U.S. patent application number 10/092791 was filed with the patent office on 2003-09-11 for concealed biaxial card to frame grounding scheme.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Ennis, Amanda Elisa, Lamp, Greg Steven, Laning, Ray Clement, Marroquin, Christopher Michael, Shurson, Scott Alan.
Application Number | 20030168233 10/092791 |
Document ID | / |
Family ID | 27787881 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030168233 |
Kind Code |
A1 |
Ennis, Amanda Elisa ; et
al. |
September 11, 2003 |
CONCEALED BIAXIAL CARD TO FRAME GROUNDING SCHEME
Abstract
A ground from a printed circuit board to the frame of an
electronic system is formed by a biaxially-compressible conductive
spring that is captivated between the printed circuit board and a
plastic stiffener to which the board is fastened. The spring makes
contact with a ground pad on the underside of the printed circuit
board. As the board is fully installed in the electronic system,
standoffs attached to the system frame make contact with the
conductive spring, completing the ground path. Keyhole-shaped
cutouts in the printed circuit board secure the board without the
use of tools. When the board assembly is lowered onto the
standoffs, the head of the standoff passes through the circular
opening of the keyhole. The board assembly is secured in place by
sliding it on the standoffs to a position in which the head of the
standoff is over the narrower slot portion of the keyhole.
Inventors: |
Ennis, Amanda Elisa;
(Rochester, MN) ; Lamp, Greg Steven; (Grand
Meadow, MN) ; Laning, Ray Clement; (Kasson, MN)
; Marroquin, Christopher Michael; (Rochester, MN)
; Shurson, Scott Alan; (Mantorville, MN) |
Correspondence
Address: |
IBM Corporation
Intellectual Property Law
Dept. 917/Bldg. 006-1
3605 Highway 52 North
Rochester
MN
55901-7829
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
ARMONK
NY
|
Family ID: |
27787881 |
Appl. No.: |
10/092791 |
Filed: |
March 7, 2002 |
Current U.S.
Class: |
174/535 |
Current CPC
Class: |
H05K 9/0039 20130101;
H05K 7/142 20130101 |
Class at
Publication: |
174/52.1 |
International
Class: |
H02G 003/08 |
Claims
What is claimed is:
1. A board assembly mountable to a plurality of standoffs attached
to a system frame, comprising: a printed circuit board having a
grounding pad formed on one side and a securing means proximate to
the grounding pad for securing the printed circuit to one of the
plurality of standoffs without the use of tools; and a conductive
spring compressible along two axes that makes electrical contact
with both the grounding pad and the one standoff when the printed
circuit board is mounted on and secured to the one standoff.
2. The board assembly according to claim 1, further comprising: a
stiffener to which the printed circuit board is attached, the
stiffener having a retaining means for retaining the conductive
spring in position.
3. The board assembly according to claim 2, wherein the stiffener
is comprised of a plastic material.
4. The board assembly according to claim 2, wherein the retaining
means is a boss formed on the stiffener, and the conductive spring
includes a hole that fits over the boss.
5. The board assembly according to claim 4, wherein the conductive
spring has a first portion that is adapted to exert a first spring
force in a first direction along one of the axes, and a second
portion that is adapted to exert a second spring force in a second
direction along another one of the axes, the hole being between the
first portion and the second portion.
6. The board assembly according to claim 5, wherein the first
direction is essentially perpendicular to the second direction.
7. The board assembly according to claim 5, wherein the first
spring force and the second spring force are each separately
exertable.
8. The board assembly according to claim 2, wherein the conductive
spring is captivated between the printed circuit board and the
stiffener when the printed circuit board is attached to the
stiffener.
9. The board assembly according to claim 1, wherein the securing
means is a keyhole-shaped hole in the printed circuit board, having
a circular portion and a slotted portion, the slotted portion
having a width less than a diameter of the circular portion.
