Patent Application
20150070120
1. Field of the Invention
The present technical field relates to a coil component having an exterior body that has an anisotropic thermal conductivity, a method for manufacturing the coil component, and a coil electronic component using the coil component.
2. Description of the Related Art
A coil component of the present disclosure has a wound coil, a coil magnetic body, and an exterior body. The coil magnetic body has a magnetic core inside winding of the wound coil. The exterior body covers a surface of the coil magnetic body. This coil component has a mount surface, and a thermal conductivity in a direction parallel to a surface of the exterior body is greater than a thermal conductivity in a direction perpendicular to the surface of the exterior body.
With the above configuration, this coil component allows heat generated from the coil magnetic body to be conducted preferentially to the mounting substrate through the exterior body. Hence, it is possible to suppress radiation of the heat to outside air, and to reduce an influence on other mounted components.
Prior to the description of an exemplary embodiment of the present disclosure, a problem of the conventional coil component will be briefly described. In coil component 108 illustrated in
Hereinafter, coil component 13 according to the exemplary embodiment of the present disclosure will be described with reference to the drawings.
Coil component 13 has wound coil 2, coil magnetic body 3, and exterior body 4. Coil magnetic body 3 has a magnetic core inside winding of wound coil 2. Exterior body 4 covers a surface of coil magnetic body 3. Coil component 13 has mount surface 29, and a thermal conductivity in a direction parallel to a surface of exterior body 4, indicated by arrow 5, is greater than a thermal conductivity in a direction perpendicular to the surface of exterior body 4, indicated by arrow 6.
That is, exterior body 4 has an anisotropic thermal conductivity. The thermal conductivity in the direction parallel to the surface of exterior body 4 is greater than the thermal conductivity in the direction perpendicular to the surface of exterior body 4. Therefore, heat generated in coil magnetic body 3 is transferred preferentially in a direction toward mounting substrate 10. Hence, it is possible to suppress radiation of the heat to the outside air. As described above, by transferring the heat more preferentially to mounting substrate 10 than to the outside air, it is possible to reduce an influence by the heat on other mounted components. Although it is possible to dispose each of the components in consideration of the influence by the heat on the other mounted components, such restriction causes an increase in area of the mounting substrate and leads to an increase in product size. However, the use of coil component 13 eliminates the need for considering such a disposition.
Note that coil component 13 and mounting substrate 10 configure the coil electronic component. Coil component 13 is mounted to mounting substrate 10 at mount surface 29.
Next, magnetic body 1 will be described. Examples of a main material for magnetic body 1 include a variety of ferrite sintered bodies such as an Ni—Zn based ferrite sintered body and an Mn—Zn based ferrite sintered body, and soft magnetic metal magnetic powders such as a Fe powder, a Fe—Ni alloy powder, a Fe—Si alloy powder, a Fe—Al—Si alloy powder, an amorphous alloy powder, and a metal glass alloy powder. Magnetic body 1 is a powder magnetic core formed by molding the above material at high pressure, or a laminate formed by laminating thin plates or thin bands.
Next, wound coil 2 will be described. Examples of a raw material for wound coil 2 include metals having a small electric resistivity, such as Au, Ag, and Cu, and an alloy whose main component is any of these metals. Further, in consideration of reducing a weight of coil component 13, a light metal such as Al may be used as the main component.
An insulating film is formed on a surface of wound coil 2. This film can suppress contact between portions of the wire of wound coil 2. Alternatively, when adjacent portions of the wires are electrically insulated from each other, there is no need to provide the insulating film.
It is not limited to use just one wound coil 2, and a plurality of wound coils 2 may be used. Further, examples of a cross sectional shape of the wire of wound coil 2 include shapes of a round, a square, and a rectangular, or the cross sectional shape may be elliptical or polygonal transformed from those wire shapes. Moreover, in order to improve a withstand voltage and insulating resistance, a bobbin may be provided between magnetic body 1 and wound coil 2. In the case of using the rectangular wire as wound coil 2, a winding method is not particularly limited, and edgewise winding, flatwise winding, and the like can be applied.
