Improved conductive heat sink retainer assembly

Abstract

A heat sink retainer assembly includes heat sinks installed with a bracket, with the bracket attached to a lower tray. Semiconductor switches are received and retained in the lower tray, and the heat sinks are brought into contact with the semiconductor switches. The lower tray includes bumpers that bias the semiconductors into contact with a lower surface of the heat sink, such that a conductive pad of the semiconductor switch is in contact with the heat sink to improve thermal conductivity. A printed circuit board is attached to the lower tray, and pins from the switches project downward through the tray and are attached to the PCB. The heat sink retainer assembly may be inserted into an opening of a motor housing in a sealed manner to expose an upper face of the heat sinks to the internal cavity of the housing.

Description

Attorney Docket No. 25065-2220 (713583PCT)IMPROVED CONDUCTIVE HEAT SINK RETAINER ASSEMBLYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 714,197, filed October 31, 2024, the entire content of which is hereby incorporated by reference in its entirety.FIELD

[0002] The present disclosure is generally related to the design and method of assembly for a heat sink retainer assembly with an integrated preloading device acting against a semiconductor switch in conjunction with a thermal interface material to increase potential thermal conductivity between the semiconductor switch and heat sink. The heat sink retainer assembly further provides electrical isolation between adjacent heat sinks and mounting structures for connecting the heat sink retainer to surrounding components. The heat sink is designed to have an increased heat storage capability that is passively cooled in intervals dependent on the operation of an electrically driven gearbox.BACKGROUND

[0003] This section provides background information related to the present disclosure which is not necessarily prior art.

[0004] A power converter is utilized to convert one type of current, which can be direct current or alternating current, into the other. In this respect, the power converter is differentiated according to the type of conversion - that is, an input and an output current type: rectifiers convert an alternating current into a direct current, inverters convert a direct current into an alternatingAttorney Docket No. 25065-2220 (713583PCT) current, and converters convert an alternating current into an alternating current with a different frequency and / or amplitude. A method known from practice for this purpose includes a clocked control of at least one power module, which typically has an arrangement of semiconductor switches (MOSFETs, IGBTs, etc.) to control current provided to electric machines. When the semiconductor switches are clocked, the resulting switching and conduction losses generate waste heat as power loss, which must be dissipated away from the semiconductor switches to protect them and ensure the fault-free functioning, otherwise it may be damaged or destroyed. Heat sinks intended for transferring the waste heat are fixed directly to the semiconductor, so that the waste heat can effectively pass from the semiconductor into the heat sink and provide a way to keep the semiconductor switch operating at an acceptable temperature. A further ethylene glycol-based inverter coolant cooling system is often used in conjunction with the heat sinks to remove the waste heat from the system.SUMMARY

[0005] In view of the above, a power converter for converting one type of current into another, having at least one semiconductor mated to at least one heat sink, wherein the semiconductor switches and the heat sink are in a thermally operative connection with one another is provided for improved functionality. A heat sink retainer assembly is utilized with an integrated bumper which provides a preload to a semiconductor in conjunction with a thermal interface material to ensure increased thermal conductivity between the non-isolated semiconductor switch and heat sink. Because the invention is utilized where the heat sink is sized to function as a heat block or heat capacitor absorbing heat transferred from the semiconductor over a given duty cycle, and then releasing waste heat based on intermittent exposure to oil within an electric drive module,Attorney Docket No. 25065-2220 (713583PCT) it is important to improve the heat transfer into the heat sink as much as possible. The heat sink retainer assembly provides features for mounting to a printed circuit board of the power converter on a first side, and a sealed connection to the housing that encloses the cooling oil on a second side, and is further housed within the power converter. The heat sink retainer assembly may be used in a non-isolated discrete power module where the heat sink retainer assembly ensures heat sinks to be electrically isolated from one another.

[0006] It is an aspect of the present disclosure to provide a heat sink retainer assembly with an integrated preloading device acting against a semiconductor switch in conjunction with a thermal interface material to increase potential thermal conductivity between the semiconductor switch and heat sink

[0007] It is an aspect of the present disclosure to provide a heat sink retainer assembly which provides electrical isolation between adjacent heat sinks and provides mounting structures for connecting the heat sink retainer to surrounding components, which may include a printed circuit board and a gearbox housing

[0008] It is an aspect of the present disclosure for the heat sink retainer assembly to provide increased heat storage capability that is passively cooled in intervals dependent on the operation of an electrically driven gearbox.

