JP2010018482A - Ferrite, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite capable of maintaining good varistor characteristics when calcining integrally with a varistor, and simultaneously having a high magnetic resonance frequency and a high initial magnetic permeability. <P>SOLUTION: The ferrite includes iron oxide, nickel oxide, zinc oxide, and manganese oxide as principal components. The principal components includes 45-49.5 mol% of iron oxide in terms of Fe<SB>2</SB>O<SB>3</SB>, 20-40 mol% of nickel oxide in terms of NiO, 14-30 mol% of zinc oxide in terms of ZnO, and 0.1-2 mol% of manganese oxide in terms of Mn<SB>2</SB>O<SB>3</SB>. The principal components arbitrarily includes copper oxide where the content of copper oxide in terms of CuO in the principal components is not greater than 2 mol%. The ferrite further includes 3-10 mass% of bismuth oxide in terms of Bi<SB>2</SB>O<SB>3</SB>to the total principal components. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ferrite and a manufacturing method thereof.

  In a computer device, a multilayer varistor, an inductor (ferrite chip), a capacitor chip, and the like are incorporated in an input / output portion of a circuit board and a circuit in order to prevent noise generation and intrusion of noise from the outside.

  However, when components such as a multilayer varistor, an inductor, and a capacitor chip are provided on a circuit board, these components occupy a large area of the board, and a mounting space increases. In addition, the cost tends to increase due to an increase in the number of parts.

  In order to deal with such problems, a composite component is manufactured by integrally sintering each element chip while being bonded to each other, and installed on a circuit board, thereby reducing the number of components and making the component compact. Attempts have been made to reduce space.

  By the way, a ferrite material, which is an oxide magnetic material containing Ni, Cu, Zn or the like, has been conventionally used as a base material for an inductor. For example, Ni—Cu—Zn ferrite has excellent magnetic properties and is widely used as a core (magnetic core) material for various electronic components or as a material for inductor components such as multilayer chip inductors. It is known that the Cu component contained in this Ni—Cu—Zn ferrite has an effect of promoting sintering.

However, in the case of producing the composite parts as described above, Ni—Cu—Zn ferrite is used as the base material of the inductor, and when this inductor and the varistor are integrally sintered, the Ni—Cu—Zn ferrite constituting the inductor base is formed. Since the Cu component contained in the metal diffuses and moves to the varistor element side, there is a problem that the varistor characteristics deteriorate. For this reason, Zn ferrite with reduced Cu content has been proposed (for example, Patent Document 1).
JP 2007-91539 A

  However, since the Zn ferrite of Patent Document 1 is non-magnetic, for example, in order to improve inductor characteristics, noise suppression effects, etc., the inductor base material itself is required to have magnetism. Therefore, there is a demand for a ferrite that has magnetism and is suitable as a base material for composite parts including varistors and inductors.

  The present invention has been made in view of the above circumstances, and provides a ferrite having excellent magnetism and a method for producing the ferrite capable of maintaining good varistor characteristics when integrally fired with a varistor. With the goal.

In the present invention, the iron oxide as a main component, nickel oxide, a ferrite containing zinc oxide and manganese oxide, the main component, 45～49.5Mol% iron oxide calculated as _Fe 2 _{O 3,} nickel oxide NiO 20～40Mol% in terms of zinc oxide 14～30Mol% calculated as ZnO, and manganese oxide containing 0.1 to 2 mol% in _Mn 2 _{O 3} in terms of the major component contains the optionally oxidized copper, the main component the content of copper oxide in is not more than 2 mol% in terms of CuO relative to the total principal component, provides a ferrite containing 3 to 10 wt% of bismuth oxide in terms _{of Bi} 2 _{O 3.}

  Such a ferrite can maintain good varistor characteristics such as ESD resistance even when fired integrally with a varistor, and can obtain a high initial permeability. The reason why such an effect is obtained is, for example, the following factors. The ferrite of the present invention contains a specific amount of bismuth oxide while the content of copper oxide is sufficiently reduced. For this reason, for example, when integrally fired with a varistor, the diffusion of Cu components to the varistor side can be sufficiently reduced to maintain good varistor characteristics, and high sintering can be achieved by sufficiently sintering at low temperatures. It can be set as the sintered compact which has a density. In addition to having such a high sintered density, since it contains specific amounts of iron oxide, nickel oxide, zinc oxide and manganese oxide, it is possible to achieve both a high magnetic resonance frequency and a high initial permeability. . The reason why the effect is obtained is not limited to the above factors.

