Laminated electronic component and method of manufacturing laminated electronic component

A laminated electronic component includes a first magnetic material portion, a low-magnetic-permeability portion laminated on the first magnetic material portion, a second magnetic material portion laminated on the low-magnetic-permeability portion, at least one annular or spiral coil disposed within the low-magnetic-permeability portion, and a plurality of columnar magnetic material portions disposed within the low-magnetic-permeability portion so as to extend through inside of the coil and connecting the first magnetic material portion to the second magnetic material portion.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Application No. 2012-046538 filed on Mar. 2, 2012, the entire contents of this application being incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technical field relates to a laminated electronic component including a coil therein and a method of manufacturing the same.

BACKGROUND

In a conventional electronic component such as a common mode choke coil, a wire is generally wound on a core made of ferrite or the like. However, downsizing is a significant challenge also for coil components, and laminated electronic components which include a coil therein and are manufactured using ceramic lamination technology have widely been used in recent years. As an example of such a laminated electronic component, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2005-268455) discloses a common mode choke coil.FIG. 7is an exploded perspective view showing the configuration of a conventional common mode choke coil200.

The common mode choke coil200has a structure in which a low-magnetic-permeability portion102is laminated on a first magnetic material portion101and a second magnetic material portion103is laminated on the low-magnetic-permeability portion102.

The first magnetic material portion101has a structure in which a plurality of magnetic material sheets101aare laminated.

The low-magnetic-permeability portion102has a structure in which a plurality of low-magnetic-permeability sheets102aare laminated and spiral coil conductors104a,104b,104c, and104dare each interposed between the two low-magnetic-permeability sheets102aadjacent in the lamination direction. Each low-magnetic-permeability sheet102ahas a rectangular hole102bextending therethrough in the lamination direction. In the magnetic material sheet102a, the hole102bis formed in a portion corresponding to the inside of the coil conductors104ato104d. In addition, predetermined sheets among the low-magnetic-permeability sheets102ahave via conductors108aand108bformed in predetermined portions for electrically connecting front and back sides.

Within the low-magnetic-permeability portion102, the coil conductors104aand104bare connected to each other via the via conductor108ato form a first coil105a. In addition, the coil conductors104cand104dare connected to each other via the via conductor108bto form a second coil105b. Then, the first coil105aand the second coil105bare electromagnetically coupled to each other to constitute a common mode choke coil.

The second magnetic material portion103has a structure in which a plurality of magnetic material sheets103aare laminated.

On the surface of the common mode choke coil200, external electrodes106a,106b,106c, and106dare formed. The external electrode106ais connected to an end of the coil conductor104a, the external electrode106bis connected to an end of the coil conductor104b, the external electrode106cis connected to an end of the coil conductor104c, and the external electrode106dis connected to an end of the coil conductor104d.

The common mode choke coil200having such a structure is manufactured, for example, through the following processes. First, unfired magnetic material sheets101a, unfired low-magnetic-permeability sheets102a, and unfired magnetic material sheets103aare prepared. Among them, in the low-magnetic-permeability sheets102a, the holes102b, the via conductors108aand108b, and the coil conductors104ato104dare previously formed. A predetermined number of such magnetic material sheets101a, a predetermined number of such low-magnetic-permeability sheets102a, and a predetermined number of such magnetic material sheets103aare laminated in a predetermined order and then press-bonded. The laminate formed thus is fired at a predetermined profile. Then, the external electrodes106ato106dare formed on the surface of the fired laminate by burning a conductive paste. In the above manner, the common mode choke coil200is manufactured.

When the magnetic material sheets101a, the low-magnetic-permeability sheets102a, and the magnetic material sheets103aare laminated and press-bonded to form the laminate, the magnetic material sheet101aon the lower side and the magnetic material sheet103aon the upper side enter the holes102bformed in the low-magnetic-permeability sheets102adue to the pressure. In addition, the magnetic material sheet101aon the lower side and the magnetic material sheet103aon the upper side are connected to each other within the holes102b. In other words, the common mode choke coil200has a structure in which the first magnetic material portion101and the second magnetic material portion103are connected to each other by extending in a columnar manner through the low-magnetic-permeability portion102present therebetween and the coil conductors104ato104dare arranged around the columnar magnetic materials extending through the low-magnetic-permeability portion102.

