Patent Publication Number: US-2022224206-A1

Title: Planar power module with high power density packaging

Description:
INTRODUCTION 
     The present disclosure relates to systems and methods for constructing a power module with condensed packaging and a relatively high power density, with an exemplary power module being a power inverter for use in converting a direct current (DC) voltage to an alternating current (AC) voltage, or vice versa, in a high-voltage electrical system. In an onboard electrical system of an electric vehicle, for instance, high-speed semiconductor switching and filtering operations are used to convert a DC input voltage, typically from a high-voltage propulsion battery pack and DC voltage bus, to an AC output voltage suitable for energizing stator field windings of the electric machine. In a bi-directional inverter embodiment, an AC input voltage from the electric machine, when operating as an electric generator, is similarly converted into a DC output voltage suitable for storage in electrochemical battery cells of the propulsion battery pack. 
     As understood in the art, a full-bridge inverter is a particular type of power module commonly used to perform the above-noted AC-to-DC and DC-to-AC conversion functions, with the inverter output precisely controlled using pulse width modulation (PWM) or another application-suitable switching control technique. Throughout the switching control process, individual semiconductor switches residing within the inverter change their respective ON/OFF conductive states at a high rate of speed. This switching operation, when sustained over time, generates substantial amounts of heat. Inverters are therefore typically cooled via circulation of coolant, such as through conductive plates or tubing, to help ensure that the inverter and its constituent semiconductor switches remain within allowable thermal limits. 
     SUMMARY 
     The present disclosure pertains to improved packaging solutions that enable construction of a full-bridge inverter as a planar power module having a high power density and flat/planar packaging, with the latter enabling double-sided cooling. The disclosed solutions may be applied as part of an integrated power conversion system, such as in the representative application of a traction power inverter module (TPIM) when used aboard a battery electric vehicle (BEV), a fuel cell vehicle, a hybrid electric vehicle (HEV), or another mobile electrified platform. As described herein, the generally planar structure of the disclosed power module and its optional internal cooling features, possibly aided by temperature sensing in the various embodiments, help to efficiently remove generated heat during ongoing operation of the power module. 
     That is, the planar construction described herein allows for double-sided direct cooling, e.g., by sandwiching the planar power module between external conductive cooling plates of a double-sided cooling system. Such direct cooling may be further optimized using internal coolant passages as described herein. Additionally, the packaging solutions reduce the overall footprint of the power module relative to state-of-the-art designs while providing improved thermal management. The disclosed circuit topologies and integral cooling and temperature sensing features likewise enable higher performance semiconductor switches to be used within the power module, e.g., wide band gap (WBG) devices, which further enables construction of power modules having the increased power density noted above. 
     According to an exemplary embodiment of the power module, which as noted above is usable with a double-sided direct cooling system, the power module includes parallel first and second substrates. The substrates have respective dielectric layers interposed between conductive layers. The power module also includes DC bus bars, AC bus bars, and a plurality of semiconductor switching dies. The respective switching dies, which contain one or more MOSFETs, IGBTs, thyristors, diodes, or other semiconductor switches, and are arranged between the substrates and electrically connected to the DC and AC bus bars. Each respective die is electrically connected to a conductive layer of the first or second substrate. 
     A suitable polymer molding material such as epoxy surrounds edges substrates and the semiconductor switching dies to form a dielectric support structure, leaving external surfaces of the conductive layers exposed as main surfaces of the power module. The power module is configured as a full-bridge inverter circuit in the described embodiments. 
     A first temperature sensor may be connected to an external conductive surface of the first substrate, while a second temperature sensor may be similarly connected to the external conductive surface of the first substrate or the second substrate. Other embodiments may include more temperature sensors as needed. The temperature sensors in some configurations include respective pairs of conductive, e.g., copper, meander resistor traces built on or etched onto the external surface(s). The meander resistor traces in such an embodiment are electrically connected to a respective pair of temperature sensing pins. 
     The respective external conductive surfaces of the first and second substrates are constructed in a non-limiting embodiment from direct bond copper (DBC), in which case the meander resistor traces are etched directly onto the DBC. 
