Abstract:
A modular heat sink assembly is disclosed. The heat sink assembly includes a main (larger) heat sink member having one or more voids through the member. The heat sink assembly also includes one or more additional (smaller) heat sink members that fit within the voids of the main heat sink member and are able to move (float) within the voids while thermally connected to main heat sink member. The thermal connection to the main heat sink member may be accomplished by incorporating heat pipes as a bridge between the heat sink members, so that heat spreading, and regulation thereof, occurs over the additional heat sink members and the main heat sink member.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention is related to the field of heat sinks, and in particular, to a modular heat sink assembly that has a larger main heat sink member with one or more smaller additional heat sink members that are assembled within voids in the main heat sink member in a movable fashion. The additional heat sink members are thermally connected to the main heat sink member, such as through heat pipes, but are able to move within the voids in the main heat sink member to accommodate different component heights on circuit boards. 
         [0003]    2. Statement of the Problem 
         [0004]    Computers, routers, and other electronic devices are built with processors, memory, and other electronic components that are fabricated on circuit boards. Each of the active components on the circuit board draws a current in order to operate. When a component draws a current, thermal energy (or heat) is created in the component. If the thermal energy in the component increases above a maximum threshold level, then the component may be damaged. One way to protect the component is to use a heat sink to remove heat from electronic components. 
         [0005]    A heat sink is a device that absorbs and dissipates heat from a component which is in thermal contact with the heat sink. A heat sink functions to efficiently transfer thermal energy from the component to the heat sink, which has a much greater surface area and heat removal capacity. A typical heat sink is formed from a metal, such as copper or aluminum, which has a high thermal conductivity. One surface of the heat sink includes a plurality of fins which creates a large surface area for dissipating heat. When the thermal energy is transferred from the component to the heat sink, the thermal energy is rapidly dissipated to the surrounding environment due to the large surface area of the fins, which cools the component. 
         [0006]    Circuit boards may include multiple components that have a high enough thermal energy, and consequently a higher temperature, that heat sinks are needed or desired. For example, microprocessors, power-handling semiconductors, Application-Specific Integrated Circuits (ASIC), etc, typically draw higher currents than other components, and consequently operate at a higher temperature. To provide the desired heat dissipation for the components on the circuit board, an individual heat sink is typically mounted on each of the components on the circuit board. The size of an individual heat sink may depend on the heat dissipation needs for a given component. 
         [0007]    As the size of circuit boards decreases to accommodate smaller electronic devices, there is much less room for individual heat sinks. If two or more components are mounted on a circuit board next to each other, there may not be room to mount an individual heat sink on each of the components. This may result in damage to one or more of the components if the heat generated during operation exceeds a maximum rated temperature for the component. 
         [0008]    One solution to the problem of individual heat sinks is to use one or more larger heat sinks. A large heat sink is simultaneously mounted on multiple components in order to dissipate the heat from the components. Unfortunately, there can also be problems associated with a large heat sink. For one, a large heat sink may conduct excessive thermal energy from one component to another, creating the potential for thermal damage. Also, the components on the circuit board may have varying heights in relation to the top of the circuit board, which makes using a large heat sink difficult to use. The large heat sink can also apply excessive or uneven force to the components with the greater heights, which can damage the components. 
         [0009]    This can especially be a problem when the covers or lids on a component are removed or are omitted during fabrication. Lids are formed on components to protect the fragile components from damage. The lid of a component, commonly formed from aluminum or plastic, may have thermal impedance that negatively affects the dissipation of the heat from the active component underneath the lid. Thus, the lids are sometimes removed, or are omitted during fabrication, so that the heat sink can directly contact the active element instead of contacting the lid. However, when the lid is removed, the component is very susceptible to damage. If a large heat sink is used on a circuit board having one or more lid-less components, then the force applied by the large heat sink can damage the components. 
       SUMMARY OF THE SOLUTION 
       [0010]    Embodiments of the invention solve the above and other related problems with an improved modular heat sink assembly. The heat sink assembly includes a main (larger) heat sink member having one or more voids through the member. The heat sink assembly also includes one or more additional (smaller) heat sink members that fit within the voids and are able to move within the voids. For example, an additional heat sink member may be of a size and dimension that it is able to pass through a void in the main heat sink member. Also, an additional heat sink member may be movably coupled to the main heat sink member through a spring attachment or some other connecting member that applies a downward force on the additional heat sink member, yet the additional heat sink member is movable within the void. The additional heat sink member(s) is thermally connected to the main heat sink member so that heat spreading occurs over the additional heat sink member(s) and the main heat sink member. For example, one or more heat pipes may connect the main heat sink member and the additional heat sink member(s) so that thermal energy may be transferred from the additional heat sink member(s) to the main heat sink member. 
