Coil device

Details Coil device Coil device

2002-10-17

2004-03-23

Mai, Anh (Department: 2832)

Inductor devices

Coil or coil turn supports or spacers

Printed circuit-type coil

C336S232000, C336S223000

Reexamination Certificate

active

06710694

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coil devices, and particularly relates to a coil device such as a transformer and a common-mode choke coil.
2. Description of the Related Art
Conventional coil devices includes a coil device (conventional art 1) shown in
FIGS. 7A and 7B
, and such a coil device is disclosed in Japanese Unexamined Patent Application Publication No. 8-203737. This coil device is a surface mounted type and is for high frequency use. The coil device has a laminated body
51
including an insulator, in which two spiral coils
52
and
53
, magnetic substrates
54
and
55
, and external electrodes
56
and
57
are arranged. The spiral coils
52
and
53
face each other with a portion of the insulator disposed therebetween, are sandwiched between the magnetic substrates
54
and
55
, and are connected to external electrodes. In
FIG. 7B
, only the spiral coil
52
is connected to the external electrodes
56
and
57
. This coil device has various characteristics including compactness, low profile, better high-frequency properties than a laminated body having a ferrite element assembly in which coils are arranged, no difference in inductance caused by a difference in the relative magnetic permeability, and good coupling between coils in a common-mode choke coil.
Another coil device (conventional art 2) having a configuration shown in
FIG. 8
is disclosed in Japanese Unexamined Patent Application Publication No. 11-54326. This coil device has upper and lower magnetic substrates
54
and
55
, two spiral coils
52
and
53
, a laminated body (layered region)
51
having a ring shape, and an adhesive layer (magnetic layer)
58
having a relative magnetic permeability of 1 or more, wherein the laminated body
51
contains the spiral coils
52
and
53
therein and is disposed on the lower magnetic substrates
54
, and the adhesive layer
58
is disposed between the upper and lower magnetic substrates
54
and
55
.
In this coil device, since the laminated body
51
disposed on the lower magnetic substrate
54
is covered with the adhesive layer
58
having a relative permeability of 1 or more, the lines of magnetic force generated by the spiral coils
52
and
53
form closed magnetic circuits, as shown in FIG.
8
. The adhesive layer
58
and an insulator other than a region where coil patterns are located include a material having a relative permeability of 1 or more, and therefore, the degree of electromagnetic coupling between the spiral coils
52
and
53
is increased. Thus, a large inductance can be obtained.
However, in the coil device of the conventional art 1 disclosed in Japanese Unexamined Patent Application Publication No. 8-203737, there is a problem in that a large inductance and miniaturization cannot be achieved simultaneously because the adjustable range of the inductance is limited.
On the other hand, in the coil device of the conventional art
2
disclosed in Japanese Unexamined Patent Application Publication No. 11-54326, the adhesive layer
58
having a relative permeability of 1 or more covers the laminated body
51
disposed on the lower magnetic substrate
54
to increase the inductance. In order to prepare an adhesive layer having a relative permeability of 1 or more, the adhesive layer must include an adhesive material and a magnetic material. In order to obtain a larger relative permeability, the magnetic material content must be very high. However, there is a maximum magnetic material content when the adhesive layer is to have a large relative permeability and a predetermined adhesive force in combination. Therefore, there is a problem in that the product reliability is decreased when the magnetic material content exceeds the maximum value.
Since layered coils are disposed in the adhesive layer having a relative permeability of 1 or more, the inductance is increased in proportion to an increase in the relative permeability of the magnetic layer. There is a problem in that a difference in the relative permeability in the magnetic layer has a strong effect on the inductance.
SUMMARY OF THE INVENTION
In order to solve the above-described problems, preferred embodiments of the present invention provide a coil device in which miniaturization and a large inductance are achieved simultaneously, and which has high reliability.
A coil device according to a preferred embodiment of the present invention includes a first magnetic substrate, a laminated body disposed on the first magnetic substrate and including insulating layers, coil patterns, and at least one through-hole, a magnetic layer covering the upper surface of the laminated body, an adhesive layer disposed on the magnetic layer, and a second magnetic substrate disposed on the adhesive layer and bonded to the magnetic layer with the adhesive layer, wherein the insulating layers define an insulator and the coil patterns for defining coils are stacked so that the coils are disposed in the insulator, the at least one through-hole is located at an area where the coils are not located and extends from the upper surface of the laminated body to the first magnetic substrate, the magnetic layer has at least one portion extending through the at least one through-hole to contact the first magnetic substrate, the adhesive layer is nonmagnetic, and the laminated body is sandwiched between the first and second substrates.
In the above-described coil device, the at least one through-hole is located at an area where the coils are not located in the laminated body and extends from the upper surface of the laminated body to the first magnetic substrate, the magnetic layer is disposed on the laminated body, and the magnetic layer has a portion extending through the through-hole to contact the first magnetic substrate. Therefore, a large impedance can be obtained without increasing the coil device size and the magnetic layer is securely joined to the second magnetic substrate with the nonmagnetic adhesive layer located therebetween. Since a very thin adhesive layer is disposed between the magnetic layer and the second magnetic substrate and functions as a nonmagnetic zone, stable inductance characteristics in a higher frequency band can be obtained as compared with a configuration in which a magnetic layer directly contacts the second magnetic substrate.
Usually, it is difficult to reduce the difference in relative permeability of magnetic bodies to the range of approximately −30% to approximately 30%. In a configuration having perfect closed magnetic circuits, the difference in relative permeability of magnetic bodies has a strong effect on the electrical characteristics. However, in the coil device of the present preferred embodiment, the inductance and the impedance are only slightly changed depending on the difference in relative permeability of the magnetic substrates and the magnetic layer. Therefore, the coil device has high accuracy due to a small difference in the characteristics.
In a preferred embodiment of the present invention, the coil device preferably functions as a common-mode choke coil having a configuration in which a plurality of the coils are arranged to face one another in the laminated body with each of the insulating layers being disposed therebetween, and the main portion of each coil and each insulating layer are alternately stacked. The main portion of each coil includes an area except for portions for connecting to the terminal electrodes of the coil.
In this coil device, since the common-mode choke coil has the above-described configuration, a magnetic flux is allowed to converge in the magnetic substrates and the magnetic layer. Since the common magnetic flux generated between a pair of coils facing each other can be increased compared with conventional common-mode choke coils, the degree of coupling between the coils can be increased. Thus, for the electrical characteristics, the impedance in a differential mode can be decreased, thereby reducing the influence on the transmitted waveform.
In the coil device of a prefe

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