     In some configurations, the power module defines internal coolant passages in proximity to the semiconductor switching dies, e.g., a network of coolant passages routed around or surrounding a perimeter of each of the various dies. In a non-limiting implementation, such coolant passages are formed or defined within the polymer molding material noted above, such that coolant passing through the coolant passages does not directly contact the semiconductor switching dies. In other embodiments, an electrical coolant may be used to enable direct contact with the semiconductor switching dies and the conductive layers, in which case the coolant passages may be open to the dies and conductive layers. 
     The internal coolant passages may have different diameters. The use of different diameters would help provide a more even flow rate of the coolant through the power module. 
     In an aspect of the disclosure, one or more of the semiconductor switching dies may optionally include multiple semiconductor dies arranged in parallel or series, with or without a diode, to form a single switch. 
     An electric powertrain system is also disclosed herein. In an exemplary embodiment, the electric powertrain system includes a polyphase rotary electric machine having phase windings and an output member, a battery pack, and a traction power inverter module (TPIM). The TPIM, which is connected to the battery pack and to the phase windings, includes the planar power module. In this particular embodiment, the planar power module is internally cooled and constructed as a three-phase, full-bridge inverter circuit. 
     Also disclosed herein is a motor vehicle having road wheels, a three-phase electric traction motor having phase windings and an output member coupled to at least one of the road wheels, a propulsion battery pack, and a TPIM. The TPIM is connected to the propulsion battery pack and to the phase windings, and includes a double-sided cooling system and a planar power module positioned therewithin, with the power module being constructed as the above-noted three-phase full-bridge inverter circuit. A polymer molding material of the power module, which surrounds the dies and the first and second substrates as described above, defines internal coolant passages in proximity to the semiconductor switching dies. 
     The above summary does not represent every embodiment or every aspect of this disclosure. Rather, the above features and advantages, and other features and attendant advantages of this disclosure, will be readily apparent from the following detailed description of illustrative examples and modes for carrying out the present disclosure when taken in connection with the accompanying drawings and the appended claims. Moreover, this disclosure expressly includes combinations and sub-combinations of the elements and features presented above and below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a representative electrical system having an internally cooled power module configured as a full-bridge inverter circuit and thus usable as part of a traction power inverter module (TPIM), with the power module constructed in accordance with the present disclosure. 
         FIG. 1A  is a schematic circuit topology of an exemplary three-phase inverter circuit usable as part of the TPIM within the electrical system shown in  FIG. 1 . 
         FIG. 2  is a schematic perspective view illustration of a representative power module constructed in accordance with the present disclosure. 
         FIG. 3  is a schematic plan view illustration of the power module shown in  FIG. 2 . 
         FIGS. 4A and 4B  are schematic cross-sectional illustrations of respective first/bottom and second/top substrates of the power module depicted in  FIGS. 2 and 3 . 
         FIGS. 5A, 5B, and 5C  are schematic cross-sectional side view illustrations of the power modules shown in  FIGS. 2-4B  in accordance with different embodiments. 
         FIG. 6  is a schematic cross-sectional plan view illustration of the power module with internal coolant passages in accordance with yet another embodiment. 
         FIG. 7  is a schematic illustration of a possible embodiment of a semiconductor switch implemented using more than one semiconductor switching die. 
         FIG. 8  is a perspective exploded view illustration of the power module described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is susceptible of embodiment in many different forms. Representative examples of the disclosure are shown in the drawings and described herein in detail as non-limiting examples of the disclosed principles. To that end, elements and limitations described in the Abstract, Introduction, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference, or otherwise. 
     For purposes of the present description, unless specifically disclaimed, use of the singular includes the plural and vice versa, the terms “and” and “or” shall be both conjunctive and disjunctive, “any” and “all” shall both mean “any and all”, and the words “including”, “containing”, “comprising”, “having”, and the like shall mean “including without limitation”. Moreover, words of approximation such as “about”, “almost”, “substantially”, “generally”, “approximately”, etc., may be used herein in the sense of “at, near, or nearly at”, or “within 0-5% of”, or “within acceptable manufacturing tolerances”, or logical combinations thereof. 
