Coil device

Abstract

To provide a coil device with improved magnetic properties and stable magnetic properties for each product.SOLUTION: A coil device 10 has a first magnetic body 20 and a second magnetic body 60. The first magnetic body 20 is fixed to the second magnetic body 60 via an adhesive layer 70, and the adhesive layer 70 includes a spherical magnetic material 74.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a coil device.

Background Art

[0002] Conventionally, a coil device that forms a closed magnetic circuit by combining a magnetic body forming a coil part with another magnetic body has been known. In such a coil device, an air gap occurs at the combination part of the magnetic body forming the coil part and the other magnetic body, resulting in a deterioration of magnetic characteristics, and the advantage of forming a closed magnetic circuit has not been fully obtained.

[0003] In Patent Document 1, in order to improve the magnetic characteristics of the coil device, magnetic powder with a small particle size is sandwiched between the irregularities on the mating surfaces of the respective magnetic cores that cause an air gap to eliminate the air gap.

[0004] However, such a conventional coil device has a problem that the magnetic characteristics are difficult to be stabilized for each product.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of such a situation, the present invention has been made, and an object thereof is to provide a coil device having improved magnetic characteristics and stable magnetic characteristics for each product.

Means for Solving the Problems

[0007] In order to achieve the above object, the coil device according to the present invention is a coil device having a first magnetic body and a second magnetic body, The first magnetic material is fixed to the second magnetic material via an adhesive layer. The adhesive layer includes a spherical magnetic material.

[0008] Our research has revealed that when a large amount of magnetic material is sandwiched between the first and second magnetic materials, the change in permeability becomes significant with changes in the amount of magnetic material. With the above configuration, by controlling the amount of magnetic material in the adhesive layer to a predetermined range, it is possible to improve the magnetic properties and stabilize the magnetic properties of each product. In addition, by including spherical magnetic material in the adhesive layer, the adhesive strength is improved compared to conventional methods, and it becomes possible to make the adhesive layer thinner.

[0009] Preferably, the adhesive layer forms a gap between the first magnetic material and the second magnetic material with a thickness of 2 to 10 μm. Such an adhesive layer ensures strong adhesion between the magnetic materials. Furthermore, by controlling the content of the magnetic material in the gap to a predetermined range, the magnetic properties of each coil device are stabilized.

[0010] Preferably, the spherical magnetic material is ferrite powder. By using ferrite powder as the spherical magnetic material, it is possible to improve magnetic properties while ensuring insulation.

[0011] Preferably, the average particle size of the spherical magnetic material is 0.59 to 1.25 μm. In an adhesive layer containing such spherical magnetic material, it is possible to improve magnetic properties while controlling the amount of magnetic powder, and to stabilize the magnetic properties of each product.

[0012] Preferably, the adhesive layer contains 40 to 60 wt% of the spherical magnetic material. More preferably, it contains 10 to 40 vol% of the spherical magnetic material. Having such an adhesive layer significantly improves the magnetic properties.

[0013] Preferably, the spherical magnetic material is formed by thermal spraying. By using thermal spraying, substantially uniform spherical magnetic powder can be easily formed. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is an overall perspective view of a coil device according to one embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view of the coil device shown in Figure 1 along line II-II. [Figure 3] Figure 3 is a partially enlarged cross-sectional view of the coil device shown in Figure 2. [Figure 4] Figure 4 is a graph showing the relationship between the ferrite powder content in the adhesive and the viscosity of the adhesive. [Figure 5] Figure 5 is a graph showing the relationship between the ferrite powder content in the adhesive and its magnetic permeability. [Modes for carrying out the invention]

[0015] The present invention will be described below based on the embodiments shown in the drawings.

[0016] As shown in Figure 1, the coil device 10 according to the first embodiment of the present invention has a chip shape and functions as an inductor, for example. The coil device 10 includes a first magnetic material 20 (drum core), a coil 30, a first electrode 40, a second electrode 50, and a second magnetic material (plate core).

[0017] In the figure, the Y-axis is parallel to the axial direction of the winding core 23 of the first magnetic material 20, the X-axis is perpendicular to the axial direction of the winding core 23, and the Z-axis is perpendicular to the mounting surface. In Figure 1, the mounting surface of the coil device 10 is the side above the Z-axis, that is, the side where the first electrode 40 and the second electrode 50 are located.

