Patent Publication Number: US-2007114060-A1

Title: EMC gasket with built-in chassis retention

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      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, New York. The application listed below is hereby incorporated herein by reference in its entirety the following U.S. Pat. No. 6,794,571 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      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.  
      2. Description of Background  
      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.  
      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.  
      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 both 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.  
      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.  
      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.  
      Related patent 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.  
      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.  
      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.  
     SUMMARY OF THE INVENTION  
      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 protrusions for securing at least one end of the gasket. The other end of the gasket is also secured to the chassis in a manner to provide facility of compression. The other end of the gasket is secured to the chassis either through adhesive bonding, through use of other alternate protrusions or another similar manner.  
      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  
      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:  
       FIG. 1  is a perspective docking cassette inside which the gasket of present embodiment will be disposed in one embodiment;  
       FIG. 2  is an isometric view of the docking cassette of  FIG. 1  with its cover removed;  
       FIG. 3  is an isometric view of the docking cassette of  FIG. 1  and  2  with the printed board card removed;  
       FIG. 4  is a top down embodiment of the present invention showing gasket and chassis assembly in the docking cassette of  FIG. 1 ;  
       FIG. 5  is a cross sectional illustration of the gasket as per one embodiment of the present invention; and  
       FIG. 6  is a perspective illustration showing better gasket details. 
    
    
     DESCRIPTION OF THE INVENTION  
      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.  
      FIGS.  5  provides a cross sectional illustration of one embodiment of the present invention. The illustration of  FIG. 5 , 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. Related U.S. Pat. No. 6,794,571, while solving many of the problems that were associated with prior art proposed a solution with a retainable feature that required extra mounting steps, such as adhesion, and that were provided of additional materials, such as plastic, that had to be fabricated separately and then disposed individually adding an yet an additional fabricating step as per an exemplary embodiment.  
      Before discussing the unique features comprising the EMC gasket of the present invention,  FIGS. 1 through 4  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.  
       FIG. 1  provides for a perspective view of a docking cassette which will be used in conjunction with the gasket of the present invention. The illustration of  FIG. 1 , provides for a docking apparatus  1  for mounting a printed circuit board (not illustrated in this figure). The docking apparatus provides structural support to the printed circuit board. The illustrated docking apparatus of  FIG. 1  is shown with its cover, referenced as  10 , in mounted position though cover opening components  46 . The cover  10  is disposed over the cassette housing  32 . Printed circuit board connector  42  is disposed to one side of the housing  32  as illustrated. Cable connectors  44  are also illustrated that provide electrical and electronic connection between the docking apparatus and other such components.  
      Elements referenced as  24  and  26  in  FIG. 1  respectively can be called a first and second protruding components, not to be mistaken with the chassis protruding elements as will be later discussed. These components are preferably provided and used to secure the docking apparatus to a main board of a computer as will be discussed in conjunction with later figures. A housing bezel  6  is also provided that houses a chassis assembly  140 , over which the EMC gasket will be eventually be mounted as will be further discussed below.  
       FIG. 2  provides for an isometric view illustration of the embodiment of  FIG. 1 . In  FIG. 2 , the cover  10  is removed to provide an illustration of some of the components that are disposed inside of the docking assembly  1 .  
      In addition to the removal of the cover  10 , the illustration of  FIG. 2  provides for the addition of a computer main board  100  that is engaged in this depiction with the docking apparatus  1 .  
      The removal of the cover  10  provides for a view of cavity  14  and walls  12 . Referring back to  FIG. 1  and viewing it now in conjunction with  FIG. 2 , it should be noted that housing cover  10  preferably includes at least one cover opening disposed as to allow communication with mounting structures, not visible in  FIG. 1  but shown in  FIG. 3  and referenced as  28  (visible in  FIG. 3 ) when housing cover  10  is associated with housing wall  12 . The housing cover  10  may be movably or non-movably associated with housing base  8  (also only visible in  FIG. 3 ) and/or housing wall  12  using any mounting device or method suitable to the desired end purpose.  