The ferrite of the present invention preferably has a sintered density of 5.0 g / cm ³ or more. Such ferrite has a much better initial permeability.

Further, in the present invention, iron oxide is 45 to 49.5 mol% in terms of Fe ₂ O ₃ , nickel oxide is 20 to 40 mol% in terms of NiO, zinc oxide is 14 to 30 mol% in terms of ZnO, and manganese oxide is Mn _2. A calcining step of obtaining a calcined body by calcining a mixed raw material containing 0.1 to 2 mol% in terms of O ₃ and having a copper oxide content of 2 mol% or less in terms of CuO, And a firing step of adding 3 to 10% by mass of bismuth oxide to the entire fired body and firing.

  In the production method of the present invention, since a specific amount of bismuth oxide is added, low temperature firing is possible, and the specific resistance of the obtained sintered body can be increased. Moreover, since the calcined body containing specific amounts of iron oxide, nickel oxide, zinc oxide and manganese oxide is used, a sintered body capable of achieving both a high magnetic resonance frequency and a high initial permeability can be obtained.

  In the firing step in the production method of the present invention, it is preferable to add bismuth-based glass containing bismuth oxide to the calcined body. Also in this case, similarly to bismuth oxide, low-temperature firing is possible, and the density of the sintered body can be increased. Further, if the composition of the main component is adjusted, the specific resistance can be increased as compared with the case where bismuth oxide is added alone.

  According to the present invention, it is possible to maintain good varistor characteristics when integrally fired with a varistor, and it is possible to provide a ferrite having excellent magnetism and a method for producing the ferrite.

  In the following, preferred embodiments of the present invention will be described with reference to the drawings as the case may be. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

The ferrite of this embodiment contains iron oxide, nickel oxide, zinc oxide and manganese oxide as essential components of the main component, and contains copper oxide as an optional component of the main component. Iron oxide, the content of nickel oxide, zinc oxide and manganese oxide, based on the total principal component, 45～49.5Mol% iron oxide calculated as _Fe 2 _{O 3,} 20～40Mol% nickel oxide in terms of NiO, Zinc oxide is contained in an amount of 14 to ₃₀ mol% in terms of ZnO, and manganese oxide is contained in an amount of 0.1 to ₂ mol% in terms of Mn2O3.

  Further, since copper oxide is an optional component, the ferrite of this embodiment may not contain copper oxide at all. When the ferrite contains copper oxide, the main component of the ferrite contains copper oxide in a range of more than 0 and 2 mol% or less.

  The ferrite in this embodiment may optionally contain copper oxide as a main component. The content of copper oxide in the main component is preferably 1.5 mol% or less in terms of CuO, and preferably 1.0 mol%, from the viewpoint of achieving both high sintering density and ESD resistance of the varistor. Is more preferable. On the other hand, when the content of copper oxide exceeds 2 mol%, the Cu component diffuses into the varistor laminated portion 7 and deteriorates varistor characteristics such as ESD tolerance. The lower the copper oxide content, the better the ESD resistance of the varistor can be maintained. The main component is a component constituting the main phase of ferrite.

Ferrite contains bismuth oxide as a subcomponent in addition to the main component. The content of bismuth oxide is ₃ to 10% by mass in terms of Bi ₂ O ₃ , preferably 3 to 9% by mass, and more preferably 4 to 6% by mass with respect to the entire main component. By setting the content to 3 to 10% by mass, low-temperature (about 900 ° C.) sintering is possible, and a high-density ferrite sintered body can be obtained.

When the content of bismuth oxide is less than 3% by mass in terms of Bi ₂ O _{3 with} respect to the entire main component, low-temperature sintering tends to be difficult, and a sufficiently high sintered density tends to be difficult to obtain. On the other hand, when the content exceeds 10% by mass, abnormal grain growth tends to occur during sintering, and the specific resistance of the obtained sintered body tends to be low.

