Common mode choke coil

A common mode choke coil includes a multilayer body obtained by stacking insulating layers, first and second coils inside the multilayer body, and first to fourth outer electrodes on outer surfaces of the multilayer body. The first and second outer electrodes are respectively connected to first and second ends of the first coil. The third and fourth outer electrodes are respectively connected to first and second ends of the second coil. The first coil includes first to third spiral conductors connected to one another through via conductors. The second coil includes fourth to sixth spiral conductors connected to one another through via conductors. The first spiral conductor is adjacent to the second and fourth spiral conductors. The fourth spiral conductor is adjacent to the first and fifth spiral conductors. The distance between the first and fourth spiral conductors is smaller than the distances between other spiral conductors.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority to Japanese Patent Application No. 2018-020113, filed Feb. 7, 2018, the entire content of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to a common mode choke coil.

Background Art

Common mode choke coils are used to reject common mode noise that can occur in internal circuits of electronic appliances. Japanese Unexamined Patent Application Publication No. 2001-44033 describes a multilayer common mode choke coil, in which a first coil is formed by forming a spiral conductor pattern having one or more turns on each of insulating layers, stacking the resulting insulating layers, and connecting the conductor patterns by using through holes, a second coil is formed by forming a spiral conductor pattern having one or more turns on each of insulating layers, stacking the resulting insulating layers, and connecting the conductor patterns by using through holes, and the insulating layers for the first coil and the insulating layers for the second coil are alternately stacked. The center position of a through hole that connects the spiral conductor patterns is shifted inward or outward from a continuous line extending from a center line of the spiral conductor pattern immediately in front of the through hole.

SUMMARY

As electronic appliances become increasingly high-speed and multifunctional, demand for common mode choke coils having high common mode impedances and high cut-off frequencies has grown. However, existing common mode choke coils tend to have low cut-off frequencies when the common mode impedance is increased, and it has been difficult to achieve both a high common mode impedance and a high cut-off frequency.

It is desirable to provide a common mode choke coil that has a high common mode impedance and a high cut-off frequency. The inventor of the present disclosure has found that a common mode choke coil that has a high common mode impedance and a high cut-off frequency can be obtained by decreasing the distance between spiral conductors in a portion where coupling between a primary coil and a secondary coil is strong, and thus made the present disclosure.

An aspect of the present disclosure provides a common mode choke coil including a multilayer body obtained by stacking a plurality of insulating layers; a first coil and a second coil disposed inside the multilayer body; and a first outer electrode, a second outer electrode, a third outer electrode, and a fourth outer electrode disposed on outer surfaces of the multilayer body. The first outer electrode and the second outer electrode are respectively electrically connected to a first end and a second end of the first coil. The third outer electrode and the fourth outer electrode are respectively electrically connected to a first end and a second end of the second coil. The first coil includes at least a first spiral conductor, a second spiral conductor, and a third spiral conductor that are connected to one another in a stacking direction of the multilayer body through via conductors. The second coil includes at least a fourth spiral conductor, a fifth spiral conductor, and a sixth spiral conductor that are connected to one another in the stacking direction of the multilayer body through via conductors. In the stacking direction, the first spiral conductor is adjacent to the second spiral conductor and the fourth spiral conductor, and the fourth spiral conductor is adjacent to the first spiral conductor and the fifth spiral conductor. Among distances between the spiral conductors adjacent in the stacking direction, a distance between the first spiral conductor and the fourth spiral conductor is smaller than other distances.

The common mode choke coil according to an aspect of the present disclosure and having the aforementioned features has a high common mode impedance and a high cut-off frequency.

DETAILED DESCRIPTION

The embodiments of the present disclosure will now be described with reference to the drawings. The embodiments described below are for the illustrative purposes and do not limit the scope of the present disclosure. The dimensions, materials, shapes, relative positions, etc., of the constituent elements described below are merely illustrative examples and do not limit the scope of the present disclosure unless otherwise specified. Furthermore, the size, shapes, positional relationships, etc., of the constituent elements illustrated in the drawings are sometimes exaggerated to simplify the illustration.

First Embodiment

A schematic perspective view of a common mode choke coil30according to a first embodiment of the present disclosure is shown inFIG. 1. The common mode choke coil30of the first embodiment includes a multilayer body31including a plurality of insulating layers stacked on top of each other, a first coil and a second coil disposed inside the multilayer body31, and a first outer electrode43, a second outer electrode44, a third outer electrode45, and a fourth outer electrode46disposed on outer surfaces of the multilayer body31. In this description, the length, the width, and the thickness (height) of the common mode choke coil30may be respectively referred to as “L”, “W”, and “T” (seeFIG. 1). In this description, the direction parallel to the length L of the multilayer body31may be referred to as the “L direction”, the direction parallel to the width W may be referred to as the “W direction”, and the direction parallel to the thickness T may be referred to as the “T direction”. A surface parallel to the L direction and the T direction may be referred to as the “LT surface”, a surface parallel to the W direction and the T direction may be referred to as the “WT surface”, and a surface parallel to the L direction and the W direction may be referred to as the “LW surface”.

