U.S. patent application number 10/028841 was filed with the patent office on 2003-06-26 for captive low-profile emi grounding clip.
Invention is credited to Hastings, Robert J., Thompson, Daniel T..
Application Number | 20030116337 10/028841 |
Document ID | / |
Family ID | 21845756 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030116337 |
Kind Code |
A1 |
Thompson, Daniel T. ; et
al. |
June 26, 2003 |
Captive low-profile EMI grounding clip
Abstract
An EMI clip retaining system comprising a flexible EMI clip with
a center contact portion that bows upwards and inwards from acute
bends situated at the outer ends of the EMI clip and also
comprising enlarged end portions that extend flatly inwards from
the acute bends. The EMI clip is captively installable in a planar
mounting surface with tapered mounting holes through which the
enlarged end portions of the EMI clip are inserted, such that once
the EMI clip is installed, the enlarged ends of the EMI clip reside
on a bottom side of the mounting surface while the center contact
portion bows upward from the opposite, top side of the mounting
surface. When the center portion is compressed flat against the top
side of the mounting surface, the EMI clip lies flat against both
the top and bottom sides of the mounting surface.
Inventors: |
Thompson, Daniel T.;
(Houston, TX) ; Hastings, Robert J.; (Spring,
TX) |
Correspondence
Address: |
CONLEY ROSE, P.C.
P. O. BOX 3267
HOUSTON
TX
77253-3267
US
|
Family ID: |
21845756 |
Appl. No.: |
10/028841 |
Filed: |
December 20, 2001 |
Current U.S.
Class: |
174/354 ;
174/363 |
Current CPC
Class: |
H05K 9/0016
20130101 |
Class at
Publication: |
174/35.00R |
International
Class: |
H05K 009/00 |
Claims
What is claimed is:
1. An EMI shielding device comprising: an elastically deformable
body portion capable of applying a contact force between a top
compressing surface and a planar bottom mounting surface; and more
than one enlarged, planar end portions that may each be installed
in separate apertures in the mounting surface to captively retain
the EMI shielding device on the mounting surface; wherein when an
installed EMI shielding device is compressed between the
compressing and mounting surfaces, the deformable body portion of
the EMI shielding device lies flat between the compressing and
mounting surfaces and the enlarged end portions lie substantially
flat on the side of the mounting surface opposite the side facing
the compressing surface.
2. The EMI shielding device of claim 1 further comprising: an
obtuse bend at the top of the shielding device configured to bend
elastically from some static angle larger than 90 degrees to an
angle of 180; flat planar surfaces on either side of the obtuse
bend; and acute bends at the end of the planar surfaces opposite
the obtuse bend; wherein the enlarged end portions extend inward
from the side of the acute bend opposite the planar surfaces.
3. The EMI shielding device of claim 2 comprising two enlarged,
planar end portions.
4. The EMI shielding device of claim 2 wherein the radius of each
acute bend is roughly equal to half the thickness of the mounting
surface.
5. The EMI shielding device of claim 4 wherein: the acute bends are
also elastically deformable to permit compression of the EMI
shielding device between the mounting and compressing surfaces and
also to permit extension of the EMI shielding device during
installation of the EMI shielding device onto the mounting
surface.
6. The EMI shielding device of claim 5 further comprised of an
electrically conductive material.
7. An EMI clip retaining system comprising: a flexible EMI clip
with a center portion that bows upwards and inwards from acute
bends situated at the outer ends of the EMI clip and also
comprising enlarged end portions that extend flatly inwards from
the acute bends; and a planar mounting surface with mounting holes
through which the enlarged end portions of the EMI clip are
inserted during installation of the EMI clip onto the mounting
surface, such that once the EMI clip is installed, the enlarged
ends of the EMI clip reside on a bottom side of the mounting
surface while the center portion bows upward from the opposite, top
side of the mounting surface; wherein once the EMI clip is
installed onto the mounting surface, the EMI clip is captively
retained by the shape of the mounting holes and also by the elastic
forces within the EMI clip; and wherein if the center portion is
compressed flat against the top side of the mounting surface, the
EMI clip lies flat against both the top and bottom sides of the
mounting surface.
