Title: Method for manufacturing an inductor
Abstract: A method for manufacturing an inductor is performed in such a manner that the surface of a metal wire provided with an insulating film thereon is coated with a thermal melting resin. The thickness of the thermal melting resin is, for example, approximately 1 .mu.m. As the thermal melting resin, a thermoplastic resin or a thermosetting resin, such as a polyimide resin or an epoxy resin, containing 85 wt % of a powdered ferrite is used. This coated metal wire is densely wound to form a solenoid-type coil conductor. Next, the thermal melting resin is softened by a heat treatment at, for example, 180.degree. C. and is then solidified by spontaneous cooling. Accordingly, the portions of the coil conductor adjacent to each other are bonded together by the thermal melting resin.
Patent Number: 6,859,994 Issued on 03/01/2005 to Oshima, et al.
| Inventors:
|
Oshima; Hisato (Takefuj, JP);
Shikama; Takeshi (Yokaichi, JP);
Hamatani; Junichi (Matsumoto, JP);
Fukutani; Iwao (Shiga-ken, JP);
Saito; Kenichi (Fukui-ken, JP)
|
| Assignee:
|
Murata Manufacturing Co., Ltd. (Kyoto, JP)
|
| Appl. No.:
|
950899 |
| Filed:
|
September 10, 2001 |
Foreign Application Priority Data
| Sep 08, 2000[JP] | 2000-273997 |
| Current U.S. Class: |
29/602.1; 29/605; 29/608; 29/825; 156/169; 174/120R; 336/84M; 427/116 |
| Intern'l Class: |
H01F 007//06 |
| Field of Search: |
29/592.1,602.1,605-609,618,825,842,846,857
156/169,173,175,308.2,309.6
336/15,84 M
174/120,150 SC,105 SC,120 SR,120 SC,120 R
427/104,116,117,128,132,175,375,372.2
528/403,423
|
References Cited [Referenced By]
U.S. Patent Documents
| 4388371 | Jun., 1983 | Bolon et al. | 156/169.
|
| 4555422 | Nov., 1985 | Nakamura et al. | 428/34.
|
| 6087592 | Jul., 2000 | Nagel et al. | 174/120.
|
| 6198373 | Mar., 2001 | Ogawa et al. | 336/83.
|
| 6204744 | Mar., 2001 | Shafer et al. | 336/83.
|
| 6275132 | Aug., 2001 | Shikama et al. | 336/83.
|
| Foreign Patent Documents |
| 62-31103 | Feb., 1987 | JP.
| |
| 1-199415 | Aug., 1989 | JP.
| |
| 06-036937 | Feb., 1994 | JP.
| |
| 7-320938 | Dec., 1995 | JP.
| |
| 09-289129 | Nov., 1997 | JP.
| |
| 10-210726 | Aug., 1998 | JP.
| |
Primary Examiner: Tugbang; A. Dexter
Assistant Examiner: Nguyen; Donghai D.
Attorney, Agent or Firm: Keating & Bennett, LLP
Claims
What is claimed is:
1. A method for manufacturing an inductor, comprising the steps of:
coating a surface of a metal wire having an insulating film thereon with a
thermoplastic resin containing magnetic powder to form a coated metal
wire;
winding the coated metal wire in a single layer to form a solenoid-type
coil conductor which is hollow in the inside of the solenoid-type coil
conductor;
performing a heat treatment on the coil conductor to soften the
thermoplastic resin so that portions of the coil conductor that are
adjacent to each other are bonded together by the thermoplastic resin;
filling a resin containing magnetic powder by injection-molding inside and
outside the solenoid-type coil conductor which is placed within a molding
die to from an encapsulating molded body having a predetermined shape so
as to encapsulate the coil conductor;
removing the encapsulating molded body from the molding die; and
providing external terminal electrodes on surfaces of the removed
encapsulating molded body so as to be electrically connected with the ends
of the coil conductor; wherein
the steps of winding the coated metal wire, performing heat treatment and
filling a resin are performed in this order.
2. A method for manufacturing an inductor according to claim 1, wherein the
metal wire has a diameter of about 200 .mu.m.
3. A method for manufacturing an inductor according to claim 1, wherein the
metal wire includes a material selected from the group consisting of Ag,
Pd, Pt, Au, and Cu.
4. A method for manufacturing an inductor according to claim 1, wherein the
insulating film is made of one of a polyester resin and a polyamide-imide
resin.
5. A method for manufacturing an inductor according to claim 1, wherein the
thickness of the thermoplastic resin is approximately 1 .mu.m.
