U.S. patent application number 14/461900 was filed with the patent office on 2016-12-15 for printed circuit board with reduced cross-talk.
The applicant listed for this patent is Cray Inc.. Invention is credited to Jeffrey Scott Conger, Hyunjun Kim, Gregory Erwin Scott.
Application Number | 20160366759 14/461900 |
Document ID | / |
Family ID | 48743138 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160366759 |
Kind Code |
A1 |
Kim; Hyunjun ; et
al. |
December 15, 2016 |
PRINTED CIRCUIT BOARD WITH REDUCED CROSS-TALK
Abstract
A multi-layer printed circuit board has a number of landing pads
that are configured to engage a connector secured thereto. Between
the landing pads associated with different signals is at least one
micro via that is electrically connected to a ground plane on an
outer surface of the multi-layer printed circuit board, and a
ground plane on an inner layer of the multi-layer printed circuit
board.
Inventors: |
Kim; Hyunjun; (Chippewa
Falls, WI) ; Conger; Jeffrey Scott; (Eau Claire,
WI) ; Scott; Gregory Erwin; (Snohomish, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cray Inc. |
Seattle |
WA |
US |
|
|
Family ID: |
48743138 |
Appl. No.: |
14/461900 |
Filed: |
August 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13345247 |
Jan 6, 2012 |
8885357 |
|
|
14461900 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 1/0222 20130101;
H05K 1/0298 20130101; H05K 3/42 20130101; Y10T 29/49165 20150115;
H05K 3/4007 20130101; H05K 2201/093 20130101; H05K 2201/09336
20130101; H05K 2201/09618 20130101; H05K 1/0219 20130101; H05K
2201/09609 20130101; H05K 1/0225 20130101; H05K 1/114 20130101;
H05K 1/115 20130101; Y10T 29/49155 20150115; H05K 1/0245
20130101 |
International
Class: |
H05K 1/02 20060101
H05K001/02; H05K 3/42 20060101 H05K003/42; H05K 3/40 20060101
H05K003/40; H05K 1/11 20060101 H05K001/11 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with United States Government
support under Agreement No. HR0011-07-9-0001 awarded by DARPA. The
Government has certain rights in the invention.
Claims
1. A multi-layer printed circuit board, comprising: a multi-layer
board having a number of conductive traces for carrying signals and
one or more ground planes that are connected by a number of
conductive grounding vias; wherein the printed circuit board
includes a series of conductive landing pads on an outer layer of
the printed board that are configured to electrically engage
contacts of a connector mounted on the printed circuit board and
further includes one or more micro vias positioned between landing
pads associated with different signals, wherein each micro via is
electrically connected to a ground plane on the outer layer of the
printed circuit board and a ground plane on an inner layer of the
printed circuit board.
2. The multi-layer printed circuit board of claim 1, wherein
signals are carried differentially on a pair of traces, such that
there are two landing pads for each signal that is electrically
coupled to the connector, and wherein each micro via is positioned
between the two landing pads associated with different signals.
3. The multi-layer printed circuit board of claim 1, wherein the
landing pads are aligned and the micro vias are symmetrically
placed between the landing pads associated with different
signals.
4. The multi-layer printed circuit board of claim 1, wherein the
landing pads are aligned and the micro vias are asymmetrically
placed between the landing pads associated with different
signals.
5. The multi-layer printed circuit board of claim 1, wherein the
micro vias extend between an outer layer of the printed circuit
board and an adjacent layer of the printed circuit board.
6. The multi-layer printed circuit board of claim 1, wherein the
micro vias extend between an outer layer of the printed circuit
board and a non-adjacent layer of the printed circuit board.
7. A method of manufacturing a multi-layer printed circuit board
comprising: forming a number of landing pads on an outer layer of
the printed circuit board that electrically connect to a connector;
forming a portion of a ground plane between landing pads that are
associated with different signals to be coupled to the connector;
and forming one or more micro vias between the landing pads that
are associated with different signals, wherein the micro vias are
electrically connected to a ground plane on the outer layer of the
circuit board and to a ground plane on an inner layer of the
circuit board.
8. A multi-layer printed circuit board, comprising: a plurality of
circuit board layers including an outer layer with landing pads
there that connect to a circuit board connector; one or more
circuit tracers on which signals are routed to different landing
pads; and one or more shielding structures positioned between the
landing pads associated with different signals.
9. The multi-layer printed circuit board of claim 8, wherein the
shielding structures are micro vias.
10. The multi-layer printed circuit board of claim 9, wherein the
micro vias have one end electrically connected to a grounding pad
adjacent to the landing pads and another end electrically connected
to a grounding pad on an inner layer of the multi-layer printed
circuit board.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/345,247 filed Jan. 6, 2012, entitled
"PRINTED CIRCUIT BOARD WITH REDUCED CROSS-TALK" which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0003] The technology disclosed herein relates to printed circuit
boards in general, and in particular to, printed circuit boards
with structures for reducing cross-talk between signal traces.