However, the common mode choke coil200disclosed in Patent Document 1 has a problem that when the amounts of the magnetic material sheet101aon the lower side and the magnetic material sheet103aon the upper side which enter the holes102bof the low-magnetic-permeability sheets102aare insufficient, both sheets are not connected to each other. In other words, the common mode choke coil200does not have a structure in which the first magnetic material portion101and the second magnetic material portion103are connected to each other by extending through the low-magnetic-permeability portion102present therebetween, and thus the common mode choke coil200becomes defective.

As a solution to this problem, a solution of previously filling a magnetic material into the holes102bof the low-magnetic-permeability sheets102ais conceivable. Such a solution is disclosed, for example, in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2000-321341). Specifically, a magnetic material is previously filled into holes formed in low-magnetic-permeability sheets (nonmagnetic material sheets). Then, a coil conductor (coil pattern) is inserted between the two low-magnetic-permeability sheets adjacent in a lamination direction. A plurality of lower magnetic material sheets, a plurality of the low-magnetic-permeability sheets between which the coil conductors have been interposed, and a plurality of upper magnetic material sheets are laminated and press-bonded. The laminate formed thus is fired. As a result, a coil is formed within the laminate.

For manufacturing the coil disclosed in Patent Document 2, for example, the following method may be used to fill the magnetic material into the holes formed in the low-magnetic-permeability sheets.

First, a plurality of retaining sheets to be processed are prepared.

Next, a low-magnetic-permeability slurry, namely, a material obtained by kneading a low-magnetic-permeability material, a binder, and a solvent, is applied onto each retaining sheet with a constant thickness, thereby forming a plurality of low-magnetic-permeability sheets.

Next, a frame-shaped blade is pressed against the low-magnetic-permeability sheet on each retaining sheet and separated therefrom. Then, only a low-magnetic-permeability sheet portion corresponding to inside of the blade is removed. By so doing, a hole is formed in each low-magnetic-permeability sheet. In addition, a hole for a via conductor is also formed in some of the low-magnetic-permeability sheets.

Next, a magnetic material slurry, namely, a material obtained by kneading a magnetic material, a binder, and a solvent, is filled into the hole formed in each low-magnetic-permeability sheet. Specifically, from one principal surface side of the low-magnetic-permeability sheet, the magnetic material slurry is applied to the hole formed in the low-magnetic-permeability sheet and the periphery of the hole, thereby filling the magnetic material slurry.

In addition, a conductive paste is filled into the above-described hole for a via conductor.

Next, coil conductors having a predetermined shape are formed on surfaces of predetermined sheets among a plurality of the low-magnetic-permeability sheets by printing a conductive paste. The coil conductors may be formed prior to forming the holes in the low-magnetic-permeability sheets.

At the end, the low-magnetic-permeability sheet in which the magnetic material has been filled is peeled off from each retaining sheet.

A coil manufactured by using the low-magnetic-permeability sheets obtained through such processes has a structure in which a first magnetic material portion and a second magnetic material portion are assuredly connected to each other via a columnar magnetic material formed so as to extend through a low-magnetic-permeability portion.

SUMMARY

The present disclosure provides a laminated electronic component which allows its productivity to be improved and a method of manufacturing the same.

In an aspect of the present disclosure, a laminated electronic component includes a first magnetic material portion, a low-magnetic-permeability portion laminated on the first magnetic material portion, a second magnetic material portion laminated on the low-magnetic-permeability portion, at least one annular or spiral coil disposed within the low-magnetic-permeability portion, and a plurality of columnar magnetic material portions disposed within the low-magnetic-permeability portion so as to extend through inside of the coil and connect the first magnetic material portion to the second magnetic material portion.

In another aspect of the present disclosure, a method of manufacturing a laminated electronic component includes the steps of preparing a plurality of magnetic material sheets; preparing a plurality of low-magnetic-permeability sheets; forming, in the low-magnetic-permeability sheets, a plurality of holes extending through the low-magnetic-permeability sheets; filling a magnetic material into the plurality of holes; forming an annular or spiral coil conductor on a surface of a predetermined sheet among the plurality of low-magnetic-permeability sheets; laminating a predetermined number of the magnetic material sheets to form a first magnetic material portion; laminating the plurality of low-magnetic-permeability sheets in which the magnetic material has been filled into the holes and the coil conductor has been formed on the surface of the predetermined sheet, on the first magnetic material portion in a predetermined order to form a low-magnetic-permeability portion; laminating a predetermined number of the magnetic material sheets on the low-magnetic-permeability portion to form a second magnetic material portion; and firing a laminate composed of the first magnetic material portion, the low-magnetic-permeability portion, and the second magnetic material portion.

