Abstract:
A heat sink has a structure fabricated of aluminum, with at least a portion of this structure having a surface with at least a portion thereof exposed to a device to be cooled and/or to a coolant liquid at least this portion being hard-anodized. This portion of the structure is rendered electrically insulating and/or corrosion resistant by a hard-anodized surface layer thereon.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to heat sinks of the type usable, for example, for cooling electrical components and relates especially, though not exclusively, to heavy duty heat sinks that are constructed to accept a flow of liquid coolant therethrough.  
         [0003]     2. Description of the Prior Art  
         [0004]     As greater demands in terms of power handling and functional capabilities are imposed upon electrical components, there is a correspondingly greater requirement for cooling such components, to ensure that they run at temperatures consistent with their operational limitations.  
         [0005]     Accordingly, considerable effort has been expended on the development of adequate cooling devices for such components and, whilst liquid-cooled heat sinks currently used are, generally speaking, quite effective, they have been developed piecemeal, with individual problems discovered in service being addressed with individual solutions. This leads to difficulties associated with (a) the construction of complex structures and the accompanying cost, and (b) the creation of heat sinks which offer limited overall efficiency, in terms of cooling power in relation to space occupied.  
       SUMMARY OF THE INVENTION  
       [0006]     An object of the present invention is to overcome or reduce at least one of the above-mentioned difficulties. It is a further object of the invention to provide a liquid-cooled heat sink of unitary construction. A still further object of the invention is to provide a liquid-cooled heat sink requiring no external pipe-work links between internal liquid conduits, thereby permitting the effective dimensions of the heat sink to be increased as compared with those for a heat sink with external pipe-work connections.  
         [0007]     The invention also encompasses methods of making heat sinks of the kinds mentioned in the immediately preceding paragraph.  
         [0008]     The above object is achieved in accordance with the present invention by a heat sink having an aluminum structure having a first surface having at least a portion thereof in thermal communication with a device to be cooled, and a second surface that is exposed to a coolant liquid, the second surface having a hard-anodized surface layer thereon that is resistant to attack, such as corrosion, by the coolant liquid.  
         [0009]     The above object also is achieved in accordance with the present invention by a method for manufacturing a heat sink including the steps of fabricating a heat sink structure from aluminum, forming a channel in the structure that is configured to accept a liquid coolant flowing therein, and applying a surface coating to a surface of the channel, which is resistant to attack, such as corrosion, by the coolant liquid, the surface coating being applied by hard-anodizing the surface of the channel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIGS. 1A and 1B  show, in elevation and plan views, respectively, a typical prior art heat sink.  
         [0011]      FIGS. 2A and 2B  show, in views comparable to those of  FIGS. 1A and 1B  respectively, a heat sink in accordance with an embodiment of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     Referring now to  FIGS. 1A and 1B , a typical prior art heat sink  10 , provided for cooling an electrical device  20 , comprises an extruded plate  11  of aluminum. The plate  11  may be finned or otherwise treated to promote dissipation of heat from the external surfaces thereof.  
         [0013]     Similar heat sinks are available from R-Theta Thermal Solutions Inc (www.r-theta.com) under the “Aquasink” brand.  
         [0014]     The plate  11  is formed with internal channels such as  12  though which, in use, liquid coolant such as water is caused to flow. The channels such as  12  are fitted with tubular copper liners such as  13  used to provide resistance to corrosion of the plate  11  by the liquid coolant. The tubular liners such as  13  may be threaded at their ends, and are interconnected, externally of the aluminum plate  11 , for example by stainless steel pipe-work interconnects, such as  14 , creating a desired liquid flow pattern through the plate  11  to promote enhanced dissipation of heat generated by the device  20 .  
         [0015]     Typically, the device  20  needs to be attached to the heat sink  10 , so as to establish good thermal contact therewith, whilst remaining electrically insulated therefrom. This is usually achieved by means of an adhesive pad or film  15  of thermally conductive but electrically insulating material.  
