Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
2001-09-25
2004-03-02
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C174S01100R, C174S260000, C174S262000
Reexamination Certificate
active
06700061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to composite electronic components defining duplexers for use in portable telephones, for example, and in particular relates to a composite electronic component including a surface acoustic wave device that has a package structure having an electromagnetic shielding effect.
2. Description of the Related Art
The size and weight of mobile and cellular telephones have recently been reduced, and electronic components used therein also have been miniaturized, reduced in height, and combined. When the combination and high-packaging density of electronic components are promoted, signal interference is likely to arise within the device. Therefore, the prevention of signal interference is an important aspect in an electronic component and a composite electronic component formed by combining a plurality of electronic components.
To prevent signal interference, various measures have been taken.
FIG. 16
is a schematic sectional view illustrating a surface acoustic wave filter as an example of a conventional surface acoustic wave device. In a surface acoustic wave filter
101
, a surface acoustic wave element
103
is accommodated within a package
102
. The package
102
includes a package body
104
and a lid
105
. The package body
104
is formed of an insulating ceramic such as alumina. The package body
104
is provided with a plurality of electrodes that are connected to the surface acoustic wave element
103
, and via bonding wires
106
and
107
, the surface acoustic wave element
103
and these electrodes are electrically connected together.
In the plurality of electrodes provided in the package body
104
, an electrode
108
is connected to the ground electric potential, and a terminal to be connected to the ground electric potential of the surface acoustic wave element
103
is connected to the electrode
108
via a bonding wire.
The lid
105
made of a metal protects the surface acoustic wave element
103
accommodated in the inside from external electromagnetic waves. The lid
105
is electrically connected to an electrode to be connected to the ground electric potential of the surface acoustic wave element
103
and an electrode of the package body
104
, such that noises from the outside of the package are prevented from entering therein. Such a structure is disclosed in Japanese Unexamined Patent Application Publication No. 12-049565, for example.
In a composite electronic component including the surface acoustic wave device described above, similar measures have also taken. For example, in Japanese Unexamined Patent Application Publication No. 9-181567, a duplexer is schematically shown in FIG.
17
. In the drawing, on a planar case circuit board
121
, surface acoustic wave devices
122
and
123
, capacitors
124
and
125
, and a coil
126
are mounted. A metallic cover member
127
is provided on the case circuit board
121
and is fixed thereto so as to surround these elements.
In addition, although the surface acoustic wave devices
122
and
123
are schematically shown, the top surface thereof is made of a conductive material to provide an electromagnetic shielding effect similar to the surface acoustic wave device
101
described above.
In the duplexer, due to the package structure of the surface acoustic wave devices
122
and
123
, a surface acoustic wave element is shielded against electromagnetic noises, and moreover, noises from the outside are prevented from entering therein by the metallic cover member
127
.
In a mobile or cellular telephone, the product is constructed by combining a plurality of electronic circuit blocks that perform different functions.
FIG. 18
is a circuit block diagram of a mobile or cellular telephone.
As is apparent from
FIG. 18
, high-frequency signals from a base station are received by an antenna
131
and are converted into IF signals by a duplexer
132
via receiving components
133
to
137
. In contrast, IF transmitting signals produced in the terminal are output to the antenna
131
via the duplexer
132
after passing through transmitting components
138
to
142
.
In this case, in a receiving system which handles weak signals, an RF receiving block
143
for filtering and amplifying high-frequency signals and an IF receiving block
144
for filtering and amplifying IF signals are shielded against external noises by covering the respective entire blocks with conductive cover members having the ground potential.
By connecting the conductive cover member mentioned above to the ground potential, not only is the electromagnetically shielding provided as described above, but also the ground potential in a composite electronic component is reinforced.
As described above, by connecting the lid of the surface acoustic wave device package to the ground potential, external noises are prevented from entering the package. Likewise, in a composite electronic component such as a duplexer, by connecting the conductive cover member to the ground potential, external noises are prevented from entering the composite electronic component and the ground potential is reinforced.
On the other hand, in a surface acoustic wave device such as a ladder type filter having a parallel arm resonator and a series arm resonator, large changes in characteristics due to an inductance component existing between the parallel-arm resonator and the ground potential are present. In the surface acoustic wave device, the inductance component is produced in a bonding wire for achieving the connection between an electrode which is connected to the ground potential and an electrode pad on a surface acoustic wave element which is connected to the ground potential, a via hole electrode in the package, or a wiring pattern.
Furthermore, in a composite electronic component having a surface acoustic wave device mounted thereon, various inductance components are provided to allow signals to pass through, such as a via hole electrode provided on a case circuit board and a patterned conductive pattern.
Therefore, the resultant total inductances existing between the parallel arm resonator and the ground potential greatly effect the characteristics of the surface acoustic wave device and the composite electronic component using the surface acoustic wave device.
Reduction in the height of an electronic component to be mounted is necessary with the miniaturization and reduction in thickness of a mobile or cellular telephone. Therefore, due to a physical impact and stress applied to a mobile or cellular telephone and conductive floating substances, such as solder scraps and dust, the conductive member providing electromagnetic shielding may come into contact with the conductive cover member of the composite electronic component in the package of the surface acoustic wave device. Accordingly, when these members come into contact, the parasitic inductance component is changed, resulting in deterioration in characteristics of the surface acoustic wave device.
That is, in a composite electronic component having a surface acoustic wave device built therein with a ladder-type circuit structure shown in
FIG. 19
, for example, there are inductances L
1
to L
3
generated by bonding wires in the surface acoustic wave device, an inductance L
4
generated by wiring or a through-hole electrode in the package of the surface acoustic wave device, and an inductance L
5
generated by wiring disposed in a case of the composite electronic component. In addition, in
FIG. 19
, numeral P
1
denotes a ground terminal of the surface acoustic wave device package. When a conductive member providing electromagnetic shielding comes in contact with a conductive cover member of the composite electronic component so as to be connected, a connecting route shown in a dotted line X is formed. Therefore, the inductance between the parallel arm resonator in the surface acoustic wave device and the ground potential is changed, resulting in deteriorating in characteristics as mentioned above.
In addition, not only in a surfac
Keating & Bennett LLP
Lee Jinhee J.
Murata Manufacturing Co. Ltd.
Reichard Dean A.
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