Patent Publication Number: US-2003226676-A1

Title: Dynamically moveable exhausting emc sealing system

Description:
[0001] This invention was made with Government support under subcontract B338307 under prime contract W-7405-ENG-48 awarded by the Department of Energy. The Government has certain rights in this invention. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention is generally directed to pluggable cartridges for inserting printed circuit cards into and for removing them from printed circuit boards. More particularly, the present invention is directed to a removable exhausting EMC sealing system incorporated with the cartridge which provides a level of EMC shielding and thermal protection.  
       BACKGROUND OF THE INVENTION  
       [0003] The past twenty-five or so years have seen the development of ever smaller electrical circuit components at the chip level. However, to take fullest advantage of achievements in electrical circuit miniaturization, one must package the resultant printed circuit cards containing these chips in an efficient manner. Clearly, the packaging of printed circuit cards in tight spaces is a direct logical extension of increasing chip level circuit densities. It should also be noted that the tight packaging of integrated circuit chips on printed circuit cards and the correspondingly dense packaging of the printed circuit cards is a design goal that is carried out for more than just the convenience of compactness. Compactness provides shorter distances between circuit components which, in turn, serves the very desirable goal of being able to operate the circuits effectively at higher frequencies, thus increasing the speed of numerous different forms of electrical systems, including but not limited to data processing systems.  
       [0004] Moreover, mainly for reasons associated with long-term system operation and reliability, it is likewise very desirable to be able to easily insert and remove these printed circuit cards even when they are disposed in very tight spaces. The insertion and removal operations are also provided as an important part of a “hot-pluggability” function which is very desirable for “on the fly” repairs, replacements, maintenance and upgrades.  
       [0005] With increased circuit density there has also been an additional constraint on packaging design. It should be appreciated that increased circuit density is more susceptible to damage and performance disruptions due to thermal effects. As components and circuits become smaller, their packaging becomes smaller thus allowing manufacturers and designers to more densely populate boards and systems. However, the smaller packaging means that there is less opportunity to dissipate heat generated by the component. As a result, any externally radiated heat from PCB&#39;s or components surrounding the smaller packaging is less likely to be dissipated, thus producing thermal damage and/or noise within the circuit and component with increased circuit density, there is also a concomitant increase in power density and heat dissipation. Accordingly, packaging designs should be fully compatible with those aspects of system design associated with cooling functions. Also, to whatever extent possible, packaging designs should be: economical to produce; function smoothly; require little or no maintenance; be producible from inexpensive, readily available materials; and be reliably operable over a large number of insertion and removal operation cycles.  
       [0006] Yet one other concern arises in electrical systems as circuit feature size shrinks, operating frequencies increase and packaging densities grow larger, namely, the generation of electromagnetic interference (EMI). Electronic circuit packaging designs should thus also be compatible with structures and configurations that are employed to prevent the leakage of electromagnetic interference. To whatever extent possible, packaging designs should also include structures which actually contribute positively to the containment of electromagnetic interference. There is an ever increasing problem of electromagnetic interference caused by such devices. Virtually every electronic device, intentionally or not, emits some form of electromagnetic radiation. While this condition could be tolerated when few devices existed, the increasing number of electronic devices has made the problem more acute. The problem has been exacerbated by the “improvement” in semiconductor devices which allows them to operate at higher speeds, generally causing emission in the higher frequency bands where interference is more likely to occur. Successful minimization of the interference problem, sometimes referred to as “electromagnetic compatibility” or “EMC”, generally requires that emissions from a given device be reduced by shielding and other means, and shielding be employed to reduce the sensitivity of a device to fields from other devices. Since shielding helps to reduce sensitivity to external fields as well as reduce emissions from the device, it is a common approach to a solution of the problem.  
       [0007] It is also noted that the present discussion refers to printed circuit boards and printed circuit cards. As contemplated herein, the printed circuit board is the larger component into which at least one printed circuit card is inserted for purposes of electrical connection. The present disclosure places no specific limits on either the size of a printed circuit board or the size of a printed circuit card. In the most general situation, a circuit board will be populated with a plurality of printed circuit cards. That is, the printed board will have a number of printed circuit cards inserted therein. Accordingly, as used herein, the terms “printed circuit board” and “printed circuit card” are considered to be relative terms.  
       [0008] Accordingly, the present inventors are presented with the following sometimes competing packaging problems: dense and close packaging, cooling, electromagnetic interference shielding, hot pluggability, the desire to provide an easy-to-load cartridge for carrying printed circuit cards, the removal of fully populated printed circuit boards and the insertion thereof, and means to provide a removable cooperative EMI shielding arrangement in a system which also provides circuit board thermal protection.  