DETAILED DESCRIPTION

The inventors realized that the manufacturing method disclosed in Patent Document 2 has a problem that in the process where the low-magnetic-permeability sheet in which the magnetic material has been filled in the hole is peeled off from each retaining sheet, if the opening area of the hole is large, the magnetic material comes off from the hole. In other words, the filled magnetic material remains on the surface of the retaining sheet, and the low-magnetic-permeability sheet in which the hole becomes hollow is peeled off from the retaining sheet. When the cross-sectional area of the hole formed in each low-magnetic-permeability sheet is larger, this problem prominently appears, and the frequency at which the magnetic material comes off from the hole is further increased. A non-defective coil cannot be manufactured by using such low-magnetic-permeability sheets. Thus, the conventional manufacturing method has a problem that high productivity cannot be obtained.

Hereinafter, an exemplary embodiment of the present disclosure that can address the above shortcomings will now be described with reference to the drawings.

FIG. 1is an exploded perspective view of a common mode choke coil100according to the exemplary embodiment.

The common mode choke coil100has a structure in which a low-magnetic-permeability portion2is laminated on a first magnetic material portion1and a second magnetic material portion3is laminated on the low-magnetic-permeability portion2. The low-magnetic-permeability portion2is formed from a material having a lower magnetic permeability than the first magnetic material portion1, the second magnetic material portion3, and further penetrating magnetic materials7a,7b, and7cdescribed later, but the material thereof may be a magnetic material or a nonmagnetic material. For example, for the low-magnetic-permeability portion2, a magnetic material which has a lower magnetic permeability than the first magnetic material portion1but is of the same composition type as the first magnetic material portion1may be used.

The first magnetic material portion1has a structure in which a plurality of magnetic material sheets1aare laminated. The common mode choke coil100according to the embodiment is formed by a laminate being integrally fired as described later, and thus the interfaces between the magnetic material sheets1amay disappear within the first magnetic material portion1. As the material of the first magnetic material portion1, for example, Ni—Cu—Zn ferrite, Mn—Zn ferrite, hexagonal ferrite, and the like can be used.

The low-magnetic-permeability portion2has a structure in which a plurality of low-magnetic-permeability sheets2aare laminated. Here, a spiral coil conductor may be interposed between the two low-magnetic-permeability sheets2aadjacent in the lamination direction. InFIG. 1, spiral coil conductors4ato4dare interposed. Each low-magnetic-permeability sheet2ahas penetrating magnetic materials7a,7b, and7chaving circular transverse sections. The penetrating magnetic materials7ato7cextend through each low-magnetic-permeability sheet2ain the lamination direction. The penetrating magnetic materials7ato7care formed in a portion of a principal surface of the magnetic material sheet2awhich corresponds to the inside of the coil conductors4ato4d. In the embodiment, for convenience of a manufacturing method, the penetrating magnetic materials7ato7care connected to each other by a film-shaped magnetic material7dformed on the upper principal surface of each low-magnetic-permeability sheet2a. In addition, in some of the low-magnetic-permeability sheets2a, via conductors8aand8bare formed in predetermined portions for electrically connecting front and back sides.

A plurality of the low-magnetic-permeability sheets2aare laminated, the penetrating magnetic materials7aformed in the respective low-magnetic-permeability sheet2aare laminated to form one columnar magnetic material portion, the penetrating magnetic materials7bare laminated to form another columnar magnetic material portion, and the penetrating magnetic materials7care laminated to form still another columnar magnetic material portion. That is, three columnar magnetic material portions are formed in total.

As the material of the low-magnetic-permeability portion2, for example, a nonmagnetic material such as glass ceramics having a magnetic permeability of about 1, Ni—Cu—Zn ferrite having a magnetic permeability of about 1 to 10, nonmagnetic ferrite, and the like can be used. In addition, as the penetrating magnetic materials7a,7b, and7c, the same material as that of the first magnetic material portion1as described above can be used. Furthermore, as the material of the coil conductors4ato4dand the via conductors8aand8b, for example, a metal such as Cu, Pd, Al, and Ag or an alloy containing at least one of these metals can be used. The common mode choke coil100according to the embodiment is formed by a laminate being integrally fired as described later, and thus the interfaces between the low-magnetic-permeability sheets2aor the interfaces between the penetrating magnetic materials7a, between the penetrating magnetic materials7b, or between the penetrating magnetic materials7cmay disappear within the low-magnetic-permeability portion2.