      The components  24  and  26  as discussed in  FIG. 1 , can be disposed anywhere on the cassette housing  2  but in this embodiment are shown to be disposed on the housing wall  12  and are placed to lockingly engage and disengage the main board  100  with the docking apparatus  1  though the respective connector  102 . Housing wall also includes a cavity  30  for receiving the mounting apparatus  32  of  FIG. 1 , which is not limited to but can include a screw.  
      The housing wall  12  also preferably includes other elements such as a cable opening  18  (shown in  FIG. 3 ), a printed circuit board connector opening  20  and a plurality of vent openings  22 .  
      The printed circuit board  16  is disposed inside the cavity  14  of the docking apparatus  1 . In the example of  FIG. 2 , the printed circuit board  16  is disposed in the cavity  14  by the help of printed circuit board mounting mechanism  40  which may include a screw, a pin, or other suitable mounting mechanisms as known by those skilled in the art that are threaded for example through a printed circuit board hole  17 .  
      In  FIG. 2 , part of a clevis  84  is also illustrated. In order to fully understand the purpose of the clevis  84  and how the printed circuit board  16  is linked to the docking apparatus  1 , a different view needs to be provided.  FIG. 3  provides such a perspective view.  
      In the isometric view of  FIG. 3 , the printed circuit board  16  is removed. The removal of printed circuit board  16 , reveal a linkage mechanism  4  and housing base  8 . The housing base  8  and the walls  12  are non-movably associated but are disposed as illustrated in a manner as to provide for the movable printed circuit board  16 . The housing base  8  includes a linkage mounting receptacle  9  for receiving the linkage mechanism  4 , as illustrated. The housing base also includes a linkage cavity  33  and four mounting devices  38  for movably holding the printed circuit board mechanism  40  to engage printed circuit board  16  of  FIG. 2 . The mounting device  38  preferably also includes a device opening  39  for slidingly containing printed circuit board mechanism  40  (which can include but is no limited to a screw or a pin).  
      The linkage mechanism includes linkage arm  83  and clevis  84  which can be pivotally coupled to the linkage arm  83  and configured to receive a shaft  88  at one end, while an opposing end includes a thread  86  engaged with an operably fixed nut (not shown) secured to either housing  2  and or housing bezel  6 . In one embodiment, linkage mechanism  4  can be operably mounted within housing cavity  14  via a complimentary configured aperture  89  for receiving linkage mounting screw  91  allowing pivotal movement of linkage arm  83  about screw  91  or with any other suitable mounting device as known to those skilled in the art, including but not limited to a clip. Furthermore, linkage mechanism  4  is operably mounted within housing cavity  14  via the nut operably secured to housing bezel  6  and associated with thread  86 .  
      Linkage arm  83  include first and second linkage arms  92  and  94  respectively substantially extending from aperture  89  and preferably perpendicular to one another. First link arm can also include an aperture provided for operable connection with corresponding aperture  98  shown and aligned therewith so as to connect printed circuit board  16  to first link arm  92  (also see  FIG. 2 ). In this way, when linkage arm  83  pivots about screw  91 , printed circuit board connector  42  ( FIG. 1 ) electrically engages and disengages with the respective connector  102  in board  100  ( FIG. 2 ). Second link arm  94  includes a second aperture proximate an end thereof for pivotally coupling with clevis  84 . The length of arm  94  is preferably several times that of arm  92  in order to provide a mechanical advantage.  
       FIG. 4  provides a top down illustration of one embodiment of present invention. The purpose of providing the illustration of  FIG. 4  is to focus on the gasket  400  alone. In this regard, other components that may have been already discussed are will no the discussed here as not to obscure the discussion of gasket  400 . Gasket  400  is placed over the chassis assembly  140  as illustrated. In a preferred embodiment, the gasket is adhesively bonded to the chassis assembly  140  as illustrated at  401 .  
