, a protective layer (overglaze layer) may be formed so as to cover the main surface 10a of the varistor element body 10 and the connection body 20 after the trimming step. The protective layer can be formed by printing glaze glass (for example, glass made of SiO ₂ , ZnO, B, Al ₂ O _3, etc.) and baking at 500 to 700 ° C. If the varistor has the resistors 64 interspersed between the connecting bodies (resistors), the adhesion between the protective layer and the varistor element body can be improved by the anchor effect.

  In addition, the varistor manufacturing method of the present embodiment may include a varistor element forming step of manufacturing a varistor element having a specific composition before the external electrode forming step. Hereinafter, the varistor element forming step will be described.

(Varistor body forming process)
In the varistor element formation step, first, zinc oxide as the main component and rare earth metal oxide, calcium oxide, silicon oxide, and other components as the main component so that the varistor element satisfies the composition described later. Each component is weighed, and each component is mixed to prepare a varistor raw material.

  As the varistor layer-forming coating material (slurry), an organic coating material or a water-based coating material can be used. The organic paint is obtained by kneading a varistor raw material and an organic vehicle. An organic vehicle is obtained by dissolving a binder in an organic solvent. The binder used for the organic vehicle is not particularly limited, and may be appropriately selected from usual various binders such as ethyl cellulose and polyvinyl butyral. Also, the organic solvent used at this time is not particularly limited, and can be appropriately selected from terpineol, butyl carbitol, acetone, toluene, and the like according to the method for forming the varistor layer such as a printing method or a sheet method.

  The content of the organic vehicle and the varistor raw material in the paint is not particularly limited. For example, an organic vehicle can be mix | blended so that a binder may be about 1-10 mass% and an organic solvent may be about 10-50 mass% with respect to the whole coating material. The paint may contain additives selected from various dispersants, plasticizers, dielectrics, insulators, and the like as necessary.

  Examples of the water-based paint include water-soluble binders, dispersants and the like dissolved in water. The water-soluble binder is not particularly limited, and can be appropriately selected from polyvinyl alcohol, cellulose, water-soluble acrylic resin, emulsion and the like.

  The above-described varistor layer-forming coating material (slurry) can be prepared by mixing and pulverizing materials such as the above-described varistor raw material, binder, solvent (organic solvent or water), and various additives using a ball mill or the like. it can. The mixing ratio of the raw materials when preparing the slurry can be appropriately changed in order to adjust the fluidity of the slurry.

  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. A plurality of such green sheets are produced.

  An electrode portion having a predetermined shape to be an internal electrode is formed on the produced green sheet. For example, the electrode portion is formed by printing a conductive paste mixed with metal powder such as oxide, Ag particles, and Pd particles, glass frit, an organic binder, and an organic solvent by a printing method such as screen printing and drying. Can be formed.

  The organic binder used for the conductive paste for internal electrodes is not particularly limited, and may be appropriately selected from various binders such as ethyl cellulose and polyvinyl butyral. The organic solvent can be appropriately selected from various organic solvents such as terpineol, butyl carbitol, acetone and toluene. There is no restriction | limiting in particular in the compounding ratio of an electrically conductive paste, For example, 1-20 mass parts of the said organic binder and 1-40 mass parts of said organic solvents may be mix | blended with respect to 100 mass parts of total amounts of a metal and an oxide powder. it can. These blending ratios can be appropriately changed in order to adjust the fluidity of the conductive paste.

  FIG. 8 is a process diagram showing a process of forming a sheet laminate. The green sheets GS11, GS12, and GS13 on which the electrode portions EL2, EL3, and EL4 are respectively formed and the green sheets GS11 on which the electrode portions are not formed are stacked in a predetermined order to form a green body LS2 that is a sheet laminate. .

  Next, the green body LS2 is subjected to heat treatment at 180 to 400 ° C. for about 0.5 to 24 hours to remove the binder, and then fired at 850 to 1400 ° C. for about 0.5 to 8 hours. Thus, the varistor element body 10 can be obtained. By this firing, the green sheets GS11 to GS14 in the green body LS2 become varistor layers, and the electrode portions EL2, EL3, EL4 become internal electrodes.

  The varistor 100 can be obtained by forming the external electrode and the resistor by the above-described method on the surface (main surface 10a) from which the internal electrode of the obtained varistor element body 10 is drawn.

