Patent Application
20160155550
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-241984, filed on Nov. 28, 2014, the entire contents of which are incorporated herein by reference.
The present invention relates to a coil component.
Coil components such as surface mount-type planar coil elements are conventionally used in various electrical products such as household devices and industrial devices. In particular, small portable devices have come to be required to obtain two or more voltages from a single power source to drive individual devices due to enhanced functions. Therefore, surface mount-type planar coil elements are used also as power sources to satisfy such a requirement.
One of such coil components is disclosed in, for example, Japanese Unexamined Patent Publication No. 2014-60284. The coil component disclosed in this document comprises a coil conductor and a metal magnetic powder-containing resin covering the coil conductor, and the metal magnetic powder-containing resin contains three kinds of metal powders different in average grain diameter (first, second, and third magnetic powders). Such a coil component can have improved magnetic permeability due to a reduction in the distance between metal powder grains achieved by the second magnetic powder having a medium grain diameter.
In order to further enhance the insulating properties of an element body of the coil component or further reduce the core loss of the coil component, the metal powders may be covered with an insulating coating. In this case, however, magnetic permeability is reduced due to a reduction in magnetic flux density.
In order to solve the above problem, it is an object of the present invention to provide a coil component that comprises a metal magnetic powder-containing resin having improved insulation properties and that achieves a reduction in core loss while suppressing a reduction in magnetic permeability.
A coil component according to one aspect of the present invention comprises: a coil unit including a substrate and a conductor pattern for planar coil provided on the substrate; and a metal magnetic powder-containing resin covering the coil unit, wherein the metal magnetic powder-containing resin contains three or more kinds of metal powders different in average grain diameter, and wherein, out of the metal powders contained in the metal magnetic powder-containing resin, at least part of the metal powder having a minimum average grain diameter is not covered with an insulating coating, and the remaining metal powders are covered with an insulating coating.
In such a coil component, out of the three or more kinds of metal powders different in average grain diameter contained in the metal magnetic powder-containing resin, at least part of the metal powder having a minimum average grain diameter is not covered with an insulating coating. The present inventors have newly found that the metal powder having a minimum average grain diameter greatly influences magnetic permeability, and a reduction in magnetic permeability is suppressed by not covering at least part of the metal powder having a minimum average grain diameter with an insulating coating. On the other hand, the remaining metal powders are covered with an insulating coating, which improves the insulating properties of the metal magnetic powder-containing resin and reduces the core loss of the coil.
Further, the metal powder having a minimum average grain diameter may comprise two or more kinds of metal powders different in constituent material.
Further, the metal powder having a minimum average grain diameter may comprise an Fe powder and an Ni powder. Further, the Ni powder constituting the metal powder having a minimum average grain diameter may be covered with an insulating coating.
Further, the insulating coating covering the remaining metal powders may be a glass coating.
Further, the metal powders contained in the metal magnetic powder-containing resin may be three kinds of metal powders different in average grain diameter.
According to one aspect of the present invention, it is possible to provide a coil component that comprises a metal magnetic powder-containing resin having improved insulation properties and that achieves a reduction in core loss while suppressing a reduction in magnetic permeability.
Hereinbelow, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. It is to be noted that in the following description, the same elements or elements having the same function are represented by the same reference numerals, and description thereof will not be repeated.
First, the structure of a planar coil element that is a kind of coil component according to an embodiment of the present invention will be described with reference to
A planar coil element 10 includes a main body 12 having a rectangular parallelepiped shape and a pair of external terminal electrodes 14A and 14B provided to cover a pair of opposing end faces 12a and 12b of the main body 12. The planar coil element 10 is designed to have, for example, a long side of 2.5 mm, a short side of 2.0 mm, and a height of 0.8 to 1.0 mm.
The main body 12 has a coil unit 19 having a substrate 16 and conductor patterns 18A and 18B for planar air core coil which are provided on both upper and lower sides of the substrate 16.
The substrate 16 is a plate-like rectangular member made of a non-magnetic insulating material. In the central part of the substrate 16, an approximately-circular opening 16a is provided. As the substrate 16, a substrate can be used which is obtained by impregnating a glass cloth with a cyanate resin (BT (bismaleimide triazine) resin: trademark) and has a thickness of 60 μm. It is to be noted that polyimide, aramid, or the like may be used instead of BT resin. As a material of the substrate 16, ceramics or glass may also be used. Preferred examples of the material of the substrate 16 include mass-produced printed circuit board materials, and particularly, resin materials used for BT printed circuit boards, FR4 printed circuit boards, or FR5 printed circuit boards are most preferred.
Both the conductor patterns 18A and 18B are planar spiral patterns constituting a planar air core coil and are formed by plating with a conductive material such as Cu. It is to be noted that the surfaces of the conductor patterns 18A and 18B are coated with an insulating resin (not shown). A winding wire C of the conductor patterns 18A and 18B has, for example, a height of 80 to 260 μm, a width of 40 to 260 μm, and a winding pitch of 5 to 30 μm.
The conductor pattern 18A is provided on the upper surface of the substrate 16, and the conductor pattern 18B is provided on the lower surface of the substrate 16. The conductor patterns 18A and 18B are almost superimposed with the substrate 16 being interposed therebetween, and both of them are provided to surround the opening 16a of the substrate 16. Therefore, a through hole (magnetic core 21) is provided in the coil unit 19 by the opening 16a of the substrate 16 and the air cores of the conductor patterns 18A and 18B.