In the structure illustrated inFIG. 1, the multilayer body31has a structure that includes a glass ceramic layer32sandwiched between two ferrite layers33and34. Alternatively, in this embodiment, the multilayer body31may be formed solely of the glass ceramic layer32, or may further include an additional glass ceramic layer on a lower surface side of the ferrite layer33and an additional glass ceramic layer on an upper surface side of the ferrite layer34. Alternatively, the multilayer body31may further include an additional glass ceramic layer on a lower surface side of the ferrite layer33, another additional glass ceramic layer on an upper surface side of the ferrite layer34, and additional ferrite layers on a lower surface side and an upper surface side of the additional glass ceramic layers, respectively.

The glass ceramic layer32is formed of a glass ceramic material. In order to obtain satisfactory high-frequency characteristics, a glass ceramic material is preferably used. In this case, a borosilicate glass mainly composed of Si and B is preferably used. For example, a borosilicate glass having a composition of SiO2: 70 wt % or more and 85 wt % or less (i.e., from 70 wt % to 85 wt %), B2O3: 10 wt % or more and 25 wt % or less (i.e., from 10 wt % to 25 wt %), K2O: 0.5 wt % or more and 5 wt % or less (i.e., from 0.5 wt % to 5 wt %), and Al2O3: 0 wt % or more and 5 wt % or less (i.e., from 0 wt % to 5 wt %) can be used. The glass ceramic layer32may further contain a non-magnetic material such as a Cu—Zn ferrite or a magnetic material such as a Ni—Cu—Zn ferrite. For example, the glass ceramic layer32may be formed of a magnetic material composed of a composite material containing a glass ceramic material and a Ni—Cu—Zn ferrite material.

When the glass ceramic layer32contains a borosilicate glass, the glass ceramic layer32preferably further contains about 2 wt % or more and 30 wt % or less (i.e., from about 2 wt % to 30 wt %) of a filler component, such as quartz (SiO2), forsterite (2 MgO·SiO2), and alumina (Al2O3). A borosilicate glass has a low relative permittivity, and satisfactory high-frequency characteristics can be obtained. Furthermore, since quartz has a relative permittivity lower than the borosilicate glass, addition of quartz can further improve the high-frequency characteristics. Moreover, since forsterite and alumina have high bending strength, adding these can improve the mechanical strength.

Examples of the material constituting the ferrite layers33and34include magnetic materials, such as Ni—Cu—Zn ferrite materials, and nonmagnetic materials, such as Cu—Zn ferrite materials. When the ferrite layers33and34are formed of a magnetic material, namely, a Ni—Cu—Zn ferrite, the inductance (L) of the common mode choke coil can be increased. When the ferrite layers33and34are formed of a nonmagnetic material, the mechanical strength of the common mode choke coil can be improved. As the Ni—Cu—Zn ferrite, the one having a composition of Fe2O3: 40 mol % or more and 49.5 mol % or less (i.e., from 40 mol % to 49.5 mol %), ZnO: 5 mol % or more and 35 mol % or less (i.e., from 5 mol % to 35 mol %), CuO: 4 mol % or more and 12 mol % or less (i.e., from 4 mol % to 12 mol %), and the balance: NiO and trace additives (including unavoidable impurities) can be used. In this embodiment, the ferrite layers33and34are not essential.

When the multilayer body31further includes a glass ceramic layer on a lower surface side of the ferrite layer33and a glass ceramic layer on an upper surface side of the ferrite layer34, structural defects, such as separation between the glass ceramic layer32and the ferrite layer33and between the glass ceramic layer32and the ferrite layer34, can be suppressed. These additional glass ceramic layers are preferably formed of the same material as the glass ceramic layer32. In this embodiment, the additional glass ceramic layers on the lower surface side and the upper surface side of the ferrite layer33and the ferrite layer34, respectively, are not essential.

When the multilayer body31further includes additional glass ceramic layers on a lower surface side of the ferrite layer33and on an upper surface side of the ferrite layer34, respectively, and additional ferrite layers on a lower surface side and an upper surface side of these additional glass ceramic layers, respectively, the flexural strength of the multilayer body31can be improved. These additional ferrite layers are preferably formed of the same material as the ferrite layers33and34. In this embodiment, these additional ferrite layers are not essential.

The first outer electrode43, the second outer electrode44, the third outer electrode45, and the fourth outer electrode46are formed on the outer surfaces of the multilayer body31. Specifically, the first outer electrode43and the fourth outer electrode46are located at a side surface47of the multilayer body31, and the second outer electrode44and the third outer electrode45are located at a side surface48facing the side surface47. The outer electrodes43to46can be formed of a conductor material such as a metal such as Cu, Pd, Al, or Ag or an alloy thereof. The first outer electrode43and the second outer electrode44are respectively electrically connected to a first end and a second end of the first coil, and the third outer electrode45and the fourth outer electrode46are respectively electrically connected to a first end and a second end of the second coil.

