1. Field of the Invention
The present invention relates to a coil component used as a main component of a common mode choke coil or a transformer and a method of manufacturing the same.
2. Description of the Related Art
Reductions in the size of electronic apparatus such as personal computers and portable phones have resulted in demand for reductions in the size and thickness (low height) of electronic components such as coils and capacitors mounted on internal circuits of electronic apparatus.
However, a wire-wound coil obtained by winding a copper wire or the like around a ferrite core has a problem in that it is difficult to make compact because of structural limitations. Under the circumstance, research and development is active on chip-type coil components which can be provided with a small size and a low height. Known chip-type coil components include multi-layer type coil components provided by forming coil conductor patterns on surfaces of magnetic sheet made of ferrite or the like and stacking the magnetic sheets and thin film type coil components provided by forming insulation films and coil conductors constituted by metal thin films alternately using thin film forming techniques.
Patent Documents 1 to 3 disclose common mode choke coils that are thin film type coil components.
An open region 63 is formed on an inner peripheral side of the coil conductors 59 and 61 having a spiral configuration by removing the insulation layer 57. An open region 65 is formed on an outer peripheral side of the spiral coil conductors 59 and 61 by removing the insulation layer 57. Magnetic layers 67 are formed to fill the open regions 63 and 65. Further, a bonding layer 69 is formed on the magnetic layers 67 and the insulation layer 57 to bond a magnetic substrate 55.
When the coil conductors 59 and 61 are energized, a magnetic path M is formed such that it passes through the magnetic substrate 53, the magnetic layer 67 in the open region 63, the bonding layer 69, the magnetic substrate 55, the bonding layer 69 again and the magnetic layer 67 in the open region 65 in the section including the center axes of the coil conductors 59 and 61. The bonding layer 69 is a film having a thickness on the order of a few μm, although it is non-magnetic. Therefore, substantially no leakage of the magnetic flux occurs in this part, and the magnetic path M may be regarded as a substantially closed path.
In order to improve differential transmission (balanced transmission) characteristics of the common mode choke coil 51, a capacitance (stray capacitance) C which is generated between the coil conductors 59 and 61 must be made small. The capacitance C is parasitically generated in parallel with inductances of the coil conductors 59 and 61. Therefore, when a relatively high capacitance C is generated, the capacitance C will dominantly constitute the impedance of the common mode choke coil 51 in high frequency bands. Since the impedance constituted by the capacitance C is inversely proportionate to a frequency, the impedance of the common mode choke coil 51 decreases, which results in degradation of differential transmission characteristics.
The capacitance C between the coil conductors 59 and 61 can be expressed by C=ε×(S/d) where d represents the inter-layer distance between the coil conductors 59 and 61; S represents the area in which the conductors face each other; and ε represents the dielectric constant of the region between the coil conductors 59 and 61 (the dielectric constant of the insulation layer 7). Since section of the coil conductors 59 and 61 are formed with a rectangular configuration, the area S over which the coil conductors 59 and 61 face each other is relatively large. Further, the coil conductors 59 and 61 are formed such that the inter-layer distance d between them becomes very small to provide the common mode choke coil 51 with a low height and to maintain predetermined common mode filter characteristics. As a result, a relatively high capacitance C is generated between the coil conductors 59 and 61, and differential transmission characteristics are therefore degraded.
Patent Document 4 discloses a pair of coils disposed in a face-to-face relationship and having a sectional configuration in which corners of the coils are rounded. In comparison to coils having a rectangular section like the coil conductors 59 and 61, the area over which the coils having a sectional configuration with rounded corners face each other at a minimum inter-layer distance between them is smaller, therefore a capacitance generated between the upper and the lower coils become a slightly lower. However, since the area over which the upper and the lower coils face each other at a minimum inter-layer distance is still relatively large in spite of the fact that the coil section has rounded corners, the differential transmission characteristics of the coils cannot be sufficiently improved.
Patent Documents 5 to 7 disclose sectional configurations of a pair of coils provided in a face-to-face relationship in a thin film magnetic head. Surfaces of such coils facing each other are curved or formed in a trapezoidal configuration when viewed in their sections. Since the purpose of such sectional configurations is to achieve effects such as a reduction in the magnetic path length between the magnetic poles of a thin film magnetic head, conductive parts of the upper and lower coils are interleaved between each other, and there are fundamental structural differences between those coils and the common mode choke coil 51, including a difference in wiring between upper and lower coils, i.e., series and parallel wiring.
