U.S. patent application number 10/785029 was filed with the patent office on 2004-12-30 for thin-film type common-mode choke coil and manufacturing method thereof.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Ito, Tomokazu, Kudo, Takashi, Otomo, Makoto.
Application Number | 20040263309 10/785029 |
Document ID | / |
Family ID | 33542934 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040263309 |
Kind Code |
A1 |
Ito, Tomokazu ; et
al. |
December 30, 2004 |
Thin-film type common-mode choke coil and manufacturing method
thereof
Abstract
A common-mode choke coil including a first magnetic substrate 1,
electrically insulating layers and coil pattern-including coil
conductor layers 5 and 7 formed alternately on the first magnetic
substrate 1, and a second magnetic substrate 13 for covering an
uppermost one of the electrically insulating layers, wherein:
central regions of the electrically insulating layers surrounded by
the coil patterns and portions of the electrically insulating
layers corresponding to outer circumferential regions of the coil
patterns are removed; a magnetic powder-containing resin (magnetic
layer 11) is provided on the uppermost one of the electrically
insulating layers and embedded in the removed portions of the
electrically insulating layers; and the second magnetic substrate
13 is bonded to a flattened surface of the magnetic
powder-containing resin by an adhesive layer 12.
Inventors: |
Ito, Tomokazu; (Tokyo,
JP) ; Kudo, Takashi; (Tokyo, JP) ; Otomo,
Makoto; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TDK CORPORATION
Tokyo
JP
|
Family ID: |
33542934 |
Appl. No.: |
10/785029 |
Filed: |
February 25, 2004 |
Current U.S.
Class: |
336/200 |
Current CPC
Class: |
H01F 2017/048 20130101;
H01F 2017/0093 20130101; H03H 2001/0085 20130101; H03H 2001/0092
20130101; H01F 41/042 20130101; H01F 41/046 20130101; H01F 17/0013
20130101 |
Class at
Publication: |
336/200 |
International
Class: |
H01F 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2003 |
JP |
2003-050016 |
Feb 26, 2003 |
JP |
2003-050124 |
Claims
What is claimed is:
1. A common-mode choke coil comprising: a first magnetic substrate;
multi-layer coil part in that electrically insulating layers and
coil patterns formed alternately on said first magnetic substrate,
the multi-layer coil part having a central portion surrounded by
the coil patterns and an outer removal portion at where the
electrically insulating layers corresponding to outer
circumferential regions of the coil patterns are removed; a
magnetic powder containing region provided on the uppermost one of
the electrically insulating layers and in the outer removal
portion, a surface of the magnetic powder containing region being
flattened; and a second magnetic substrate on the flattened layer
of the magnetic powder containing region through an adhesive.
2. A common-mode choke coil array comprising a plurality of
common-mode choke coils, each comprising: a first magnetic
substrate; multi-layer coil part in that electrically insulating
layers and coil patterns formed alternately on said first magnetic
substrate, the multi-layer coil part having a central portion
surrounded by the coil patterns and an outer removal portion at
where the electrically insulating layers corresponding to outer
circumferential regions of the coil patterns are removed; a
magnetic powder containing region provided on the uppermost one of
the electrically insulating layers and in the outer removal
portion, a surface of the magnetic powder containing region being
flattened; and a second magnetic substrate on the flattened layer
of the magnetic powder containing region through an adhesive.
3. A method of producing a common-mode choke coil, comprising the
steps of: forming electrically insulating layers and coil patterns
alternately on a first magnetic substrate; removing central regions
of said electrically insulating layers surrounded by said coil
patterns and portions of said electrically insulating layers
corresponding to outer circumferential regions of said coil
patterns; applying a magnetic power-containing resin onto an
uppermost one of said electrically insulating layers and embedding
said magnetic power-containing resin in removed portions of said
electrically insulating layers; polishing a surface of said
magnetic powder-containing resin after curing said magnetic
powder-containing resin to flatten said surface; and bonding a
second magnetic substrate onto said flattened surface of said
magnetic powder-containing resin by an adhesive agent.
4. A method of producing a common-mode choke coil according to
claim 3, wherein said magnetic powder-containing resin is applied
and formed by a printing process.
5. A method of producing a common-mode choke coil according to
claim 3, wherein said magnetic power-containing resin provided by
said coating step has a thickness not smaller than 1.5 times as
large as a difference in level of said removed portions of said
electrically insulating layers.
6. A method of producing a common-mode choke coil according to
claim 3, wherein said etching step is performed whenever one of
said electrically insulating layers is formed.