[0018] The first magnetic material 20 is a so-called drum core and has a first flange portion 21, a second flange portion 22, and a winding core portion 23. The size of the drum core 20 is not particularly limited, but its length in the X-axis direction is 0.2 to 6 mm, its length in the Y-axis direction is 0.4 to 6 mm, and its length in the Z-axis direction is 0.2 to 3 mm.

[0019] The drum core 20 is formed of a material containing a magnetic material and a resin. In the present embodiment, the magnetic material forming the drum core 20 is formed of ferrite particles. Examples of the ferrite particles include Mn-based ferrite, Ni-Zn-based ferrite, Mn-Zn-based ferrite, and the like. Further, the magnetic material may be metal magnetic particles or the like. The metal magnetic particles are not particularly limited, and examples thereof include Fe-Ni alloy powder, Fe-Si alloy powder, Fe-Si-Cr alloy powder, Fe-Co alloy powder, Fe-Si-Al alloy powder, amorphous iron, and the like. The resin forming the drum core 20 is not particularly limited, and examples thereof include epoxy resin, phenolic resin, polyester resin, polyurethane resin, polyimide resin, other synthetic resins, or other non-magnetic materials. Note that the drum core 20 may be a sintered body of a metal magnetic material.

[0020] The winding core portion 23 has a columnar shape and has a substantially rectangular cross-sectional shape. The cross-sectional shape of the winding core portion 23 is not particularly limited and may be circular, substantially octagonal, or other polygons. A coil 30 is attached to the outer peripheral surface of the winding core portion 23. Note that, as the wire forming the coil 30, for example, a core material made of a good conductor such as copper (Cu) is covered with an insulating material made of imide-modified polyurethane or the like, and the outermost surface is further covered with a thin resin film such as polyester can be used.

[0021] The first flange portion 21 is formed at one end in the axial direction of the winding core portion 23, and the second flange portion 22 is formed at the other end in the axial direction of the winding core portion 23. The first flange portion 21 has a substantially cuboid shape, and the second flange portion 22 has a shape that is rotationally symmetric by 180 degrees with respect to the first flange portion 21.

[0022] A first electrode 40 is formed on the lower surface 212 of the first flange portion 21. The first electrode 40 is located on the mounting surface side of the drum core 20 and is continuously (integrally) connected along the X-axis direction. The edge of the first electrode 40 may wrap around to the inner and outer end surfaces of the first flange portion 21 in the Y-axis direction, as well as to both sides in the Y-axis direction. The first electrode 40 functions as a connection surface (mounting portion) with the mounting substrate and is connected to the mounting substrate, for example, by solder.

[0023] The thickness of the first electrode 40 is not particularly limited, but is preferably 50 to 300 μm. The central part of the first electrode 40 along the X-axis functions as a connecting portion 41 to the lead portion 30a of the coil 30. The lead portion 30a is connected to the connecting portion 41 of the first electrode 40, for example, by thermocompression bonding.

[0024] The first electrode 40 can be formed by applying a conductive paste to the upper surface 211 of the first flange portion by a method such as screen printing and curing it. The first electrode 40 may also be formed by applying a conductive paste to the upper surface 211 of the first flange portion and baking it, and an upper electrode by applying a conductive paste to cover the lower electrode and curing it.

[0025] Here, the conductive paste forming the first electrode 40 comprises conductive particles and an organic binder. The conductive paste contains at least one metal selected from, for example, Au, Ag, Cu, Ni, C, Pd, Ag-Pd alloy, etc., as the metal constituting the conductive particles. As the organic binder, for example, epoxy resin, phenolic resin, acrylic resin, urethane resin, silicone resin, polyimide resin, etc., can be used.

[0026] Furthermore, the first electrode 40 may have a plating layer formed on top of the conductive paste layer. For example, one can appropriately select from Cu plating, Ni plating, Sn plating, Ni-Sn plating, Cu-Ni-Sn plating, Ni-Au plating, Au plating, etc. The plating layer may be a single layer or multiple layers.