One example of an internal structure of the multilayer body in the common mode choke coil of the first embodiment is schematically illustrated inFIG. 2. The glass ceramic layer32has a multilayer structure constituted by a stack of insulating layers that include eight insulating layers301to308illustrated inFIG. 2. The insulating layers may each be formed of a single insulator sheet, or multiple insulator sheets may be stacked to serve as one insulating layer. The insulating layers301to308are stacked in this order from the bottom. Spiral conductors501to506are respectively formed on the insulating layers302to307. The spiral conductors501to506each have an inner peripheral end portion, which is located relatively near the center of the corresponding one of the insulating layers302to307, and an outer peripheral end portion, which is located relatively near the outer periphery. The spiral conductors501to506are actually formed to extend along the interfaces between the adjacent insulating layers301to308; however, for the purpose of the description, the spiral conductors501to506are assumed to be disposed on the insulating layers302to307.

A first coil and a second coil are formed inside the multilayer body31, more specifically, inside the glass ceramic layer32. The first coil includes at least a first spiral conductor, a second spiral conductor, and a third spiral conductor that are connected to one another through via conductors in the stacking direction of the multilayer body31. The second coil includes at least a fourth spiral conductor, a fifth spiral conductor, and a sixth spiral conductor that are connected to one another through via conductors in the stacking direction of the multilayer body31. In the example illustrated inFIG. 2, the first coil includes spiral conductors501,504, and505and via conductors603and606, and the second coil includes spiral conductors502,503, and506and via conductors604and605. The first coil further includes an extended conductor702electrically connected to the second outer electrode44, a via conductor602connecting the extended conductor702to the spiral conductor501, an extended conductor704electrically connected to the first outer electrode43, and a via conductor607connecting the extended conductor704to the spiral conductor505. The second coil further includes an extended conductor701electrically connected to the third outer electrode45, a via conductor601connecting the extended conductor701to the spiral conductor502, an extended conductor703electrically connected to the fourth outer electrode46, and a via conductor608connecting the extended conductor703to the spiral conductor506.

First, the connection configuration of the spiral conductors501,504, and505constituting the first coil is described. The description is provided in the order of stacking from the bottom. That is, the outer peripheral end portion of the spiral conductor501formed on the insulating layer302is connected to the extended conductor702formed on the insulating layer301through the via conductor602penetrating through the insulating layer302. The extended conductor702is extended as far as the outer peripheral edge of the insulating layer301. Meanwhile, the inner peripheral end portion of the spiral conductor501is connected to the via conductor603penetrating through the insulating layers303,304, and305.

Next, the via conductor603is connected to the inner peripheral end portion of the spiral conductor504formed on the insulating layer305. As a result, the inner peripheral end portion of the spiral conductor501and the inner peripheral end portion of the spiral conductor504are connected to each other through the via conductor603. The outer peripheral end portion of the spiral conductor504is connected to the via conductor606penetrating through the insulating layer306.

Next, the via conductor606is connected to the outer peripheral end portion of the spiral conductor505formed on the insulating layer306. As a result, the outer peripheral end portion of the spiral conductor504and the outer peripheral end portion of the spiral conductor505are connected to each other through the via conductor606. The inner peripheral end portion of the spiral conductor505is connected to the via conductor607penetrating through the insulating layers307and308.

Next, the via conductor607is connected to the extended conductor704formed on the insulating layer308, and the extended conductor704is extended as far as the outer peripheral edge of the insulating layer308.

As described above, the first coil is formed by connecting the spiral conductors501,504, and505sequentially through the via conductors603and606.

Next, the connection configuration of the spiral conductors502,503, and506constituting the second coil is described. The description is provided in the order of stacking from the bottom. That is, the inner peripheral end portion of the spiral conductor502formed on the insulating layer303is connected to the extended conductor701formed on the insulating layer301through the via conductor601penetrating through the insulating layers303and302. The extended conductor701is extended as far as the outer peripheral edge of the insulating layer301. Meanwhile, the outer peripheral end portion of the spiral conductor502is connected to the via conductor604penetrating through the insulating layer304.

Next, the via conductor604is connected to the outer peripheral end portion of the spiral conductor503formed on the insulating layer304. As a result, the outer peripheral end portion of the spiral conductor502and the outer peripheral end portion of the spiral conductor503are connected to each other through the via conductor604. The inner peripheral end portion of the spiral conductor503is connected to the via conductor605penetrating through the insulating layers305,306, and307.

Next, the via conductor605is connected to the inner peripheral end portion of the spiral conductor506formed on the insulating layer307. As a result, the inner peripheral end portion of the spiral conductor503and the inner peripheral end portion of the spiral conductor506are connected to each other through the via conductor605. The outer peripheral end portion of the spiral conductor506is connected to the via conductor608penetrating through the insulating layer308.

Next, the via conductor608is connected to the extended conductor703formed on the insulating layer308, and the extended conductor703is extended as far as the outer peripheral edge of the insulating layer308.

As described above, the second coil is formed by connecting the spiral conductors502,503, and506sequentially through the via conductors604and605.

Examples of the conductor material contained in the spiral conductors501to506, the via conductors601to608, and the extended conductors701to704include conductive metals, such as Cu, Pd, Al, and Ag, and alloys thereof.

