Multilayer printed circuit board

Details Multilayer printed circuit board Multilayer printed circuit board

2000-08-09

2001-12-11

Gaffin, Jeffrey (Department: 2841)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C174S258000, C174S261000, C174S262000, C174S266000, C361S792000, C361S794000, C361S795000, C361S818000

Reexamination Certificate

active

06329604

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a multilayer printed circuit board, and in particular, to a multilayer printed circuit board including, for example, four layers, six layers, or the like.
DESCRIPTION OF THE PRIOR ART
Heretofore, a multilayer printed circuit board includes in general a power source plane.
FIGS. 1
to
3
show, in cross-sectional views, configurations of multilayer printed circuit boards of the prior art.
FIG. 1
shows a cross section of constitution a four-layer printed circuit board as a prior art example 1. Example 1 includes, beginning at an upper-most layer of board, a first signal wiring layer
111
, a ground layer
112
, a power source layer
113
, and a second signal wiring layer
114
. Disposed between layers
111
to
114
are an inter-layer insulating layers
115
to
117
, respectively.
In prior art example 1 of
FIG. 1
, a signal wiring
118
is formed in first signal wiring layer
111
, signal wiring
119
is arranged in second signal wiring layer
114
, a planar ground plane
120
is fabricated in ground layer
112
, and a planar power source plane
121
is disposed in power source layer
113
.
When a signal current, which returns to a ground point, flows in signal wiring
118
, a return current is induced in ground plane
120
of ground layer
112
adjacent via inter-layer insulator
115
to signal wiring
118
to form a small loop including signal wiring
118
and ground plane
120
. The loop emits weak electromagnetic waves unnecessary for operation.
FIG. 2
shows in a cross-sectional view a configuration example of a six-layer printed circuit board as a prior art example 2. The board of prior art example 2 includes, beginning at an upper-most layer, a first signal wiring layer
131
, a second signal wiring layer
132
, a ground layer
133
, a power source layer
134
, a third signal wiring layer
135
, and a fourth signal wiring layer
136
. Fabricated between layers
131
to
136
are inter-layer insulating layers
137
to
141
, respectively.
In prior art example 2 shown in
FIG. 2
, signal wiring
142
is arranged in first signal wiring layer
131
, signal wiring
143
is formed in second signal wiring layer
132
, signal wiring
144
is manufactured in third signal wiring layer
135
, signal wiring
145
is formed in fourth signal wiring layer
136
, a planar ground plane
146
is formed in ground layer
133
, and a planar power source plane
147
is disposed in power source layer
134
. When a signal current returning to a ground point flows through signal wiring
143
, a return current is induced in ground plane
146
of ground layer
133
adjacent via inter-layer insulator
138
to signal wiring
143
to form a small loop including signal wiring
143
and ground plane
146
. The loop radiates weak, unnecessary electromagnetic waves.
FIG. 3
shows a cross section of a configuration example of a six-layer printed circuit board as a prior art example 3. Prior art example 3 includes, beginning at an upper-most layer, a first signal wiring layer
151
, a ground layer
152
, a second signal wiring layer
153
, a third signal wiring layer
154
, a power source layer
155
, and a fourth signal wiring layer
156
. Disposed respectively between layers
151
to
156
are interlayer insulating layers
157
to
161
.
In the circuit board of prior art example 3 shown in
FIG. 3
, signal wiring
162
is arranged in first signal wiring layer
151
, signal wiring
163
is formed in second signal wiring layer
153
, signal wiring
164
is manufactured in third signal wiring layer
154
, signal wiring
165
is formed in fourth signal wiring layer
156
, a planar ground plane
166
is formed in ground layer
152
, and power source plane
167
is disposed in power source layer
155
. When a signal current returning to a ground point flows through signal wiring
162
and/or signal wiring
163
, a return current is induced in ground plane
166
of ground layer
152
adjacent via inter-layer insulator
157
or
158
to signal wiring
162
or
163
to form a small loop including signal wiring
162
and/or signal wiring
163
and ground plane
166
. The loop emits weak electromagnetic waves unnecessary for operation.
Japanese laid-Open Patent Application. No. Showa 63-004695 (4695/1988) entitled “multi-layer printed circuit board” describes a fourth prior art example analogous to the prior art of the present invention. Prior art example 4 includes a substrate on which heat radiator fins are disposed to efficiently radiate heat to reduce noise.
A fifth prior art example is a “multi-layer printed circuit board” described in Japanese laid-Open Patent Application. No. Heisei 7-273468 (273468/1995). This circuit board includes a signal wiring layer and a power source layer as inside layers. A conductor pattern is fabricated in the signal wiring layer or the power source layer to substantially extend an area of a ground pattern. This stabilizes ground potential of the board to minimize noise caused by emission of electromagnetic waves.
However, in the four-layer printed circuit board of prior art example 1 shown in
FIG. 1
, when a signal current returning to a ground point flows in signal wiring
119
, no return current is induced in power source plane
121
of power source layer
113
adjacent via an inter-layer insulator
117
to signal wiring
119
. Namely, a return current is induced at a faraway ground point. As a result, there is formed a large loop with signal wiring
119
and the faraway ground point at which the return current is induced. Therefore, strong, unnecessary electromagnetic waves are emitted from the loop. When signal wiring
111
is connected via through-hole
122
to signal wiring
114
, a return current is similarly induced at a faraway ground position to form a large loop including through-hole
122
, signal wiring
114
, and the faraway ground point. This leads to a problem of strong, unnecessary electromagnetic waves emitted from the loop.
In the six-layer printed circuit board of prior art example 2 of
FIG. 2
, when a signal current returning to a ground point flows through signal wiring
142
,
144
, and/or
145
, there is induced no return current in signal wiring
142
of signal wiring layer
132
, power source plane
147
of power source layer
134
, or signal wiring
145
of signal wiring layer
132
adjacent respectively to inter-layer insulator films
137
,
140
, or
141
. A return current is induced at a faraway ground point. Consequently, a large loop is configured by signal wiring
142
,
144
, or
145
and the faraway ground point at which the return current is induced. In consequence, unnecessary electromagnetic waves radiated from the loop become stronger. When at least two or more signal wiring selected from wiring
142
to
145
are connected to each other by through-hole
148
, a return current is induced at a faraway ground point. There is formed a large loop including the signal wiring thus connected to each other, through-hole
148
, and the faraway ground point. This leads to a problem that the loop emits strong electromagnetic waves not required.
In the six-layer printed circuit board of prior art example 3 shown in
FIG. 3
, when a signal current returning to a ground point flows through signal wiring
164
and/or
165
, no return current is induced in power source plane
167
of power source layer
155
adjacent via inter-layer insulator
160
or
161
to the signal wiring. A return current is induced to a faraway ground point. This results in a large loop including signal wiring
164
or
165
and the faraway ground point. The loop emits strong unnecessary electromagnetic waves. When at least one of signal wiring
164
and
165
is connected to another signal wiring in a different signal wiring layer via through-hole
168
, a return current is similarly induced at a faraway ground point. This forms a large loop including at least one of signal wiring
164
and
165
, through-hole
168
, and the faraway ground point. There arises a problem of strong, unnecessary electromagnetic waves em

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