8. The EMI clip retaining system of claim 7 wherein the mounting
surface holes further comprise: a single aperture corresponding to
each enlarged end of the EMI clip; wherein the aperture shapes are
mirrored about an axis centered between the apertures.
9. The EMI clip retaining system of claim 8 wherein the mounting
hole apertures further comprise: a narrow inner width that is wider
than the width of the center portion of the EMI clip but narrower
than the width of the enlarged end portions of the EMI clip; a
wider outer width that is wider than the width of the enlarged end
portions of the EMI clip; and contoured sides that transition from
the narrow inner width to the wider outer width; wherein when the
EMI clip is installed onto the mounting surface, the EMI clip is
elastically stretched to insert the enlarged ends of the EMI clip
through the wider outer width of the corresponding mounting hole
apertures; and wherein once the EMI clip is installed onto the
mounting surface, the enlarged portions of the EMI clip contract to
reside under the narrow inner width of the corresponding mounting
hole apertures thereby captively retaining the EMI clip.
10. The EMI clip retaining system of claim 9 wherein: the mounting
hole apertures are positioned so that the narrow inner widths of
the apertures are approximately the same distance apart as are the
insides of the acute bends in the EMI clip; and wherein the wider
outer widths of the apertures are not so far as to induce plastic
deformation of the EMI clip as it is stretched during
installation.
11. The EMI clip retaining system of claim 10 wherein: the mounting
surface thickness is approximately twice the thickness of the radii
of the acute bends in the EMI clip.
12. The EMI clip retaining system of claim 11 wherein each EMI clip
comprises two enlarged ends.
13. An EMI clip retaining system comprising: a flexible EMI clip
with a narrow center portion and enlarged end portions; and a
planar mounting surface with mounting holes through which the
enlarged end portions of the EMI clip are inserted such that the
narrow center portion of the EMI clip reside on a top side of the
mounting surface and the enlarged end portions of the EMI clip
reside on the opposite, bottom side of the mounting surface;
wherein once the EMI clip is inserted onto the mounting surface,
the EMI clip is captively retained by the shape of the mounting
holes and also by the elastic forces within the EMI clip; and
wherein if the center portion is of the EMI clip compressed flat
against the top side of the mounting surface, the EMI clip lies
flat against both the top and bottom sides of the mounting
surface.
14. The EMI clip retaining system of claim 13 wherein the narrow
center portion of the flexible EMI clip further comprises: acute
bends situated at the outer ends of the EMI clip; and a contact
portion that bows upwards and inwards from the acute bends; wherein
the enlarged end portions extend flatly inwards from the acute
bends.
15. The EMI clip retaining system of claim 14 wherein the mounting
surface holes further comprise: a single aperture corresponding to
each enlarged end of the EMI clip; wherein the aperture shapes are
mirrored about an axis centered between the apertures.
16. The EMI clip retaining system of claim 15 wherein the mounting
hole apertures further comprise: a narrow inner width that is wider
than the width of the narrow center portion of the EMI clip but
narrower than the width of the enlarged end portions of the EMI
clip; a wider outer width that is wider than the width of the
enlarged end portions of the EMI clip; and tapered sides that
transition from the narrow inner width to the wider outer width;
wherein when the EMI clip is installed onto the mounting surface,
the EMI clip is elastically stretched to insert the enlarged ends
of the EMI clip through the wider outer width of the corresponding
mounting hole apertures; and wherein once the EMI clip is installed
onto the mounting surface, the enlarged portions of the EMI clip
contract to a position under the narrow inner width of the
corresponding mounting hole apertures thereby captively retaining
the EMI clip.
17. The EMI clip retaining system of claim 16 wherein: the mounting
hole apertures are positioned so that the narrow inner widths of
the apertures are approximately the same distance apart as are the
insides of the acute bends in the EMI clip; and wherein the wider
outer widths of the apertures are not so far as to induce plastic
deformation of the EMI clip as it is stretched during
installation.