10. The board assembly according to claim 9, wherein the one
standoff has a head with a diameter less than the diameter of the
circular portion of the keyhole and greater than the width of the
slotted portion, and wherein the board assembly is secured to the
one standoff by passing the head of the one standoff through the
circular portion of the keyhole and then sliding the printed
circuit board into a secured position such that the head is over
the slotted portion.
11. The board assembly according to claim 10, wherein the
conductive spring makes electrical contact with the one standoff
when the printed circuit board is in its secured position.
12. The board assembly according to claim 10, further comprising:
means for locking in place the printed circuit board when it is in
its secured position.
13. The board assembly according to claim 12, wherein the means for
locking includes fasteners in at least two places to fasten the
printed circuit board to the plurality of standoffs.
14. A method of grounding a printed circuit board through a
plurality of standoffs attached to a system frame, comprising:
securing the printed circuit board to one of the plurality of
standoffs using a securing device that does not require the use of
tools; and positioning a conductive spring, compressible in two
axes, such that it makes electrical contact with both the one
standoff and a grounding pad formed on one side of the printed
circuit board in proximity to the securing device for the one
standoff.
15. The method according to claim 14, further comprising: attaching
the printed circuit board to a stiffener, the stiffener having a
retaining device for retaining the conductive spring in
position.
16. The method according to claim 15, wherein the stiffener is
comprised of a plastic material.
17. The method according to claim 15, wherein the retaining device
is a boss formed on the stiffener, and the conductive spring
includes a hole that fits over the boss.
18. The method according to claim 15, wherein the conductive spring
is captivated between the printed circuit board and the stiffener
when the printed circuit board is attached to the stiffener.
19. The method according to claim 14, wherein the securing device
is a keyhole-shaped hole in the printed circuit board, having a
circular portion and a slotted portion, the slotted portion having
a width less than a diameter of the circular portion.
20. The method according to claim 19, wherein the one standoff has
a head with a diameter less than the diameter of the circular
portion of the keyhole and greater than the width of the slotted
portion, and wherein the board assembly is secured to the one
standoff by passing the head of the one standoff through the
circular portion of the keyhole and then sliding the printed
circuit board into a secured position such that the head is over
the slotted portion.
21. The method according to claim 20, wherein the conductive spring
makes electrical contact with the one standoff when the printed
circuit board is in its secured position.
22. The method according to claim 20, further comprising: locking
in place the printed circuit board when it is in its secured
position, by means of fasteners in at least two places to fasten
the printed circuit board to the plurality of standoffs.
23. A system having a concealed biaxial card to frame grounding
scheme, comprising: a system frame; a plurality of conductive
standoffs attached, and conductively coupled, to the system frame;
and a card assembly mountable to the plurality of standoffs that
includes: a printed circuit board having a grounding pad formed on
one side and a keyhole-shaped hole proximate to the grounding pad
for securing the printed circuit board to one of the plurality of
standoffs without the use of tools; a conductive spring
compressible along two axes that makes electrical contact with both
the grounding pad and the one standoff when the printed circuit
board is mounted on and secured to the plurality of standoffs; and
a plastic stiffener to which the printed circuit board is attached
prior to being mounted on the plurality of standoffs; wherein the
conductive spring is captivated between the printed circuit board
and the stiffener when the printed circuit board is attached to the
stiffener, wherein the keyhole-shaped hole in the printed circuit
board has a circular portion and a slotted portion, the slotted
portion having a width less than a diameter of the circular
portion, wherein the one standoff has a head with a diameter less
than the diameter of the circular portion of the keyhole and
greater than the width of the slotted portion, and wherein the
board assembly is secured to the one standoff by passing the head
of the one standoff through the circular portion of the keyhole and
then sliding the printed circuit board into a position such that
the head is over the slotted portion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a scheme for grounding a printed
circuit board to a frame of an electronic system, and more
particularly to a grounding scheme in which a concealed biaxial
spring is used to provide electrical contact between a grounding
pad on the printed circuit board and a standoff used to mount the
printed circuit board to the frame of the electronic system.