[0009] These and other features and advantages of the present disclosure will become more readily appreciated when considered in connection with the following detailed description and drawings.Attorney Docket No. 25065-2220 (713583PCT)BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings described herein are for illustrative purposes only of selected embodiments and are not intended to limit the scope of the present disclosure. The inventive concepts associated with the present disclosure will be more readily understood by reference to the following description in combination with the accompanying drawings wherein:

[0011] FIG. 1 illustrates an electrically driven gearbox according to the present disclosure;

[0012] FIG. 2 is a cross-sectional view of a heat sink assembly;

[0013] FIG. 3 is a detailed cross-sectional view of a portion of the heat sink assembly;

[0014] FIG 4. is an perspective view of the heat sink assembly bracket;

[0015] FIG 5. is a view of the heat sink assembly lower tray including integrated bumpers;

[0016] FIG. 6 is an exploded view of the heat sink assembly; and

[0017] FIG. 7 is a perspective view of the heat sink assembly.DETAILED DESCRIPTION

[0018] Referring to FIG. 1, an electrically driven gearbox 10 is shown where heat sink assembly 12 may be utilized. Such an electrically driven gearbox 10 may be utilized as the prime mover in a vehicle. This gearbox 10 includes an electric motor 14 providing input power to a motor drive gear 16. Electric motor 14 is provided power delivered by power converter 18 via electrical connection 20. Motor drive gear 16 is in meshed engagement with a driven gear 22, which drives at least one output 23, which may be connected to a driven wheel of a vehicle. Driven gear 22 is enclosed by housing 24. Electric motor 14 and power converter 18 are both mounted to or within housing 24. Heat sink assembly 12 mostly resides within power converter 18. An extending portionAttorney Docket No. 25065-2220 (713583PCT)26 of heat sink assembly 12 extends out of power converter 18, into an opening 19 formed in housing 24. The extending portion 26 is disposed in an internal volume 28 of housing 24.

[0019] The extending portion 26 of heat sink assembly 12 that extends into internal volume 28 includes an exposed heat sink face 30. When the semiconductor switches 32 of power converter 18 are clocked or operated, the resulting switching and conduction losses generate waste heat as power loss within switch 32. This heat must be dissipated away from the semiconductor switches 32 to protect them and ensure the fault-free functioning without damage. Heat sinks 38 within heat sink assembly 12 are utilized to transfer the waste heat away from semiconductor 32 based on a conductive contact between heat sink 38 and switch 32. With the improvements described herein, waste heat within heat sink assembly 12 is effectively passed from the semiconductor 32 into the heat sinks 38 to keep the semiconductor switches 32 operating at an acceptable temperature.

[0020] A volume of lubricant, such as oil 34, is provided within housing 24 and internal volume 28, reaching a level that results in a portion of driven gear 22 being in contact with the oil 34. As electric motor 14 rotates, based on the commands of power converter 18, driven gear 22 passes through the volume of oil 34, resulting in a portion of clung oil 34A on driven gear 22. The clung oil 34a on driven gear 22 is flung from driven gear 22 due to centrifugal force as driven gear 22 rotates, resulting in a delivered oil 34B being directed toward and contacting the exposed portion of heat sink face 30. This delivery of oil to the heat sinks 38 results in heat transfer from the heat sinks 38 of heat sink assembly 12 into returned oil 34C. Returned oil 34C then returns to join remaining oil 34 in the bottom portion of internal volume 28. The motion of the oil 34 around driven gear 22 to cool heat sinks 38 within heat sink assembly 12 continues while driven gear 22 rotates, either by being driven by electric motor 14 (via drive gear 16) or from external rotational motion of the output shafts of gearbox 10. It is important to note there may be operationalAttorney Docket No. 25065-2220 (713583PCT) conditions where electric motor 14 will be excited by the power converter 18 with minimal rotational movement yet high-power requests resulting in heat generation within power converter 18 and the inability to cool heat sink assembly 12 with oil 34 as oil 34 cannot be delivered by a slowly rotating driven gear 22 as previously described. Improvements to this thermal transmitting connection between semiconductor switch 32 and heat sink 38 is provided by heat sink assembly 12. These improvements, in combination with a high level of heat storage by heat sink 38 and passive heat sink cooling via a delivered oil 34B to heat sink face 30, will be further described.