[0027] A second electrode 50 is formed on the lower surface 222 of the second flange portion 22. The shape and function of the second electrode 50 are the same as those of the first electrode 40, so a detailed explanation is omitted. The lead portion 30b of the coil 30 is connected to the connecting portion 51 of the second electrode 50 by thermocompression bonding.

[0028] As shown in Figures 1 and 2, the second magnetic material 60 is a so-called plate core and has a roughly rectangular parallelepiped shape. The size of the plate core 60 is not particularly limited, but its length in the X-axis direction is 0.4 to 6 mm, its length in the Y-axis direction is 0.2 to 6 mm, and its length in the Z-axis direction is 0.2 to 3 mm.

[0029] The plate core 60 is formed from a material containing a magnetic material and a resin. In this embodiment, the magnetic material forming the plate core 60 is ferrite particles, but is not limited to this. Examples of magnetic materials forming the plate core 60 include the magnetic material forming the drum core 20. In this embodiment, the magnetic material forming the plate core 60 is the same as that of the drum core 20, but may be different.

[0030] As shown in Figure 2, the upper surfaces 211 and 221 of the flange are abutted against the lower surface 61 of the plate core 60, and the upper surfaces 211 and 221 of the flange are fixed to the lower surface 61 of the plate core 60 via the adhesive layer 70 shown in Figure 3.

[0031] The adhesive layer 70 can be formed by preparing a predetermined adhesive (for example, containing an uncured adhesive component and a spherical magnetic material), applying it to the upper surfaces 211 and 221 of the flange portion, pressing it down with the lower surface 61 of the plate core 60 to sandwich the adhesive between the upper surfaces 211 and 221 of the flange portion and the lower surface 61 of the plate core 60, and heating it to a predetermined temperature.

[0032] As shown in Figure 3, the adhesive layer 70 contains an adhesive component 72 and a spherical magnetic material 74. The adhesive component 72 is an epoxy resin, but is not limited to this. For example, the adhesive component 72 can be a silicone-based adhesive, a modified acrylic resin, a urethane resin, a polyimide resin, etc.

[0033] The spherical magnetic body 74 is formed from ferrite powder, but is not limited to this. Examples of ferrite powder include Mn-based ferrite, Ni-Zn-based ferrite, and Mn-Zn-based ferrite. In addition to ferrite powder, metallic magnetic powder may also be used. Examples of metallic magnetic powder include Fe-Ni alloy powder, Fe-Si alloy powder, Fe-Si-Cr alloy powder, Fe-Co alloy powder, Fe-Si-Al alloy powder, amorphous iron, and the like.

[0034] As shown in Figure 3, the adhesive layer 70 is present with a substantially uniform thickness L between the upper surfaces 211, 221 of the flange portion and the lower surface 61 of the plate core 60. The thickness L is not particularly limited, but is preferably 2 to 10 μm, and more preferably 2 to 6 μm.

[0035] The adhesive forming the adhesive layer 70 can be manufactured by mixing spherical magnetic powder with a base resin or the like, which will serve as the adhesive component, in a predetermined ratio. The spherical magnetic powder can be manufactured, for example, by thermal spraying.

[0036] In thermal spraying, raw materials are directly introduced into a flame, causing them to melt and then sphericalize due to surface tension. For example, in thermal spraying, oxide powders are mixed in a predetermined ratio, water is added and pulverized to create a slurry, and granules of this slurry are obtained using a spray dryer. By spraying these granules at a predetermined flow rate into a combustion flame of a flammable gas mixture of propane and oxygen, the resulting magnetic powder can be made spherical with a small average particle size and minimal variation.

[0037] Furthermore, the average particle size of the magnetic material powder can be measured by laser diffraction and calculated from the resulting particle size distribution. Also, the shape and size of the magnetic material mixed with the adhesive are maintained even in the adhesive layer 70.

[0038] In this embodiment, the adhesive containing spherical magnetic material exhibits improved adhesive strength compared to conventional adhesives, allowing for a thinner adhesive layer. Furthermore, such adhesives are less prone to deterioration in adhesive strength. In addition, in this embodiment, by controlling the content of spherical magnetic material in the adhesive layer 70 within a predetermined range, the magnetic properties can be improved, and the magnetic properties of each product can be stabilized.