  The ratio of the main component to the entire ferrite of the present embodiment is preferably 80 to 97% by mass, more preferably 85 to 97% by mass, and further preferably 90 to 97% by mass. As a result, it is possible to make the initial permeability and the magnetic resonance frequency compatible at a higher level.

  The content of nickel oxide in the main component is more preferably 25 to 35 mol% in terms of NiO. If the content is too high, a sufficiently high initial permeability μi tends to be difficult to obtain, and sufficient inductance tends to be difficult to obtain when used as a substrate for a multilayer chip inductor. On the other hand, if the content is too low, the magnetic resonance frequency fr tends to be low.

  The content of zinc oxide in the main component is preferably 15 to 27 mol%, more preferably 16 to 24 mol% in terms of ZnO. If the content is too high, the magnetic resonance frequency fr tends to be low. On the other hand, if the content is too low, a sufficiently high initial permeability μi tends to be difficult to obtain.

  The ferrite of this embodiment can obtain desired initial permeability μi and magnetic resonance frequency fr by changing the contents of nickel oxide and zinc oxide.

The content of manganese oxide in the main component is preferably 0.2 to 2 mol% in _Mn 2 _{O 3} in terms of, and more preferably 0.5 to 2 mol%. If the content is too high, good sinterability is impaired and the specific resistance of the ferrite sintered body is reduced. Also, if the content is too low, the specific resistance of the ferrite sintered body becomes small, and in the plating process of the terminal electrode, which is a part of the manufacturing process of the multilayer chip inductor, the plating is easily extended, and the multilayer chip inductor There is a tendency for defects to occur easily in the characteristics.

Iron oxide content in the main component is preferably 46～49Mol% in terms _{of Fe} 2 _{O 3,} and more preferably 46~48mol%. When the content is too high, it becomes difficult to obtain sufficient sinterability and the specific resistance tends to be low. On the other hand, if the content is too low, the specific resistance tends to be low, and high initial permeability tends to be impaired.

  The ferrite of the present embodiment may be in the form of an unsintered ferrite composition, for example, a powder, a slurry, or an aggregate, or may be a sintered body (ferrite sintered body). Since the ferrite of this embodiment is excellent in sinterability, a sintered body having a sufficiently high sintered density (sintered body density) can be obtained even when fired at a low temperature. For this reason, for example, it can be suitably used as a material for a multilayer chip inductor using Ag, which is required to be sintered at a low temperature, as a conductor. In addition, when the powdered or slurry-like ferrite of this embodiment is used as a composite part by integrally firing with a varistor, varistor characteristics such as ESD resistance can be maintained well. The ferrite sintered body of the present embodiment has a high specific resistance and can achieve both a high magnetic resonance frequency and a high initial permeability.

  Next, a preferred embodiment of a method for producing a ferrite sintered body will be described below.

In the method for producing a ferrite sintered body according to the present embodiment, iron oxide is 45 to 49.5 mol% in terms of Fe ₂ O ₃ , nickel oxide is 20 to 40 mol% in terms of NiO, and zinc oxide is 14 to 30 mol% in terms of ZnO. And 0.1 to 2 mol% of manganese oxide in terms of Mn ₂ O ₃ , and a preparation step for adjusting an oxide mixed powder in which the content of copper oxide is 2 mol% or less in terms of CuO, and the oxide mixed powder A calcining step of calcination of the calcined material, an addition step of pulverizing the obtained calcined product, and adding 3 to 10% by mass of bismuth oxide based on the whole calcined product, and bismuth oxide And a calcination step of forming and baking a mixed powder obtained by mixing the pulverized product of the calcined body and the calcined body.

