Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-09-21
2002-02-19
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S748000, C361S760000, C361S761000, C361S778000, C361S800000, C361S816000, C361S818000, C174S034000, C174S261000
Reexamination Certificate
active
06349038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to printed circuit boards.
2. Description of the Related Art
A printed circuit board is a board made of non-conducting material, such as plastic, glass, ceramic, or some other dielectric on which chips and other electronics are mounted. A multilayer printed circuit board is a printed circuit board consisting of two or more layers of board material. Each separate layer has its own metallic tracings to provide electrical connections between various electronic components and to provide connections to other layers. The layers are laminated together to produce a single circuit board to which the components, such as integrated circuits, resistors, and capacitors are attached.
One common multilayer printed circuit board scenario is to have alternating layers, where a first layer is composed in all or part of conducting materials, a second layer is composed mostly of insulating material, and a third layer is composed in all or part of conducting materials, with portions of the conducting materials in the first and third layer connected by conducting materials interposed within channels within the second insulating layer. Such first, second, and third layers typically form part or all of an electric circuit. Many such alternating layers are often used to construct a final circuit.
With reference now to
FIG. 1
, shown is a perspective view of a grossly simplified example of alternating layers within an multilayer printed circuit board which form equivalent electric circuit
150
. Depicted is that equivalent electric circuit
150
has a current loop
152
from driver
102
to receiver
106
. Current loop
152
travels an electrically conductive path provided by multilayer printed circuit board structure
154
. Multilayer printed circuit board structure
154
depicts a first layer (not shown) having driver
102
, metallic trace
104
, and receiver
106
which are contained within a first layer (not shown) of printed circuit board structure
154
. Driver
102
is illustrated as electrically connected to metallic trace
104
(e.g., a copper trace). Metallic trace
104
is shown electrically connected to receiver
106
. Receiver
106
is depicted as electrically connected to metallic wire
112
. Metallic wire
112
is depicted as electrically connected at point
162
with conducting plane
116
. Conducting plane
116
is illustrated as electrically connected at point
164
to metallic wire
118
. Metallic wire
112
and metallic wire
118
are depicted as contained within a cylindrical channel hollowed out from a second insulating layer (not shown) of printed circuit board structure
154
. For sake of illustration and coordination with equivalent electrical circuit
150
, electrical current loop
152
is shown flowing from driver
102
to receiver
106
through metallic trace
104
. Thereafter, electrical current loop
152
is shown flowing through metallic wire
112
, metallic conducting plane
116
, and metallic wire
118
back to driver
102
.
Referring now to
FIG. 2A
, depicted is an isolated perspective view of metallic conducting plane
116
and metallic trace
104
of FIG.
1
. As has been described, metallic wires
112
,
118
(of
FIG. 1A
) respectively electrically connect with conducting plane
116
at points
162
,
164
on conducting plane
116
which are shown relatively “in line” with metallic trace
104
. Viewed from the perspective of conducting plane
116
, when relatively high frequency alternating current (e.g., current with frequencies substantially in excess of 10 kHz) is flowing in current loop
152
(of FIG.
1
), metallic wires
112
,
118
(of
FIG. 1A
) are respectively sourcing and sinking current into points
162
,
164
on conducting plane
116
. Insofar as conducting plane
116
typically has relatively uniform characteristics, return current
160
, flowing between point
162
to point
164
, will tend to follow a path substantially underneath metallic trace
104
, since for relatively high frequency alternating current the path underneath metallic trace
104
is the path of least impedance for reasons well-known to those in the art. The magnitude of return current
160
will be substantially the same as that of source current
159
, since together source current
159
and return current
160
make up loop current
152
. However, since conducting plane
116
is of greater width physical width than metallic trace
104
, although the majority of return current
160
will attempt to flow under metallic trace
104
, in actuality it will be distributed across width
170
of conducting plane
116
in a fashion illustrated by FIG.
2
B.
With reference now to
FIG. 2B
, illustrated is an example of distribution
161
of return current
160
(of
FIGS. 1 and 2A
) on conducting plane
116
. Shown is that the majority of return current
160
(of
FIGS. 1 and 2A
) is distributed, or flowing, through the portion of conducting plane
116
which lies substantially directly below metallic trace
104
.
Referring again to
FIG. 1
, those skilled in the art will recognize that it is not necessary for metallic wires
112
,
118
to be present in order for a return current to be present on conducting plane
116
. That is, the mere presence of an alternating current in metallic trace
104
proximate to conducting plane
116
is sufficient to induce a return current such as return current
160
(although metallic trace
104
is shown in a plane above conducting layer
116
, metallic trace
104
could be coplanar with conducting plane
116
, as will be demonstrated in the detailed description). See e.g., M. Zahn,
Electromagnetic Field Theory: A Problem Solving Approach
361-363 (1979). Furthermore, in point of fact, in an actual implementation it is likely that both current resulting from metallic wires
112
,
118
and from magnetic induction will be present on conducting plane
116
. However, for ease of description the discussion herein focuses on the current resulting from the presence of metallic wires
112
,
118
, although it is to be understood that in addition to or in the alternative to such current resulting from the presence of metallic wires connecting at points
162
,
164
, a return current can be present arising solely from the presence of alternating current within metallic trace
104
, when metallic trace
104
is located proximate to conducting plane
116
. This fact is to be borne in mind whenever discussion is made of any return current described in the present application.
Unfortunately, as printed circuit board densities have increased, the structure illustrated in
FIGS. 1
,
2
A, and
2
B is becoming less and less practicable. Instead, it is becoming common within the art for conducting plane
116
to be split into two pieces, for a variety of reasons. Splitting conducting plane
116
gives rise to a number of practical problems, a few of which will now be described.
Referring now to
FIG. 3
, shown is a modified version of multilayer printed circuit board structure
154
, referred to as multilayer printed circuit board structure
300
, which is structurally similar to printed circuit board structure
154
except that a conducting plane is shown broken into first metallic conducting part
302
and second metallic conducting part
304
, thereby forming split conducting plane
316
. Depicted is that first metallic conducting part
302
and second metallic conducting part
304
are separated by dielectric-filled moat
306
which is typically composed of a dielectric material. Shown is that metallic wires
112
,
118
respectively connect with split conducting plane
316
at points
362
,
364
on split conducting plane
316
.
Those skilled in the art will recognize that even though there is no contiguous return path from receiver
106
to driver
102
through split conducting plane
316
, driver
102
and receiver
106
will still function because second metallic conducting part
304
and first metallic conducting part
302
function as a sort of “parallel-plate”
Dell USA L.P.
Gaffin Jeffrey
Skjerven Morrill & MacPherson LLP
Terrile Stephen A.
Tran Thanh Y.
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