18. The EMI clip retaining system of claim 16 wherein: the mounting
hole apertures are positioned so that the narrow inner widths of
the apertures are a larger distance apart than the insides of the
acute bends in the EMI clip so as to create an interference contact
between the EMI clip and the mounting surface; and wherein the
wider outer widths of the apertures are not so far as to induce
plastic deformation of the EMI clip as it is stretched during
installation.
19. The EMI clip retaining system of claim 18 wherein: the mounting
surface thickness is approximately twice the thickness of the radii
of the acute bends in the EMI clip.
20. The EMI clip retaining system of claim 19 wherein each EMI clip
comprises two enlarged ends and two corresponding mounting hole
apertures.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION 1. Field of the Invention
[0003] The present invention generally relates to electromagnetic
or EMI shielding. More specifically, the invention relates to an
EMI grounding clip for maintaining a grounding path between
separable portions of electronic device enclosures.
BACKGROUND OF THE INVENTION
[0004] In the field of electronics, radio frequency (RF) and
electromagnetic interference (EMI) are important factors to
consider in product designs. On the one hand, EMI waves from
external sources have the potential to affect the operation of
components inside an electronics package. On the other hand, the
FCC and other regulatory agencies impose limits on the frequency
and levels of EMI signals that may emanate outwards from the inside
of an electronics product. One way to control EMI problems is to
package electronics products in an appropriately shielded
enclosure. A conventional technique for providing such shielding is
to surround internal components with a continuously grounded
enclosure. Unfortunately, assembly and service constraints prohibit
housing products in a one piece enclosure. Consequently,
electronics housings are usually comprised of separate pieces that
are fastened together to create a uniform enclosure.
[0005] To prevent the EMI problems discussed above, the various
pieces of an electronics enclosure must be electrically conductive
and coupled to one other. By coupling all pieces of the cover to
one another, the entire enclosure can be effectively coupled to
ground to form an EMI barrier around the electrical components.
Under normal circumstances, simply fastening the pieces of a cover
together is not sufficient to ensure electrical conductivity over
the anticipated range of operating temperatures and conditions.
Internal and external temperature variations may cause some
portions of the enclosure to expand or contract at different rates,
thereby producing gaps or increasing electrical resistance between
pieces of an enclosure. To eliminate this problem, conductive
gaskets, clips, or springs may be placed between pieces of an
enclosure to maintain electrical conductivity between the pieces.
EMI gaskets, clips, or springs are typically compressible and are
designed to deflect with enough spring force to always maintain
contact with the conductive surfaces of mating pieces of an
enclosure.
[0006] The use of these conductive EMI devices is well known to
those skilled in the art. Representative examples of conventional
EMI clips are illustrated and described in U.S. Pat. Nos. 4,554,400
and 4,640,979, both to Schmalzl. These EMI clips provide the
necessary grounding to ensure RF shielding of electronic devices
and, as with many conventional EMI clips, are installed by
inserting a portion or portions of the clip into holes in the
mounting surface. Conventional EMI clips such as these are
therefore retained with tabs that are bent around a mounting hole
or with an interference fit between the clip and the mounting hole.
There are no other retaining means on these conventional clips.
Thus, with these mounting configurations, a common problem is that
the clips may become detached and fall out of their mounting
locations. This problem is exacerbated by the fact that many
conventional EMI clips are low compression clips that are very
flexible and very easily deflected. Such characteristics are
desirable to permit easier installation of enclosure panels, but
also make it much easier for the clips to be pulled out of their
mounting locations. Loose EMI clips are naturally a problem in
electronics devices because of the potential damage they may cause
by electrically coupling and shorting components and electrical
traces inside the unit.
