JP6553279B2 - Multilayer inductor - Google Patents

Description

  The present invention relates to a laminated inductor.

  Conventionally, as one of the manufacturing methods of a laminated inductor, a method is known in which an internal conductor pattern is printed on a ceramic green sheet containing ferrite or the like, and these sheets are laminated and fired. According to a typical production method of the method, through holes are formed at predetermined positions in a ceramic green sheet obtained using ferrite powder. Next, a coil conductor pattern (internal conductor pattern) in which a spiral coil is formed by stacking and connecting through holes on one main surface of a sheet on which through holes are formed is printed with a conductive paste.

  Next, the sheets on which the through holes and the coil conductor patterns are formed are stacked in a predetermined configuration, and ceramic green sheets (dummy sheets) on which the through holes and the coil conductor patterns are not formed are stacked on the top and the bottom. Next, the obtained laminate is pressure-bonded and then fired, and an external electrode is formed on the end face from which the coil end is derived, to obtain a laminated inductor. Here, a high L value can be obtained by using a material with high magnetic permeability for the dummy sheet.

  In recent years, a multilayer inductor has been required to have a large current (meaning a high rated current), and in order to satisfy the requirement, it is considered to switch the material of the magnetic body from a conventional ferrite to a soft magnetic alloy It is done. In Patent Document 1, for the purpose of providing a laminated powder magnetic core having a low cost, a simple structure, and high characteristics, an alloy powder mainly composed of Fe, Si, Al and borosilicate glass or silica are used. It is disclosed to laminate a magnetic layer composed of a composite of a heat-resistant adhesive and a conductive layer made of conductive powder. In Patent Document 2, a metal magnetic layer formed using a metal magnetic paste containing metal magnetic particles and a thermosetting resin and a conductor pattern formed using a conductor paste are laminated, and these It is disclosed to form a coil within the stack.

Unexamined-Japanese-Patent No. 9-148118 gazette JP 2007-27353 A

  As described above, in a multilayer inductor using alloy powder as a magnetic substance, the resistance value of the material powder may be low, and plating elongation may occur. In particular, plating elongation tends to occur on the outermost surface in the stacking direction. The term “plating elongation” refers to the fact that the plating is attached to extend to the part of the magnetic body other than the external electrode. If the length of the plating elongation (elongation amount) is short relative to the size of the multilayer inductor as a product, it will not be a specific problem. However, the problem of plating elongation can be a limiting factor for product miniaturization in multilayer inductors.

  In consideration of these, the present invention uses a soft magnetic alloy as a magnetic material, and an object of the present invention is to provide a laminated inductor in which plating elongation hardly occurs.

As a result of intensive studies by the present inventors, the following present invention has been completed.
The multilayer inductor of the present invention includes a multilayer body made of a plurality of magnetic material layers, and a coil conductor formed in a spiral shape inside the multilayer body. The magnetic material layer includes a plurality of metal particles made of a soft magnetic alloy, and an oxide film made of an oxide of the soft magnetic alloy formed on the surface of the metal particles. The magnetic material layer has a coupling portion through an oxide film formed on the surface of the adjacent metal particle. A coating of insulating oxide is applied to at least a part of the surface of the laminate.
The surface resistivity of the coating is preferably at least 1 MΩ / sq.
The coating is preferably applied to the upper and lower surfaces in the laminating direction of the laminate.
In the laminate, when there is an air gap between the metal particles, it is preferable that part of the coating penetrates at least a part of the air gap from the upper and lower surfaces.
The insulating oxide is preferably glass, and more preferably has a softening point of 500 to 800 ° C. The glass preferably contains B, Si, Ba, Li, Na, K, Mg, Ca, Sr, Al, Cu, Zn, Zr or Bi.