7. A thin-film type common-mode choke coil comprising: a laminated
structure having a magnetic substrate; and electrically insulating
layers and conductor layers laminated on said magnetic substrate in
a direction of thickness, wherein said conductor layers form at
least two coil conductors; at least two of said conductor layers
are provided as spiral conductor patterns; and said spiral
conductor patterns satisfy the expression: 5
.mu.m.ltoreq.W1.ltoreq.36 .mu.m in which W1 is the conductor width
of each of said spiral conductor patterns.
8. A thin-film type common-mode choke coil according to claim 7,
wherein said spiral conductor patterns satisfy the expression: 100
.mu.m.sup.2.ltoreq.T*W1 in which T is the conductor thickness of
each of said spiral conductor patterns.
9. A thin-film type common-mode choke coil according to claim 7,
wherein said spiral conductor patterns satisfy the expression:
W2<T.times.2 in which W2 is the space between said spiral
conductor patterns, and T is the conductor thickness of each of
said spiral conductor patterns.
10. A thin-film type common-mode choke coil according to claim 7,
wherein each of said spiral conductor patterns is composed of an
undercoat conductor formed as a thin film, and a thickened
conductor formed on said undercoat conductor and provided as a
Cu-plating layer.
11. A thin-film type common-mode choke coil according to claim 10,
wherein said undercoat conductor is made of a combination of a
lower layer of Cr and an upper layer of Cu or a combination of a
lower layer of Ti and an upper layer of Cu.
12. A thin-film type common-mode choke coil according to claim 10,
wherein a surface of each of said spiral conductor patterns is
covered with an Ni-plating film.
13. A thin-film type common-mode choke coil according to claim 7,
wherein an upper surface of said laminated structure is covered
with a magnetic material.
14. A thin-film type common-mode choke coil according to claim 7,
wherein another magnetic substrate is bonded to an upper surface of
said laminated structure.
15. A thin-film type common-mode choke coil array comprising a
plurality of thin-film type common-mode choke coils, each
comprising: a laminated structure having a magnetic substrate; and
electrically insulating layers and conductor layers laminated on
said magnetic substrate in a direction of thickness, wherein said
conductor layers form at least two coil conductors; at least two of
said conductor layers are provided as spiral conductor patterns;
and said spiral conductor patterns satisfy the expression: 5
.mu.m.ltoreq.W1.ltoreq.36 .mu.m in which W1 is the conductor width
of each of said spiral conductor patterns.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a common-mode choke coil, a
method for producing the same, and a common-mode choke coil array.
Particularly it relates to a filter used for suppressing a
common-mode current as a cause of electromagnetic interference
becoming an issue in a balanced transmission system, and a method
for producing the filter.
[0002] A laminated type choke coil is heretofore known as a chip
common-mode choke coil. This component has a structure in which a
first coil magnetic sheet having a coil conductor pattern formed on
a surface of a sheet of magnetic substance such as ferrite to form
a first coil and a second coil magnetic sheet formed in the same
manner as the first coil magnetic sheet are laminated
alternately.
[0003] A common-mode choke coil described in Patent Document
JP-A-8-203737 is known as a choke coil produced by a thin-film
process. This component has a structure in which: a lead-out
electrode is formed on a magnetic substrate by a thin-film process;
an electrically insulating layer, a first coil conductor, an
electrically insulating layer, a second coil conductor and an
electrically insulating layer are then formed successively thereon
by a thin-film process; and another magnetic substrate is put on an
upper surface of the resulting laminate.
[0004] Patent Document JP-A-11-54326 has described a common-mode
choke coil produced by a thin-film process. In this document,
central and outer circumferential portions of each electrically
insulating layer produced by the thin-film process are etched
(developed) in order to improve the degree of magnetic coupling
between coils and increase common impedance. The upper magnetic
substrate is bonded by a resin as a mixture of an electrically
insulating material and magnetic powder to thereby form a closed
magnetic circuit structure.
[0005] In the background-art laminated type choke coil, the sheet
of magnetic substance is interposed between the first and second
coil conductors. When this choke coil is used as a common-mode
choke coil, magnetic coupling between two coils is lowered. This
becomes a characteristic issue.
[0006] In the common-mode choke coil produced by the thin-film
process described in Patent Document JP-A-8-203737, the first and
second coil conductors are sandwiched between the upper and lower
magnetic substrates. Because this structure cannot be provided as a
closed magnetic circuit structure, there is a problem in the degree
of magnetic coupling and common impedance (it is difficult to
improve the degree of magnetic coupling and common impedance).
