Abstract:
A floating heatsink is disclosed for components mounted within an electromagnetic enclosure. The floating heatsink includes an aperture within the enclosure wall against which a floating heatsink is disposed on the interior of the enclosure. The floating heatsink is dimensioned to overlap the enclosure around the aperture. A resilient bias member is disposed along the overlap between the floating heatsink and the enclosure. The resilient bias member acts as an electromagnetic gasket while urging the floating heatsink against the component. In certain embodiments the component is replaceable via a second aperture in the enclosure. The floating heatsink is particularly useful for overcoming the need for thermal compounds of heatsinks using the enclosure known in the art.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/945,075, filed on Sep. 20, 2004, now U.S. Pat. No. 7,224,582 and owned in common herewith. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a floating heatsink for removable components and is particularly concerned with heatsinks for components requiring removal for servicing or replacement. 
     BACKGROUND OF THE INVENTION 
     Heat dissipation is a by-product of most modern electronic equipment, and when heat dissipation from a component or assembly is sufficiently large, heatsinks are used to keep the component or assembly at a sufficiently low temperature. 
     An additional requirement of high-speed electronics is the containment and/or shielding of electromagnetic radiation developed by the circuitry during operation. Such electromagnetic radiation can disturb the functioning of other nearby electronic equipment, and vice versa. In order to contain electromagnetic radiation, it is known in the art to provide enclosures which either block or greatly attenuate emissions from a circuit in operation. 
     Under some circumstances, the electromagnetic containment enclosure can serve as a heatsink for components mounted within the enclosure. Typically, components are mounted within a circuit board within the enclosure, and means, such as a compliant thermal compound, are used to bridge gaps between a component and the enclosure wall that is to be used as a heatsink. 
     This approach does not provide for ready heatsinking of removable components, as there is no simple method for ensuring adequate replacement of the thermal compound when a component is replaced. 
     In view of the foregoing, it would be desirable to provide a technique for allowing removal of components from an electromagnetic enclosure which overcomes the above-described inadequacies and shortcomings, by providing a mechanism which does not require a compliant thermal compound replacement but does provide heatsinking of the removable component and integrity of the electromagnetic enclosure. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention there is provided an apparatus for removing heat from a component to be mounted within an enclosure, where the enclosure has a first aperture adjacent to the component when the component is in an operating position. The apparatus has a floating heatsink disposed interior to the enclosure adjacent to the first aperture, and the floating heatsink is dimensioned to overlap the enclosure around the periphery of the first aperture. Furthermore, the floating heatsink includes a peripheral edge having a top surface facing an underside of the enclosure adjacent the aperature. There is also a resilient bias member disposed between at least a portion of an overlap between the floating heatsink and the enclosure, wherein the resilient bias member acts as an electromagnetic gasket between the floating heatsink and the enclosure, wherein the first resilient bias member is disposed atop at least a portion of the topp surface, and whereby the resilient bias member urges the floating heatsink against the component in the operating position. 
     In one aspect, the present invention provides a controllable thermal contact to a removable component while maintaining electromagnetic shielding integrity of the enclosure. 
     In one embodiment, the resilient bias member may be a formed metallic strip. The formed metallic strip may have a plurality of fingers, and the formed metallic strip may have a plurality of formed ridges. In another embodiment, the resilient bias member may be formed from an elastomeric compound having electrically conductive media dispersed therethrough. 
     According to an aspect of the present invention there may be provided an apparatus for removing heat from a component to be mounted within an enclosure, where the enclosure has a first aperture adjacent to the component when the component is in an operating position. The apparatus has a floating heatsink disposed interior to the enclosure adjacent to the first aperture, and the floating heatsink is dimensioned to overlap the enclosure around the periphery of the first aperture. There is also a first resilient bias member disposed between at least a portion of an overlap between the floating and the enclosure, wherein the first resilient bias member acts as an electromagnetic gasket between the floating heatsink and the enclosure, and whereby the first resilient bias member urges the floating heatsink against the component in the operating position. The apparatus also has a second resilient bias member disposed between the floating heatsink and the enclosure, the a second resilient bias member bearing against the enclosure to urge the floating heatsink against the component in the operating position. 