The conductor pattern 18A and the conductor pattern 18B are electrically connected to each other by a via-hole conductor 22 provided to penetrate through the substrate 16 near the magnetic core 21 (i.e., near the opening 16a). Further, the conductor pattern 18A provided on the upper surface of the substrate spirals outwardly in a counterclockwise direction when viewed from the upper surface side, and the conductor pattern 18B provided on the lower surface of the substrate spirals outwardly in a counterclockwise direction when viewed from the lower surface side, which makes it possible to pass an electrical current through the conductor patterns 18A and 18B connected by the via-hole conductor 22 in a single direction. When an electrical current is passed through the conductor patterns 18A and 18B in a single direction, a direction in which the electrical current passing through the conductor pattern 18A rotates and a direction in which the electrical current passing through the conductor pattern 18B rotates are the same, and therefore magnetic fluxes generated by both the conductor patterns 18A and 18B are superimposed and enhance each other.
Further, the main body 12 has a metal magnetic powder-containing resin 20 enclosing the coil unit 19. As a resin material of the metal magnetic powder-containing resin 20, for example, a thermosetting epoxy resin is used. The metal magnetic powder-containing resin 20 integrally covers the conductor pattern 18A and the upper surface of the substrate 16 on the upper side of the coil unit 19 and integrally covers the conductor pattern 18B and the lower surface of the substrate 16 on the lower side of the coil unit 19. Further, the metal magnetic powder-containing resin 20 also fills the through hole provided in the coil unit 19 as the magnetic core 21.
As shown in
As shown in
Similarly to the first metal magnetic powder 30A, as shown in
As shown in
It is to be noted that the metal magnetic powder-containing resin 20 is designed so that the mixing ratio by weight among the first metal magnetic powder 30A, the second metal magnetic powder 30B, and the third metal magnetic powder 30C is 6:1:1.
The pair of external terminal electrodes 14A and 14B are provided to connect the element to the circuit of a substrate on which the element is to be mounted, and are connected to the conductor patterns 18A and 18B. More specifically, the external terminal electrode 14A that covers the end face 12a of the main body 12 is connected to the end of the conductor pattern 18A exposed at the end face 12a, and the external terminal electrode 14B that covers the end face 12b opposed to the end face 12a is connected to the end of the conductor pattern 18B exposed at the end face 12b. Therefore, when a voltage is applied between the external terminal electrodes 14A and 14B, for example, an electrical current flowing from the conductor pattern 18A to the conductor pattern 18B is generated.
In this embodiment, each of the external terminal electrodes 14A and 14B is formed by applying a resin electrode material onto the end faces and then coating the resin electrode material with metal plating. The metal plating used to form the external terminal electrodes 14A and 14B may be made of, for example, Cr, Cu, Ni, Sn, Au, or solder.
As described above, the metal magnetic powder-containing resin 20 of the planar coil element 10 contains the three or more kinds of metal powders 30A, 30B, and 30C different in average gran diameter. Part of the third metal magnetic powder 30C (i.e., the Fe powder) is not coated with glass, and the remaining metal magnetic powders (i.e., the first metal magnetic powder 30A, the second metal magnetic powder 30B, and the Ni powder contained in the third metal magnetic powder 30C) are coated with glass.
The metal magnetic powder 40 shown in
However, the metal magnetic powder 40 shown in
As shown in
That is, in the coil component (planar coil element) 10, at least part of the third metal magnetic powder 30C contained in the metal magnetic powder 30 and having a minimum average grain diameter is uncoated, which suppresses a reduction in magnetic permeability. On the other hand, the remaining metal powders are coated with glass, which improves the insulating properties of the metal magnetic powder-containing resin 20 and reduces the core loss of the coil.
Further, the metal magnetic powder 30C not coated with glass is small in size because its grain diameter is reduced by the absence of a glass coating, that is, its grain diameter does not include the thickness of a glass coating. Therefore, the metal magnetic powder 30C easily enters between grains of the first and second metal magnetic powders 30A and 30B having a larger diameter, and as a result, the filling rate of the metal magnetic powder can be improved.
It is to be noted that the present invention is not limited to the above-described embodiment, and various changes may be made.
For example, the constituent material of the first and second metal magnetic powders may be an amorphous metal, an FeSiCr-based alloy, or Sendust instead of an iron-nickel alloy (permalloy). Further, the third metal magnetic powder does not always need to comprise two or more kinds of metal powders different in constituent material, and may comprise one kind of metal powder (e.g., only Fe). In this case, the third metal magnetic powder may be provided by not covering the one kind of metal powder with an insulating coating at all or by not covering only part of the one kind of metal powder with an insulating coating.
Further, the insulating coating is not limited to a glass coating, and may be, for example, a resin coating. Further, the metal magnetic powder-containing resin is not limited to one containing three kinds of metal powders different in average grain diameter, and may be one containing four or more kinds of metal powders different in average grain diameter. Also in this case, the same functions and effects as those of the above-described embodiment can be obtained by not covering at least part of a metal powder having a minimum average grain diameter with an insulating coating.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-241984 | Nov 2014 | JP | national |
