Abstract:
A power module for a motor in which the module is arranged to house both the high power devices needed to drive the phase windings of the motor and the control electronics needed to control the operation of the high power devices. The components are arranged such that the thermal energy generated by the high power devices is directed away from the control electronics for subsequent dissipation. An insulated metal substrate is used as the base of the module for directing the thermal energy. Further, the module components can be easily assembled through the use of solderless resilient connections from the control electronics to the other components in the module. The module employs a base, a power shell coupled to the base, and a circuit board positioned within the internal chamber of the power shell. The power shell has a plurality of walls forming an internal chamber and at least one conductive region. At least one electronic device is mounted to the conductive region.

Description:
This is a division of application Ser. No. 09/375,716, filed Aug. 17, 1999. 
     This application is based on, and claims priority to, U.S. Provisional Application No. 60/097,637. filed Aug. 24, 1998, entitled POWER MODULE, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to power modules and, more specifically, to an integrated power package for motor control utilizing internal terminals for heat dissipation. 
     Power modules employing semiconductor devices are used in many different applications. One popular use for power modules is for driving and controlling motors. These power modules often use field effect transistors (FETs), particularly power metal oxide FETs (MOSFETs) to supply power to drive the motor based on signals received from a low power control circuit. While FETs are capable of switching the high currents needed to drive a powerful motor such as might be found in an automotive power steering mechanism, they also generate a significant amount of thermal energy when switching these large currents. 
     Large heat sinks are often used to dissipate the thermal energy generated by the FETs. This leads to large module package sizes and complicated semiconductor mounting arrangements. Also, locating the sensitive low power control circuitry close to the power semiconductors can reduce the reliability of the module and effect its operation due to the damaging thermal energy radiated by the FETs. 
     These module packaging requirements can be particularly onerous in automotive applications where the power module must be small and be co-located with the motor being driven. For example, a power steering electric motor driver module is optimally mounted directly to the mechanical power steering components it is driving. The presence of large heat sinks or extensive wiring and cabling between the power semiconductors and the module control circuitry is undesired as it prevents an efficient use of power semiconductor devices to control an electric motor. 
     SUMMARY OF THE INVENTION 
     The present invention provides a power semiconductor module that is compact, capable of driving high torque electric motors including switched reluctance motors and has the control circuit integrated within the module. The power, ground and motor terminals extend through the shell of the module such that the high power devices are mounted directly thereto. High power devices are interconnected without the use of wires or cables. 
     The power module of the present invention is arranged to direct thermal energy away from the control electronics such that thermal energy generated by the high power devices is transferred to a metallic substrate base, thereby providing a reliable module which is also compact such that is can be mounted proximate to the motor it is controlling. 
     The present invention provides an electronic module in which there is a base and a power shell coupled to the base. The power shell has a plurality of walls forming an internal chamber and at least one conductive region. At least one electronic device is mounted to at least one conductive region. A circuit board is positioned within the internal chamber of the power shell. 
     The present invention further provides an insulated metal substrate plate for an electronic module, in which the plate has a thermally conductive metallic substrate. A first insulating layer is affixed to the metal substrate in which the first insulating layer substantially covers the metal substrate. At least two conductive regions are affixed to the insulating layer, the at least two conductive regions being etched to form a plurality of discrete regions. A second insulating layer is disposed between the at least two conductive regions, and a solder mask is disposed on the at least one conductive region. 
    
    
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an assembled power module of the present invention; 
     FIG. 2 is a front side view of an assembled power module of the present invention; 
     FIG. 3 is a lateral side view of an assembled power module of the present invention; 
     FIG. 4 is an exploded perspective view of the assembled power module shown in FIGS. 1-3; 
     FIG. 5 is a bottom view of a power shell used in a power module of the present invention; 
     FIG. 6 is a top view of a power shell used in a power module of the present invention; 
     FIG. 7 is a top view of a base plate used in a power module of the present invention; 
     FIG. 8 is a section view of a portion of the base plate shown in FIG. 7; 
     FIG. 9 is a perspective view of a power module of the present invention showing a base plate, power shell and high power devices mounted to the power shell; 
     FIG. 10 is a circuit diagram showing a high power circuit for a 4-phase switched reluctance motor convertor using the components shown in FIG.  9 . 
    
    
     For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentality shown. 
