Abstract:
A heat sink assembly for use with edge connectors, e.g., card edge connectors, of cards or printed circuit boards. The heat sink assembly provides a relatively large heat transfer capacity to control temperatures in contacts of the edge connectors which increases the current rating of the connector by allowing more current to pass through the connector. The heat sink assembly includes fins attached to the edge connector power and ground leads by direct thermal connection, such as soldering, to traces in the board. The fins are connected to the power and ground leads in an alternating or interweaved fashion. The fins are fabricated from thermal conducting material and heat is conducted to the fins where it is removed by the relatively large surface area of the fins. Adjacent fins are electrically isolated such that power and ground fins do not contact.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to systems and methods of dissipating heat from electronic components, and more particularly, to a heat sink assembly for use with an edge connector, such as connectors used with PC cards, printed circuit boards, and the like, that includes a plurality of fins connected to power and ground traces to conduct heat away from the edge connector contacts. 
     2. Relevant Background 
     In the computer industry, there is a continuing demand for improvements in electrical devices, such as power supplies, to enhance performance while also trying to reduce size of components. Many of these electrical devices are provided using integrated circuits or chips that are provided on printed circuit boards (PCBs). While decreasing in overall size, operating speeds, chip sizes, and numbers of transistors and other components on each printed circuit board is increasing. This leads to increased power consumption, with many chips consuming 30 watts or more of power, which in turn significantly increases the amount of heat generated by the components. Excessive heat can reduce capacity of the components and also reduce component life and reliability. As a result, many efforts have been made to control or limit heat generated during operation of the electrical components and to dissipate generated heat to reduce operating temperatures. 
     More specifically, many printed circuit boards, PC cards, and other thin electrical components utilize edge connectors to allow them to be plugged into a socket of another circuit board to exchange electrical signals, such as power and data signals. Typically, edge connectors generally include connectors on the edge of boards or cards made of strips of copper, gold, or other conductive metals that provide the signal, power, and ground contacts. All connectors, though, are limited in the amount of current that can be safely and effectively carried. Current flowing through the contact resistance generates heat and this raises the temperature of the contact. The temperature of each contact must be controlled to establish operating temperatures that allow reliable operation of the contact and to avoid heat damage to adjacent components. 
     Edge connectors in particular are designed to pass low level logic signals and not necessarily to pass higher levels of current. The current rating of edge connector contacts is typically further reduced as the ambient temperature near the connector increases. The ambient temperature is a concern in many existing edge connector designs that use a large number of parallel contacts to carry higher currents, such as in a power supply. The heat dissipating, by radiation and convection, from the contacts creates localized heating that further reduces the current that can be drawn through the edge connector. 
     In an attempt to control temperatures of power and ground contacts, printed circuit boards have been manufactured with continuous wiring board etches or traces between adjacent contacts. This increases the amount of surface area available to dissipate generated heat but has not been effective in meeting the continually increasing demands for higher current capacity for connectors. The demand for reduced sizes of electronic components, including edge connectors, increases the difficulty of providing additional surface area for heat transfer. For example, structural integrity is a challenge facing electronic, component manufacturers as most components are manufactured from electrically conductive material with lower mechanical strengths and with very small dimensions, e.g., a few millimeters or less in thickness. Vibration and shock can rapidly damage heat dissipation assemblies, such as metal fins, that are attached to printed circuit boards, and such assemblies are often difficult to install without damage, e.g., bending that crimps fins which reduces surface areas and can cause electrical shorting of adjacent components. Alternatively, increasing the number of contacts can sometimes be used to control individual contact temperatures but typically is not a viable option as the number of contact pairs in a connector is usually fixed. 
     Hence, there remains a need for an improved method and apparatus for dissipating heat from edge connectors. Preferably, such a method and apparatus would be relatively inexpensive to manufacture, would be structurally reliable, and would increase the current rating and reliability of the edge connector. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above discussed and additional problems by providing a heat sink assembly for use with typical edge connectors, e.g., card edge connectors, of cards or printed circuit boards. The heat sink assembly is adapted to provide a relatively large heat transfer capacity to control temperatures in contacts. In effect, this increases the current rating of the connector by allowing more current to pass through the connector while remaining below a preset maximum temperature. Significantly, the heat sink assembly includes a plurality of fins that are attached to the edge connector leads, such as the power and ground leads, through direct thermal connection to traces in the board. In a preferred embodiment, the fins are connected to the power and ground configuration in an alternating or interweaved fashion, such as with a pair of power leads being connected to a first fin and a pair of ground leads being connected to a second fin and so on across the edge connector. The fins are fabricated from thermal conducting material, such as copper, and heat is conducted to the fins where it is removed by convection and/or radiation due to the relatively large surface area of the fins. Since current is also conducted to the fins, adjacent fins are electrically isolated within the heat sink assembly such that power and ground fins do not come in contact. 
