Abstract:
The invention relates. to modular heat-dissipating housing covers for opto-electronic modules, e.g. transceivers. The housing covers according to the present invention are constructed out of various different parts, which provide different levels of heat dissipation depending on the desired implementation, while maintaining a seal against EMI leakage. Extra heat sinking portions are provided to dissipate heat generated from specific heat generating sources. The extra heat sinking portions are configured into a shape and/or out of a material that provides more thermal dissipation than the standard cover provided. Independent control over the different heat sinking portions enables a better fit and appropriate dissipation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present invention claims priority from U.S. patent applications Ser. Nos. 60/361,654 filed Mar. 5, 2002 and 60/397,630 filed Jul. 23, 2002. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to a heat sink for an opto-electronic device, and in particular to a modular heat sink cover for an optical transceiver providing both thermal dissipation and electromagnetic interference shielding.  
         BACKGROUND OF THE INVENTION  
         [0003]    Opto-electronic devices, e.g. optical transceivers, include optical subassemblies (OSA) for converting electronic signals into optical signals and/or vice versa. Optical transceivers include a transmitter optical subassembly (TOSA), which includes a laser, and a receiver optical subassembly (ROSA), which includes a photodiode detector. Conventional transceivers have not required specially designed heat sinks, as the metal housings or the electromagnetic interference (EMI) shielding have provided sufficient heat dissipation. However, the latest generation of transceiver modules, which transmit at 10 Gb/s, include heat sources that generate heat that cannot be dissipated by normal means. Moreover, these heat sources are spread out over the transceivers printed circuit board, and extend upwardly therefrom by various amounts. An initial solution to this problem is to provide heat dissipating fins on the upper surface of the top cover of the module&#39;s housing, and to provide raised portions on the lower surface of the top cover for contacting the heat sources. This solution, while providing constant heat dissipation over the entire upper surface of the module&#39;s housing, does not provide any versatility for accommodating particularly hot heat sources. Moreover, it is very difficult to match the corresponding raised portions on the lower surface of the top cover with a plurality of heat sources without one or more of the contacts being less than optimum.  
           [0004]    U.S. Pat. No. 5,808,236 issued Sep. 15, 1998 to Johnny Brezina et al discloses a high density heat sink attachment for mounting multiple heat sinks directly onto a printed circuit board. Unfortunately, the Brezina et al device does not provide an enclosure for the entire module. Moreover, since the heat sinks are held down only by torsion clips and do not completely seal the opening in the frame, the Brezina et al device does not ensure the proper EMI shielding.  
           [0005]    An object of the present invention is to overcome the shortcomings of the prior art by providing a modular heat sink cover for an opto-electronic device that provides the versatility to accommodate for various heat sources, while providing sufficient EMI shielding.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, the present invention relates to an opto-electronic device of the type for transmitting signals between an optical waveguide and a host computer comprising:  
           [0007]    an optical sub-assembly for converting optical signals into electrical signals or electrical signals into optical signals;  
           [0008]    a thermally conductive housing for supporting the optical sub-assembly;  
           [0009]    an optical connector on one end of said housing for receiving the optical waveguide, and for aligning the optical waveguide with the optical sub-assembly;  
           [0010]    a printed circuit board mounted in said housing including circuitry for controlling the optical sub-assembly, the printed circuit board including a first heat source; and  
           [0011]    an electrical connector extending from another end of said housing for transmitting electrical signals between the printed circuit board and the host computer.  
           [0012]    The housing including: a lower portion for supporting the optical sub-assembly and the printed circuit board; a heat dissipating cover fixed on top of the lower portion for dissipating heat from inside the housing; and a first heat sink mounted on the heat dissipating cover above the first heat source for dissipating heat therefrom.  