[0003] 2. Background Information
[0004] The integration of printed circuit boards into electronic
systems, such as servers, requires that the boards be mechanically
fastened and electrically grounded to the system frame, usually
accomplished by securing the boards to the frame with screws. These
screws provide a ground path from the boards to the frame and
electrically carry the ground from the contact pads, which are
wired to the ground planes on the boards, to the sheet metal of the
frame. However, there are disadvantages to this type of design.
[0005] In the above-described arrangement, time is required to
install the necessary screws through the board into the system
frame. It also requires adequate space to access the screws with a
tool. In addition to the screw space constraint, the location of
ground pads dictates where the printed circuit board assembly must
be mechanically fastened and electrically grounded. In some
applications, these desired locations might reside under a part
that is secured to the printed circuit board assembly, making it
impossible to install the board assembly using screws. Thus, there
is a need for a toolless arrangement for fastening and grounding
printed circuit boards in such situations. There is further a need
of a toolless arrangement that solves the problem of space and
access constraints faced by conventional fasteners, such as screws,
and also helps reduce board installation time while still providing
an adequate grounding scheme.
SUMMARY OF THE INVENTION
[0006] It is, therefore, a principle object of this invention to
provide a concealed biaxial card to frame grounding scheme.
[0007] It is another object of the invention to provide a concealed
biaxial card to frame grounding scheme that solves the
above-mentioned problems.
[0008] These and other objects of the present invention are
accomplished by the concealed biaxial card to frame grounding
scheme disclosed herein.
[0009] In an exemplary aspect of the invention, a board assembly is
mounted and secured to a plurality of standoffs attached to the
frame of an electronic system. The assembly includes a printed
circuit board having a grounding pad formed on one side, and a
conductive spring compressible along two axes that makes contact
with both the grounding pad and one of the standoffs when the
printed circuit board is mounted and secured to the standoffs. The
conductive spring completes a ground path from the printed circuit
board to the system frame through the one standoff. In the
preferred embodiment, the printed circuit board is attached to a
plastic stiffener that includes means for retaining the conductive
spring in position. Preferably the retaining means is a boss formed
on the stiffener and the conductive spring is formed with a hole
that fits over the boss, so that no additional hardware is required
to retain the conductive spring. The conductive spring has two
portions, with the hole being between them. The first portion is
adapted to exert a first spring force in a first direction along
one axis, and the second portion is adapted to independently exert
a second spring force in a second direction along another axis that
is essentially perpendicular to the first axis. When the printed
circuit board is attached to the stiffener, the conductive spring
is concealed and captivated between them.
[0010] In another exemplary aspect of the invention, the printed
circuit board has a securing means proximate to the grounding pad
for securing, without the use of tools, the printed circuit board
to the one standoff with which the conductive spring makes contact.
The securing means is preferably a keyhole shaped hole in the
printed circuit board that has a circular portion and a slotted
portion, the slotted portion having a width less than a diameter of
the circular portion. The end of the corresponding standoff has a
head with a diameter less than the diameter of the circular portion
of the keyhole and greater than the width of the slotted portion.
When the printed circuit board is lowered onto the standoffs, the
head of the one standoff passes through the circular portion of the
keyhole. To secure the printed circuit board, it is slid into a
position such that the head is over the slotted portion of the
keyhole. In this position, the conductive spring presses against
and makes contact with the one standoff, thus completing the
electrical path from the board ground to the system frame.
[0011] In yet another aspect of the invention, the printed circuit
board is locked in place in its secured position, preferably by
using fasteners in at least two places to fasten the printed
circuit board to the plurality of standoffs.
[0012] The concealed biaxial card to frame grounding scheme
described herein advantageously reduces the time required to fasten
and ground the printed circuit board, as well as creating a
solution that requires only two locations where space for a tool is
a consideration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows an exploded view of the board assembly,
including the printed circuit board, stiffener and conductive
spring, according to the present invention.