Within the low-magnetic-permeability portion2, the coil conductor4aand the coil conductor4bare connected to each other via the via conductor8ato form a first coil5a. In addition, the coil conductor4cand the coil conductor4dare connected to each other via the via conductor8bto form a second coil5b. The first coil5aand the second coil5bare electromagnetically coupled to each other to constitute a common mode choke coil. The second magnetic material portion3has a structure in which a plurality of magnetic material sheets3aare laminated. As the material of the second magnetic material portion3, the same material as that of the first magnetic material portion1can be used. The common mode choke coil100according to the embodiment is formed by a laminate being integrally fired as described later, and thus the interfaces between the magnetic material sheets3amay disappear within the second magnetic material portion3.

External electrodes6a,6b,6c, and6dare formed on the surface of the common mode choke coil100. The external electrode6ais connected to an end of the coil conductor4a, the external electrode6bis connected to an end of the coil conductor4b, the external electrode6cis connected to an end of the coil conductor4c, and the external electrode6dis connected to an end of the coil conductor4d. As the material of the external electrodes6a,6b,6c, and6d, for example, a metal such as Cu, Pd, Al, and Ag or an alloy containing at least one of these metals can be used.

In the common mode choke coil100according to the embodiment, within the low-magnetic-permeability portion2, the three columnar magnetic material portions, namely, the laminate of the penetrating magnetic materials7a, the laminate of the penetrating magnetic materials7b, and the laminate of the penetrating magnetic materials7c, are formed, and they connect the first magnetic material portion1to the second magnetic material portion3. The transverse section of each columnar magnetic material portion is small, but the sum of the cross-sectional areas of the three columnar magnetic material portions is equivalent to that in the related art. Therefore, electrical properties equivalent to those in the related art can be obtained.

Next, an example of a method of manufacturing the common mode choke coil100according to the embodiment will be described with reference toFIGS. 2A to 5B.

First, as shown inFIG. 2A, a retaining sheet9a, which is formed from PET (polyethylene terephthalate) or the like and is to be processed, is prepared. A magnetic material slurry is applied onto the retaining sheet9awith a predetermined thickness to produce a mother magnetic material sheet1A (3A) in which a large number of magnetic material sheets1aor3aare arranged in a matrix manner. InFIG. 2A, the interfaces between the adjacent magnetic material sheets1a(3a) of the mother magnetic material sheet1A (3A) are indicated by chain lines. The magnetic material slurry is applied, for example, by a doctor blade method. A plurality of the mother magnetic material sheets1A (3A) as described above are produced according to need.

In addition, as shown inFIG. 2B, a retaining sheet9b, which is formed from PET or the like and is to be processed, is prepared. A low-magnetic-permeability slurry is applied onto the retaining sheet9bwith a predetermined thickness to produce a mother low-magnetic-permeability sheet2A in which a large number of low-magnetic-permeability sheets2aare arranged in a matrix manner. InFIG. 2B, the interfaces between the adjacent low-magnetic-permeability sheets2aof the mother low-magnetic-permeability sheet2A are indicated by chain lines (the same applies to the following drawings). The low-magnetic-permeability slurry is applied, for example, by a doctor blade method. A plurality of the mother low-magnetic-permeability sheets2A as described above are produced according to need.

Next, as shown inFIG. 2C, three holes7a′ to7c′ for forming the penetrating magnetic materials7ato7care formed in each low-magnetic-permeability sheet2aof the mother low-magnetic-permeability sheet2A.FIG. 2Cshows a cross section corresponding to a portion of the low-magnetic-permeability sheet2ataken along a broken-line arrow X-X inFIG. 1, and thus only the hole7a′ appears and the holes7b′ and7c′ do not appear inFIG. 2C. The holes7a′ to7c′ are formed, for example, by pressing an annular blade against each low-magnetic-permeability sheet2aformed on the retaining sheet9b, separating the blade therefrom, and removing a low-magnetic-permeability sheet portion corresponding to inside of the blade.

In addition, although not shown, a hole8a′ or8b′ for forming the via conductor8aor8bis formed in each low-magnetic-permeability sheet2aformed in a portion of the mother low-magnetic-permeability sheet2A. The hole8a′ or8b′ is formed, for example, by applying a laser beam.

