Patent Publication Number: US-2022225547-A1

Title: Power electronics unit having at least one semiconductor module attached by means of a plastic holder

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase of PCT Appln. No. PCT/DE2020/100368 filed May 4, 2020, which claims priority to DE 102019114001.3 filed May 24, 2019, the entire disclosures of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a power electronics unit for an electric motor of a motor vehicle drive, i.e., an electric motor preferably provided in a motor vehicle drive train. 
     BACKGROUND 
     In the field of e-mobility, power semiconductors are usually directly liquid-cooled, whereby the impermeability of the power semiconductor modules should also be guaranteed in addition to a most ideal possible flow through the cooling medium. On the one hand, the semiconductors are typically connected to the two DC contacts, and on the other to the AC output to the electric motor. The power semiconductors are connected via what are termed auxiliary contacts to a driver board (gate driver board), which controls the semiconductors depending on the torque and speed specifications of the motor vehicle. At the same time, vibration resistance of the electrical components must be ensured. Correspondingly, sufficient rigidity and possibilities for targeted damping of frequencies, such as those that occur in the automotive sector through excitations from the internal combustion engine in hybrids and on the road, must be taken into account. If non-positive fastening elements are used to fix the power semiconductors to the cooling element, the static seals are subject to a relatively high axial compression. As an alternative to this, it is in principle possible to use terminal blocks, with no holes for screwing on the power semiconductors and the power semiconductors being pressed against the cooling plate by the terminal blocks. The terminal blocks in turn are then screwed in directly. 
     There is still the requirement to achieve a high specific performance in relation to the existing volume/installation space of the power electronics. The power electronics should be built as compact as possible. At the same time, it is necessary to adhere to certain insulation specifications, such as air gaps and creepage distances. Another requirement is to assemble the electrical contact in the HV and LV region easily and to make the connections easy to construct. At the same time, the vibration resistance of the power electronics must be guaranteed. 
     SUMMARY 
     It is therefore the object of the present disclosure to provide a compact and securely mounted power electronics unit that is equipped with at least one semiconductor module and which enables simpler assembly. 
     This is achieved according to the disclosure described herein. Accordingly, a power electronics unit for an electric motor of a motor vehicle drive is equipped with a plate-like cooling element, at least one semiconductor module and a module holder which consists of plastic and secures the at least one semiconductor module relative to the cooling element, wherein the module holder is fixed to the cooling element via an interlocking snap connection. 
     This interlocking snap connection between the module holder and the cooling element allows the semiconductor modules to be easily mounted during assembly. At least the relatively complex handling of previously used screws is avoided. It is also possible before attaching the module holder to the cooling element to insert the individual elements of the snap connection into the module holder and to fasten them together to the cooling element in one step. Thus, the assembly effort is significantly reduced, wherein it is ensured that a sufficient fastening force and vibration resistance are guaranteed. 
     Further advantageous embodiments are claimed and explained in more detail below. 
     Accordingly, it is also advantageous if the snap connection is implemented by a (first) interlocking element formed integrally with the module holder, forming a snap-hook contour, and/or by a (second) interlocking element formed separately from the module holder. 
     In this context, it is also useful if a first interlocking element of the snap connection, which is integrally molded with the module holder, is latched/snapped into place with receiving holes in the cooling element. The assembly effort is further reduced by the integral construction. 
     It is also advantageous if a second interlocking element of the snap connection, which is formed separately from the module holder, is received in an interlocking manner on the module holder and the cooling element. The preferably sleeve-shaped latching element is latched accordingly with receiving holes in the module holder and the cooling element. This results in a snap connection that can be produced particularly cost-effectively. 
     In addition, it is expedient if the at least one interlocking element, preferably the second interlocking element, is secured by a securing element against loosening of the snap connection. As a result, the most robust possible design of the power electronics unit is achieved. 
     If a circuit board is attached directly to the module holder, the result is as direct an assignment as possible of the circuit board relative to the semiconductor modules. Relative movements between the circuit board and the semiconductor modules are largely reduced. 
     In this context, it is also advantageous if the circuit board is attached to the module holder by fastening elements formed separately from the module holder and the circuit board, preferably by self-tapping screws, and/or attached to the module holder by fastening elements formed integrally with the module holder. The integral fastening elements are preferably implemented as plastic projections which penetrate a through-hole in the circuit board and have a material deformation (in the sense of riveting) towards a free end. In this way the manufacturing effort is further simplified. 