[0021] Referring to FIGS. 2 and 3, cross-sectional views of heat sink assembly 12 are provided. Heat sink assembly is shown in an orientation with the extending portion 26 facing upwards in the view. Housing 24 includes a housing mounting flange 40 which surrounds opening 19. The extending portion 26 can be seen extending into internal volume 28, while the remaining portion of heat sink assembly 12 is housed in the power converter 18. Heat sink assembly 12 provides several main functionalities. Heat sink assembly 12 ensures each heat sink 38 is held in tight contact with semiconductor switch 32 to provide increased thermal conductivity between the semiconductor 32 copper thermal pad 102 and heat sink 38. Heat sink assembly 12 also provides oil tight sealing to housing 24 via flange 40, as well as preventing the oil cooling medium 34 to seep between the heat sink 38 and walls 42 of bracket 44, which could damage the components within the power converter 18. Heat sink assembly 12 includes two sets of mounting features, with a first attaching the bracket 44 to housing flange 40, and a second fixing PCB 46 to the bracket 44 with lower tray 47 captured in between.

[0022] Heat sink assembly 12 also ensures electrical isolation between each adjacent heat sink 38, because the heat sink 38 is not electrically isolated from its respective semiconductorAttorney Docket No. 25065-2220 (713583PCT) switches 32. Each heat sink 38 must be isolated with a non-conductive material ensuring each heat sink 38 is separated from any surrounding heat sinks 38 a sufficient distance to prevent arcing.

[0023] Heat sink assembly 12 is a multi-part assembly including two primary structural components surrounding a plurality of individual heat sinks 38. In this non-limiting example, six separate heat sinks 38 are provided with twelve semiconductor switches 32. Each heat sink 38 in this example is in contact with a pair of semiconductor switches 32 controlling either the high side or low side power for each of the three phases of electric motor 14, but a single semiconductor 32 may also be used depending on power requirements. For instance, a single heat sink 38 may be provided for at least one semiconductor switch 32 for controlling a high side “U” phase and a second single heat sink 38 is provided to be in contact with at least one semiconductor switch 32 for controlling a low side “U” phase.

[0024] The first primary structural component is lower tray 47. Lower tray 47 may be an injection molded plastic component. Lower tray 47 material should provide a stiff structure and be electrically non-conductive. Lower tray 47 includes a primary bottom portion 48 including pockets 50 to receive and locate semiconductor switches 32 relative to the lower tray 47. The pocket 50 is defined by a lower surface 52 and surrounding walls 54. A bumper 56 is provided in the bottom portion of pocket 50. Bumper 56 may be made of a compliant material such as rubber and may be formed into the lower tray 47 during the creation of the component if made via injection molding to reduce overall part count and assembly. Bumper 56 extends upward from the lower surface 52 and may be located in the center portion of pocket 50. Bumper 56 provides a force to semiconductor switch 32 from the bottom surface 52 of pocket 50, towards heat sink 38 when assembled. A singular semiconductor switch 32 is positioned in pocket 50 with at least oneAttorney Docket No. 25065-2220 (713583PCT) connector pin 58 directed downwards towards and through an opening or adjacent space in lower tray 47, towards PCB 46.

[0025] The second primary structural component of heat sink assembly 12 is bracket 44. Bracket 44 may also be injection molded of a non-conductive stiff material such as injection molded plastic. Bracket 44 includes two arrangements of boss features 60 and 62. The first boss feature 60 is provided on the upper portion. First boss feature 60 is utilized to attach heat sink assembly 12 to housing 24 with a plurality of fasteners 64. Second boss feature 62 (FIG. 4) is utilized to attach heat sink assembly 12 to a printed circuit board (PCB) 46. PCB 46 includes electrical connections and traces which join the connector pins 58 of semiconductor switch 32 extending from the primary bottom portion 48 of lower tray 47. A permanent soldered connection between semiconductor 32 connector pins 58 and PCB 46 may be provided. PCB 46 may be further mounted within power converter 18. Boss features 60 and 62 are best seen in FIG. 4.