A description will be given below of coil magnetic body 3 configured by wound coil 2 and magnetic body 1 that is disposed inside the winding of wound coil 2. There are a variety of shapes for coil magnetic body 3. In particular, a shape of magnetic body 1 may be a variety of variant shapes such as a toroidal shape, a U-shape, an E-shape, an I-shape, a pod shape, and a spherical shape. Further, these shapes may be combined. Moreover, for the purpose of suppressing decrease in inductance value during passage of a current through wound coil 2, a non-magnetic body or a clearance can be provided as a gap part in a part of magnetic body 1.
Next, mounting substrate 10 for mounting coil component 13 thereto will be described. A material for mounting substrate 10 is not particularly limited, and metal, ceramic, or a resin can be used, or a compound of these materials can also be used. Note that, in order to dissipate heat generated in coil component 13, it is preferable that a thermal conductivity of mounting substrate 10 be high. Further, mounting substrate 10 is preferably cooled by some configuration. For example, there can be used a technique such as water cooling by use of water or a liquid coolant such as an anti-freezing solution, or air cooling by forced air cooling or natural air cooling.
Next, exterior body 4 will be described. As illustrated in
As a raw material for exterior body 4, a resin material, a metal material, or a ceramic material can be used, or the raw material for exterior body 4 can also be formed by combining these materials. Further, exterior body 4 can be provided on the surface of coil magnetic body 3 by a method of separately preparing exterior body 4 and coil magnetic body 3 and combining exterior body 4 with coil magnetic body 3, or by a method of integrally forming exterior body 4 with coil magnetic body 3 as described below. From a viewpoint of efficiently sending the heat generated from coil magnetic body 3, it is preferable that exterior body 4 and coil magnetic body 3 be integrally formed with no gap therebetween.
A shape of coil component 13 is not particularly limited, and whole of coil magnetic body 3 may be covered with exterior body 4 as illustrated in
Coil component 13 transfers the heat generated from coil magnetic body 3 preferentially to mounting substrate 10, thereby reducing radiation of the heat to the outside air. That is, a portion of exterior body 4 which is arranged on top surface 7 has an anisotropic thermal conductivity, and a thermal conductivity in the direction parallel to the surface of exterior body 4 is greater than a thermal conductivity in the direction perpendicular to this surface. Further, a configuration is preferred in which the heat is radially transferred with an any point on a top surface of exterior body 4 as a center, and the heat is then sent to mounting substrate 10 via a portion of exterior body 4 which is disposed on side surface 8. By taking a point close to a center of top surface 7 as this any point, deviation of the heat is small on the top surface of exterior body 4, and the heat can be transferred through portions along side surfaces 8 in a more uniform manner. The number of any points is preferably one for the purpose of uniformly diffusing the heat, but a plurality of any points may be present.
Further, the portion of exterior body 4 which is disposed on side surface 8 also has an anisotropic thermal conductivity, and the thermal conductivity in the direction parallel to the surface of exterior body 4 is greater than the thermal conductivity in the direction perpendicular to this surface. In other words, a thermal conductivity in the direction toward mounting substrate 10 is maximal in this portion. With this configuration, it is possible to efficiently transfer the heat generated in coil magnetic body 3 to mounting substrate 10. As a result, a heat release effect throughout coil component 13 is enhanced.
As described above, it is preferable that exterior body 4 be provided on at least top surface 7 and side surface 8, and it is further preferable that the thermal conductivity in the portion of exterior body 4 which is provided on side surface 8 is maximal in a direction in which bottom surface 9 and top surface 7 are opposed to each other. Particularly, it is further preferable that the thermal conductivity in the portion of exterior body 4 provided on side surface 8 in the direction in which bottom surface 9 and top surface 7 are opposed to each other be maximal throughout exterior body 4.