  According to the present invention, even if the degree of oxidation in the magnetic material layer is reduced to increase the permeability, the surface resistance of the laminate can be increased, and the failure mode of the plating elongation can be reduced. As a result, it has been found that there is a possibility of achieving both high permeability and product miniaturization at a higher level. In addition, when the coating is made of glass, the glass sheet may be added as the outermost layer at the time of lamination, and thus the production is easy.

It is a schematic cross section of the multilayer inductor of this invention. It is a schematic cross section of a magnetic material layer. It is a typical exploded view of a layered product.

  Hereinafter, the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited to the illustrated embodiment, and because the characteristic parts of the invention may be emphasized and expressed in the drawings, the scale accuracy may not necessarily be guaranteed in each part of the drawings. Not.

  FIG. 1 is a schematic cross-sectional view of a laminated inductor. According to the present invention, the multilayer inductor 1 has a multilayer body 2 and a coil conductor 20. The coil conductor 20 has a structure embedded in the interior of the laminate 2. Typically, the coil conductor 20 is a coil formed in a spiral shape, and in this case, a conductor pattern such as a substantially annular or semi-annular shape is printed on a green sheet by a screen printing method etc. Can be formed by laminating the sheets. The green sheet on which the conductor pattern is printed contains a magnetic material which will be described later, and through holes are provided at predetermined positions. Examples of the coil conductor 20 include a spiral coil, a meander (meandering) conductor, a linear conductor, and the like in addition to the illustrated spiral coil.

  The laminate 2 is configured by stacking magnetic material layers 10. In FIG. 1, magnetic material layers 10 are stacked in the vertical direction on the paper surface, and the depiction of the layer structure is omitted in the drawing. FIG. 2 is a schematic cross-sectional view of a part of the magnetic material layer. In the magnetic material layer 10, a large number of metal particles 11 made of a soft magnetic alloy are accumulated. As soft magnetic alloys, Fe-M-Si alloys (where M is a metal that is more easily oxidized than iron) and Fe-M 'alloys (where M' is a metal that is more susceptible to oxidation than iron). And Fe-Si alloys. Examples of M and M 'include Ni, Co, Cr, Al and the like. As the soft magnetic alloy, an Fe—Si—B—Cr alloy can also be adopted. More specific examples of soft magnetic alloys include, for example, Fe—Si alloys, Fe—Ni alloys, Fe—Co alloys, Fe—Cr—Si alloys, Fe—Si—Al alloys, Fe— A Si-B-Cr type alloy etc. are mentioned.

  When the soft magnetic alloy is an Fe—Cr—Si alloy, the chromium content is preferably 2 to 8 wt%. The presence of chromium is preferable in that it forms passive state during heat treatment to suppress excessive oxidation and at the same time exerts strength and insulation resistance, but from the viewpoint of improvement of the magnetic properties, it is preferable that chromium be small. The above preferred range is proposed in consideration of the above.

  The Si content in the Fe—Cr—Si based soft magnetic alloy is preferably 1.5 to 7 wt%. A high Si content is preferable in terms of high resistance and high magnetic permeability, and a low Si content provides good moldability, and the above preferable range is proposed in consideration of these.

  In the Fe—Cr—Si alloy, the balance other than Si and Cr is preferably iron except for inevitable impurities. Metals which may be contained other than Fe, Si and Cr include aluminum, magnesium, calcium, titanium, manganese, cobalt, nickel, copper and the like, and nonmetals include phosphorus, sulfur, carbon and the like .

An oxide film 12 is formed over substantially the entire periphery of each metal particle 11, and the oxide film 12 ensures insulation of the magnetic material layer 10. Preferably, the oxide film 12 is formed by oxidizing a soft magnetic alloy constituting the metal particles 11. Adjacent metal particles 11 generally constitute a magnetic material layer 10 by bonding oxide films 12 of the respective metal particles 11 to each other. In addition to the bonding portion 13 via such an oxide film, a bonding portion 14 between metal parts of adjacent metal particles 11 may partially exist. Further, in the vicinity of the coil conductor 20, the metal particles 11 and the coil conductor 20 are in close contact with each other mainly via the oxide film 12 (not shown). When the metal particles 11 are made of an Fe-M-Si alloy (where M is a metal that is more easily oxidized than iron), the oxide film 12 is made of Fe ₃ O _{4 which} is a magnetic material and nonmagnetic material. It has been confirmed that it contains at least some Fe ₂ O ₃ and MO _x (x is a value determined in accordance with the oxidation number of the metal M).

