Note: Descriptions are shown in the official language in which they were submitted.
3 ~ 3
.
PRINTED CI~CUIT BO~RD
TE~CHNICAL FIELD
The present invention relates to a printed circuit board for
electrically interconnecting electronic components, the printed circuit
board being either flexible or non flexible.
~BACKGROUND ART
Printed circuit boards (PCBs) embedding parallel conductive
wires therein are widely used throughout the electronics industry
particularly in applications for interconnecting electronic modules on
which electronic components are mounted in high density. Ribbon cables
are also widely used to connect PCBs to each other and to other
e~uipment. In United States Patent No. 4,660,125 issued to Purdy et al on
April 21,1987, ribbon cables provide interconnection o a cabinet and a
slidable drawer in which the PCB circuit car~ls of electronic components
are mounted. A standard ribbon cable asseIIIbly, however, has no electric
or magnetic shielding.
To provide electric and magnetic shields, flexible printed circuit
boards in which parallel conductive wires are sandwiched between a
mesh, have been proposed. In telecommunication applications, these
conductive wires include pairs of tip and ring conductive wires for
telephone lines. The conductive wires interconnect components to
transmit electric signals between components. In known flexible printed
circuit boards, the conductors forming the mesh generally intersect each
other at right angles; and the longitudinal axes of the tip and ring
conductive wires are oriented to r~m parallel to the intersections oiF the
mesh. In such an arrangement, it is difficult to control placemerlt of the
parallel conductive wires relative to the intersections of the mesh. As a
result, one conductive wire may be closer to the intersections of ~e
conductors of the mesh than the other conductive wire. Should this
happen, the capacitance between that one conductive wire and the mesh
will be less than the capacitance between the other conductive wire and
the mesh. Due to this unbalance, higher levels of cross talk are
unavoidable, par~cularly between adjacent pairs of conductive wires
.i:.. : . ... . . . .
;, . , ~ ,...................... .
~,, . ... ~, . ~
~) ~ iJ ~i 3 ~ ~
transmitting signals. At audio frequencies, this was not a serious problem.
However, at the very high frequencies and bit rates now being transmitted,
this unbalance has become a critical problem.
5 SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved
printed circuit board.
According to its most general aspect, the present invention
10 provides a printed circuit board for electrically interconnecting electronic
components, comprising: a non-conductive supporting member; a first
conductive mesh supported by the supporting member, the conductive
mesh defining an array of intersecting conductors; and at least one pair of
parallel conductive wires supported by the supporting member equidistant
15 from the conductive mesh. In the printed circuit board, the longitudinal
axes of the pair of conductive wires are oriented at an angle relative to
intersections of the conductors of the conductive mesh, so that the offset
of the intersections from the conductive wires incrementally changes
along the longitudinal axes of the pair of conductive wires so that the
20 capacitances between the conductive wires and the conductive mesh are
substantially balanced regardless of the lateral position of the wires.
In such an arrangement of the conductive wires and the
conductive mesh, the capacitance between the one conductive wire and
the conductive mesh will be substantially equal to the capacitance between
25 the other conductive wire and the conductive mesh. Due to this
substantial balance of the capacitances, low cross talk between adjacen~
pairs of parallel conductive wires transmitting signals is ensured.
In a preferred embodiment, the non-conductive supporting
member is flexible and the printed circuit board includes a second
30 conductive mesh defining an array of intersecting conductors supported by
the sheet, parallel to the first conductive mesh. In this printed circuit
board, the parallel conductive wires are sandwiched between and
substantially equidistant from each of the concluctive meshes. The
longitudinal axes of the pair of conductive wires are oriented at an angle
35 relative to intersections of the conduc~ors of bo~h of the conductive
meshes. The conductors of the one conductive mesh are substantially
parallel to those of the further conductive mesh; and the pitch of the
", . .... ... .... .. . . .... . . .. ...
3 ~ 3
intersections of both s)f the conductive meshes is substantially identical.
Also, in these preferred embodiments, the angle between the longitudinal
axes of the pair of conductive wires and the longitudinal axes in the
direction of the intersections of the conductors of the conductive mesh is
small. Such an angle provides good flexibility of the printed circuit board
and balanced capacitance regardless of the lateral position of the pair of
conductive wires. As well, with the two conductive meshes sandwichin
the parallel conductive wires, ideal electric and magnetic shielding is
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present inven~ion will now be described by
way of example only with reference to the accompanying drawings in
which:
Figure 1 is a plan and partially broken view of the printed c;rcuit
board according to the present invention;
Figure 2 is an enlarged vertically sectional view of the printed
circuit board on line II-II in Figure 1;
Figure 3 is a sectional view of ~e printed circuit board on line
III-III in Figure 2;
Figure 4 is an enlarged vertically sectional view of another
printed circuit board according to the present invention;
Figure 5 is an enlarged partially excluded plan view of the
printed circuit board on line V-V in Figure 4;
Figure 6 is an enlarged vertically sectional view of another
printed circuit board according to the present invention; and
Figure 7 illustrates another ground conductive mesh which is
used for the printed circuit board according to ~e present invention.