[0039] In this embodiment, the adhesive layer 70 forms a gap of 2 to 10 μm in thickness between the drum core 20 and the plate core 60. In the adhesive layer 70 of this embodiment, sufficient adhesive strength between the cores can be ensured. Furthermore, in the adhesive layer 70 of this embodiment, the magnetic properties are stabilized for each coil device by controlling the magnetic material content in the gap to a predetermined range.

[0040] In this embodiment, the spherical magnetic material 74 is made of ferrite powder. By making the spherical magnetic material 74 of ferrite powder, it is possible to improve magnetic properties while ensuring insulation.

[0041] The spherical magnetic material 74 does not have to be a perfect sphere and may have some distortion. In this specification, as shown in Figure 3, even if the spherical magnetic material 74 has distortion in shape, the major axis and minor axis are determined from SEM images, etc., and a magnetic material whose ratio of major axis a to minor axis b / a is 0.92 or greater is considered a spherical magnetic material.

[0042] In this embodiment, the particle size of the spherical magnetic material 74 is not particularly limited, but is preferably 4 μm or less. Furthermore, the average particle size of the spherical magnetic material 74 is particularly preferably 0.59 to 1.25 μm. Such spherical magnetic material can be manufactured by thermal spraying, and in an adhesive layer formed from an adhesive containing such spherical magnetic material, it is possible to improve magnetic properties while controlling the magnetic powder content to a low level, and to stabilize the magnetic properties of each product.

[0043] The content of spherical magnetic material 74 in the adhesive layer 70 is not particularly limited. Preferably, the content of spherical magnetic material 74 in the adhesive layer 70 is 40 to 60 wt%, more preferably 45 to 55 wt%, and more preferably 47.5 to 52.5 wt%. It is also preferable that the adhesive layer 70 contains 10 to 40 vol% of spherical magnetic material 74. Furthermore, by keeping the content of spherical magnetic material 74 below a predetermined value, it is possible to prevent the viscosity of the adhesive from increasing and the application workability from decreasing. In addition, with adhesives of high viscosity, it is possible to suppress the thickness of the gap. By having the adhesive layer 70, the application workability is improved, and it becomes possible to form a gap of a predetermined thickness, which particularly improves the magnetic properties.

[0044] Furthermore, the mass of spherical magnetic material 74 in the adhesive layer 70 can be considered equivalent to the mass of spherical magnetic material contained in the adhesive forming the adhesive layer 70. In addition, the volume ratio of spherical magnetic material 74 in the adhesive layer 70 can be measured from the SEM image of the cross-section of the adhesive layer 70 shown in Figure 3.

[0045] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways within the scope of the present invention.

[0046] For example, the first and second magnetic materials may not be a combination of a drum core and a plate core, but rather drum cores together, for instance. [Examples]

[0047] (Measuring the viscosity of adhesives) Mn-based ferrite was prepared using iron oxide and manganese oxide as raw materials by thermal spraying, and this was designated as Sample 1. The particle size distribution of the ferrite powder of Sample 1 was measured by laser diffraction. The results of the laser diffraction showed that the particle size of the ferrite powder was 4 μm or less, and the average particle diameter was 0.7 μm.

[0048] Adhesives were prepared by mixing the ferrite powder from Sample 1 with the epoxy resin base resin, so that the ferrite content in the adhesive was 50 wt%, 60 wt%, and 70 wt%, respectively.

[0049] The viscosity of the adhesive prepared in this manner was measured. Figure 4 shows the relationship between the viscosity of the adhesive and the ferrite powder content. As shown in Figure 4, it was found that increasing the ferrite powder content in the adhesive increased the viscosity and reduced the workability of applying it to the core. Considering the workability of applying it to the core, it was found that a ferrite powder content of 50% was the most suitable.

[0050] (Observation of the adhesive layer) A coil device, as shown in Figure 1, was fabricated using an adhesive containing 50 wt% ferrite powder from sample 1. This coil device was cut, and an SEM image of the cross-section of the adhesive layer 70, as schematically shown in Figure 3, was taken. The major axis a and minor axis b of the spherical magnetic material 74, as captured in the SEM image, were measured. The ratio of major axis to minor axis b / a was 0.958 to 0.979. In the SEM image, the cross-sectional area of ​​the spherical magnetic material 74 within the cross-sectional area of ​​the adhesive layer 70 was 36.8 vol%.

