Bead inductor and method of manufacturing same

Inductor devices – Core surrounding linear conductor

Reexamination Certificate

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Details

C336S172000

Reexamination Certificate

active

06242995

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a bead inductor and a bead inductor produced by such method such that the bead inductor is adapted for use in a noise controlling circuit and other circuits.
2. Description of the Related Art
As a noise-controlling device, especially a device for use with a microprocessor, for example, which is required to pass a large electric current therethrough, an experimental bead inductor has been proposed and tested. Such a bead inductor is an example of an experimental device which has not been publicly disclosed and is formed of a resin material or a rubber material including a powdery magnetic substance such as ferrite powder having a conductor coil embedded therein. In such a bead inductor, a conductor coil is embedded into a resin material or a rubber material via injection molding or other process, to form a molded body which is cut off at both ends thereof to expose both ends of the coil disposed therein. Then, metal caps are connected thereto via conductive resin paste or spot welding so as to define external terminals.
FIGS. 5 and 6
are sectional views illustrating a method for manufacturing the bead inductor. Referring to
FIGS. 5 and 6
, a metallic mold for injection molding to manufacture the bead inductor includes an upper mold
1
and a lower mold
2
. A cavity is formed in the upper mold
1
and defines a space for molding a resin member. In the lower mold
2
, a pin
4
is provided so as to be disposed in the cavities
3
when the upper mold
1
and the lower mold
2
are mated with each other. The upper mold
1
has a gate
1
a
for supplying a melted resin material into the cavity
3
.
In order to manufacture a molded body of the bead inductor using the metallic mold shown in
FIG. 5
, the pin
4
is inserted into a conductor coil, which is formed by winding a metallic wire such as a copper wire coated by a polyester resin, etc., for insulation. Then, the melted resin including a powdery magnetic substance such as ferrite powder is injected into the cavity
3
via the gate
1
a.
As a result, the outer portion of the conductor coil having the pin
4
inserted therein is molded of the melted resin.
FIG. 6
is a sectional view showing the state of the outside portion of a coil
5
molded in this manner. After the step shown in
FIG. 5
, the pin
4
is removed and the same resin material used for the outside portion of the coil
5
is injected into the space produced by the removing the pin
4
, so as to mold the inside of the coil
5
of the melted resin, so that the coil
5
is embedded in the resin.
Both ends of the molded body obtained in this manner are cut off by a dicing saw or other cuffing instrument, such that the ends of the coil embedded in the resin of the molded body are exposed.
FIG. 7
is a side view showing the molded body after the cutting step described above is performed and
FIG. 8
is a plan view thereof. A molded body
7
is formed by embedding the conductor coil
5
into a resin molding
6
. On one of the cutting planes
7
a
of the molded body
7
, one end portion
5
a
of the conductor coil
5
is exposed. On the other of the cutting planes
7
b
of the molded body
7
, the other end portion
5
b
of the conductor coil
5
is exposed. In a conventional manufacturing method, metallic caps which define external terminals are attached so that the end portions
5
a
and
5
b
of the conductor coil
5
are electrically connected thereto via conductive resin paste or spot welding. Solder may be used to attach the metallic cap, and in this case, solder paste, etc., is coated on the end portions of the conductor coil exposed on the end planes of the molded body or on the metallic caps.
In a conventional bead inductor, the conductor coil inside of the molding is electrically connected to the external terminal via conductive resin paste, spot welding, etc., as described above. As a result, there has been a problem of a low degree of reliability in the electrical connection between the conductor coil and the external terminal. That is, it is difficult to secure the spot welding on the ends
5
a
and
5
b
of the conductor coil
5
in the respective cutting planes
7
a
and
7
b
of the molded body
7
, because the surfaces of the ends are flat as shown in
FIG. 7
, resulting in a low degree of reliability of the electrical connection when the external terminal such as a metal cap is welded thereon. When the external terminals such as the metal caps are bonded onto the ends
5
a
and
5
b
of the conductor coil
5
via conductive resin paste, the connecting reliability is also low because of poor adhesive properties.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing a bead inductor and a bead inductor produced by such method such that the connection reliability between the conductor coil and the external terminal is greatly improved.
In accordance with one preferred embodiment of the present invention, a method of manufacturing a bead inductor includes the steps of forming a molded body of at least one of a resin material and a rubber material including a powdery magnetic substance, the molded body having a conductor coil including a wound coated metallic wire embedded therein; cutting both ends of the molded body so as to expose ends of the conductor coil; forming convex portions on the ends of the conductor coil, which are exposed by the cutting step; and attaching external terminals to the convex portions so that the external terminals are electrically connected to the conductor coil.
Because the convex portion is provided at the end of the conductor coil, the connection by spot welding or soldering is much easier and much more reliable so as to further securely connect the conductor coil to the external terminal electrically. Therefore, the connecting reliability between the conductor coil and the external terminal is greatly increased.
The step of forming convex portions according to a preferred embodiment of the present invention may be achieved by plating the ends of the conductor coil. The method of plating is not specifically limited. Electrolytic plating or electroless plating may be utilized. In the case of the electrolytic plating, the plating may be performed with a plurality of layers, for example. In order to improve solder wetting properties in spot welding or soldering, after Ni layer plating is performed, Sn layer plating may be performed thereon.
The step of forming convex portions according to a preferred embodiment of the present invention may be achieved by applying solder onto the ends of the conductor coil. As a method for applying solder, for example, the convex portions made of solder may be formed by immersing the ends of the conductor coil on the surface of the molded body into a melting soldering bath after coating flux thereon so as to deposit the solder on the ends of the conductor coil.
In accordance with a preferred embodiment of the present invention, when the step of forming convex portions is achieved by applying solder onto the ends of the conductor coil, solder having a high melting point may be utilized. When the inductor is mounted on a substrate via flow and reflow soldering, standard solder can be used for forming the convex portion. When occasion demands that the inductor is soldered on a substrate at a high temperature, it is preferable that the convex portion be formed of solder having a high melting point, which is the so-called high-temperature solder.
The step of forming convex portions according to a preferred embodiment of the present invention may be achieved by sandblast treating the ends of the molded body so as to expose the ends of the conductor coil by scraping the surfaces of the ends of the molded body. Because the convex portion is formed so that the conductor coil is exposed to protrude by scraping the surfaces of the ends of the molded body, there is no possibility of exfoliation of the c

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