     More particularly, a printed circuit board with enhanced heat dissipation, and therefore, higher current rating is provided that includes a board with an edge connector. The edge connector is made up of a plurality of power leads and ground leads. Traces or conductor lines are provided in the board and are connected to the leads to pass current between the leads and other devices on the board. A heat sink assembly is mounted on the board to dissipate the heat generated by the leads and is thermally connected to the traces to create a heat transfer path away from the power and ground leads. In one embodiment, the power leads are positioned in one layer or surface of the board and the ground leads are positioned in a second layer or surface of the board. Slots are provided in the board for receiving contacts of the heat sink assembly, which allows connection to traces in either of the two layers. In a preferred embodiment, the heat sink assembly includes a plurality of fins and the fins are alternatively connected to power and ground leads. The heat sink assembly includes fin holders with base members having slots for receiving tips of the fins and isolation members between the slots for electrically isolating adjacent fins which are oppositely charged by the traces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially exploded perspective view of a printed circuit board with edge connectors in thermal communication with heat sink assemblies according to the present invention; 
     FIG. 2 is an elevation view of a heat transfer fin used in the heat sink assemblies of FIG. 1; 
     FIG. 3 is an elevation view of a fin holder used in the heat sink assemblies of FIG. 1 to structurally support and position the fins and to electrically isolate adjacent fins; 
     FIG. 4 is a side elevation view of the fin holder of FIG. 3 illustrating features that facilitate assembly of the heat sink assemblies and installation on the board of FIG. 1; and 
     FIG. 5 is a top view of the fin holder of FIG. 3 illustrating fin receiving slots in the base of the holder and electrical isolation cross members between the slots. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a printed circuit board or card  10  utilizing edge connector heat transfer features of the present invention. As will become clear, the heat transfer features are particularly suited for use with edge connectors having data, power, and ground leads along a board edge or other edge (e.g., the flat strips along an edge used in standard card edge connectors in which mating contacts are sometimes called leafs). However, the invention is not limited to such connectors, and the breadth of the following description is intended to cover other connectors that use contacts to transfer power between electrical components and for which heat generation is a concern in obtaining a desired current rating. 
     As shown in FIG. 1, the printed circuit board  10  includes a board  12  having top and bottom surfaces  14  and  16 , respectfully. To allow the board  12  to be electrically connected with other components of an electrical device, such as a computing device, the board  12  includes edge connectors  20  that are adapted to allow data and power to be passed to a connecting device or board. For example, the edge connectors  20  or edge may be inserted into a female edge connector or socket which in turn is plugged or otherwise connected to a mating component to supply power and/or to enable data transfer. In this regard, the edge connectors  20  include a plurality of leads  24  fabricated of an electrically conductive material, such as copper, gold, and the like. The number and specific arrangement of the leads  24  can be widely varied to practice the invention. 
     As shown, the leads  24  are used for power and ground but in many embodiments data leads are included without connection to the heat sink members (such as by running data traces between fins or heat transfer connections). Further, in the specific embodiment shown, the contacts or leads  24  are paired to carry currents that exceed the rating of a single contact but the invention is also useful with connectors in which each lead  24  has a dedicated trace. Referring again to FIG. 1, the leads  24  in the top surface  14  are typically all power or ground leads with the leads (not shown) in the bottom surface  16  being the opposite leads (i.e., ground leads if the leads  24  in the top surface  14  are power leads). 