Another example of the internal structure of the multilayer body in the common mode choke coil of the first embodiment is schematically illustrated inFIG. 3. The glass ceramic layer32has a multilayer structure constituted by a stack of insulating layers that include eight insulating layers311to318illustrated inFIG. 3. The insulating layers311to318are stacked in this order from the bottom. Spiral conductors511to516are respectively formed on the insulating layers312to317. The spiral conductors511to516each have an inner peripheral end portion, which is located relatively near the center of the corresponding one of the insulating layers312to317, and an outer peripheral end portion, which is located relatively near the outer periphery. The spiral conductors511to516are actually formed to extend along the interfaces between the adjacent insulating layers311to318; however, for the purpose of the description, the spiral conductors511to516are assumed to be disposed on the insulating layers312to317.

In the example illustrated inFIG. 3, the first coil includes spiral conductors511,514, and515and via conductors612and615, and the second coil includes spiral conductors512,513, and516and via conductors611,613, and614. The first coil further includes an extended conductor712electrically connected to the first outer electrode43, and a via conductor616connecting the extended conductor712to the spiral conductor515. The second coil further includes an extended conductor711electrically connected to the third outer electrode45, and a via conductor611connecting the extended conductor711to the spiral conductor512. The connection configuration of the spiral conductors511,514, and515constituting the first coil is the same as the example illustrated inFIG. 2except that the outer peripheral end portion of the spiral conductor511is extended to the outer peripheral edge of the insulating layer312so as to be electrically connected to the second outer electrode44. In the same manner, the connection configuration of the spiral conductors512,513, and516constituting the second coil is the same as the example illustrated inFIG. 2except that the outer peripheral end portion of the spiral conductor516is extended to the outer peripheral edge of the insulating layer317so as to be electrically connected to the fourth outer electrode46.

In the structural example illustrated inFIG. 2, the first spiral conductor constituting the first coil corresponds to the spiral conductor504, the second spiral conductor corresponds to the spiral conductor505, and the third spiral conductor corresponds to the spiral conductor501. Furthermore, the fourth spiral conductor constituting the second coil corresponds to the spiral conductor503, the fifth spiral conductor corresponds to the spiral conductor502, and the sixth spiral conductor corresponds to the spiral conductor506. Similarly, in the structural example illustrated inFIG. 3, the first spiral conductor constituting the first coil corresponds to the spiral conductor514, the second spiral conductor corresponds to the spiral conductor515, and the third spiral conductor corresponds to the spiral conductor511. Furthermore, the fourth spiral conductor constituting the second coil corresponds to the spiral conductor513, the fifth spiral conductor corresponds to the spiral conductor512, and the sixth spiral conductor corresponds to the spiral conductor516. Although the distances between the spiral conductors are described below by using the structure illustrated inFIG. 2as an example, the description below equally applies to the structural example illustrated inFIG. 3.

A section taken in parallel to the stacking direction of the common mode choke coil of the first embodiment is schematically illustrated inFIG. 4. As illustrated inFIG. 4, in the stacking direction of the multilayer body31, the first spiral conductor504is adjacent to the second spiral conductor505and the fourth spiral conductor503, and the fourth spiral conductor503is adjacent to the first spiral conductor504and the fifth spiral conductor502.

Among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distance between the first spiral conductor504and the fourth spiral conductor503(indicated by reference sign A inFIG. 4) is smaller than other distances. By setting the distance between the first spiral conductor504and the fourth spiral conductor503to be smaller than other distances, the common mode impedance can be increased, and the cut-off frequency can be increased. It should be noted that, among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distances other than the distance between the first spiral conductor504and the fourth spiral conductor503may be simply referred to as “other distances”. Here, when, among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distances other than the distance between the first spiral conductor504and the fourth spiral conductor503are not all the same, the phrase “the distance between the first spiral conductor and the fourth spiral conductor is smaller than other distances” means that the distance between the first spiral conductor and the fourth spiral conductor is smaller than the smallest distance among these “other distances”.

The distance between the adjacent spiral conductors can be measured by the following method. First, a sample of the common mode choke coil30is positioned upright and is surrounded by a resin to immobilize. At this stage, the LT surface (for example, the side surface47or48) is exposed. Using a polisher, the sample is polished to a depth of about ½ of the width W in the W direction so as to expose a section (LT section) parallel to the LT surface. Subsequently, in order to remove sagging of the coil conductors caused by polishing, ion milling (ion milling system IM 4000 produced by Hitachi High-Technologies Corporation) is used to polish the surface. The resulting polished surface of the sample is photographed with a digital microscope (VHX-6000 produced by Keyence Corporation). As illustrated inFIG. 5, a perpendicular line P substantially bisecting the length L of the multilayer body31is drawn in the photograph thus taken, a horizontal line C extending in the L direction and connecting the lower ends of one (spiral conductor A) of the adjacent two spiral conductors to be measured is drawn, and a horizontal line D that connects the upper ends of the other one (spiral conductor B) of the adjacent two spiral conductors is drawn. The distance between the horizontal line C and the horizontal line D is measured along the perpendicular line P, and this distance is assumed to be the distance between the adjacent spiral conductors A and B. Note that, although the cross-sectional shape of the spiral conductor is substantially elliptical inFIG. 5, the cross-sectional shape of the spiral conductor is not limited to the shape illustrated inFIG. 5.