[0014] FIG. 2 shows the installation of the conductive spring on
the stiffener, according to the present invention.
[0015] FIG. 3 shows in detail the conductive spring, according to
the present invention.
[0016] FIG. 4 shows the board assembly mounted to a standoff,
according to the present invention.
[0017] FIG. 5 shows in detail the head of the standoff in its
initial and fastened positions relative to the keyhole cutout in
the printed circuit board, according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The invention will now be described in more detail by way of
example with reference to the embodiments shown in the accompanying
figures. It should be kept in mind that the following described
embodiments are only presented by way of example and should not be
construed as limiting the inventive concept to any particular
physical configuration.
[0019] Further, if used and unless otherwise stated, the terms
"upper," "lower," "front," "back," "over," "under," and similar
such terms are not to be construed as limiting the invention to a
particular orientation. Instead, these terms are used only on a
relative basis.
[0020] The present invention is directed toward a grounding scheme
in which one or more concealed biaxially-compressible springs are
used to provide electrical contact between grounding pads on a
printed circuit board and standoffs used to mount the printed
circuit board to the frame of an electronic system. In the
embodiment illustrated in FIG. 1, a spring 1 is captivated between
a printed circuit board 2, to which electronic components have
already been assembled, and a stiffener 3. The stiffener 3,
preferably manufactured from a plastic material, is in the general
shape of a tray to which the printed circuit board 2 can be
fastened. As illustrated in detail in FIG. 2, the spring 1 fits on
a boss 3a that is formed as part of the stiffener 3. This
attachment method allows the spring 1 to slightly float upon
installation, but keeps the spring 1 in place without use of any
mechanical fasteners. The spring 1, illustrated in further detail
in FIG. 3, is made with a shaped hole 1a that fits over boss 3a to
keep the spring in position laterally. The spring 1 is formed so
that it is compressible along two orthogonal axes--vertically so as
to press against and make contact with the printed circuit board 2,
and horizontally so as to press against and make contact with one
of the standoffs to which the printed circuit board will be
mounted, as discussed in further detail below. The spring 1 is
fabricated from flat metal stock. Stainless steel is preferably
used for this purpose, but any other suitable conductive material
with equivalent mechanical and electrical properties can be
substituted.
[0021] When assembled, the printed circuit board is secured to the
plastic stiffener 3 using screws or other suitable fasteners. As
illustrated in FIG. 1, the printed circuit board has holes 2b
through which screws (not shown) can be inserted into matching
holes 3b in stiffener 3. When the printed circuit board 2 is
secured to the plastic stiffener 3, grounding pads 2d on the bottom
side of the printed circuit board 2 make contact with the spring 1
providing the first grounding axis. These pads are wired directly
to the ground planes of the printed circuit board 2, thus
connecting the spring 1 to the board ground.
[0022] In the embodiment described in this application, the board
assembly 5, comprising the printed circuit board 2, stiffener 3 and
spring 1, is mounted to the frame 15 of an electronic system using
metal standoffs 10 like the one illustrated in FIG. 4. The
stiffener 3 is present but not shown in FIG. 4, in order to more
clearly reveal the interaction of the conductive spring 1, printed
circuit board 2 and standoff 10. Typically, five standoffs attached
to the frame of the system are used to mount each board assembly.
The board assembly is mechanically secured to the standoffs without
the use of tools by utilizing a keyhole slot technique. As shown in
FIG. 1, a "keyhole" shaped cut out 2c is formed in the printed
circuit board 2 in a position adjacent to the grounding pad 2d that
makes contact with the spring 1. Another keyhole slot 3c is formed
in stiffener 3 so as to be aligned with the first keyhole slot 2c
when the printed circuit board 2 is fastened to the stiffener 3.