  The presence of the bond 13 between the above-described oxide films 12 is, for example, by visually recognizing that the oxide films 12 of the adjacent metal particles 11 are in the same phase in an SEM observation image or the like enlarged about 3000 times. It can be clearly judged. The presence of the coupling between the oxide films 12 can improve the mechanical strength and insulation of the multilayer inductor 1. It is preferable that the oxide films 12 of the adjacent metal particles 11 be bonded to each other in as many regions as possible of the multilayer inductor 1, but if they are partially bonded, the corresponding mechanical strength and insulation properties will be improved. Such a form is also an embodiment of the present invention.

  Similarly, for the bonding portion 14 between the metal parts of the metal particles 11 described above, adjacent metal particles 11 have bonding points while maintaining the same phase, for example, in an SEM observation image magnified about 3000 times, etc. The presence of the bond can be clearly determined by visually recognizing the symbol. The presence of the bond between the metal particles 11 further improves the permeability.

  It should be noted that there may be a form in which adjacent soft magnetic alloy particles are merely merely in physical contact or proximity without any bonding of the oxide films 12 or bonding of the metal particles 11 being present. .

  In the multilayer inductor 1, there are a multilayer body 2 composed of a magnetic material layer 10 and a coil conductor 20 having a form such as a spiral coil provided so as to be embedded in the magnetic material layer 10. The conductor which comprises the coil conductor 20 can use suitably the metal normally used in a laminated inductor, and can illustrate silver, a silver alloy, etc., without limitation. The both ends of the coil conductor 20 are typically drawn out to opposing end faces of the outer surface of the laminated inductor 1 via respective lead conductors (not shown), and connected to external terminals (not shown).

  The average particle diameter of the soft magnetic alloy particles used in the magnetic material layer 10 is a d50 value obtained by acquiring an SEM image and subjecting it to image analysis. Specifically, an SEM image (about 3000 times) of the cross section of the magnetic material layer 10 is acquired, 300 or more particles of average size in the measurement portion are selected, and the area in the SEM image is measured. The mean particle size is calculated assuming that the particles are spheres. Examples of methods for selecting particles include the following methods. If less than 300 particles are present in the SEM image, all particles in the SEM image are sampled, and this is carried out at a plurality of locations to select 300 or more. When 300 or more particles are present in the SEM image, a straight line is drawn at a predetermined interval in the SEM image, and all particles on the straight line are sampled to select 300 or more. In the laminated inductor using soft magnetic alloy particles, the particle diameter of the raw material particles and the particle diameter of the metal particles 11 made of the soft magnetic alloy constituting the magnetic material layer 10 after heat treatment are substantially the same. Are known. For this reason, it is also possible to estimate the average particle size of the metal particles 11 contained in the laminated inductor 1 by measuring the average particle size of the soft magnetic alloy particles used as the raw material.

  According to the present invention, the coating is applied to at least a part of the surface of the laminate 2. This coating comprises an insulating oxide. In the form of FIG. 1, coatings 30 and 40 are provided on the upper surface and the lower surface in the stacking direction of the stacked body 2. When the coatings 30 and 40 are applied, the surface resistance value is increased and plating elongation is suppressed.