     If the circuit board is attached to a side of the plate-like module holder facing away from the at least one semiconductor module, an even more compact design of the power electronics unit is achieved. 
     Furthermore, it is expedient to increase the rigidity of the module holder if it is formed with stiffening ribs. 
     In this context, it is expedient if the module holder is formed from a fiber-reinforced plastic, for example a glass fiber-reinforced plastic. This makes it possible to adapt the module holder to the stiffness specifications in a defined manner with regard to the vibration resistance. 
     In other words, a connection of multiple semiconductor modules is implemented according to the disclosure by means of a plastic holder (module holder). The power semiconductor devices (semiconductor modules) are attached by means of a snap connection to a heat sink (cooling element) using the holder (module holder) made of a plastic material. The snap connection can be formed by separate elements or integrally with the holder. Inadvertent loosening of the snap connection by a fastening element (locking pin/securing pin) is preferably avoided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will now be explained in more detail with reference to figures, in which connection various exemplary embodiments are also shown. 
       In the figures: 
         FIG. 1  shows a perspective view of a power electronics unit according to the disclosure, designed according to a first exemplary embodiment, 
         FIG. 2  shows a perspective exploded representation of the power electronics unit according to  FIG. 1 , wherein a plurality of semiconductor modules attached to a cooling element via a module holder can be clearly seen, 
         FIG. 3  shows a further perspective representation of the power electronics, wherein a circuit board fixed on the module holder is shown transparently, 
         FIG. 4  shows a sole perspective representation of the inserted module holder used in  FIGS. 1 to 3  from a side facing the circuit board, 
         FIG. 5  shows a side representation of the module holder according to  FIG. 4 , 
         FIG. 6  shows a view from an underside of the module holder according to  FIGS. 4 and 5 , 
         FIG. 7  shows a perspective view of the underside according to  FIG. 6 , 
         FIG. 8  shows a perspective detail view of the module holder according to  FIGS. 4 to 7  with an interlocking element to be attached in a receiving hole of the module holder, wherein the interlocking element is secured by a securing element in the fully assembled position before the snap connection with the cooling element is released again, 
         FIG. 9  shows a perspective representation of a module holder designed according to a second exemplary embodiment according to the disclosure, which differs from the first exemplary embodiment in terms of the design of the plurality of interlocking elements, and 
         FIG. 10  shows a representation of the underside of the module holder according to  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     The figures are only schematic in nature and serve only for understanding the disclosure. The same elements are provided with the same reference symbols. 
     In connection with  FIGS. 1 to 3  of the first exemplary embodiment, power electronics unit  1  according to the disclosure, which can be easily recognized, is designed for use in/on an electric drive motor, i.e., in an electric motor used for a drive of a motor vehicle. The power electronics unit  1  is shown in the region of a converter unit. The power electronics unit  1  consequently has multiple semiconductor modules  3   a ,  3   b ,  3   c  which convert the voltage provided by the vehicle electrical system to the drive of the electric motor, or a voltage generated by the electric motor itself, into a voltage of the vehicle electrical system. 
     The power electronics unit  1  has a plate-like cooling element  2 , which can be seen clearly in  FIG. 2 . During operation, the cooling element  2  is typically connected to a cooling device to form a cooling element and a cooling medium flows therethrough. A plurality of receiving regions  15   a  to  15   c  are provided on the cooling element  2  towards one side of the cooling element  2  to accommodate multiple semiconductor modules  3   a  to  3   c . The cooling element  2  has a first receiving region  15   a  for a first semiconductor module  3   a . This first receiving region  15   a  is essentially formed as a trough in the cooling element  2 , into which the first semiconductor module  3   a  is inserted. The two further receiving regions  15   b  and  15   c  are arranged in a row along with the first receiving region  15   a  along the rectangular cooling element  2 . The two further receiving regions  15   b  and  15   c  are shaped essentially in accordance with the first receiving region  15   a . A second semiconductor module  3   b  is inserted in a second receiving region  15   b , and a third semiconductor module  3   c  is inserted in a third receiving region  15   c.    