     In accordance with another aspect of the present invention there is provided an apparatus for removing heat from a component to be mounted within an enclosure, where the enclosure has an underside surface and defines an aperture adjacent to the component when the component is in an operating position. The apparatus has a floating heatsink disposed interior to the enclosure adjacent to the first aperture, and the floating heatsink is dimensioned larger than the aperture such that a peripheral portion of the floating heatsink overlaps with a portion of the underside surface adjacent the aperture. There is also a resilient bias member disposed between the peripheral portion of the floating heatsink and the portion of the underside surface adjacent the aperture, wherein the resilient bias member acts as an electromagnetic gasket between the floating heatsink and the enclosure and whereby the resilient bias member bears against the underside surface to urge the floating heatsink against the component in the operating position. 
     The present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. It should be recognized that the diagrams are not intended to convey any indication of scale. While the present invention is described below including preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments which are within the scope of the present invention as disclosed and claimed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further understood from the following detailed description of embodiments of the invention and accompanying drawings in which: 
         FIG. 1  is a perspective view of a component and heatsink assembly according to the prior art. 
         FIG. 2  is a perspective view from the bottom of a fixed portion of a heatsink assembly according to an embodiment of the invention. 
         FIG. 3A  is a perspective view from the top of a movable portion of a heatsink assembly according to an embodiment of the invention. 
         FIG. 3B  is a perspective view from the top of a movable portion of a heatsink assembly according to another embodiment of the invention. 
         FIG. 4  is a exploded perspective view from the top of a heatsink assembly according to an embodiment of the invention. 
         FIG. 5  is a perspective view from the top of a heatsink assembly and removable component according to an embodiment of the invention. 
         FIG. 6  is a cross-sectional view of the heatsink assembly of  FIG. 5  taken along section line  2  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Certain terminology may be employed in the description to follow for convenience rather than for any limiting purpose. For example, the terms “top”, “bottom”, “forward”, “rearward”, “right”, “left”, “rightmost”, “leftmost”, “upper”, and “lower” designate directions in the drawings to which reference is made. Terminology of similar import other than the words specifically mentioned above is likewise to be considered as being used for purposes of convenience rather than in any limiting sense. In the description and figures to follow, corresponding characters are used to designate corresponding elements throughout the several views, with equivalent elements being referenced with prime or sequential alphanumeric designations where appropriate to assist understanding. 
     Modern electronic circuit assemblies are progressively moving towards denser and denser concentrations of heat generating components within given package sizes. Increased density brings a need for enhanced means to remove heat, and as well, means to contain electromagnetic radiation generated by the circuitry during its operation. One approach known in the art is to completely enclose the electronic circuit board and attendant circuitry with a thermally conductive and electromagnetic radiation containing enclosure. A common term for such an enclosure which conforms relatively closely to the dimensions of a circuit card is that of a “clamshell”. The clamshell enclosure has additional advantages in assisting in preventing penetration of exterior interfering radiation, such as that from adjacent circuit assemblies, from interfering with circuitry within the enclosure. 
     A relative disadvantage of a clamshell enclosure is the difficulty in replacing components. Within telecommunications systems, there are electronic assemblies with subassemblies which may have an operational life significantly less than the life of the remainder of the assembly. One example is the laser transceivers used in modern optical networking equipment. With a clamshell enclosure which contains multiple such laser transceiver assemblies, the failure of one assembly would require the removal of the entire clamshell if the failed assembly were to be replaced. Clearly, it would be desirable to have a clamshell enclosure which would admit removable subassemblies. However, in the case of laser transceiver assemblies, for example, there is a strong need for effective heatsinking of the transceiver assembly. In an assembly with permanently mounted transceivers, it is common in the art to use the wall of the clamshell enclosure as a heatsink, and appropriate means for securing the transceiver in good thermal contact with the wall are used. 
     In the case of removable assemblies, it is necessary to be able to remove the subassembly, yet when the subassembly is mounted in operational position, to also ensure adequate thermal contact. 
