Abstract:
A method and associated apparatus for providing an electromagnetic seal in electrical enclosure of a device. The apparatus comprising of an electromagnetic gasket formed of a thin conductive material, having a first end and an opposing end. The apparatus also includes a conductive chassis disposed in the electrical enclosure and having a first and second protrusions for securing the end of the gasket to the chassis in a manner to provide facility of compression.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application contains subject matter which is related to the subject matter of the following co-pending applications, filed on the same day, which is assigned to the same assignee as this application, International Business Machines Corporation of Armonk, N.Y. The following applications and patents listed below is hereby incorporated herein by reference in its entirety: U.S. Pat. No. 6,816,390 and U.S. patent application Ser. No. 11/284,744—filed Nov. 22, 2005 (Docket POU920050160US1 and assigned to the same assignee as this application. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an electromagnetic compatibility (EMC) sealing apparatus and related method; and more particularly to a dynamic EMC sealing apparatus and method for an electrical enclosure used in computing system environments.  
         [0004]     2. Description of Background  
         [0005]     It is an industry goal to continuously increase the number of electronic components inside an electronic device. This goal is driven by several key and important reasons. The first and more obvious one is for the convenience of compactness. Compactness allows for selective fabrication of smaller and lighter devices that are more attractive to the consumer. Some of the reasons for such appeal stem from a desire for easier transportation, shipping, installation and storage of such devices. In other instances, when compactness per se is not a driving factor, providing the same number of devices in only a fraction of available footprint allows the remaining space to be filled with more components which will increase system performance and speed. In addition, compactness also allows many of the circuits to operate at higher frequencies and at higher speeds due to shorter electrical distances in these devices. Unfortunately, despite many of the advantages associated with this industry goal, there are several important challenges that have to be overcome by the designers of these systems.  
         [0006]     One area where the challenges and advantages provided by such compact densities is increased is in the computer industry. The reliance of many businesses on computers and computer networks in recent years, demands an ever increasing need to provide fast and accurate systems in the smallest and lightest allowable footprint. In a computing environment, whether comprising of a simple personal computer, or a complex system comprising of a number of computers in processing communication with one another, a plurality of printed circuit boards and cards are provided that house many electronic components and even devices.  
         [0007]     A particularly challenging area for the designers of these systems is the issue of resolving electromagnetic interference (EMI). As the number of components are increased, electromagnetic leakage concerns continue to grow. This is because every electronic device, emits some form of electromagnetic radiation. If unresolved, EMI can affect system performance, data integrity and speed. Obviously, in larger system environments, the increased number of components that are stored in close proximity to one another, greatly increases the EMI concerns. This is because while such effects can be tolerated when few devices and components exist, the increasing number of components and devices can seriously impact system integrity and performance. This problem is further exacerbated by the improvement in semiconductor devices which allow them to operate at higher speeds, generally causing emission in higher frequency bands where interference is more likely to occur.  
         [0008]     Prior art attempts have been made to minimize the interference problem. Electromagnetic compatibility (EMC) requires that emissions from a given device be reduced by shielding or other similar means. Such shieldings are designed not only to reduce emissions from the device itself, but also to reduce sensitivity of the device to external fields such as fields from other devices. One type of such EMI shieldings are EMI gaskets.  
         [0009]     In recent designs, it is necessary to use a metallic type of electromagnetic gaskets to provide better conduction with an electrical enclosure in which the printed circuit boards or cards are engaged. A common problem with such gaskets, however, are that they are easily damaged as a result of deflection of gasket during insertion or removal of printed circuit cards that reside in the computing system environment during mundane activities such as during servicing calls. Once the gasket has been damaged, not only does it no longer provides EMI protection for the device but it may even pose a threat for a potential short.  
         [0010]     Related U.S. Pat. No. 6,794,571 by Barringer et al. (hereinafter Barringer patent), owned by the same assignee, International Business Machines Corporation, and coauthored by at least some of the inventors of this application, provided a method and apparatus for providing an electromagnetic conduction seal in a device disposed within an electrical enclosure including a metal EMC gasket.  