[0007] In the thin-film process described in Patent Document
JP-A-11-54326, the aforementioned problem is solved because the
closed magnetic circuit structure is formed. The magnetic
power-containing resin is however low in adhesive property. There
is a problem in adhesion of the magnetic substrate.
[0008] As measures to solve this problem, it is possible to bond
the magnetic substrate by an adhesive agent after the magnetic
powder-containing resin is applied on the magnetic
substrate-bonding side of an electrically insulating layer with a
built-in coil conductor and cured. The magnetic powder-containing
resin is however shrunk when cured. Because the magnetic
powder-containing resin embedded in the etching portion (the place
where the central and outer circumferential portions of the
electrically insulating layer are etched to form a closed magnetic
circuit structure) of the electrically insulating layer is shrunk,
only the adhesive layer (non-magnetic) as the upper portion of the
electrically insulating layer is thickened. Accordingly, it is
impossible to obtain a sufficient effect in increasing common
impedance.
[0009] In the latest balanced transmission line, it is however
necessary to perform high-speed transmission of a transmission
signal with a frequency of the order of GHz. The thin-film type
common-mode choke coil cannot meet such high-speed
transmission.
[0010] Measures to meet high-speed transmission are suggested as
follows.
[0011] Firstly, matching of characteristic impedance is suggested.
The fact that matching is important is a commonly known fact on a
transmission circuit.
[0012] Secondly, greater improvement in magnetic coupling is
suggested. This improvement is however structurally limited.
[0013] Thirdly, reduction in capacitance between conductors is
suggested. If the space between the conductors is merely increased
in order to reduce such capacitance, increase in size cannot be
avoided.
SUMMARY OF THE INVENTION
[0014] Upon such circumstances, an object of the invention is to
provide a common-mode choke coil, a method for producing the same,
and a common-mode choke coil array in which the degree of magnetic
coupling substantially equal to that of a closed magnetic circuit
and high common impedance can be obtained while adhesion of a
magnetic substrate can be improved.
[0015] Upon such circumstances, an object of the invention is to
provide a micro-size thin-film type common-mode choke coil and a
common-mode choke coil array in which high-speed transmission of a
transmission signal with a frequency of the order of GHz can be
performed.
[0016] In order to attain the above-mentioned object, according to
the present invention, a common-mode choke coil comprises a first
magnetic substrate, electrically insulating layers and coil
patterns formed alternately on said first magnetic substrate, and a
second magnetic substrate for covering an uppermost one of said
electrically insulating layers, wherein central regions of said
electrically insulating layers surrounded by said coil patterns and
portions of said electrically insulating layers corresponding to
outer circumferential regions of said coil patterns are removed; a
magnetic powder-containing resin is provided on said uppermost one
of said electrically insulating layers and embedded in said removed
portions of said electrically insulating layers; and said second
magnetic substrate is bonded to a flattened surface of said
magnetic powder-containing resin by an adhesive layer.
[0017] A method of producing a common-mode choke coil, comprises
the steps of: forming electrically insulating layers and coil
patterns alternately on a first magnetic substrate (film-forming
step); removing central regions of said electrically insulating
layers surrounded by said coil patterns and portions of said
electrically insulating layers corresponding to outer
circumferential regions of said coil patterns (etching step);
applying a magnetic power-containing resin onto an uppermost one of
said electrically insulating layers and embedding said magnetic
power-containing resin in removed portions of said electrically
insulating layers (coating step); polishing a surface of said
magnetic powder-containing resin after curing said magnetic
powder-containing resin to flatten said surface (polishing step);
and bonding a second magnetic substrate onto said flattened surface
of said magnetic powder-containing resin by an adhesive agent
(bonding step).
[0018] Furthermore, a thin-film type common-mode choke coil
comprises: a laminated structure having a magnetic substrate, and
electrically insulating layers and conductor layers laminated on
said magnetic substrate in a direction of thickness, wherein: said
conductor layers form at least two coil conductors; at least two of
said conductor layers are provided as spiral conductor patterns;
and said spiral conductor patterns satisfy the expression:
5 .mu.m.ltoreq.W1.ltoreq.36 .mu.m
[0019] in which W1 is the conductor width of each of said spiral
conductor patterns.