BEST MODE lFOR CAI~RYING Ol)T THE INVENTION
Referring to Figures 1-3, a flexible printed circuit board 10
comprises a flexible non-conductive sheet 12, a plurality of pairs of tip (T)
and ring (R) conductive wires 14 and 16 and a pair of conduc~ve upper
and lower meshes 18 and 20 which each lform a ground plane. The tip and
ring conductive wires 14 ancl 1~ which run in parallel are supported by the
.j,: , .
; .
' ' ' '
~ ;3~3~.3
flexible non-conductive sheet 12 and are equidistant from the upper and
lower meshes 18 and 20. The upper and lower meshes 18 and 20 have a
plurality of conductors 22 and 24, respectively. The conductors 22 of the
upper mesh 18 and the conductors 24 of the lower mesh 20 are both
5 embedded in the flexible non-conductive sheet 12. Each of the conductors
22 and 24 forms a matrix, defining an array of intersectin;g conductors. The
pitch of the intersections of both conductors 22 and 24 is identical and
thus, the mat~ix of both upper and lower meshes 18 and 20 is also
identical. The conductors 22 are overlaid the conductors 24.
10Typically, the conductive wires 14 and 16 are of copper. The
width of the conductive wires 14 and 16 is 0.010 inches and the distan~e D
between the two wires 14 and 16 is 0.025 inches. The distance t between
each of the upper and lower meshes 18 and 20 and the conductive wires 14
and 16 is 0.014 inches. The width of the conductors 22 of the upper mesh
1518 and the conductors 24 of the lower mesh 20 is 0.008 inches and the
distance S between the conductors 22 or the conductors 24 is 0.040 inches.
The width of the wires and the distances D, S and will vary with the
application of the printed circuit board.
The conductors 22 of the upper mesh 18 (or the conductors 24 of
20 the lower mesh 20) run substantially at right angles to each other. The
longitudinal axes of the tip and ring conductive wires 14 and 16 are
oriented at an offset angle 0 related to a phantom line 26, which is one
running through the intersections of the conductors 22 of the upper mesh
18 or the conductors 24 of the lower mesh 20, as shown in Figure 3. The
25 offset angle 0 is preferably quite small to optimize ~lexibility of the printed
circuit board 10. In the present example, the chosen offset angle 0 is 7.
Accordingly, with orientation of the longitudinal axes of the tip and ring
conductive wires 14 and 16 at the offset angle 0 (= 7), the offset of the
intersections from the conductive wires 14 and 16 incrementally changes
30 along the longitudinal axes of the conductive wires. In such an
arrangement of the tip and ring conductive wires 14 and 16 and ~e upper
and lower meshes 18 and 20, both conductive wires 14 and 16 of one pair
will, over an extended length, evenly cross the intersections of the
conductors 22 of the upper mesh 18 and the conductors 24 of the lower
35 mesh 20 regardless of the lateral position of the wires 14 and 16.
The flexible non-conductive sheet 12 is effectively divided by the
upper mesh 18, the tip and ring conductive wires 14 and 16, and the lower
3 ~ 3
mesh 20 into four layers: a first layer 28, a second layer 30, a third layer 32
ancl a fourth layer 34. The first and fourth layers 28 and 34 are merely
insulating layers. The second layer 30 and third layer 3~ are impedance
control and insulating layers. Thus, the impedance of the tip and ring
conductive wires 14 and 16 is determined by the material of the flexible
non-conductive sheet 12, the distance between the conductive wires 14
and 16 and the distance between them and the upper and lower meshes 18
and 20.
When used for electrically interconnecting electronic
components, the flexible printed circuit board 10 would typically have
respective mating connectors (not shown) at both its ends, each of the
mating connectors containing a plurality of connection pins. The
connection pins would be electrically and physically connected to the tip
and ring conductive wires 14 and 16 and the conductors 22 and 24 of the
upper and lower meshes 18 and 20. With the tip and ring conductive
wires 14 and 16 of the flexible printed circuit board 10, electrical signals canbe transmitted between the electrical components. The conductors 22 and
24 in turn are connected to each other and further connected to a ground
terminal (not shown) to provide a ground plane.
In the flexible printed circuit board, both tip and ring conductive
wires 14 and 16 evenly cross the intersec~ons of the upper and lower
meshes 18 and 20 o~er an extended length. As a result, the overall
capacitances between the tip conductive wire 14 and the upper and lower
meshes 18 and 20 (i.e., ground) are the same as those between the ring
conductive wire 16 and the upper and lower meshes 18 and 20. Because
the capacitances are substantially balanced, cross talk is relatively low
between adjacent pairs of conductive wires 14 and 16, as shown in Figure
1. In comparison, cross talk can be up to 30 dB higher in prior art flexible
printed circuit boards, in which the conductors 22 and 24 run at 45 to the
longitudinal axes of the conductive wires 14 and 16 so that the offset angle
Q is 0. To optimize flexibility of the flexible printed circuit board, it is
preferable that the offset angle 0 be close to but not equal to 0. It will be
evident that equally effective results can be obtained with other ofiset
angles particularly if flexibility of the printed circuit board is not a concern.
