Abstract:
The disclosure describes directly cooling a three-dimensional, direct metallization (DM) layer in a power electronics device. To enable sufficient cooling, coolant flow channels are formed within the ceramic substrate. The direct metallization layer (typically copper) may be bonded to the ceramic substrate, and semiconductor chips (such as IGBT and diodes) may be soldered or sintered onto the direct metallization layer to form a power electronics module. Multiple modules may be attached to cooling headers that provide in-flow and out-flow of coolant through the channels in the ceramic substrate. The modules and cooling header assembly are preferably sized to fit inside the core of a toroidal shaped capacitor.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority from and is related to U.S. Provisional Patent Application Ser. No. 61/037,129 filed Mar. 17, 2008, entitled DIRECT COOLED POWER ELECTRONICS SUBSTRATE. Patent Application Ser. No. 61/037,129 is incorporated by reference in its entirety herein. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention. 
     
    
     FIELD 
       [0003]    This invention relates to structures for transferring heat from power electronics devices. More particularly, this invention relates to a system for directly cooling an electrically insulating ceramic substrate to which the power electronics devices are attached. 
       BACKGROUND 
       [0004]    As depicted in  FIG. 1 , conventional cooling for power electronics is based on heat conduction through multiple layers that are in contact with a heat sink that convects the heat to the ambient. These layers typically consist of a silicon power device or “chip” that is soldered to a conventional Direct Metallization (DM) layer, usually copper. The DM layer is soldered to a copper base plate/heat spreader. The copper base plate/heat spreader is connected via a thermal interface material, such as thermal grease, to an aluminum heat sink. The typical conventional power inverter design is based on a two-dimensional layout where all the heat generating devices are located in a single plane. The heat transfers perpendicularly to this plane to the heat sink. 
         [0005]    This conventional serial heat flow path—from chip into solder layer into DM layer into solder layer into copper base plate/heat spreader layer into thermal interface layer and finally into heat sink—introduces significant thermal resistance. As the thermal resistance in the heat flow path increases, so does the size, weight, cost and manufacturing complexity of the heat sink to accommodate it. A more efficient structure for transferring heat from the power electronics chip is needed. 
       SUMMARY 
       [0006]    Typical embodiments described herein provide a solution to the aforementioned problem by eliminating the copper base plate/heat spreader, the thermal grease interface and the aluminum heat sink. While these embodiments render those components expendable, they involve a specific modification of a necessary subcomponent in any power electronic device—an electrically insulating ceramic. Typical embodiments further provide for directly cooling the DM layer by providing coolant flow channels in a ceramic substrate to which the DM layer is directly bonded. The power electronics chips, which may be insulated-gate bipolar transistor (IGBT) devices or diodes, as well as other types of devices such as MOSFETs, silicon carbide devices, etc., may be soldered or sintered onto the DM layer to form a power electronics module. Multiple modules may be packaged in cooling headers that provide in-flow and out-flow of coolant through the channels in the ceramic substrate. The power electronics modules and cooling header assembly are typically sized to fit inside the core of a toroidal shaped capacitor. 
         [0007]    Benefits provided by various embodiments of the subject invention include a reduction in the thermal resistance in the heat flow path and a corresponding reduction in the size of the heat sink. This results in a reduction in cost, mass and volume of the heat sink, which is a large portion of the volume of a power inverter. Some embodiments enable the use of 105° C. ethylene glycol/water coolant, such as may be obtained from a vehicle&#39;s cooling system to transfer heat from the power electronic devices as opposed to a separate 70° C. loop. In other embodiments, 85° C. transmission oil may be used as the coolant. The application of three-dimensional inverter packaging with direct substrate cooling generally enables an approximately 20% reduction in the volume of the heat sink and a more efficient design. A 10% reduction in power inverter volume may be realized by the elimination of the conventional heat exchanger. 
         [0008]    It is anticipated that various embodiments will have a significant beneficial impact on automotive manufacturers by reducing the cost, mass, and volume of power inverters in hybrid electric vehicles and plug-in electric vehicles. The use of 105° C. coolant and the removal of the 70° C. stand-alone cooling loop could result in manufacturer cost savings of approximately $175 per vehicle (in 2008 dollars). 