[0020] Preferably, the spiral conductor patterns satisfy the
expression: W2<T*2
[0021] in which W2 is the space between said spiral conductor
patterns, and T is the conductor thickness of each of said spiral
conductor patterns.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is an exploded perspective view showing the case
where a common-mode choke coil is formed according to an embodiment
of the invention;
[0023] FIG. 2A is an explanatory view showing a process for
producing the common-mode choke coil according to the
embodiment;
[0024] FIG. 2B is an explanatory view showing the process for
producing the common-mode choke coil according to the
embodiment;
[0025] FIG. 2C is an explanatory view showing the process for
producing the common-mode choke coil according to the
embodiment;
[0026] FIG. 3 is an exploded perspective view showing the case
where a common-mode choke coil array is formed according to another
embodiment of the invention;
[0027] FIG. 4 is an exploded perspective view showing the case
where a thin-film type common-mode choke coil is formed according
to an embodiment of the invention;
[0028] FIG. 5 is a perspective view showing the external appearance
of the thin-film type common-mode choke coil according to the
embodiment;
[0029] FIG. 6 is a graph showing differential-mode attenuation
characteristic of the common-mode choke coil;
[0030] FIG. 7A is an explanatory view showing a process for
producing a spiral conductor pattern in the embodiment;
[0031] FIG. 7B is an explanatory view showing the process for
producing the spiral conductor pattern in the embodiment;
[0032] FIG. 7C is an explanatory view showing the process for
producing the spiral conductor pattern in the embodiment;
[0033] FIG. 7D is an explanatory view showing the process for
producing the spiral conductor pattern in the embodiment;
[0034] FIG. 7E is an explanatory view showing the process for
producing the spiral conductor pattern in the embodiment;
[0035] FIG. 7F is an explanatory view showing the process for
producing the spiral conductor pattern in the embodiment;
[0036] FIG. 8 is an exploded perspective view showing the case
where a thin-film type common-mode choke coil array is formed
according to another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] (First Embodiment)
[0038] Embodiments of the invention as to a common-mode choke coil,
a method for producing the same and a common-mode choke coil array
will be described below with reference to the drawings.
[0039] FIG. 1 and FIGS. 2A to 2C show an embodiment of the
invention. FIG. 1 is an exploded perspective view showing the case
where a chip common-mode choke coil is formed. FIGS. 2A to 2C are
explanatory views showing a process for producing the common-mode
choke coil. Although a plurality of components are produced
simultaneously on a substrate at the time of actual production,
this embodiment will be described on the case where a single device
is formed.
[0040] As shown in FIG. 1 and FIGS. 2A to 2C, the chip common-mode
choke coil has: a first magnetic substrate 1; and an electrically
insulating layer 2, a first lead-out electrode layer 3, an
electrically insulating layer 4, a first coil conductor layer
(spiral coil conductor pattern) 5, an electrically insulating layer
6, a second coil conductor layer (spiral coil conductor pattern) 7,
an electrically insulating layer 8, a second lead-out electrode
layer 9, an electrically insulating layer 10, a magnetic layer 11,
an adhesive layer 12 and a second magnetic substrate 13 laminated
successively on a principal surface of the first magnetic substrate
1 so as to be integrated into one body.
[0041] On this occasion, the first lead-out electrode layer 3 and
the first coil conductor layer 5 are electrically connected to each
other through a through-hole whereas the second lead-out electrode
layer 9 and the second coil conductor layer 7 are electrically
connected to each other through a through-hole. One end of each
lead-out electrode layer and one end of each coil conductor layer
are connected to external electrodes (formed on an outer
circumferential surface of the chip) respectively.
[0042] The magnetic layer 11 is formed in such a manner that a
magnetic powder-containing resin is applied and cured. After cured,
the magnetic powder-containing resin is polished to reduce surface
roughness. The second magnetic substrate 13 is integrally bonded to
the flattened surface of the magnetic layer 11 through the adhesive
layer 12.
[0043] Each of the magnetic substrates 1 and 13 is made of a
material such as sintered ferrite or composite ferrite in that
resin is mixed therein. Each of the electrically insulating layers
2, 4, 6, 8 and 10 is made of a material excellent in electrically
insulating property and good in processability, such as a polyimide
resin or an epoxy resin. The magnetic powder-containing resin used
for forming the magnetic layer 11 is a mixture of a resin such as
an epoxy resin and magnetic powder such as ferrite powder.
[0044] The chip common-mode choke coil is produced by the following
procedure. Incidentally, the procedure is based on the case where
the lead-out electrode layers 3 and 9 and the first and second coil
conductor layers 5 and 7 as spiral coil conductor patterns are
formed by a vacuum film-forming method (such as vapor deposition or
sputtering) or a plating method.
