JP2013153119A - Multilayer inductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable multilayer inductor having a high permeability in which conduction failure is reduced by using a soft magnetic alloy as a magnetic material.SOLUTION: The multilayer inductor includes a plurality of magnetic layers 10 formed of Fe-Si-M-based soft magnetic alloy particles, and a plurality of coils and relay segments 21 and 22 composed of an Ag-containing material. An oxide coating formed by oxidation of the soft magnetic alloy is present around the soft magnetic alloy particles at least partially. The coil segments 21 and the relay segments 22 configure an internal conductor 20 integrated electrically. In the magnetic layer 10 on the periphery of the internal conductor 20, there is an Ag diffusion region 11 having a protrusion 31 consisting of an Ag particle 30 and/or Ag growing from the internal conductor 20 into a soft magnetic layer 19, and there is an Ag absent region 12 in the magnetic layer 10 held between the coil segments 21. Between adjoining soft magnetic alloy particles, there is a coupling part with an oxide film interposed therebetween, and also there is the mutual coupling part of metal portions.

Description

  The present invention relates to a multilayer inductor.

  Conventionally, as one method of manufacturing a multilayer 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.

Patent Document 1 discloses a composite magnetic material in which a mixture of an alloy powder mainly composed of iron (Fe), aluminum (Al), and silicon (Si) and a binder is compression-molded and then heat-treated in an oxidizing atmosphere. A manufacturing method is disclosed.
In Patent Document 2, a plurality of strip conductors are provided in parallel to the laminated surface of the ceramic laminate, and a connection conductor composed of a plurality of via holes connecting the ends of two or more strip conductors sandwiching the ceramic laminate, A laminated coil component is disclosed in which a coil conductor is configured in a ceramic laminate.
Patent Document 3 is obtained by laminating 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. A method of manufacturing a laminated electronic component in which a coil is formed in a laminated body is disclosed.

  In recent years, there has been a demand for higher current (meaning higher rated current) in multilayer inductors, and in order to satisfy this requirement, switching the magnetic material from conventional ferrite to a soft magnetic alloy has been studied. Has been. Fe-Cr-Si alloys and Fe-Al-Si alloys proposed as soft magnetic alloys have a higher saturation magnetic flux density than the ferrite itself.

JP 2001-11563 A JP 2005-259878 A JP 2007-27353 A

  A multilayer inductor having a magnetic layer made of a soft magnetic alloy instead of ferrite can meet the demand for a large current as described above, but on the other hand, the conduction failure rate of the obtained multilayer inductor tends to be high. An object of the present invention is to provide a multilayer inductor that uses a soft magnetic alloy as a magnetic material, increases the magnetic permeability, exhibits a high L value, and can cope with the miniaturization of devices.

As a result of intensive studies by the present inventors, the invention of a multilayer inductor having the following characteristics has been completed.
The multilayer inductor of the present invention includes a plurality of magnetic layers made of Fe-Si-M soft magnetic alloy (where M is a metal element that is more easily oxidized than Fe) and a plurality of Ag-containing materials. It has a coil segment and a relay segment made of an Ag-containing material. An oxide film formed by oxidizing the soft magnetic alloy is present at least partly around the soft magnetic alloy particles. In this magnetic layer, there are a magnetic layer in which a coupling portion is formed through an oxide film formed around adjacent soft magnetic alloy particles, and a coupling portion between soft magnetic alloy particles in a metal portion where no oxide film exists. The coil segments constitute a laminated structure that is alternately laminated. The relay segment is formed so as to pass through the magnetic layer and conduct between the coil segments, and the coil segment and the relay segment constitute an electrically integrated internal conductor. Each magnetic layer has an Ag diffusion region in contact with the coil segment and an Ag non-existing region located on the opposite side of the coil segment as viewed from the Ag diffusion region. In the Ag diffusion region, there are (A) Ag particles in the magnetic layer around the inner conductor, and / or (B) a convex portion made of Ag extending from the inner conductor in the soft magnetic layer.
Preferably, the thickness of the Ag diffusion region is 1 μm or more. Preferably, the thickness of the Ag absent region is 3 μm or more.