         [0009]    One preferred embodiment provides a power electronics module that is operable in conjunction with a cooling system. The power electronics module of this embodiment includes a substrate having a three-dimensional outer peripheral surface. The module includes a first end portion disposed at a first end of the substrate and a second end portion disposed at a second end of the substrate. The first and second end portions are operable to attach and seal to a coolant input header or a coolant output header of the cooling system. One or more coolant flow channels pass through the interior of the substrate and carry liquid coolant from the cooling system. A plurality of planar facets are disposed on the three-dimensional outer peripheral surface of the substrate and between the first and second end portions. At least one of the planar facets is disposed in a nonparallel relationship with another of the planar facets. A metal layer is disposed on one or more of the planar facets, and one or more power electronic devices are attached to the metal layer. 
         [0010]    In some embodiments, the coolant flow channels are disposed adjacent and spaced radially around the outer peripheral surface of the substrate. In some embodiments, the coolant flow channels are helical. In some embodiments, the coolant flow channels have an opening at the first end of the substrate for receiving the liquid coolant from the cooling system and an opening at the second end of the substrate for returning the liquid coolant to the cooling system. In some embodiments, the coolant flow channels have a first opening at the first end of the substrate for receiving the liquid coolant from the cooling system and a second opening at the first end of the substrate for returning the liquid coolant to the cooling system. Some embodiments of the coolant flow channels may include various hole patterns, hole shapes (e.g., oval cross-section, helical axis, etc.), or one or more holes filled with conduction enhancing metal foam inserts. 
         [0011]    Another preferred embodiment provides a power electronics assembly that includes a toroidal-shaped capacitor having an interior cavity, a cooling system disposed within the interior cavity of the toroidal-shaped capacitor, and a plurality of power electronics modules as described above disposed within the interior cavity of the toroidal-shaped capacitor. The cooling system includes a first header and a second header, with one end of the substrate of the power electronics modules connected to the first header and the second end of the substrate connected to the second header. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further advantages of various embodiments are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
           [0013]      FIG. 1  depicts a prior art structure for transferring heat from a power electronics device; 
           [0014]      FIG. 2  depicts a perspective view of a three-dimensional philosophy of a liquid-cooled electronics module according to a preferred embodiment; 
           [0015]      FIG. 3  depicts a perspective cutaway view of multiple liquid-cooled electronics modules attached to a cooling header within the core of a toroidal shaped capacitor according to a preferred embodiment; and 
           [0016]      FIG. 4  depicts a perspective view of a three-dimensional philosophy of a liquid-cooled electronics module according to a preferred embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 2  and  FIG. 4  depict a liquid-cooled power electronics module  10  according to a preferred embodiment. The module  10  includes a three-dimensional, electrically insulating ceramic substrate  12  having a first end portion  12   a  and a second end portion  12   d . A first faceted portion  12   b  and a second faceted portion  12   c  are disposed between the first and second end portions  12   a  and  12   d . Preferably, the first and second end portions  12   a  and  12   d  are circular in cross-section, and the first and second faceted portions  12   b  and  12   c  are polygonal (i.e. triangular, hexagonal, etc.) in cross-section. Although the substrate  12  is formed from ceramic in preferred embodiments, it may also be formed from other high thermal conductivity electrical insulators that have sufficient temperature capability and that are impervious to and environmentally compatible with liquid coolants. Passing through the substrate  12  are coolant-flow channels  14 . As discussed in more detail below, when the first and second end portions  12   a  and  12   d  of the substrate  12  are connected to coolant in-flow and out-flow headers, liquid coolant may be forced through the channels  14  to transfer heat away from the module  10 . 
         [0018]    The coolant channels  14  may be substantially straight, as shown in  FIG. 2  and  FIG. 4 , or they may be disposed in a helical or other curved configuration. In an alternative embodiment, the channels  14  form a loop through the substrate  12 , so that the coolant in-flow and out-flow headers may both attach at one end of the substrate  12  rather than at opposing ends. Another embodiment of the coolant channels may include raised, splined, or otherwise enhanced internal surfaces to improve heat transfer to the fluid. Another embodiment consists of coolant channels filled with metallic foam to enhance heat transfer into the coolant. 