[0045] The electrically insulating layer 2 made of an electrically
insulating resin is formed on the magnetic substrate 1. A spin
coating method, a dip coating method, a spray coating method or a
printing method is used as the method for forming the electrically
insulating layer 2. Then, the electrically insulating layer 2 is
etched (developed) to remove a central region which will be
surrounded by a spiral coil conductor pattern and outer
circumferential regions which will become the outside of the spiral
coil conductor pattern.
[0046] A film of a metal is formed on the electrically insulating
layer 2 by a vacuum film-forming method or a plating method. It is
preferable from the point of view of electrical conductivity and
processability that Cu, Al or the like is used as the metal. Then,
a pattern is formed to thereby form the lead-out electrode layer 3.
The patterning is performed by a method such as an etching method
using photolithography or an additive method (plating) using
photolithography.
[0047] Then, the electrically insulating layer 4 made of an
electrically insulating resin is formed in the same manner as the
electrically insulating layer 2. On this occasion, a contact hole
for connecting the lead-out electrode layer 3 and the coil
conductor layer 5 to each other are formed while regions
corresponding to central and outer circumferential portions of the
coil conductor pattern (which will be formed) are etched.
[0048] Then, the first coil conductor layer 5 as a spiral coil
conductor pattern is formed. The method for forming the first coil
conductor layer 5 is the same as the method for forming the
lead-out electrode layer 3.
[0049] Then, the electrically insulating layer 6 made of an
electrically insulating resin is formed. The method for forming the
electrically insulating layer 6 is the same as the method for
forming the electrically insulating layer 2.
[0050] Then, the second coil conductor layer 7 as a spiral coil
conductor pattern, the electrically insulating layer 8
(electrically insulating resin), the lead-out electrode layer 9 and
the electrically insulating layer 10 (electrically insulating
resin) are formed successively in the same manner as described
above.
[0051] When the film-forming process for forming electrically
insulating layers each made of an electrically insulating resin and
conductor layers containing spiral coil conductor patterns
alternately on the first magnetic substrate 1 and the etching
process for removing the central regions of the respective
electrically insulating layers surrounded by the coil conductor
patterns and the outer circumferential regions of the respective
electrically insulating layers corresponding to the outside of the
coil conductor patterns are performed as described above, a
laminate 20 including coil conductor patterns on the first magnetic
substrate 1 is obtained as shown in FIG. 2A. A resin removal
portion 21 (recess) and resin removal portions 22 (cut portions) in
which the electrically insulating layers are removed are formed in
the central and outer circumferential regions of the laminate
20.
[0052] Then, a magnetic powder-containing resin (which serves as a
magnetic layer when cured) 11 is printed on the upper surface of
the electrically insulating layer 10 (the upper surface of the
laminate 20 in FIGS. 2A to 2C) by a coating process shown in FIG.
2B. Then, the magnetic powder-containing resin 11 is cured. At the
time of printing, the magnetic powder-containing resin 11 is
applied so as to be embedded in the resin removal portions 21 and
22. At the time of curing, the resin 11 is however shrunk, so that
the surface of the magnetic powder-containing resin 11 is roughened
(dented in places of the resin removal portions 21 and 22). To
reduce surface roughness as sufficiently as possible, it is
preferable that the thickness t of the magnetic powder-containing
resin 11 provided by the coating process is set to be not smaller
than 1.5 times as large as the depth d of the resin removal
portions 21 and 22.
[0053] Then, the upper surface of the magnetic powder-containing
resin 11 is polished up to the height of the chain line P as shown
in FIG. 2B to thereby perform a flattening process (to reduce
surface roughness).
[0054] Then, in a bonding process shown in FIG. 2C, an adhesive
agent is applied on the magnetic layer 11 which is formed by
polishing and flattening the whole upper surface of the magnetic
powder-containing resin after curing. The second magnetic substrate
13 is bonded to the magnetic layer 11 through the adhesive layer 12
provided in this manner.
[0055] Although description has been made on the case where one
device is formed, a plurality of devices are produced
simultaneously on a substrate in actual production. The product on
the substrate is cut into one-device chips. Then, external
electrodes are formed on an outer surface of each chip. In this
manner, each common-mode choke coil is completed.
[0056] According to this embodiment, the following effects can be
obtained.
[0057] The second magnetic substrate 13 can be bonded surely, so
that structural reliability can be ensured. In addition, because
the second magnetic substrate 13 is bonded after surface roughness
of the magnetic layer 11 made of the magnetic powder-containing
resin cured is flattened, the degree of magnetic coupling
substantially equal to that of a closed magnetic circuit and high
common impedance can be obtained.