In the preparation step, essential powders of iron oxide, nickel oxide, zinc oxide, and manganese oxide are prepared. Iron oxide is 45 to 49.5 mol% in terms of Fe ₂ O ₃ , nickel oxide is 20 to 40 mol% in terms of NiO, zinc oxide is 14 to 30 mol% in terms of ZnO, and manganese oxide is 0.00 in terms of Mn ₂ O ₃ . An oxide mixed powder is prepared by weighing to 1 to 2 mol% and mixing with, for example, a ball mill. Under the present circumstances, you may mix the copper oxide which is an arbitrary component in the ratio of 2 mol% or less. In addition, the ratio of each oxide is a molar content ratio in the oxide mixed powder.

  An organic vehicle containing an organic solvent and an organic binder may be mixed with the oxide mixed powder and mixed as a magnetic slurry. Thus, the oxide mixed powder can be mixed more uniformly by mixing in a slurry state, that is, in a wet manner.

  In the calcination step, the oxide mixed powder obtained in the preparation step or the slurry containing the same is calcined in an air atmosphere at 600 to 1000 ° C. for 1 to 20 hours. When the calcination temperature becomes too low, or when the calcination time becomes too short, the uniformity of the obtained ferrite sintered body tends to be impaired. On the other hand, when the calcining temperature is too high, or when the calcining time is too long, the obtained calcined body tends to aggregate and become difficult to pulverize.

  In the addition step, the calcined body is pulverized with a ball mill or the like, and bismuth oxide powder is added to obtain a mixed powder. The addition amount of bismuth oxide is preferably 3 to 9% by mass, and preferably 3 to 6% by mass based on the entire calcined body. When the added amount is less than 3% by mass, the ferrite sintered body becomes difficult to be densified and tends to be difficult to fire at a low temperature. On the other hand, when the added amount exceeds 9% by mass, the specific resistance of the obtained ferrite sintered body tends to decrease.

As the bismuth oxide source, bismuth-based glass may be used instead of the bismuth oxide powder. As the bismuth glass, commercially available glass can be used. Bismuth glass usually contains SiO ₂ , B ₂ O _{3 and the} like in addition to Bi ₂ O ₃ . Even when bismuth-based glass is used as the bismuth oxide source, densification of the ferrite sintered body is promoted, and a high sintered density can be obtained. As a result, a ferrite sintered body that can achieve both high specific resistance and initial permeability can be obtained.

  In the firing step, a mixed powder obtained by adding bismuth oxide to the pulverized product of the calcined body is formed to produce a formed body, and the formed body is fired to obtain a sintered body. The molded body can be produced by a general method such as press molding. Firing of the molded body can be performed under conditions of a firing temperature of 800 to 940 ° C. and a firing time of 1 to 10 hours. When the firing temperature is too low, or when the firing time is too short, a sintered body having a high sintered density tends to be difficult to obtain. On the other hand, when the firing temperature is too high, or when the firing time is too long, abnormal grain growth of the obtained ferrite sintered body occurs and the mechanical strength tends to be impaired.

The composition of the ferrite sintered body thus obtained usually corresponds to the usage ratio of each oxide used as a raw material. According to the method for manufacturing a ferrite sintered body of the present embodiment, a sintered body having a high sintered density of 5.0 g / cm ³ or more can be obtained even when the firing temperature in the firing step is a low temperature around 900 ° C. Such a sintered body has a high initial permeability in a high frequency region, and has a sufficiently high specific resistance. Therefore, it can be suitably used as a magnetic layer of an inductor. Further, since the ESD resistance of the varistor layer is hardly lowered, it is suitably used as a material for a composite component of an inductor and a varistor.

  Next, a multilayer filter that is a composite component of an inductor and a varistor manufactured using the ferrite of the present invention will be described.

  FIG. 1 is an external perspective view showing an example of a multilayer filter using the ferrite of the present invention. The multilayer filter 1 has an input terminal electrode 3 and an output terminal electrode 4 at both ends in the longitudinal direction of the element body 2, and has a pair of ground terminal electrodes 5 on both side surfaces in the longitudinal direction.

  FIG. 2 is an exploded perspective view showing an element body 2 portion of the multilayer filter 1 shown in FIG. As shown in FIG. 2, the element body 2 includes a magnetic laminate 6 in which a plurality of magnetic layers 6 a to 6 i are sequentially laminated, and a varistor laminate 7 in which a plurality of varistor layers 7 a to 7 d are sequentially laminated. Become.