As described below, existing common mode choke coils tend to have low cut-off frequencies when the common mode impedance is increased, and it has been difficult to achieve both a high common mode impedance and a high cut-off frequency. A conceivable approach to increasing the common mode impedance is to decrease the distances between the spiral conductors. However, decreasing the distances between the spiral conductors increases the stray capacitance between the primary coil and the secondary coil, and a high cut-off frequency cannot be achieved.

In the common mode choke coil of this embodiment, the coupling between the primary coil and the secondary coil (first coil and the second coil) is strongest between the first spiral conductor504and the fourth spiral conductor503. Thus, decreasing the distance between spiral conductors in the region where the coupling between the primary coil and the secondary coil is strongest further strengthens the coupling between the primary coil and the secondary coil, and the cut-off frequency can be increased. Meanwhile, by relatively increasing distances between other spiral conductors in the regions where the coupling between the primary coil and the secondary coil is relatively weak, the stray capacitance between the primary coil and the secondary coil can be reduced while suppressing degradation of the coupling between the coils, and thus, the cut-off frequency can be increased. In this manner, the common mode choke coil of this embodiment can achieve both a high common mode impedance and a high cut-off frequency.

The distance between the first spiral conductor504and the fourth spiral conductor503is preferably 2 μm or more smaller than other distances. By setting the distances between the spiral conductors as such, the cut-off frequency can be made even higher.

In a preferred embodiment, the distance between the first spiral conductor504and the fourth spiral conductor503is 2 μm or more and 30 μm or less (i.e., from 2 μm to 30 μm), and other distances are 4 μm or more and 32 μm or less (i.e., from 4 μm to 32 μm). By setting the distances between the spiral conductors as such, a satisfactory filling ratio can be ensured for the via conductors that connect the spiral conductors to one another, and the short-circuiting risk caused by diffusion of the conductor material (such as Ag) constituting the via conductors into the glass ceramic layer can be reduced.

A section taken in parallel to the stacking direction of a modification example of the common mode choke coil of the first embodiment is schematically illustrated inFIG. 6. As illustrated inFIG. 6, among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distance between at least one of the spiral conductors501and506located in two ends in the stacking direction and the spiral conductor502and/or spiral conductor505adjacent to the spiral conductor501and/or spiral conductor506is preferably larger than other distances. Note that in the structure illustrated inFIG. 6, the distance (indicated by reference sign B) between the spiral conductor501and the spiral conductor502and the distance (indicated by reference sign B) between the spiral conductor505and the spiral conductor506are both larger than other distances. The regions between the spiral conductors located in two ends in the stacking direction and the spiral conductors adjacent to these spiral conductors are regions where the coupling between the primary coil and the secondary coil is weakest. Thus, by increasing the distances between the spiral conductors in these regions, the stray capacitance between the primary coil and the secondary coil can be decreased while suppressing degradation of coupling between the coils, and the cut-off frequency can be made even higher.

Among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distance between at least one of the spiral conductors501and506located in two ends in the stacking direction and the spiral conductor502and/or spiral conductor505adjacent to the spiral conductor501and/or spiral conductor506is preferably 2 μm or more larger than other distances. By setting the distances between the spiral conductors as such, degradation of the coupling between the coils can be further suppressed, the stray capacitance between the primary coil and the secondary coil can be further decreased, and the cut-off frequency can be made even higher.

In a preferred embodiment, among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distance between the first spiral conductor504and the fourth spiral conductor503is 2 μm or more and 28 μm or less (i.e., from 2 μm to 28 μm), the distance between at least one of the spiral conductors501and506located in two ends in the stacking direction and the spiral conductor502and/or spiral conductor505adjacent to the spiral conductor501and/or spiral conductor506is 6 μm or more and 32 μm or less (i.e., from 6 μm to 32 μm), and other distances are 4 μm or more and 30 μm or less (i.e., from 4 μm to 30 μm). By setting the distances between the spiral conductors as such, a satisfactory filling ratio can be ensured for the via conductors that connect the spiral conductors to one another, and the short-circuiting risk caused by diffusion of the conductor material (such as Ag) constituting the via conductors into the glass ceramic layer can be reduced.

Next, a method for manufacturing a common mode choke coil is described below; however, the method for manufacturing the common mode choke coil of this embodiment is not limited to the method described below.

Preparation of Glass Ceramic Sheets

A borosilicate glass powder having a particular composition is prepared. Particular amounts of quartz (SiO2), forsterite (2MgO·SiO2) and alumina (Al2O3), etc., are added thereto to serve as a filler, and the resulting mixture is placed in a pot mill together with an organic binder, an organic solvent, a plasticizer, and partially stabilized zirconia (PSZ) balls, and the resulting mixture is mixed and pulverized. The obtained slurry is formed into sheets by a doctor blade method or the like, and rectangular glass ceramic sheets are punched out from the obtained sheets.

Preparation of Ferrite Sheets

Ferrite raw materials, such as Fe2O3, ZnO, CuO, and NiO, are weighed to yield a particular composition, and the weighed materials are placed in a pot mill together with pure water and PSZ balls. The resulting mixture is wet-mixed and pulverized, dried by evaporation, and calcined for a particular length of time at a temperature of 700° C. or higher and 800° C. or lower to prepare a calcined powder.