[0058] Because the thickness t of the magnetic powder-containing
resin provided by the coating process is set to be not smaller than
1.5 times as large as the depth d of the resin removal portions 21
and 22, surface roughness of the magnetic layer 11 made of the
magnetic powder-containing resin cured can be reduced so that the
quantity of polishing in the flattening process can be reduced.
[0059] FIG. 3 shows the case where a common-mode choke coil array
is produced according to another embodiment of the invention. In
this case, two common-mode choke coils each equivalent to the
common-mode choke coil according to the previous embodiment are
arranged on a first magnetic substrate 1 to thereby form the array.
Parts equal or equivalent to parts in the previous embodiment are
referred to by identical numerals for the sake of omission of
duplicated description.
[0060] Although the embodiments of the invention have been
described above, the invention is not limited thereto and it is
self-evident to those skilled in the art that various changes or
modifications may be made without departing from the scope of
claim.
[0061] As described above, in accordance with the invention, there
can be achieved a common-mode choke coil and a common-mode choke
coil array in which the degree of magnetic coupling substantially
equal to that of a closed magnetic circuit and high common
impedance can be obtained while adhesion of the magnetic substrate
can be improved.
[0062] (Second Embodiment)
[0063] Embodiments of the invention as to a thin-film type
common-mode choke coil and a common-mode choke coil array will be
described below with reference to the drawings.
[0064] FIGS. 4 and 5 show second embodiment of the invention. FIG.
3 is an exploded perspective view showing the case where a
thin-film type common-mode choke coil is formed. FIG. 5 is a
perspective view showing the external appearance of the common-mode
choke coil. Although a plurality of components are produced
simultaneously on a substrate at the time of actual production,
this embodiment will be described on the case where a single device
is formed.
[0065] As shown in FIGS. 4 and 5, the thin-film type common-mode
choke coil shaped like a chip in terms of external form has: a
first magnetic substrate 1; and an electrically insulating layer 2,
a first lead-out electrode layer 3, an electrically insulating
layer 4, a first coil conductor layer (spiral coil conductor
pattern) 5, an electrically insulating layer 6, a second coil
conductor layer (spiral coil conductor pattern) 7, an electrically
insulating layer 8, a second lead-out electrode layer 9, an
electrically insulating layer 10 and a second magnetic substrate 11
laminated successively on a principal surface of the first magnetic
substrate 1 so as to be integrated into one body. The first coil
conductor layer 5 and the second coil conductor layer 7 are
arranged so as to be magnetically coupled with each other. When
differential-mode currents flow in the two conductor layers 5 and
7, two kinds of magnetic flux in the two conductor layers 5 and 7
cancel each other. When common-mode currents flow in the two
conductor layers 5 and 7, two kinds of magnetic flux in the two
conductor layers 5 and 7 are added up.
[0066] On this occasion, the first lead-out electrode layer 3 and
the first coil conductor layer 5 are electrically connected to each
other through a through-hole 4a whereas the second lead-out
electrode layer 9 and the second coil conductor layer 7 are
electrically connected to each other through a through-hole 8a. One
end of each lead-out electrode layer and one end of each coil
conductor layer are connected to external electrodes 15 (formed on
an outer circumferential surface of the chip as shown in FIG. 5)
respectively.
[0067] Each of the magnetic substrates 1 and 11 is made of a
material such as sintered ferrite or composite ferrite in that
resin is mixed therein. Each of the electrically insulating layers
2, 4, 6, 8 and 10 is made of a material excellent in electrically
insulating property and good in processability, such as a polyimide
resin or an epoxy resin.
[0068] The relation between the conductor width of the first and
second coil conductor layers 5 and 7 as spiral coil conductor
patterns and the attenuation characteristic of a transmission
signal is as shown in FIG. 6. In FIG. 6, the curve a shows
frequency characteristic of differential-mode attenuation
characteristic (dB) in the case where the conductor width, the
conductor thickness and the space between the two conductors are 45
.mu.m, 18 .mu.m and 20 .mu.m respectively, the curve b shows
frequency characteristic of differential-mode attenuation
characteristic (dB) in the case where the conductor width, the
conductor thickness and the space between the two conductors are 36
.mu.m, 18 .mu.m and 13 .mu.m respectively, and the curve c shows
frequency characteristic of differential-mode attenuation
characteristic (dB) in the case where the conductor width, the
conductor thickness and the space between the two conductors are 12
.mu.m, 18 .mu.m and 12 .mu.m respectively. The data transmission
attenuation characteristic is improved as the width of the spiral
conductors decreases. It is obvious from FIG. 6 that reducing the
conductor width to a value not larger than 36 .mu.m is effective in
increasing the cutoff frequency (attenuation -3 dB) of the
transmission signal to a value not lower than 2.4 GHz (800 MHz
transmission.times.3). On the other hand, in view of stability of
plating of the fine conductor pattern and the resolution of the
resist layer, the conductor width should be larger than 5 .mu.m. It
can be therefore said that high-speed transmission is obtained
effectively when the conductor width W1 of the first and second
conductor layers 5 and 7 satisfies the following expression.