  That is, the multilayer filter 1 includes a varistor having an inductor portion 10 having magnetic layers 6a to 6i, conductor portions 8a to 8h and conductor portions including via conductors 9a to 9g, varistor layers 7a to 7d, and electrodes 11 and 12. The magnetic layers 6a to 6i include the ferrite according to the present embodiment.

  Conductor patterns 8a to 8h having desired shapes are formed on the magnetic layers 6b to 6i of the magnetic layered portion 6, respectively. Specifically, substantially C-shaped conductor patterns 8c, 8e, 8g corresponding to approximately 3/4 turns of the coil are formed on the magnetic layers 6d, 6f, 6h, respectively, and the magnetic layers 6c, 6e, On the 6g, substantially U-shaped conductor patterns 8b, 8d and 8f corresponding to approximately 3/4 turns of the coil are formed. On the magnetic layers 6b and 6i, lead electrodes 8a and 8h connected to the input terminal electrode 3 and the output terminal electrode 4 are formed. Furthermore, via conductors 9a to 9g are formed which penetrate through the magnetic layers 6b to 6h, respectively, and electrically connect the conductor patterns in contact with the magnetic layers 6b to 6h. As a result, a spiral coil (conductor portion) having approximately 4.5 turns in which the lead electrodes 8a and 8h, the conductor patterns 8b to 8g, and the via conductors 9a to 9g are electrically connected is formed. An inductor portion 10 is formed in the portion 6.

  A substantially rectangular ground electrode 11 electrically connected to the ground terminal electrode 5 is formed on the varistor layer 7 b of the varistor laminated portion 7. A substantially rectangular hot electrode 11 electrically connected to the output terminal electrode 4 is formed on the varistor layer 7c. The hot electrode 11 and the ground electrode 12 are opposed to each other, and partially overlap with each other through the varistor layer 7b when viewed from the stacking direction. Thus, the varistor part 20 which expresses a varistor function is formed.

  The multilayer filter 1 having the above-described multilayer structure prevents a current that has flowed suddenly due to the varistor effect from passing as noise when high-voltage noise exceeding the varistor voltage is applied to the input side. Can do.

  The magnetic layers 6a to 6i are composed of the ferrite sintered body of the present embodiment. Since the ferrite sintered body of the present embodiment has a sufficiently reduced copper oxide content as compared with ordinary Ni—Cu—Zn ferrite, the Cu component from the magnetic body laminated portion 6 to the varistor laminated portion 7 is reduced. Diffusion can be sufficiently suppressed. For this reason, even if the varistor is combined with the inductor, the varistor characteristics such as the ESD resistance can be sufficiently satisfactorily maintained.

  The varistor layers 7a to 7d are made of, for example, a ceramic material mainly composed of ZnO. This ceramic material may contain Pr, Bi, Co, Al or the like as an additive component. When Co is contained in addition to Pr, it has excellent varistor characteristics and also has a high dielectric constant (ε). Further, when Al is further contained, the resistance becomes low. Moreover, other additives, for example, elements such as Cr, Ca, Si, and K may be included as necessary.

  As the conductive material used for the hot electrode 11 and the ground electrode 12, a metal material that can be fired simultaneously with the ceramic material forming the varistor layers 7a to 7d is used. That is, since the firing temperature of the varistor ceramic is usually about 800 ° C. to 1400 ° C., a metal material that does not melt at that temperature is used. For example, Ag, Pd, or an alloy thereof can be preferably used.

  Next, a method for manufacturing the above-described multilayer filter will be described.

  In the same manner as the preparation step in the method for manufacturing a ferrite sintered body described above, a magnetic slurry containing an oxide mixed powder blended at a predetermined ratio is prepared. A magnetic material slurry is applied on a PET (polyethylene terephthalate) film by a doctor blade method or the like to form, for example, a magnetic material green sheet having a thickness of about 20 μm.

  Subsequently, a through hole is formed at a desired position of the magnetic green sheet, that is, a position where via conductors 9a to 9g as described above are to be formed. The through hole can be formed by a laser processing machine or the like.