[0026] Bracket 44 further includes features to fully surround the sides 66 of the internally positioned heat sink 38. Heat sink 38 may be rectangular in shape with a bottom face 68, four side faces 66, and surrounding a shoulder portion 67, providing a lateral sealing face 70 and a perpendicularly extending face 72 (facing upward in FIG. 3 at the shoulder 67). Bracket 44 is arranged such that when heat sink 38 is installed, heat sink face 30 extends out from the body of bracket 44. Heat sink 38 is not captured or surrounded on its bottom face 68 by bracket 44. Bracket walls 42 are provided as a solid surface when positioned between pairs of heat sink 38. As can be better seen in FIG. 4, walls 42 are shown separating pockets 74, which receive each heat sink 38. Walls 42 or corner structures 76 and edge 78 define a heat sink pocket 74. At the end portions of the heat sink assembly 12, where there is not an adjacent heat sink 38, the solid wall feature may be excluded, and only corner structure 76 of bracket 44 may be provided, such that the heat sinksAttorney Docket No. 25065-2220 (713583PCT)38 at the ends are exposed. In FIG. 7, exposed faces 80 of heat sink 38, internal to power converter 18, can be seen where only corner structures 76 surround the heat sink 38.

[0027] As seen in FIGS. 3 and 4, each heat sink 38 will interface with a heat sink sealing element 82, which in this non-limiting case is shown as an O-ring disposed in a receiving grove 84 (FIG. 3) of bracket 44. Heat sink sealing element 82 seals against the entire circumference of lateral sealing face 70 of heat sink 38. Sealing element 82 prevents oil 34 from seeping between the bracket 44 and each heat sink 38. An additional bracket sealing element 86 is provided between bracket 44 and flange 40. Bracket sealing element 86 is shown as an O-ring. A receiving groove 88 on the outer surface 90 of bracket 44 is provided to receive bracket sealing element 86 which seals circumferentially against inward face 92 of flange opening 19. Bracket sealing element 86 prevents oil 34 from seeping into power converter 18 between bracket 44 and housing 24.

[0028] FIG. 5 provides a view of bottom tray 47 better illustrating the pocket features 50 and bumpers 56. Pockets 50 are configured to surround semiconductor switch 32 on three sides with raised pocket walls 54 extending from tray bottom 48. A cutout 94 is provided to engage a similarly shaped tab feature of semiconductor 32 on pocket wall 54A. Pocket wall 54B and 54C further form the pocket and surround semiconductor 32 to provide additional electrical isolation to surrounding components. Openings 96 allow passage of connector pins 58 of the semiconductor 32 to connection with PCB 46. Locating tabs 98 are provided on each side of lower tray 47 to provide alignment with bracket 44 during assembly.

[0029] Referring back to FIG. 3, additional detail is shown, focusing on a single heat sink 38 and semiconductor switch 32 arranged in heat sink assembly 12. The semiconductor switch 32 includes a body 100 with a copper thermal pad 102 on the upper surface of the switch 32. An example of this semiconductor switch 32 available on the market is a TO-267 package. The copperAttorney Docket No. 25065-2220 (713583PCT) thermal pad 102 is used to conduct heat via contact with a surrounding component, in this case heat sink 38. The copper thermal pad 102 may also be electrically conductive as it provides for a connection to the collector of the semiconductor switch 32. As the semiconductor 32 rejects its heat via the thermal pad 102, it is important that heat sink 38 is in contact with as much surface area as possible for the highest amount of conductive heat transfer.

[0030] To aid in the heat transfer a TIM or Thermal Interface Material 104 is provided between the copper thermal pad 102 and the bottom face 68 of heat sink 38. Bottom face 68 may be a surface that is not specifically machined or held to a tight tolerance. A machined channel 106 may be included on the bottom face 68 of heat sink 38 to ensure a proper thickness of TIM 104 will be maintained between copper thermal pad 102 and the bottom face 68 of heat sink 38. The machined channels 106 in the bottom of the heat sink 38 are machined to a specific depth, so that when the semiconductor body 100 presses against the non-machined bottom surface 68 of heat sink 38, the gap between semiconductor switch 32 copper thermal pad 102 top surface 110 and heat sink channel 106 is properly spaced to provide the optimal thickness of TIM 104. This optimizes the effectiveness of heat sink assembly 12. Bumper 56 can be better seen providing a force to the bottom side 52 of semiconductor switch 32 towards heat sink 38 when assembled. A datum bond line 108 defines a thickness within heat sink assembly between the upper surface 105 of channel 106 (on the bottom side 68 of heat sink 38) relative to the top surface 110 of thermal pad 102. The theoretical bond line 108 is an important thickness to maintain in the overall assembly, because it ensures the optimal thickness of TIM 104 applied in channel 106 is maintained once fully assembled and the highest possible conductivity between the semiconductor 32 and heat sink 38. Because there are tolerances from part to part in the assembly stack up between bracket 44, heat sink 38, lower tray 47, and semiconductor 32, the bumper 56 is dimensioned andAttorney Docket No. 25065-2220 (713583PCT) utilized to ensure that, under all tolerance conditions, acceptable contact will occur between the top surface 110 of semiconductor body 100 and bottom surface 68 of heat sink 38 to maintain a proper bond line 108.