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the Figures in which like reference numerals refer to like elements, FIGS. 1,  2  and  3  show a perspective view, a front side view and a lateral side view, respectively, of an assembled module  2  of the present invention. Power module  2  is comprised of three main sub-components, namely, power shell  4 , base plate  6  and circuit board  8 . As shown, power shell  4  is mounted on base plate  6 , and circuit board  8  is fit into the cavity in power shell  4 . Each of these subcomponents are discussed in detail below. 
     In a preferred embodiment, power module  2  is used in an electrically powered automotive steering application in which the electrical components form a 4-phased switched reluctance motor convertor. Accordingly, semiconductor components, such as power MOSFETs, are employed to convert an input source of DC power into suitable AC output power to drive the motor. It is also contemplated that the power module of the present invention can be easily adapted for use as a three phase DC brushless motor convertor. 
     Power shell  4  includes input power terminals  10   a,    10   b  and  10   c  which are preferably adapted to receive DC input power from an external source (not shown). For example, terminal  10   a  is a positive voltage terminal, terminal  10   b  is a negative voltage terminal and terminal  10   c  is a chassis ground terminal. Power shell  4  also includes motor phase terminals  12   a,    12   b,    12   c,    12   d,    12   e  and  12   f  which are preferably adapted to provide electrical conductivity from power module  2  to the various phase windings of a 4-phased switched reluctance motor for which the power module is designed to control. It should be noted that motor phase terminals  12   a-f  are integrally molded with power shell  4 . A preferred power electronics section circuit for power module  2  is described in detail below. 
     Circuit board  8  provides the necessary low power control circuitry to drive the high power controller electronics, such as high current carrying power MOSFETs and diodes. The low power control circuit typically provides the gate drive voltage for the high power MOSFET semiconductors. The individual low power circuit devices are preferably mounted on the upper side  14  of circuit board  8 . Connector  16  is mounted to circuit board  8  to provide external connectivity for the low power circuit. 
     Electrical connectivity between the low power circuit on circuit board  8  and the high power devices  18  mounted on power shell  4 , as discussed below, is accomplished by S-pin connectors  20 . Although FIG. 3 shows only two such connectors, it should be noted that additional connectors can be used, as needed. Although the connectors  20  shown are preferably “S” shaped, the connectors can take any shape as long as they provide resilient soldered or wire bonded contact between circuit board  8  and power shell  4 . As shown, S-pin connectors  20  provide a springly resilient connection between circuit board  8  and power shell  4  such that by mounting circuit board  8  within the cavity in power shell  4 , S-pin connectors  20  directly contact metallic tab  22  on power shell  4  or directly contact a pad area on base plate  6 . 
     The use of S-pin connectors  20  avoids the need to use a header row or rows of connecting pins. Connecting pins arranged as a header require that the signals to be carried to other module components such as power shell  4  or base plate  6  be run to the same general location on the circuit board. This adds unnecessary length to the signal paths and increases susceptibility to noise. In contrast, the use of S-pin connectors  20  allows signals on circuit board  8  to be connected to power shell  4  or base plate  6  by making each connection independent of each other. In other words, S-pin connectors  20  allow a signal to be connected to a module component at any appropriate point in the signal path. This avoids the need to introduce added signal trace length and provides better noise immunity for power module  2 . 
     Power module  2  may be mounted via mounting tabs  24  adapted to receive suitable fastening elements, such as bolts, as is well known in the art. Power module  2  is preferably mounted to a heatsink via base plate  6  so as to dissipate the heat generated by the high power devices. As is described in detail below, base plate  6  provides a thermal path from the high power components such that base plate  6  is preferably an insulated metal substrate (IMS) structure having a thick copper or aluminum substrate covered by a relatively thin insulation film on which a thin patternable copper or other conductive, solderable surface has been disposed. 
     FIG. 4 shows an exploded view of power module  2  of the present invention. Power shell  4 , base plate  6  and circuit board  8  are arranged for compact assembly and efficient utilization of available surface area. 
     Power shell  4  is aligned with, and coupled to, base plate  6  by inserting mounting posts  26  into mounting holes  28 . Power shell  4  is molded to include conductive regions  30  upon which high power devices  18  are mounted as by soldering, a conductive epoxy, or the like. When power shell  4  is mounted to base plate  6 , conductive regions  30  are positioned above respective contact trace regions  32  and are connected by soldering or a conductive adhesion. This provides an electrical connection between high power devices  18  and base plate  6 . 
