Wave transmission lines and networks – Transmission line inductive or radiation interference...
Reexamination Certificate
1999-03-09
2001-03-06
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Transmission line inductive or radiation interference...
C333S02200F, C361S794000, C361S818000
Reexamination Certificate
active
06198362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laminated printed circuit board that has at least two layers and that are used for electronic devices such as information processing devices and communicating devices, in particular, to a laminated printed circuit board having a function for suppressing an undesired electromagnetic wave from radiating.
2. Description of the Related Art
In advanced information society, undesired electromagnetic waves radiated from electronic devices such as information processing devices and communicating devices disturb broadcasting and radio communication systems and cause devices to malfunction. To suppress undesired electromagnetic waves from radiating and prevent them from entering such devices, shields and filters are used.
As a method for suppressing an undesired electromagnetic wave radiated from an electronic device, an electromagnetic wave radiated from a printed circuit board as a radiation source is enclosed with a shield. Alternatively, a printed circuit board is suppressed from radiating an electromagnetic wave.
For example, in a printed circuit board disclosed as Japanese Utility Model Registration Laid-Open Publication No. 05-13095, as shown in
FIG. 20
, a ground layer of a printed circuit board
101
is electrically connected to a cage
107
through a leaf spring
102
and a metal guide rail
103
so that the voltage of the ground layer is the same as the voltage of the cage
107
. In this structure, the ground layer
104
functions as a metal plate so as to prevent electromagnetic noise from leaking out.
In an IC card disclosed as Japanese Patent Laid-Open Publication No. 07-192105, as shown in
FIG. 21
, a printed circuit board
113
and a metal panel
114
oppositely disposed with a frame
112
is electrically connected with a ground terminal
115
secured to the metal panel
114
. Thus, the metal panel
114
effectively functions as a shield against external electrostatic induction and electromagnetic induction. Consequently, an IC chip
113
can be prevented from malfunctioning and breaking against interference of an undesired electromagnetic wave and radiation of static electricity.
In a liquid crystal displaying device
120
disclosed as Japanese Patent Laid-Open Publication No. 06-82803, as shown in
FIG. 22
, a metal plate
122
is electrically connected to a ground line of a printed circuit board
121
. Thus, a ground line voltage is stably supplied. In addition, a liquid crystal displaying screen
124
and a metal frame
123
function as shields for suppressing an undesired electromagnetic wave from radiating.
As a main cause of which a printed circuit board radiates an undesired electromagnetic wave, a voltage between a ground for supplying a reference voltage and a power supply layer for supplying a power supply voltage to an IC and so forth fluctuates. In particular, when a system composed of a power supply layer and a ground layer resonates, an electromagnetic wave in very high level is radiated. To suppress a radiation due to the fluctuation of a power supply voltage, several structures of printed circuit boards have been proposed.
In a printed circuit board disclosed as Japanese Patent Laid-Open Publication No. 06-224562, as shown in
FIG. 23
, a part
131
of a power supply plane layer
133
is separated. The separated power supply plane layer
131
is disposed on a substrate
134
that is disposed adjacent to a ground plane layer
132
. The power supply plane layer
131
separated from the power supply plane layer
133
is connected with a connecting means
135
. Thus, the electrostatic capacity between the separated power supply plane layer
131
and the ground plane layer
132
increases.
In a laminated printed circuit board disclosed as Japanese Patent Laid-Open Publication No. 07-111387, as shown in
FIG. 24
, a power supply layer
141
and a ground layer
142
are laminated. A slit
143
is diagonally formed on a conductor of at least one of the power supply layer
141
and the ground layer
142
.
In a printed circuit board
150
disclosed as Japanese Patent Laid-Open Publication No. 09-205290, as shown in
FIG. 25
, a power supply layer
151
and a ground layer
152
are disposed on a first surface and a second surface of the printed circuit board
150
. At a peripheral portion of the first surface, fine conductor patterns
154
and
155
are alternately formed. At a peripheral portion of the second surface, fine conductor patterns
153
and
156
are alternately formed. The conductor patterns
154
are connected to the ground layer
152
. The conductor patterns
155
are connected to the power supply layer
151
. The conductor patterns
153
opposite to the conductor patterns
154
are connected to the power supply layer
151
. The conductor patterns
156
opposite to the conductor patterns
155
are connected to the ground layer
152
.
In a printed circuit board disclosed as Japanese Patent Laid-Open publication No. 09-283974, as shown in
FIG. 26
, a power supply layer
162
and a first ground layer
163
are oppositely disposed with a dielectric layer
166
and thereby a capacitor C
1
is formed. A power supply layer
162
and a second ground layer
164
are oppositely disposed with a dielectric layer
167
and thereby a capacitor C
2
is formed. In addition, the first ground layer
163
and the second ground layer
165
are connected through a resistor layer
166
.
However, in the cage structure of the printed circuit board shown in
FIG. 20
, the printed board
101
and the cage
107
function as shields. Thus, when a substrate or a nonconductive cage made of plastic is used, it does not function as a shield. In this case, the cage structure cannot suppress an electromagnetic wave from radiating. In the IC card
111
shown in FIG.
21
and the liquid crystal displaying device shown in
FIG. 22
, since the printed circuit board requires a metal panel, the mounting density decreases and the fabrication cost increases.
In the printed circuit boards shown in
FIGS. 23
,
24
,
25
, and
26
, they that are radiation sources suppress undesired electromagnetic waves from radiating. In these printed circuit boards, the voltage fluctuation between the ground for supplying a reference voltage and the power supply layer for supplying a power supply voltage is suppressed. However, in the printed circuit board
130
shown in
FIG. 23
, even if the power supply plane layer and part of the ground plane layer are adjacently disposed, the increase of the resultant electrostatic capacitance is very small. Thus, the fluctuation of the power supply voltage cannot be sufficiently suppressed. In the printed circuit board
140
shown in
FIG. 24
, since the slit
143
formed on the power supply layer
141
or/and the ground layer
142
function as slot antennas, the radiation of the electromagnetic waves further increases.
In the printed circuit board
150
shown in
FIG. 25
, since the polarity of the voltage generated between the conductor patterns
154
and
153
is reverse from the polarity of the voltage generated between the conductor patterns
155
and
156
adjacent to the conductor patterns
154
and
153
, the voltages at the end portions of the printed circuit board are offset so as to suppress an electromagnetic wave from radiating. However, since the voltage fluctuation between the power supply layer
151
and the ground layer
152
still takes place, undesired electromagnetic waves radiated from the power supply layer
151
and the ground layer
152
cannot be suppressed. In the laminated printed circuit board
161
shown in
FIG. 26
, although the radiation of undesired electromagnetic waves and the malfunction of device due to the voltage fluctuation between the power supply and the ground are suppressed, another ground layer
164
and a second dielectric layer
167
should be additionally disposed along with the ground layer
163
. Thus, the structure becomes complicated and the cost increases.
In the above-descried related art references, the structures of the pr
Harada Takashi
Sasaki Hideki
Bettendorf Justin P.
NEC Corporation
Young & Thompson
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