     Referring to  FIG. 1 , a motor vehicle  10  includes an electric powertrain system  11 , the latter of which is inclusive of a generally flat or planar power module  200 , which is internally cooled and constructed as a three-phase full-bridge inverter circuit in accordance with the present disclosure. While the motor vehicle  10  and the electric powertrain system  11  are representative of a type of electrified system in which the power module  200  may be used, the present teachings are not limited to mobile systems in general or to vehicular applications in particular. Rather, the power module  200  may be used in other electrical systems, whether mobile or stationary, in which compact/high power density packaging and direct double-sided cooling would be beneficial. Exemplary applications include, without limitation, watercraft, aircraft, robots, conveyor equipment, power stations, and the like. However, for illustrative consistency and solely for illustrating the present teachings, the power module  200  will be described below in the context of the motor vehicle  10 . 
     The electric powertrain system  11  contemplated herein includes at least one polyphase electric machine (M E )  14  having a stator  14 S and a rotor  14 R, the latter of which is coupled to an output member  17 . When the electric machine  14  is energized via a high-voltage direct current (DC) battery pack (B HV )  16  or another DC voltage supply, the electric machine  14  generates output torque (arrow T O ), which in turn is delivered to a coupled driven load via the output member  17 . In the representative vehicular embodiment of  FIG. 1 , for instance, such a driven load includes a set of road wheels  15  and one or more drive axles  19 . 
     When the electric machine  14  is configured as a polyphase/alternating current (AC) device as shown, energization of the electric machine  14 , or more precisely windings of the stator  14 S thereof, involves a carefully controlled high-speeding switching control of a traction power inverter module (TPIM)  20 . That is, during a typical DC-to-AC conversion process, a DC input voltage (VDC) is provided by the battery pack  16  to the TPIM  20 . Pulse-width modulation (PWM) or other high-speed switching operations of the TPIM  20  provided in response to switching control signals (arrow CC O ) from an onboard controller (C)  50  provides an AC output voltage (VAC) to the stator  14 S. In a bi-directional embodiment of the TPIM  20 , the reverse process is used to convert an AC voltage from the electric machine  14 , in this case an AC input voltage, to a DC output voltage for charging constituent battery cells (not shown) of the battery pack  16 . 
     With respect to the controller  50 , such a device or several networked computer devices include memory (M) and one or more processors (Pr). In response to input signals (arrow CC I ) from various sensors (not shown) and/or other electronic control units of the motor vehicle  10 , the controller  50  generates the switching control signals (arrow CC O ) noted above, among other possible control signals. That is, the controller  50  may receive inputs such as an operator&#39;s torque request, braking request, steering inputs, ambient and specific component temperatures, etc., and may thereafter determine appropriate drive parameters for powering the electric machine  14 . Although the controller  50  is depicted schematically as a unitary box in  FIG. 1  for illustrative clarity and simplicity, the controller  50  could include one or more networked devices each with a central processing unit or another processor (Pr) and sufficient amounts of memory (M), including a non-transitory (e.g., tangible) medium that participates in providing data/instructions that may be read by the processor (Pr). 
     Other components may be included in the construction of the electric powertrain system  11  of  FIG. 1 , including a DC-DC converter  18  and a low-voltage/auxiliary battery (B AUX )  160 . Thus, when 12-15V auxiliary voltage levels (V AUX ) are required aboard the motor vehicle  10 , with the battery pack  16  being a propulsion battery pack having a voltage capability of 300V or more in some configurations, such voltages may be provided via operation of the DC-DC converter  18 , as is well understood in the art. 
     With respect to the power module  200  possibly residing within the TPIM  20  in the illustrated configuration, this component is constructed as set forth herein to enable construction of a three-phase, full-bridge inverter with compact packaging, high power density, integral internal cooling features, and temperature sensing configurations. The stacked construction of the power module  200  in the various embodiments described herein has the effect of concentrating internally generated heat from switching operations into a smaller than typical volume. The double-sided planar configuration of the power module  200 , however, lends itself to direct double-sided cooling via a double-sided cooling system  300  as explained below. In general, a pump (P)  12  may be operated to circulate coolant  51  from a sump  13 , with the coolant  51  passing through the power module  200  in some embodiments, and/or through the double-sided cooling system  300  in other embodiments. The beneficial increase in power density, double-sided cooling, and other disclosed features collectively enable construction of higher performance components, and ultimately provides improved thermal management relative to existing circuit topologies. 