[0031] Referring to FIG. 6, the assembly process and stackup for heat sink assembly 12 is illustrated. Lower tray 47 receives a plurality of semiconductors 32 in pockets 50, where each semiconductor 32 is placed in contact with bumpers 56. Once all semiconductors 32 are positioned in lower tray 47, tray 47 is brought into position above PCB 46, resulting in connector pins 58 of semiconductors 32 being aligned and received in connector openings of PCB 46. An assembly fixture ensures lower tray 47, semiconductors 32, and PCB 46 are positioned correctly and tightly together, by applying pressure against all semiconductors 32 to compress bumpers 56 to a controlled height equivalent to bond line 108. When components of this assembled bottom tray assembly 112 are appropriately positioned, connector pins 58 may be soldered to PCB 46. The assembly fixture may be released, and bottom tray assembly 112 may be set aside. This result in semiconductor switch 32 being forced slightly upward, above theoretical bond line 108, by bumpers 56 because they are no longer compressed by the fixture.

[0032] Continuing to refer to FIG. 6, each heat sink 38 is installed into bracket 44. Bracket 44 includes heat sink sealing element 82 and bracket sealing element 86 previously installed. Bracket 44 may also include threaded mounting inserts 114 and compression stop 116 installed or overmolded into bosses 60 and 62. As each heat sink 38 is installed into cavity 78, the tight interference contact between heat sink 38 and heat sink sealing element 82 will hold heat sink 38 in the bracket 44 as shoulder 67 of heat sink 38 is brought into contact with bracket 44. Once all heat sinks 38 are installed into bracket 44, forming bracket assembly 118, TIM 104 may be applied to the bottom surfaces 68 of heat sink 38 in channel 106 of each heat sink 38. Bracket assemblyAttorney Docket No. 25065-2220 (713583PCT)118 may then be installed into the bottom tray assembly 112 that was set aside, where locating tabs 98 help to align the assemblies 112 and 118 together to form heat sink assembly 12. Heat sink assembly 12 may be fixed to PCB 46 via fasteners 120 threaded into inserts 114. Tightening fasteners 120 into boss 62 with threaded insert 114 will result in pulling bracket assembly 118 tightly in contact with bottom tray assembly 112, resulting in each heat sink 38 pushing semiconductor 32 downward slightly and level into pocket 50 while compressing bumpers 56, which will in turn bias semiconductor 32 upwards into contact with heat sink 38 and the TIM 104. The heat sink assembly 12 and PCB 46 may then be further installed into power converter 18 via fasteners 122 inserted through boss 60 into flange 40, thereby closing off the opening 19, and providing a seal via housing assembly seal 86.

[0033] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of disclosure.

Claims

Attorney Docket No. 25065-2220 (713583PCT)CLAIMSWhat is claimed:

1. A heat sink retainer assembly, comprising: at least one heat sink; a bracket, wherein the bracket receives and locates the at least one heat sink; a lower tray attached to the bracket; at least one semiconductor switch having a conductive pad; wherein the lower tray receives and locates the at least one semiconductor; wherein the bracket is attached to the lower tray and positions the heat sink adjacent to the at least one semiconductor switch; a bumper attached to the lower tray between the lower tray and the at least one semiconductor switch; wherein the bumper applies a pressure against the at least one semiconductor switch such that the semiconductor switch contacts the heat sink to improve thermal conductivity between the semiconductor and the heat sink.

2. The heat sink retainer assembly of claim 1, wherein the bumper is integral with the lower tray such that the lower tray and the bumper are one piece.

