Abstract:
The present invention provides a system for conducting heat away from an electrical component wherein the system has an elastically deformable member providing thermal communication with an electrical component. The system for conducting heat energy in an electronic assembly includes an electrical component, an elastically deformable member, and a housing. The elastically deformable member is placed in a compressed position between the electrical component and the housing such that the elastically deformable member is fixed into an assembled location. The elastically deformable member conducts heat energy away from the electrical component into the housing where it is dissipated into the environment. Since the compressed position fixes the location of the elastically deformable member, the system does not require a mechanical fastening to the electrical component thereby reducing thermo-mechanical fatigue. The elastically deformable member is made of a metal material allowing it to easily conduct the heat energy.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    The present invention claims priority to U.S. Provisional Application Serial No. 60/387,621, filed Jun. 10, 2002, entitled “Power electronics thermal management”. 
     
    
     
       BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to a system for transferring heat from electrical components.  
           [0004]    2. Description of Related Art  
           [0005]    Thermal management is a critical issue that must be considered during the development of electronic assemblies. With the advances in the functionality of electrical components, power and heat dissipation requirements for electronic assemblies have increased. In addition, the development of bare die packages that do not have housings or heat sinks has created a need for systems and methods that can conduct the heat away from the silicon die. Current methods include physical interconnects which have the undesired effect of increasing the thermo-mechanical fatigue applied to the electronic assembly.  
           [0006]    The desired path for conducting heat away from the die is through the top or bottom of the die. Typically, conducting heat through the bottom of the die requires the addition of heat sinks mechanically attached to the electrical component to improve the thermal conduction. The heat sink is usually incorporated in the die package in an overmolding process. The heat sink is then soldered to thermal vias or mechanically fastened to the housing of the module. Incorporating heat sinks into the electrical component adds cost to the component. Electrical components which are fastened to a heat sink or the module housing require a pad or clip for fastening. Processing mechanically fastened components adds cost and operations to the manufacture of an electronic assembly.  
           [0007]    In view of the above, it is apparent that there exists a need for a system and method for conducting heat from electrical components that provides improved heat dissipation and provides an easy to manufacture thermal connection to the electrical components.  
         SUMMARY  
         [0008]    In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a system for conducting heat away from an electrical component. The system includes a deformable member that provides a thermal communication path to the electrical component for extracting heat from the component.  
           [0009]    The system for transferring heat energy in an electronic assembly includes an electrical component, an elastically deformable member, and a housing. The elastically deformable member is placed in a compressed position between the electrical component and the housing such that the elastically deformable member is fixed into an assembled location. The elastically deformable member conducts heat energy away from the electrical component into the housing where it is dissipated into the environment. Since the compressed position fixes the location of the elastically deformable member, the system does not require a mechanical fastening to the electrical component thereby reducing thermo-mechanical fatigue.  
           [0010]    The elastically deformable member is made of a metal material allowing it to easily conduct the heat energy. More specifically, the elastically deformable member can be made of a metal foam. The metal foam is porous increasing the surface area of the elastically deformable member allowing it to more quickly dissipate heat. In addition, the porous nature of the metal foam can allow it to contain a thermally conductive liquid or grease to increase thermal conductance. Metal foam also provides many possible techniques for fixing the elastically deformable member to the housing.  
           [0011]    The present invention also provides for a counter support to reduce the amount of mechanical fatigue on the component caused by the compression force of the elastically deformable member. The counter support can be an extension of the housing or an individual piece made of elastomer, metal foam or other elastic material.  
           [0012]    Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a side cutaway view of an electronic assembly showing a system for conducting heat energy away from an electrical component according to the present invention;  
         [0014]    [0014]FIG. 2 is a side cutaway view of another embodiment of a system for thermally conducting heat from an electrical component according to the present invention;  
         [0015]    [0015]FIG. 3A is a side cutaway view of a housing of an electronic assembly showing an elastically deformable layer used for forming elastically deformable members to conduct heat from electrical components;  
         [0016]    [0016]FIG. 3B is a cutaway view of a housing of an electronic assembly showing elastically deformable members for conducting heat away from an electrical component formed from the elastically deformable layer shown in FIG. 3A;  
         [0017]    [0017]FIG. 4A is a side cutaway view of a housing of an electronic assembly showing a removable mask attached to the housing;  
         [0018]    [0018]FIG. 4B is a side cutaway view of a housing of an electronic assembly showing an elastically deformable material being deposited on the housing;  
         [0019]    [0019]FIG. 4C is a side cutaway view of a housing of an electronic assembly showing the elastically deformable members for thermally conducting heat away from an electrical component after the mask shown in FIGS. 4A and 4B is removed;  
         [0020]    [0020]FIG. 5A is a side cutaway view of a housing of an electronic assembly showing a cavity for receiving elastically deformable members;  
         [0021]    [0021]FIG. 5B is a side cutaway view of a housing of an electronic assembly showing the elastically deformable members inserted into the cavities of the housing;  
         [0022]    [0022]FIG. 6A is a side cutaway view of the housing of an electronic assembly showing pads on the metal housing for attaching the elastically deformable members; and  
         [0023]    [0023]FIG. 6B is a side cutaway view of a housing of an electronic assembly showing the elastically deformable members attached to the pads on the housing for conducting heat from an electrical component. 