[0007] To combat this problem, other conventional retaining methods
have been used, such as the use of adhesive-backed EMI clips to
secure the clips in place. This solution is effective as long as
the adhesive retains its bonding power. It is widely recognized,
however, that adhesives have the propensity to deteriorate over
time and therefore do not provide an effective long-term solution.
Another solution has been to combine a series of EMI clips into a
single chain of grounding fingers as shown in U.S. Pat. No.
5,917,147 to Lewis. This retaining method presumes that it is more
difficult to displace or loosen a large array of grounding clips
than smaller, individual clips. While this presumption is not
without merit, the large array also requires that there is enough
mounting space available to install the chain of grounding fingers.
However, given the wide assortment of mounting and spacing
configurations in electronics enclosures, it may be desirable to
use individual grounding clips instead of such a large array.
[0008] Other improved methods of retaining EMI clips are described
in U.S. Pat. Nos. 4,803,306 to Malmquist and 5,532,428 to Radloff
et al, each of which provide more robust retaining schemes than the
methods heretofore described. Images from the former of these two
patents (Malmquist) are reproduced in FIG. 1, while images of the
latter (Radloff) are reproduced in FIG. 2. The Malmquist clip
comprises a U-shaped attaching portion 12 with a retaining notch 18
formed on each side of the U-shaped portion 12. These retaining
notches 18 are configured to keep the EMI clip securely in place
once the U-shaped portion 12 is inserted into a properly shaped
mounting hole 32 in a retaining panel. One distinct disadvantage to
this EMI clip is the depth D occupied on the insertion side of the
EMI clip. The retaining notches 18 on the U-shaped portion 12
increase the volume requirements for this particular solution.
Consequently, additional clearance must be designed into the
electronics enclosure so as to prevent interference with the EMI
clip.
[0009] By way of comparison, the retaining scheme used by Radloff
shown in FIG. 2 also occupies additional space on the backside of
the mounting surface. In this particular solution, the EMI clip 10
comprises end portions 20 that are substantially wider (dimension
L) than the center portion (dimension W) of the clip. The EMI clip
is installed into a mounting surface by inserting the end portions
20 through a slot 36 in the mounting surface one end portion at a
time. The enlarged end portions 20 are captively held in place by a
lance structure 34 that forms a cavity on the backside of the
mounting surface in which the end portions 20 reside. When a mating
cover is attached to the mounting surface, the EMI clip is
compressed such that most of the clip is deflected into the volume
between the lance structure 34 and the mounting surface.
Unfortunately, this design, as with the Malmquist design, occupies
a large volume of space behind the mounting surface (as denoted by
dimension D).
[0010] Despite the effectiveness of these prior art captivation
techniques, each occupies a large volume of space behind the
mounting surface. Given the compact nature of electronics
packaging, it is desirable, therefore, to provide a robust,
low-profile means of captively retaining an EMI clip onto a
mounting surface. The novel technique would advantageously decrease
the amount of space required to hold the EMI clip in place, thereby
permitting lower profile electronics enclosures.
BRIEF SUMMARY OF THE INVENTION
[0011] The problems noted above are solved in large part by a
novel, low-profile, captive retaining scheme for an EMI clip. The
EMI clip is preferably an EMI shielding device comprised of an
electrically conductive material and further comprising an
elastically deformable body portion capable of applying a contact
force between a top compressing surface and a planar bottom
mounting surface. The EMI clip includes more than one enlarged,
planar end portions that may each be installed in separate
apertures in the mounting surface to captively retain the EMI
shielding device on the mounting surface. When an installed EMI
shielding device is compressed between the compressing and mounting
surfaces, the deformable body portion of the EMI shielding device
lies flat between the compressing and mounting surfaces. The
enlarged end portions lie substantially flat on the side of the
mounting surface opposite the side facing the compressing
surface.