The insulating oxide typically includes glass. Examples of the glass include silica glass and borosilicate glass. These glasses may contain a metal element. Examples of the metal element that may be contained in the glass include Ba, Li, Na, K, Mg, Ca, Sr, Al, Cu, Zn, Zr, Bi, etc., and one or more of these may be used. It may be included. More specific examples of suitable _{glass, SiO 2 -B 2 O 3 -Na} 2 O, SiO 2 -B 2 O 3 -ZrO 2 -Na 2 O, etc. SiO ₂ -B ₂ O ₃ -MgO can be mentioned Be The softening point of the glass is preferably 500 to 800 ° C., and the temperature range is about the same as the heat treatment temperature at the time of producing the laminated inductor.

  The coating is preferably applied to the upper surface and the lower surface of the stacked body 2 in the stacking direction. This is because, according to the knowledge of the present inventors, plating elongation tends to occur particularly on the upper surface and the lower surface. Here, in the case where there is a void 15 between the metal particles 11 on the upper and lower surfaces of the laminate 2 in the stacking direction, the coatings 30 and 40 preferably enter the void 15. Due to the presence of the coating that has entered the gap 15, the coatings 30 and 40 provided on the upper and lower surfaces in the stacking direction of the stacked body 2 are difficult to peel off. This is because the retention of the coatings 30 and 40 is physically achieved in addition to the presence of a chemical adhesive effect.

Ni-Zn ferrite etc. are illustrated as insulating oxides other than glass. Further, as a mixture of the _glass, Al ₂ O 3, SiC, may be contained AlN or the like.
The surface resistivity is preferably 1 MΩ / sq or more, more preferably 5 to 50 MΩ / sq, at these locations where the coating made of an insulating oxide including glass is applied. By exhibiting the surface resistivity within the above range, it is possible to more efficiently suppress plating elongation defects.

  Hereinafter, a typical manufacturing method of the multilayer inductor 1 according to the present invention will be described. In the manufacture of the multilayer inductor 1, first, a magnetic paste (slurry) prepared in advance is coated on the surface of a base film made of resin or the like using a coating machine such as a doctor blade or a die coater. The resultant is dried by a drier such as a hot air drier to obtain a green sheet. The magnetic paste includes metal particles made of the above-described soft magnetic alloy, typically a polymer resin as a binder, and a solvent.

  For an alloy constituting each soft magnetic alloy particle in the multilayer inductor 1, for example, the cross section of the multilayer inductor 1 is photographed using a scanning electron microscope (SEM), and then energy dispersive X-ray analysis (EDS) Chemical composition can be calculated by the ZAF method according to

  The particle diameter of the soft magnetic alloy metal particles used as a raw material for the magnetic material layer 10 is preferably 2 to 20 μm, more preferably 3 to 10 μm on a volume basis. The d50 of the soft magnetic alloy particles is measured using a particle diameter / particle size distribution measuring apparatus (for example, Microtrac manufactured by Nikkiso Co., Ltd.) using a laser diffraction scattering method. In the multilayer inductor 1 using soft magnetic alloy particles, it is known that the particle size of the soft magnetic alloy particles as the raw material particles is approximately equal to the particle size of the metal particles constituting the magnetic body portion 12 of the multilayer inductor 1.

  The above-mentioned magnetic paste preferably contains a polymer resin as a binder. The type of the polymer resin is not particularly limited, and examples thereof include polyvinyl acetal resins such as polyvinyl butyral (PVB). The type of solvent for the magnetic paste is not particularly limited, and for example, glycol ethers such as butyl carbitol can be used. The compounding ratio of the metal particles, the polymer resin, the solvent and the like in the magnetic paste can be appropriately adjusted, and it is also possible to set the viscosity and the like of the magnetic paste.

  Conventional techniques can be used as appropriate for a specific method for obtaining a green sheet by applying and drying the magnetic paste.

  Next, the green sheet is perforated using a punching machine such as a punching machine or a laser processing machine to form through holes (through holes) in a predetermined arrangement. The arrangement of the through holes is set such that when the respective sheets are stacked, the coil conductor 20 is formed by the through holes filled with the conductor and the conductor pattern. As for the arrangement of the through holes and the shape of the conductor pattern for forming the internal conductors, the prior art can be used as appropriate, and specific examples will be described in the following embodiments with reference to the drawings.