         [0016]     Referring now to  FIGS. 2A and 2B , which show, as an example only, an embodiment of the invention. The heat sink  30  of this embodiment is provided for cooling an electrical device  40  and has an extruded aluminum plate  31 , containing, as is conventional, parallel flow channels such as  32  for liquid coolant such as water. In this case, however, unlike the prior art configuration described with reference to  FIGS. 1A and 1B , no liners such as  13  are used in the coolant flow channels. In accordance with this embodiment of the invention, resistance to corrosion of the aluminum by the coolant fluid, with no substantial reduction in thermal transfer efficiency, is provided by hard anodizing the exposed surfaces of the channels, such as  32 .  
         [0017]     This procedure advantageously allows the cooling channels to have a larger bore compared to the prior art, since the copper liners such as  13  are not used.  
         [0018]     In a further refinement employed by this embodiment, the external pipe-work connections between channels, such as shown at  14  in the prior art heat sink of  FIG. 1B , are not required. According to this refinement, individual channels such as  32  are plugged, as shown at  36 , and an orthogonal linking channel  37 , also hard-anodized and plugged, is provided to interlink the channels such as  32  to provide a desired flow pattern for the liquid coolant. Further linking channels such as  37  may be provided as required to establish a required coolant flow path. Each linking channel serves to join at least two of the channels  32 .  
         [0019]     Such interconnection of channels within the material of the plate is not possible with the prior art heat sinks such as shown in  FIGS. 1A and 1B , since interconnection of copper liners  13  would then be required. Since the described embodiment of the present invention employs no liners, but rather employs channels formed in the bulk material of the aluminum plate  31 , such interconnection is made possible by the present invention.  
         [0020]     The plugging  36  may be of aluminum or any other material suitable for the intended temperature range of operation, and compatible with the aluminum material of the plate  31 . The linking channel  37  is drilled into the aluminum plate  31  generally perpendicularly to the channels  32 , parallel to the plane of the channels  32  to connect at least two of the channels  32 . If desired, further linking channels may be provided at other positions within the aluminum plate. Hard-anodizing of the channels should be done after formation of the linking channel(s)  37 . Depending on the material used for plugging  36  channels  32 ,  37 , the hard-anodizing may need to be done after plugging is complete.  
         [0021]     As can be seen from a comparison of  FIGS. 1B and 2B , this refinement not only provides a significant component and cost reduction, but also permits an increase in the size of the active heat sinking volume of the heat sink  30  compared with that of the heat sink  10 , since the volume previously occupied by the external pipe-work connections such as  14  can now be assigned to the bulk of the heat sink  30  itself, giving greater heat sink volume within the same external volumetric envelope. It will be appreciated that the dimensions of the external volumetric envelope are frequently pre-assigned in any given configuration, so that an increase in the active heat sinking volume within this pre-assigned envelope provides added cooling efficiency.  
         [0022]     The invention also provides, in this embodiment, efficient electrical insulation between the heat sink  30  and the electrical device  40 , by hard-anodizing that part of the surface area of the plate  32  to which the device  40  is attached. The hard-anodized surface area provides excellent thermal transfer efficiency coupled with electrical insulation.  
         [0023]     It will be understood that the hard-anodizing required by the invention can be employed in relation to the surfaces of the coolant channels and/or the surface area or areas at which devices to be cooled are attached to the heat sink.  
         [0024]     It will be further understood that the hard-anodizing can be implemented in any suitable manner and that, if desired or if convenient, the entire external and internal surface area of the aluminum structure, such as plate  31 , may be hard-anodized.  
         [0025]     The present invention has been described with particular reference to extruded aluminum plates  31 , containing parallel cooling channels  32  formed during the extrusion process. In alternative embodiments, the required channels may be formed by drilling or otherwise machining into a solid block of material. In a further alternative, linking channel(s)  37  are formed during extrusion of an extruded aluminum plate, with coolant channels  32  formed by drilling or otherwise machining into the extruded plate.  
         [0026]     The present invention accordingly provides hard-anodizing both to the interior surfaces of the channels, to provide a thin corrosion resistant coating, and to the surface area of the plate to which the device  40  is attached, to provide electrical isolation between the plate and the cooled device. It has been found simplest to perform anodizing over the entire internal and external surfaces of the aluminum plate.  
         [0027]     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.