Next, as shown inFIG. 3A, the magnetic material slurry is filled into the three holes7a′ to7c′ formed in each low-magnetic-permeability sheet2aof the mother low-magnetic-permeability sheet2A, whereby the penetrating magnetic materials7ato7care formed. The magnetic material slurry is filled, for example, by a screen printing method.

In the embodiment, at that time, the circular film-shaped magnetic material7dis formed in a region on the upper principal surface of each low-magnetic-permeability sheet2awhich includes the holes7a′ to7c′. The film-shaped magnetic material7dis connected to each of the penetrating magnetic materials7ato7c. The film-shaped magnetic material7dis not an essential component in the embodiment, and the magnetic material slurry may be supplied into only the holes7a′ to7c′.FIG. 3Ashows a cross section corresponding to the portion of the low-magnetic-permeability sheet2ataken along the broken-line arrow X-X inFIG. 1, and thus only the penetrating magnetic material7aappears and the penetrating magnetic materials7band7cdo not appear inFIG. 3A.

In addition, although not shown, a conductive paste is filled into the hole8a′ or8b′ formed in the portion of the mother low-magnetic-permeability sheet2A, whereby the via conductor8aor8bis formed. The conductive paste is filled, for example, by a screen printing method.

Next, as shown inFIG. 3B, any one of the coil conductors4ato4dis formed on each low-magnetic-permeability sheet2aformed in the portion of the mother low-magnetic-permeability sheet2A. The coil conductors4ato4dare formed, for example, by screen printing the conductive paste into a desired shape. The coil conductors4ato4dhave shapes different from each other.

Next, although not shown, the mother magnetic material sheets1A and3A are peeled off from the retaining sheets9a.

In addition, as shownFIG. 3C, the mother low-magnetic-permeability sheet2A is peeled off from the retaining sheet9b. The process of peeling off the mother low-magnetic-permeability sheet2A from the retaining sheet9bwill be separately described with reference to the plan view ofFIG. 6A.FIG. 6Ashows one low-magnetic-permeability sheet2ain the mother low-magnetic-permeability sheet2A, and thus a description will be given below with the low-magnetic-permeability sheet2aas one unit.

As shown inFIG. 6A, when the low-magnetic-permeability sheet2ais peeled off from the retaining sheet9bin an arrow D direction, the penetrating magnetic material7cinitially starts being peeled off. Subsequently, while the penetrating magnetic material7cis peeled off, the penetrating magnetic material7astarts being peeled off. Subsequently, after the penetrating magnetic material7cis completely peeled off and while the penetrating magnetic material7ais peeled off, the penetrating magnetic material7bstarts being peeled off. As described above, the penetrating magnetic materials7ato7care preferably peeled off in order at different timings. When a portion where the penetrating magnetic materials7ato7care present (a portion where the holes are present) is peeled off, an unstable tensile force is applied to the low-magnetic-permeability sheet2a. Thus, the low-magnetic-permeability sheet2ais easily broken when the penetrating magnetic materials7ato7care simultaneously peeled off. However, when the penetrating magnetic materials7ato7care peeled off in order at different timings, breaking of the low-magnetic-permeability sheet2acan be prevented.

As shown inFIG. 6B, the formed positions of the penetrating magnetic materials7ato7cmay be changed to positions different from those in the example ofFIG. 6A. In the example ofFIG. 6B, the penetrating magnetic materials7ato7care formed such that the penetrating magnetic material7astarts being peeled off after the penetrating magnetic material7cis completely peeled off and the penetrating magnetic material7bstarts being peeled off after the penetrating magnetic material7ais completely peeled off. With this configuration, the effect of preventing the low-magnetic-permeability sheet2afrom being broken is further enhanced.

As described above, although the low-magnetic-permeability sheet2a, namely, the mother low-magnetic-permeability sheet2A, is peeled off from the retaining sheet9b, a columnar magnetic material portion formed within the low-magnetic-permeability portion2is divided into a plurality of portions and the transverse sectional area of each portion is small in the embodiment. Thus, the surface area of each of the penetrating magnetic materials7ato7cformed in the low-magnetic-permeability sheet2ais also small, and hence when the low-magnetic-permeability sheet2ais peeled off from the retaining sheet9b, the penetrating magnetic materials7ato7care unlikely to remain on the retaining sheet9b, and the possibility is reduced that the penetrating magnetic materials7ato7ccome off from the low-magnetic-permeability sheet2a.