         [0011]     Related patent solved the prior art problem of minimizing damages to such gaskets. This is especially true with EMC metal gaskets that have a spring design. In such gaskets, often one end of the gasket is only attached to a chassis with the other end left hanging without any retention. This other end is especially vulnerable to being damaged by being for example caught in some other object. The Barringer patent introduced a retention mechanism that provided for a lock strip to be fixed to the device. The gasket in that patent was secured to a device that provided limits of deflection of an intermediate portion to the gasket using an external part.  
         [0012]     While the Barringer patent solves many of the prior art problems, it is desirable to introduce a mechanism that can be fabricated at the same time as the chassis itself. In addition, providing a mechanism that does not provide a lock strip can allow the gasket to be used in environments where the installation or later exposure to high temperatures (such as caused by heat dissipation issues) can cause the lock strip to come unhinged. An example would be where glue is used and heat or installation can cause the glue to come undone.  
         [0013]     Consequently, it would be desirable to introduce an EMC gasket that can be secured to a device without the use of chemical bonding and adhesives. It would be even more beneficial to fabricate such a gasket during the same fabrication process steps as the device itself.  
       SUMMARY OF THE INVENTION  
       [0014]     The shortcomings of the prior art are overcome and additional advantages are provided through the method and associated apparatus for providing an electromagnetic seal in electrical enclosure of a device. The apparatus comprising of an electromagnetic gasket formed of a thin conductive material, having a first end and an opposing end. The apparatus also includes a conductive chassis disposed in the electrical enclosure and having a first and second protrusions for securing at the ends of the gasket to the chassis.  
         [0015]     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0017]      FIG. 1  is a perspective docking cassette as per one embodiment of the present invention;  
         [0018]      FIG. 2  is an isometric view of the docking cassette of  FIG. 1  with its cover removed;  
         [0019]      FIG. 3  is an isometric view of the docking cassette of  FIG. 1  and  2  with the printed board card removed;  
         [0020]      FIG. 4  is a partial view of the operating mechanism of the docking cassette of  FIG. 1, 2  and  3  with the card bracket removed;  
         [0021]      FIG. 5  is a top down illustration of the gasket as per one embodiment of the present invention; and  
         [0022]      FIG. 6  is a perspective illustration showing better gasket details.  
         [0023]      FIG. 7  is a cross sectional illustration of the segmentation of the gasket of  FIG. 5 ; and  
         [0024]      FIG. 8  is a cross sectional illustration of the gasket and chassis assembly as per one embodiment of the present invention. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0025]     The embodiments provided in conjunction with the following figures provide for a preferred embodiment where the EMC gasket of present embodiment is disposed in a computing environment. It should be noted that this embodiment is only provided for ease of understanding and the teaching of the present invention can equally apply to other devices and in conjunction with other electrical disclosures.  
         [0026]      FIG. 8  provides a cross sectional illustration of one embodiment of the present invention. The illustration of  FIG. 8 , provides for an EMC gasket with a unique retain feature that can be fabricated at the same time and the same material of the gasket and does not require additional adhesives and other such components. Before discussing the unique features comprising the EMC gasket of the present invention,  FIGS. 1 through 7  will be discussed so as to provide a general understanding of how the gasket of present invention will be mounted and used in conjunction with other components of a computing environment.  
         [0027]      FIG. 1  provides for a perspective view of a docking cassette  10  which will be used in conjunction with the gasket of the present invention. The cassette  10  has a defined cavity  12  containing a carrier  13  for carrying a printed circuit board (PCB) not illustrated in this view. The cassette has a housing  14  which can incorporate an additional cover (not illustrated) that may be selectively mounted on the housing  14  cover to provide better insulation.  
         [0028]     Projections  28  and  29  extend from the carrier  13  within cassette  10  through respective slots  30  and  31  to align the carrier  13  with other features and mechanisms that is provided for the cassette  10  as will be discussed later.  FIG. 2  is a perspective view of the cassette  10  of  FIG. 1  with the housing  14  removed. As illustrated a rod  22  is shown in this embodiment as being threaded through a threaded bore. The rod has a slightly enlarged head  24  with a socket  25  into which is inserted a tool such as to turn rod  22  to activate the mechanism for seating the PCB as will be discussed.  