  According to the present invention, the Ag particles are present in the magnetic layer in the vicinity of the inner conductor and / or the soft magnetic layer has a convex portion made of Ag extending from the inner conductor. Even when it is subjected to a cycle, a difference in thermal expansion hardly occurs between the inner conductor and the magnetic layer, and the adhesion between the inner conductor and the magnetic layer is improved. As a result, poor conduction is reduced. Further, in the magnetic layer, the coexistence of the bond by the oxide film and the bond between the metal parts can achieve both insulation and mechanical strength at a high level. In a preferred embodiment, the oxide film around the soft magnetic alloy particles has large irregularities, Ag migration is suppressed, and reliability is unlikely to deteriorate even when a moisture resistance load is applied.

It is a schematic cross section of a multilayer inductor. It is a typical exploded view of a multilayer inductor.

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

  FIG. 1A is a schematic cross-sectional view of a multilayer inductor. FIG.1 (b) is the elements on larger scale of Fig.1 (a). The multilayer inductor 1 that is the subject of the present invention has a structure in which most of the inner conductor 20 is buried in a magnetic part (laminate of the magnetic layer 10). Typically, the inner conductor 20 is a coil formed in a spiral shape, and other examples include a spiral coil, a meander (meandering) conductor, a linear conductor, and the like.

  The inner conductor 20 has a coil segment 21 and a relay segment 22. The coil segment 21 and the magnetic layer 10 constitute a laminated structure in which they are alternately laminated. The relay segment 22 is formed so as to penetrate the magnetic layer 10. The relay segment 22 is formed so as to conduct the plurality of coil segments 21. FIG. 2 is a schematic exploded view of a typical multilayer inductor. In the illustrated embodiment, the inner conductor 20 has a coil structure in which coil segments CS1 to CS5 and relay segments IS1 to IS4 connecting the coil segments CS1 to CS5 are spirally integrated. The coil segments CS1 to CS4 have a U shape, the coil segment CS5 has a strip shape, and each relay segment IS1 to IS4 has a column shape penetrating the magnetic layers ML1 to ML4.

  According to the present invention, the coil segment 21 and the relay segment 22 are made of an Ag-containing material. The Ag-containing material is typically Ag that is substantially free of other metals, in other words, Ag that does not actively add other metals. In another embodiment, it may be a mixture or alloy of 100 parts by weight of Ag and 50 parts by weight or less of other metals, such as, but not limited to, Au, Cu, Pt, Pd, etc. Is exemplified.

  The particle diameter of the Ag-containing material of the coil segment 21 and the relay segment 22 is not particularly limited, and is preferably 1 to 10 μm. The particle diameter is measured by acquiring SEM images of cross sections of the coil segment 21 and the relay segment 22. Here, it is known that the particle size of the Ag-containing material (powder) as the raw material is approximately equal to the particle size of the Ag-containing material constituting the coil segment 21 and the relay segment 22. Therefore, in order to obtain the coil segment 21 and the relay segment 22 made of an Ag-containing material having a desired particle diameter, raw material particles having such a particle diameter may be used.

  FIG. 1B is a schematic enlarged view of the two coil segments 21 and the magnetic layer 10 sandwiched between them. Unlike FIG. 1A, in FIG. 1B, the hatching notation indicating the magnetic layer 10 is omitted. According to the present invention, there are Ag particles 30 in the magnetic layer 10 around the inner conductor 20 and / or convex portions 31 made of Ag extending from the inner conductor 20 in the soft magnetic layer 10. . As described above, a region where the Ag particles 30 and / or the convex portions 31 made of Ag extending from the internal conductor 20 exists is referred to as an Ag diffusion region 11. In the illustrated embodiment, both the Ag particles 30 and the convex portions 31 exist in the Ag diffusion region 11. The Ag particles 30 are preferably made of Ag present discontinuously between the soft magnetic alloy particles in the magnetic layer 10 around the inner conductor 20. The convex portion 31 is preferably made of Ag that continuously exists between the inner conductor 20 and the soft magnetic alloy particles in the magnetic layer 10 around the inner conductor 20. Although the coil segment 21 is depicted as a part of the inner conductor 20 in FIG. 1B, Ag particles and / or convex portions made of Ag extending from the relay segment also exist in the vicinity of the relay segment. It is preferable to do. The Ag particles 30 and the convex portions 31 are derived from, for example, an Ag-containing material constituting the internal electrode 20. Typically, Ag “diffuses” from the Ag-containing material constituting the inner conductor 20, and the Ag particles 30 and the convex portions 31 exist.