     According to an important aspect of the invention, the leads or contacts  24  are placed in direct contact with heat transfer elements, e.g., fins, active heat transfer sinks, and the like such that excess heat is transferred rapidly from the leads  24  to control the operating temperatures. In this regard, the board  12  includes slots  30  for receiving the heat transfer elements. The leads  24  are connected to the slots  30  with electrically conductive traces  26  in the top surface  14  and with traces  28  in the bottom surface  16 . Hence, in a preferred embodiment, the slots  30  extend through both the top and bottom surfaces  14 ,  16  to place the heat transfer elements in direct contact with the traces  26 ,  28  which generally extend (not shown) past the slots  30  to other devices (not shown) on the board  12 . As will be explained in more detail, the thermal (and electrical) contact is typically achieved by soldering the heat transfer elements to the traces  26 ,  28  but other suitable connection techniques may be used, such as well-known mechanical fastening methods including press fitting. 
     Temperature control is provided by the inclusion of a heat sink assembly  40  which is placed in heat conducting contact with the board  12  and more importantly, with the traces  26 ,  28  extending from the edge connectors  20 . As shown, a heat sink assembly  40  is provided for each edge connector  20  but in some embodiments, it is useful to provide a single larger heat sink. To assist in positioning the heat sink assembly  40 , a hole  32  is provided in the board  12  to mate with a post  64  on the assembly  40 . The heat sink assembly  40  is configured to provide a relatively large surface area for convective heat transfer with surrounding air. To this end, the heat sink assembly  40  includes a number of fins  44  that are thermally connected to the traces  26 ,  28  upon installation on the board  12 . The fins  44  may be fabricated from numerous materials, such as metals, with high thermal conductivities, and preferably, from a metal that is suitable for contact and bonding with the traces  26 ,  28 (such as by soldering). 
     The heat sink assembly  40  is preferably configured to provide structural integrity while also providing electrical isolation between electrically conductive fins  44 . Structural integrity is a concern due to the size of the individual components. Upon installation, the fins  44  will conduct electricity from the traces  26 ,  28  and must not be allowed to be crimped or bent into contact. In one embodiment, structural integrity is enhanced by providing a number of fins  44  that are positioned within the heat sink assembly  40  by an upper fin holder  46  and a lower fin holder  48 . 
     The fins  44  may be fabricated with a variety of shapes and sizes that suit space constraints of a particular printed circuit board  10  or edge connector  20  design. For example, the fins  44  may have numerous cross-sections including planar, S-shaped, W-shaped, and the like. The materials used for the fins  44  preferably are selected to have a relatively high thermal conductivity while also allowing easy assembly of the printed circuit board  10  and connection with the traces  26 ,  28 . For example, in one embodiment, the fins  44  are fabricated from copper, gold, and other materials used for traces  26 ,  28 , and more preferably from copper that is pre-plated with tin electroplate to facilitate soldering to the traces  26 ,  28 . 
     FIG. 2 illustrates a preferred planar fin  44  design in which the fin  44  includes a contact tip  50  for providing a bonding surface to the traces  26 ,  28  and a thermal path to the rest of the fin  44  surfaces. Adjacent to the contact tip  50  is the heat transfer portion  52  of the fin  44 , which is typically fully exposed to ambient air to provide a large convective heat transfer surface. To facilitate insertion and mating with the upper and lower fin holders  46 ,  48 , the fin  44  includes shoulders  54  for extending beyond the slots  70  in the holders  46 ,  48  and the tips  50  typically may have rounded corners  56  to account for manufacturing tolerances and ease assembly. The specific dimensions of the fin  44  may be varied widely to practice the invention. The tip  50  preferably extends outward from the heat transfer portion  52  to allow thermal contact with the traces  28  in the bottom surface  16  of the board  12  (e.g., about the thickness of the board  12  plus the thickness of the lower fin holder  48 ). 
     To illustrate the difficulty in maintaining structural integrity of the heat sink assembly  40 , one embodiment of the fin  44  calls for the overall length, L 1 , to be between 1 and 2 inches, the heat transfer length, L 2 , to be less than 1 inch, the overall width, W 1 , to be less than 0.5 inches, the tip width, W 2 , to be less than about 0.4 inches, and the thickness to be less than about 0.05 inches (i.e., less than 2 millimeters). While providing a large extended heat: transfer area, without structural support, these fins  44  may readily become deformed during fabrication or even vibrate during operation to an extent that could cause shorting. 