[0012] The EMI shielding device includes a narrow, center, contact
portion that bows upwards and inwards from acute bends at the outer
ends of the clip. At the top of the contact portion is an obtuse
bend configured to bend elastically from some static angle larger
than 90 degrees to an angle of 180. The clip also includes flat
planar surfaces that ramp upwards from the acute bends towards the
common obtuse bend. The enlarged end portions extend flatly inward
from the side of the acute bend opposite the planar surfaces. The
preferred embodiment of the EMI clip comprises two enlarged, planar
end portions. The acute bends on the EMI clip are also elastically
deformable to permit compression of the EMI shielding device
between the mounting and compressing surfaces and also to permit
extension of the EMI shielding device during installation of the
EMI shielding device onto the mounting surface.
[0013] The preferred EMI clip works in conjunction with a tapered
mounting hole pattern in the mounting surface to create an EMI clip
retaining system. The planar mounting surface comprises mounting
holes through which the enlarged end portions of the EMI clip are
inserted such that the narrow center portion of the EMI clip
resides on a top side of the mounting surface and the enlarged end
portions of the EMI clip reside on the opposite, bottom side of the
mounting surface. Once the EMI clip is inserted onto the mounting
surface, the EMI clip is captively retained by the tapered shape of
the mounting holes and also by the elastic forces within the EMI
clip. The mounting surface holes comprise an aperture corresponding
to each enlarged end of the EMI clip. The aperture shapes are
preferably mirrored about an axis centered between the apertures.
Each aperture in the mounting hole pattern comprises a narrow inner
width that is wider than the width of the narrow center portion of
the EMI clip but narrower than the width of the enlarged end
portions of the EMI clip. The aperture also includes a wider outer
width that is wider than the width of the enlarged end portions of
the EMI clip. The sides of the aperture are tapered and transition
from the narrow inner width to the wider outer width.
[0014] When the EMI clip is installed onto the mounting surface,
the EMI clip is elastically stretched to insert the enlarged ends
of the EMI clip through the wider outer width of the corresponding
mounting hole apertures. Once inserted, the enlarged portions of
the EMI clip contract to a position under the narrow inner width of
the corresponding mounting hole apertures thereby captively
retaining the EMI clip. The mounting hole apertures are positioned
so that the narrow inner widths of the apertures are approximately
the same distance apart as are the insides of the acute bends in
the EMI clip. By the same token, the wider outer widths of the
apertures are not so far apart as to induce plastic deformation of
the EMI clip as it is stretched during installation. Alternatively,
the mounting hole apertures may be positioned so that the narrow
inner widths of the apertures are a larger distance apart than the
insides of the acute bends in the EMI clip so as to create an
interference contact between the EMI clip and the mounting surface.
The preferred mounting surface thickness is approximately twice the
thickness of the radii of the acute bends in the EMI clip.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a detailed description of the preferred embodiments of
the invention, reference will now be made to the accompanying
drawings in which:
[0016] FIG. 1 shows a first prior art EMI clip with a captive
mounting scheme;
[0017] FIG. 2 shows a second prior art EMI clip with a captive
mounting scheme;
[0018] FIG. 3 shows isometric, top, profile, and bottom views of a
preferred EMI clip;
[0019] FIG. 4 shows top and profile views of a flat, unbent
representation of the preferred EMI clip;
[0020] FIG. 5 shows isometric views of a preferred mounting
configuration for the EMI clip;
[0021] FIG. 6 shows a preferred mounting hole pattern for the
preferred EMI clip;
[0022] FIG. 7 shows top, profile, and bottom views of the preferred
EMI clip mounted in the preferred mounting configuration; and
[0023] FIG. 8 shows section views of an assembled EMI clip in
compressed and uncompressed contact with a mating cover.
NOTATION AND NOMENCLATURE
[0024] Certain terms are used throughout the following description
and claims to refer to particular system components. As one skilled
in the art will appreciate, computer companies may refer to a
component by different names. This document does not intend to
distinguish between components that differ in name but not
function. In the following discussion and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus should be interpreted to mean "including, but not limited to .
