Abstract:
An electronic module includes a printed circuit board with a heat producing electrical component assembled in an insulating housing. The component is adjacent a thermally conducting heat sink with a thermally conductive material disposed therebetween. Integral with the heat sink is a thermally conductive runner, partially encased in the housing wall, connecting the heat sink to a thermally conductive port. The port is coupled to a base structure when the housing is attached to the base, forming a heat conduction path from the component to the base. This conductive path may also provide an electrical ground path from the printed circuit board to the base.

Description:
TECHNICAL FIELD OF INVENTION 
       [0001]    The invention relates to an electronic module, configured to be mounted on a base, and housing a heat producing electrical component. More particularly, the invention comprises an insulating housing with an embedded heat sink for convective dissipation of heat and a conductive runner extending from the heat sink to the port for conductive dissipation of heat. The port is coupled to the base structure, providing both a conductive heat sink and an electrical ground. 
       BACKGROUND OF INVENTION 
       [0002]    It is known to package a printed circuit board (PCB) with heat producing electrical components in an electronic enclosure. The enclosure includes a thermal heat sink to prevent overheating of the electrical components. Metal enclosures with heat sinks, although efficient at removing heat, are less amenable to the intricate geometries that are desirable for electronic enclosures. Plastic enclosures are poor conductors of heat and are not as efficient at removing excess heat from heat producing electrical components. It is desired to have an electronic enclosure, made of a thermally insulating material such as plastic, which provides mechanisms for heat sinking and electrically grounding electrical components on a PCB. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with this invention, an electronic module comprises a housing formed at least partially of an insulating material which includes a wall and a means for mounting the housing to a conductive base. The module further includes a heat sink adjacent a heat producing electrical component within the housing. The heat sink conducts thermal energy from the component and expels it by thermal convection external the housing. The module also includes a thermally conductive port on the exterior surface of the housing, which is coupled to the conductive base. A thermally conductive runner insert molded in the wall of the housing connects the heat sink with the port. This runner provides a thermal conduction path between the housing and the base to further expel heat from the heat producing electronic device. 
         [0004]    In one aspect of the invention, an electronic module comprises a housing formed at least partially of an insulating material. The housing includes a means for mounting the housing to a conductive base including a thermally conducting port on the external surface of the housing. The port is configured to accept the integrally formed mounting means of the base, enabling thermal energy transfer from the port to the base. The housing further includes a heat sink having a contact surface and a thermally conductive material disposed between the heat producing electrical component and the contact surface to enhance heat transfer. The heat sink also comprises fins, located opposite the contact surface and external the housing, to dissipate heat by thermal convection. Finally, the electronic module comprises a thermally conductive runner interconnecting the heat sink and the port to conduct heat from the heat sink in the housing to the conductive base. The runner is at least partially embedded in the wall of the housing. 
         [0005]    In another aspect of this invention, an electronic module comprises a housing formed at least partially of an injection molded thermoplastic material which includes a wall and a means for mounting the housing to a conductive base. A printed circuit board with at least one electrical ground lead is disposed inside the housing. An electrical connector disposed within the housing is in contact with the electrical ground lead on the PCB. The housing also comprises an electrically conductive port on the external surface of the housing. This port is configured to accept the integrally formed mounting means of the base, enabling electrical grounding from the port to the base. The electronic module further includes an electrically conductive runner at least partially insert molded within the wall of the housing. The runner interconnects the electrical connector and the port and provides an electrical ground path from the printed circuit board to the base. 
         [0006]    Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    This invention will be further described with reference to the accompanying drawings in which: 
           [0008]      FIG. 1  is a broken, perspective, exploded view of the electronic module with the plastic case removed; and 
           [0009]      FIG. 2  is a perspective view of the electronic module attached to the base. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0010]    In accordance with a preferred embodiment of this invention, referring to  FIGS. 1 and 2 , an electronic module  10  is comprised of a housing  12 , made at least partially of an insulating material such as plastic, mounted to a conductive base  14 . The base is preferably made of metal and comprises a lug  16  to accept mounting means  18  defined by the housing. The base  14  provides mechanical support for the housing  12  when it is secured using a lug nut  20 . The lug  16  is integrally formed on the base which, in combination with lug nut  20 , provides suitable means for connecting the base  14  to the electronic module  10 . However, any means of connecting the housing to the base would be acceptable. The mounting means  18  of the housing  12  comprises a thermally conductive port  22 . The port  22  is made of metal and provides enhanced structural integrity to the mounting means of the housing  12 . 
         [0011]    The electronic module  10  also comprises a printed circuit board  24 , with at least one heat producing electrical component  26 , enclosed within the housing  12 . The printed circuit board  24  physically supports the electrical component  26  and provides an electric circuit  28  to operate all the components on the circuit board. Any other suitable substrate, including ceramic substrates, could be substituted for the printed circuit board in this invention. The heat producing electrical component  26  is adjacent a heat sink  30 , with thermally conductive material  32  disposed between the component  26  and the heat sink  30 . Heat generated by the component  26  is transferred by thermal conduction through the thermally conductive material  32  into the foundation  34  of the heat sink. Heat is then transferred by thermal conduction from the foundation  34  to heat sink fins  36 , where it is dissipated by thermal convection due to fluid flow across the fins  36 . The heat sink  30  is preferably made of a metal with high thermal conductivity and is insert molded into the housing  12  so as to align the foundation  34  with the heat producing electrical component  26 . Thermally conductive material  32  is used to enhance thermal conduction between the component  26  and the heat sink foundation  34 . The fins  36  are disposed on the exterior of the housing to enable fluid flow for convective cooling. 