         [0019]    In the preferred embodiment, the first faceted portion  12   b  of the substrate  12  has six rectangular faces  16 , and the second faceted portion  12   c  has six rectangular faces  18 . It will be appreciated that in alternative embodiments, the first and second faceted portions  12   b  and  12   c  of the substrate  12  may have other numbers of faces, such as eight or ten or twelve. For wire bonding purposes, the number of facets in the first portion  12   b  is preferably equal to the number of facets in the second portion  12   c , but this is not required. Thus, the invention is not limited to any particular number of faces on the first or second faceted portions  12   b  and  12   c.    
         [0020]    In the embodiment of  FIG. 2 , each of the faces  16  is covered by a Direct Metallization (DM) layer  20   a , and each of the faces  18  is covered by a DM layer  20   b . The layer  20   a  is preferably continuous around the faces  16  of the first faceted portion  12   b , and the layer  20   b  is preferably continuous around the faces  18  of the second faceted portion  12   c . In portion  12   b , the DM layer  20   a  is electrically connected to either a DC− supply on power connector tab  26   a  or a phase output connection. In the portion  12   c , the DM layer  20   b  is electrically connected to either a DC+ supply on power connector tab  26   b  or a phase output connection. Whether the tabs  26   a  and  26   b  are connected to a DC supply connection or to a phase output connection depends on whether the specific module is being used for an upper leg or lower leg in the inverter topology ( FIG. 3 ). In alternative embodiments, the DC voltage polarities applied to connector tabs  26   a  and  26   b  may be reversed. Power chips, diodes, and input/output tabs will be arranged so as to minimize stray inductance and adverse magnetic effects. 
         [0021]    Power electronics chips, which may include but are not limited to insulated-gate bipolar transistor (IGBF) devices  24  or diodes  22 , are typically soldered or sintered onto the DM layer  20   b  of the second faceted portion  12   c . During operation of the power electronics chips, heat is transferred from the chips through the DM layer  20   b , into the substrate  12  and into the coolant flowing through the channels  14 . In some embodiments, electronics devices may also be attached to the DM layer  20   a  of the first faceted portion  12   b.    
         [0022]      FIG. 3  depicts a preferred embodiment of a power electronics assembly  30  which includes multiple power electronics modules  10  disposed within a toroidal shaped capacitor  32 . For clarity of illustration, a portion of the capacitor  32  is cut away. The coolant channels of the modules  10  are in fluid communication with a first header  34  disposed adjacent an interior portion of the capacitor  32 . A second header is disposed adjacent to an opposing interior portion of the capacitor  32 . For clarity of illustration, the second header is not shown. However, one skilled in the art will appreciate that the second header may have the same or similar configuration as the first header  34 . Coolant is provided to or removed from the first header  34  via coolant ports  36 . 
         [0023]    As shown in  FIG. 3 , in the top row of modules  10 , the second end portion  12   d  of each substrate  12  is inserted into the header  34 . In the bottom row of modules  10 , the first end portion  12   a  of each substrate  12  is inserted into the header, which is not shown. The modules  10  are positioned so the power connector tabs  26   b  of the modules  10  in the top row are abutted against the power connector tabs  26   a  of the modules  10  in the bottom row to form phase out connections  38 . In a typical embodiment, the open tabs  26   a  in  FIG. 3  are electrically connected to form the DC− connection, and the open tabs  26   b  are connected likewise to DC+. The three tabs  38  would be separately and electrically connected to three phase outputs when functioning as a three phase inverter. 
         [0024]    In preferred embodiments, the coolant flowing from the first header  34  through the modules  10  is a 50/50 water/ethylene glycol (WEG) mixture. 
         [0025]    In one embodiment, the first end portion  12   a  of each module  10  is configured to attach and seal to a second end portion  12   d  of an adjacent module  10 . In this embodiment, the modules  10  may be “stacked” end-to-end so that coolant may flow from the coolant channels  14  of one module  10  into the coolant channels  14  of an adjacent module. 
         [0026]    The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.