     To provide structural support and electrical isolation of the fins  44 , the heat sink assembly  40  includes the upper and lower fin holders  46 ,  48  as shown in FIGS. 3-5. To reduce the cost of fabrication and later assembly, the upper and lower fin holders  46 ,  48  have identical manufacturing dimensions in a preferred embodiment and, similarly, the fins  44  are symmetrically designed. However, it will be understood that the invention is not limited to the illustrated arrangement and numerous shapes and arrangements of fins  44  and structural supports may be utilized to provide desired structural and electrical characteristics. 
     As shown, the holders  46 ,  48  include a base member  60  and a side member  62  that are positioned substantially perpendicular to the base member  60  (and parallel to the installed fins  44 ). The base member  60  has a length, L H , that is generally at least the length of the edge connector  20  (such as less than about 2 inches) and a width, W H , that is at least as large as the fin width, W 1 , (such as less than about 0.5 inches) shown in FIG.  2 . The side member  62  has a height, H H , that is slightly larger than the length of the fin heat transfer portion, L 2 , (such as about 1 inch or less) and more specifically, is selected such that when assembled the shoulders  54  of the fins  44  contact the base members  60  of the upper and lower fin holders  46 ,  48 . To enable the upper and lower fin holders  46 ,  48  to be interconnected, a tongue or tip  66  is provided on the end of the base member  60  and a groove or hole  68  is provided in the side member  62 . A post  64  is provided on the base member  60  to facilitate placement and bonding of the assembly  40  to the board  12 , and during assembly of the printed circuit board  10 , the post  64  mates with hole  32  in the board  12 . 
     Assembly of the heat sink fin assembly  40  simply involves placing each of the fins  44  within the slots  70  of the lower fin holder  48 . Assembly is completed by placing the upper contact tip  50  of the fins  44  into the slots  70  of the upper fin holder  46  and snapping the tongues  66  of the upper and lower fin holders  46 ,  48  into the grooves  68  of the lower and upper fin holders  48  and  46 , respectively. When assembled, the heat sink assembly  40 . provides structural support for the readily deformed fins  44  at both ends of the heat transfer portion  52  of the fins  44  (i.e., by encasing at least a portion of the upper and lower contact tips  50 ). As will be appreciated, the assembled heat sink assembly  40  can be manufactured and distributed as a standalone part that can later be inserted and thermally connected to the edge connector of a board or other electronic device. 
     According to a significant feature of the invention, the heat sink assembly  40  is adapted to electrically isolate adjacent fins  44  within the assembly  40 . As discussed above, in a preferred embodiment, the fins  44  in the assembly  40  are alternatively connected to ground and power traces  26 ,  28  (i.e., power fin  44 , ground fin  44 , power fin  44 , and so on). Clearly, it is important that adjacent fins  44  do not come into contact to prevent electrical shorting or at least significantly reduce the likelihood of such shorting. In some embodiments, the fins  44  themselves may be configured with electrical isolators or insulators integrally provided such-as at the tips  50  or other surfaces for which contact with-adjacent fins  44  is a concern. In more preferred embodiments, such as the assembly  40  shown, the fin holders  46 ,  48  are adapted to provide the desired electrical isolation of adjacent fins  44 . 
     As illustrated in FIGS. 1 and 5, the bases  60  of each holder  46 ,  48  include electrical isolation members or electrical insulators  72 . These members  72  are positioned as cross members between each slot  70  to provide structural support to the fins  44  and provide an isolation distance between adjacent fins  44 . The distance, i.e., the thickness of each member  72 , is preferably selected to be large enough to allow air to readily flow between the fins  44  and across the heat transfer portions  52  while being small enough to limit the overall size of the heat sink assembly  40 . For example, in preferred embodiments, the overall length of the holders, L H , is about the length of the edge connector  20  or slightly longer so as to position the fins  44  substantially adjacent the leads  24  to minimize the required lengths of the traces  26 ,  28  needed to provide thermal connection with the slots  30  and fins  44 . The thickness of each member  72  is also selected to minimize the risk of arcing between adjacent fins  44  and may depend on the power and/or current levers in the leads  24 . For illustration purposes, but not as a limitation, the thickness of the members  72  will typically be less than about ⅛ inch to provide adequate electrical isolation and adequate separation to provide a channel or pathway for air to flow to obtain adequate convective heat transfer from the heat transfer portion  52  of the fins  44 . 