In the configuration illustrated in
Next, modified examples of the coil component according to the exemplary embodiment will be described with reference to
In coil component 13A illustrated in
In coil component 13B illustrated in
In coil component 13C illustrated in
Next, a specific configuration to impart anisotropy to the thermal conductivity of exterior body 4 will be described. As such a specific method, there are a method in which exterior body 4 is formed of a liquid crystal polymer, and a method in which exterior body 4 is formed of a resin and an inorganic filler. First, the former method will be described with reference to
In coil component 13D, exterior body 4 is formed of a liquid crystal polymer. Molecules 14 of the liquid crystal polymer are oriented along the surface of exterior body 4. Molecules 14 of the liquid crystal polymer in a molten state have a property of being oriented in a flowing direction. Therefore, injection-molding the liquid crystal polymer on the surface of coil magnetic body 3 allows molecules 14 to be oriented along the surface of exterior body 4. With such orientation of molecules 14, it is possible to allow exterior body 4 to have the anisotropic thermal conductivity. Specifically, the thermal conductivity in the direction parallel to the surface of exterior body 4, indicated by arrow 5, is greater than the thermal conductivity in the direction perpendicular to the surface of exterior body 4, indicated by arrow 6.
For example, coil magnetic body 3 is disposed in a mold, and the liquid crystal polymer in the molten state is poured into a gap between the mold and coil magnetic body 3. At this time, orientation of molecules 14 can be controlled by appropriately adjusting a structure of the mold, a position or an angle of an inlet for the liquid crystal polymer, pressure or a quantity of the poured liquid crystal polymer, or the like. The clearance between coil magnetic body 3 and the mold is preferably not less than 0.2 mm and not more than 30 mm. By making the clearance between coil magnetic body 3 and the mold not less than 0.2 mm, it is possible to inject the liquid crystal polymer in the molten state into this clearance with good fluidity. Meanwhile, by making the clearance not more than 30 mm, it is possible to effectively orient molecules 14 in the direction of an outer surface of exterior body 4 and to impart the anisotropy to the thermal conductivity. As described above, when forming exterior body 4, the gap between coil magnetic body 3 and a wall surface of the mold can be filled with the liquid crystal polymer in the molten state by injection molding, and the liquid crystal polymer can be cured such that molecules 14 of the liquid crystal polymer are oriented along the surface of exterior body 4.
Generally, the liquid crystal polymer is categorized, in terms of its structure, into a main-chain liquid crystal polymer, a side-chain liquid crystal polymer, a complex liquid crystal polymer, and the like. The liquid crystal polymer in the present disclosure is not particularly limited, and any of the above liquid crystal polymers can be used.
Further, as illustrated in
Moreover, by making the clearance between coil magnetic body 3 and the mold not less than 0.5 mm and not more than 20 mm, and further, not less than 0.8 mm and not more than 15 mm, it is possible to allow the liquid crystal polymer in the molten state to have good fluidity, and to form exterior body 4 having an anisotropic thermal conductivity. Note that, if a resin whose molecules or the like have orientation properties is used, anisotropy can be imparted to a thermal conductivity in a manner similar to the above. By using the liquid crystal polymer with an excellent anisotropic thermal conductivity among such resins, the configuration of the present disclosure can be effectively realized.
Next, another technique for allowing exterior body 4 to have the anisotropy in the thermal conductivity will be described with reference to
In coil component 13E, exterior body 4 contains resin 16 and the inorganic filler. The inorganic filler is contained in resin 16, and is made of a plurality of particles 15 each having a long axis and a short axis shorter than the long axis. An aspect ratio of the long axis and the short axis of particle 15 is larger than 1. A quantity (number) of particles 15, in each of which an angle formed by an extending direction of the long axis and the direction parallel to the surface of exterior body 4 is not less than 0° and less than 45°, is larger than a quantity (number) of particles 15, in each of which the angle is not less than 45° and not more than 90°, per unit volume of exterior body 4. With this configuration, the thermal conductivity in the direction parallel to the surface of exterior body 4, indicated by arrow 5, is greater than the thermal conductivity in the direction perpendicular to the surface of exterior body 4, indicated by arrow 6.
For realizing this configuration, for example, a mixture of resin 16 in a flowable state such as a molten state and an uncured state and particles 15 may be injection-molded in a manner similar to the example of the liquid crystal polymer described above. Further, the clearance between coil magnetic body 3 and the mold at that time is preferably not less than 0.3 mm and not more than 25 mm. When the clearance between coil magnetic body 3 and the mold is not less than 0.3 mm, it is possible to readily inject the mixture of resin 16 in the flowable state and particles 15 into this gap. Meanwhile, when the clearance is not more than 25 mm, it is possible to effectively orient the extending direction of the long axis of particles 15 in the direction parallel to the surface of exterior body 4, and to allow exterior body 4 to have the anisotropic thermal conductivity.