Patent Document 1: Japanese Patent Laid-Open No. JP-A-2003-133135
Patent Document 2: Japanese Patent Laid-Open No. JP-A-11-54326
Patent Document 3: Japanese Patent Application No. 2003-307372
Patent Document 4: Japanese Patent No. 2011372
Patent Document 5: Japanese Patent No. 2677415
Patent Document 6: Japanese Patent Laid-Open No. JP-A-2000-182213
Patent Document 7: Japanese patent No. 3086212
To reduce the height of the common mode choke coil 51 and maintain predetermined common mode filter characteristics, the inter-layer distance d between the coil conductors 59 and 61 must be reduced. As a result, a relatively high capacitance C is generated between the coil conductors 59 and 61, which results in a problem in that the differential transmission characteristics cannot be sufficiently improved.
It is an object of the invention to provide a compact and low-height coil component having high differential transmission characteristics and a method of manufacturing the same.
The above object is achieved by a coil component characterized in that it has a first coil conductor which is formed on a magnetic substrate and a second coil conductor which is formed directly above the first coil conductor with an insulation film interposed between them and whose bottom portion, in a section of the coil, has a width different from a width of a top portion of the first coil conductor in a coil section.
The coil component according to the invention is characterized in that the first coil conductor is in a convex configuration in the middle of the top portion thereof when viewed in the coil section.
The coil component according to the invention is characterized in that the top portion of the first coil conductor is in a planar configuration when viewed in the coil section.
The coil component according to the invention is characterized in that the bottom portion of the second coil conductor is in a planar configuration when viewed in the coil section.
The above object is achieved by a method of manufacturing a coil component characterized in that it has the steps of forming a first coil conductor on a magnetic substrate, forming an insulation film on the first coil conductor and forming a second coil conductor on the insulation film, a bottom portion of the second coil conductor, in a section of the coil, having a width different from a width of a top portion of the first coil conductor in a coil section.
The method of manufacturing a coil component according to the invention is characterized in that the first and second coil conductors are formed using a frame plating process.
The method of manufacturing a coil component according to the invention is characterized in that it has the steps of forming resist frames which have side faces located in a plane in parallel with the coil section and inclined at a predetermined angle and forming at least either of the first and second coil conductors between the resist frames.
The method of manufacturing a coil component according to the invention is characterized in that the predetermined angle is in the range from 5° to 30°.
The present invention makes it possible to manufacture a compact and low-height coil component having high differential transmission characteristics.
A coil component and a method of manufacturing the same according to an embodiment of the invention will now be described with reference to
As shown in
The coil conductor 11 is disposed directly above the coil conductor 9 in a face-to-face relationship therewith with the insulation film 7b interposed between them. Planes of the coil conductors 9 and 11 orthogonal to the direction of a flow of a current through the conductors (sections of the coils) have a trapezoidal general configuration. The top portions of the coil sections are formed in a convex configuration such that they bulge in the middle, and the bottom portions of the coil sections are formed in a planar configuration. The width of the top portions of the coil sections is longer than the width of the bottom portions of the coil sections. Therefore, the inter-layer distance between the coil conductors 9 and 11 is shortest when measured at the convexes of the top portions of the coil section of the coil conductor 9 and gradually increases from the value at the convexes toward both sides of the top portions. Thus, a capacitance (stray capacitance) generated between the coil conductors 9 and 11 decreases, and differential transmission (balanced transmission) characteristics are therefore improved.
An open region 13 is formed on an inner peripheral side of the coil conductors 9 and 11 by removing the insulation layer 7. An open region 15 is formed on an outer peripheral side of the coil conductors 9 and 11 by removing the insulation layer 7. A magnetic layer 17 is formed such that it fills the open regions 13 and 15 to improve the degree of magnetic coupling between the coil conductors 9 and 11 and to improve impedance characteristics through an increase in common impedance. The magnetic layer 17 is formed of a composite ferrite obtained by mixing magnetic powder made of ferrite in polyimide resin. Further, a bonding layer 19 is formed on the magnetic layer 17 and the insulation film 7c to bond a magnetic substrate 5 formed of ferrite.