     
    
     DETAILED DESCRIPTION  
       [0024]    Referring now to FIG. 1, a electronic assembly  18  configured to transfer heat from an electrical component embodying the principles of the present invention is illustrated therein. Assembly  18  includes an electrical component  22  and an elastically deformable member  24 . Electronic assembly  18  has a circuit board  12  with electrical components mounted on the circuit board  12 . Electronic assembly  18  also has a housing  17  including a top half  14  and a bottom half  16  that are fastened together with screws  20  to protect and support the printed circuit board  12 . Heat generated by electrical components  22  needs to be conducted away from the electrical components to provide for the proper functioning of the electrical components.  
         [0025]    The elastically deformable member  24  contacts electrical components  22  at a first end and housing  17  at a second end. In an embodiment of the present invention, deformable member  24  is attached to the housing  17  and is compressed between the housing  17  and the electrical component  22  when the electronic assembly  18  is assembled. The compression force generated by the elastically deformable member  24  ensures physical contact between both housing  17  and electrical component  22 . While embodiments of the present invention provide for mechanically attaching deformable member  24  to housing  17  it should be understood that device  24  need not be mechanically fastened to electrical component  22 .  
         [0026]    Deformable member  24  is made of a thermally conductive material and conducts the heat away from electrical component  22 . For example, deformable member  24  includes a metal material and is in an embodiment of the present invention a metal foam. Metal foam is commercially available such as RECEMAT® metal foam provided by Recemat International of the Netherlands. Metal foam is an excellent thermal conductor and is very porous. The porosity of the metal foam provides a very large surface area that facilitates heat dissipation. The porosity of the metal foam also allows deformable member  24  to contain grease or liquids which improve the heat transfer rate between component  22  and deformable member  24 . One such commercially available liquid is FLOURINERT® provided by 3M® of St. Paul, Minn. These materials are especially effective at the interfacing surface between deformable member and the electrical component  22  for high vibration applications.  
         [0027]    The heat energy transferred by deformable member  24  is either transferred to housing  17  or dissipated into the cavity  21  of electronic assembly  18 . The air in the cavity  21  may be static or forced. The natural convection that occurs enhances heat transfer from electrical component  22 . The heat that is transferred to housing  17  is dissipated into the environment. Features such as fins  28  may be used to further increase the surface area of the housing and improve the dissipation of the heat energy into the environment.  
         [0028]    The compression force created by deformable member  24  is balanced by a counter support  26  made of an elastomeric material. The counter support  26  improves the physical contact of the elastically deformable member  24  with the electrical component  22  by preventing the compression force generated by deformable member  24  from flexing printed circuit board  12 . Further, counter support  26  reduces mechanical fatigue on the connections between the printed circuit board  12  and the electrical component  22 .  
         [0029]    Still referring to FIG. 1, deformable member  34  is shown in contact with another electrical component  32  that generates heat during operation. In another embodiment of the present invention counter support  36  is shown as an extension of housing  17  and again functions to prevent flexing of printed circuit board  12 .  
         [0030]    Other electrical components, such as electrical component  42  includes heat sinks  43  and  44  embedded in a surface of electrical component  42  to enhance the transfer of heat energy away from electrical component  42 . The use of deformable member  24  further enhances the dissipation of the heat transferred through heat sink  43  by providing a heat conduction path to the heat sink. As previously mentioned, the porosity of deformable member  24  will increase the surface area allowing the heat energy to more quickly dissipate into cavity  21  of electronic assembly  18 . Further, deformable member  24  will transfer heat energy to housing  17  for dissipation into the surrounding environment. Thermal vias  48  are also provided in printed circuit board  12  to enhance the transfer of heat from heat sink  45  disposed on one side of the printed circuit board  12  through the printed circuit board  12  to an additional deformable member  24  disposed in the other side of printed circuit board  12  to dissipate the heat energy within the cavity  21  and transfer heat energy to housing  17 .  
         [0031]    Alternatively, other electrical components such as electrical component  52 , shown as a T0220 package, includes a heat sink  53  mechanically fastened to printed circuit board  12 . Thermal vias  58  are provided and are primarily used to transfer the heat to deformable member  54 , where the heat energy is dissipated into cavity  21  or transferred to housing  17 . To counteract the compression force created by deformable member  54 , a counter support  56  shown as an elastomer is placed between housing  17  and electrical component  52  to reduce mechanical fatigue.  