  A conductor paste is preferably used for filling the through holes and for printing the conductor pattern. The conductive paste contains conductive particles, typically a polymer resin as a binder, and a solvent.

  Silver particles or the like can be used as the conductor particles. As for the particle diameter of the conductor particles, d50 is preferably 1 to 10 μm on a volume basis. The d50 of the conductor particles is measured using a particle size / size distribution measuring apparatus (for example, Microtrac manufactured by Nikkiso Co., Ltd.) using a laser diffraction scattering method.

  The conductor paste preferably contains a polymer resin as a binder. The type of the polymer resin is not particularly limited, and examples thereof include polyvinyl acetal resins such as polyvinyl butyral (PVB). The kind of the solvent of the conductor paste is not particularly limited, and for example, glycol ether such as butyl carbitol can be used. The compounding ratio of the conductor particles, the polymer resin, the solvent and the like in the conductor paste can be appropriately adjusted, and it is also possible to set the viscosity and the like of the conductor paste.

  Then, using a printing machine such as a screen printing machine or a gravure printing machine, the conductor paste is printed on the surface of the green sheet, and this is dried by a dryer such as a hot air dryer to obtain a conductor pattern corresponding to the internal conductor. Form. During printing, a part of the conductor paste is also filled in the above-described through hole. As a result, the conductor paste filled in the through hole and the printed conductor pattern constitute the shape of the internal conductor.

  Preferably, separately from the above, a slurry (paste) containing insulating oxide particles, preferably glass particles is prepared, and a sheet is obtained from the slurry (paste). The thickness of this sheet is preferably 10 to 50 μm.

  The green sheets after printing are stacked in a predetermined order using an adsorption conveyance machine and a press machine, and thermocompression bonded to produce a laminate. At this time, preferably, sheets obtained from a slurry (paste) containing the above-described insulating oxide particles are stacked as the top layer and the bottom layer of the laminate. Subsequently, using a cutting machine such as a dicing machine or a laser processing machine, the laminated body is cut into a component body size, and a pre-heat treatment chip including a magnetic body portion and an internal conductor before heat treatment is manufactured.

  Using a heating device such as a firing furnace, the chips before heat treatment are heat-treated in an oxidizing atmosphere such as air. This heat treatment usually includes a binder removal process and an oxide film forming process, and the binder removal process is a temperature at which the polymer resin used as a binder disappears, for example, about 300 ° C. for about 1 hour. The oxide film forming process includes, for example, conditions of about 750 ° C. and about 2 hours.

  In chips before heat treatment, a large number of fine gaps exist between individual soft magnetic alloy particles, and the fine gaps are usually filled with a mixture of a solvent and a binder. These disappear in the binder removal process, and after the binder removal process is completed, the fine gap changes to pores. Further, in the pre-heat treatment chip, there are many fine gaps between the conductor particles. This fine gap is filled with a mixture of solvent and binder. These also disappear in the binder removal process.

  In the oxide film forming process following the binder removal process, metal particles are densely packed to form the magnetic material layer 10, and typically, the surface of each of the metal particles 11 and the vicinity thereof are oxidized to form the particles 11. An oxide film 12 is formed on the surface. At this time, the conductor particles are sintered to form the coil conductor 20. Thereby, a laminate 2 is obtained. Preferably, the oxide film 12 is formed by oxidizing the metal particles 11 by the heat treatment. Further, preferably, the bond 13 via the oxide film 12 is formed by oxidation and bonding of the metal portion of the metal particle 11 in the heat treatment.