     Referring briefly to  FIG. 1A , the TPIM  20  includes a DC link capacitor (C DC )  21  and a plurality of semiconductor switching dies  22 . Nominally, the semiconductor switching dies  22  are arranged in top and bottom locations as set forth herein, with each phase of the polyphase/AC electric machine  14  shown in  FIG. 1  thus having a top/high/positive and bottom/low/negative switching pair. The electric machine  14  may be a three-phase device in a typical embodiment, in which case the TPIM  20  would include three phase legs. For each phase leg, with the semiconductor switching dies  22  labeled SW t1 , SW t2 , SW t3 , SW b1 , SW b2 , and SW b3  configured as exemplary MOSFETs shown, the high-side switches SW t1 , SW t2 , SW t3  and the low side switches SW b1 , SW b2 , and SW b3  are connected to the DC-side of the illustrated TPIM  20 , as appreciated in the art. The AC side in this particular arrangement is thus taken from the middle of the high-side and low-side switches SW t1 , SW t2 , SW t3 , SW b1 , SW b2 , and SW b3  as shown. While the non-limiting six-switch embodiment of  FIG. 1A  may be used to implement a three-phase full-bridge inverter as shown, it is also possible to implement the present teachings with a different number of semiconductor switching dies  22 , such as but not limited to a twelve-switch six-phase embodiment. 
     Referring to  FIG. 2 , an exemplary perspective view is provided of a possible embodiment of the power module  200  described herein. As noted above with reference to FIG.  1 A, the power module  200  contains the semiconductor switching dies  22  in a double-sided stack up, with such a circuit topology shown in  FIGS. 4A-8  and explained in detail below. In order to support such structure in a compact planar package as shown, the power module  200  includes an edge support structure  24  constructed of a thermally-conductive dielectric polymer material, such as an application suitable grade of plastic. The edge support structure  24  may be rectangular or square as shown, with its cage-like structure exposing opposing external conductive surfaces  41  and  141  and four lateral surfaces  26  extending therebetween. A periphery of the external conductive surfaces  41  and  141  may be perforated to include perimeter cooling passages (not shown) that are collectively configured to admit the coolant  51  of  FIG. 1  in some embodiments. 
     Protruding from the lateral surfaces  26  are conductive DC bus bars  28  (+, −) and conductive AC bus bars  30  nominally labeled U, V, and W. The DC bus bars  28  and the AC bus bars  30  may be constructed of copper, aluminum, or another suitable electrically conductive material. Also visible from the perspective of  FIG. 2 , gate control pins  32  are used to control the ON/OFF switching operation of the resident semiconductor switching dies  22  of  FIG. 2  located within the power module  200 , as appreciated in the art. Such gate control pins  32  are connected to the controller  50  of  FIG. 1 , via a gate driver (not shown), to enable voltage control signals to be transmitted to the gates of the individual semiconductor switching dies  22  when controlling a duty cycle thereof. 
     As shown in  FIG. 3 , embodiments of the power module  200  include one or more temperature sensors  34  configured to measure a corresponding temperature of the particular external conductive surface  41  or  141 . As the power module  200  is internally cooled, flow of coolant  51  may be controlled in a feedback loop using measured temperatures from such temperature sensors  34 . While the external conductive surface  41  is visible from the perspective of  FIG. 3 , similarly configured temperature sensors  34  may be arranged on the external conductive surface  141  located diametrically opposite the external conductive surface  41 . 
     As shown, the temperature sensors  34  may include a respective pair of conductive meander resistor traces  134 , e.g., copper traces, which may be etched on the external conductive surface  41  and  141 . Each one of the copper meander resistor traces  134  is electrically connected to a respective pair of temperature sensing pins  132  and coated with a dielectric material  35 . In a non-limiting exemplary embodiment, the external conductive surfaces  41  and  141  may be embodied as direct bond copper (DBC), with the copper meander resistor traces  134  possibly being etched onto the DBC, on either the outer or inner layers thereof relative to the location of the power module  20 . Internal construction of the power module  200  will now be described with reference to the remaining Figures. 