Next, as shown inFIG. 4, a plurality of the mother magnetic material sheets1A, a plurality of the mother low-magnetic-permeability sheets2A, and a plurality of the mother magnetic material sheets3A are laminated.

Next, as shown inFIG. 5A, the laminated mother magnetic material sheets1A, mother low-magnetic-permeability sheets2A, and mother magnetic material sheets3A are integrated by pressure bonding to form an unfired mother laminate10A.

Next, although not shown, the unfired mother laminate10A is fired at a predetermined profile to produce a fired mother laminate10A.

Next, as shown inFIG. 5B, the fired mother laminate10A is divided into individual laminates10. The division into the individual laminates may be conducted prior to the above firing.

At the end, although not shown, the external electrodes6ato6dare formed on the surface of each laminate10obtained by the division, to complete the common mode choke coil100. The external electrodes6ato6dare formed, for example, by applying a conductive paste into a desired shape and firing the conductive paste.

The structure of the common mode choke coil100according to the exemplary embodiment and the example of the manufacturing method thereof has been described above. However, embodiments consistent with the present disclosure are not limited to the above contents, and various modifications can be made according to the principles of the present disclosure.

For example, the laminated electronic component is not limited to the common mode choke coil, and may be another type of a coil component or another type of an electronic component including a coil therein. In addition, the laminated electronic component is not limited to a component including two coils as in a common mode choke coil, and may be a component including a single coil or three or more coils.

In addition, the number of the columnar magnetic materials formed within the low-magnetic-permeability portion is not limited to three, and may be two or four or more.

Furthermore, the shape of the transverse section of each columnar magnetic material formed within the low-magnetic-permeability portion is not limited to a circular shape, and may be, for example, elliptical, rectangular, or other polygonal shape.

The inventors conducted the following experiment in order to confirm that the laminated electronic component according to the present disclosure has electrical properties equivalent to those of an existing one and that even when one of a plurality of the columnar magnetic material portions becomes non-penetrating, deterioration of the electrical properties is lower than when a columnar magnetic material portion of a laminated electronic component having only the single columnar magnetic material portion becomes non-penetrating.

As an example, the common mode choke coil100according to the exemplary embodiment described above was prepared. The diameter of each of the three columnar magnetic material portions of the common mode choke coil100, namely, the laminate of the penetrating magnetic materials7a, the laminate of the penetrating magnetic materials7b, and the laminate of the penetrating magnetic materials7c, was set to 0.065 mm.

In addition, as a comparative example, a common mode choke coil including one columnar magnetic material portion within a low-magnetic-permeability portion2was prepared. The transverse section of the columnar magnetic material portion was set to 0.12 mm×0.10 mm. Other than this, there is no difference between the example and the comparative example. More specifically, the configuration of the other portion is the same as that of the example, and the manufacturing method is also the same as that of the example.

The sum of the transverse sectional areas of the three columnar magnetic material portions of the example is 0.01 mm2, the transverse sectional area of the columnar magnetic material portion of the comparative example is 0.012 mm2, and both are substantially equal to each other.

The inventors measured a common-mode impedance (Ω) at 100 MHz with an impedance analyzer for the example and the comparative example. As a result, as shown in Table 1, the common-mode impedance was 160Ω in the example and 180Ω in the comparative example, and the electrical properties of both examples were substantially equal to each other.

TABLE 1Common mode impedance (Ω)PenetratingNon-penetratingmagnetic pathmagnetic pathChange rateExample160130*−19%Comparative18085−53%example*Case where one of three columnar magnetic material portions became non-penetrating.

Next, the inventors measured a common-mode impedance (Ω) at 100 MHz by simulation using an electromagnetic field simulator, when one of the three columnar magnetic material portions became non-penetrating in the example, and when the columnar magnetic material portion became non-penetrating in the comparative example.

As a result, as shown in Table 1, the common-mode impedance was 130Ω in the example and 85Ω in the comparative example. Whereas the change rate in the comparative example when the columnar magnetic material portion became non-penetrating was −53%, the change rate in the example when one of the columnar magnetic material portions became non-penetrating was −19%. Thus, it is recognized that the example has higher robustness when the columnar magnetic material portion becomes non-penetrating, than the comparative example.