[0051] (Permeability measurement) In addition to the ferrite powder of Sample 1, ferrite powders with the same composition as Sample 1 were prepared for Sample 2 (average particle size: 1.9 μm), Sample 3 (average particle size: 18 μm), and Sample 4 (average particle size: 30 μm). Adhesives with different ferrite content were prepared using each sample and the base resin used for viscosity measurement, and coil devices were fabricated for each.

[0052] Furthermore, using the same base resin as each adhesive, an adhesive without ferrite powder was prepared, and a coil device was fabricated. The magnetic permeability was measured using the fabricated coil device.

[0053] Figure 5 shows the relationship between the permeability of each coil device and the ferrite content in the adhesive. As shown in Figure 5, it was found that the permeability increased as the ferrite powder content in the adhesive increased. Furthermore, it was found that when the ferrite powder content in the adhesive was low, the change in permeability was smaller compared to the region with a high ferrite content. In particular, when the ferrite content in the adhesive was between 40 wt% and 60 wt%, it was found that there was little variation in permeability due to the particle size of the ferrite powder. It was found that the permeability was almost the same for all adhesives when the ferrite content was 50 wt%.

[0054] Furthermore, as shown in Figure 5, it was found that the smaller the average particle size of the ferrite powder contained in the adhesive, the lower the magnetic permeability tended to be. In a coil device using an adhesive containing 50 wt% ferrite powder, the adhesive with ferrite powder having an average particle size of 30 μm and the adhesive mixed with ferrite powder having an average particle size of 1.9 μm in a 7:3 ratio achieved substantially the same properties. In contrast, in a coil device using an adhesive containing 80 wt% ferrite powder, the adhesive with ferrite powder having an average particle size of 30 μm showed lower magnetic permeability than the adhesive mixed with ferrite powder having an average particle size of 30 μm and ferrite powder having an average particle size of 1.9 μm in a 7:3 ratio. This is thought to be because the larger ferrite powder content and particle size resulted in a larger adhesive film thickness, and thus a larger gap between the first and second magnetic materials.

[0055] Based on the above, if the ferrite powder content in the adhesive is 40 wt% to 60 wt%, it becomes possible to maintain nearly constant magnetic properties even if the particle size and content of the spherical magnetic material contained in the adhesive layer change slightly, thereby reducing variations in magnetic properties from product to product. [Explanation of Symbols]

[0056] 10... Coil device 20... Drum core (first magnetic material) 21… Part 1 211…above 212…below 22…Second part 221…above 222…below 23…volume core part 30…コイル 30a, 30b… Introduction 40…Electrode 1 41…Line Department 50…Electrode 2 51…Line Department 60…Itaka (the second magnetic body) 61…Below 70…then the next layer 72…The next part 74…Spherical magnetic body

Claims

1. A coil device having a first magnetic material and a second magnetic material, The first magnetic material is fixed to the second magnetic material via an adhesive layer. The adhesive layer includes a spherical magnetic material, The coil device wherein the adhesive layer contains 45 to 55 wt% of the spherical magnetic material having an average particle diameter of 0.7 to 30 μm.

2. The coil device according to claim 1, wherein the adhesive layer forms a gap between the first magnetic material and the second magnetic material with a thickness of 2 to 10 μm.

3. The coil device according to claim 1 or 2, wherein the spherical magnetic material is ferrite powder.

4. A coil device having a first magnetic material and a second magnetic material, The first magnetic material is fixed to the second magnetic material via an adhesive layer. The adhesive layer includes a spherical magnetic material, The coil device wherein the adhesive layer contains 45 to 55 wt% of the spherical magnetic material having an average particle diameter of 0.59 to 1.25 μm.

5. The coil device according to any one of claims 1 to 4, wherein the adhesive layer contains 10 to 40 vol% of the spherical magnetic material.

6. The coil device according to any one of claims 1 to 5, wherein the spherical magnetic material is formed by thermal spraying.

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