BACKGROUND
[0004] As circuit board densities and clock speeds increase, the
electromagnetic fields between signals routed on a printed circuit
board interfere with signals transmitted on nearby leads. This
cross-talk increases the signal to noise ratio of the signals,
which in turn lessons the ability of different circuit components
to communicate with each other.
[0005] One technique that has been used to reduce cross-talk
between traces on a printed circuit board is to place ground planes
in one or more areas and/or different layers of the printed circuit
board. These ground planes may be connected with one or more
grounding vias, (i.e., small conductive tunnels that extend though
the various layers of the printed circuit board). While the ground
planes and ground vias do aid in reducing cross-talk between the
signal traces, it is desirable to further reduce cross-talk
whenever possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a partial isometric view of a multi-layer printed
circuit board constructed in accordance with an embodiment of the
disclosed technology;
[0007] FIG. 2 is a top view of a multi-layer printed circuit board
constructed in accordance with an embodiment of the disclosed
technology; and
[0008] FIG. 3 is a cross-sectional view of a multi-layer printed
circuit board constructed in accordance with an embodiment of the
disclosed technology.
DETAILED DESCRIPTION
[0009] As will be explained in further detail below, the technology
disclosed herein relates to multi-layer printed circuit boards, and
in particular to structures for reducing cross-talk between signal
traces in a multi-layer circuit board.
[0010] Disclosed herein is a design for a printed circuit board
that includes features to further reduce cross-talk that occurs in
the area of conductive landing pads that engage a circuit board
connector. In particular, a multi-layer printed circuit board
includes one or more landing pads on an outer layer that are
configured to make electrical contact with a connector. Between the
landing pads that are associated with different signals are one or
more "micro" vias. In one embodiment, each micro via is
electrically connected to a ground plane on an outer layer of the
printed circuit board and a ground plane on an inner layer of the
printed circuit board.
[0011] In one disclosed embodiment, signals in the printed circuit
board are carried on differential signal traces such that each
signal to be transmitted to the connector is associated with two
conductive landing pads. One or more micro vias are positioned
between adjacent contact landing pads associated with different
signals.
[0012] In one embodiment, the micro vias are placed symmetrically
between the conductive landing pads of the printed circuit board.
In another embodiment, the micro vias are asymmetrically placed
between the conductive landing pads.
[0013] FIG. 1 illustrates a partial isometric view of a multi-layer
printed circuit board 10 constructed in accordance with an
embodiment of the disclosed technology. The multi-layer circuit
board includes an outer top layer 12 and one or more inner ground
plane layers 14, 16. It will be appreciated by those skilled in the
art of printed circuit board design that there are generally one or
more additional layers between layers 14 and 16 such as signal
layers, power layers, etc.
[0014] In the embodiment of the multi-layer printed circuit board
illustrated, signals are carried differentially on the board by
pairs of traces 22, 24, 26. In the embodiment shown, each of these
pairs of traces is located on an inner signal layer of the
multi-layer printed circuit board. Each of the individual signal
traces is connected to a vertical signal via 30 that extends
through the multi-layer printed circuit board, so that the signals
carried on the traces can change layers in the printed circuit
board.
[0015] In the embodiment shown, each of the signal vias 30 is
electrically connected to a conductive landing pad 40 that is
configured to engage an electrical connector (not shown), that is
mounted to the multi-layer printed circuit board. In the embodiment
shown, each landing pad 40 is a rectangular strip of conductive
metal. The landing pads 40 are aligned in a strip along the top
layer of the printed circuit board 10. In the embodiment shown,
each landing pad is associated with one signal of a pair of
differentially transmitted signals. The signal vias 30 are arranged
on the circuit board 10 such that the signal vias 30 that connect
to the landing pads 40 are alternately oriented along the length of
the set of the landing pads.
[0016] To reduce cross-talk between signal traces within the
printed circuit board, the printed circuit board includes a number
of grounding vias 50. Each grounding via 50 is electrically coupled
to a ground plane 60 on the outer layer of the multi-layer printed
circuit board and one or more other ground planes located on
different inner layers of the multi-layer printed circuit board.
The ground plane 60 on the outer layer of the multi-layer printed
circuit board also extends between the landing pads 40 that are
associated with different signals. In addition, the ground plane 60
surrounds the landing pads 40 and the signal vias 30 in order to
provide shielding and reduce cross-talk. Cutouts or "anti-pads" in
the ground planes allow room for the different electrical contacts
and the vias on each layer.