         [0011]    The heat sink assembly described above provides many advantages. If the heat sink assembly is connected to or mounted on a circuit board having multiple components, then the main heat sink member can thermally connect with one or more components on the circuit board. The components thermally connected to the main heat sink member may have similar heights, similar thermal energies, etc. At the same time, one of the additional heat sink members may be thermally connected to another component on the circuit board. This component may have a different height than the components connected to the main heat sink member. Because the additional heat sink member is movable within the void, the additional heat sink member is able to adjust for the different height of the component. Thus, the component is less susceptible to damage from the heat sink assembly, which is especially an advantage if the component is lid-less. 
         [0012]    The component in thermal contact with the additional heat sink member may have a different thermal energy than the components connected to the main heat sink member. If a spring force is applied to the additional heat sink member, then a thin layer of thermally conductive grease may be used between the additional heat sink member and the component, which has low thermal impedance. Thermal energy may then be efficiently transferred from the component to the additional heat sink member, and be done in such a way as to control the amount of heat transfer to the adjacent components, thereby preventing thermal damage. Also, there is heat spreading from the additional heat sink member to the main heat sink member, such as through heat pipes, to allow for effective dissipation of heat from the component having the high thermal energy. 
         [0013]    The heat sink assembly as described herein can be effectively used on a circuit board in place of individual heat sinks for each of the components. Thus, if components are connected to a circuit board in a small area, then the heat sink assembly may be used in place of the individual heat sinks that may not fit in the small area. And because the heat sink assembly includes the additional heat sink members, the heat sink assembly can be used on circuit boards that have different types of components that have different heights, different thermal energies, etc. 
         [0014]    The invention may include other exemplary embodiments described below. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]    The same reference number represents the same element or same type of element on all drawings. 
           [0016]      FIG. 1  is an isometric view of a heat sink assembly in an exemplary embodiment of the invention. 
           [0017]      FIG. 2  is another isometric view of an additional heat sink member with a connecting member in an exemplary embodiment of the invention. 
           [0018]      FIG. 3  is an isometric view of the heat sink assembly with one or more heat pipes connecting an additional heat sink member to a main heat sink member in an exemplary embodiment of the invention. 
           [0019]      FIG. 4  is an isometric view of the top of another heat sink assembly in an exemplary embodiment of the invention. 
           [0020]      FIG. 5  is an isometric view of the bottom of the heat sink assembly in an exemplary embodiment of the invention. 
           [0021]      FIG. 6  is an isometric view of a circuit board in an exemplary embodiment of the invention. 
           [0022]      FIG. 7  is an isometric view of the top of another heat sink assembly in an exemplary embodiment of the invention. 
           [0023]      FIG. 8  is an isometric view of the bottom of the heat sink assembly in an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIGS. 1-8  and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents. 
         [0025]      FIG. 1  is an isometric view of a heat sink assembly  100  in an exemplary embodiment of the invention. Heat sink assembly  100  includes a main heat sink member  102  and one or more additional heat sink members  106 . Main heat sink member  102  comprises any structure that is adapted to absorb and dissipate heat from another object, such as a component on a circuit board. Main heat sink member  102  has one or more voids  104 , which are openings or cut-outs in main heat sink member  102 . Void  104  is shown as being located within the outer boundary of main heat sink member  102 , but one or more voids  104  may additionally or alternatively be located on the outer boundary of main heat sink member  102 . 
         [0026]    Additional heat sink member  106  of heat sink assembly  100  is adapted to fit within void  104 . Additional heat sink member  106  comprises any structure that is adapted to absorb and dissipate heat from another object, such as a component on a circuit board. Although only one additional heat sink member  106  is illustrated in  FIG. 1 , heat sink assembly  100  may include multiple additional heat sink members  106  that are positioned in multiple voids  104  in main heat sink member  102 . 
         [0027]      FIG. 1  illustrates a top view of heat sink assembly  100  (i.e., the side opposite a circuit board is visible). The top surface of main heat sink member  102  and/or additional heat sink member  106  may include a plurality of fins as is common in heat sinks. The fins create additional surface area to assist in dissipating heat to the surrounding environment. Embodiments illustrating fins on the top surfaces are shown below and in  FIGS. 4-5  and  7 - 8 . 