Here, the “diffusion” is described in detail below.
The magnetic layer 10 is formed by accumulating a large number of soft magnetic alloy particles. In addition, voids are formed between the soft magnetic alloy particles. There are also air gaps in the magnetic layer 10 around the inner conductor 20. A part of Ag constituting the inner conductor 20 enters a gap in the peripheral magnetic layer 10. Such a state is referred to herein as “diffusion”.

  Due to the presence of the Ag particles 30 and / or the convex portions 31, a difference in thermal expansion hardly occurs between the inner conductor 20 and the magnetic layer 10 during the heat cycle, and the inner conductor 20 and the magnetic layer 10 As a result, poor conduction is reduced. The presence of the Ag diffusion region 11 in the magnetic layer 10 means that, for example, a cross section of the multilayer inductor 1 is photographed using a scanning electron microscope (SEM), and then energy dispersive X-ray analysis (EDS). This can be confirmed by obtaining the chemical composition by the ZAF method. The size (equivalent sphere diameter) of the Ag particles 30 is not particularly limited, and is preferably 1 to 10 μm. It is preferable that the Ag particles 30 occupy voids between the soft magnetic alloy particles constituting the magnetic layer 10. The Ag particles 30 may be present in an oxide film (not shown) around the individual soft magnetic alloy particles.

  According to the present invention, there is an Ag-free layered region (hereinafter also referred to as “Ag-free region”) 12 in the magnetic layer 10 sandwiched between the coil segments 21. As schematically illustrated in FIG. 1B, the region 12 includes Ag that is a part of the inner conductor 20 itself, and Ag particles 30 that are separated from the inner conductor 20 and are in the magnetic layer 10. The above-mentioned convex part 31 also means a layered region where none exists. The presence of such an Ag absent region 12 means that the diffusion of Ag does not extend over the entire area of the magnetic layer 10, and therefore, it is difficult for an undesired initial interlayer short circuit to occur.

  In the figure, as indicated by a dotted line, an average boundary between the coil segment 21 and the magnetic layer 10 is defined as a plane, and further, an Ag diffusion region and an Ag absence region 12 are set so as to be substantially parallel to the plane. Is defined so as to be substantially parallel to the coil segment 21. As shown in the figure, a layer structure is formed in which a coil segment 21 and an Ag non-existing region exist on both sides of the Ag diffusion region 12. The thickness of the layer of the Ag diffusion region 11 is preferably 1 μm or more, and the upper limit value of the thickness is not particularly limited, and is preferably 15 μm. The thickness of the Ag-free region 12 is preferably 3 μm or more, more preferably 5 μm or more, and the upper limit value of the thickness is not particularly limited, and is preferably 25 μm.

According to the present invention, in the multilayer inductor 1, a large number of soft magnetic alloy particles are accumulated to constitute a magnetic part having a predetermined shape. The magnetic body portion can be evaluated as an assembly of the magnetic layer 10 divided by the coil segment 21, and at the same time, it is evaluated that the magnetic layer 10 and the coil segment 21 constitute a laminated structure. Can do. Each of the soft magnetic alloy particles has an oxide film formed on at least a part of the periphery thereof, preferably substantially the whole, and this oxide film ensures the insulation of the magnetic part. Adjacent soft magnetic alloy particles are generally bonded via an oxide film of each soft magnetic alloy particle to constitute a magnetic part having a certain shape. The oxide film is preferably a film formed by oxidizing the soft magnetic alloy particles themselves. In part, metal portions of adjacent soft magnetic alloy particles are bonded to each other. Further, in the vicinity of the inner conductor 20, the soft magnetic alloy particles and the inner conductor 20 are in close contact mainly through the oxide film. The soft magnetic alloy particles are preferably made of an Fe-M-Si alloy (where M is a metal that is more easily oxidized than iron), and in this case, the oxide film is preferably formed by oxidation of the soft magnetic alloy. It is confirmed that at least the magnetic material Fe ₃ O ₄ and the non-magnetic materials Fe ₂ O ₃ and MO _x (x is a value determined according to the oxidation number of the metal M) are included. Yes.