  Subsequently, conductive patterns 8a to 8h are formed on the magnetic green sheet by a screen printing method or the like. In addition, via conductors 9a to 9g are formed by filling a through hole formed in the magnetic green sheet with a conductive paste. As the conductive paste used for printing the conductor patterns 8a to 8h and the via conductors 9a to 9g, a paste containing Pd or Ag—Pd alloy powder as a main component can be used.

Subsequently, a varistor slurry is prepared by mixing the varistor raw material powder constituting the varistor layers 7a to 7d after firing and an organic vehicle containing an organic solvent and an organic binder. The form of the varistor raw material powder is not particularly limited as long as it becomes a varistor having a predetermined composition after being integrally fired. Use a mixed powder containing a predetermined amount of various metal compounds such as Pr ₆ O ₁₁ , CoO, Cr ₂ O ₃ , CaCO ₃ , SiO ₂ , K ₂ CO ₃ and Al ₂ O ₃ as an additive to ZnO as a main component. Can do. Moreover, you may use the varistor powder which preliminarily calcined and ground the varistor ceramic of predetermined composition.

  Subsequently, a varistor slurry is applied on the PET film by a doctor blade method or the like to form, for example, a varistor green sheet having a thickness of about 30 μm.

  Subsequently, a hot electrode and a ground electrode are formed on the varistor green sheet using a conductive paste by a screen printing method or the like. As the conductive paste, a paste containing Pd or an Ag—Pd alloy powder as a main component can be used.

  Subsequently, a magnetic green sheet on which conductor patterns 8a to 8h and via conductors 9a to 9g having a predetermined shape were formed, a magnetic green sheet on which no electrode was formed, and a hot electrode 11 or a ground electrode 12 were formed. A varistor green sheet and a varistor green sheet on which no electrode is formed are sequentially laminated and pressed as shown in FIG. 2 and then cut into a predetermined shape to obtain a green laminated body of the multilayer filter element (element body) 2. . Thereafter, the green laminate is baked under predetermined conditions (for example, 1100 ° C. to 1200 ° C. for 2 hours in the air) to obtain the multilayer filter element 2. The obtained multilayer filter element 2 has good varistor characteristics because there is almost no diffusion of the Cu component to the varistor multilayer part 7 in the vicinity of the interface between the magnetic material multilayer part 6 and the varistor multilayer part 7.

  Subsequently, a conductive paste is applied to the end portion in the longitudinal direction of the multilayer filter element 2 and the center of both side surfaces in the longitudinal direction, and heat treatment is performed under predetermined conditions (for example, 700 ° C. to 800 ° C. for 2 hours in the atmosphere). Bake the terminal electrode. As the conductive paste, a paste containing powder containing Ag as a main component can be used. Thereafter, the terminal electrode surface is plated to obtain the multilayer filter 1 in which the input terminal electrode 3, the output terminal electrode 4, and the ground terminal electrode 5 are formed. The plating is preferably electrolytic plating, and for example, Ni / Sn, Cu / Ni / Sn, Ni / Pd / Au, Ni / Pd / Ag, Ni / Ag, or the like can be used.

  As described above, in the multilayer filter 1, since the magnetic layers 6 a to 6 i are formed of a ferrite sintered body having a specific composition, the magnetic layer stack 6 and the varistor stack 7 are integrally sintered. However, the deterioration of the varistor characteristics can be sufficiently suppressed.

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

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

(Production Examples 1 to 30)
Commercially available Fe ₂ O ₃ powder, ZnO powder, NiO powder, Mn ₂ O ₃ powder and CuO powder were weighed so as to have the composition (mol%) shown in Table 1 or 2 as the main component raw material powder. These raw material powders were wet mixed using a steel ball mill for 40 hours to obtain oxide mixed powders. The obtained oxide mixed powder was calcined at 700 ° C. for 10 hours. Bi ₂ O ₃ powder is added to the obtained calcined body at a ratio shown in Table 1 or 2 on the basis of the total amount of the calcined body, and mixed and pulverized in a steel ball mill for 36 hours. Was prepared.