       SUMMARY OF THE INVENTION  
       [0009] A docking apparatus for printed circuit boards including a cassette housing, having a housing base, a housing cover and a housing wall, wherein the housing base and the housing wall are disposed relative to each other so as to define a housing cavity for containing a printed circuit card and wherein the housing wall includes a cable opening disposed so as to be communicated with the housing cavity, a housing bezel, disposed relative to the cassette housing so as to be associated with the cable opening, the housing bezel includes an outer bezel having a first plurality of openings and an inner bezel having a second plurality of apertures, the inner bezel in electrical communication with the printed circuit card, wherein said housing bezel is removable, and an EMC gasket disposed between the outer and inner bezels of said housing bezel, the EMC gasket configured to provide a removable EMC seal proximate the cable opening while still allowing airflow through the first and second plurality of apertures having the EMC gasket therebetween. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:  
     [0011]FIG. 1 is an exploded overall view of a docking cassette and a computer system in accordance with an embodiment of the invention.  
     [0012]FIG. 2 is a perspective view of a docking cassette in accordance with an embodiment of the invention;  
     [0013]FIG. 3 is an exploded view of a docking cassette in accordance with an embodiment of the invention;  
     [0014]FIG. 4 is a perspective view of an exemplary housing bezel disposed on the docking cassette of FIG. 3; and  
     [0015]FIG. 5 is a top view of the exemplary housing bezel of FIG. 4 attached to a printed circuit card.  
     [0016]FIG. 6 is a perspective view of the exemplary housing bezel of FIG. 5 attached to the printed circuit card with an outer tail-stock bezel removed;  
     [0017]FIG. 7 is an exploded perspective view of the exemplary housing bezel of FIG. 5 attached to the printed circuit card;  
     [0018]FIG. 8 is a perspective view of a perspective view of the exemplary housing bezel of FIG. 5 attached to the printed circuit card;  
     [0019]FIG. 9 is a partial cross section view of the exemplary housing bezel of FIGS. 5 and 8 taken along lines  9 - 9 ;  
     [0020]FIG. 10 is a top view of an exemplary EMC sealing gasket used with the exemplary housing bezel in the FIGURES;  
     [0021]FIG. 11 is a partial perspective view of the exemplary EMC sealing gasket used with the exemplary housing bezel in the FIGURES; and  
     [0022]FIG. 12 is a partial enlarged top perspective view of the exemplary housing bezel of FIG. 4 illustrating cooperation between vents in the outer tail-stock bezel and the exemplary EMC sealing gasket. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0023] Referring generally to the FIG. 1, a docking apparatus or cassette  10  for mounting a printed circuit card (PCC) into a computer system  12  is shown, in accordance with an embodiment of the invention. Docking apparatus  10  preferably provides structural support to the PCC so as to allow for the easy insertion and removal of the PCC from computer system  12 , as well as thermal and electrical isolation from other PCC&#39;s and components within the computer system.  
     [0024] Docking cassette  10  is disposed onto a computer system main board  14  or main printed circuit board (PCB) having a PCB connector receptacle  16 , a first receptacle  18  and a second receptacle  20 . Docking cassette  10  is preferably disposed onto computer system main board  14  such that a PCB connector is adjacent to PCB connector receptacle  16 . In addition, main board  14  is slidably engaged with a cable tray  22  for releasably supporting and securing computer system  12  in a system rack (not shown).  
     [0025] Referring to FIGS. 2 and 3, docking apparatus  10  for mounting to a printed circuit board (PCB) in computer system  12  is shown, in accordance with an embodiment of the invention. Docking apparatus  10  preferably includes a cassette housing  24 , a linkage mechanism  26  and a housing bezel  30 . Cassette housing  24  preferably includes a housing base  32 , a housing cover  34  and a housing wall  36 , wherein housing base  32  and housing wall  36  are non-movably associated with each other and disposed relative to each other so as to define a housing cavity  38  for movably containing a PCC  40 .  
     [0026] In accordance with an exemplary embodiment, housing base  32  preferably includes a linkage cavity  42  and four mounting devices  44  for movably holding PCC  40 . PCC  40  preferably includes a PCC mounting mechanism  46  and mounting device  44  preferably includes a device opening  48  for slidingly containing PCC mounting mechanism  46 , wherein PCC mounting mechanism  46  may be a screw, a pin or any mounting mechanism suitable to the desired end purpose. In addition, housing base  32  preferably includes a linkage mounting receptacle  50  for associating linkage mechanism  26  with housing base  32 . In accordance with an exemplary embodiment, although linkage mounting receptacle  50  is preferably a receptacle opening for receiving a linkage mounting screw  52 , linkage mounting receptacle  50  may be any receptacle device suitable to the desired end purpose, such as a clip receptacle. In accordance with an exemplary embodiment, it is considered within the scope of the disclosure that PCC  40  may be movably associated with housing base  32  using any device or method suitable to the desired end purpose, such as a screw or pin.  