  The presence of the bond through the oxide film described above is clear, for example, by visually confirming that the oxide film of the adjacent soft magnetic alloy particles is in the same phase in an SEM observation image magnified about 3000 times. Can be judged. The presence of the bond through the oxide film improves the mechanical strength and insulation of the multilayer inductor 1. Moreover, since the oxide film usually has relatively large irregularities, the migration of Ag is suppressed and the moisture resistance is improved. The multilayer inductor 1 is preferably bonded through the oxide film of the adjacent soft magnetic alloy particles. However, if even a part of the multilayer inductor 1 is bonded, the corresponding mechanical strength and insulation can be improved. Such a form is also an embodiment of the present invention.

  Similarly, with regard to the bonding between the metal portions where the oxide film of the soft magnetic alloy particles does not exist, the adjacent soft magnetic alloy particles maintain the same phase in, for example, an SEM observation image magnified about 3000 times. The presence of a bond between metal parts can be clearly determined by visually confirming that a bond point is present. The magnetic permeability can be further improved by the presence of the coupling between the soft magnetic alloy particles. Here, the “joint part between metal parts where no oxide film is present” means a part in which adjacent alloy particles are in direct contact with each other, for example, in a strict sense. It is a concept including a metal bond, a mode in which metal parts are in direct contact with each other, and an exchange of atoms is not seen, and an intermediate mode between them. The metal bond in the strict sense means that the requirement such as “the atoms are regularly arranged” is satisfied.

  In addition, even if the soft magnetic alloy particles adjacent to each other are partially in contact with or in close proximity to each other without both the bond through the oxide film and the bond between the soft magnetic metal particles. Good.

  The following effects and effects of the present invention which are manifested only when the bond between the Ag diffusion region, the Ag non-diffusion region, the oxide film, and the bond between the metal particles coexist are listed below. The adhesion of Ag is not only diffused into the voids of the magnetic alloy particles, but is enhanced by adhering to the magnetic alloy there. Ag does not enter between the particles at the bonding site via the oxide film, but at the bonding part between the metal particles, Ag enters between the particles, and the reaction between Ag and the particles (atomic level diffusion). And alloying) and the mutual ductile deformation adhesion proceeds, the adhesion is improved. Thereby, the electrical conductivity after a heat cycle improves. Further, the magnetic permeability is improved by causing bonding between the metals.

  Here, the particle diameter of the individual soft magnetic alloy particles in the magnetic body part 10 is not particularly limited, and is typically 2 to 20 μm, more preferably 3 to 10 μm. The particle diameter is measured by acquiring an SEM image of the cross section of the magnetic body 10. 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 soft magnetic alloy particles constituting the magnetic part of the multilayer inductor 10. . Therefore, in order to obtain the magnetic body portion 10 made of soft magnetic alloy particles having a desired particle diameter, raw material particles having such a particle diameter may be used.

  In the multilayer inductor 1, both ends of the inner conductor 20 are typically drawn to opposite end surfaces of the outer surface of the multilayer inductor 1 through lead conductors (not shown), respectively, and external terminals (not shown). Connected to. Conventional technology can be used as appropriate for the structure and connection mode of the external terminals.

  Hereinafter, a typical and non-limiting manufacturing method of the multilayer inductor 1 according to the present invention will be described. In manufacturing the multilayer inductor 1, first, a magnetic paste (slurry) prepared in advance is applied to 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. This is dried with a dryer such as a hot air dryer to obtain a green sheet. The magnetic paste includes soft magnetic alloy particles, typically a polymer resin as a binder, and a solvent.

  Soft magnetic alloy particles are particles exhibiting soft magnetism mainly composed of an alloy. Examples of the alloy include Fe-M-Si alloys (where M is a metal that is more easily oxidized than iron). Examples of M include Cr and Al, and Cr is preferable. Examples of the soft magnetic alloy particles include particles produced by an atomizing method.