     THREE-PHASE FULL-BRIDGE INVERTER:  FIGS. 4A and 4B  respectively depict schematic plan view illustrations of a lower/bottom substate  40  and an upper/top substate  140  of the power module  200  shown in  FIGS. 2 and 3 . The illustrated topology enables construction of a representative three-phase full-bridge “6-in-1” power module  200 , in which six semiconductor switching dies  22  are electrically connected to the DC bus bars  28  and the AC bus bars  30 , with the bus bars  28  and  30  together providing a simplified five-terminal topology. 
     With respect to the lower/bottom substrate  40  of  FIG. 4A , the high/positive semiconductor switching dies  22  are labeled U-H, V-H, and W-H for the nominal U, V, and W phases. The low/negative semiconductor switching dies  22  are labeled U-L, V-L, and W-L for the same nominal U, V, and W electrical phases. The top substrate  140  of  FIG. 4B  is flipped relative to the orientation of the bottom substrate  40  of  FIG. 4A . In both Figures, the shaded background of certain semiconductor switching dies  22  indicates a source-side of the respective dies, while an unshaded background indicates a drain/collector side. That is, the dies  22  labeled U-H, VH and WH are oriented such that drain is facing up, while the dies  22  labeled UL, VL, WL have their sources facing up. 
     Internal cooling construction usable with the exemplary circuit topology of  FIGS. 4A and 4B  is shown in the cross-sectional illustrations of  FIGS. 5A-C , which depict the power module  200  as different planar circuit assemblies, i.e., power modules  200 ,  200 A, and  200 B. The embodiments of  FIGS. 5A-C  each include the bottom substrate  40  and the top substrate  140 . As “top” and “bottom” are relative terms, and the orientation of the power module  200  could change in different applications, the term top substrate  140  is hereinafter referred to as second substrate  140 , with the bottom substrate  40  hereinafter referred to as a first substrate  40 . 
     The second substrate  140  includes a second dielectric layer  142  interposed between a second pair of conductive layers, i.e., conductive layers  144 A and  144 B. An external conductive surface  141  of the second pair of conductive layers  144 A and  144 B forms a second external conductive surface of the power module  200 . The similarly constructed first substrate  40  has a first dielectric layer  42  interposed between a first pair of conductive layers, i.e., conductive layers  44 A and  44 B. An external conductive surface  41  of the power module first pair of conductive layers  44 A and  44 B is parallel to the second external conductive surface, i.e., external conductive surfaces  41  and  141  are parallel to each other. 
     The respective first and second substrates  40  and  140  each include respective lateral surfaces  45  and  145 . The second external conductive surface  141  and the first external conductive surface  41  are configured to be directly cooled by a double-sided cooling system  300 , as noted above. The semiconductor switching dies  22  of  FIGS. 4A and 4B , abbreviated “SEMI-COND” in  FIGS. 5A-5C , are arranged in a cavity  46  between the first substrate  40  and the second substrate  140 . Although not visible from the perspective of  FIGS. 5A-C , the gate control pins  32  of  FIGS. 4A and 4B  are electrically connected to each of the semiconductor switching dies  22 . Additionally, each of the semiconductor switching dies  22  is electrically connected to the conductive layers  44 B and  144 B. A polymer molding material  48  partially surrounds the lateral surfaces  45  and  145 , i.e., the edges of the power module  200 , and at least partially fills the cavity  46  as shown. A portion of the cavity  46  may remain open within the polymer molding material to define internal coolant passages  49  surrounding perimeter edges of the semiconductor switching dies  22  as set forth below, and as depicted in  FIGS. 5B, 5C, and 6 . 
     In a possible embodiment, the semiconductor switching dies  22  may be in the form of a bipolar transistor, an insulated-gate bipolar transistor (IGBT), a power metal-oxide-semiconductor field-effect transistor (MOSFET), a thyristor, a diode, or another suitable high-speed semiconductor switching device. The polymer molding material  48  may be constructed from an application-suitable polymeric dielectric material, e.g., an epoxy-based or silicone-based material. Connection of the semiconductor switching dies  22  may be made via die attachment materials  52 , possibly using conductive spacers  53  or a lead frame  54 , both of which are well understood in the art. 