     [0027] Housing wall  36  preferably includes a cable opening  54 , a PCB connector opening  56  and a plurality of vent openings  58 . In addition, housing wall  36  preferably includes a first protrusion  60  and a second protrusion  62 , wherein first protrusion  60  and second protrusion  62  are disposed so as to lockingly engage with main board  14  of computer system  12 . In accordance with an embodiment of the invention, first protrusion  60  and second protrusion  62  are shown as being disposed on housing wall  36 . However, it is considered within the scope of the invention that first protrusion  60  and second protrusion  62  may be disposed anywhere on cassette housing  24  in a manner suitable to the desired end purpose. Moreover, housing wall  36  preferably includes at least one mounting structure  64  which defines a threaded cavity  66  for receiving a mounting apparatus  68 , such as a screw. In addition, PCB connector opening  56  and cable opening  54  are preferably disposed so as to allow communication with the PCB connector  70  and the PCC cable connections  72  when PCC  40  is disposed within housing cavity  38 .  
     [0028] Housing cover  34  preferably includes at least one cover opening  74  disposed so as to allow communication with mounting structure  64  when housing cover  34  is associated with housing wall  36 . Cover opening  74  is preferably disposed so as to allow mounting apparatus  68  to communicate with threaded cavity  66  for removably securing housing cover  34  with housing wall  36 . Although an exemplary embodiment describes housing cover  34  being removably secured with housing wall  36 , it is considered within the scope of the disclosure that housing cover  34  may also be removably secured with housing base  32  and/or housing wall  36  using any mounting device or method suitable to the desired end purpose.  
     [0029] Referring now to FIGS.  3 - 5 , housing bezel  30  preferably includes an inner tail-stock bezel  76 , an EMC gasket  80  and an outer tail-stock bezel  82 . Inner bezel  76  preferably includes a forward bezel wall  84  having at least one forward opening  86  (FIG. 3). EMC gasket  80  preferably includes a plurality of apertures  88  disposed along a length defining gasket  80  and plurality of retaining clips  90  extending from an edge of gasket  80  for attachment to a flange extending from inner bezel  76  described more fully below having apertures aligned with apertures  88  of gasket  80  for venting air therethrough. Outer tail-stock bezel  82  preferably includes a tail-stock front  92  having a tail-stock front opening  94  and a tail-stock wall  96  having a tail-stock top  98 , a tail-stock bottom  100  and a tail-stock side  102 . In accordance with an embodiment of the invention, tail-stock front  92  and tail-stock wall  96  are preferably non-movably associated with each other so as to form a tail-stock cavity  104 . In addition, tail-stock bottom  100  preferably includes at least one flanged opening  106 . Tail-stock top  98  also preferably includes at least one tail-stock mounting hole  108  for mounting housing bezel  30  to cassette housing  24 .  
     [0030] Still referring now to FIGS. 3 and 5, inner tail-stock bezel  76  includes a flange  110  extending from forward bezel wall  84 . Flange  110  includes apertures  112  disposed in a length thereof for allowing air to pass therethrough. Retaining clips  88  extending from an edge defining a surface of EMC gasket  80  are configured to clip onto flange  110  such that apertures  90  of gasket  80  are aligned with apertures  112  disposed along flange  110 . Inner bezel  76  further includes a mounting lip  114  extending from an opposite edge of wall  84  in the same direction and substantially parallel to flange  110 . Mounting lip  114  is configured to mount PCC  40  in an offset position within docking apparatus  10  so that a bottom surface of PCC  40  is not positioned against housing base  32  (shown in FIG. 9).  
     [0031] Referring now to FIGS. 3, 4,  8 , and  9 , inner bezel  76  having EMC gasket  80  coupled thereto is disposed within tail-stock cavity  104  such that apertures  90  of gasket  80  and apertures  112  of inner bezel are aligned with vents  120  configured in tail-stock wall  96  of outer tail sock bezel  82 . In a preferred embodiment, apertures  90  and  112  align with two rows of vents  120  for allowing air to flow therethrough. The two rows of vents  120  is best seen in FIG. 4.  