5 .mu.m.ltoreq.W1.ltoreq.36 .mu.m
[0069] Reduction in conductor width on this occasion causes
increase in DC resistance. It is therefore necessary to increase
the conductor thickness in order to suppress the reduction in
conductor width. As mentioned above, the conductor width W1 is
necessitated to set within the range 5 .mu.m.ltoreq.W1.ltoreq.36
.mu.m. Thickness T of the conductor is necessitated to satisfy the
expression T.ltoreq.5*W1 in view of the fabrication limitation.
Further, in order to prevent the DC resistance from excessively
increasing, a cross section T*W1 is set to be larger than 100
.mu.m.sup.2. (100 .mu.m.sup.2.ltoreq.T*W1) In case the conductor
thickness increases, side etching twice as large as the conductor
thickness T is produced when a vacuum film-forming/etching process
is used. It is actually difficult to thicken the conductors because
the space between the conductors is not smaller than T.times.2 when
the conductor thickness is increased. (It is necessary to increase
the spiral area because the space between the conductors is
widened).
[0070] This problem can be solved when the spiral coil conductor
layers 5 and 7 are formed by an electroplating method (additive
method). The relation between the thickness of the spiral
conductors and the space between the conductors can be set as
follows. The thick spiral coil conductor layers 5 and 7 can be
formed in a small space.
W2<T.times.2
[0071] The procedure for forming the spiral coil conductor layers 5
and 7 satisfying the aforementioned condition by a plating method
is as follows.
[0072] As shown in FIG. 7A, an undercoat conductor film 20 is
formed on each of the electrically insulating layers 4 and 6 by a
vacuum film-forming method (such as sputtering). This undercoat
conductor film 20 has a two-layered structure, which is
manufactured by continuous sputtering. On this occasion, the
undercoat conductor film 20 is preferably made of Cr/Cu (a
combination of a lower layer of Cr and an upper layer of Cu) or
Ti/Cu if consideration is given to adhesion to the resin of each of
the electrically insulating layers 4 and 6 and electroplating which
will be made. The lower Cu or Ti layer contributes toward adhesion
to the resin and the upper Cu layer contributes toward adhesion to
the electroplating layer.
[0073] A photo resist 21 is applied on the undercoat conductor film
20. On this occasion, the photo resist 21 applied is preferably
thicker than the spiral conductor which will be formed by
electroplating.
[0074] Then, the resist 21 is exposed to light while a photo mask
having a pattern necessary for obtaining the spiral conductor
pattern is used. The resist 21 is developed. In this manner, a
resist pattern shown in FIG. 7B is formed. That is, the undercoat
conductor film 20 is revealed in accordance with the spiral
shape.
[0075] Then, as shown in FIG. 7C, while the undercoat conductor
film 20 which has been already formed is used as an electrode, a
thickening conductor 22 is formed by electroplating. On this
occasion, the pattern of the resist 21 serves as a dam, so that
electroplating is performed spirally.
[0076] Then, as shown in FIG. 7D, the resist becoming unnecessary
after electroplating is peeled. Further, as shown in FIG. 7E, the
undercoat conductor film 20 except the thickening conductor 22
formed in the spiral plating portion is removed by etching. In this
manner, the spiral coil conductor layers 5 and 7 are completed.
[0077] The electroplating metal used in the thickening conductor is
preferably Cu if consideration is given to plating characteristic,
cost, electrical conductivity, etc.
[0078] It is effective that the thickening conductor 22 of Cu
formed by electroplating is further plated with Ni as shown in FIG.
7F if consideration is given to corrosion resistance and adhesion
of a resin which will be applied on the thickening conductor
22.
[0079] The procedure for producing the thin-film type common-mode
choke coil will be described below with reference to FIG. 4. The
electrically insulating layer 2 is formed on the first magnetic
substrate 1. A spin coating method, a dip coating method, a spray
coating method or a printing method is used as the method for
forming the electrically insulating layer 2.
