Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2002-12-20
2003-10-28
Ngo, Hung V. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
Reexamination Certificate
active
06639147
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
Field of the Invention
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
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.
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.
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 Schmalz. 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.
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.
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 (Malnquist) 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.
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).
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.
SUMMARY OF THE INVENTION
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 devi
Hastings Robert J.
Thompson Daniel T.
Hewlett--Packard Development Company, L.P.
Ngo Hung V.
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