Next, an aqueous polyvinyl alcohol solution was added as a binder to the prepared calcined powder and granulated to obtain granules having an average particle size of 70 μm. The granules thus obtained are press-molded to form a toroidal shape (outer diameter 13 mm, inner diameter 6 mm, height 3 mm) with a molding density of 3.10 g / cm ³ and a disk shape (outer diameter: 12 mm, thickness 2 mm). ) Were produced.

  Each of these compacts was fired in the atmosphere at a firing temperature of 900 ° C. for 2 hours to obtain a toroidal and disk-shaped ferrite sintered body. As shown in Tables 1 and 2, each of these ferrite sintered bodies contains a main component and a subcomponent (bismuth oxide) having a predetermined composition.

<Evaluation of sintered density>
The sintered density was determined from the mass of each toroidal ferrite sintered body and the volume of the sintered body determined from the measured values of the outer diameter, inner diameter, and thickness. The results were as shown in Tables 1 and 2.

<Evaluation of specific resistance>
The resistance R of each disk-shaped ferrite sintered body was measured using a high resistance meter (trade name: R8340, manufactured by Advantest) with the measurement voltage set to 10V. Specific resistance ρ (ρ = R × circular partial area of sintered body / thickness of sintered body) was calculated from the measured value of resistance R. The results were as shown in Tables 1 and 2.

<Evaluation of Initial Permeability (μi) and Magnetic Resonance Frequency (fr)>
After winding the wire around each toroidal ferrite sintered body 20 times, the initial permeability (μi) at 1 MHz was measured using an LCR meter (trade name: HP4192, manufactured by Hewlett-Packard Company). Further, the magnetic resonance frequency (fr) of the ferrite sintered body was evaluated by the same method using the same apparatus.

<ESD tolerance evaluation of varistor>
Samples for evaluation of ESD tolerance were prepared as follows. First, commercially available Fe ₂ O ₃ powder, ZnO powder, NiO powder, Mn ₂ O ₃ powder and CuO powder were weighed as raw material powders so as to have the main component composition (mol%) shown in Table 1 or 2. . These raw material powders and an organic vehicle were mixed to prepare a magnetic slurry. Further, Bi ₂ O ₃ powder was added to the slurry at a ratio shown in Table 1 or 2 with respect to the total amount of the raw material powder.

  This magnetic material slurry was applied onto a PET film by the doctor blade method to prepare a magnetic green sheet having a thickness of 20 μm. Thereafter, a through hole is formed at a predetermined position on the magnetic green sheet by a laser processing machine, and a conductive pattern having a predetermined shape and a via conductor are formed in the through hole by screen printing using a conductive paste mainly composed of Pd. Then, a green sheet for forming an inductor layer was produced.

Subsequently, a varistor raw material powder in which a predetermined amount of ZnO, Pr ₆ O ₁₁ , CoO, Cr ₂ O ₃ , CaCO ₃ , SiO ₂ , K ₂ CO _3, and Al ₂ O ₃ is mixed with an organic vehicle is mixed. A slurry was prepared.

  This varistor slurry was applied onto a PET film by a doctor blade method to produce a varistor green sheet having a thickness of 30 μm. Thereafter, an electrode having a predetermined pattern was formed on the varistor green sheet by screen printing using a conductive paste containing Pd as a main component to form a varistor layer forming green sheet.

  Subsequently, a green sheet for forming an inductor layer, a green sheet for forming a varistor layer, a magnetic green sheet on which no conductor pattern is printed, and a varistor sheet on which no conductor pattern is printed are prepared and laminated in the order shown in FIG. Thus, a green laminate for a multilayer filter was produced. This green laminate for a multilayer filter is cut into a rectangular parallelepiped having a length of 2.0 mm, a width of 1.2 mm, and a thickness of 1.0 mm after firing, and then fired in the atmosphere at 900 ° C. for 2 hours to obtain a multilayer type A filter element was produced. Thereafter, a conductive paste containing silver as a main component is applied to the end of the multilayer filter element body, and the terminal electrode is baked by baking at 700 ° C. to 800 ° C. for 1 hour in the air. Sn (Ni, Sn in this order) was electroplated to produce a sample for ESD tolerance test (multilayer filter).