6. A method for manufacturing an inductor according to claim 1, wherein the
resin includes one of an epoxy resin and a polyimide resin, containing
powdered ferrite at a ratio of about 85 wt %.
7. A method for manufacturing an inductor according to claim 1, wherein the
step of performing the heat treatment includes softening the thermoplastic
resin by heating the coil conductor at a temperature of about 180.degree.
C.
8. A method for manufacturing an inductor according to claim 7, further
comprising the step of solidifying the thermoplastic resin via cooling the
thermoplastic resin after the heat treatment.
9. A method for manufacturing an inductor according to claim 1, wherein the
step of filling includes using a molding compound that is formed by
compounding one of a synthetic resin and a polyethylene terephthalate
resin as a primary component, a dispersing agent, and a powdered
Ni--Cu--Zn--based ferrite.
10. A method for manufacturing an inductor according to claim 1, further
comprising the step of removing the resin containing the powdered ferrite
at both ends of the encapsulating molded body before the step of providing
the external terminal electrodes.
11. A method for manufacturing an inductor according to claim 1, wherein
the step of providing the external terminal electrodes includes forming an
electroless plating film on ends of the encapsulating molded body, forming
a resist on both ends of the encapsulating molded body, removing
unnecessary portions of the electroless plating film, and removing the
resist.
12. A method for manufacturing an inductor according to claim 1, wherein
the step of winding the coated metal wire includes the step of densely
winding the coated metal wire such that adjacent portions of the
thermoplastic resin are in contact with one another.
13. A method for manufacturing an inductor according to claim 1, wherein
the step of winding the coated metal wire includes the step of winding the
metal wire such that no portion of the metal wire overlaps another portion
of the metal wire in a radial direction thereof.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to inductors, and more particularly, relates
to a high-current inductor preferably for use in eliminating noise
transmitted to and generated from electronic apparatuses and other
devices, and to a manufacturing method for such an inductor.
2. Description of the Related Art
Recently, in accordance with the trends towards miniaturization of
circuits, higher integration thereof, and high frequency processing,
high-current inductors that are compact and surface-mountable have been
increasingly in demand. Conventional inductors include a wire-wound
inductor having a coil conductor embedded in an encapsulating molded body.
This wire-wound inductor is manufactured by densely winding a metal wire
having an insulating film thereon without forming spaces between portions
of the metal wire adjacent to each other to form a solenoid-type coil
conductor, placing the coil conductor in a molding die, and injecting an
encapsulating resin in the molding die so as to form an encapsulating
molded body having the coil conductor embedded therein.
However, according to this method for manufacturing a conventional
wire-wound inductor, when a thin metal wire is used for forming a
solenoid-type coil conductor, it is difficult for the coil conductor to
retain its shape by itself, and as a result, deformation of the coil
conductor is likely to occur. Accordingly, when these coil conductors are
fed in an automated manufacturing line, the coil conductors are deformed,
and hence, an automated machine such as a coil inserting machine becomes
unable to place the coil conductors in molding dies, which causes many
problems such as automated manufacturing lines being interrupted, and
other significant problems.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of
the present invention provide an inductor which has a greatly improved
shape retaining property, is superior in mass-productivity, and is easily
and effectively applied to an automated manufacturing line, and also
provide a method of manufacturing such an inductor.
According to a preferred embodiment of the present invention, a method for
manufacturing an inductor includes the steps of coating the surface of a
metal wire having an insulating film thereon with a thermal melting resin
to form a coated metal wire, winding the coated metal wire to form a
solenoid-type coil conductor, performing a heat treatment on the coil
conductor to soften the thermal melting resin so that portions of the coil
conductor adjacent to each other are bonded together by the thermal
melting resin, molding a resin containing magnetic powder into an
encapsulating molded body having a predetermined shape so as to
encapsulate the coil conductor, and providing external terminal electrodes
on surfaces of the encapsulating molded body so as to be electrically
connected with the ends of the coil conductor.
In the method described above, as the thermal melting resin, for example, a
thermoplastic resin or a thermosetting resin may be used. In addition, the
thermal melting resin may include magnetic powder.
According to the method described above, since the portions of the
solenoid-type coil conductor adjacent to each other are bonded together by
the thermal melting resin, the shape of the solenoid-type coil conductor
is maintained reliably. As a result, the coil conductor is easily handled
in a backend process, and interruption of a manufacturing facility caused
by the deformation of the coil conductors is prevented.