     Referring to  FIG. 1A  there may be seen an exploded view of a circuit board  180  having mounted thereon a frame  182 , a heatsink  184 , and a clip assembly  186 . The frame  182  serves as a mounting enclosure for a removable component or assembly, while heatsink  184  is mechanically attached to frame  182  via clip assembly  186 . Not shown is a connector mounted on circuit board  180 , to which the removable component connects upon insertion into frame  182 . Referring to  FIG. 1B , there may seen a perspective view of the heatsink  184 , secured to frame  182  with clip  186 , while removable component  110  is shown prior to mounting within frame  182 . In  FIG. 1C , removable component  110  is shown mounted within frame  182 . In the mounted position, heatsink  184 , in mechanical contact with removable component  110 , acts to reduce thermal resistance from removable component  110  to the ambient environment, thereby dissipating heat generated within removable component  110 . The resulting reduction in temperature rises within removable component  110  act to keep temperatures within operational limits and enhance long term reliability of removable component  110 , as is well known in the art. 
     One possible problem with the approach diagrammed in  FIG. 1  is the sliding friction occurring between heatsink  184  and the removable component  110 . Close mechanical contact between removable component  110  and heatsink  184  is necessary for good thermal flow, however manufacturing tolerances work against achieving the necessary fit. Intermediate resilient thermally conductive materials may be used to mediate the gap resulting from manufacturing tolerances, however the high coefficient of friction that results from use of such materials results in unacceptably high forces being generated upon insertion and removal of removable component  110 . 
     Referring to  FIG. 2 , there may be seen a perspective view from the bottom, of one side  200  of a clamshell enclosure. On the enclosure side  200  may be seen mounting holes  202 , for securing the enclosure side  200  to the circuit board and opposite side of the enclosure. Also visible is aperture  204 , an opening in enclosure side  200 , for the receiving of a floating heatsink which will be described below. Mounting tabs  206 , at the front of enclosure side  200 , are for the installation of card ejectors (not shown), mechanical latches which assist in insertion and removal of the clamshell assembly upon installation. The clamshell enclosure is conveniently made from a castable, extruded or machined aluminum alloy, providing both thermal conductivity and electromagnetic interference shielding. 
     Reference is now made to  FIG. 3A , which shows a floating heatsink  330  having a resilient bias member  332  disposed on the top surface of floating heatsink  330  around its periphery. In this embodiment, the resilient bias member  332  is an electromagnetic gasket formed from an elastomeric compound having electrically conductive media disbursed therethrough. The electromagnetic gasket acts so as to contain electromagnetic energy within the clamshell enclosure. Resilient bias member  332  also operates to urge floating heatsink  330  downwards against a removable component. In particular, the floating heatsink  330  is dimensioned larger than the aperture  204  ( FIG. 2 ) within the clamshell enclosure. Accordingly, the floating heatsink  330  is dimensioned such that its periphery overlaps with the enclosure side  200  ( FIG. 2 ) of the clamshell enclosure surrounding the aperture  204 . Thus, the resilient bias member  332  is disposed between the enclosure side  200  of the clamshell enclosure and the peripheral overlap portion of the floating heatsink  330 . Resilient bias member  332  acts against the underside of the clamshell enclosure so as to urge the floating heatsink  330  downwards against a removable component. Although in this embodiment, resilient bias member  332  is formed of an elastomeric compound, in general any resilient gasketing material known to those skilled in the art having a compression-set over its operating life sufficient to provide an appropriate biasing force to provide good thermal contact against a removable component while providing adequate electromagnetic interference gasketing could be employed. 
     Under certain applications, the amount of bias provided by the resilient gasketing material may be insufficient to provide the amount of bias desired. In these circumstances an additional bias element  340 , for example a separate spring element, may be used to augment the bias provided by the resilient gasketing material that makes up the resilient bias member  332 . Such an additional bias element  340  may comprise a spring element running parallel to the resilient gasketing material, or a plurality of spaced smaller springs, for example. The additional bias element  340  may be disposed in a channel  334  formed between the resilient bias member  332  and an upper portion of the floating heatsink  330 . 
     It is also clear that certain applications, for example circuitry having low frequency signals, may not require a continuous gasket around the periphery of the overlap. In this case, the resilient gasketing material may be disposed only over a portion of the overlap, or at a plurality of discontinuous portions, insofar as the emissions or susceptibility requirements regarding electromagnetic leakage through any gaps meet the requirements of the particular apparatus. 
