Abstract:
A heat-activated self-aligning heat sink is built thermally connecting at least one heat-generating devices on a substrate to the heat sink body, where the heat-generating devices may not be co-planar with each other due to tolerance stack-up or parallel with the heat sink body. A pedestal is attached to the substrate to support the heat sink body. A plug or floating pedestal is placed on top of each heat-generating device and held within the pedestal allowing sufficient movement for the bottom surface of the plug to fully contact the top surface of the heat-generating device. A quantity of a low melting temperature, thermally conductive material, such as solder, or a thermally conductive liquid, is placed over each plug and a heat sink body is placed over the assembly. When heated, the thermal material melts, forming a low impedance thermal junction between the plug and the heat sink body regardless of planarity differences between the two devices.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of heat sinks and more specifically to the field of heat sinks configured to self-align with heat generating devices that may not be parallel to the heat sink. 
     BACKGROUND OF THE INVENTION 
     Modern electronics have benefited from the ability to fabricate devices on a smaller and smaller scale. As the ability to shrink devices has improved, so has their performance. Unfortunately, this improvement in performance is accompanied by an increase in power as well as power density in devices. In order to maintain the reliability of these devices, the industry must find new methods to remove this heat efficiently. 
     By definition, heat sinking means that one attaches a cooling device to a heat-generating component and thereby removes the heat to some cooling medium, such as air or water. Unfortunately, one of the major problems in joining two devices to transfer heat through a common surface is that a thermal interface is created at the junction. This thermal interface is characterized by a thermal contact impedance. Thermal contact impedance is a function of contact pressure, surface finish, and gap size. Thermal contact impedance also raises dramatically when the surfaces of the two devices are non-parallel. With non-parallel devices, only a small percentage of the possible contact area between the two devices is actually in contact and conducting heat. 
     As the power density of electronic devices increases, heat transfer from the heat generating devices to the surrounding environment becomes more and more critical to the proper operation of the devices. Many current electronic devices incorporate heat sink fins to dissipate heat to the surrounding air moving over the fins. These heat sinks are thermally connected to the electronic devices by a variety of techniques. Some devices use a thermally conductive paste in an attempt to lower the contact resistance. Others may use solder between the two elements both for mechanical strength and thermal conductance. Once again, if the two surfaces to be thermally coupled are not parallel difficulties may arise since the region of contact between the two surfaces forms a line instead of a plane. Thermal paste and solder are only usable for junctions with small amounts of non-co-planarity. 
     Many present electronic modules include a plurality of heat-generating electronic devices on a single substrate. Often these devices do not have a co-planer upper surface that would allow a single heat sink to be thermally coupled to the plurality of devices. Thermal paste and other thermally conductive materials, such as solder, may be used to fill small gaps between the heat-generating electronic devices and the single heat sink, however large gaps are often not capable of being filled by a paste or solder. In such cases, multiple heat sinks may be used, however, this adds cost and reduces the efficiency of the heat dissipation. 
     SUMMARY OF THE INVENTION 
     A heat-activated self-aligning heat sink is built thermally connecting at least one heat-generating devices on a substrate to the heat sink body, where the heat-generating devices may not be co-planar with each other due to tolerance stack-up or parallel with the heat sink body. A pedestal is attached to the substrate to support the heat sink body. A plug or floating pedestal is placed on top of each heat-generating device and held within the pedestal allowing sufficient movement for the bottom surface of the plug to fully contact the top surface of the heat-generating device. A quantity of a low melting temperature, thermally conductive material, such as solder, or a thermally conductive liquid, is placed over each plug and a heat sink body is placed over the assembly. When heated, the thermal material melts, forming a low impedance thermal junction between the plug and the heat sink body regardless of planarity differences between the two devices. 
    
    
     Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. 
     FIG. 2 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 1 after heat is applied. 
     FIG. 3 is a cross-sectional view of an example embodiment of five heat-activated self-aligning heat sinks according to the present invention before heat is applied. 
     FIG. 4 is a cross-sectional view of the example embodiment of five heat-activated self-aligning heat sinks according to the present invention from FIG. 3 after heat is applied. 
     FIG. 5 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. 
     FIG. 6 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 5 after heat is applied. 
     FIG. 7 is a flow chart of a method for constructing a heat-activated self-aligning heat sink according to the present invention. 
     FIG. 8 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. 
     FIG. 9 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 8 after heat is applied. 
     FIG. 10 is a flow chart of a method for constructing a heat-activated self-aligning heat sink according to the present invention. 
     FIG. 11 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. 
     FIG. 12 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 11 after heat is applied. 