In this manner, when forming exterior body 4, the gap between coil magnetic body 3 and the wall surface of the mold is filled by injection molding with the mixture of uncured resin 16 and the plurality of particles 15 of the inorganic filler. It is thereby possible to cure resin 16 such that, the number of particles 15 of the inorganic filler, in each of which the angle formed by the extending direction of the long axis and the direction parallel to the surface of exterior body 4 is not less than 0° and less than 45°, is larger than the number of particles 15 of the inorganic filler, in each of which the angle is not less than 45° and not more than 90°, per unit volume of exterior body 4. Further, by making the clearance between coil magnetic body 3 and the mold to be not less than 0.5 mm and not more than 20 mm, and further, not less than 1 mm and not more than 15 mm, it is possible to allow resin 16 in the molten state to have good fluidity. Then, the quantity of particles 15 per unit volume, each of which having an aspect ratio larger than 1 and in each of which the angle formed by the direction of the long axis and the direction along the outer surface of exterior body 4 is not less than 0° and less than 45°, can be made still larger than the quantity of particles 15 per unit volume, in each of which the angle is not less than 45° and not more than 90°. This allows formation of exterior body 4 having a more anisotropic thermal conductivity in the direction parallel to the surface.
Examples of a material for resin 16 include a thermosetting resin and a thermoplastic resin. Further, examples of the inorganic filler include a variety of oxides such as alumina, mica, talc, kaolin, and silica, a variety of nitrides such as boron nitride and silicon nitride, glass, and graphite. Moreover, particle 15 may have any shape with an aspect ratio of a long axis and a short axis being larger than 1, preferably not less than 5, and specific examples of the shape include a scale shape, a fiber shape, and a spheroid shape.
Furthermore, exterior body 4 is not limited to a material or the like if exterior body 4 has an anisotropic thermal conductivity and if, among these thermal conductivities, the thermal conductivity in the direction parallel to the surface of exterior body 4 is greater than the thermal conductivity in the direction perpendicular to the surface. However, the most preferable example is a method in which exterior body 4 is formed of the liquid crystal polymer or formed of the mixture of the resin and the inorganic filler made of particles 15 each having an aspect ratio larger than 1, as described above.
As described above, in the method for manufacturing the coil component according to the present exemplary embodiment, firstly, wound coil 2 and coil magnetic body 3 having the magnetic core are disposed inside the mold having the wall surface such that the magnetic core of coil magnetic body 3 is located inside the winding of wound coil 2. Next, exterior body 4 that covers the surface of coil magnetic body 3 is formed such that the thermal conductivity in the direction parallel to the surface of exterior body 4 is greater than the thermal conductivity in the direction perpendicular to the surface of exterior body 4.
Note that the direction in which the long axis of molecule 14 of the liquid crystal polymer or the long axis of particle 15 of the inorganic filler extends can be measured by tissue observation of the surface and the cross section of exterior body 4 or by a variety of methods such as X-ray diffraction and Raman spectroscopy.
Hereinafter, the method for manufacturing the coil component according to the present exemplary embodiment will be described in detail by use of specific examples. Note that the present disclosure is not limited to the following examples.
First, a mixed powder prepared by mixing a Fe—Si alloy powder and a silicone resin is press-molded with a molding pressure of 10 ton/cm2, to prepare an E-shaped molded body. Subsequently, this E-shaped molded body is thermally treated at 500° C., to form E-shaped magnetic body 17.
E-shaped magnetic body 17 has middle magnetic leg 18, two outer magnetic legs 19, and rear magnetic body 20. Middle magnetic leg 18 is located at a center of E-shaped magnetic body 17, and outer magnetic legs 19 are located on both sides of middle magnetic leg 18. Rear magnetic body 20 connects middle magnetic leg 18 and outer magnetic leg 19 together.