         [0032]    Referring to FIG. 2, another embodiment of the present invention is illustrated as electronic assembly  118 . Electronic assembly  118  includes again deformable member  24  and a plurality of electrical components. Similar to the previous embodiments, electronic assembly  118  further includes a printed circuit board  112  and a housing  117  formed by a top shell  114  and a bottom shell  116  joined by fasteners  120 . In the present embodiment, housing  117  contains a recess  128  for receiving deformable member  124 . Recess  128  allows the deformable member  124  to be manufactured as an independent replaceable piece that is a press fit into recess  128  of housing  117  during assembly. Similar to the previous embodiments, deformable member  124  is preferably made out of a metal foam material. Deformable member  124  is compressed between recess  128  of housing  117  and electrical component  122  to provide a physical contact therebetween. The compressed deformable member  124  facilitates thermal conduction of heat energy away from electrical component  122 . The heat energy conducted by deformable member  124  is either dissipated into cavity  121  of electronic assembly  118  or transferred through the surface of recess  128  to housing  117  to be dissipated by housing  117  and to the environment.  
         [0033]    The present embodiment also provides for a counter support  126  to reduce thermal fatigue caused by the compression force of deformable member  124 .  
         [0034]    With continuing reference to FIG. 2, deformable member  24  made as an independent insert can also be used as the counter support. Electrical component  132  is mounted to printed circuit board  112  containing vias  139  for transferring heat energy through printed circuit board  112 . Deformable member  24  conducts heat from the top surface of electrical component  132  and dissipates the heat energy into cavity  121  of housing  117  or transfers the heat energy by conduction to housing  117  through a surface of recess  138  to housing  117 . Similarly, deformable member  24  disposed opposite component  132  acts as a counter support. Deformable member  24  being compressed between recess  137  and housing  117  and printed circuit board  112  provides a compression force to reduce the mechanical fatigue caused by the compression force of deformable member  24 . In addition, deformable member  24  also transfers heat energy from the vias  139  and dissipates the heat energy into the cavity  121  or transfers the heat energy to the housing  117 .  
         [0035]    The size and shape of recesses disposed in housing  117  can have many forms. For example, deformable member  24  is received in recess  148  that is elongated to provide additional support to deformable member  24 . The shape of the recess  148  may also be modified to increase or decrease the surface area thereby changing the amount of heat energy transferred to housing  117  relative to the amount of heat energy dissipated in cavity  121 .  
         [0036]    Referring now to FIGS. 3A and 3B, deformable member  24  may be attached to housing  210  by soldering a deformable layer  220  to the inside of housing  210 . Deformable layer  220  is made of a material such as the metal foam periodically described. Deformable layer  220  can be machined to form deformable members  24  as shown in FIG. 3B. The deformable members  24  may be machined in different shapes and sizes. The shape of deformable member  24  may be changed to accommodate the shape of any particular electrical component, the size of the electrical component, and the distance from housing  210  to the electrical component. In addition, the shape of the deformable member can be made to increase the surface area to provide better heat dissipation.  
         [0037]    Referring now to FIGS. 4A and 4B, a portion of a housing  210  of an electronic assembly is illustrated attached to a mask  230  made of resist or removable sintering filler. A deformable material  24  is applied to housing  210 . Deformable material  24  is sintered attaching to housing  210  on regions  228  of housing  210  where the mask  230  is not applied.  
         [0038]    Referring now to FIG. 4C, mask  230  is removed leaving deformable members  24  attached to housing  210 . The depth and shape of the mask can be varied to result in deformable members  24  having various shapes and sizes.  
         [0039]    Referring now to FIG. 5A, housing  210  is manufactured with recesses  248 ,  252  and  254  for receiving deformable member  24  having various configurations. Deformable members  24  may be manufactured independently and press fit into recess  248 ,  252  and  254  of housing  210 . As specifically shown on deformable member  24  to be received in recess  248 , barbs  256  may be incorporated into deformable member  24  to aid in the retention of deformable member  24  into recess  248 . Further, deformable members  24  are manufactured as inserts allowing easy replacement of same.  
         [0040]    Referring now to FIGS. 6A and 6B, in another embodiment of the present invention, housing  210  is illustrated having pads  262  to aid in the attachment of deformable members  24 . The pads  262  can be made of solder or brazed material that may be used to form a mechanical bond with deformable member  24 . The mechanical bond of deformable member  24  to pad  262  aids in the transfer of heat energy from deformable member  24  to housing  210 .  
         [0041]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.