  FIG. 9 is a schematic cross-sectional view showing an example of a varistor 100 obtained by the varistor manufacturing method of the present invention. A pair of external electrodes 32 and 34 are provided on the main surface 10 a of the varistor element body 10. Further, a resistor 62 is provided so as to be in contact with the main surface 10a, and this resistor 62 is provided so as to connect the pair of external electrodes 32 and 34. The varistor 100 has a protective layer (overglaze) 14 as the outermost layer. The protective layer 14 is provided so as to cover the varistor element body 10, the pair of external electrodes 32 and 34, and the resistor 62.

  The varistor element body 10 in the present embodiment contains zinc oxide (ZnO) as a main component, and also contains rare earth metal oxide, calcium oxide, and silicon oxide as subcomponents. From the viewpoint of obtaining excellent varistor characteristics, the ZnO content in the varistor element body 10 as a whole is preferably 70 to 99 atomic% in terms of Zn. This makes it possible to achieve both excellent varistor characteristics and high surge resistance at a high level.

  Rare earth metal oxides contained as auxiliary components in the varistor element body 10 are a group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. An oxide containing at least one rare earth metal selected from the above is preferable. The content of the rare earth metal oxide is preferably 0.01 to 10 atomic% in terms of rare earth metal element with respect to zinc oxide as the main component. If the content of the rare earth metal oxide is too low, voltage non-linear characteristics tend to be difficult to develop, and if the content is too high, the varistor voltage tends to increase rapidly. The rare earth oxide is more preferably an oxide of Pr.

  The content of calcium oxide in the varistor element body 10 is 2 to 80 atomic% in terms of calcium atoms with respect to the main component (zinc oxide) of the varistor element body 10. Moreover, content of the silicon oxide in the varistor element | base_body 10 is 1-40 atomic% in conversion of a silicon atom with respect to this whole main component. Moreover, the ratio of the calcium oxide with respect to a silicon oxide is 1 or more and less than 3 in conversion of the atomic ratio (Ca / Si) converted into a silicon atom and a calcium atom, respectively.

  The varistor element body 10 having the above composition can maintain sufficiently high varistor characteristics even if the surface of the varistor element body 10 is altered by laser light irradiation in the removal process or trimming process. In the manufacturing method of the present embodiment, a varistor having a high initial surface insulation resistance is used and a method of removing the resistor by laser irradiation is adopted, so that excellent surface insulation resistance is maintained even if the structure is miniaturized. The manufactured varistor can be easily manufactured. The surface insulation resistance of the varistor element body 10 is preferably 1 MΩ or more, and more preferably 10 MΩ or more.

Examples of the calcium oxide contained in the varistor element body 10 include CaO and composite oxides such as CaSiO ₃ and Ca ₂ SiO ₄ containing calcium, silicon, and oxygen. Examples of the silicon oxide contained in the varistor element include SiO ₂ and composite oxides such as CaSiO ₃ , Ca ₂ SiO ₄ , and Zn ₂ SiO ₄ containing calcium, silicon, and oxygen.

  The varistor element body 10 preferably contains an oxide containing at least one element selected from an oxide of Co or a group IIIB element in addition to the above-described subcomponents. Preferred IIIB elements include B, Al, Ga, or In.

  The content of Co oxide is preferably 0.05 to 10 atomic% in terms of Co element with respect to the entire main component. When the content is less than 0.05 atomic%, it tends to be difficult to obtain a desired varistor voltage. When the content exceeds 10 atomic%, the varistor voltage increases and the voltage nonlinear characteristics are increased. It tends to decrease.

  The content of at least one oxide selected from Group IIIB elements is preferably 0.0005 to 0.5 atomic% in terms of the selected Group IIIB elements with respect to the entire main component. When the content is less than 0.0005 atomic%, the varistor voltage tends to increase. When the content exceeds 0.5 atomic%, the insulation resistance is low and the varistor voltage tends not to be obtained. .

  The varistor element body 10 preferably contains an oxide containing at least one element selected from Group IA elements as another subcomponent. Preferred group IA elements include Na, K, Rb, or Cs.

  The content of at least one oxide selected from Group IA elements is preferably less than 5 atomic% in terms of the selected Group IA elements with respect to the entire main component. When the content is 5 atomic% or more, the melting point as a ceramic is lowered and tends to melt during firing.

  The varistor element body 10 preferably contains an oxide containing at least one element selected from Group IIA elements excluding Ca as another subcomponent. Preferred group IIA elements include Mg, Sr, or Ba.

  The content of the oxide containing at least one element selected from Group IIA elements excluding Ca is preferably less than 1 atomic% in terms of the selected Group IIA element with respect to the entire main component. When the content is 1 atomic% or more, the varistor voltage tends to increase.