         [0028]    Additional heat sink member  106  is of the proper size and dimensions relative to void  104  to be able to move within void  104 . In  FIG. 1 , additional heat sink member  106  is adapted to move within void  104  along the Z-axis. Additional heat sink member  106  may be movably coupled to main heat sink member  102  by one or more connecting members. The connecting member(s) support additional heat sink member  106  within void  104 , but allow additional heat sink member  106  to move along the Z-axis. 
         [0029]      FIG. 2  is an isometric view of additional heat sink member  106  with a connecting member  200  in an exemplary embodiment of the invention. Connecting member  200  in this embodiment comprises a screw  202  adapted to pass through a hole  204  in additional heat sink member  106  and connect with main heat sink member  102 . Main heat sink member  102 , although not visible in  FIG. 2 , has a corresponding threaded hole adapted to receive screw  202 . Connecting member  200  also includes a spring  206  between the head of screw  202  and additional heat sink member  106 . Screw  202  may thus be inserted down hole  204  into the corresponding threaded hole in main heat sink member  102 , and tightened onto spring  206 . The strength of the spring, commonly referred to as the “spring-rate”, determines how much force is applied to additional heat sink member  100  downward in the Z-direction. Thus, the amount of spring force applied by connecting member  200  is adjustable by selecting the appropriate spring-rate to apply the appropriate force. 
         [0030]    There may be multiple connecting members  200  that movably couple additional heat sink member  106  to main heat sink member  102 , although only one is shown. Connecting members  200  may also be connected at different locations, as  FIG. 2  shows just one example. Connecting members  200  would typically be placed in such a way as to ensure a even, balanced force load upon the component being cooled, especially those that are lid-less (where uneven forces distribution can lead to component damage). 
         [0031]    Additional heat sink member  106  may be movably coupled to other structures, and still be movable within void  104 . For instance, additional heat sink member  106  may be connected to a support structure (not shown in  FIG. 1 ), an enclosure (not shown in  FIG. 1 ) surrounding heat sink assembly  100 , or some other structure. 
         [0032]    Additional heat sink member  106  is also thermally connected to main heat sink member  102 . Additional heat sink member  106  may be thermally connected to main heat sink member  102  by any heat transfer mechanism adapted to transport thermal energy from additional heat sink member  106  to main heat sink member  102 . One example of a heat transfer mechanism is a heat pipe. 
         [0033]      FIG. 3  is an isometric view of heat sink assembly  100  with one or more heat pipes  300  connecting additional heat sink member  106  to main heat sink member  102  in an exemplary embodiment of the invention.  FIG. 3  illustrates a bottom view of heat sink assembly  100  (i.e., the side toward a circuit board is visible). Although heat pipes  300  are shown on the bottom surface in this embodiment, heat pipes  300  may be formed on the top surface in other embodiments. 
         [0034]    A typical heat pipe  300  consists of a sealed hollow tube formed from a thermo-conductive metal, such as copper or aluminum. The heat pipe  300  is filled with a relatively small quantity of a coolant, such as water, with the remainder of the pipe being filled with vapor phase of the coolant. The internal surface of the heat pipe  300  has a wicking structure that exerts a capillary force on the liquid phase of the coolant. If the heat tube  300  is attached to something hot (i.e., additional heat sink member  106 ), coolant at the hot end of the heat tube  300  is vaporized and travels toward the cooler end (i.e., where heat pipe  300  connects to main heat sink member  102 ). The vaporized coolant then condenses, and the condensed coolant travels back toward the hot end due to the capillary action. This process continues to transfer the thermal energy from additional heat sink member  106  to main heat sink member  102 . 
         [0035]      FIG. 3  also shows a plurality of pads  310  on the bottom surface of main heat sink  102 . Pads  310  each represent a Thermal Interface Material (TIM) that is adapted to interface with a component on a circuit board. A TIM comprises any material used to fill the gaps between thermal transfer surfaces, such as between components and heat sinks, in order to increase thermal transfer efficiency. 
         [0036]    The bottom surface of additional heat sink member  106  is adapted to thermally contact a component on the circuit board. The bottom surface should be substantially flat and smooth in order to make good thermal contact with the component. A thermally conductive grease may be applied to the bottom surface of additional heat sink member  106  to ensure optimal thermal contact. 