           [0013]    The heat dissipating cover and/or the first heat sink enclose and seal the housing to prevent leakage of electro-magnetic interference (EMI) from the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:  
         [0015]    [0015]FIG. 1 is an exploded isometric view of a first embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is an exploded isometric view of a second embodiment of the present invention;  
         [0017]    [0017]FIG. 3 is an isometric view of a third embodiment of the present invention;  
         [0018]    [0018]FIG. 4 a  is an isometric view of a fourth embodiment of the present invention installed in a suitable cage;  
         [0019]    [0019]FIG. 4 b  is an isometric view of the embodiment of FIG. 4 a  mounted on a host computer circuit board; and  
         [0020]    [0020]FIG. 5 is an isometric view of a fifth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]    With reference to FIG. 1, an optical transceiver, generally indicated at  1 , includes a transmitter optical sub-assembly (TOSA)  2  and a receiver optical sub-assembly (ROSA)  3 , which are mounted on a printed circuit board  4 . An optical connector  6  is disposed on one end of the optical transceiver  1 , and includes an output port  7  for transmitting outgoing signals from the TOSA  2  and an input-port  8  for transmitting incoming signals to the ROSA  3 . Ideally, the optical connector  6  is adapted to receive a conventional SC duplex optical connector, but any form of optical connector is within the scope of the invention. An electrical connector (not shown) is found on the other end of the optical transceiver  1  for electrically connecting the device to a printed circuit board in a host computer system. Typically, the electrical connector is in the form of electrical pins extending downwardly from the transceiver  1  through holes in the host computer&#39;s print circuit board for soldering thereto. Alternatively, the electrical connector can be in the form of a pluggable electrical connector, such as a card edge connector well known in the art.  
         [0022]    The transceiver  1  is provided with a housing, which includes a rectangular open-topped lower portion  11  and a modular heat dissipating upper portion, generally indicated at  12 . The lower portion  11  supports the printed circuit board  4 , along with the TOSA  2  and the ROSA  3 . The upper portion  12  includes a heat dissipating cover  13 , which substantially encloses the lower portion  11 , except for generally rectangular openings  14 . The openings  14  are positioned directly adjacent, i.e. above, major heat sources  16 . The upper portion  12  also includes extra heat sinking portions  17 , one for each opening  14 , i.e. one for each major heat source  16 . Each heating sinking portion  17  includes a generally rectangular or frusto-pyramidal raised portion  18  for mating with an opening  14 . The raised portion  17  extends through the opening  14  into proximity with the major heat source  16 , and preferably into thermal contact therewith. The modular arrangement enables each heat sinking portion  17  to be tailored to the corresponding major heat source  16 . In particular, the raised portions  18  can be designed and positioned in an optimum position without effecting the other heat sinking portions  17 . Moreover, the form and material of each heat sinking portion  17  can be independently chosen to satisfy the thermal requirements of each major heat source  16 . For example, the surface area of the heat sinking portions  17  can be increased by adding more or larger projections and/or the material making up the heat sinking portions  17 , e.g. aluminum or copper, can be more thermally conductive than the material making up the heat dissipating cover  13 . The material making up the heat dissipating cover  13 , e.g. cast zinc, is selected more for its versatility, i.e. formability or workability, to facilitate manufacture of a lower cost cover, which requires more intricate detail. This is particularly advantageous for use in a large product line, in which one or more heat sinking portions  17  can be changed in response to different needs rather than redesigning the entire top cover  12 .  
         [0023]    Another feature of the present invention is the containment of electromagnetic interference (EMI). With the use of multiple heat sinks, there is the potential for EMI leakage; however, with the aforementioned modular design, an adhesive bond line with each heat sinking portion  17  can be controlled independently, thereby providing sufficient EMI protection. In particular, a solid thin bond line of thermal adhesive or other suitable gel, illustrated by broken line  19 , is applied surrounding each hole  14  to contain EMI leakage and, if necessary, fix the heat sinking portions  17  to the cover  13 . The heat sinking portions  17  may be press fit into the cover  13 , whereby the bond line simply prevents EMI leakage.  
         [0024]    In an alternative embodiment, illustrated in FIG. 2, a heat dissipating cover  23 , substantially encloses the rest of the transceiver housing (not shown) except for holes  24  and  25 . A circular heat sinking portion  26  mates with heat dissipating cover  23  by fitting almost completely into the hole  24  for contact with a first major heat source (not shown), while a rectangular heat sinking portion  27  fits into the hole  25  for contact with a second major heat source or second and third major heat sources (not shown). As above, the heat sinking portions  26  and  27  are press fit into the holes  24  and  25 , respectively, or they are fixed using a thermal adhesive or gel to ensure that the cover  23  and the heat sinking portions  26  and  27  are thermally connected and sealed against EMI leakage. Fins  28  or other raised projections are provided on the heat dissipating cover  23 , while fins  29   a  and  29   b  or other raised projections are provided on the heat sinking portions  26  and  27 , respectively, to increase the amount of heat dissipation. In a preferred embodiment, the heat sinking portions  26  and  27  are also formed of a material, e.g. aluminum, copper, which is more thermally conductive than the cover  23 . The material for the cover  23  is chosen for strength as well as thermal conductivity. Furthermore, the size and shape of the fins  29   a  and  29   b  may also be different than those of the fins  28  to further increase heat dissipation.  