[0080] Then, a film of a conductor is formed on the electrically
insulating layer 2 so that the first lead-out electrode layer 3 is
formed by photolithography. Sputtering, vapor deposition, plating
or the like is used as the method for forming the conductor film.
In the photolithography, a photo resist is used. After exposure and
development, an unnecessary metal portion is etched and then the
resist is peeled.
[0081] Then, the electrically insulating layer 4 is formed.
Although the electrically insulating layer 4 is formed in the same
manner as the electrically insulating layer 2, photolithography is
used for forming a through-hole 4a by development so that the
lead-out electrode layer 3 and the spirally shaped first coil
conductor layer 5 can be connected to each other. The lead-out
electrode layer 3 and the first coil conductor layer 5 are
electrically connected to each other by the through-hole 4a.
[0082] Then, the spirally shaped first coil conductor layer 5 is
formed and patterned by an electroplating method (additive method)
as shown in FIGS. 7A to 7F.
[0083] Then, the electrically insulating layer 6 is formed in the
same manner as the electrically insulating layer 2. The spirally
shaped second coil conductor layer 7 is formed and patterned on the
electrically insulating layer 6 in the same manner as the first
coil conductor layer 5.
[0084] Then, the electrically insulating layer 8 is formed in the
same manner as the electrically insulating layer 4.
Photolithography is used for forming a through-hole 8a by
development so that the second lead-out electrode layer 9 and the
spirally shaped second coil conductor layer 7 can be connected to
each other.
[0085] Then, the second lead-out electrode layer 9 is formed in the
same manner as the first lead-out electrode layer 3.
[0086] Then, the electrically insulating layer 10 is formed in the
same manner as the electrically insulating layer 2. The second
magnetic substrate 11 is bonded onto the electrically insulating
layer 10.
[0087] Although description has been made on the case where one
device is formed, a plurality of devices are produced
simultaneously on a substrate in actual production. After the
product on the substrate is cut into one-device chips, external
electrodes 15 are formed as shown in FIG. 5. In this manner, each
common-mode choke coil is completed.
[0088] According to this embodiment, the following effects can be
obtained.
[0089] The conductor width (W1) of the first and second coil
conductor layers 5 and 7 as two spiral conductor patterns satisfies
the following expression.
5 .mu.m.ltoreq.W1.ltoreq.36 .mu.m
[0090] As is obvious from FIG. 6, the cutoff frequency of a
transmission signal can be selected to be not lower than 2.4 GHz.
The common-mode choke coil can meet high-speed transmission.
[0091] When the thickening conductor 22 is formed on the undercoat
conductor film 20 by an electroplating method (additive method)
shown in FIGS. 7A to 7F, the relation between the conductor
thickness (T) of the spiral coil conductor layers 5 and 7 and the
space (W2) between the conductors can be selected to satisfy the
following expression.
W2<T.times.2
[0092] The space between the conductors can be reduced to attain
reduction in size (area) of the spiral shape.
[0093] Because the undercoat conductor film 20 is made of a
combination of a lower layer of Cr and an upper layer of Cu or a
combination of a lower layer of Ti and an upper layer of Cu,
adhesion to the resin of each electrically insulating layer can be
made good to be adapted to electroplating of the thickening
conductor 22 of Cu.
[0094] When each of the spiral coil conductor layers 5 and 7 is
plated with Ni, corrosion resistance and adhesion to the
electrically insulating layer of the resin applied on the spiral
coil conductor layer can be improved.
[0095] FIG. 8 shows the case where a thin-film type common-mode
choke coil array is produced according to another embodiment of the
invention. In this case, two common-mode choke coils each
equivalent to the common-mode choke coil according to the previous
embodiment are arranged on a first magnetic substrate 1 to thereby
form the array. In this configuration, a 2010 type (2 mm long by 1
mm wide by 1 mm thick) common-mode choke coil arraycanbe achieved.
Incidentally, parts equal or equivalent to parts in the previous
embodiment are referred to by identical numerals for the sake of
omission of duplicated description.
[0096] In each embodiment, the technique of bonding the second
magnetic substrate may be replaced by a technique of providing a
magnetic material such as a magnetic powder-containing resin by a
coating method or the like to cover the common-mode choke coil with
the magnetic material.
[0097] Although the embodiments of the invention have been
described above, the invention is not limited thereto and it is
self-evident to those skilled in the art that various changes or
modifications may be made without departing from the scope of
claim.
[0098] As described above, in accordance with the invention, there
can be achieved a micro-size thin-film type common-mode choke coil
and a common-mode choke coil array in which a transmission signal
with a frequency of the order of GHz can be transmitted at a high
speed.
* * * * *