Wave transmission lines and networks – Plural channel systems
Reexamination Certificate
1999-03-18
2001-10-09
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Plural channel systems
C174S033000, C174S261000
Reexamination Certificate
active
06300846
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to a flexible printed circuitry or cable (“FPC”) and more particularly, to a new and improved FPC having ground conductors associated with at least a pair of pseudo-twisted conductors in the FPC.
BACKGROUND OF THE INVENTION
Electrical circuitry often should be protected from electromagnetic interference (EMI) and radio frequency interference (RFI) emanating from or impinging on the electrical circuitry. Although EMI and RFI often are referred to interchangeably, EMI has been used to connote energy occurring anywhere in the electromagnetic spectrum whereas RFI tends to connote interference in the radio communication band. EMI energy can be generated outside as well as inside the electrical circuitry. External EMI energy can interfere with the operation of the electrical circuitry or electronic equipment coupled thereto, while internal EMI energy can create “cross talk” and “noise” which can cause errors in the signals, such as data, transmitted through the electrical circuitry.
Electrical connectors are particularly prone to problems caused by EMI energy because of the density of contacts within the connectors and the openings in the connectors for electrical terminals and cables. While various electrical connectors have been designed with shielding that is effective against EMI/RFI energy, it often is desirable to shield the cables extending to the connectors as well as shielding the connectors themselves.
One type of cable used to reduce the effects from interference is referred to as a “twisted pair” cable. This type of cable includes two adjacent conductors or differential pairs twisted with respect to each other so that the lateral position of each conductor is reversed at each twist. In a given differential pair, electric currents flow in opposite directions in each of the conductors so that the benefits of the differential pair configuration are twofold.
First, the relative position of the conductors with respect to each other is constantly being reversed. As a result, any exterior magnetic or electric field in the vicinity of the twisted pair of conductors has a generally uniform effect upon that differential pair of conductors. In view of the fact that the current is flowing in opposite directions in the signal conductors of the differential pair and the impact of an induced or coupled noise component is generally uniform on both of those signal conductors and any harmful effects from exterior electromagnetic fields is reduced, if not eliminated, by stripping this common mode noise from the differential signal thereby lessening the chances that errors will be introduced into the data being transmitted on those signal conductors.
Second, an electromagnetic field is generated when current runs through a conductor. The orientation of that field is dependent upon the direction of the current flow in the conductor. With the constant changing of the juxtaposition of the conductors that form the differential signal pair, the field orientation for a given region is constantly being reversed and can be considered self-canceling. This canceling effect can substantially suppress the radiated emissions from a given differential pair.
FPC is another medium used for high speed data transmission between computers and the peripherals connected thereto. FPC is typically formed using a process in which a conductor such as copper is deposited uniformly over a flexible insulator substrate. A mask in a desired pattern is then applied to the conductor and the conductor is chemically removed everywhere except at the location of the mask. When the mask is removed, only the conductor remains in the desired pattern on the substrate. An insulator, such as tape or a flexible film, is applied over the conductor and to the flexible substrate in order that the conductor is sandwiched between two insulators.
While conductors on the same side of the insulator substrate of a FPC cannot be crossed, a “pseudo-twisted” arrangement can be achieved in a FPC by placing conductors of a given pair on opposite sides of the insulator substrate. The paths of these conductors are slightly and oppositely offset with respect to a common nominal path and this offset is periodically reversed at predetermined locations. An example of a “pseudo-twisted” FPC arrangement is shown in U.S. Pat. No. 3,761,842, dated Sep. 25, 1973. Another example of a “pseudo-twisted” FPC arrangement is shown in U.S. Pat. No. 5,939,952, dated Aug. 17, 1999 and assigned to the assignee of the present invention.
Pseudo-twisted FPC of the prior art typically has not included a grounding system when the cable is of a two layered construction having only two conductive layers, or when the cable has each of the pair of conductors on an opposite side of an insulative carrier or substrate. Such a prior art flexible printed circuit or FPC is illustrated in
FIGS. 1 and 2
of the drawings and is generally designated by the reference numeral
1
. The FPC
1
includes a flexible dielectric substrate
2
on opposite sides of which is disposed a plurality of pairs of pseudo-twisted conductors
3
a
and
3
b
. Conductor
3
a
is disposed on one side or surface of the flexible dielectric substrate
2
and the other conductor
3
b
is disposed on the opposite other side or surface of the substrate
2
. An insulative film or coating can be disposed over the conductors
3
a
and
3
b
or can be disposed over the entire opposite surfaces of the flexible dielectric substrate
2
such that the conductors
3
a
and
3
b
will be covered by the film. In this way, each of the conductors
3
a
and
3
b
is sandwiched between the flexible substrate
2
and the protective film covering the surface on which the conductors
3
a
and
3
b
are disposed.
Each conductor
3
a
and
3
b
runs lengthwise of the FPC
1
in an oscillating pattern formed by alternate straight sections
4
and oblique sections
5
. As a result, these conductors
3
a
and
3
b
extend in a periodic pattern symmetrically with respect to each other but on opposite sides or surfaces of the flexible substrate
2
. The straight sections
4
of each conductor
3
a
and
3
b
are generally parallel to each other, but alternate along two parallel but spaced apart lines
4
a
and
4
b
(FIG.
1
). The oblique sections
5
of each of the conductors
3
a
and
3
b
connects a pair of adjacent straight sections
4
and thus extends generally between straight-to-oblique transfer points or intersections
7
located at the lines
4
a
and
4
b
. In view of the fact that the conductors
3
a
and
3
b
are arranged symmetrically but opposite to each other, the straight sections
4
of the conductors
3
a
and
3
b
extend longitudinally generally parallel to each other but spaced apart laterally with respect to each other (left. to right as the sections
4
are viewed in FIG.
1
). Consequently, the straight section
4
of the conductor
3
a
on one side of the substrate
2
is in alignment with the line
4
a
when the straight section
4
of the other conductor
3
b
on the opposite side of the substrate
2
is in alignment with the line
4
b
, and vice versa. As a result, the oblique sections
5
of the conductors
3
a
and
3
b
cross each other on opposite sides of the substrate
2
at crossover points
8
.
Each of the conductors
3
a
and
3
b
separately terminates in one of a plurality of pads
9
(
FIGS. 1-2
) at edges
2
a
and
2
b
of the flexible substrate
2
. The pads
9
of some of the conductors (for example, the conductor
3
b
) may include an associated through-hole or via
10
. These pads
9
are arranged at equal intervals along the edges
2
a
and
2
b
of the FPC
1
for engagement with equally spaced contacts of an associated electrical connector. Therefore, either opposite edge of the FPC
1
having the pseudo-twisted conductors
3
a
and
3
b
can be inserted into such an electrical connector to establish a required electrical connection.
In the prior art FPC illustrated in
FIGS. 1-2
, the straight sections
4
of conductors
3
a
an
Cohen Charles S.
Lee Benny
Molex Incorporated
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