     Reference is now made to  FIG. 3B , which shows another embodiment of a floating heatsink  330  with resilient bias member  332 . In this embodiment, resilient bias member  332  includes a multi-fingered metallic gasketing strip surrounding the periphery of floating heatsink  330 . The metallic gasketing strip is formed from a plurality of fingers or ridges  338  (individually indicated as  338   a ,  338   b , . . . ,  338   n ). The succession of fingers or ridges  338  within the ridged metallic gasketing strip provides resilience as well as effective electromagnetic shielding. The fingers or ridges  338  bias the floating heatsink  330  in a downward direction relative to the surrounding clamshell enclosure by bearing against the enclosure side  200  surrounding the aperture  204  within the clamshell enclosure. 
     Referring to  FIG. 4 , there may be seen an exploded perspective view of a clamshell enclosure using a floating heatsink according to an embodiment of the invention. A top side clamshell enclosure portion  420  is securable to a bottom side clamshell enclosure portion  421 . Circuit board  400 , located within the clamshell enclosure when top side  420  is secured to bottom side  421 , has component frame  402  mounted thereon. Component frame  402 , for receiving a removable component, is mounted adjacent aperture  423  which is located on a front face of bottom side enclosure portion  421 . Upon assembly of the clamshell enclosure, floating heatsink  430  mounts within aperture  424  in top side clamshell enclosure portion  420 , immediately adjacent component frame  402 . In operation, resilient bias member  432  urges floating heatsink  430  against a component housed within frame  402 . Resilient bias member  432  also provides an electromagnetic interference gasket function within the gap between floating heatsink  430  and top side clamshell enclosure portion  420 . 
     Referring to  FIG. 5 , there may be seen an assembled clamshell enclosure  525 , having a removable component  510  in position for insertion into aperture  523 . Upon insertion into aperture  523 , removable component  510  passes into the component frame (not seen in this diagram) and bears against floating heatsink  532 . The resilient bias member mounted between the top surface  520  and floating heatsink  532  urges heatsink  532  against removable component  510 , providing good thermal contact. Also, as described previously, the resilient bias member also serves as a gasket, blocking or attenuating electromagnetic radiation that might enter or exit the clamshell enclosure around the periphery of floating heatsink  532 . 
     Referring to  FIG. 6A , there may be seen a cross-sectional view of  FIG. 5  taken at section  2  and a corresponding cross-sectional view with the removable component  610  inserted at  FIG. 6B . More specifically, clamshell enclosure  625  has top side enclosure member  620  having aperture  624  therein. Floating heatsink  630  resides within aperture  624 , having resilient bias member  632  between heatsink  630  and top side enclosure member  620 . Removable component  610 , illustrated in the removed position in  FIG. 6A , upon insertion, bears against heatsink  630 . In the inserted position, illustrated in  FIG. 6B , resilient bias member  632  urges the heatsink  630  against removable component  610 , providing good thermal contact. 
     As may be seen, the assemblies described above provide one skilled in the art a method and apparatus for providing thermal contact for removable components and maintenance of the integrity of an electromagnetic screening enclosure so as to prevent either emissions or admission of electromagnetic radiation. As well, the aforedescribed assemblies provide allowance for mechanical tolerances incurred in manufacturing and over the operational life of the assembly, as well as control of contact forces via the resilient bias member for proper thermal and interconnection performance. Further, the described design provides for a reduction in size over approaches which do not integrate the bias member functionality with electromagnetic gasketing. This reduction in size allows for greater utilization of the interior space of the clamshell enclosure. 
     While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. 
     For example, the floating heatsink assembly within a clamshell enclosure could be adapted to non-removable components fixed to the circuit board, eliminating the usual need for a compliant thermal compound to fill the space between the fixed component and the heatsink. In this type of application, the elimination of the thermal compound would both simplify initial manufacturing processes and any subsequent repair processes. 
     As well, the clamshell type of enclosure exemplifies but one kind of containment enclosure. It is contemplated that electronic assemblies having portions of the assembly enclosed, albeit not wholly as in the clamshell embodiment, could also make use of the floating heatsink for removable components requiring heatsinking within the enclosed portion. 
     Therefore, what has been described are embodiments providing means for mounting a removable component to a circuit pack where the circuit pack is enclosed in a fixed heatsink. By utilizing a floating heatsink mounted within an aperture of the fixed heatsink, in coordination with a resilient bias member that also acts as an electromagnetic containment gasket, component removability is obtained while still effecting electromagnetic shielding and thermal contact between the heatsink and component. 
     Numerous modifications, variations and adaptations may be made to the particular embodiments of the invention described above without departing from the scope of the invention, which is defined in the claims. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.