     In some embodiments, the first and second substrates  40  and  140  may have a composite structure, e.g., a ceramic substrate sandwiched between and directly bonded to layers or sheets of copper or another electrically conductive metal. Such a metallized ceramic substrate may be in the form of a direct bonded copper (DBC) or a direct bonded aluminum (DBA) ceramic substrate, or active metal brazing (AMB). In either case, the ceramic substrate, i.e., dielectric layers  42  and  142 , may be made of a ceramic material such as aluminum-oxide (Al 2 O 3 ), aluminum-nitride (AlN), silicon nitride (Si 3 N 4 ), and/or beryllium oxide (BeO). In a DBC construction, the ceramic substrate is sandwiched between and directly bonded to layers or sheets of copper (Cu) and/or copper oxide (CuO). In DBA ceramic substrates, the ceramic substrate is sandwiched between and directly bonded to layers or sheets of aluminum (Al), as will be readily appreciated by those skilled in the art. 
     In addition to the internal cooling described in detail herein, cooling of the power module  200  shown in  FIG. 5A  may be accomplished from two sides via the double-sided cooling system  300 . Such direct two-sided cooling via the double-sided cooling system  300  may be used in conjunction within internal cooling in the alternative embodiments of  FIGS. 5B and 5C  to provide additional thermal regulation of the power module  200 . In such configurations, inserts or sacrificial materials may be used to construct internal coolant passages  49  within the polymer molding material  48 . Coolant  51  may be circulated via an external pump (not shown) through the internal coolant passages  49  to remove heat from the power module  200 . 
     The  FIG. 5B  embodiment, for example, surrounds a periphery of the cavity  46  (see  FIG. 5A ) and the semiconductor switching dies  22  with the polymer molding material  48  to ensure that the polymer molding material  48  is disposed between the coolant  51  and conductive surfaces of the power module  200 , thus allowing for different compositions of the coolant  51 . That is, the coolant  51  shown in the  FIG. 5B  embodiment is prevented from directly contacting the semiconductor switching dies  22  and the conductive layers  44 A,  44 B,  144 A, and  144 B, thus enabling use of dielectric coolants as well as conductive coolants.  FIG. 5C  in contrast places an electrical coolant  151  in direct contact with the semiconductor switching dies  22  and conductive layers  44 B and  144 B, thus necessitating the use of a dielectric/non-conductive type of coolant. 
     Referring briefly to  FIG. 6 , the power module  200  is shown from the same perspective as  FIG. 4A , i.e., as the first/bottom substrate  40 . The internal coolant passages  49  may be used within the polymer molding material  48  to allow the coolant  51  or  151  of  FIGS. 5B and 5C  to cool the semiconductor switching dies  22 , respectively, with the coolant  151  directly contacting the semiconductor switching dies  22  and other conductive structure. Coolant  51 , for instance, may be pumped into the internal coolant passages  49 , as indicated by arrow I, with the circulated coolant  51  picking up heat as the coolant  51  flows around the various semiconductor switching dies  22 . The heated coolant  51  then exits the power module  200  (arrow O), with heat thereafter removed from the coolant  51  via a heat exchanger (not shown) before being recirculated to the power module  200 . In the illustrated embodiment, the coolant inlet and outlet are located diametrically opposite the DC bus bars  28  to facilitate packaging, but can be placed or routed in other ways to improve cooling based on the particular application. 
     In a possible construction, the internal coolant passages  49  extending toward the gate control pins  32 , i.e., vertically from the perspective of  FIG. 6 , may be made with progressively larger diameters as one moves toward the DC bus bars  28 . For instance, the internal coolant passages  49  located in close proximity to the semiconductor switching dies  22  labeled W-H and W-L may be larger in diameter than the internal coolant passages  49  located in close proximity to the semiconductor switching dies  22  labeled U-H and U-L. Such a construction would help even the flow despite the different path lengths. Alternative constructions may use a larger supply and sink channel, as will be appreciated by those skilled in the art. 