  When M is Cr, that is, the chromium content in the Fe—Cr—Si alloy is preferably 2 to 8 wt%. The presence of chromium is preferable in that it forms a passive state during heat treatment to suppress excessive oxidation and develop strength and insulation resistance. On the other hand, from the viewpoint of improving magnetic properties, it is preferable that there is little chromium. The above preferred range is proposed in consideration.

  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. Examples of metals that may be contained in addition to Fe, Si, and Cr include aluminum, magnesium, calcium, titanium, manganese, cobalt, nickel, and copper, and examples of nonmetals include phosphorus, sulfur, and carbon. .

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

  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 blending ratio of soft magnetic alloy particles, polymer resin, solvent and the like in the magnetic paste can be adjusted as appropriate, and the viscosity of the magnetic paste can be set accordingly.

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

  Next, using a punching machine such as a punching machine or a laser processing machine, the green sheet is punched to form through holes (through holes) in a predetermined arrangement. The arrangement of the through holes is set so that when the sheets are laminated, the internal conductor 20 is formed by the through hole (that is, the relay segment 22) filled with the conductor and the coil segment 21. As for the arrangement of the through holes for forming the inner conductor and the shape of the conductor pattern for forming the coil segment, conventional techniques can be used as appropriate, and specific examples are described with reference to the drawings in the following embodiments. Explained.

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

  The conductive 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 mixing ratio of Ag-containing material, polymer resin, solvent, etc. in the conductive paste can be adjusted as appropriate, and the viscosity of the conductive paste can be set accordingly.

  Next, 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 with a dryer such as a hot air dryer to form a conductor pattern corresponding to the coil segment. 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 20.

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. From the viewpoint of facilitating the formation of bonds between metal parts and increasing the specific resistance, the pressure in this thermocompression bonding is preferably 4 to 10 ton / cm ² . Subsequently, using a cutting machine such as a dicing machine or a laser processing machine, the multilayer body is cut into a component body size, and a pre-heat treatment chip including a magnetic body portion and an internal conductor before the 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. The heat treatment atmosphere is not particularly limited as long as it is an oxidizing atmosphere, and air or dry air is desirable in consideration of production. From the viewpoint of diffusing Ag from the pattern for the inner conductor into the magnetic layer to facilitate the presence of the above-described Ag particles 30 and convex portions 31, and at the same time ensuring an Ag-free region, The temperature is maintained at 300 to 600 ° C. for 1 to 600 minutes, more preferably 60 to 600 minutes, and then the temperature is further raised. The maximum temperature is preferably 600 ° C. or higher, more preferably 700 to 900 ° C., and the maximum temperature is preferably maintained for 0.5 to 3 hours in more detail.

  In the chip before heat treatment, there are many fine gaps between individual soft magnetic alloy particles, and the fine gaps are usually filled with a mixture of a solvent and a binder. These mixtures disappear during the heating process, and the fine gaps turn into pores. In the high temperature range close to the maximum temperature, the soft magnetic alloy particles are densely formed to form a magnetic part, and typically, an oxide film is formed on the surface of each soft magnetic alloy particle. At this time, the Ag-containing material is sintered to form the internal conductor 20. Thereby, the multilayer inductor 1 is obtained. The magnetic permeability of the magnetic layer 10 in the multilayer inductor thus obtained is preferably 25 to 45.

  Usually, external terminals are formed after the heat treatment. Using a coating machine such as a dip coating machine or a roller coating machine, a conductor paste prepared in advance is applied to both ends in the length direction of the multilayer inductor 1, and this is applied using a heating device such as a firing furnace, for example, about 600. An external terminal is formed by performing a baking process at a temperature of about 1 hr. 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.

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

[Concrete structure of multilayer inductor]
A specific structural example of the multilayer inductor 1 manufactured in this embodiment will be described. The multilayer inductor 1 as a part 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. 2 is a schematic exploded view of the multilayer inductor. The magnetic part in the region where the inner conductor is formed has a structure in which a total of five magnetic layers ML1 to ML5 are integrated. An upper cover region and a lower cover region exist so as to sandwich the region where the inner conductor is formed, and the upper cover region has a structure in which eight magnetic layers ML6 are integrated. The lower cover region has a structure in which seven magnetic layers 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 and a width of about 1.6 mm. Each of the magnetic layers ML1 to ML6 is formed mainly from soft magnetic alloy particles having the composition shown in Table 1 which are soft magnetic alloy particles, and does not contain a glass component.