. . ". In addition, the phrase EMI is intended to refer to
electromagnetic interference and is also intended to be fully
synonymous with other similarly used terms of art, including, but
not limited to, radio frequency (RF) interference or radio
interference. Furthermore, the preferred EMI clip is intended to be
used for creating an electrically conductive contact element
between mating surfaces of an electronics enclosure so as to
provide EMI shielding or grounding.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Referring now to FIG. 3, the preferred embodiment of an EMI
clip 40 comprises a thin conductive strip of material bent into the
configuration shown. The preferred clip material is copper alloy,
but other conductive materials may be used, including silver alloys
and perhaps even composite materials impregnated with conductive
material. The EMI clip preferably comprises at least two different
cross section widths denoted by W1 and W2. The innermost portion 42
of the EMI clip has a width of W1 whereas the two outermost
portions 44 have a width of W2. As FIG. 3 shows, W2 is larger than
W1 and thus, the outermost portions 44 of the EMI clip 40 are wider
than the innermost portion 42 of the clip.
[0026] As shown in the front profile view of FIG. 3, the clip 40 is
preferably a uniform thickness across the entire length of the
clip. Manufacturing considerations are one reason for this
constraint since the clips may be economically stamped from sheets
of raw stock. After stamping the preferred pattern from raw sheets
of material, the blanks may be bent and heat treated to the proper
dimensions and flexibility. However, there may be advantages to
using EMI clips with varying cross sections. For example, it may be
desirable for the EMI clip to deflect more easily at some bends
rather than others. Thus, the thickness at a bend may be increased
to reduce flexibility or the thickness may be decreased to promote
flexibility. Naturally, elasticity of the material as well as
fatigue strength of the material may determine the appropriate clip
thickness. Those skilled in the art will recognize the advantages
and disadvantages to manufacturing EMI clips with cross sections
having varying thicknesses.
[0027] The shape of the preferred EMI clip is characterized by an
inner portion 42 that bows upward from enlarged end portions 44.
The inner portion comprises an obtuse bend 46 at the top of the EMI
clip and acute bends 48 at the lower, outer ends of the clip. The
planar surfaces 45 between the obtuse and acute bends ramp upwards
from the acute bends 48 to the commonly adjoined obtuse bend 46.
The enlarged ends 44 of the clip 10 extend inward from the acute
bends 48. The obtuse bend 46 at the top of the EMI clip is
preferably configured to deflect elastically to approximately 180
degrees under a compressive force applied to the top of the clip.
Upon removal of this compressive force, the bend 46 preferably
returns to the static, ramped position shown. The elasticity of
this bend preferably provides the requisite contact force between
the surface to which the EMI clip is attached and a mating surface
that applies the compressive force. Section views of an assembled
EMI clip 40 in the compressed and uncompressed states are shown in
FIG. 8. The acute bends 48 shown at opposite ends of the clip 40
are also preferably configured to deflect elastically, thereby
permitting the clip 40 to lie substantially flat when compressed
between two mating surfaces of an electronics enclosure.
[0028] The profile view in FIG. 3 also shows an installation
dimension L, which is critical to the design of the mounting holes
in which the preferred EMI clip 40 is installed. This dimension and
its relationship to the preferred mounting hole configuration are
discussed in further detail below.
[0029] Referring now to FIG. 4, a flattened representation of
preferred EMI clip 40 is shown to aid in conceptualizing the shape
of the clip. If the bends 46, 48 in the preferred EMI clip 40 are
straightened out and the clip is laid flat, the representations
shown in FIG. 4 will result. From these views, it is easy to
identify the widened end portions 44 and their relation to the
narrower central portion 42. The overall length OL of the preferred
EMI clip may be varied according to space and design constraints,
but the length of the clip will necessarily define the mounting
hole configuration, which is shown in FIGS. 5-7. As mentioned
above, this flattened representation may be used as a template for
stamping or machining individual clips as a preliminary process in
manufacturing the final product.
