Inductor devices – Core forms casing
Reexamination Certificate
2001-03-14
2003-09-02
Mai, Ann (Department: 3729)
Inductor devices
Core forms casing
C336S200000, C336S223000, C336S192000
Reexamination Certificate
active
06614338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates inductors and a method for manufacturing inductors. In particular, the present invention relates to an inductor and a method for manufacturing inductors, in which a molded magnetic body provided with a pair of external electrodes connected to an internal conductor-coil embedded in the molded magnetic body is made by molding a magnetic material which includes a powdered magnetic material and a resin.
2. Description of the Related Art
A conventional surface-mounting-type inductor
60
shown in
FIG. 12
includes a coil (internal conductor-coil)
52
defining an inductance element is embedded in a molded magnetic body
53
formed by molding a magnetic material
51
including a powdered magnetic material and a resin. The molded magnetic body
53
is provided at ends thereof with a pair of external electrodes
54
a
and
54
b
connected to the coil
52
at ends
52
a
and
52
b,
respectively, of the coil
52
.
The inductor
60
is manufactured, for example, such that a coil (an air-core coil) formed by densely winding an insulative covered copper wire and cutting the same by a predetermined length is provided in a mold, a magnetic molding compound made by kneading a powdered magnetic material and a resin is injected into the mold and is provided around the coil (inside and outside the coil), and the mold is released, thereby producing a molded magnetic body. The molded magnetic body is provided with external electrodes made of metallic films at ends of the molded magnetic body including exposed portions of the coil, the external electrodes are formed by coating, baking, deposition, or sputtering of a conductive paste, such that the external electrodes are connected to the exposed portions of the coil.
The inductor
60
can be manufactured only by forming the molded magnetic body
53
by molding the magnetic material
51
which is made by kneading a powdered magnetic material and a resin, and providing the external electrodes
54
a
and
54
b
made of metallic films. Therefore, a firing process at a high temperature and a baking process for the electrodes, which are necessary in manufacturing a conventional ceramic inductor including a magnetic ceramic, are not necessary, whereby manufacturing costs are reduced.
In the inductor
60
, the external electrodes
54
a
and
54
b
are arranged to connect to exposed portions
52
a
and
52
b
which are portions of final windings of wire of a coil
52
. The shape and the position (for example, the position in a vertical direction of the exposed portion
52
a
or
52
b
) of the exposed portion
52
a
or
52
b
of the coil
52
often differ according to each inductor
60
due to deformation of the coil
52
during injection of the magnetic material
51
.
In a conventional manufacturing method, since the coil
52
is deformed due to being pressed by the mold when the length of the coil
52
is greater than that of the molded magnetic body
53
, the length of the coil
52
must be substantially the same as that of the molded magnetic body
53
. Therefore, as shown in
FIG. 13
, the exposed portion
52
a
or
52
b
of the coil
52
is formed partially in the final winding of wire of the coil
52
at the end of the molded magnetic body
53
, and the area of the exposed portion
52
a
or
52
b
is reduced because of the difficulty in forming the exposed portion
52
a
or
52
b
which significantly protrudes from the end of the molded magnetic body
53
.
Therefore, the connection between the coil
52
and the external electrodes
54
a
and
54
b
is not secure and an overcurrent is applied to the coil.
In another conventional inductor, the inductor
60
is provided with the external electrodes
54
a
and
54
b
which are defined by a plurality of layers such that the external electrodes
54
a
and
54
b
are easily soldered, a metallic film, such as solder, tin, or silver, to which solder easily adheres, being used as an outermost layer. When the inductor
60
is mounted on a mounting body such as a printed circuit board
61
via a method such as reflow-soldering, as shown in
FIG. 14
, a solder fillet
62
is raised to a height Hs which is at least ⅓ of a height H of the inductor
60
because the solder easily adheres to the external electrodes
54
a
and
54
b.
The inductor
60
is mounted such that the solder fillet
62
is electrically connected to the external electrodes
54
a
and
54
b.
In the conventional method of manufacturing an inductor, a magnetic molding compound is injected into the mold in which a coil is not firmly affixed in a desired position in the mold. Therefore, there is a risk that the coil will move depending on the direction of flow of the magnetic molding compound during the injection process.
For example, when the inductor
60
in which the coil
52
is displaced, as shown in
FIG. 15
, is mounted on the printed circuit board
61
, the solder fillet
62
does not reach the positions of the exposed portions
52
a
and
52
b
of the coil
52
with the external electrodes
54
a
and
54
b
therebetween even when the solder fillet
62
is raised to the height Hs which is at least ⅓ of the height H of the inductor
60
, because the exposed portions
52
a
and
52
b
of the coil
52
are excessively elevated, and a gap G is produced between a lower end of the exposed portion
52
a
or
52
b
and an upper end of the solder fillet
62
. The current applied to the inductor
60
flows through only the external electrodes
54
a
and
54
b
at the gap portion. Therefore, when the external electrodes
54
a
and
54
b
are made of a metallic thin film such as a solder film, long-term reliability and unsafe operation when an overcurrent is applied occur, due to insufficient current capacity in the portion having the gap.
To overcome these problems, the thickness of the metallic film defining the external electrodes
54
a
and
54
b
may be increased. However, the manufacturing costs also increase with the increased thickness of the film.
The external electrodes
54
a
and
54
b
may be formed by bonding metallic plates to the ends of the molded magnetic body
53
, each of the metallic plates having a sufficient thickness required for the current capacity. However, the manufacturing costs are also increased with this method.
SUMMARY OF THE INVENTION
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide an inductor and a method for manufacturing the inductor, in which reliable connection between an internal conductor-coil and external electrodes, long-term reliability after mounted, and safety when applied with an overcurrent are achieved.
An inductor according to a preferred embodiment of the present invention includes a molded magnetic body formed by molding a magnetic material including a powdered magnetic material and a resin-based material, an internal conductor-coil embedded in the molded magnetic body such that both ends of the internal conductor-coil are exposed from both end surfaces of the molded magnetic body, respectively, and a pair of external electrodes provided at the respective end surfaces of the molded magnetic body to connect to the internal conductor-coil at the respective ends thereof. At least two thirds of a final winding of wire at each of the ends of the internal conductor-coil project from the end surface of the molded magnetic body by at least about one fifth of the diameter of the wire of the internal conductor-coil. The external electrodes are each connected with at least about two thirds of the final winding of wire at each of the ends of the internal conductor-coil, which project from the end surface of the molded magnetic body by at least about one fifth of the diameter of the wire of the internal conductor-coil.
At least about ⅔ of a final winding of wire at each end of the internal conductor-coil project from the end surface of the molded magnetic body by an amount of at least about ⅕ of the diameter of a wire, and the external
Hamatani Junichi
Oshima Hisato
Keating & Bennett LLP
Mai Ann
Murata Manufacturing Co. Ltd.
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