     Referring briefly to  FIG. 7 , while the power module  200  is described above for simplicity as a representative six-switch device in which each switch includes is implanted as a single semiconductor switching die  22 , those skilled in the art will appreciate that other embodiments may be constructed using additional switches per semiconductor switching die  22 . For instance, a semiconductor switching die  122  as shown schematically in  FIG. 7  may be implemented as two semiconductor switches  22 A and  22 B, each having a MOSFET or IGBT, and possibly a diode D1. The alternative semiconductor switching die  122  may therefore include multiple semiconductor switches  22 A and  22 B arranged in parallel or series, with the latter possibly used to form other three phase topologies, such as a current source inverter which requires a MOSFET in series with a diode. Thus, each switch used to construct the power module  200  in its various embodiments may be implemented using a different type and/or number of the semiconductor switching dies  22  within the scope of the disclosure, with the semiconductor switching die  122  of  FIG. 7  being representative of a simplified two-switch configuration. 
       FIG. 8  depicts the power module  200  of the present disclosure according to a representative construction, with the first and second substrates  40  and  140  sandwiching the die attachment materials  52 , conductive spacers  53 , and semiconductor switching dies  22  therebetween. To construct the power module  200 , one may stack the semiconductor switching dies  22  with the die attachment materials  52  and then mount the semiconductor switching dies  22  with the conductive spacers  53 . The semiconductor switching dies  22  and the conductive spacers  53  are then attached to the first and second substrates  40  and  140 , with the first substrate  40  connected to the lead frame  54 . 
     At this point, sacrificial materials  60  may be applied with a predefined pattern, with various examples of the sacrificial materials  60  explained below. For simplicity, the sacrificial materials  60  are shown on one plane, but would fill voids or openings that are not otherwise filled by other structure or materials. The second substrate  140  is then attached. Thereafter, the polymer molding materials  48 , not shown in  FIG. 8  but depicted in  FIGS. 5A-5C , are applied to encapsulate the illustrated components of the power module  200 . The lead frame  54  is thereafter trimmed to form the DC bus bars  28  and the AC bus bars  30 , along with the gate control pins  32 . Thereafter, the sacrificial materials  60  are removed to form the internal coolant passages  49  of  FIG. 6 . 
     As part of a manufacturing method, the sacrificial materials  60  may be introduced by compression molding, vacuum forming, thermoforming, injection molding, blow molding, profile extrusion, or a combination of such techniques. In some embodiments, the sacrificial materials  60  may be introduced in the form of a liquid or relatively soft material and allowed to solidify or harden by cooling and/or by curing. The sacrificial materials  60  are of a type easily removed without harming the physical and/or structural integrity of the other components of the power module  200 . In some embodiments, the sacrificial material  60  may be a material that exhibits a solid phase at ambient temperature, but transitions to a liquid phase or a gas phase upon heating to a temperature less than 175° C. The sacrificial materials  60  additionally or alternatively may be a material that exhibits a solid phase at ambient temperature, but thermally decomposes (e.g., pyrolyzes or oxidizes) upon heating to a temperature greater than ambient temperature but less than 175° C. In other embodiments, the sacrificial materials  60  may be soluble in an aqueous medium (e.g., water) or a nonaqueous medium (e.g., acetone), or a material that can be dissolved by a chemical etchant (e.g., an acid such as hydrochloric acid, sulfuric acid, and/or nitric acid). 
     In terms of acceptable materials of construction, the sacrificial materials  60  may be embodied as polyethylene carbonate, polypropylene carbonate, polypropylene/cyclohexene carbonate, polycyclohexene carbonate, or polybutylene carbonate material in different non-limiting exemplary embodiments. Such materials are configured to depolymerize at relatively low temperatures, which could be further lowered by the addition of an appropriate catalyst, e.g., tetra(n-butyl) ammonium acetate or a photo-acid generator. Combustible compounds may also be used to construct the sacrificial materials  60 . 
     Regardless of the number and type of semiconductor switching dies  22  used to construct the power module  200  of the present disclosure, the present teachings enable double-sided direct cooling of a planar construction, e.g., of a full-bridge electrical topology using five terminals. Cooling may be enhanced using the internal coolant passages  49  described above and shown in  FIGS. 5B .  5 C, and  6 . Using the forgoing teachings, one may greatly increase the available power density of power electronics using power modules  200  constructed of a reduced size relative to competing technologies. These and other benefits will be readily appreciated by those skilled in the art in view of the forgoing disclosure. 
     The detailed description and the drawings or figures are supportive and descriptive of the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other embodiments for carrying out the present teachings have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims. Moreover, this disclosure expressly includes combinations and sub-combinations of the elements and features presented above and below.