The dimensions of the keyhole slot 3c are slightly larger than
those of keyhole slot 2c in order to avoid manufacturing tolerance
problems. To mount the board assembly 5, the board assembly is
lowered onto the standoffs, with the head 10a of each standoff 10
projecting through the large, circular opening in the keyhole slot,
as illustrated in FIGS. 4. Once the board assembly 5 is resting on
the shoulders 10b of the standoffs 10, the board assembly is locked
into place by sliding, or moving it laterally, on the standoffs, so
that the shank portion 10c of the standoff 10 is positioned in the
narrower slot portion of keyhole slot 2c. The shank portion 10c,
which is immediately below the head 10a of the standoff 10, has a
smaller diameter than the head 10a. When the board assembly 5 is
moved from its initial position (Position A) to its fastened
position (Position B), as illustrated in FIG. 5, the head 10a of
the standoff 10 is over the smaller opening in the slot 2c on the
printed circuit board 2, preventing the board assembly 5 from
moving in the vertical direction. A spacer 3d, formed around the
keyhole opening 3c on the plastic stiffener 3, prevents the
downward deflection of the printed circuit board 2 when the board
assembly 5 is in Position B. When the board assembly 5 is in the
fastened position (Position B), the spring 1 is compressed against
and contacts the standoff 10, which carries the circuit board
ground to the frame ground of the electronic system, providing the
second grounding axis. This biaxial interaction of the spring 1
with the printed circuit board 2 and the standoff 10 is shown in
FIG. 4.
[0023] To prevent the board assembly 5 from for moving relative to
the standoffs 10 and breaking free, the board assembly is typically
screwed into the frame of the electronic apparatus in two
locations. This is preferably accomplished by making two of the
standoffs with tapped holes in their upper ends and using screws,
for example, to secure the board assembly to these standoffs
instead of using the keyhole slot arrangement described above. The
standoffs chosen for securing the board assembly with screws are in
positions readily accessible to tools.
[0024] As illustrated in FIG. 4, a second printed circuit board 20
may be mounted on the bottom of the plastic stiffener (not shown
for clarity) to increase the overall packaging density of the
electronic system of which the board assembly forms a part. The
second printed circuit board 20 also has an elongated opening (not
shown) that aligns with the keyhole opening in the stiffener (not
shown in FIG. 4). When the board assembly 5 is in its fastened
position on the standoff 10, the back of the second printed circuit
board 20 rests on the shoulder 10b of the standoff. Grounding of
the second printed circuit board 20 can be accomplished with a
grounding pad formed around the opening on the bottom surface of
the second printed circuit board, so as to be directly in contact
with the shoulder 10b of standoff 10.
[0025] In summary, the method described herein for grounding a
printed circuit board to a plurality of standoffs attached to the
frame of an electronic system involves securing the printed circuit
board to at least one of the plurality of standoffs using a
securing means that does not require the use of tools, and
positioning a conductive spring, compressible in two axes, such
that it makes electrical contact with both the one standoff and a
grounding pad formed on the printed circuit board. Preferably, the
biaxially-compressible conductive spring is captivated between the
printed circuit board and a plastic stiffener to which the board is
fastened. In the preferred embodiment, the securing means is a
keyhole-shaped hole in the printed circuit board having a circular
portion through which the head of the one standoff can pass, but
which secures the board when the board is slid into a position such
that the head is over the slotted portion of the keyhole. When the
board is fully installed in its secured position in the electronic
system, the one standoff makes contact with the conductive spring,
completing the ground path.
[0026] It should be understood that the invention is not
necessarily limited to the specific process, arrangement, materials
and components shown and described above, but may be susceptible to
numerous variations within the scope of the invention.
[0027] It will be apparent to one skilled in the art that the
manner of making and using the claimed invention has been
adequately disclosed in the above-written description of the
preferred embodiments taken together with the drawings.
[0028] It will be understood that the above description of the
preferred embodiments of the present invention are susceptible to
various modifications, changes and adaptations, and the same are
intended to be comprehended within the meaning and range of
equivalents of the appended claims.
* * * * *