[0017] Despite the presence of the grounding vias 50 in the printed
circuit board, many multi-layer printed circuit boards still
exhibit some level of cross-talk between signals. In accordance
with an embodiment of the disclosed technology, it has been
discovered that one source of the cross-talk occurs between the
adjacent landing pads 40 that are adapted to engage a connector on
the printed circuit board. Despite the presence of a ground plane
60 that extends between the landing pads associated with different
signal traces, cross-talk still occurs.
[0018] To further reduce cross-talk occurring between landing pads
that are associated with different signals, a printed circuit board
in accordance with an embodiment of the disclosed technology
includes one or more micro vias 80 that are positioned between
landing pads 40. Each micro via 80 is electrically coupled at one
end to the ground plane 60 on an outer layer 12 of the multi-layer
printed circuit board 10 and at the other end to a ground plane on
an inner layer 14 of the multi-layer printed circuit board. In the
embodiment shown, the inner layer 14 is adjacent to the outer layer
12. However, the micro vias 80 may extend further than two layers
in the multi-layer circuit board if desired.
[0019] In the embodiment shown, the inner layer 14 that connects to
an end of the micro vias 80 only contains a ground plane and does
not contain any signal traces or other circuit board patterns
(power pads, etc.). The ground plane lies completely underneath
each of the landing pads 40 that engage a connector, thereby
limiting the places where electromagnetic fields can radiate to
other layers of the printed circuit board. In other embodiments,
the inner layer 14 may include signal traces or other circuit board
patterns if desired.
[0020] FIG. 2 illustrates a top view of the multi-layer printed
circuit board 10 in accordance with an embodiment of the disclosed
technology. The printed circuit board 10 includes landing pads
labeled 40a-40f that are associated with differential signal traces
22, 24 and 26 respectively. A micro via 80a is positioned between
landing pads 40b and 40c that are associated with different
signals. Similarly, a micro via 80b is placed between landing pads
40d and 40e that are associated with different signals. Also shown
in FIG. 2 are the ground vias 50, which are positioned outside of
the signal vias 30 that connect to the landing pads 40a-40f.
[0021] In the embodiment shown, the micro vias 80 are symmetrically
placed along the length of the landing pads 40. However the micro
vias 80 can also by asymmetrically placed, (i.e., off center, with
respect to the landing pads). In addition, there may be more than
one micro via 80 positioned between the landing pads associated
with different signals.
[0022] FIG. 3 illustrates a cross-section of a multi-layer printed
circuit board constructed in accordance with an embodiment of the
disclosed technology. The cross-section shows the difference in
length between the signal vias 30, the ground vias 50 and the micro
vias 80. In the embodiment shown, the ground vias 50 and the signal
vias 30 extend through the entire thickness of the multi-layer
printed circuit board 10. However, the micro vias 80 only extend
between an outer layer of the multi-layer printed circuit board and
an inner layer of the printed circuit board. In the illustrated
embodiment, the micro vias 80 extend between an outer layer and a
first adjacent layer of the multi-layer printed circuit board
10.
[0023] In one embodiment, the micro vias 80 are manufactured by
drilling or laser-etching holes in the multi-layer printed circuit
board and filling the holes with a conductive material, such as
solder. In one embodiment, each micro via 80 has a diameter of
approximately 0.008 inches. The circuit board is then heated to
form an electrical connection between the micro vias and the ground
planes on the outer and inner layers of the circuit board. Although
the micro vias are shown as being round, other shapes such as;
square, rectangular, triangular, hexagonal, etc., could be used if
desired. With the micro vias 80 placed between the landing pads 40
associated with different signals, computer modeling has shown a
reduction of cross-talk between adjacent signals by an additional
-15 dB at 4 GHz, compared with a printed circuit without the micro
vias.
[0024] Although the disclosed embodiment illustrates a circuit
board with landing pads 40 for use with a connector that carries
differential signals, it will be appreciated that the disclosed
technology can also be used to reduce cross-talk between landing
pads associated with connectors for single-ended signals. In this
case, one or more micro vias can be placed between each landing pad
that is associated with a different signal.
[0025] In one embodiment, the connector that is coupled to the
landing pads 40 on the outer surface of the multi-layer circuit
board 10 is a QSH/QTH high-speed socket connector produced by
Samtec, or the like. However, it will be appreciated that other
types of connectors associated with other shapes or configurations
of landing pads could also benefit from the micro vias placed
between the landing pads.
[0026] From the foregoing, it will be appreciated that specific
embodiments of the invention have been described herein for
purposes of illustration, but that various modifications may be
made without deviating from the spirit and scope of the invention.
For example, other configurations of shielding structures such as,
conductive slats, sheets, or the like, can be placed between the
landing pads that connect to a circuit board connector.
Accordingly, the invention is not limited, except as by the
appended claims.
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