Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-11-02
2004-10-12
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S184000, C361S321200, C361S321300
Reexamination Certificate
active
06803839
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multilayer inductor-capacitor (LC) composite components including a coil unit and a capacitor unit, and more specifically relates to a multilayer LC composite component which includes a capacitor unit having a ground-side capacitor electrode and a signal-side capacitor electrode which oppose each other with an insulating layer therebetween, the ground-side capacitor electrode having an electrode-free area at a central region thereof and the signal-side capacitor electrode being electrically connected to the coil unit via the electrode-free area.
2. Description of the Related Art
FIGS. 9
,
10
, and
11
show a perspective view, an exploded perspective view, and an equivalent circuit diagram, respectively, of a multilayer LC noise filter as an example of a known multilayer LC composite component. This multilayer LC noise filter is a so-called T-type LC noise filter constructed by disposing a first external electrode
55
a
, a second external electrode
55
b
, and an external grounding electrode
56
on a device
54
including a first coil unit
51
, a second coil unit
52
, and a capacitor unit
53
including signal-side capacitor electrodes
63
and ground-side capacitor electrodes
65
. The first external electrode
55
a
is electrically connected to a base end portion (IN-side end portion)
51
a
of the first coil unit
51
, the second external electrode
55
b
is electrically connected to a base end portion (OUT-side end portion)
52
a
of the second coil unit
52
, and the external grounding electrode
56
is electrically connected to the ground-side capacitor electrodes
65
.
The manufacturing process of this multilayer LC composite component will be described below with reference to FIG.
12
. First, magnetic ceramic green sheets
62
having internal electrodes (coil patterns)
61
which define the first coil unit
51
, dielectric ceramic green sheets (dielectric layers)
64
having the signal-side capacitor electrodes
63
(see
FIG. 13B
) which define the capacitor unit
53
, dielectric ceramic green sheets (dielectric layers)
66
having the ground-side capacitor electrodes
65
(see
FIG. 13A
) which are to be grounded, magnetic ceramic green sheets
68
having internal electrodes (coil patterns)
67
which define the second coil unit
52
, and external layer sheets (not shown) are laminated and press-bonded. Then, the patterns (electrodes) are electrically connected to each other by via holes, and firing is performed under predetermined conditions. Lastly, as shown in
FIG. 9
, the first external electrode
55
a
, the second external electrode
55
b
, and the external grounding electrode
56
are formed.
The above-described conventional multilayer LC composite component suffers from problems in that the insulation resistance decreases because of cracks which occur in the device
54
along the surfaces of the ground-side capacitor electrodes
65
due to the following reasons:
(1) As shown in
FIG. 13A
, each of the ground-side capacitor electrodes
65
has an oblong rectangular shape in plan view with an electrode-free area
71
at the central region thereof, and is formed such that the main portion of the corresponding ceramic green sheet
66
is covered by the ground-side capacitor electrode
65
. Therefore, sufficient bonding strength cannot be obtained between the surfaces of the ceramic green sheets
66
on which the ground-side capacitor electrodes
65
are formed and the adjacent ceramic green sheets
64
.
(2) The main portions of the ground-side capacitor electrodes
65
are located at the inside of the internal electrodes (coil patterns)
61
and
67
disposed at both sides of the capacitor unit
53
, and penetrating electrodes (via-hole electrodes)
70
(see
FIG. 13A
) extend through the dielectric ceramic green sheets
64
and
66
at the center thereof. Therefore, pressure cannot be applied effectively in a pressing step of the laminating process, and sufficient bonding strength cannot be obtained between the layers.
(3) The external grounding electrode
56
, which is electrically connected to the ground-side capacitor electrodes
65
, is disposed on the device
54
so as to completely surround the region where the capacitor unit
53
is disposed. Therefore, the device
54
receives a large thermal stress at the region where the capacitor unit
53
is disposed in the firing process or in the process of attaching the external electrodes by firing due to the difference in the degree of thermal expansion and contraction between the external grounding electrode
56
and the device
54
.
Although the thermal stress applied to the device can be reduced to some extent by forming the external grounding electrode only at a portion of the device so that it does not completely surround the device, this does not satisfactorily solve the above-described problem.
In addition, similarly to the case of the ground-side capacitor electrodes
65
, cracks also occur along the surfaces of the signal-side capacitor electrodes
63
due to thermal contraction in the firing process, and therefore the insulation resistance decreases, although this is not such a big problem since the area of the signal-side capacitor electrodes
63
is generally smaller than that of the ground-side capacitor electrodes
65
in the capacitor unit
53
.
SUMMARY OF THE INVENTION
Accordingly, in order to solve the above-described problems, preferred embodiments of the present invention provide a high-reliability multilayer LC composite component in which separation between layers at the capacitor unit including the ground-side capacitor electrodes and the signal-side capacitor electrodes is prevented so that the insulation resistance does not decrease.
According to a first preferred embodiment of the present invention, a multilayer LC composite component includes a coil unit including a stack of coil conductors, two adjacent coil conductors being separated by an insulating layer and being electrically connected to each other, and a capacitor unit including a ground-side capacitor electrode and a signal-side capacitor electrode which oppose each other with an insulating layer disposed therebetween, the ground-side capacitor electrode having an electrode-free area at an approximately central region thereof and the signal-side capacitor electrode being electrically connected to the coil unit via the electrode-free area, wherein the ground-side capacitor electrode extends to at least two opposing sides of the insulating layer and has a cut portion which extends continuously from the electrode-free area.
As described above, the ground-side capacitor electrode has the electrode-free area at the approximately central region, and a penetrating electrode (via hole electrode) used for providing electrical connection to the signal-side capacitor electrode is disposed in the electrode-free area. By forming the cut portion (another electrode-free area) in the ground-side capacitor electrode such that the cut portion and the above-described electrode-free area are connected to each other, the area where the electrode is not formed in the insulating layer on which the ground-side capacitor electrode is formed can be increased, so that the bonding strength between the insulating layer and the adjacent layer can also be increased. Accordingly, cracks in the device along the surface of the ground-side capacitor electrode due to the thermal contraction in the firing process are effectively prevented and minimized. As a result, a highly reliable multilayer LC composite component in which the insulation resistance does not decrease can be obtained.
In addition, since the electrode-free area and the cut portion of the ground-side capacitor electrode are connected to each other on the insulating layer, the bonding strength between the insulating layer and the adjacent layer can also be further increased.
Furthermore, in the case in which the electrode is formed by the screen printing method using an electrode paste, the area of a continu
Azuma Takahiro
Fukuda Yoshihiro
Glenn Kimberly
Keating & Bennett LLP
Pascal Robert
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