[0030] Referring now to FIG. 5, isometric perspective views of a
representative mounting flange 55 comprising two sets of mounting
holes 50 for the preferred EMI clip 40 are shown. The upper view
represents a view of the top of the mounting flange 55 and one EMI
clip 40 installed in one of the two mounting hole sets 50 on the
mounting flange 55. The lower view represents the same mounting
flange 55 and EMI clip 40 viewed from underneath the mounting
flange 55. In accordance with the preferred embodiment, a mounting
hole set 50 for one EMI clip 40 comprises two separate apertures 52
through which the enlarged ends 44 of the clip 40 are inserted.
Each of the apertures 52 in each mounting hole set are preferably
identical in shape, but mirrored about a centerline between the two
apertures.
[0031] The preferred shape for the apertures 52 in a mounting hole
set 50 are more clearly shown in FIG. 6. Four critical dimensions
are qualitatively shown: AW1, AW2, IL1, and IL2. Dimensions AW1 and
AW2 define the inner and outer aperture widths for both apertures
52. The sides 60 of each aperture 52 are predominantly tapered and
preferably follow a contoured spline that transitions between the
inner and outer aperture widths AW1 and AW2. The portions of the
aperatures that are closest to one another are preferably narrower
than the portions that are the farthest from one another.
Dimensions IL1 and IL2 are installation lengths and define the
distance between respective features of the apertures 52 in a
single mounting hole set 50. Dimension IL1 reflects the dimension
between the closest surfaces of separate apertures 52 in a mounting
hole set. Dimension IL2 reflects the dimension between one aperture
and the point in the other aperture where the contoured side
surface 60 transitions from a curved spline to the maximum aperture
width AW2.
[0032] The apertures in a mounting hole set are preferably shaped
to permit the enlarged ends 44 of an EMI clip 40 to pass through
the aperture during installation, but also to retain the ends of
the clip 40 once installed in the mounting hole set 50.
Accordingly, the dimension AW2 is preferably larger than the width
W2 of the enlarged ends 44 of the EMI clip, thereby permitting each
end 44 of the EMI clip 40 to be inserted into each aperture 52 (see
also FIGS. 5, 7, 8). The retaining method of the preferred
embodiment also requires that the dimension AW1 be smaller than the
width of the enlarged ends W2, but larger than the width WI of the
narrow center portion 42 of the EMI clip 40. In this application,
it is desirable that the dimension AW1 be closer to width W1 than
to width W2. Thus, once the EMI clip 40 is installed in a mounting
hole set 50, the enlarged ends 44 are captively retained by the
inner portions of the apertures 52. In addition, the spring forces
of the obtuse 46 and acute 48 bends serve to prevent the enlarged
ends 44 of the EMI clip 40 from exiting the apertures in the
absence of externally applied removal forces.
[0033] Referring still to FIG. 6, dimension IL1 is roughly the same
magnitude as installation dimension L shown in FIG. 3. The
relationship between these dimensions is shown qualitatively in the
profile section view at the center of FIG. 7. In practice, it may
be desirable to provide a nominal interference between the clip and
the mounting holes such that dimension L is slightly less then
dimension IL1. This dimensioning scheme may provide an additional
guarantee that the EMI clip 40 will be captively retained in the
mounting hole set 50. However, it should be understood that the
preferred mounting hole set may include a distance IL1 between
apertures 52 that is smaller, equal to, or larger than dimension
L.
[0034] Dimension IL2 defines the distance between one aperture and
the point in the other aperture where the contoured side surface 60
transitions from a curved spline to the maximum aperture width AW2
(i.e., where the aperture width is at its largest). Because the
apertures are mirror images of one another, a duplicate dimension
can be drawn between the other corresponding set of points in the
same mounting hole set. Hence, dimension IL2 is shown twice in FIG.
6.
