Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
2001-03-15
2002-11-19
Mai, Anh (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S232000, C029S602100
Reexamination Certificate
active
06483414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a multilayer-type chip inductor, and in particular, a multilayer-type chip inductor having a small DC resistance.
2. Description of the Related Art
A method of reducing the DC resistance of a multilayer-type chip inductor involves increasing the cross-sectional area of an internal conductor. In order to increase the cross-sectional area of an internal conductor, the width and the thickness of the internal conductor may be increased. If the width of the internal conductor is increased, however, the inductance decreases. Increasing the cross-sectional area of the internal conductor also may cause various manufacturing problems. Therefore, it is difficult in practice to increase the cross-sectional area of the internal conductor. For this reason, a coil comprising parallel internal conductors has been conceived as a method for decreasing the DC resistance of an inductor.
First, a multilayer-type chip inductor of a first conventional example in which coils are connected in parallel will be described with reference to
FIGS. 4 and 5
.
FIG. 5
is a cross-sectional view of the device shown in FIG.
4
.
With reference to both
FIGS. 4 and 5
, a multilayer-type chip inductor
1
is formed in such a way that green sheets
2
a
to
2
e
having electrode films
3
a
to
3
e
formed thereon, respectively, are multilayered in two upper and lower stages and sintered together. Further, external electrodes (not shown) are formed on both ends of this sintered body.
The first green sheets
2
a
to
2
e
are formed into sheets from an insulating ceramic slurry, such as ferrite or a dielectric. The electrode films
3
a
to
3
e
, which become internal conductors, are formed on one surface of the sheets by printing or like technique. Furthermore, in the first green sheets
2
b
to
2
e
, via holes
4
b
to
4
e
are provided at one end of each of the electrode films
3
b
to
3
e
. The upper and lower stages of first green sheets
2
a
to
2
e
are multilayered in sequence, causing the electrode films
3
a
to
3
e
to conduct in order to form two inductors
5
. In parts of the electrode films
3
a
and
3
e
, one end of each film is extended to the end of each of the green sheets
2
a
and
2
e
so that it connects to and provides conduction with the external electrode (not shown), forming extension electrodes
6
a
and
6
e
, respectively.
The multilayer-type chip inductor
1
is obtained in the following way. As shown in
FIG. 4
, a predetermined number of dummy green sheets
2
f
on which no electrode film is formed are multilayered in sequence to form a bottom portion of the device. Next, the first green sheets
2
a
to
2
e
containing the electrode films
3
a
to
3
e
on their respective top faces are multilayered on top of the dummy green sheets
2
f
. Further, in the same manner, another series of green sheets
2
a
to
2
e
are multilayered, and a predetermined number of dummy green sheets
2
f
are applied. Then, the body is contact-bonded and sintered. Then, external electrodes are formed at both ends (the right side and the left side in
FIG. 4
) of this sintered body.
Since the first green sheets
2
a
to
2
e
shown in
FIG. 4
are formed with the electrode films
3
a
to
3
e
of a ¾ turn, respectively, two inductors
5
of 3.5 turns are formed inside the sintered body.
The external electrode on the right side is made to conduct with the extension electrodes
6
a
and
6
a
of the inductors
5
and
5
, and the external electrode on the left side is made to conduct with the extension electrodes
6
e
and
6
e
of the inductors
5
and
5
. Therefore, as shown in
FIG. 5
, the multilayer-type chip inductor
1
is such that the two upper and lower inductors
5
and
5
are connected in parallel.
Next, a multilayer-type chip inductor of a second conventional example comprising a coil of parallel internal conductors will be described with reference to
FIGS. 6 and 7
. Components in
FIGS. 6 and 7
which are the same as those of the above-described first conventional example are given the same reference numerals and a detailed description thereof is omitted.
A multilayer-type chip inductor
11
is formed in such a way that first green sheets
2
a
to
2
e
have electrode films
3
a
to
3
e
formed thereon, respectively. First green sheets
12
a
to
12
e
are similar to the first green sheets
2
a
to
2
e
. The green sheets
2
a
to
2
e
are alternately arranged (e.g., interleaved) in a multilayered fashion with the green sheets
12
a
to
12
e
. These multiple layers are then sintered, and then external electrodes (not shown) are formed at both ends of this sintered body.
The first green sheets
12
a
to
12
e
are formed into sheets from an insulating ceramic slurry in the same manner as the first green sheets
2
a
to
2
e
, and electrode films
13
a
to
13
e
are formed on one surface thereof. Further, in the first green sheets
12
b
to
12
e
, via holes
14
b
to
14
e
are formed at the ends of the electrode films
13
b
to
13
e
, respectively. In the first green sheets
12
a
to
12
d
, via holes
17
a
to
17
d
are provided at the other ends of the electrode films
13
a
to
13
d
, respectively.
The multilayer-type chip inductor
11
is obtained in the following way. As shown in
FIG. 6
, a predetermined number of dummy green sheets
2
f
are multilayered in sequence to from a bottom portion. Next, the first green sheets
2
a
,
12
a
,
2
b
,
12
b
,
2
c
,
12
c
,
2
d
,
12
d
,
2
e
, and
12
e
are multilayered on top of the bottom portion, with each surface having an electrode formed on its top side. Further, a predetermined number of dummy green sheets
2
f
are applied on top of the body, and then the body is contact-bonded and sintered. Then, external electrodes are formed at both ends (the right side and the left side in
FIG. 6
) of this sintered body.
Therefore, in the multilayer-type chip inductor
11
, an inductor
15
of 3.5 turns which is made to branch into two lines via the respective via holes is formed within the multilayered body. The external electrode on the right side is made to conduct with the extension electrodes
6
a
and
16
a
of the inductor
15
, and the external electrode on the left side is made to conduct with extension electrodes
6
e
and
16
e
of the inductor
15
.
However, in the above-described conventional first and second examples, although the DC resistance of the inductor is reduced, the following problems are present. In the first conventional example, because the decrease in inductance is large, the number of windings of the coil must be increased to maintain the inductance at a desired value. In the second conventional example, although the decrease in inductance is small, the number of via holes corresponding to via holes
17
a
to
17
d
provided in the first green sheets
12
a
to
12
d
and the number of types of first green sheets increases, causing the manufacturing process to become more complex.
SUMMARY OF THE INVENTION
An object of the present invention is to solve at least the above-described problems. More specifically, an object of the present invention is to provide a method of manufacturing a multilayer-type chip inductor such that the DC resistance of the inductor is small without decreasing the inductance and the impedance.
To achieve the above-described object, according to the present invention, there is provided a method of manufacturing a multilayer-type chip inductor, comprising the steps of: preparing a ceramic green sheet; forming an electrode film on one surface of the green sheet; multilayering a plurality of the green sheets in such a way that the surfaces having electrode films formed thereon face each other for pairs of the green sheets; contact-bonding the green sheets; and sintering the green sheets.
More specifically, the present invention provides a method of manufacturing a multilayer-type chip inductor, comprising the steps of: preparing a ceramic green sheet; overlaying a
Ikeda Masaharu
Nishii Motoi
Takeuchi Hiroyuki
Mai Anh
Murata Manufacturing Co. Ltd.
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