According to another preferred embodiment of the present invention, an
inductor includes an encapsulating molded body including a resin
containing magnetic powder, a solenoid-type coil conductor encapsulated in
the encapsulating molded body, external terminal electrodes which are
provided on surfaces of the encapsulating molded body and which are
electrically connected with the ends of the coil conductor, wherein the
coil conductor is coated with a thermal melting resin and portions of the
coil conductor adjacent to each other are bonded together by the thermal
melting resin, and the inside and the outside of the solenoid portion of
the coil conductor are filled with the resin containing the magnetic
powder.
According to the unique structure of the preferred embodiment of the
inductor described above, since the portions of the coil conductor
adjacent to each other are bonded together by the thermal melting resin
containing no magnetic powder, the magnetic resistance between the
portions of the coil conductor adjacent to each other is greatly
increased, and hence, a short path of the magnetic flux is prevented. As a
result, most of the magnetic flux passing inside the solenoid portion of
the coil conductor contributes to the inductance, and hence, DC
superposition characteristics of the inductor are greatly improved.
Other features, elements, characteristics and advantages of the present
invention will become more apparent from the detailed description of
preferred embodiments below with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing a metal wire for illustrating a method
for manufacturing an inductor according to a preferred embodiment of the
present invention;
FIG. 2 is a front view showing a coil conductor for illustrating a step
subsequent to that shown in FIG. 1;
FIG. 3 is a cross-sectional view showing the coil conductor before and
after a heat treatment for illustrating a step subsequent to that shown in
FIG. 2;
FIG. 4 is a perspective view showing an encapsulating molded body
encapsulating the coil conductor for illustrating a step subsequent to
that shown in FIG. 3;
FIG. 5 is a partial view of the inductor for illustrating a step subsequent
to that shown in FIG. 4;
FIG. 6 is a cross-sectional view showing a state of a magnetic flux inside
the inductor shown in FIG. 5; and
FIG. 7 is a cross-sectional view showing a modified example of the inductor
shown in FIG. 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, an inductor and a manufacturing method therefor according to
preferred embodiments of the present invention will be described with
reference to accompanying drawings.
As shown in FIG. 1, a metal wire 1 provided with an insulating film 2
thereon is first prepared. As the metal wire 1, for example, a metal of
about 200 .mu.m in diameter including at least a material selected from
the group consisting of Ag, Pd, Pt, Au, and Cu, or an alloy wire
containing at least one metal mentioned above is preferably used. However,
other suitable materials may also be used. As the insulating film 2, for
example, a resin such as a polyester resin or a polyamide-imide resin, or
other suitable material, is preferably used. A thermal melting resin 3 is
coated on the surface of the insulating film 2 covering the metal wire 1.
The thickness of the thermal melting resin 3 is, for example,
approximately 1 .mu.m. As the thermal melting resin 3, a thermosetting
resin or a thermoplastic resin, such as an epoxy resin or a polyimide
resin, containing powdered ferrite at a ratio of about 85 wt % is
preferably used. Other suitable materials and compositions for the thermal
melting resin 3 may also be used. Since heat is applied thereto in an
injection molding step of a backend process, the thermal melting resin 3
is preferably formed of a thermosetting resin.
Next, this insulated metal wire 1 is densely wound as shown in FIG. 2 so as
to form a solenoid-type coil conductor 10. The solenoid portion 11 of the
coil conductor 10 preferably has a diameter D of approximately 2.2 mm and
a length L of approximately 4.6 mm. Both ends of the solenoid portion 11
are linear lead portions 12.
Next, as shown in FIG. 3, the thermal melting resin 3 is softened by
performing a heat treatment on the coil conductor 10 at, for example,
about 180.degree. C. and is then solidified by spontaneous cooling. As a
result, the portions of the coil conductor 10 adjacent to each other are
bonded together by the thermal melting resin 3.
Subsequently, the coil conductor 10 is placed in a molding die (not shown)
preferably formed of polystyrene so that the coil axis is in conformity
with the axis of the molding die. In this step, when an alignment hole is
provided in the molding die for placing the lead portions 12 of the coil
conductor 10, the coil conductor 10 can be easily placed at a
predetermined position in the molding die.
In the molding die receiving the coil conductor 10 therein, a molding
compound (slurry) is injected. The molding compound is preferably formed
by compounding a synthetic resin, such as an epoxy resin, a polyphenylene
sulfide resin, or a polyethylene terephthalate resin, as a primary
component, a dispersing agent, and a powdered Ni--Cu--Zn--based ferrite.
After the molding compound is solidified, the molded body is removed from
the molding die, whereby a chip-type encapsulating molded body 15 having
insulating properties and having a substantially rectangular
parallelepiped shape as shown in FIG. 4 is obtained, and is formed of the
resin containing the ferrite therein. The inside and outside of the
solenoid portion 11 of the coil conductor 10 are filled with the resin
containing the powdered ferrite.