         [0037]      FIGS. 4-5  illustrate a more detailed heat sink assembly  400  in an exemplary embodiment of the invention.  FIG. 4  is an isometric view of the top of a heat sink assembly  400  in an exemplary embodiment of the invention. Heat sink assembly  400  in  FIG. 4  includes a larger main heat sink member  402  with a plurality of voids  404 - 405  formed through main heat sink member  402 . Smaller additional heat sink members  406 - 407  are placed within each of the voids  404 - 405  and are movably coupled to main heat sink member  402  with a plurality of connecting members  420 . Although two additional heat sink members  406 - 407  are shown, those skilled in the art will appreciate that more or less than two additional heat sink members may be used in other embodiments. 
         [0038]    Main heat sink member  402  is comprised of a base  410  with a plurality of fins  412  formed on a first (top) side. A second (bottom) side of main heat sink member  402  is illustrated in  FIG. 5 . Additional heat sink members  406 - 407  are comprised of a base (not visible in  FIG. 4 ) with a plurality of fins  422  formed on a first (top) side. A second (bottom) side of additional heat sink members  406 - 407  is illustrated in  FIG. 5 . 
         [0039]      FIG. 5  is an isometric view of the bottom of heat sink assembly  400  in an exemplary embodiment of the invention. Each of additional heat sink members  406 - 407  are thermally connected to main heat sink member  402  by heat pipes. For example, additional heat sink member  406  is thermally connected to main heat sink member  402  through heat pipes  531 - 532 . One end of heat pipe  531  is connected to additional heat sink member  406 , and the other end of heat pipe  531  is connected to main heat sink member  402 . Heat pipe  532  is connected in a similar manner. Additional heat sink member  407  is also thermally connected to main heat sink member  402  through heat pipes  533 - 534 . One end of heat pipe  533  is connected to additional heat sink member  407 , and the other end of heat pipe  533  is connected to main heat sink member  402 . Heat pipe  534  is connected in a similar manner. Although two heat pipes are connected to each additional heat sink member  406 - 407 , more or less than two heat pipes may be connected to each additional heat sink member  406 - 407  in other embodiments. Also, although heat pipes are illustrated in this embodiment, other heat transfer mechanisms may be used in other embodiments. 
         [0040]    The bottom side of main heat sink member  402  includes a plurality of pads  513 - 519  formed from a Thermal Interface Material (TIM) that are adapted to interface with components on a circuit board. The pattern of the pads  513 - 519  will depend on the pattern of the components on a circuit board. The bottom sides of additional heat sink members  406 - 407  are substantially flat and smooth to interface with components on the circuit board. A thermally conductive grease may be applied to the bottom surface of additional heat sink members  406 - 407  to ensure optimal thermal contact. 
         [0041]      FIG. 6  is an isometric view of a circuit board  600  in an exemplary embodiment of the invention.  FIG. 6  illustrates a circuit board  600  onto which heat sink assembly  400  in  FIGS. 4-5  may be mounted for heat dissipation. Circuit board  600  includes a plurality of mounted components  601 - 609 . Components  601 - 602  generate more thermal energy during operation as compared to components  603 - 609 . For instance, components  601 - 602  may comprise microprocessors or an ASIC, while components  603 - 609  comprise memory chips or some other component that operates at a low temperature. Components  601 - 602  also have a different height than components  603 - 609 . For example, components  601 - 602  may have a taller profile than components  603 - 609 . 
         [0042]    Assume for example that heat sink assembly  400  as illustrated in  FIGS. 4-5  is mounted on circuit board  600 . Main heat sink member  402  includes nuts  540  (see  FIG. 5 ) that match the pattern of holes  640  in circuit board  600 . A screw or bolt may be passed through holes  640  in order to mate with nuts  540  in main heat sink member  402  to secure main heat sink member  402  to circuit board  600 . 
         [0043]    When main heat sink member  402  is mounted on circuit board  600 , pads  513 - 519  interface with components  603 - 609  of circuit board  600 , respectively. Pads  513 - 519  have a desired thickness in order to thermally contact components  603 - 609 . For example, pads  513 - 519  may have a thickness of about 1-2 millimeters. 
         [0044]    At the same time, additional heat sink members  406 - 407  interface with components  601 - 602  of circuit board  600 , respectively. The bottom surface of additional heat sink member  406  interfaces with component  601  through a thermally conductive grease. Likewise, the bottom surface of additional heat sink member  407  interfaces with component  602  through a thermally conductive grease. 