     The connection between conductive regions  30  and contact regions  32  serves two useful functions. First, it provides an electrical path to the base plate, thereby allowing for distribution of power, ground and high power signals between the various high power devices  18 . Second, a thermally conductive path is provided from high power devices  18  to base plate  6 . This thermally conductive path allows thermal energy to be removed from high power devices  18  and transferred to a suitable heatsink (not shown) coupled to base plate  6 . 
     High power devices  18  are mounted on the upper side of conductive regions  30  inside power shell  4 , while the bottom side of conductive regions  30  is in contact with contact regions  32  on base plate  6 . 
     Circuit board  8  is adapted to fit into power shell  4  such that alignment notch  34  on circuit board  8  meets with alignment tab  36  on power shell  4 . This ensures proper alignment of circuit board  8 , and thereby simplifying power module assembly. Upon insertion into power shell  4 , S-pin connectors  20  engage one or more conductive regions  30  and/or one or more respective pads  38  on base plate  6 . This allows electrical conductivity between circuit board  8  and base plate  6 , while simplifying fabrication. 
     During fabrication, circuit board  8  and its associated componentry can be assembled separately from high power devices  18  and power shell  4 . Once power shell  4  and base plate  6  are assembled, and all wire bonds completed, as discussed below, circuit board  8  is easily assembled with power shell  4 . Adverse effects of thermal energy on circuit board  8  are avoided using the configuration of the present invention. Thermal energy is transferred from high power devices  18  to a heatsink attached to base plate  6  in a direction away from circuit board  8 . 
     The interior cavity formed by power shell  4 , base plate  6  and the cover (not shown) is filled with a potting gel such as a siliconal elastomer. 
     High power devices  18  include power MOSFETs, shunt resistors, schottky diodes, and a capacitor, as discussed in detail below, and are used, for example, to provide a switched reluctance motor convertor. Although the power module of the present invention is described with respect to a switched reluctance motor convertor, those of ordinary skill in the art would appreciate that power module  2  can be adapted to any configuration employing power semiconductor devices and low power control circuitry. 
     FIGS. 5 and 6 show a bottom view and a top view, respectively, of power shell  4  of the present invention. FIGS. 5 and 6 show conductive regions  30  in more detail. Each of conductive regions  30  is an extension of terminals  10   a-c,  motor phase terminals  12   a-f  or a recessed portion  40  embedded into the molded plastic portion  42  of power shell  4 . In the case of terminals  10   a-c  or motor phase terminals  12   a-f,  conductive regions  30  extend through, and are affixed by, molded plastic  42 . 
     FIG. 5 shows bottom side  44  of conductive regions  30 . FIG. 6 shows the top side  46  of conductive regions  30 . Each of terminals  10   a-c  and motor phase terminals  12   a-f  have a conductive region  30 , comprised of a bottom side  44  and top side  46 . As discussed above, high power devices  18  are mounted on a respective top side  46 , while bottom side  44  is in electrical contact with a respective contact region  32  on base plate  6 . 
     The use of contiguous terminals  10   a-c  and motor phase terminal  12   a-f  upon which high power devices  18  are mounted simplifies construction and aids in heat distribution and dissipation. 
     Power shell  4  is further adapted with through-holes  49  for reception of a suitable cover (not shown). 
     FIG. 7 shows a top view of base plate  6  of the present invention. As discussed above, base plate  6  is preferably an insulated metal substrate (IMS) structure and may be formed using known techniques. Base plate  6  is patterned to provide ground access to the substrate  48  through ground etch  50 . Such an IMS structure provides good thermal conductivity from the pattern contact regions  32  through the IMS to the substrate  48 . The substrate  48  is preferably aluminum and is preferably approximately 0.125 inches thick. The metallic substrate is a better conductor of thermal energy as compared with many other materials such as plastic, rubber, glass, etc. Also, the rigidity of the metallic substrate protects the module from breakage. 