     [0032] When PCC  40  is operably connected to mounting lip  114  and inner bezel  76  is disposed within tail-stock cavity  104 , inner bezel  76  is adjacent to tail-stock front  92  such that the tail-stock front opening  94  and forward opening  86  are also adjacent. Inner bezel  76  is disposed such that tail-stock top  98  electrically engages a top surface of flange  110  via gasket  80 . Housing bezel  30  is preferably disposed over cable opening  54  so as to enclose housing cavity  38 . In addition, housing bezel  30  is preferably disposed such that tail-stock mounting hole  108  is in communication with cover opening  74  and threaded cavity  66 . Housing cover  34 , linkage mechanism  26  and tail-stock mechanism  82  are then securely associated with housing wall  36  using mounting apparatus  68 .  
     [0033] Referring to FIGS.  9 - 11 , gasket  90  is configured to provide electrical continuity between PCC  40 , inner tail-stock bezel  76  and outer tail-stock bezel  82  and thus provide EMC shielding while allowing air to flow through vents  120 , apertures  90  and  120  aligned with each other. In an exemplary embodiment, gasket  80  includes apertures  90  extending a length of gasket  80 . Each aperture  90  is configured defining a hexagon. Three spokes  122  extend radially inwardly and upwardly from three side edges  124  of the six sided edges  124  defining each hexagon shaped aperture  90  terminating in a center  126  to define a compressible pyramid shaped structure  130 . Each spoke  122  is configured having at least one bend  128  in a length thereof intermediate said edge  124  and said center  126  to increase compressibility of the pyramid structure  130  formed by the three spokes  122 . The pyramid structure  130  is outlined with three spokes  122  terminating to a point at center  126  which is substantially a center of the hexagon defined by aperture  90  while still allowing air to flow through aperture  90 . Pyramid structure  130  is compressible to provide electrical continuity between inner bezel  76  and outer bezel  82  when gasket  80  is disposed therebetween providing air flow and EMC sealing, while allowing universal fit and adaptability. Compressible pyramid  130  allows universal fit and adaptability because it is clipped onto inner bezel  76  via clips  88  and allows installation with different dimensioned outer bezels  82  while maintaining EMC sealing as a result of the compressible spokes  122  extending from a surface of gasket  80  to provide contact with outer bezel  82 . It will be understood that although EMC gasket  80  has been described with apertures  90  defining a hexagon, a number of different configurations may optionally be employed to provide suitable airflow therethrough. In addition, although raised spokes  122  have been described as forming a pyramid structure, more and less than three spokes  122  may be employed to form other configurations, such as, including for example, but not limited to, a hemisphere, a box frame structure, and the like.  
     [0034] Referring to FIG. 12, an enlarged view of FIG. 5 is shown detailing cooperation between EMC gasket  80  providing electrical continuity between inner bezel  76  via clips  88  and outer bezel  82  via an intermediate rib  132  separating one row of vents  120  from another row of vents  120 . More specifically a bottom surface of EMC gasket  80  and clips  88  contact inner bezel  76  while center  126  contacts a bottom surface defining rib  132  of outer bezel  82  while allowing air to flow through corresponding apertures aligned with each other as shown in FIG. 12. Again, it will be appreciated that although spokes  122  meet at center  126  corresponding to generally to a center thereof or within aperture  90  and  110 , it is contemplated that spokes  122  may form other compressible configurations that also do not necessarily form an apex of the resulting structure disposed above apertures  90  and  110 .  
     [0035] In accordance with an embodiment of the invention and referring to FIGS. 10 and 11, EMC gasket  80  is preferably constructed from a rigid material having sufficient strength and electromagnetic compatibility properties, such as beryllium copper and/or stainless steel. However, it is considered within the scope of the invention that gasket  80  may be constructed from any material suitable to the desired end purpose. It will also be understood that although EMC gasket has been described having a pyramid structure disposed over aperture  90  to provide electrical continuity between inner and outer bezels  76  and  82 , a different configuration and/or number of spokes  122  are contemplated and do not necessarily extend over aperture  90  or terminate above aperture  90  as described above for one exemplary embodiment. The EMC gasket described herein is a movable seal that allows for PCC insertion and extraction with the docking cassette that is universally adaptable for use with differently configured housing bezels, while still making suitable ground contact and allowing proper air flow therethrough.  
     [0036] In accordance with an embodiment of the invention, inner tail-stock bezel  76  and outer tail-stock bezel  82  are preferably constructed from a rigid material having sufficient strength, such as steel and/or stainless steel. However, it is considered within the scope of the invention that inner tail-stock bezel  76  and outer tail-stock bezel  82  may be constructed from any material suitable to the desired end purpose.  
     [0037] While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.