         [0025]    [0025]FIG. 3 illustrates another embodiment of the present invention, in which an extra heat sinking portion  36  is inserted into the heat dissipating cover  33  during the casting process forming an integrated unit. One or more heat sinking portions  36  are made from a highly thermally conductive material, such as aluminum or copper, while the remaining cover  33  is molded from a more versatile material such as cast zinc, which is much easier to cast small features in. As before, the heat sinking portions  36  are positioned adjacent to, i.e. directly above and/or in thermal contact with, the major heat sources to maximize heat dissipation. Preferably, the heat sinking portions  36  and the cover  33  include raised projections, such as fins or pins (see FIG. 2), which extend upwardly providing additional surface area for convective cooling in the air stream.  
         [0026]    In FIGS. 4 a  and  4   b  a pluggable transceiver  40  is illustrated mounted in a cage  42 . Leads  41  extend downwardly from the cage  42  for connecting and grounding the cage  42  to a circuit board  45  of a host computer. The transceiver  40  includes a heat dissipating cover  43 , which completely encloses the transceiver housing&#39;s lower portion providing the necessary EMI shielding. Pins  44  or other raised projections extend upwardly from the heat dissipating cover  43 , and provide a first level of cooling within a given size restraint. For example, the pins  44  are capable of fitting through the opening of the cage  42 , and provide adequate heat dissipation for lower power modules. When a greater amount of heat dissipation in required, e.g. for a higher power module, an extra heat sinking portion  46  is mounted on top off the cover  43 . Preferably, the pins  44  are inserted into corresponding recesses in the heat sinking portion  46  to provide the best possible thermal connection. The greater amount of heat dissipation is preferably provided by wider and taller pins  47 , although, as is hereinbefore described, the heat sinking portion  46  may also be made out of a material, which is more thermally conductive than the cover  43 .  
         [0027]    In the preferred embodiment illustrated in FIGS. 4 a  and  4   b , the extra heat sinking portion  46  is mounted on top of the cage  42  after the transceiver  41  has been inserted therein. A spring clip  48  is used to secure the heat sinking portion  46  to the cage  42  on top of the transceiver  40 . One end of the spring clip is interconnected to tabs  49  formed in the sides of the cage  42 , while the other end of the spring clip  48  is comprised of spring fingers biasing the extra heat sinking portion  46  down onto the transceiver  40 . Alternatively, the heat sinking portion  46  can be secured to the host printed circuit board  45  or to the host frame by a spring clip or other suitable means.  
         [0028]    With reference to FIG. 5, a pluggable transceiver  51  includes an optical coupler  52  and an electric coupler (not shown) mounted on housing  53 . The optical coupler  52  connects a ROSA and a TOSA of the transceiver  51  with a suitable optical fiber communication line using a standard connector, e.g. SC or LC connector. The transceiver&#39;s electrical connector mates with a corresponding electrical connector  54  mounted on a printed circuit board  55  of a host device. The housing  53  includes a heat dissipating cover  56 , which has extra heat sinking portions in the form of spring loaded pins or fins  57 , which are preferably constructed from a material that is more thermally conductive than the material making up the heat dissipating cover  56 . Preferably, the spring loaded pins  57  are removable, whereby they can be positioned above specific heat sources or evenly distributed over the cover  56 . Typically, the spring loaded pins  57  are biased upwardly and get momentarily deflected downwardly into a retracted position by a faceplate  58  while the transceiver  51  is being inserted into a cage  59  mounted on the printed circuit board  55 . After which, the spring loaded pins  57  resume their extended position in the flow of air to increase the amount of heat dissipation. Alternatively, the spring loaded pins  57  can be held in the retracted position by a mechanical lever, which can be actuated to release the spring loaded pins  57  after the transceiver  51  has been fully inserted into the cage  59 . Ideally, the spring loaded pins  57  are actuated by the same mechanism that locks the transceiver  51  in the cage  59 , e.g. a bail mechanism as disclosed in U.S. Pat. No 5,901,263, which is incorporated herein by reference. The bail mechanism includes a bail  61 , which is pivoted to disengage an arm  62  on the transceiver  40  from a hole  63  in the cage  59  or to disengage an arm on the cage  59  from a recess on the transceiver  40 . Simultaneously, the rotation of the bail  61  causes the rotation or translation of linkage  64 , which retract the pins  57  into a position parallel with the cover  56 . When the transceiver  51  is fully inserted into the cage  59  and the bail  61  is rotated so that the cage  59  and the transceiver  51  are interlocked, the linkage  64  releases the pins  57 , whereby they extend into their expanded position.