  Using the obtained sample, an ESD tolerance test was performed as follows. In the ESD tolerance test, measurement is performed by an electrostatic discharge immunity test (level 4, contact discharge, test voltage: 8 kV, number of discharges: 10 times) defined in IEC (International Electrotechnical Commission) standard IEC61000-4-2. When the withstand voltage was 8 kV or more, it was determined that the ESD resistance was sufficient and determined as “A”, and when the ESD resistance was less than 8 kV, it was determined as “B”. The reason why the criterion is 8 kV or more is that if it is 8 kV or more, the level 4 of IEC61000-4-2 is satisfied.

  In addition, before and after the above-described electrostatic discharge immunity test, the varistor voltage was measured, and the change width (ΔV1 mA (%), (value after test−value before test) / value before test × 100) Calculated). The varistor voltage is measured using a source-measure unit (manufactured by KEITHLEY, model number: 237), and when the voltage applied to the external terminal of the sample is gradually increased, a current of 1 mA flows through the sample. The voltage value of The results of the ESD tolerance test were as shown in Tables 1 and 2.

(Production Examples 31-37)
Ferrite sintered bodies and multilayer filters were produced in the same manner as in Production Examples 1 to 30 except that bismuth-based glass (trade name: ASF1100B, manufactured by Asahi Glass Co., Ltd.) was used instead of Bi ₂ O ₃ powder. . The bismuth-based glass was added so that the ratio of the bismuth-based glass to the total amount of the calcined body (total amount of raw material powder) was the ratio shown in Table 3 in terms of Bi ₂ O ₃ . And each evaluation was performed like the said manufacture examples 1-30. The results were as shown in Table 3.

  From the results of Tables 1 to 3, the ferrite of the present invention can be sintered at a low temperature, so that the sintered density can be sufficiently increased, and the specific resistance, initial permeability, and magnetic resonance frequency are all at a high level. Could be the value of It was also confirmed that when combined with a varistor, the ESD resistance of the varistor can be maintained well.

It is an external appearance perspective view which shows an example of the laminated filter using the ferrite of this invention. FIG. 2 is an exploded perspective view showing an element body 2 portion of the multilayer filter 1 shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer filter, 2 ... Element body (multilayer filter element), 3 ... Input terminal electrode, 4 ... Output terminal electrode, 5 ... Ground terminal electrode, 6a-6i ... Magnetic material layer, 7a-7d ... Varistor layer, DESCRIPTION OF SYMBOLS 10 ... Inductor part, 11 ... Hot electrode (electrode), 12 ... Ground electrode (electrode), 20 ... Varistor part.

Claims (4)

A ferrite containing iron oxide, nickel oxide, zinc oxide, and manganese oxide as main components,
The main component, 45～49.5Mol% the iron oxide calculated as _Fe 2 _{O 3,} 20～40Mol% the nickel oxide in terms of NiO, 14～30Mol% the zinc oxide in terms of ZnO, and the manganese oxide 0.1 to ₂ mol% in terms of Mn ₂ O ₃ ,
The main component optionally contains copper oxide, the content of the copper oxide in the main component is 2 mol% or less in terms of CuO,
Ferrite containing 3 to 10% by mass of bismuth oxide in terms of Bi ₂ O ₃ with respect to the entire main component. The ferrite according to claim 1, which has a sintered density of 5.0 g / cm ³ or more. Iron oxide is 45 to 49.5 mol% in terms of Fe ₂ O ₃ , nickel oxide is 20 to 40 mol% in terms of NiO, zinc oxide is 14 to 30 mol% in terms of ZnO, and manganese oxide is 0.00 in terms of Mn ₂ O ₃ . A calcining step of obtaining a calcined body by calcining a mixed raw material containing 1 to 2 mol% and having a copper oxide content of 2 mol% or less in terms of CuO;
And a firing step of adding 3 to 10% by mass of bismuth oxide to the calcined body and firing the calcined body.   The manufacturing method according to claim 3, wherein in the firing step, bismuth-based glass containing the bismuth oxide is added to the calcined body.

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