  Usually, external terminals are formed after heat treatment. The conductor paste prepared in advance is applied to both ends in the lengthwise direction of the laminated inductor 1 using an applicator such as a dip applicator or a roller applicator, and this is applied, for example, to about 600 using a heating device such as a firing furnace. An external terminal is formed by performing a baking process at a temperature of about 10 min. As the conductor paste for the external terminals, the above-described paste for printing a conductor pattern or a paste similar thereto can be used as appropriate.

  In the above example, the insulating oxide coating is heat-treated after the sheets are laminated. Even if it is other than this method, for example, it is also possible to apply a coating by forming insulating oxides into a paste, printing on upper and lower surfaces, and then heat treating at a temperature above the softening point of glass.

  Hereinafter, the present invention will be more specifically described by way of examples. However, the present invention is not limited to the embodiments described in these examples.

[Specific structure of laminated inductor]
The multilayer inductor manufactured in this example has a length of about 3.2 mm, a width of about 1.6 mm, a height of about 1.0 mm, and the whole has a rectangular parallelepiped shape.

FIG. 3 is a schematic exploded view of the multilayer body 2 of the multilayer inductor. The magnetic material layer 10 has a structure in which the magnetic layers ML1 to ML6 are integrated. The length of the multilayer inductor 1 is about 3.2 mm, the width is about 1.6 mm, and the height is about 1.0 mm. Each of the magnetic layers ML1 to ML6 has a length of about 3.2 mm, a width of about 1.6 mm, and a thickness of about 30 μm. Each magnetic layer ML1~ML6 is soft magnetic alloy particles Fe-Cr-Si alloy (Cr: 4.5wt%, Si: 3.5wt%, balance Fe) or Ni-Zn ferrite _(Fe 2 _{O 3} It is formed mainly of particles having an average particle diameter (d50) of 10 μm and consisting of 49 mol%, NiO: 15 mol%, ZnO: 25 mol%, CuO: 11 mol) and does not contain a glass component.

  The coil conductor 20 has a coil structure in which a total of five coil segments CS1 to CS5 and a total of four relay segments IS1 to IS4 connecting the coil segments CS1 to CS5 are spirally integrated, The number of turns is about 3.5. The coil conductor 20 is mainly obtained by heat-treating silver particles, and the volume-based d50 of the silver particles used as a raw material is 5 μm.

  Four coil segments CS1 to CS4 have a U-shape, and one coil segment CS5 has a band shape, and each coil segment CS1 to CS5 has a thickness of about 20 μm and a width of about 0.2 mm It is. The uppermost coil segment CS1 continuously has an L-shaped lead-out portion LS1 used for connection with the external terminal, and the lowermost coil segment CS5 is L-shaped used for connection with the external terminal In the form of a continuous line. Each of the relay segments IS1 to IS4 has a columnar shape penetrating the magnetic layers ML1 to ML4, and the diameter of each is about 15 μm.

  Each external terminal (not shown) extends to each end face in the longitudinal direction of the multilayer inductor 1 and to four side faces near the end face, and the thickness thereof is about 20 μm. One external terminal is connected to the end of the lead portion LS1 of the uppermost coil segment CS1, and the other external terminal is connected to the end of the lead portion LS2 of the lowermost coil segment CS5. These external terminals were obtained mainly by heat-treating silver particles having a volume-based d50 of 5 μm.

  A glass layer having a thickness of about 10 μm was provided on the upper and lower surfaces of the laminate 2 in the stacking direction under the conditions shown in Table 1.

[Manufacture of multilayer inductors]
A magnetic paste comprising 85 wt% of metal particles (or ferrite particles) shown in Table 1, 13 wt% of butyl carbitol (solvent), and 2 wt% of polyvinyl butyral (binder) was prepared. The magnetic paste was applied to the surface of a plastic base film using a doctor blade, and dried with a hot air dryer at about 80 ° C. for about 5 minutes. Thus, a green sheet was obtained on the base film. Thereafter, the green sheets were cut to obtain first to sixth sheets having sizes corresponding to the magnetic layers ML1 to ML6 (see FIG. 3) and adapted to the multi-cavity.