  The varistor element body 10 preferably contains an oxide containing one or both of Cr and Mo as another subcomponent. The content of the oxide is preferably less than 10 atomic% in terms of each Cr element and Mo element with respect to the entire main component. When the content exceeds 10 atomic%, the varistor voltage tends to increase.

The external electrodes 32 and 34 are conductors and contain an oxide as a main component. The oxide may contain for example _SiO 2, NiO, MnO, and _Al 2 _{O 3.} The external electrodes 32 and 34 preferably contain a single metal in addition to the oxides described above. As a metal simple substance, Ag, Pd, Pt etc. can be contained suitably.

  The total content of oxides in the external electrodes 32 and 34 is preferably 0.01 to 20% by mass with respect to the entire external electrode. When the total oxide content is less than 0.01% by mass, the adhesion strength to the substrate tends to be low, and when it exceeds 20% by mass, the electrical conductivity tends to be impaired. The thickness of the external electrodes 32 and 34 can be set to 1 to 30 μm, for example.

The resistor 62 is made of a conductive oxide such as RuO ₂ , SnO ₂ , LaB ₆ , an oxide such as Al ₂ O ₃ , B ₂ O ₃ , SiO ₂ , and a simple metal such as Pd, Ag, Pt. Can be contained.

  The resistor 62 contains an oxide as a main component, and the content of the oxide in the resistor 62 is preferably 50 to 99% by mass. Thereby, the variation in resistance value can be further suppressed. In addition, the thickness of the resistor 62 can be 1-30 micrometers, for example.

The varistor 100 may have a base glass layer (not shown) so as to cover the main surface 10a. By providing such a base glass layer, alteration of the varistor element body 10 due to laser irradiation is suppressed, and deterioration of varistor characteristics can be sufficiently suppressed. The underlying glass layer is provided between the varistor element body 10 and the pair of external electrodes 32 and 34 and the resistor 62. The base glass layer can contain oxides generally contained in glass, such as HfO ₂ , CaO, Al ₂ O ₃ , SiO ₂ , ZnO, BaO, and B ₂ O ₃ . In addition, the thickness of a base glass layer can be 1-30 micrometers, for example.

  The varistor 100 may have an external electrode functioning as an input / output terminal electrode and an external electrode functioning as a ground terminal electrode on the main surface opposite to the main surface 10a. That is, the varistor 100 can be a multilayer chip varistor formed as a BGA (Ball Grid Array) package. Such a varistor electrically and mechanically connects each external electrode provided on the main surface opposite to the main surface 10a and a land of an external substrate corresponding to each external electrode using a solder ball. Thus, it can be mounted on an external substrate.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  Hereinafter, the present invention will be described more specifically based on examples and comparative examples with reference to the drawings. However, the present invention is not limited to the following examples.

(Example 1)
<Varistor element formation process>
A varistor element body was formed by the following procedure. A powder raw material containing zinc oxide as a main component and the components shown in Table 1 as a subcomponent was prepared. The contents in Table 1 indicate the ratio to zinc oxide. These powder raw materials, organic binder, organic solvent, and additives were mixed and pulverized for 20 hours using a ball mill to prepare a slurry for a varistor element body.

  The slurry for the varistor element body prepared as described above was applied onto a film made of polyethylene terephthalate by the doctor blade method and then dried to form a film having a thickness of 30 μm. The film thus obtained was peeled from the film to form a plurality of green sheets. An electrode portion having a predetermined shape was formed on a part of the obtained green sheet. The electrode portion was formed by printing a normal conductive paste by a screen printing method and drying.

  Next, the green sheet LS2 (see FIG. 8), which is a sheet laminate, was obtained by stacking the green sheet on which the electrode part was formed and the green sheet on which the electrode part was not formed in a predetermined order.

  Next, the green body LS2 was subjected to heat treatment to remove the binder, and then fired to obtain a varistor element body. The initial surface insulation resistance of this varistor element body was 200 MΩ or more.

<External electrode formation process>
A mixed raw material containing Ag as a main component and a metal oxide as a subcomponent, an organic binder, and an organic solvent were mixed for 20 hours using a ball mill to prepare a conductive paste for forming an external electrode.

  On one main surface 10a of the varistor element body 10, the conductive paste prepared as described above is printed by a screen printing method and dried to form an electrode portion corresponding to the external electrode pair 30 in FIG. . And this electrode part was baked at 850 degreeC, and as shown in FIG. 1, on the main surface 10a of the varistor element | base_body 10, the some external electrode pair 30 arranged in the same direction was formed. In addition, after printing the commercially available Ag-Pt-type paste on the other main surface of the varistor element body 10 by the screen printing method, it was made to dry and baked at 800-1100 degreeC, and the external electrode was formed.

