Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1998-06-24
2001-04-17
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C361S816000, C361S818000, C174S034000
Reexamination Certificate
active
06218610
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a structure for shielding an electronic circuit from radio waves, and more particularly to a structure for shielding a radiofrequency circuit equipped with an antenna.
2. Description of the Related Art
A conventional structure for shielding a radio-frequency circuit is comprised of a shield case composed of metal for encasing a radio-frequency circuit therein to shield the circuit from radio-waves. Accordingly, since an antenna has to be arranged outside the shield case, the radio-frequency circuit is electrically connected to the antenna through a connector and a cable.
In order to solve this problem, Japanese Unexamined Utility Model Publication No. 64-40910 published on Mar. 10, 1989 has suggested such a plastic shield case as illustrated in
FIGS. 1A and 1B
.
FIG. 1A
is a perspective view of the suggested plastic shield case, and
FIG. 1B
is a cross-sectional view taken along the line
1
B—
1
B in FIG.
1
A.
The plastic shield case is constituted of an upper half
2
a
and a lower half
2
b
. A radio-frequency circuit (not illustrated) is formed on an upper surface of a printed wiring board
1
. The upper and lower halves
2
a
and
2
b
are assembled in such a manner that the printed wiring board
1
is sandwiched between the upper and lower halves
2
a
and
2
b
. Each of the upper and lower halves
2
a
and
2
b
are formed with two cavities, and inner surfaces of those two cavities are covered with an electrically conductive layer
3
composed of metal for radio-waves shielding. The electrically conductive layer
3
partially extends outside the upper half
2
a
to thereby form an antenna element
4
.
In accordance with the suggested shield case, the radio-frequency circuit can be electrically connected to the antenna element
4
without a connector and a cable.
However, the above-mentioned plastic shield case has to have the two halves
2
a
and
2
b
for sandwiching the printed wiring board
1
therebetween. The reason is as follows. If the printed wiring board
1
is shielded only at an upper surface on which an electronic circuit is mounted, external radio-waves enter the electronic circuit and internal radio-waves leaks from the electronic circuit both through a lower surface of the printed wiring board. Thus, it is absolutely necessary to shield the printed wiring board at upper and lower surfaces thereof
The use of the upper and lower halves
2
a
and
2
b
causes a problem that the shield structure is totally heavy, big in size, and high in fabrication cost.
In addition, in the above-mentioned plastic shield case, the antenna element
4
is formed on the upper half
2
a
separately from the printed wiring board
1
on which a radio-frequency circuit is formed. Hence, when the printed wiring board
1
is shielded with the upper and lower halves
2
a
and
2
b
, it is necessary to electrically connect the radio-frequency circuit to the antenna element
4
.
As a result, assembly of the plastic shield case would take much time and much labor. In addition, when the plastic shield case is disassembled to take out the printed wiring board
1
for inspection and is assembled again, laborious work has to be done, specifically, the radio-frequency circuit is disconnected from the antenna element
4
and connected again to the antenna element
4
, in which case, the radio-frequency circuit may be imperfectly, electrically connected to the antenna element
4
.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the present invention to provide a structure for shielding an electronic circuit, which can be formed in a smaller size, a smaller weight, and a lower cost, and which can be readily assembled.
In one aspect of the present invention, there is provided a structure for shielding an electronic circuit from radio waves, including (a) a shield case open in one side and covered at an inner surface thereof with a first electrically conductive layer, and (b) a printed wiring board including a second electrically conductive layer which cooperates with the first electrically conductive layer to form a shielded space in which an electronic circuit is to be mounted, when the printed wiring board is put onto the open side of the shield case.
There is further provided a structure for shielding an electronic circuit from radio waves, including (a) a shield case formed therein with a cavity which is open in one side of the shield case, (b) a first electrically conductive layer formed on an inner surface of the cavity, and (c) a printed wiring board including (c-
1
) a main board closing the cavity therewith as a cover, (c-
2
) an electronic circuit mounted on a lower surface of the main body, and (c-
3
) a second electrically conductive layer coextensive with the main body and making electrical contact with the first electrically conductive layer when the printed wiring board is put onto the open side of the shield case, the second electrically conductive layer cooperating with the first electrically conductive layer to form a shielded space in which an electronic circuit is to be mounted.
In accordance with the above-mentioned shield structure, the shield case and the printed wiring board cooperate with each other to form a shielded space, in which an electronic circuit formed on a lower surface of the printed wiring board is put. In addition, since the first electrically conductive layer makes electrical contact with the second electrically conductive layer to thereby form an electrically shielded space, the electronic circuit is also put in the thus formed electrically shielded space. Thus, since the printed wiring board forms a part of the shield structure, only one shield case is necessary for forming the shield structure unlike the conventional shield structure wherein two halves are required for forming a shield case. Hence, the shield case in accordance with the present invention can be formed in a smaller weight, a smaller volume, and a lower cost.
It is preferable that the shield case is formed at the open side thereof with a stepped portion on which the main board of the printed wiring board is to be put.
For instance, the first electrically conductive layer may be composed of an electrically conductive coating film which is composed of, for instance, a coating including metal powders therein. For instance, the shield case is made of plastics.
For instance, the second electrically conductive layer may be composed of a metal foil, or a metal film evaporated onto the main board of the printed wiring board.
In a preferred embodiment, the shield structure further includes an antenna formed on an upper surface of the main board of the printed wiring board in such a manner that the antenna is in electrical connection with the electronic circuit.
In accordance with this embodiment, since an antenna and an electronic circuit are formed on opposite surfaces of the main body, and the antenna is electrically connected to the electronic circuit, it is no longer necessary to carry out a step of electrically connecting an antenna to an electronic circuit, which ensures that an imperfect contact between an antenna and an electronic circuit does not occur.
When the shield structure further includes an antenna, it is preferable that the main board is formed with at least one through-hole extending between upper and lower surfaces thereof, and the antenna and the electronic circuit make electrical connection with each other through a wire extending in the through-hole.
The printed wiring board may further include a plurality of printed boards, in which case the main board and the second electrically conductive film are sandwiched between two of the printed boards. When the printed wiring board includes two printed boards, the main board is sandwiched between them. When the printed wiring board further includes a plurality of printed boards, it is preferable that the printed wiring board includes (a) an upper electrode layer formed at a marginal region of an upper surface of an uppe
NEC Corporation
Reichard Dean A.
Walkenhorst W. David
Young & Thompson
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