70 wt% glass (softening point: 600 ° C.) having a composition of SiO ₂ —B ₂ O ₃ —Na ₂ O and a particle size of d50 of 5 μm, 15 wt% of butyl carbitol (solvent), polyvinyl butyral (binder) ) A glass paste consisting of 3 wt% was prepared. Using a doctor blade, this glass paste was applied onto the surface of a plastic base film, and this was dried with a hot air dryer at about 80 ° C. for about 5 minutes. Thus, a glass sheet (not shown) was obtained on the base film. The thing of Table 1 was prepared as thickness of a glass sheet.

  Subsequently, the first sheet corresponding to the magnetic layer ML1 was perforated using a perforation machine to form through holes corresponding to the relay segment IS1 in a predetermined arrangement. Similarly, in the second to fourth sheets corresponding to the magnetic layers ML2 to ML4, through holes corresponding to the relay segments IS2 to IS4 are formed in a predetermined arrangement.

  Subsequently, using a printing machine, a conductor paste consisting of 85 wt% of the Ag particles, 13 wt% of butyl carbitol (solvent) and 2 wt% of polyvinyl butyral (binder) is printed on the surface of the first sheet. Then, this was dried with a hot air dryer under conditions of about 80 ° C. and about 5 minutes to produce a first print layer corresponding to the coil segment CS1 in a predetermined arrangement. Similarly, the second to fifth print layers corresponding to the coil segments CS2 to CS5 were formed on the surfaces of the second to fifth sheets in a predetermined arrangement.

  Since the through-hole formed in each of the first to fourth sheets exists at a position overlapping the end of each of the first to fourth printed layers, a part of the conductor paste is formed when printing the first to fourth printed layers. Filling each through-hole, the first to fourth filling portions corresponding to the relay segments IS1 to IS4 are formed.

  Subsequently, the first to fourth sheets provided with the printing layer and the filling unit, the fifth sheet provided only with the printing layer, and the printing layer and the filling unit are provided using an adsorption conveyance machine and a press. The not-sixth sheets were stacked in the order shown in FIG. 3, and the above-described glass sheets were stacked on the top and bottom surfaces and thermocompression bonded. Thereafter, the pressure-bonded product was cut into a component body size with a cutting machine to obtain a pre-heat treatment chip.

  Subsequently, a number of pre-heat treatment chips were heat treated in a lump in an air atmosphere using a firing furnace. First, heating was performed at about 300 ° C. for about 1 hour as a binder removal process, and then heating was performed at about 750 ° C. for about 2 hours as an oxide film 12 forming process. By this heat treatment, soft magnetic alloy particles (or ferrite particles) are densely formed to form the magnetic material layer 10, and silver particles are sintered to form the coil conductor 20, thereby obtaining a component main body. At this time, a glass layer was generated from the glass sheet by heat.

  Subsequently, external terminals were formed. A conductor paste containing 85 wt% of the silver particles, 13 wt% of butyl carbitol (solvent) and 2 wt% of polyvinyl butyral (binder) is applied to both end portions in the longitudinal direction of the component body with a coating machine, and fired. The baking was performed in a furnace at about 600 ° C. for about 10 minutes. As a result, the solvent and the binder disappeared, the silver particles were sintered, the external terminals were formed, and the multilayer inductor 1 was obtained.

  With respect to the obtained multilayer inductor, the surface resistivity was measured by the four-terminal method when the glass layer was present, and the glass layer portion was measured by the four-terminal method when the glass layer was not present.