<Resistor forming process>
A mixed material of a metal oxide mainly composed of RuO ₂ and SiO ₂ , an organic binder, and an organic solvent were mixed for 20 hours using a ball mill to prepare a resistor paste for forming a resistor.

  Next, the resistance paste prepared as described above is screen-printed so as to span all the first external electrodes 32 and all the second external electrodes 34 formed on the main surface 10a of the varistor element body 10. Printed by the law. This resistance paste was dried and baked at 850 ° C. to form a resistor 60 as shown in FIG. As a result, the first external electrode 32 and the second external electrode 34 are connected by the resistor 60.

<Resistance removal process>
Using a commercially available laser trimming apparatus, the main surface 10a of the varistor element body 10 on which the resistor 60 and the external electrode pair 30 were formed was irradiated with laser light. The laser beam was irradiated while moving from the upper side to the lower side in FIG. 3 along the laser beam irradiation line 40 in FIG. The irradiation conditions (movement speed, frequency, output) of the laser beam were as shown in Table 3. In addition, when the number of times of laser light irradiation was multiple times, the laser light irradiation was repeated a plurality of times along the laser light irradiation line 40.

  A varistor having a plurality of connecting bodies 20 formed on the main surface 10a of the varistor element body 10 as shown in FIG. In the varistor, the distance S (FIG. 1) between the opposed external electrodes 32 and 34 and the width T of the external electrodes 32 and 34 were 500 μm and 150 μm, respectively. The interval L between adjacent external electrode pairs 30 was 100 μm, and the width R of the resistor 62 was 150 to 250 μm.

<Trimming process>
Next, the resistor 62 was trimmed. Specifically, using the laser trimming apparatus used in the resistor removal process, laser light was irradiated to a predetermined position of the resistor 62 to remove a part of the resistor 62 to form a trimming portion. The laser light irradiation conditions in the trimming process were a frequency of 20 kHz and an output of 0.50 W. The varistor for evaluation was obtained by the above process.

(Examples 2 and 3)
A varistor for evaluation was produced in the same manner as in Example 1 except that the irradiation condition of the laser beam in the resistor removing step was changed as shown in Table 3. The width T of the external electrode, the distance S between the opposed external electrodes 32 and 34, the distance L between adjacent pairs of external electrodes, and the width R of the resistor were the same as in Example 1.

(Comparative Example 1)
<Varistor element formation process>
A varistor element body was formed by the following procedure. A powder raw material containing zinc oxide as a main component and the components shown in Table 2 as subcomponents was prepared. The contents in Table 2 indicate the ratio to zinc oxide. These powder raw materials, organic binder, organic solvent, and additives were mixed and pulverized for 20 hours using a ball mill to prepare a slurry for a varistor element body.

  A varistor element body was formed in the same manner as in Example 1 except that the slurry for the varistor element body prepared as described above was used. The initial surface insulation resistance of this varistor element body was 200 MΩ or more. Then, in the same manner as in Example 1, an external electrode forming step, a resistor forming step, a resistor removing step, and a trimming step were performed to produce an evaluation varistor.

(Evaluation of surface insulation resistance)
In the varistor 100 for evaluation (FIG. 4) produced in each example and comparative example, in order to measure the surface insulation resistance between the adjacent connecting members 20, the resistance value between the external electrode 32a and the external electrode 34b ( Surface insulation resistance) was measured using a measuring instrument built in the laser trimming apparatus. The results are shown in Table 3.

  As shown in Table 3, in the varistors of Examples 1 to 3, a sufficiently large surface insulation resistance was maintained even after the resistor removing process and the trimming process for performing laser irradiation, and good varistor characteristics were obtained. It was possible to produce a varistor having the same.

  On the other hand, in the varistor of Comparative Example 1, the varistor element body was altered by laser irradiation, and the surface insulation resistance was small.

(Comparative Example 2)
In the same manner as in Example 1, a varistor element body was formed, and an external electrode was formed on the main surface of the varistor element body. In the resistor forming step, as shown in FIG. 10, the same resistance as that of the first embodiment is applied so that each external electrode pair 130 formed on the main surface 110a of the varistor element body 110 is individually spanned. The paste was printed by screen printing. This resistance paste was dried and baked at 850 ° C. to form an evaluation varistor 200 shown in FIG.