     FIG. 13 is a cross-sectional view of an example embodiment of five heat-activated self-aligning heat sinks according to the present invention before heat is applied. 
     FIG. 14 is a cross-sectional view of the example embodiment of five heat-activated self-aligning heat sinks according to the present invention from FIG. 13 after heat is applied. 
     FIG. 15 is a flow chart of a method for constructing a heat-activated self-aligning heat sink according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. A heat-generating device  100  is placed on a substrate  102  along with a pedestal  104 . The pedestal  104  includes openings over the heat-generating device  100  allowing placement of a plug or floating pedestal  106  over the heat-generating device. The floating pedestal  106  fits within the pedestal  104  in such a way that it is able to move up or down to rest on the top surface of the heat-generating device  100  and may tilt slightly to match any tilt of the top surface of the heat-generating device  100 . Some example embodiments of the present invention may include a quantity of thermally-conductive deformable material between the floating pedestal  106  and the heat-generating device  100 , in order to minimize the thermal resistance between the floating pedestal  106  and the heat-generating device  100 . A quantity of thermal material  110  is placed above the plug and the heat sink body  108  is placed over the assembly. The thermal material  110  comprises a low melting temperature, thermally conductive material such as solder. Note that the heat sink body  108  includes a cavity  114  in its bottom surface to accept the thermal material  110 . When the heat sink body  108  is heated above the melting point of the thermal material  110  and compressive force is applied to the heat sink body  108  and the substrate  102 , the thermal material  110  melts filling the cavity  114  between the heat sink body  108  and the floating pedestal  106 . Note that the compressive force does not need to be large. Some example embodiments of the present invention may use the weight of the heat sink or the substrate to compress the heat sink assembly, and no external compressive force is required at all. The heat sink body  108  then moves down to rest on the pedestal  104  as shown in FIG.  2 . 
     FIG. 2 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 1 after heat is applied. Once heat and compressive force have been applied, the liquid thermal material  200  fills the cavity between the heat sink body  108  and the floating pedestal  106 . Any excess thermal material travels up the vent hole  112 . Note that at this point the heat sink body  108  may be mechanically attached to the pedestal  104  or directly to the substrate  102  to keep it from moving. 
     FIG. 3 is a cross-sectional view of an example embodiment of five heat-activated self-aligning heat sinks according to the present invention before heat is applied. In an example embodiment of the present invention, five heat-generating devices with two different heights are attached to a substrate  300 . Short devices  302  are interspersed between tall devices  304 . A pedestal  310  is attached to the substrate, and plugs or floating pedestals  306  are placed above the devices. Note that all of the floating pedestals  306  in this example embodiment are the same height. Other embodiments of the present invention may use floating pedestals  306  with different heights on the same assembly. Quantities of thermal material  308  are placed above each floating pedestal  306  and a heat sink body  312  is placed above the assembly. The heat sink body  312  includes vent holes  314  to allow any excess thermal material  308  to escape upon melting. 
     FIG. 4 is a cross-sectional view of the example embodiment of five heat-activated self-aligning heat sinks according to the present invention from FIG. 3 after heat is applied. Upon heating and applying a compressive force to the heat sink body  312  and the substrate  300 , the thermal material  308  melts to form a liquid. Above the short devices  302 , the liquid thermal material fills a larger cavity  400 , while above the tall devices  304 , the liquid thermal material fills a smaller cavity  402 . Also note that more solder was expelled through the vent holes  314  over the tall devices  304  than through the vent holes  314  over the short devices  302 . 
     FIG. 5 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. The heat-activated self-aligning heat sink shown in this figure is identical to that of FIG. 1, except that it is used to make contact with a heat-generating device  500  that is not parallel with the bottom of the heat sink body  508 . A heat-generating device  500  and a pedestal  504  are attached to a substrate  502 . The pedestal  504  includes openings over the heat-generating device  500  allowing placement of a plug or floating pedestal  506  over the heat-generating device  500 . The floating pedestal  506  fits within the pedestal  504  in such a way that it is able to move up or down to rest on the top surface of the heat-generating device  500  and has tilted slightly to match the tilt of the top surface of the heat-generating device  500 . A quantity of thermal material  510  is placed above the plug and the heat sink body  508  is placed over the assembly. Note that the heat sink body  108  includes a cavity  514  in its bottom surface to accept the quantity of thermal material. When the heat sink body  508  is heated above the melting point of the thermal material  510  and compressive force is applied to the heat sink body  508  and the substrate  502 , the thermal material  510  melts filling the cavity  514  between the heat sink body  508  and the floating pedestal  506  with a liquid. Note that the compressive force does not need to be large. Some example embodiments of the present invention may use the weight of the heat sink or the substrate to compress the heat sink assembly, and no external compressive force is required at all. The heat sink body  508  then moves down to rest on the pedestal  504  as shown in FIG.  6 . 