  About the cross section of the magnetic material layer 10 of the obtained laminated inductor, the SEM observation expanded about 3000 times is performed, and the presence or absence of the coupling part 13 via the oxide film 12 which the metal particle 11 which consists of adjacent soft magnetic alloys has The presence or absence of the bonding portion 14 between the metal portions where the oxide film 12 of the metal particles 11 does not exist was examined. In the case where the coupling portion 13 via the oxide film 12 is present, most of the oxide film 12 included in the adjacent metal particles 11 exhibits the same phase in the SEM observation image. When there was a bonding portion 14 between metal parts, it was visually recognized in the SEM observation image that adjacent metal particles 11 have bonding points while maintaining the same phase. As a result, in Production Examples 1 to 3, both the coupling portion 13 and the coupling portion 14 between the metal portions via the oxide film 12 were present. In Production Example 4, since the material itself is not a metal, there is no bonding between metals, and as a result of SEM observation, ferrite crystal grains and their grain boundaries were observed.

  Similar SEM observations were performed at the interface of the glass layer and the laminate. As a result, in Production Examples 1, 2, and 4, a part of the glass layer penetrates into the gaps of particles (metal particles in Production Examples 1 and 2 and ferrite particles in Production Example 4). confirmed.

The manufacturing conditions of the laminated inductor are as shown in Table 1.

[Joint evaluation]
When a joint made of glass (indicated as “glass layer” in Table 1) and the interface at the interface with the laminate 2 was visually examined, in Production Examples 1 and 2, there was no “crack”, and the production example In 4, it was broken.

[Inductance measurement]
The inductance of the obtained laminated inductor was measured at a value of 1 MHz with an Agilent Technologies impedance analyzer 4294A.

[Evaluation of plating elongation]
Each of the upper and lower surfaces of the obtained multilayer inductor was observed with a length measuring microscope. Starting from the positions of the ends of the both side external electrodes on the magnetic material surface, the distance to the position where the plating was most extended was measured. Since the above measurement is performed on the left and right sides of the upper and lower surfaces, the number of measurements is four at each laminated inductor. If the length of the plating elongation was 3 μm or more even in one of these four measurements, it was judged to be "plating elongation failure". This measurement was performed on 50 laminated inductors to calculate a failure rate.

The above measurement results are summarized in Table 2

  As described above, by providing the coating (glass layer) of the insulating oxide, it was possible to significantly reduce the failure mode of the plating elongation.

Reference Signs List 1 laminated inductor, 10 magnetic material layers, 11 metal particles, 12 oxide films, 13 bonding portions through oxide films, 14 bonding portions of metal portions, 20 coil conductors, 30 and 40 coatings.

Claims (8)

A laminate comprising a plurality of magnetic material layers,
And a coil conductor formed inside the laminate.
The magnetic material layer includes a plurality of metal particles made of a soft magnetic alloy and an oxide film made of an oxide of the soft magnetic alloy formed on the surface of the metal particles, and is formed on the surface of the adjacent metal particles It has a joint part through an oxide film and a non-joint part surrounded by the metal particles that become voids at the same time,
A coating having a surface resistivity of 1 MΩ / sq or more is applied to the upper surface and the lower surface in the laminating direction of the laminate, and the coating is made of ferrite,
Multilayer inductor. The multilayer inductor according to claim 1, wherein the metal particles are made of an Fe—M—Si based alloy (where M is a metal that is more easily oxidized than iron), and the oxide film includes a magnetic substance. The multilayer inductor according to claim 2, wherein the magnetic body contains a ferrite component. The multilayer inductor according to claim 3, wherein the ferrite component contains iron ferrite (Fe ₃ O ₄ ). The multilayer inductor according to claim 1, wherein the metal particles are made of a Fe-M-Si alloy (where M is a metal that is more easily oxidized than iron), and the oxide film contains a nonmagnetic material. The multilayer inductor according to claim 5, wherein the nonmagnetic material contains ferric oxide (Fe ₂ O ₃ ). The multilayer inductor according to any one of claims 1 to 6, wherein the coating is applied to an upper surface and a lower surface in the stacking direction of the multilayer body. The laminated inductor according to any one of claims 1 to 7, wherein a part of the coating penetrates at least a part of the air gap from the upper and lower surfaces.

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