In a case where the conductors 22 of the upper mesh 18 are
parallel to and off-set from the conductors 24 of the lower mesh 20, the
pitch of the intersections of both conductors 22 and 24 is identical, and the
. - ~,
. ~ .
.
h 1 d ~` 3 ~ 3
offset angle 0 is 7. This arrangement provides the same advantages as
those in Figures 1-3.
Figures 4 and 5 show another example structure of a flexible
printed circuit board. Referring to Figures 4 and 5, a plurality of pairs of
5 parallel tip and ring conductive wires 40 and 42 (only one pair is shown in
Figure 5) run and are equidistant from the upper and lower mesh
conductors 36 and 38. The upper mesh conductors 36 are parallel to the
lower mesh conductors 38, the pitch of the intersections of both
conductors 36 and 38 is identical, and the lower mesh conductors 38 are
10 off-set from the upper mesh conductors 36. The longitudinal axes of the
tip and ring conductive wires 40 ancl 42 are oriented at an offset angle 0
related to a phantom line 44, which runs through the intersections of the
upper mesh conductors 36 or the lower mesh conductors 38. Both tip and
ring wires 40 and 42 cross the intersections of the mesh over a distance y.5 The parameters of the mesh are de~ined by the following equation:
S = D/((sin 0) x n x ~l2);
y=nxsx~12
where, n is the number of intersections of the upper or lower mesh
conductors 36 or 38 between t~e points where the tip conductive wirP 40
and then the ring conductive wire 42 cross the phantom line 44. In one
example, the distanc~ D between the two wires 40 and 42 is 0.025 inches
25 and the distance S between the conductors 36 or 38 is 0.0754 inches. T~ble I
shows the relationship between the offset angle 0, the number of
intersection n between the two conductive wires 40 and 42 along the
phantom line 44 and the distance y.
3û TABLE I
n 0
13.48 0.107 inches
2 6.73 0.213 inches
3 4.3G 0.320 inches
4 3.36 0.427 inches
?,
2.69 0.533 inches
6 2.24 0.640 inches
7 1.92 0.746 inches
8 1.68 0.853 inches
9 1.49 0.960 inches
1.34 1.066 inches
To maintain good capacitance balance, it is impnrtant that n be
small. For instance, in a case where the offset angle 0 is 2.69, one
10 conductive wire 40 crosses the intersections of the mesh conductors five
intersections along the phantom line 44 after the other conductive wire 42.
This maintains good capacitance balance over a short leng~ of the
conductive wires 40 and 42. For best results, the o~fset angle 0 should be
chosen so that the slope of the phantom line 44 is not a simple ratio.
15 Thus, slopes such as 1~ 2,1:3, 2:3, 3:4, etc. should be avoided. Hence,
cross talk between adjacent pairs of conductive wires 40 and 42 is
effectively minimized, and the flexibility of the printed circuit board is
optimized.
As shown in Figure 6, only one conductive ground mesh 46 may
20 be used in the flexible non-conductive sheet of a flexible printed circuit
board. The conductor in ~is form of a matrix of the mesh 46 oYerlays a
plurality of pairs of parallel tip and ring conductive wires 48 and 5û.
The grou~d mesh may be replaced by a conductive sheet having
a plurality of holes in the form of a matrix as shown in ~igure 7. The
25 mesh conducti~e sheet also overlays parall~l conductiYe wires.
In a typical application, where the flexible printed circuit board is
installed in telecommunications equipment, it is used to interconnect
mating sockets, one of which is on a board in a pull-out drawer of an
electronic equipment cabinet and ~he o~her socl<e~ typically is mounted on
3û the wall of the cabinet. E~etwecn the electronlc components mounted on
the circuit board and the counterparts mounted on a module connected to
the electronic equipment cabinet, electrical signals (e.g., telephone ancl
control signals and power) are transmitted through the parallel
conductive wires of the flexible printed circuit board. With the two
35 meshes sandwiching the parallel tip and ring conduc~ive wires, ideal
electric and magnetic shielding of the wires is provided. Using flexible
printed circuit boards be~ween the pull-out drawer and the electronic
- :. ... ,;, ~ : . . .
,~.. , ,: ....................... .. . . . .
,
,, ,
v ~ ~ 3
equipment cabinet, the pull-out drawer on which the circuit boards are
mounted can be withdrawn from the electronic equipment cabinet
without suspending the operation of the equipment, so as to access the
circuit boards.
It will be apparent that various other mesh angles and spacings
may be used to incrementally change the offset of the intersections of ~e
mesh from the conductive wires. Also, this inven~on may use a rigid
printed circuit board in which the non-conductive sheets supporting the
meshes and tip and ring conductive wires are made of non flexible
material. Furthermore, this invention may be applied to a printed circuit
board of multiple structure in which two pairs of conductive wires
sandwich a common ground mesh.
,, ... . ~ ~ .. ... . . . . . ...... . ........ . . ..
,. ~ ~ . . ~.. . .
..... . .... ~ . , .. : . ,