     The holders  46 ,  48  may be manufactured from a variety of materials according to the invention. In one preferred embodiment, manufacturing costs are reduced by fabricating the holders  46 ,  48  as a single piece from a material that is selected based on its electrical insulation properties, resistance to heat, and structural strength. Many readily available plastics may be utilized to provide these desired properties, such as plastic resins reinforced with glass or other materials. The holders  46 ,  48  may also be manufactured as assemblies of one or more parts with the bases  60  being fabricated-from an electrical insulator material. 
     Note, for electrical isolation, a single fin holder (such as lower fin holder  48 ) or even a single base (such as base  60  of lower fin holder  48 ) may be utilized to isolate adjacent fins  44 . For example, in some embodiments, the upper fin holder  46  may be eliminated (and even the side member  62  of lower fin holder  48 ) to practice the invention. In this embodiment, structural integrity may be enhanced by selecting fins  44  having a shorter heat transfer portion length, L 2 , and/or by increasing the thickness of the fins  44 . This alternative embodiment may further include electrical isolators (not shown) at upper portions of the fins  44  that encase or wrap around the upper contact tips  50  or, as discussed previously, the fins  44  themselves may include electrical isolation members that contact each other on adjacent fins. 
     Assembly of the printed circuit board  10  includes first assembling the heat sink assembly  40  and fabricating a board  12  with power traces  26  and ground traces  28  contacting edges of fin receiving slots  30 . The number of traces  26 ,  28  thermally linked to each slot may vary from less than one per slot  30  to a plurality of traces  26 ,  28  to each slot  30 . The assembled heat sink assembly  40  is then inserted into the board  12  as shown in FIG. 1 with plug  64  inserted into hole  32  and lower contact tips  50  of the fins  44  inserted into slots  30 . Thermal connection may be achieved simply with the physical insertion of the tips  50  into a tightly fit or low tolerance slot  30  to tip  50  design. In this arrangement, mechanical fasteners, such as screws and the like, (not shown) can be used to rigidly connect the assembly  40  to the board  10 . More preferably, the contact tips  50  are bonded to the traces  26 ,  28  by soldering (e.g., wave soldering) or other well-known techniques to produce a more efficient thermal connection point and heat transfer pathway between the leads  24  and the heat transfer portions  52  of the fins  44 . To enhance the solderability of the fins  44 , the fins  44  may be plated, such as with tin electroplate, in a secondary plating step after stamping the fins  44  from copper, aluminum, or other metallic sheets. The fins  44  may also be stamped or cut from pre-plated material. 
     In the above manner, the heat sink assemblies  40  increase the current rating of the edge connectors  20  of the printed circuit board  10 . This is achieved by decreasing the size of the temperature rise experienced during operation of the printed circuit board  10  when current is flowing through the leads  24 . For example, in a power supply implementation of the invention, the use of the heat sink assemblies  40  shown in FIG. 1 allowed the total current through the parallel leads  24  to be raised from  20  amps (which is typical of many conventional edge connectors) to 30 amps. This 50 percent increase was achieved with a smaller temperature rise than when 20 amps were delivered without the installation of the heat sink assemblies  40  and was achieved without the need for increasing the number of leads  24 . 
     Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed. For example, some electrical devices may be configured to allow fins to extend outward from both sides of the board  12 . In these devices, an alternative embodiment for printed circuit board  10  may include having a heat sink thermally connected to each side of the board  12  to the differing leads. Hence, electrical isolation is achieved by connecting power traces  26  to one heat sink and ground traces  28  to a heat sink on the opposite side of the board  12 . In this embodiment, the heat sink may be fabricated entirely of a thermal conductive metal without concern for electrical isolation or with electrical isolators to reduce risk of shorting to nearby components (such as with edge and tip guards fabricated of rubber or plastic). 
     Numerous heat sink assemblies may be used to provide the desired heat transfer away from the edge connector leads  24 . The invention includes devices that vary from the heat sink assembly  40  but are thermally, and electrically, connected to the leads  24 , via traces  26 ,  28  or otherwise. For example, a fan may be provided to increase convection from the fins  44 . The fins  44  may be replaced with active heat transfer or heat sink devices or with passive devices that provide enlarged heat transfer surfaces.