Next, the calcined powder is placed in a pot mill again together with an organic binder, an organic solvent, and PSZ balls, and the resulting mixture is mixed and pulverized. The obtained slurry is formed into sheets by a doctor blade method or the like, and rectangular ferrite sheets are punched out from the obtained sheets.

Preparation of Common Mode Choke Coil

Via holes are formed at particular positions in the glass ceramic sheets by laser irradiation, and the via holes are filled with a conductive paste (Ag paste or the like). Next, spiral conductors and extended conductors are formed by screen printing using a conductive paste. The conductive paste may contain a metal oxide such as Al2O3. The content of the metal oxide, such as Al2O3, is preferably about 0.02 wt % or more and 0.2 wt % or less (i.e., from about 0.02 wt % to 0.2 wt %) relative to the total weight of the metal, such as Ag, and the metal oxide. The method for forming the spiral conductors and the extended conductors is not limited to screen printing and may be formed by plating, for example.

The glass ceramic sheets (in other words, the insulating layers) are stacked in the order illustrated inFIG. 2, a particular number of the ferrite sheets are stacked above and under the resulting stack of the glass ceramic sheets, and, in some cases, a particular number of glass ceramic sheets are further stacked above and under the resulting stack of the glass ceramic sheets and the ferrite sheets. The obtained stack is press-bonded under heating and is cut with a dicer or the like into individual pieces. As a result, a multilayer formed body is prepared. Press bonding may be performed by a process such as isostatic pressing. Next, the multilayer formed body is heated to 350° C. or higher and 500° C. or lower (i.e., from 350° C. to 500° C.) in a firing furnace in an air atmosphere to perform debinding, and then fired at a temperature of 850° C. or higher and 920° C. or lower (i.e., from 850° C. to 920° C.) to obtain a multilayer body. The multilayer body is subjected to a barrel treatment, an outer electrode conductive paste containing a Ag powder and a particular amount of glass frit is applied to a particular position of the multilayer body and fired at a temperature of about 900° C. so as to form a base electrode. Plating is performed on the base electrode by using Ni, Cu, Sn, and the like. For example, a Ni layer and a Sn layer may be sequentially formed on the base electrode by plating. As a result, a common mode choke coil is obtained.

Second Embodiment

Next, a common mode choke coil according to a second embodiment of the present disclosure is described below. One example of an internal structure of a multilayer body in the common mode choke coil of the second embodiment is schematically illustrated inFIG. 7. The common mode choke coil of the second embodiment differs from the common mode choke coil of the first embodiment in that the first coil further includes a seventh spiral conductor and the second coil further includes an eighth spiral conductor. The structures related to these differences are described below. For other features, the common mode choke coil of the second embodiment has similar structures as those of the first embodiment, and the descriptions therefor are omitted. The common mode choke coil according to the second embodiment has a high common mode impedance and a high cut-off frequency, as with the common mode choke coil of the first embodiment.

The glass ceramic layer in the structure illustrated inFIG. 7has a multilayer structure constituted by a stack of insulating layers that include eight insulating layers321to328. The insulating layers may each be formed of a single insulator sheet, or multiple insulator sheets may be stacked to serve as one insulating layer. The insulating layers321to328are stacked in this order from the bottom. Spiral conductors521to528are respectively formed on the insulating layers322to327. The spiral conductors521to528each have an inner peripheral end portion, which is located relatively near the center of the corresponding one of the insulating layers321to328, and an outer peripheral end portion, which is located relatively near the outer periphery. The spiral conductors521to528are actually formed to extend along the interfaces between the adjacent insulating layers321to328; however, for the purpose of the description, the spiral conductors521to528are assumed to be disposed on the insulating layers321to328.

A first coil and a second coil are formed inside the multilayer body, more specifically, inside the glass ceramic layer. The first coil includes a first spiral conductor, a second spiral conductor, a third spiral conductor, and a seventh spiral conductor that are connected to one another through via conductors in the stacking direction of the multilayer body. The second coil includes a fourth spiral conductor, a fifth spiral conductor, a sixth spiral conductor, and an eighth spiral conductor that are connected to one another through via conductors in the stacking direction of the multilayer body. In the structure illustrated inFIG. 7, the first coil includes spiral conductors521,523,524, and527and via conductors621,623, and624, and the second coil includes spiral conductors522,525,526, and528and via conductors622,625, and626. The outer peripheral end portion of the spiral conductor521of the first coil is extended as far as the outer peripheral edge of the insulating layer321so as to be electrically connected to the first outer electrode, and the outer peripheral end portion of the spiral conductor527is extended as far as the outer peripheral edge of the insulating layer327so as to be electrically connected to the second outer electrode. The outer peripheral end portion of the spiral conductor522of the second coil is extended as far as the outer peripheral edge of the insulating layer322so as to be electrically connected to the fourth outer electrode, and the outer peripheral end portion of the spiral conductor528is extended as far as the outer peripheral edge of the insulating layer328so as to be electrically connected to the third outer electrode.