Two E-shaped magnetic bodies 17 having the shape as described above are prepared, and the respective three magnetic legs are abutted so as to be opposed to each other as illustrated in
The coil magnetic body as thus formed is placed inside a mold. A bottom surface inside this mold is a substantially square with a side of 42 mm, and a surface of 40 mm×40 mm in the coil magnetic body is disposed so as to face the bottom surface. That is, the height of the coil magnetic body with respect to this bottom surface is 20 mm. A height inside this mold is 22 mm. Hence, the coil magnetic body is placed with a 1-mm gap provided between an inner surface of the mold and each of a top surface, side surfaces, and a bottom surface of the coil magnetic body. In this case, the exterior body is formed on each of the top surface, the side surfaces, and the bottom surface of the coil magnetic body, with a thickness of 1 mm. By positioning the coil magnetic body with a pin or the like, the coil magnetic body can be placed more accurately inside the mold.
Each of tips of terminals of the wound coil is drawn from a hole provided in the mold to the outside of the space. This portion becomes a connection electrode with an external circuit.
Next, Table 1 shows results of measuring heat generation characteristics obtained from materials for the exterior body and with methods for molding the exterior body.
As shown in Table 1, in Samples No. 1, 2, 5, 6, and 9, an aromatic polyester resin that is a thermoplastic liquid crystal polymer is used for the exterior body, and in Samples No. 3, 4, 7, 8, and 10, an epoxy resin that is a thermosetting resin is used.
In Samples No. 3, 4, 5, 6, and 10, 5 wt % of a scale-shaped boron nitride powder with an average aspect of 20 as the inorganic filler is mixed with the epoxy resin or the aromatic polyester resin, to be used as a material for the exterior body. In Sample No. 8, 5 wt % of a spherically shaped silicon nitride powder with an average aspect ratio of 1 is mixed with the epoxy resin, to be used as the material for the exterior body.
As to Samples No. 1 to 8, the exterior body is formed by injection-molding the above materials. Conditions for injection are as follows. In the case of the aromatic polyester resin, a cylinder temperature is 300° C., a mold temperature during molding is 130° C., and injection pressure is 40 MPa. In the case of the epoxy resin, a cylinder temperature is 175° C., a mold temperature during molding is 170° C., and injection pressure is 10 MPa.
Note that the injection molding in the present disclosure refers to a general molding method of pressurizing a material with fluidity to supply the material into the mold for molding, and this method includes a variety of molding methods such as transfer molding.
In any of Samples No. 1 to 8, an inlet for pouring the material for the exterior body into the mold is provided at one place opposed to the coil magnetic body. In Samples No. 1, 3, and 5, the inlet is provided on a side surface of the mold which is opposed to the side surface of the coil magnetic body, and in Samples No. 2, 4, 6, 7, and 8, the inlet is provided on a top surface of the mold which is opposed to the top surface of the coil magnetic body.
Meanwhile, in Samples No. 9 and 10, the exterior body is formed by resin potting. That is, a ceiling block forming a substantially parallelepiped space provided inside the mold is removed and a material heated and brought into a flowing state is poured into the mold, to form the exterior body.
In any of Samples No. 1 to 10, after injection molding or potting, coil magnetic body 3 is left inside the mold until the material to form the exterior body is cured, and after the exterior body is sufficiently cured, a coil component integrally formed of the coil magnetic body and the exterior body is taken out of the mold. Note that, as to sample No. 10, the mold is heated to 175° C. after potting to perform curing treatment so that the epoxy resin as the thermosetting resin is cured.
Next, results of evaluating heat generation characteristics of Samples No. 1 to 10 will be described. A space calorific value is measured on the following conditions. That is, an aluminum substrate of 150 mm×150 mm×5 mm is used as the mounting substrate, and the coil component is installed such that a mount surface that is a bottom surface of the exterior body makes contact with a top surface of the mounting substrate. Further, the mounting substrate is cooled by water with a temperature of 20° C.
Subsequently, the sample mounted on the mounting substrate is enclosed by an enclosure forming a stereoscopic space of 150 mm×150 mm×150 mm. As this enclosure, a wooden enclosure having sufficient heat insulation is used, so as to block entry/exit of a gas inside/outside the space. For measuring a temperature inside the cubic space, thermocouples are installed at eight points of corners inside the cubic space. Note that an outside air temperature is controlled to be 20° C.