         [0029]     The removal of the housing  14  in  FIG. 2  enables the illustration of PCB  35  to which a plurality of electrical components (not shown) are connected. An electrical connector  36  is also shown. The rod  22  can be used to seat or unseat the PCB  35  and/or the electrical connector  36 , through the use of a mechanism  49  which is connected to the PCB  35 . A traveling component  39  can be attached to the mechanism  41 , which will be discussed in greater detail below to accomplish this.  
         [0030]      FIG. 3  provides another perspective view of the cassette  10  with the PCB and the electrical connector  36  removed, showing the carrier  13  and the operating mechanism shown to seat and unseat the PCB  35  and/or the electrical connector  36 . The mechanism includes a bell crank  42  having a first arm  43  which is pivotally connected to a PCB carrier  13  at  45 . It also has a second arm  46  pivotally connected to the traveling component  38  at  48 . The bell crank  42  can have a pin (not shown) extending into a horizontal slot  50  in the back of the cassette  10  (not illustrated in this view) to guide the movement of the traveling component  38 . In this way the when the traveling component  38  moves, the rotating bell crank  42  also moves in the same direction which causes in turn the downward movement of the carrier  13 .  
         [0031]      FIG. 4  provides for a partial view of the operating mechanism of the cassette  10  of  FIG. 1 . The rod  22  has a first enlarged portion  52  which is threaded through for example with a right hand thread. In this example, when the rod is turned clockwise, the rod  22  advances and moves the traveling component  38  toward the right. The rod  22  also has a second enlarged potion  53  which has a left hand thread. Thus, as the rod  22  is turned clockwise, the traveler  38  further moves to the right. It will be understood that the action of both threaded portions  52  and  53  and the traveling component  38  act together in an additive action to rapidly move the traveling component  38  to the right, in this example. The bell crank  42  is pivotally attached to a pin  55  to the back of the cassette illustrated here as  15 .  
         [0032]      FIG. 5  provides a top down illustration of one embodiment of present invention. The purpose of providing the illustration of  FIG. 5  is to focus on the gasket  500  alone. In this regard, other components that may have been already discussed will not be discussed here as not to obscure the discussion of gasket  500 . Gasket  500  is placed over a chassis assembly  540  which is part of the initial housing  14  as was illustrated in  FIG. 1 .  
         [0033]     The details of gasket  500  are illustrated in the embodiment of  FIG. 5  through  8 . In  FIG. 5 , as per one embodiment of the invention, gasket  500  is provided as a unitary component  500 . However, as illustrated in  FIG. 7 , in a preferred embodiment, the gasket  500  is comprised of a plurality of segments, all of which are referenced as  705  for ease of understanding.  
         [0034]     The segmentation of the gasket is related to the amount of EMC control desired. By segmenting the gasket  500 , the amount of EMC protection can be increased. In this regard, narrower or wider strips can be used for each segment  705  to selectively reduce or increase the amount of segments  705  that as a whole comprise gasket  500 . It should also be noted that while in the illustration of  FIG. 7 , the segments  705  are illustrated to have equal width, this is not a requirement. Consequently, a combination of widths can also be used such that some segments ( 705 ) end up potentially wider than others on the gasket  400 . In a preferred embodiment, as illustrated in  FIG. 7 , independent of width, the shape and topography of each segment, however, is closely similar and/or identical despite the width differences in all conditions.  
         [0035]     It should be noted that in a preferred embodiment, the gasket is made out of a single sheet transversally segmented, for example by creating slits selectively preferably such that the opposing ends of the gasket/material are not segmented (and still connected) and the gasket can be put in place as a single unit such as shown in  FIG. 5 . The slits, once the gasket is secured, form individual loops that independently enhance compression of the gasket as will be discussed later in detail. Such an arrangement is not a requirement, however, and it is possible to have a gasket  500  that is comprised of a plurality of individual segments, that are not attached and that are individually secured to the chasses  540  to collectively form the gasket  500 .  