     FIG. 6 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 5 after heat is applied. Once heat and compressive force have been applied, the liquid thermal material  600 , such as solder or other low melting temperature, thermally conductive material, fills the cavity between the heat sink body  508  and the floating pedestal  506 . Any excess thermal material travels up the vent hole  512 . Note that the thermal material has completely filled the cavity  514  creating a strong thermal connection between the floating pedestal  506  and the bottom of the heat sink body  508  even though their surfaces are not parallel. Also note that at this point the heat sink body  508  may be mechanically attached to the pedestal  504  or directly to the substrate  502  to keep it from moving. 
     FIG. 7 is a flow chart of a method for constructing a heat-activated self-aligning heat sink according to the present invention. In an optional step  700 , a substrate including heat-generating devices that need to be cooled is provided. In an optional step  702 , a pedestal is mechanically attached to the substrate. In a step  704 , at least one floating pedestal is moveably attached to the pedestal. In a step  706 , a quantity of thermal material is placed on top of each floating pedestal. In a step  708 , a heat sink body is placed over the thermal material. In an optional step  710 , the thermal material is heated to melting. In an optional step  712 , compressive force is applied to the heat sink body and the substrate until the heat sink body rests on the pedestal. In an optional step  714  the heat sink body is mechanically connected to either the substrate or the pedestal. 
     FIG. 8 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. In this example embodiment of the present invention a circuit board including a substrate  802 , a heat-generating device  800 , and a pedestal  804  is shown. A heat sink body  808  is constructed including at least one cavity  814  where the cavity  814  includes space for a quantity of thermal material and a means for capturing a plug or floating pedestal  806  allowing placement of the floating pedestal  806  over the heat-generating device  800 . The floating pedestal  806  fits within the heat sink cavity  814  in such a way that it is able to move up or down to rest on the top surface of the heat-generating device  800  and may tilt slightly to match any tilt of the top surface of the heat-generating device  800 . A quantity of thermal material  810  is placed above the plug and the heat sink body  808  is placed over the assembly. The thermal material  810  comprises a low melting temperature, thermally conductive material such as solder. Note that the cavity  814  in the bottom surface of the heat sink body  808  is configured to capture the thermal material  810  above the floating pedestal  806 . When the heat sink body  808  is heated above the melting point of the thermal material  810  and compressive force is applied to the heat sink body  808  and the substrate  802 , the thermal material  810  melts filling the cavity  814  between the heat sink body  808  and the floating pedestal  806  with a liquid. Note that the compressive force does not need to be large. Some example embodiments of the present invention may use the weight of the heat sink or the substrate to compress the heat sink assembly, and no external compressive force is required at all. The heat sink body  808  then moves down to rest on the pedestal  804  as shown in FIG.  9 . Note that this example embodiment of the present invention includes a number of heat sink fins  816  attached to the heat sink body  808 . 
     FIG. 9 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 8 after heat is applied. Once heat and compressive force have been applied, the liquid thermal material  900 , such as solder or other low melting temperature, thermally conductive material, fills the cavity between the heat sink body  808  and the floating pedestal  806  with a liquid. Any excess thermal material travels up the vent hole  812 . Note that at this point the completed heat sink may be mechanically attached to the pedestal  804  or directly to the substrate  802  to keep it from moving. In this example embodiment of the present invention, clips  902  are used to attach the heat sink to the substrate  802 . However, many other methods of attachment, such as bolts, screws, glue, and solder, may be used within the scope of the present invention. 
     FIG. 10 is a flow chart of a method for constructing a heat-activated self-aligning heat sink according to the present invention. In a step  1000 , a heat sink body is provided. In a step  1002 , a cavity is created in a bottom surface of the heat sink body. In a step  1004 , the cavity is configured to moveably capture a floating pedestal. In a step  1006 , a quantity of thermal material is placed within the cavity. In a step  1008 , the floating pedestal is moveably captured within the cavity such that a bottom surface of the floating pedestal is configured to contact an upper surface of a heat-generating device attached to a substrate, and an upper surface of the floating pedestal is within the cavity. In an optional step  1010 , the thermal material is heated to melting. In an optional step  1012 , compressive force is applied to the heat sink body and the substrate until the heat sink body rests on the pedestal. In an optional step  1014  the heat sink body is mechanically connected to either the substrate or the pedestal. 