     For ultimately positionally accurate fixing of the semiconductor modules  3   a ,  3   b ,  3   c  on the cooling element  2 , a holder designated as a module holder  4  is used. The module holder  4  is made of a plastic, namely a fiber-reinforced plastic. This module holder  4 , as it is shown alone in connection with  FIGS. 4 to 7 , is essentially plate-like. According to the disclosure, the module holder  4  is fixed by an interlocking snap connection  5  in the finally assembled state on the part of the cooling element  2 , wherein the individual semiconductor modules  3   a ,  3   b ,  3   c  are secured on the cooling element  2  ( FIGS. 1 and 3 ). From  FIG. 3  it can also be seen that the individual semiconductor modules  3   a ,  3   b ,  3   c  are held between a plate region  16  of the module holder  4  and the cooling element  2  in the fully assembled position of the power electronics unit  1 . By being accommodated within the receiving regions  15   a ,  15   b , the semiconductor modules  3   a ,  3   b ,  3   c  are at the same time secured against slipping out to the side of the module holder  4 . 
     In this embodiment, the module holder  4  has both multiple first interlocking elements  7  and multiple second interlocking elements  8  to implement the snap connection  5 . The first interlocking elements  7 , as they can be seen in connection with  FIGS. 4 to 7 , are formed integrally with the module holder  4  in one piece. The first interlocking elements  7  are therefore also formed from the plastic of the module holder  4 . The first interlocking elements  7  are implemented as snap hooks. Two first interlocking elements  7  are provided on the module holder  4  for a first axial end region  17   a ; two further first interlocking elements  7  are provided for a second axial end region  17   b  opposite the first axial end region  17   a . The first interlocking elements  7  are latched behind first receiving holes  9   a  of the cooling element  2 , which first receiving holes  9   a  are implemented in the form of elongated holes, forming the snap connection  5 . 
     In addition, several second interlocking elements  8  are provided. These second interlocking elements  8 , as can be seen in detail in  FIG. 8 , are designed separately from the module holder  4  and implemented essentially in the form of a sleeve. Each second interlocking element  8  has a collar  18  towards a first end and multiple snap-in lugs  19  towards a second end. While the snap-in lugs  19  in turn form a snap hook contour  6  and, in the fully assembled position with the formation of the snap connection  5 , are locked behind a (third) receiving hole  9   c  of the cooling element  2 , the collar  18  rests flat on the module holder  4 . The module holder  4  is provided with multiple second receiving holes  9   b  for receiving the second interlocking elements  8 . Each second interlocking element  8  is secured in the locked position thereof with a securing element  10 , which forms a securing pin. For this purpose, the securing element  10  is pushed into a central hole in the second interlocking element  8  and prevents the snap-in lugs  19  from springing back again and thus from loosening the snap connection  5 . 
     Overall, four second interlocking elements  8  are provided for each longitudinal side  20   a ,  20   b  of the module holder  4 , the interlocking elements  8  of one longitudinal side  20   a ,  20   b  being arranged in a row next to one another. In particular, on each longitudinal side  20   a ,  20   b , a second interlocking element  8  is arranged towards the first end region  17   a , another second interlocking element  8  is arranged towards the second end region  17   b  and two further second interlocking elements  8  are arranged between the first semiconductor module  3   a  and the second semiconductor module  3   b  or between the second semiconductor module  3   b  and the third semiconductor module  3   c . In the region between the semiconductor modules  3   a ,  3   b ,  3   c , support webs  21  are also provided on the module holder  4 , which rest flat on the cooling element  2 , in the region between the semiconductor modules  3   a ,  3   b ,  3   c.    
     In conjunction with  FIGS. 6 and 7 , it can be clearly seen that multiple stiffening ribs  13  are typically provided on a side of the module holder  4  facing the cooling element  2 . These stiffening ribs  13  run essentially in the longitudinal direction of the module holder  4  and parallel to one another. 
     Furthermore, a circuit board  11  is fixed directly to the module holder  4  via multiple fastening elements  12 . The circuit board  11  implemented as a gate circuit board is arranged on a side of the module holder  4  facing away from the cooling element  2 . The fastening elements  12  are implemented as self-tapping screws. Each fastening element  12  penetrates a through-hole  14  in the circuit board  11  and is screwed to a base  22  of the module holder  4 , which is formed integrally. For this purpose, the base  22  preferably already has a hole  23  which is smaller than a diameter (screw thread diameter) of the fastening element  12 . 