     The IMS is patterned to form a plurality of electrically isolated conductive regions. These conductive regions allow positive and negative power connections and phase connections to be distributed, allow for separate gate pads and support the transfer of thermal energy through the substrate without shorting the various components. Although an IMS structure is preferred, other base plate structures may be employed such as Al, AlSiC and/or Cu base plates which may be isolated, for example, using an Al 2 O 3  flame spray, direct bonded copper or active metal braze substrate. 
     FIG. 8 shows a section view taken through section  8 — 8  in FIG.  7 . The resultant structure, as used in the present invention, is shown in FIG.  8 . With reference to FIG. 8, a first dielectric layer or polymeric film  52  is positioned on substrate  48 . Conductive region  54  is positioned on first dielectric  52 , and conductive layer  56  is positioned on conductive region  54 . Second dielectric or polymeric film  58  is positioned above conductive layer  56 , and a conductive region  60  is positioned on second dielectric  58 . First dielectric  52  and second dielectric  58  are preferably approximately 0.006 inches thick. Conductive region  54  is fabricated such that, when depression  62  is etched into the conductive and dielectric regions  54 ,  56 ,  58  and  60 , conductive region  54  can be plated to extend laterally through depression  62  extending to form a layer above conductive region  60 . 
     Plating layer  64  is positioned on the upper extended portion of conductive region  54 . A suitable plating material, such as nickel plating can be used, preferably with a gold surface flash. The conductive region  54  is preferably approximately 0.0013 to approximately 0.0015 inches thick, and is preferably copper. Conductive regions  56  and  60  are preferably approximately 0.0024 to approximately 0.0030 inches thick, and are preferably made of copper. Finally, solder mask  66  is applied to plating layer  64 , where appropriate, in order to prevent undesired electrical contact during the device soldering process. 
     An example of a power module employing the high power devices needed to fabricate a 4-phase switched reluctance motor convertor mounted on conductive regions  30  is shown in FIG.  9 . Initially, it is noted that it is desirable to have a capacitor operatively coupled between the +BUS and the −BUS in a power circuit. In accordance with the invention, a capacitor  68  is operatively coupled, for example, by soldering, between positive terminal  10   a  and negative terminal  10   b.  Capacitor  68  provides local energy capable of providing relatively large current pulses into the power circuit. 
     As shown in FIG. 9, capacitor  68  is advantageously mounted on appropriate conductive regions  30  such that it does not consume valuable surface area. Mounting capacitor  68  in this manner still provides excellent electrical performance because it is integrally disposed within the power circuit in close electrical proximity to the other circuit components. 
     Also in accordance with the invention, shunt resistors  70   a  and  70   b  can be disposed within power shell  4 . Advantageously, shunt resistors  70   a  and  70   b  are placed within the power circuit in electrical proximity to high power devices  18  such that valuable surface area of the base plate is preserved. Shunt resistors  70   a  and  70   b  are preferably 1 mΩ. 
     FIG. 10 shows a schematic diagram of the example 4-phased switched reluctance motor convertor shown in FIG.  9 . As shown in FIGS. 9 and 10, motor phase terminal  12   a  represents the input to motor phase A and motor phase C. Motor phase terminals  12   b  and  c  represent the respective outputs of motor phase A and motor phase C. Similarly, motor phase terminal  12   d  represents the input to motor phase B and motor phase D, while motor phase terminals  12   e  and  f  represent the respective outputs of motor phase B and motor phase D. 
     Capacitor  68  and shunt resistors  70   a  and  70   b  are also shown at their respective placement points within the circuit. 
     As shown in FIG. 9, thermistor  72  is mounted to base plate  6  in order to monitor the temperature of power module  2 . Thermistor  72  is not an integral component of the motor convertor circuit, and is therefore not shown in FIG.  10 . 
     As shown in FIGS. 9 and 10, input MOSFETs  74   a  and  b  are mounted to a conductive region  30  and connected to another conductive region  30  through a plurality of wire bonds  76 . Wire bonds  76  used to couple one terminal of a semiconductor device to a conductive region  30  or a gate pad  78  on base plate  6  may be fabricated using any known wire bonding technique. Input MOSFETs  74   a  and  74   b  are preferably 30 volt, N-channel, die size 4.6 MOSFETs. As used herein, the die size of MOSFETs  74   a  and  74   b  along with all other semiconductor devices refer to industry standard die sizings. 