[0035] During installation of the EMI clip 40, one enlarged end 44
of the clip is installed at a time. After a first enlarged end 44
has been installed in one aperture 52, the clip must be elastically
stretched so that the second enlarged end 44 may be inserted in the
second aperture 52 of the mounting hole set. Dimension IL2 defines
the distance to which the EMI clip 40 must be stretched during such
an installation. By their very nature, EMI clips 40 are configured
to be elastically deformed when panels of an electronics enclosures
are installed. However, it is also important that the clip maintain
its shape so as to work properly. Thus, it is important that,
during installation, the clip is not plastically or permanently
deformed since this may affect the elastic deflection
characteristics of the clip. Furthermore, a bent clip may be prone
to coming loose or binding and creating interference between
enclosure panels. It is therefore preferable that dimension IL2 be
as large as possible, but not so large as to induce plastic
deformation during installation of an EMI clip 40. Those skilled in
the art will be able to assign a physical number to this dimension
based on such factors as the thickness of the EMI clip, elasticity
modulus for the clip material, and the heat treatment applied to
the clip during manufacturing. All such variations are certainly
intended to be within the scope of this description of the
preferred embodiment.
[0036] Referring now to FIG. 7, top, profile, and bottom views of
the preferred EMI clip 40 installed in the preferred mounting
configuration are shown. Some of the pertinent dimensions
heretofore discussed are duplicated in these views to further
illustrate the relationship between the dimensions of the EMI clip
40 and those of the mounting hole set 50. As shown, and as
discussed before, dimensions AW1 and AW2 are slightly larger than
dimensions W1 and W2, respectively. For the captive features of the
preferred embodiment to work property, clip dimension W2 must be
larger than aperture dimension AW1. Similarly, dimensions L and IL1
are preferably about the same magnitude. With this dimensioning
scheme, the EMI clip 40 is advantageously captively retained and
should not fall out of its mounting configuration during normal
use.
[0037] A further distinctive feature and characteristic of the
preferred embodiment is the low profile nature of the clip. FIG. 8
shows section views of an assembled EMI clip in compressed and
uncompressed contact with a mating cover. The upper view of FIG. 8
shows the uncompressed, relaxed state of the EMI clip 40 as a
mating cover comes into contact with the clip. As the lower,
compressed view shows, bend 46 in clip 40 deflects until the upper
portion of the clip (portion between the mating surfaces) lies
completely flat. Furthermore, the portion of the clip on the
underside of the mounting surface lies substantially flat. The
amount of actual protrusion on the bottom side of the mounting
surface is determined only by the thickness of the clip and the
bend radii in acute bends 48. If the bend radii are on the order of
half the thickness of the mounting surface, then the compressed EMI
clip will be substantially flush with the bottom side of the
mounting surface. Thus, the preferred embodiment provides a fully
captive, low-profile solution for mounting individual EMI clips
40.
[0038] One other design consideration deserves to be mentioned. The
arrows in the upper view of FIG. 8 indicate the relative motion of
portions of the clip that result as an upper cover comes into
contact with the clip. As mentioned above, the obtuse bend 46
flattens as a downward compressive force is applied. As the upper
portion of the clip deflects downward, the ends of the clip,
including the enlarged ends that are on the underside of the
mounting surface, deflect outwards. Hence, whereas the distance
between the inner surfaces of bends 48 starts at a dimension L
before compression, this distance increases to some larger
dimension L2 after compression. This deflection must be taken into
account when defining the mounting hole dimension IL2. It is
important that mounting apertures 52 are positioned far enough from
each other so that the EMI clip will not fall out of its mounting
configuration. This design requirement must be met while
considering of the limitations mentioned above that define the
upper limit on the distance between the apertures. Together, these
design requirements define the upper and lower distance limits
between the apertures 52 to effectively provide a captive mounting
scheme for the preferred EMI clip 40.
[0039] The above discussion is meant to be illustrative of the
principles and various embodiments of the present invention.
Numerous variations and modifications will become apparent to those
skilled in the art once the above disclosure is fully appreciated.
For example, while the preferred embodiment is described has having
two enlarged ends that are insertable into a pair of mounting
apertures, it is certainly feasible that an EMI clip can be
designed with three or more enlarged ends that are each insertable
into its own aperture. It is intended that the following claims be
interpreted to embrace all such variations and modifications.
* * * * *