      The gasket  400  as illustrated in the embodiment of  FIG. 4 , is comprised of a plurality of segments, all of which are referenced as  405  for ease of understanding. The segmentation of the gasket is related to the amount of EMC control desired. In this regard, narrower or wider strips can be used for each segment  405  to selectively reduce or increase the amount of segments  405  that as a whole comprise gasket  400 . A combination of widths can also be used such that some segments  405  are wider than others on the gasket  400 . The shape and topography of each segment, however, is closely similar and/or identical despite the width differences in all conditions.  
      In conclusion of the discussion relating to topography and placement of the gasket, the focus can now be turned back to the illustration of  FIG. 5  once again.  
      FIGS.  5  provides a cross sectional depiction of one of the gasket  400 . It should be noted, that since a cross sectional view is provided, however, the gasket  400  as a whole is not visible and only the shape of a single strip  405  is visible. Since all such segments  405 , however, are nearly identical in this embodiment and the gasket  400  is provided of a plurality of such strips, discussing the topography of a single segment  405  of the gasket  400  also reveals the topography of the gasket  400  as a whole.  
      In the illustration of  FIG. 5 , the chassis  500  is separately illustrated from chassis assembly  140 . The chassis  500  may be the entire assembly or a separate element of it. In this embodiment, chassis assembly is illustrated having a protruding element  550  on one side  551 . The chassis  500  and the protruding element  505  are preferably fabricated of sheet metal during a single fabrication process. In the embodiment of  FIGS. 1 through 4 , the chassis  500  is the lock strip  140 .  
      Gasket segment  405  is fabricated of a thin sheet of a conductive material, referenced as  505 . In a preferred embodiment the gasket  405  is fabricated out of a thin sheet of metal, such as copper. The thin sheet of material  505  has opposing ends respectively referenced as  501  and  502  and top and bottom surfaces  503  and  504  respectively.  
      One of the ends  501  of the thin sheet of material ( 505 ) forming the gasket section  405  is disposed over the chassis  500  and adhesively bonded ( 510 ) to its top side  503 . The thin sheet of material  505  is then looped around and secured to the chassis at its opposing end  502  by the use of the protruding element  550  as illustrated in such a manner that it provides facility of compression. The length of the strip  505  along with the percentage of strip  505  that is adhesively bonded to the chassis  505  determines the flexibility of the gasket  400  as a whole. In the illustration of  FIG. 5 , the arrangement that is shown provides a desired spring like quality for the gasket  400  to enhance facility of compression.  
      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 units. The slits, once the gasket is secured, form individual loops that independently enhance compression of the gasket. In such an embodiment, the portion that is being marked for adhesive bonding and the end disposed under the protruding element  550 , for example, have not slits cut out on them.  
      The protruding element  550  serves multiple functions. The more obvious purpose of the protruding element  550  is to hold the gasket securely at one end and also allow the gasket to maintain its ability to compress. A less obvious purpose is that since the protruding element  550  is preferably made of the same rigid material that forms the chassis  500 , it provides support to the thin gasket material such that gasket is not easily torn, damaged or displaced.  
      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 strip  405 . The few protruding element will hold the gasket  400  securely, but if more secure fastening is desired, the number of elements  550  as discussed above can be increased.  
      The illustration of  FIG. 5  only provides for one embodiment of the present invention and other embodiment are possible as per workings of the present invention. For example the manner of securing the first end of the gasket  400  by means of adhesive bonding is only one example as known to those skilled in the art and other similar methods can be used.  
       FIG. 6  provides a perspective view of the gasket  500  as illustrated. The embodiment of  FIG. 6  reflects embodiment of  FIGS. 5 . The unitary nature of the gasket  400  is more visible in this embodiment. Whether adhesively bonded or retained, when one end is first secured to the chassis, the other end is also well retained by the protrusions in the chassis. In one embodiment of the invention, as visibly shown in  FIG. 6 , the protrusions have clip like structures that are punched out of chassis sheet metal.  
      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.