     Output MOSFETs  80   a ,  80   b ,  80   c  and  80   d  are coupled between their respective motor phase terminals  12   b ,  12   c ,  12   e  and  12   f , and −BUS terminal  10   b . The gates of output MOSFETs  80   a-d  are wire bonded to a gate pad  78  for connection to the control circuit board  8 . Connection between gate pads  78  and circuit board  8  are accomplished, as discussed above, via S-pin connectors  20 . Output MOSFETs  80   a-d  are preferably 30 volt, N-channel, die size 4 power MOSFET devices. 
     A/C phase diode  82 , comprised of two parallel discrete semiconductor dice  82   a  and  82   b , is positioned on conductive region  30 , and located within the motor controller circuit connecting the drain of input MOSFET  74   a  at its cathode, and the −BUS input terminal  10   b  at its anode. Similarly, B/D phase diode  84  is comprised of discrete diode dice  84   a  and  84   b  and is positioned within the motor controller circuit between the drain of input MOSFET  74   b  at its cathode and −BUS terminal  10   b  at its anode. Each of diode dice  82   a ,  82   b ,  84   a  and  84   b  are preferably 45 volt Schottky, size 2 die devices. 
     Finally, diodes  86   a-d  are affixed to a conductive region  30  and positioned within the motor controller circuit such that each respective diode  86   a,    86   b,    86   c  and  86   d  is coupled, at its cathode to +BUS terminal  10   a,  and at its anode to a respective motor phase terminal  12   b ,  12   c ,  12   e  and  12   f . Diodes  86   a,    86   b,    86   c  and  86   d  are preferably 45 volt, Schottky, size 2 die devices. 
     An operation of the switched reluctance motor convertor will now be described with respect to FIG.  10 . Also, it should be noted that the operation of each individual phase in the 4-phase motor configuration operates in a similar manner. Therefore, only the operation of phase A is described herein. 
     Operation of the switched reluctance motor convertor comprises three discrete operations, namely a magnetization operation, free-wheeling operation and a forced demagnetization operation. Magnetization, free-wheeling operating and forced demagnetization are accomplished by appropriately switching power MOSFET devices on and off. During the magnetization of a phase to cause a particular motor function, input MOSFET  74   a  and output MOSFET  80   a  are switched on by applying an appropriate gate to source voltage. Switching MOSFETs  74   a  and  80   a  on creates a current path from +BUS terminal  10   a  through shunt resistor  70   a , the phase A motor winding and through −BUS terminal  10   b.    
     During the well known free-wheeling circuit operation, output MOSFET  80   a  remains switched on, while input MOSFET  74   a  is switched off. This causes current to free-wheel during the breakdown of the phase A motor winding field through shunt resistor  70   a , A phase input diode  82  and through output MOSFET  80   a.    
     The final operation is the forced demagnetization operation in which any remaining magnetic energy is transferred to capacitor  68 . During the forced demagnetization operation, input MOSFET  74   a  and output MOSFET  80   a  are switched off. This causes current to flow from −BUS terminal  10   b  through input diode  82 , through shunt resistor  70   a , and through phase A of the switched reluctance motor, completing its current path through output diode  86   a.    
     Combining the magnetization, free-wheeling and forced demagnetization operations in each of 4 motor phases allows power module  2  to efficiently control the operation of a complex motor, for example, an electric power steering mechanism in an automotive application. The compact size and thermal dissipation characteristics of power module  2  allow it to be mounted on or near the power steering mechanism without risk of damage to the sensitive control electronics on circuit board  8   
     Thus, the power module of the present invention provides a compact, yet powerful, device which integrates high power electronic components and the low power control circuitry necessary to control module operation. The power module of the present invention is arranged to efficiently transfer thermal energy from high power devices  18  through base plate  6  for dissipation away from circuit board  8  using an externally applied heatsink, or other known heat dissipation method. 
     The arrangement of power shell  4 , base plate  6 , and circuit board  8 , along with S-pin connectors  20 , allows power module  2  to be easily assembled, maximizing the use of surface area while minimizing the overall size of the module. This is further accomplished through the use of a base plate  6  which uses a highly thermally conductive material such as aluminum as a substrate which has a multilayer conductive patterns etched and positioned thereon. This arrangement allows power and ground buses and connections to be arranged separately from the individual signal pads and control electronics pads, further maximizing resource utilization. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.