  On the main surface 110 a of the varistor element body 110, a plurality of connecting bodies 120 including a pair of external electrodes 132 and 134 and a resistor 162 that connects the pair of external electrodes 132 and 134 are formed.

  In the varistor 200, the interval S between the opposed external electrodes 132, 134, the width T of the external electrode pair 130, and the interval L between the adjacent external electrode pairs 130 were the same as those in the first embodiment. However, in Comparative Example 14, since the resistor 162 is formed using the screen printing method without performing laser irradiation, it is necessary to set the interval between the adjacent resistors 162 to 150 μm. For this reason, the width 162 of the resistor 162 is 100 μm, and the width R cannot be increased any more. Since the width R of the resistor 162 is smaller than those of the first to third embodiments, it is difficult to align the laser beam for trimming, and the resistor 162 cannot be trimmed.

(Evaluation of resistance value)
The resistance values of the connection bodies of the varistors for evaluation produced in Example 1 and Comparative Example 2 were measured as follows. In each varistor 100 shown in FIG. 4, the resistance value between the first external electrode 32 and the second external electrode 34 in each connection body 20 before and after the trimming process is performed (before and after the trimming portion 50 is formed) Measurement was performed using a measuring instrument built in the laser trimming apparatus. In addition, resistance value measurement was performed in nine places between different external electrode pairs 30, and an average value, a standard deviation (σ), a minimum value, and a maximum value were derived. A value of 3σ / average value was calculated from these values, and the variation in resistance value was evaluated. The results are shown in Table 4.

  As shown in Table 4, the varistor of Example 1 was able to significantly reduce variation in resistance value by performing trimming. On the other hand, the varistor of Comparative Example 2 had a small resistor width R and could not be trimmed.

It is process drawing which shows the external electrode formation process in the manufacturing method of the varistor of this embodiment. It is process drawing which shows the resistor formation process in the manufacturing method of the varistor of this embodiment. It is process drawing which shows the removal process of the resistor in the manufacturing method of the varistor of this embodiment. It is a top view which shows an example of the varistor obtained by the manufacturing method of this invention. FIG. 5 is a partially enlarged view showing a region A on the surface of the varistor 100 shown in FIG. 4 in an enlarged manner. It is process drawing which shows the trimming process in the manufacturing method of the varistor of this embodiment. It is a scanning electron micrograph (1000 times) which shows the cross section of the VII-VII line in the varistor of FIG. It is process drawing which shows the process of forming a sheet laminated body. It is a schematic cross section which shows an example of the varistor obtained by the manufacturing method of the varistor of this invention. It is a top view of the varistor manufactured by the conventional manufacturing method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Varistor element | base_body, 10a ... Main surface (one side), 14 ... Protective layer, 20, 120 ... Connection body, 30, 130 ... External electrode pair, 32, 132 ... 1st external electrode (external electrode), 34, 134 ... second external electrode (external electrode), 40 ... laser beam irradiation, 50 ... trimming portion, 60, 62, 64, 162 ... resistor, 100, 200 ... varistor, LS2 ... green body, EL2, EL3, EL4 ... electrode part, GS11, GS12, GS13 ... green sheet.

Claims (3)

On one surface of the varistor element body, a plurality of external electrode pairs each including a first external electrode and a second external electrode provided so as to face the first external electrode are formed so as to be arranged in a predetermined direction. An external electrode forming step;
A plurality of external electrode pairs are connected to each other, and a resistance is provided on the one surface of the varistor element body such that the first external electrode and the second external electrode in the external electrode pair are connected to each other. A resistor forming step for forming a body;
Of the resistor, a portion formed in a region between adjacent external electrode pairs is removed by laser light irradiation, and the first external electrode, the second external electrode, and the first external electrode are removed. A removal step of forming a connection body having an electrode and a resistor for connecting the second external electrode, and
The varistor element includes zinc oxide as a main component, and includes calcium oxide, silicon oxide, and rare earth metal oxide as subcomponents. The ratio X is 2 to 80 atomic%, the silicon oxide equivalent ratio Y of the silicon oxide with respect to the entire main component is 1 to 40 atomic%, and the ratio of X to Y (X / Y) is expressed by the following formula (X A method for producing a varistor satisfying 1).
1 ≦ X / Y <3 (1)   The varistor manufacturing method according to claim 1, further comprising a trimming step of trimming a part of the resistor in the connection body formed in the removing step with a laser beam. The varistor manufacturing method according to claim 1, wherein the laser light irradiation is repeated a plurality of times.