Subsequently, the resin containing the powdered ferrite at both ends of the
encapsulating molded body 15 is removed by using a sand blast method or
other suitable method so that the end areas of the lead portions 12 of the
coil conductor 10 are exposed, and in addition, the insulating film 2 and
the thermal melting resin 3 covering the lead portions 12 thus exposed are
also removed.
Next, on the entire encapsulating molded body 15, an electroless plating
film including Ni, Cu, or other suitable material is formed, in which the
thickness thereof is preferably approximately 1 .mu.m or less. A resist is
then applied to the both ends of the encapsulating molded body 15, and an
electroless plating film formed on unnecessary areas is removed by
etching. The resist is then removed, and an electroplating film including
Cu, Ni, Sn, Pb--Sn, Ag, Pd, or other suitable material is formed to have a
thickness of approximately 15 .mu.m to approximately 20 .mu.m in
consideration of the solderability, loss of effective area of
electroplating film caused by soldering, and other factors. Consequently,
as shown in FIG. 5, external terminal electrodes 21 and 22 are formed on
the both ends of the encapsulating molded body 15 so as to be in
electrical contact with the lead portions 12 of the coil conductors 10.
According to the manufacturing method described above, since the portions
of the solenoid-type coil conductor 10 adjacent to each other are bonded
together by the thermal melting resin 3, the coil conductor 10 has a
greatly improved shape retaining property, and hence, the handling of the
coil conductor 10 in the backend process is much easier and error-free.
In addition, examples of the coil conductors 10 according to preferred
embodiments of the present invention were fed in an automated
manufacturing line, and the number of interruption of the automated
manufacturing line, caused by a coil inserting machine which is unable to
place the coil conductor 10 in the molding die due to the deformation of
the coil conductors 10, was counted. According to the results, almost no
interruptions of the automated manufacturing line caused by the
deformation of the coil conductors 10 were observed. In contrast, in the
case of a conventional coil conductor in which the adjacent portions are
not bonded together, during an 8-hour operation of the automated
manufacturing line, the interruption caused by the deformation of the coil
conductors occurred 5 to 100 times.
In addition, since the thermal melting resin contains a powdered ferrite,
decreases in inductance and impedance do not occur. More specifically, the
impedance of an obtained wire-wound inductor 30 is about 700 .OMEGA.,
which is equivalent to that of a conventional inductor without using a
thermal melting resin.
However, a powdered ferrite is contained in the thermal melting resin 3, a
short path flux .PHI.2 may be generated in some cases as shown in FIG. 6.
Accordingly, in order to suppress this short path flux .PHI.2, as shown in
FIG. 7, the portions of the solenoid-type coil conductor 10 adjacent to
each other may be bonded together by using a thermal melting resin 3a
containing no powdered ferrite. As a result, since a non-magnetic resinous
layers are formed between the portions of the coil conductor 10 adjacent
to each other, the magnetic resistance between the portions described
above is increased, and hence, the short path flux .PHI.2 can be
suppressed. Consequently, most of the flux .PHI.1 passing inside the
solenoid portion 11 of the coil conductor 10 contributes to the
inductance, and as a result, superior DC superposition characteristics can
be obtained.
The inductor and the manufacturing method therefor of the present invention
are not limited to preferred embodiments described above and may be
variously modified within the scope of the present invention. For example,
the encapsulating molded body may have a substantially circular
cross-section or other configuration in addition to a substantially
rectangular cross-section, and the cross-section of the solenoid portion
of the coil conductor may be substantially circular, substantially
rectangular, or other suitable shape.
As has thus been described, according to the present invention, since the
portions of the solenoid-type coil conductor adjacent each other are
bonded together by the thermal melting resin, the shape retaining property
of the coil conductor is greatly improved. As a result, the coil conductor
is easily handled in the backend process, and interruption of the
manufacturing facility or manufacturing processes caused by the
deformation of the coil conductor is prevented.
In addition, since the portions of the coil conductor adjacent to each
other are bonded together by the thermal melting resin containing no
magnetic powder, the magnetic resistance between the portions of the coil
conductor adjacent to each other is increased, and hence, the short path
of the magnetic flux is prevented. Consequently, most of the magnetic flux
passing inside the solenoid portion of the coil conductor contributes to
the inductance, and as a result, superior DC superposition characteristics
are achieved.
While preferred embodiments of the invention have been described above, it
is to be understood that variations and modifications will be apparent to
those skilled in the art without departing the scope and spirit of the
invention. The scope of the invention, therefore, is to be determined
solely by the following claims.
*