  The internal 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 inner conductor 20 is obtained by heat-treating silver particles, and the volume-based d50 of the silver particles used as a raw material is 5 μm. The d50 of Ag particles was measured using a particle size / particle size distribution measuring apparatus (for example, Microtrack manufactured by Nikkiso Co., Ltd.) using a laser diffraction scattering method. In Comparative Example 4 and Comparative Example 8, copper particles were used instead of silver particles. About the comparative example 4 and the comparative example 8, the copper particle is used instead of Ag particle in the following description.

  The four coil segments CS1 to CS4 have a U shape, and the one coil segment CS5 has a strip shape. 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 has a continuous L-shaped lead portion LS1 used for connection with an external terminal, and the lowermost coil segment CS5 is L-shaped used for connection with an external terminal. The lead-out portion LS2 is continuously formed. Each relay segment IS1 to IS4 has a columnar shape penetrating the magnetic layers ML1 to ML4, and each aperture is about 15 μm.

  Each external terminal (not shown) extends to each end face in the length direction of the multilayer inductor 1 and four side faces in the vicinity of the end face, and has a thickness of about 20 μm. One external terminal is connected to the edge of the lead portion LS1 of the uppermost coil segment CS1, and the other external terminal is connected to the edge 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. The d50 of the silver particles was measured using a particle size / particle size distribution measuring apparatus (for example, Microtrack manufactured by Nikkiso Co., Ltd.) using a laser diffraction scattering method.

[Manufacture of multilayer inductors]
Particle diameter and particle size distribution measurement using a laser diffraction scattering method has a d50 of 10 μm, soft magnetic alloy particles having a composition shown in Table 1 85 wt%, butyl carbitol (solvent) 13 wt%, polyvinyl butyral (binder) 2 wt% A magnetic paste comprising: Using a doctor blade, this magnetic paste was applied to the surface of a plastic base film, and this was dried with a hot air dryer at about 80 ° C. for about 5 minutes. In this way, a green sheet was obtained on the base film. Thereafter, the green sheet was cut to obtain first to sixth sheets corresponding to the magnetic layers ML1 to ML6 (see FIG. 2) and having a size suitable for multi-cavity.

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

  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, and a first printed layer corresponding to the coil segment CS1 was produced in a predetermined arrangement. Similarly, the 2nd-5th printing layer corresponding to coil segment CS2-CS5 was produced by the predetermined arrangement | sequence on each surface of the said 2nd-5th sheet | seat.

  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 6th sheet | seat which has not been piled up in the order shown in FIG. 2, was thermocompression-bonded, and the laminated body was produced. The pressure applied to the pressure bonding at this time is as follows.
In Examples 1 to 3 and 5 to 7, 5 ton / cm ²
In Examples 4 and 8, 7 ton / cm ²
In Comparative Examples 1-6 and 8, 5 ton / cm ²
In Comparative Example 7, ² ton / cm ²
In Comparative Example 8, 5 ton / cm ²
The obtained laminated body was cut into a component body size with a cutting machine to obtain a chip before heat treatment.

  Subsequently, a large number of chips before heat treatment were heat-treated in a lump in an air atmosphere using a firing furnace. First, as a binder removal process, heating is performed under conditions of about 300 ° C. and about 1 hr, and then heat treatment is performed according to the conditions described later, so that the soft magnetic alloy particles are densely formed to form the magnetic body portion 10. The particles were sintered to form the inner conductor 20, thereby obtaining a component main body.