         [0045]    When the circuit board  600  is put into operation, main heat sink member  402  absorbs the thermal energy from components  603 - 609 , and dissipates the absorbed thermal energy to the surrounding environment through fins  412 . Additional heat sink members  406 - 407  absorb the thermal energy from components  601 - 602 , respectfully. Some of the absorbed thermal energy is dissipated to the surrounding environment through fins  422 . Some of thermal energy is transferred to main heat sink member  402  through heat pipes  531 - 534 . Thus, additional heat sink members  406 - 407  spread the thermal energy to the larger main heat sink member  402  for dissipation. In this embodiment, additional heat sink members  406 - 407  interface with the hotter components  601 - 602  on circuit board  600 . Because there is thermal spreading to main heat sink member  402 , additional heat sink members  406 - 407  are able to effectively cool components  601 - 602  even though additional heat sink members  406 - 407  are relatively small in size. By adjusting the heat pipes  531 - 534  between the heat sink members or ratio of fin counts, the amount of thermal energy transfer from the higher dissipating components to the lesser dissipating components can be regulated in order to prevent damage to those components having a lower operational temperature. 
         [0046]    Because additional heat sink members  406 - 407  are movably coupled to main heat sink member  402 , additional heat sink members  406 - 407  are able to “float” with voids  404 - 405  to accommodate the different heights of components  601 - 602 . Consequently, there is a reduced risk of damaging components  601 - 602  of varying height with heat sink assembly  400 . Even if components  601 - 602  are lid-less, the floating structure of additional heat sink members  406 - 407  reduces the risk of damage. 
         [0047]    The amount of downward force applied to additional heat sink members  406 - 407  is adjustable through connecting members  420  (see  FIG. 4 ). Based on the maximum load rating for the components  601 - 602 , the connecting members  420  and spring sizes may be adjusted to apply the desired downward force on additional heat sink members  406 - 407 . Thus, good thermal contact may be achieved without damaging additional heat sink members  406 - 407 . 
         [0048]    Another advantage of additional heat sink members  406 - 407  having an adjustable downward force is that a TIM of a fixed thickness does not need to be used as an interface between the additional heat sink members  406 - 407  and components  601 - 602 . A thermally conductive grease, which may be applied much thinner (e.g., 3-5×10 −3  millimeters) than a typical TIM, may be used as the interface between the additional heat sink members  406 - 407  and components  601 - 602 . This allows for optimal thermal contact and heat transfer. 
         [0049]      FIGS. 7-8  illustrate another detailed heat sink assembly  700  in an exemplary embodiment of the invention.  FIG. 7  is an isometric view of the top of heat sink assembly  700  in an exemplary embodiment of the invention. As in  FIG. 4 , heat sink assembly  700  in  FIG. 7  includes a larger main heat sink member  702  with a plurality of voids  704 - 705  formed through main heat sink member  702 . Smaller additional heat sink members  706 - 707  are placed within each of the voids  704 - 705  and are movably coupled to main heat sink member  702 . Although two additional heat sink members  706 - 707  are shown, those skilled in the art will appreciate that more or less than two additional heat sink members may be used in other embodiments. 
         [0050]      FIG. 8  is an isometric view of the bottom of the heat sink assembly  700  in an exemplary embodiment of the invention. Each of additional heat sink members  706 - 707  are thermally connected to main heat sink member  702  by heat pipes. For example, additional heat sink member  706  is thermally connected to main heat sink member  702  through heat pipes  831 - 832 . One end of heat pipe  831  is connected to additional heat sink member  706 , and the other end of heat pipe  831  is connected to main heat sink member  702 . Heat pipe  832  is connected in a similar manner. Additional heat sink member  707  is also thermally connected to main heat sink member  702  through heat pipes  833 - 834 . One end of heat pipe  833  is connected to additional heat sink member  707 , and the other end of heat pipe  833  is connected to main heat sink member  702 . Heat pipe  834  is connected in a similar manner. 
         [0051]    The bottom side of main heat sink member  702  includes a plurality of pads  813 - 826  formed from a Thermal Interface Material (TIM) that are adapted to interface with components on a circuit board. The pattern of the pads  813 - 826  will depend on the pattern of the components on a circuit board. The bottom sides of additional heat sink members  706 - 707  each include a pad  811 - 812  to interface with components on the circuit board. 
         [0052]    The embodiments shown in the  FIGS. 4-5  and  7 - 8  illustrate heat sink assemblies that are able to work with a variety of circuit boards. More particularly, the heat sink assemblies may be used with circuit boards that have components of varying heights, varying thermal operating temperatures, varying sizes, etc. Thus, the heat sink assemblies can effectively be used to replace individual heat sinks on the circuit boards. 
         [0053]    Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.