     In this context, it should be pointed out in principle that the fastening elements  12  can also be implemented in other ways. According to a further preferred embodiment, which is not shown here for the sake of clarity, the bases  22  themselves are implemented directly as fastening elements. According to this further embodiment, each through-hole  14  made in the circuit board  11  is selected to be larger than the respective base  22  and pushed over this base  22  so that the base  22  penetrates the circuit board  11 . A region of the base  22  that protrudes through the circuit board  11  and forms a free end is subsequently reshaped (preferably thermally) in such a way that this free end forms a shape that engages behind the circuit board  11 , for example a mushroom shape, and the circuit board  11  is held thereby relative to the module conductor  4 . 
     In conjunction with  FIGS. 9 and 10 , reference is made to an alternative second exemplary embodiment. In this second exemplary embodiment, the rest of the structure of the power electronics  1  is designed in accordance with the first exemplary embodiment, which is why only the differences in the shape of the module holder  4  will be discussed below. As in conjunction with  FIGS. 9 and 10 , the second interlocking elements  8  are now dispensed with. The regions of the module holder  4  which previously had the second receiving holes  9   b  in the first exemplary embodiment are replaced by first interlocking elements  7  which are implemented as snap hooks. Thus, several, namely four, first interlocking elements  7  are also provided on the two longitudinal sides  20   a  and  20   b  of the module holder  4 , each of which is latched onto the cooling element  2  with a third receiving hole  9   c , not shown here for the sake of clarity. 
     In other words, according to the disclosure, power semiconductors (semiconductor modules  3   a ,  3   b ,  3   c ) are provided with a holder  4  made of plastic with the aid of snap hooks  6 ;  7  connected to the cooling element  2 . The snap hooks  6 ;  7  are additionally secured with securing elements  10  against unintentional opening. The construction enables the converter  1  to be constructed as compactly as possible. By integrating the module holder  4  and the gate driver board  11 , components can be saved. Since the gate driver  11  and the power modules (semiconductor modules  3   a ,  3   b ,  3   c ) are both mounted with the power module holder  4 , relative movements at the auxiliary contacts, such as vibration, can be reduced. These relative movements are critical for the service life of the electrical contacts. The snap hooks  6 ;  7  enable simple and inexpensive assembly. Previous screwing processes that needed to be monitored for torque and handling of the screws are no longer necessary. In the case of cooling elements  2  made of plastic, thread inserts therefore needed to be introduced before the power modules  3   a ,  3   b ,  3   c  could be screwed on. These requirements for the cooling element material do not apply with the snap hooks  6 ,  7 . Due to the plastic construction of the module holder  4 , the design of the ribs  13  and the setting of the modulus of elasticity of the plastic used by fillers, such as glass fibers, allow effective measures to stiffen and dampen vibration excitations in specific frequency ranges. The gate driver board  11  can be fastened to the module holder  4  with self-tapping screws  12 . The forces on the plate  11  are so small that thread inserts are not necessary. Thanks to the plastic module carrier  4 , hot caulking can also be used as a fastening method for the gate driver board  11 . For this purpose, instead of the holes  23  for the screws  12 , pins (base  22 ) are injection-molded onto the module holder  4 . The board  11  is threaded there onto at the fastening holes  14  and the protruding pin  22  is formed into a mushroom shape with a warm stamp (similar to a riveted connection). 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               1  Power electronics unit 
               2  Cooling element 
               3   a  First semiconductor module 
               3   b  Second semiconductor module 
               3   c  Third semiconductor module 
               4  Module holder 
               5  Snap connection 
               6  Snap hook contour 
               7  First interlocking element 
               8  Second interlocking element 
               9   a  First receiving hole 
               9   b  Second receiving hole 
               9   c  Third receiving hole 
               10  Securing element 
               11  Circuit board 
               12  Fastening element 
               13  Stiffening rib 
               14  Through-hole 
               15   a  First receiving region 
               15   b  Second receiving region 
               15   c  Third receiving region 
               16  Plate region 
               17   a  First end region 
               17   b  Second end region 
               18  Collar 
               19  Snap-in lug 
               20   a  First longitudinal side 
               20   b  Second longitudinal side 
               21  Support web 
               22  Base