The heat treatment conditions in each example and comparative example are as follows.
The maximum temperature and holding time in the heat treatment were held at 700 ° C. for 1 hour in Examples 1 to 4 and Comparative Examples 1, 3, and 4, and held at 850 ° C. for 1 hour in Comparative Example 2, Examples 5 to 8 and Comparative Examples 5, 7, and 8 were held at 800 ° C. for 2 hours, and Comparative Example 6 was held at 900 ° C. for 2 hours.
The holding conditions in the temperature raising process in the heat treatment are as follows.
In Example 1, the temperature was maintained at 600 ° C. for 1 hour during the temperature rising process.
In Example 2, the temperature was maintained at 600 ° C. for 3 hours during the temperature raising process.
In Example 3, the temperature was maintained at 600 ° C. for 10 hours during the temperature raising process.
In Example 4, the temperature was maintained at 600 ° C. for 3 hours during the temperature raising process.
In Example 5, the temperature was maintained at 600 ° C. for 1 hour during the temperature raising process.
In Example 6, the temperature was maintained at 600 ° C. for 3 hours during the temperature raising process.
In Example 7, the temperature was maintained at 600 ° C. for 10 hours during the temperature raising process.
In Example 8, the temperature was maintained at 600 ° C. for 3 hours during the temperature raising process.
In Comparative Example 1, the temperature was maintained at 600 ° C. for 20 hours during the temperature raising process.
In Comparative Examples 2 and 3, holding at a specific temperature during the temperature raising process was not performed.
In Comparative Example 4, the temperature was kept at 600 ° C. for 1 hour during the temperature raising process.
In Comparative Example 5, the temperature was maintained at 600 ° C. for 20 hours during the temperature raising process.
In Comparative Examples 6 and 7, the holding at the specific temperature during the temperature raising process was not performed.
In Comparative Example 8, the temperature was kept at 600 ° C. for 1 hour during the temperature raising process.

  Subsequently, external terminals were formed. A conductive paste containing 85 wt% of the above silver particles, 13 wt% of butyl carbitol (solvent) and 2 wt% of polyvinyl butyral (binder) is applied to both ends in the longitudinal direction of the component body, and this is fired Baking treatment was performed in a furnace under conditions of about 600 ° C. and about 1 hr. 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.

[Evaluation of multilayer inductor]
About the obtained multilayer inductor, the cross section was photographed using a scanning electron microscope (SEM), and then the chemical composition was determined by the ZAF method by energy dispersive X-ray analysis (EDS), whereby the Ag particles and the above-described components were obtained. The presence or absence of convex portions was examined. Then, the thicknesses of the Ag diffusion region 11 and the Ag absence region 12 were measured. The measurement is performed using the SEM image of the cross section, and for one example / comparative example, 100 measurement data are obtained by measuring the thickness of the Ag absence region 12 in 5 layers for each of the 20 laminated inductors. The minimum value is the thickness of the Ag absence region 12. Then, the value of 1/2 of the value obtained by subtracting the thickness of the Ag-free region 12 from the thickness of the magnetic layer 10 was set as the thickness of the Ag diffusion region 11. The distance between the two coil segments (that is, the thickness of the magnetic layer 10) is 17.8 μm in Examples 1 to 4 and Comparative Examples 1 to 4, and Examples 5 to 8 and Comparative Examples 5 to 8 are used. Then, it was 40.0 μm.

  The cross section of the magnetic layer 10 of each of the multilayer inductors of each of the examples and comparative examples was observed by SEM magnified about 3000 times, whether or not the oxide films of adjacent soft magnetic alloy particles were bonded, and soft magnetic alloy particles The presence or absence of bonding between metal parts where no oxide film exists was examined. In the case where there are bonds between the oxide films of the adjacent soft magnetic alloy particles, most of the oxide films of the adjacent soft magnetic alloy particles exhibited the same phase in the SEM observation image. When bonds between metal parts existed, it was visually confirmed that adjacent soft magnetic alloy particles had a bonding point while maintaining the same phase in the SEM observation image.

The results are summarized in Table 1.

In the column of “Composition” in Table 1, Fe—Cr—Si is 4.5 wt% Cr, 3.5 wt% Si, the balance is Fe, and Fe—Si—Al is 5.5 wt% Al. , Si is 9.5 wt%, the balance is Fe, Ni—Zn ferrite is 11 mol% NiO, 20 mol% ZnO, 10 mol% CuO, and 49 mol% Fe ₂ O ₃ .
In Comparative Example 4 and Comparative Example 8, a copper electrode is used instead of a silver electrode, and the indications in the columns of “Ag diffusion region thickness” and “Ag absence region thickness” in Table 1 are “ It means “thickness of copper diffusion region” and “thickness of copper-free region”.