An operation of the common mode choke coil 1 of the present embodiment will now be described. When the coil conductors 9 and 11 are energized, as shown in
Next, a relationship between sectional configurations of coils and a capacitance between the coil conductors will be described with reference to
Referring to
Meanwhile, referring to
Since a capacitance between coil conductors is proportionate to the width over which the conductors face each other at an inter-layer distance d as thus described, the capacitance between the coil conductors 9 and 11 is decreased by forming the conductors with coil sections in a trapezoidal configuration. For example, a capacitance ratio C′/C equals 0.777/1.786 where W1=103.5; W2=53.6; and d=50. Thus, the capacitance can be reduced by about 57% by providing the coils with a trapezoidal configuration. When the top portions of coil sections have a convex configuration as shown in
As thus described, the capacitance C′ generated between the coil conductors 9 and 11 can be made small by forming the coils with sections in a substantially trapezoidal configuration such that top portions thereof bulge in the form of convexes even if the inter-layer distance d between the coil conductors 9 and 11 is small. As a result, the common mode choke coil 1 exhibits sufficient impedance against high frequency signals and improved differential transmission characteristics, and it can be provided with a small size and a low height.
A method of manufacturing a common mode choke coil 1 according to the present embodiment will now be described with reference to
First, as shown in
As shown in
Next, as shown in
Then, development is performed using an alkali developing solution after performing a thermal process as occasion demands. For example, a tetramethyl ammonium hydrooxide (TMAH) in a predetermined concentration is used as the alkali developing solution. Next, the developing step is then followed by a cleaning step. The developing solution in the resist layer 21a is cleaned away using a cleaning fluid such as pure water, the developing and dissolving reaction of the resist layer 21a is stopped, and as shown in
When the cleaning is completed, the cleaning fluid is scattered away to dry the substrate. The magnetic substrate 3 may be heated to dry up the cleaning fluid if necessary. Next, the magnetic substrate 3 is dipped in a plating solution in a plating bath, a plating process is performed using the resist frames 21a as a mold, and a plating film 9b is formed in gaps in the resist frames 21b as shown in
When the coil conductor 9 is formed using a frame plating process, as shown in
Next, the magnetic substrate 3 is dipped in a plating solution in a plating bath, a plating process is performed using the resist frames 25 as a mold, and a plating film 11b is formed in gaps in the resist frames 25 as shown in
Next, as shown in
Next, although not shown, a magnetic layer 17 is formed by filling the open regions 13 and 15 with a composite ferrite obtained by mixing magnetic powder made of ferrite in polyimide resin. A bonding layer 19 is formed by applying a bonding agent on the magnetic layer 17 in the open regions 13 and 15 and the insulation film 7c. Next, a magnetic substrate 5 is secured on the bonding layer 19.
Next, external electrodes (not shown) in connection with the coil conductors 9 and 11 are formed on sides of the magnetic substrates 3 and 5 opposite to each other such that they extend substantially perpendicularly to the substrate surfaces and across the magnetic substrates 3 and 5. A common mode choke coil 1 as shown in
As described above, according to the method of manufacturing the common mode choke coil 1 in the present embodiment, the use of the resist frames 21b and 25 having side faces inclined at a predetermined angle make it possible to form the coil conductors 9 and 11 having a substantially trapezoidal coil section in which top portions bulge in the form of convexes in the middle thereof. Since this reduces the inter-layer distance d between the coil conductors 9 and 11 and makes the conductive surfaces facing each other at the inter-layer distance d smaller, the capacitance C′ generated between the coil conductors 9 and 11 is decreased and the common mode choke coil 1 is provided with improved differential transmission characteristics.
A first modification of the present embodiment will now be described with reference to
As shown in
A second modification of the present embodiment will now be described with reference to
As shown in
A third modification of the present embodiment will now be described with reference to
As shown in
The invention is not limited to the above-described embodiment and may be modified in various ways.
While the coil conductors 9 and 11 in the above-described embodiment and the first to third embodiments are formed to have coil sections in the same configuration, this is not limiting the invention. The coil conductors 9 and 11 may have coil sections in different configurations provided that respective resistance values of the coil conductors 9 and 11 become smaller than a predetermined value, that the conductive portions of the coil conductors 9 and 11 face each other and that the top portions of the coil conductor 9 and the bottom portions of the coil conductor 11 are formed with different widths.
For example, as described in the above embodiment and the first modification, the top portions of the coil conductor 11 may have a planar configuration instead of a convex configuration. Further, it is not essential that the bottom portions of the coil conductor 9 are shorter as described in the above embodiment and the second modification. In this case, the same effects as in the above-described embodiment can be achieved.
Number | Date | Country | Kind |
---|---|---|---|
2004-049903 | Feb 2004 | JP | national |
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A 2003-133135 | May 2003 | JP |
Number | Date | Country | |
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20050184848 A1 | Aug 2005 | US |