         [0012]    A conductive runner  38  is integrally formed connecting the heat sink foundation  34  and the port  22 . The runner  38  is formed of a metal with high thermal conductivity, preferably the same metal as the heat sink  30  and the port  22 . The runner is at least partially embedded in the plastic housing  12 . The conductive runner  38  enables a thermal conduction path from the heat producing electrical component  26 , through the thermally conductive material  32 , the heat sink foundation  34 , the thermally conductive runner  38 , the port  22 , and the lug  16  to the base  18 . This feature allows for a second heat sinking path from the component  26  to the base  18 . 
         [0013]    Thus, this invention provides an electronic module, including a housing containing a printed circuit board with a heat producing electronic component. The housing has a mounting means for connecting to a conductive base. The mounting means provides structural support for the housing as well as a conductive port integrated into the mounting means. The conductive port is integrally formed with a conductive runner connecting the port and the foundation of a heat sink. The heat sink foundation is disposed adjacent the heat producing electronic component with a thermal conductive material therebetween. Heat from the heat producing electronic component is dissipated by conduction through the thermal conductive material to the heat sink foundation. From the heat sink foundation the heat may travel in one of two possible paths. The first path is from the heat sink foundation to the heat sink fins, which are disposed external the housing and are configured to dissipate the heat by convection to the external fluid flow. The second path is from the heat sink foundation through the conductive runner, the port, the lug and finally to the conductive base. The conductive runner enables a second conduction path for heat transfer out of the heat producing electronic component, increasing the efficiency of cooling the component, and increasing the reliability of the electronic module. 
         [0014]    The manufacture of electronic module  10  will now be described. Housing  12  is formed by injection molding an insulating plastic material using a mold having the specific size and shape for receiving the heat producing electrical component  26 . Prior to injection of the plastic material, the metal port  22  is placed in the locater section of the mold to ensure proper alignment of the conductive runner  38  and the heat sink  30 . The locater section of the mold is the area that will form the mounting means  18  in the electronic module. The port  22 , runner  38 , and heat sink  30  are all one integral piece of conductive metal material. After proper location of the aforementioned metal piece, the insulating plastic material is injected into the mold, encasing a portion of both the thermally conductive runner  38  and heat sink foundation  34 , and creating a cavity in which the printed circuit board  24  can be installed. A thermally conductive material  32  is applied to the bottom surface of the heat sink foundation  34  and the printed circuit board  24  is installed in the housing  12  so that the thermally conductive material  32  is disposed between the component  26  and the heat sink foundation  34 . 
         [0015]    In an alternate embodiment an electronic module  10  is comprised of a housing  12 , made at least partially of an insulating material such as plastic, mounted to a conductive base  14 . The base  14  is preferably made of metal and comprises a lug  16  to accept the mounting means  18  of the housing. The base  14  provides mechanical support for the housing  12  when it is secured with lug nut  20 . A lug integrally formed on the base, in combination with a lug nut, provides suitable means for connecting the base to the electronic module, however any means of connecting the housing to the base would be acceptable. The mounting means  18  of the housing  12  comprises an electrically conductive port  22 . The port  22  is made of metal and provides enhanced structural integrity to the mounting means of the housing. 
         [0016]    The electronic module  10  also comprises a printed circuit board  24 , with at least one electrical ground lead  40 , enclosed within the housing  12 . The printed circuit board  24  provides the electric circuit  28  to operate all the components on the circuit board  24 . Any other suitable substrate, including ceramic substrates, could be substituted for the printed circuit board in this invention. The electrical ground lead  40  is adjacent electrical connector  42 , to facilitate electrical grounding of the printed circuit board  24 . 
         [0017]    A conductive runner  38  is integrally formed connecting the electrical ground lead  40  and the port  24 . The conductive runner  38  is formed of a metal, preferably the same metal as the electrical ground lead  40  and the port  24 . The runner  38  is at least partially embedded in the plastic housing  12 . The conductive runner  38  enables an electrical grounding path from the electrical connector  42 , through the conductive runner  38 , the port  22 , and the lug  16  to the base  18 . This feature allows for an electrical grounding path from the printed circuit board  24  to the base  18 . 
         [0018]    Thus, this embodiment provides an alternative use for the conductive runner connecting the heat sink and the base. It may be desirable to use a conductive path from the printed circuit board and the components on the printed circuit board for both a heat sink and an electrical ground path. The printed circuit board and the heat producing components on the printed circuit board may be located within the housing. The conductive runner would allow for conductive heat dissipation from the component to the base external the housing. The conductive runner would also allow for an electrical ground path from the circuit on the printed circuit board to the base external the housing. 
         [0019]    While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.