Subsequently, a 100-A direct current is allowed to flow through the wound coil of the coil component from a power source connected to the wound coil. By passage of the current through the wound coil, the coil magnetic body generates heat due to a loss and the heat is dissipated to the space and the mounting substrate. At this time, a temperature inside the space increases with time, but when certain time elapses, each region reaches thermal equilibrium, and a temperature in each region shows a substantially constant value. An average value of the temperatures in the air, measured at the eight points of the corners inside the cubic space, is recorded as a space temperature.
As shown in Table 1, in Samples No. 1 to 6, it has been observed that in any of the exterior bodies, molecules of the aromatic polyester resin, particles of the boron nitride powder, or both the molecules and particles are oriented in the direction along the surface of the exterior body. A value of the space temperature is from 22° C. to 35° C., and a temperature rise is small.
In contrast, in Samples No. 7, 8, 9, and 10, orientation in the exterior body is not observed, the space temperature is from 57° C. to 62° C., and the temperature rise is significant.
In Samples No. 1, 3, and 5, the material for the exterior body is injected from a side surface of the coil component. For this reason, on this side surface, the molecules of the aromatic polyester resin or the particles of the boron nitride powder are radially oriented from a point where the injection has been performed. Further, on other surfaces (two surfaces adjacent to the side surface where the material for the exterior body has been injected, among a top surface, a bottom surface, and three remaining side surfaces), the molecules or the particles are oriented toward the side surface on the rear side of the side surface where the material for the exterior body has been injected.
In Samples No. 2, 4, and 6, the material for the exterior body is injected from the top surface of the coil component. For this reason, on this top surface, the molecules of the aromatic polyester resin or the particles of the boron nitride powder are radially oriented from a point where the injection has been performed. Further, on the four side surfaces, the molecules or the particles are oriented toward the bottom surface. Due to such orientation, heat generated in the coil magnetic body is transferred preferentially to the mounting substrate through the side surfaces of the exterior body. Therefore, the temperature rise of the space temperature is small as compared to those in Samples No. 1, 3, and 5.
In Sample No. 2, orientation of the molecules of the aromatic polyester resin is suitable in the exterior body, and in Sample No. 4, orientation of the particles of boron nitride with an aspect ratio of approximately 20 is suitable in the exterior body. Therefore, the temperature rise is small, and it is found that most of the heat generated in the coil magnetic body is not radiated to the space but transferred preferentially to the mounting substrate. Further, in Sample No. 6, portions of the exterior body which are provided on the top surface and all the side surfaces of the coil magnetic body contain the molecules of the aromatic polyester resin and the particles of boron nitride each having an aspect ratio of approximately 20, and these molecules and particles are all oriented in the direction toward the bottom surface. Therefore, the temperature rise is especially small, and it is found that most of the heat generated in the coil magnetic body is not radiated to the space but transferred preferentially to the mounting substrate.
Meanwhile, in Sample No. 8, a spherically shaped silica powder made of particles with an aspect ratio of 1 is used as the inorganic filler. As shown in Table 1, the space temperature in Sample No. 8 is very high as compared to those in Samples No. 3, 4, 5, and 6.
That is, it is found that by the exterior body containing the inorganic filler, the inorganic filler contributes to transfer of the heat generated from the coil magnetic body, but when the aspect ratio is not larger than 1, the effect of suppressing heat radiation to the space by transferring the heat preferentially to the mounting substrate is not exerted.
Note that the inorganic filler generally has a greater thermal conductivity than that of the resin. By mixing a larger amount of the inorganic filler made of particles with an aspect ratio larger than 1 and orienting the particles, the heat generated in the coil magnetic body can be effectively transferred to the mounting substrate, which is preferable.
As described above, the coil component, the method for manufacturing the coil component, and the coil electronic component according to the present disclosure are each useful because of an excellent productivity and a significant heat dissipation. Hence, it is possible to provide an inductance component having high reliability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-185873 | Sep 2013 | JP | national |