     FIG. 11 is a cross-sectional view of an example embodiment of a heat-activated self-aligning heat sink according to the present invention before heat is applied. The example embodiment of the present invention shown in FIG. 11 is identical to that of FIG. 1 with the exception that the pedestal  1104  is attached to the head sink body  1108  in stead of the substrate  1102 . A heat-generating device  1100  is placed on a substrate  1102 . A pedestal  1104  is attached to the heat sink body  1108 . The pedestal  1104  includes openings over the heat-generating device  1100  allowing placement of a plug or floating pedestal  1106  over the heat-generating device  1100 . The heat sink body  1108  also contains a cavity  1114  to contain a quantity of thermal material  1110 . The floating pedestal  1106  fits within the pedestal  1104  in such a way that it is able to move up or down to rest on the top surface of the heat-generating device  1100  and may tilt slightly to match any tilt of the top surface of the heat-generating device  1100 . A quantity of thermal material  1110  is placed above the plug within the cavity  1114  in the heat sink body  1108 . The thermal material  1110  comprises a low melting temperature, thermally conductive material such as solder, or a thermally conductive liquid. When the heat sink body  1108  is heated above the melting point of the thermal material  1110  and compressive force is applied to the heat sink body  1108  and the substrate  1102 , the thermal material  1110  melts filling the cavity  1114  between the heat sink body  1108  and the floating pedestal  1106 . Note that the compressive force does not need to be large. Some example embodiments of the present invention may use the weight of the heat sink or the substrate to compress the heat sink assembly, and no external compressive force is required at all. The heat sink body  1108  then moves down such that the pedestal  104  rests on the substrate  1102  as shown in FIG.  12 . 
     FIG. 12 is a cross-sectional view of the example embodiment of a heat-activated self-aligning heat sink according to the present invention from FIG. 11 after heat is applied. Once heat and compressive force have been applied, the liquid thermal material  1200  fills the cavity between the heat sink body  1108  and the floating pedestal  1106 . Any excess thermal material travels up the vent hole  1112 . Note that at this point the heat sink body  1108  may be mechanically attached to the substrate  1102  to keep it from moving. 
     FIG. 13 is a cross-sectional view of an example embodiment of five heat-activated self-aligning heat sinks according to the present invention before heat is applied. In an example embodiment of the present invention, five heat-generating devices with two different heights are attached to a substrate  1300 . Short devices  1302  are interspersed between tall devices  1304 . A pedestal  1310  is attached to a heat sink body  1312 , and plugs or floating pedestals  1306  are placed within the pedestal  1310  under cavities in the heat sink body  1312 . Note that all of the floating pedestals  1306  in this example embodiment are the same height. Other embodiments of the present invention may use floating pedestals  1306  with different heights on the same assembly. Quantities of thermal material  1308  are placed within each cavity in the heat sink body  1312  above each floating pedestal  1306 . In some embodiments of the present invention, the thermal material  1308  will be placed within each cavity before the floating pedestals  1306  are placed within the pedestal  1310 . In other embodiments of the present invention where the thermal material is a thermally conductive liquid, the liquid may be placed in the chambers after assembly through vent holes  1314  within the heat sink body  1312  and the vent holes  1314  are plugged after filling the chamber with the liquid. If a low melting point solid thermal material is used, the vent holes  1314  allow any excess material to escape upon melting and compression of the assembly. 
     FIG. 14 is a cross-sectional view of the example embodiment of five heat-activated self-aligning heat sinks according to the present invention from FIG. 13 after heat is applied. Upon heating and applying a compressive force to the heat sink body  1312  and the substrate  1300 , the thermal material  1308  melts to form a liquid. Above the short devices  1302 , the liquid thermal material fills a larger cavity  1400 , while above the tall devices  1304 , the liquid thermal material fills a smaller cavity  1402 . Also note that more solder was expelled through the vent holes  1314  over the tall devices  1304  than through the vent holes  1314  over the short devices  1302 . 
     FIG. 15 is a flow chart of a method for constructing a heat-activated self-aligning heat sink according to the present invention. In a step  1500 , a heat sink body including a cavity is provided. In a step  1502 , a pedestal is attached to the heat sink body. In a step  1504 , a quantity of thermal material is placed within the cavity in the heat sink body. In a step  1506 , a floating pedestal is moveably attached to the pedestal. In an optional step  1508 , the thermal material is heated to melting. In an optional step  1510 , a compressive force is applied to the heat sink body and a substrate including a heat-generating device. In an optional step  1512 , the heat sink assembly is attached to the substrate. 
     The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.