The reliability of the obtained multilayer inductor was evaluated. Reliability evaluation was an initial Q value and a Q value after a moisture resistance load test, and was measured at a frequency of 1 MHz using an impedance analyzer 4294A manufactured by Agilent.
The evaluation indexes in the initial value evaluation are as follows.
○ ・ ・ ・ Q value is 40 or more.
X ... Q value is less than 40.
-... Q value as an inductor was not obtained.

  In the obtained multilayer inductor, the continuity after heat cycle was evaluated. The heat cycle conditions were 55 ° C. to 125 ° C. and a holding time of 30 minutes (100 cycles). In the subsequent continuity test, the case where continuity was recognized was evaluated as ◯, the case where continuity was not achieved was evaluated as x, and the case where an initial Q value was not obtained was evaluated as-.

The Q value after the moisture resistance load test in the obtained multilayer inductor was measured. The conditions of the moisture resistance load test were 60 ° C., 95% RH, 1.2 A, and 1000 hr. The measurement condition of the Q value is the same as the initial Q value measurement. The evaluation indexes based on the evaluation are as follows.
○: The rate of change of Q value from the humidity resistance load test (initial value) is less than 30% in absolute value.
X: The rate of change of the Q value from before the moisture resistance load test (initial value) is 30% or more in absolute value.
-The initial Q value could not be obtained and was not evaluated.

The results and the measurement results of magnetic permeability are shown in Table 2.

  In each example, the reliability and conductivity after heat cycle were excellent. In Comparative Examples 1 and 5, Ag diffused almost throughout the magnetic layer, and the initial Q value was low. In Comparative Examples 2 and 6, Ag migrated, the Q value after moisture resistance load was lowered, and the reliability was low. In Comparative Example 3, the Ag particles are not present in the magnetic layer, and during the heat cycle, peeling that seems to be due to the difference in thermal expansion between the internal electric wire and the magnetic layer occurs, leading to disconnection of the peeled fragile portion, and conduction. Sex deteriorated. In Comparative Examples 4 and 8, since copper was oxidized and the initial Q value was low, it was not worth performing the subsequent evaluation.

DESCRIPTION OF SYMBOLS 1 Multilayer inductor, 10 Magnetic body layer, 11 Ag diffusion area | region, 12 Ag absence area | region, 20 Inner conductor, 21 Coil segment, 22 Relay segment, 30 Ag particle, 31 Convex part, ML1-ML6 Magnetic body layer, CS1- CS5 coil segment, IS1-IS4 relay segment

Claims (2)

A plurality of magnetic layers formed of a Fe-Si-M soft magnetic alloy (where M is a metal element that is more easily oxidized than Fe), a plurality of coil segments made of an Ag-containing material, and an Ag-containing material A relay segment consisting of
An oxide film formed by oxidizing the soft magnetic alloy exists at least around the periphery of the soft magnetic alloy particles, and the magnetic layer has an oxide film formed around the adjacent soft magnetic alloy particles. There are joints between soft magnetic alloy particles in the metal part where all the joint parts and oxide film do not exist,
The magnetic material layer and the coil segment constitute a laminated structure in which the magnetic material layer and the coil segment are alternately laminated, and the relay segment is formed so as to pass through the magnetic material layer and conduct between the coil segments. The segment constitutes an electrically integrated inner conductor,
Each magnetic layer has an Ag diffusion region in contact with the coil segment and an Ag absence region located on the opposite side of the coil segment as viewed from the Ag diffusion region,
A multilayer inductor in which at least one of the following (A) and (B) is present in the Ag diffusion region.
(A) Ag particles in the magnetic layer around the inner conductor (B) Convex portion made of Ag extending from the inner conductor to the soft magnetic layer   The multilayer inductor according to claim 1, wherein the thickness of the Ag diffusion region is 1 µm or more, and the thickness of the Ag absence region is 3 µm or more.

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