A section taken in parallel to the stacking direction of the common mode choke coil of the second embodiment is schematically illustrated inFIG. 8. As illustrated inFIG. 8, in the stacking direction of the multilayer body31, the first spiral conductor524is adjacent to the second spiral conductor523and the fourth spiral conductor525, and the fourth spiral conductor525is adjacent to the first spiral conductor524and the fifth spiral conductor526.

Among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distance between the first spiral conductor524and the fourth spiral conductor525(indicated by reference sign A inFIG. 8) is smaller than other distances. By setting the distance between the first spiral conductor524and the fourth spiral conductor525to be smaller than other distances, the common mode impedance can be increased, and the cut-off frequency can be increased. It should be noted that, among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distances other than the distance between the first spiral conductor524and the fourth spiral conductor525may be simply referred to as “other distances”.

In the structure illustrated inFIG. 8, among the distances between the spiral conductors adjacent in the stacking direction of the multilayer body31, the distance (indicated by reference sign B) between at least one of the spiral conductors521and528located in two ends in the stacking direction and the spiral conductor522and/or spiral conductor527adjacent to the spiral conductor521and/or spiral conductor528is preferably larger than other distances. Thus, by setting the distances between the spiral conductors as such, the stray capacitance between the primary coil and the secondary coil can be decreased while suppressing degradation of the coupling between the coils, and the cut-off frequency can be made even higher.

Although common mode choke coils related to the present disclosure are described above by taking, as examples, structures in which the first coil and the second coil each include three or four layers of spiral conductors, the present disclosure is not limited to the structures described above. The first coil and the second coil may each include 5 or more layers of spiral conductors, and in such a case also, a common mode choke coil that has a high common mode impedance and a high cut-off frequency can be obtained.

Common mode choke coils of Examples 1 to 10 were prepared by the procedure described below.

Preparation of Glass Ceramic Sheets

A glass powder having a composition of 78 wt % SiO2, 20 wt % B2O3, and 2 wt % K2O with an average particle diameter of 1.0 μm was prepared as the borosilicate glass powder. A quartz powder and an alumina powder having an average particle diameter of 0.5 μm or more and 1.5 μm or less (i.e., from 0.5 μm to 1.5 μm) were prepared as the filler. The raw materials were weighed and mixed so as to yield a composition containing 85 wt % glass powder, 12 wt % quartz powder, and 3 wt % alumina powder, and the resulting mixture was placed in a pot mill together with an organic binder such as a polyvinyl butyral resin, an organic solvent such as ethanol and toluene, a plasticizer, and PSZ balls. The resulting mixture was thoroughly mixed and pulverized to prepare a glass ceramic slurry. The slurry was formed into sheets by a doctor blade method to prepare glass ceramic sheets.

Preparation of Ferrite Sheets

Raw materials were weighed so that the ferrite composition was 48 mol % Fe2O3, 26 mol % ZnO, 8 mol % CuO, and the balance being NiO. The weighed materials were placed in a pot mill together with pure water and balls such as PSZ balls, and the resulting mixture was thoroughly wet-mixed and pulverized, dried by evaporation, and calcined for a particular length of time at a temperature of 700° C. As a result, a calcined powder was obtained. The calcined powder was placed again in a pot mill together with an organic binder such as a polyvinyl butyral organic binder, an organic solvent such as ethanol and toluene, and PSZ balls. The resulting mixture was thoroughly mixed and pulverized to prepare a ferrite slurry. The slurry was formed into sheets by a doctor blade method to prepare ferrite sheets.

Preparation of Common Mode Choke Coil

Via holes were formed at particular positions in the glass ceramic sheets by laser irradiation, and the via holes were filled with a conductive paste (Ag paste). Next, spiral conductors were formed by screen printing. A paste containing 0.1 wt % of Al2O3powder relative to the total weight of the Al2O3powder and Ag powder was used as the conductive paste. The glass ceramic sheets were stacked in the order illustrated inFIG. 7, a particular number of the ferrite sheets were stacked above and under the resulting stack of the glass ceramic sheets, and, a particular number of glass ceramic sheets were further stacked above and under the resulting stack of the glass ceramic sheets and the ferrite sheets. The obtained stack was press-bonded under heating and was cut with a dicer or the like into individual pieces. As a result, a multilayer formed body was prepared. The thicknesses of the glass ceramic sheets were set so that the distances between the spiral conductors were as indicated in Table 1. In Table 1 and Table 2 below, the “distance between spiral conductors at the center” means the distance between the first spiral conductor and the fourth spiral conductor, and is a distance of the portion indicated by reference sign A inFIG. 8.

Next, this multilayer formed body was heated to 350° C. or higher and 500° C. or lower (i.e., from 350° C. to 500° C.) in a firing furnace in an air atmosphere to perform debinding, and then fired at a temperature of 900° C. to obtain a multilayer body.

The multilayer body was subjected to a barrel treatment, an outer electrode conductive paste containing a Ag powder and a particular amount of glass frit was applied to a particular position and fired at a temperature of about 800° C. so as to form a base electrode. Common mode choke coils of Examples 1 to 10 were prepared by sequentially forming a Ni layer and a Sn layer on the base electrode. The dimensions of the common mode choke coil were length L: 0.65 mm, width W: 0.50 mm, and thickness T: 0.30 mm.