3. The heat sink retainer assembly of claim 1, wherein for each heat sink, a pair of semiconductor switches contact the heat sink.Attorney Docket No. 25065-2220 (713583PCT)4. The heat sink retainer assembly of claim 1, wherein each of the heat sinks are electrically isolated from each other.

5. The heat sink retainer assembly of claim 4, wherein the bracket and the lower tray are non- conductive, wherein the bracket includes at least one wall portion disposed between adjacent ones of the plurality of the heat sinks and provides electrical isolation therebetween.

6. The heat sink retainer assembly of claim 1, wherein each of the heat sinks extend beyond an outermost surface of the bracket.

7. The heat sink retainer assembly of claim 6, wherein a sealing ring is disposed circumferentially around the heatsink and is disposed between the heatsink and the bracket such that lubricant is blocked from passing between the heatsink and the bracket.

8. The heat sink retainer assembly of claim 1, wherein the tray includes a plurality of pockets defined by one or more walls projecting from a lower surface of the tray, wherein the bumper is disposed on the lower surface within the pocket.

9. The heat sink retainer assembly of claim 8, wherein the semiconductor is disposed within the pocket and located by the walls of the pocket.

10. The heat sink retainer assembly of claim 9, wherein the semiconductor projects beyond the walls of the pocket when the bumper is in an uncompressed state.Attorney Docket No. 25065-2220 (713583PCT)11 . The heat sink retainer assembly of claim 1 , wherein the heat sink includes a channel formed in a bottom surface of the heat sink.

12. The heat sink retainer assembly of claim 11, wherein the channel is disposed directly adjacent the conductive pad of the semiconductor13. The heat sink retainer assembly of claim 12, wherein a thermal interface material (TIM) is disposed within the channel between the heat sink and the conductive pad of the semiconductor.

14. The heat sink retainer assembly of claim 1, wherein a printed circuit board (PCB) is attached to the lower tray on an opposite side of the tray than the semiconductors, wherein pins of the semiconductors project through the tray into electrical contact with the PCB.

15. The heat sink retainer assembly of claim 1, wherein the heat sinks each include a shoulder, wherein the bracket includes a plurality of openings defined by a surrounding edge, through which an upper face of the heat sink extends, wherein the shoulder of the heat sink is held in place against the edge.

16. The heat sink retainer assembly of claim 1, wherein the heat sink retainer assembly is mounted to a housing of an electrically driven gearbox, wherein an exposed face of the heat sink retainer assembly is exposed to an internal volume of the housing, wherein oil within the gearbox contacts the exposed face of the heat sink retainer assembly.Attorney Docket No. 25065-2220 (713583PCT)17. The heat sink retainer assembly of claim 16, wherein the housing includes defines an opening, wherein the bracket is attached to the opening, wherein an assembly sealing ring extends between the bracket and a flange portion of the housing that defines the opening, wherein a heat sink seal is disposed between each of the heat sinks and the bracket, such that the flange, assembly sealing ring, bracket, heat sink sealing ring, and exposed faces of the heat sinks combine to seal across the opening and block oil within the gearbox from entering the heat sink retainer assembly.

18. A method of assembling the heat sink retainer assembly of claim 1, the method comprising: disposed the semiconductors to the lower tray and retaining the semiconductors against the bumpers; positioning the semiconductors and the lower tray on the PCB and securing the PCB to the tray; defining a bottom tray assembly having the semiconductors, the lower tray, and the PCB secured together; inserting the heat sinks into the bracket and retaining the heat sinks on the bracket; defining a bracket assembly having the heat sinks and the bracket secured together; attaching the bracket assembly to the bottom tray assembly, wherein the heat sinks press against the semiconductors and the bumpers are compressed, such that the semiconductors are biased into contact with the heat sinks.Attorney Docket No. 25065-2220 (713583PCT)19. The method of claim 18, wherein, for each heat sink, a thermal interface material is applied to a channel formed in the bottom surface of the heat sink prior to attaching the bracket assembly to the bottom tray assembly, wherein the thermal interface material contacts the copper pad of the semiconductor following the bracket assembly being attached to the bottom tray assembly.

20. The method of claim 18, further comprising inserting the heat sink assembly into an opening formed in a housing of an electrically driven motor and sealing the opening, such than an exposed face of the heat sink assembly is exposed to internal cavity of the housing.

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