         [0036]     Referring now to  FIG. 6 , an exploded view of the chassis assembly  540  is provided. A plurality of apertures  605  and protrusions  610  are shown on the chassis assembly  540 . In a preferred embodiment, a plurality of second protrusions, marked in areas  620  which are occupied by apertures  605  will be provided. The first and second protrusions, in one embodiment as illustrated can resemble clips in their structure. The first protrusions  610  are preferably in a parallel plane with respect to one another. Similarly, the second protrusions  620  are also preferably on a parallel plane with respect with one another. In addition, the first and second protrusions  610  and  620  can either directly face one another or be in an alternate arrangement where the protrusions  620  lie between the two protrusions  610  as illustrated in  FIG. 6 . The chassis  600  and the protruding elements  610  and  620  are preferably fabricated of sheet metal during a single fabrication process  
         [0037]     Referring now to  7  and  FIG. 8 , this figure provides a cross sectional depiction of one of the gasket  500 . It should be noted, that since a cross sectional view is provided, however, the gasket  500  as a whole is not visible and only the shape of a single strip  705  is visible. Since all such segments  705 , however, are nearly identical in this embodiment and the gasket  500  is provided of a plurality of such strips, discussing the topography of a single segment  705  of the gasket  500  also reveals the topography of the gasket  500  as a whole.  
         [0038]     Gasket segment  705  is fabricated of a thin sheet of a conductive material. In a preferred embodiment the gasket  705  is fabricated out of a thin sheet of metal, such as copper. The thin sheet of material  705  has opposing ends respectively referenced as  801  and  802  and top and bottom surfaces  803  and  804  respectively.  
         [0039]     The thin material of the gasket or gasket segment  705  is attached to the chassis assembly using the protrusions  610  and  620  in the manner illustrated in  FIG. 8 . As discussed earlier, both protruding elements are preferably fabricated out of the same material as the chassis assembly  540  and are rigid in structure and therefore will hold the gasket  400  or gasket segments  705  firmly in place.  
         [0040]     In the illustrated embodiment of the invention, as visibly shown in  FIG. 7  and  8 , the protrusions have clip like structures that are punched out of chassis sheet metal. This is preferably done in a single processing step at the time of the fabrication of chassis assembly  540 .  
         [0041]     Referring now to  FIG. 8 , as illustrated the gasket  500  or alternatively the gasket segments  705  as illustrated in the figure comprise of ends  801  and  802  respectively and top and bottom sides  803  and  804  as illustrated. The ends  801  and  802  are looped around the first and second protrusions  610  and  620  such that the top side  803  of the thin segmented material  705  becomes a bottom portion in areas where the first and second protrusions are disposed over the material. In a preferred embodiment, gasket segment is secured in such a way that provides facility of compression. In the example of the illustrated figure, this means that the gasket  500  is not pulled tightly under the first and second elements  610  and  620  causing the bulbous structure illustrated by referenced element  800 .  
         [0042]     In the manner described above, each one of the ends  801  and  802  of the thin sheet of material forming the gasket  500  or gasket section  705  is disposed over the chassis assembly  540  through the clips or protrusions  610  and  620 . The length of the strip  705  along with the percentage of strip  705  that is used to create the bulbous structure discussed determines the flexibility of the gasket  500  as a whole. In the illustration of  FIG. 6 , the arrangement that is shown provides a desired spring like quality for the gasket  500  to enhance facility of compression.  
         [0043]     In reference to  FIG. 8 , it should be noted that the protruding elements  610  and  620  serves multiple functions. The more obvious purpose of the protruding elements  610  and  620  is to hold the gasket  500  securely at each end and also allow the gasket  500  to maintain its ability to compress. A less obvious purpose is that since the protruding elements  610  and  620  are preferably made of the same rigid material that forms the chassis assembly  540 , it provides support to the thin gasket material such that gasket is not easily torn, damaged or displaced.  
         [0044]     The number of the protruding elements provided can also be selectively adjusted to provide more protection if desired. In a functional regard, it is not necessary to have more that a few protruding element for the entire gasket. In such a respect, it would only be necessary to provide a protruding element for every few strips or segments  705 . The few protruding elements will hold the gasket  500  securely, but if more secure fastening is desired, the number of elements  610  and  620  as discussed above can be increased.  
         [0045]     While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.