For the obtained common mode choke coils, an impedance analyzer “E4991A” produced by Agilent Technologies was used to measure the common mode impedance at a temperature of 20±3° C. and a frequency of 100 MHz. A network analyzer “E5071B” produced by Agilent Technologies was used to measure the cut-off frequency at a temperature of 20±3° C. The results are shown in Table 1 andFIG. 9. In Table 1, the asterisked samples are comparative examples.

TABLE 1Example1234567*8*9*10*Distance between spiral1312108641418106conductors at the center (μm)Other distances (μm)1414141414141418106Common mode impedance Zc49505051515249425973(Ω)Cut-off frequency fc (GHz)3.73.844.34.65.13.64.432.4

Common mode choke coils of Examples 11 to 18 were prepared by the same procedure as in Example 1 except that the distances between the spiral conductors were set to the values shown in Table 2, and the common mode impedance and the cut-off frequency were measured. The results are shown in Table 2 andFIG. 9. In Table 2 below, the “distances between spiral conductors in two end portions” means the distances between the respective spiral conductors located in two end portions in the stacking direction and the respective spiral conductors adjacent thereto, and are distances of the portions indicated by reference sign B inFIG. 8.

As apparent from Tables 1 and 2 andFIG. 9, in Examples 7 to 10 in which the distances between the spiral conductors were all the same, the common mode impedance increased by decreasing the distances between the spiral conductors but the cut-off frequency decreased. In contrast, in Examples 1 to 6 in which only the distance between the first spiral conductor and the fourth spiral conductor is decreased, the common mode impedance increased with the decrease in the distance between the first spiral conductor and the fourth spiral conductor, and the cut-off frequency also increased. This tendency is completely different from the tendency observed in Examples 7 to 10, which are comparative examples, and has not been seen in existing common mode choke coils. The measurement results in Examples 11 to 18 show that, by setting the distances between the spiral conductors in the two end portions in the stacking direction and the spiral conductors adjacent thereto to be larger than other distances, the stray capacitance between the primary coil and the secondary coil can be decreased while suppressing degradation of the coupling between the coils, and the cut-off frequency can be increased.

The present disclosure includes the following nonlimiting aspects.

A common mode choke coil includes a multilayer body obtained by stacking a plurality of insulating layers; a first coil and a second coil disposed inside the multilayer body; and a first outer electrode, a second outer electrode, a third outer electrode, and a fourth outer electrode disposed on outer surfaces of the multilayer body. The first outer electrode and the second outer electrode are respectively electrically connected to a first end and a second end of the first coil. The third outer electrode and the fourth outer electrode are respectively electrically connected to a first end and a second end of the second coil. The first coil includes at least a first spiral conductor, a second spiral conductor, and a third spiral conductor that are connected to one another in a stacking direction of the multilayer body through via conductors. The second coil includes at least a fourth spiral conductor, a fifth spiral conductor, and a sixth spiral conductor that are connected to one another in the stacking direction of the multilayer body through via conductors. In the stacking direction, the first spiral conductor is adjacent to the second spiral conductor and the fourth spiral conductor, and the fourth spiral conductor is adjacent to the first spiral conductor and the fifth spiral conductor, and among distances between the spiral conductors adjacent in the stacking direction, a distance between the first spiral conductor and the fourth spiral conductor is smaller than other distances.

The common mode choke coil according to aspect 1, wherein the distance between the first spiral conductor and the fourth spiral conductor is 2 μm or more smaller than other distances.

The common mode choke coil according to aspect 1 or 2, wherein the distance between the first spiral conductor and the fourth spiral conductor is 2 μm or more and 30 μm or less (i.e., from 2 μm to 30 μm), and other distances are 4 μm or more and 32 μm or less (i.e., from 4 μm to 32 μm).

The common mode choke coil according to any one of aspects 1 to 3, wherein the first coil further includes a seventh spiral conductor, and the second coil further includes an eighth spiral conductor.

The common mode choke coil according to any one of aspects 1 to 4, wherein, among the distances between the spiral conductors adjacent in the stacking direction, a distance between at least one of the spiral conductors located in two end portions in the stacking direction and the spiral conductor adjacent to the at least one spiral conductor is larger than other distances.

The common mode choke coil according to aspect 5, wherein, among the distances between the spiral conductors adjacent in the stacking direction, the distance between at least one of the spiral conductors located in two end portions in the stacking direction and the spiral conductor adjacent to the at least one spiral conductor is 2 μm or more larger than other distances.

The common mode choke coil according to aspect 5 or 6, wherein, among the distances between the spiral conductors adjacent in the stacking direction, the distance between the first spiral conductor and the fourth spiral conductor is 2 μm or more and 28 μm or less (i.e., from 2 μm to 28 μm), and the distance between at least one of the spiral conductors located in two end portions in the stacking direction and the spiral conductor adjacent to the at least one spiral conductor is 6 μm or more and 32 μm or less (i.e., from 6 μm to 32 μm), and other distances are 4 μm or more and 30 μm or less (i.e., from 4 μm to 30 μm).

The common mode choke coil according to an embodiment of the present disclosure has a high common mode impedance and excellent high-frequency characteristics, and thus can be widely used in high-frequency usages such as high-frequency noise rejection.