Abstract:
One aspect relates to a power semiconductor arrangement includes a power semiconductor module which is mechanically connected to a heat sink. In order to improve the thermal cycling stability of the connection between a baseplate of the module and a circuit carrier connected thereto, recesses are provided in the baseplate. One aspect further relates to a power semiconductor module.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Utility Patent Application claims priority to German Patent Application No. DE 10 2006 045 939.3, filed on Sep. 28, 2006, which is incorporated herein by reference. 
     BACKGROUND 
     One aspect relates to power semiconductor arrangements including a power semiconductor module mechanically connected to a heat sink. 
     Power semiconductor modules may include a base plate and at least one, at least two, or more semiconductor chips that are generally arranged on a circuit carrier. One or more circuit carriers equipped in this way are in turn fixedly connected to the baseplate. To form a power semiconductor arrangement, the power semiconductor module may be mechanically pressed against a heat sink with the baseplate ahead. 
     An exemplary embodiment of such a power semiconductor module is illustrated in  FIG. 1 . The power semiconductor module  1  exhibits a semiconductor chip  6  including a semiconductor body  60  provided with metallizations  61 ,  62  on two opposite sides. The first metallization  61  is generally structured and divided at least into control and load current contacts. Furthermore, the power semiconductor module  1  includes a circuit carrier  5  including a dielectric carrier  50  provided with a structured first metallization layer  51  on one side and with a second metallization layer  52  on the opposite side. 
     The semiconductor chip  6  is connected by its metallization  62  to a portion of the structured metallization  51  of the circuit carrier  5  by means of an electrically conductive connecting layer  71 , for example, a solder layer or an NTC layer (NTC=low-temperature connection). 
     Furthermore, the first metallization  61  of the semiconductor chip  6  is connected to a further portion of the structured metallization layer  51  of the circuit carrier  5  by means of bonding wires  7 . As an alternative to a bonding connection, it is also possible to provide metal clips, for example, which are connected to the first metallization  61  by means of a soldering or low-temperature connection. 
     The circuit carrier  5  serves, on the one hand, for electrically interconnecting one or more semiconductor chips  6  arranged thereon, and, on the other hand, the heat loss arising in the semiconductor chip  6  is dissipated via it. This results in the necessity of using materials including good thermal conductivity for the circuit carrier  5 . 
     In order to increase the thermal cycling stability of the first solder layer  71 , the coefficients of thermal expansion of the circuit carrier  5  and of the semiconductor chip  6  differ as little as possible. Since the coefficient of thermal expansion of the semiconductor chip  6  is essentially determined by the low coefficient of thermal expansion of the semiconductor body  60 , DCB substrates (DCB=Direct Copper Bonding), DAB substrates (DAB=Direct Aluminum Bonding) or AMB substrates (AMB=Active Metal Brazed) are usually used as circuit carrier  5  since they likewise include a low coefficient of thermal expansion. 
     Two or more circuit carriers  5  equipped in this way are fixedly connected to a baseplate  2  by means of a second connecting layer  72  at their second metallization layer  52 . Baseplates of this type may, for example, wholly or partly include a metal such as, for example, copper or aluminum and therefore include a coefficient of thermal expansion that differs comparatively greatly from the coefficient of thermal expansion of the circuit carrier  5 . 
     Since the heat arising in the semiconductor chip  6  is dissipated via the circuit carrier  5 , the second connecting layer  72  and the baseplate  2  to a heat sink  4  that may be connected to the power semiconductor module  1 , during operation of the power semiconductor module  1  in the case of frequent temperature changes severe thermal cycling loading occurs in the second connecting layer  72 . 
     On account of the different coefficients of the thermal expansion of the baseplate  2  and of the circuit carrier  5 , von-Mises stresses act in the second connecting layer  72  and load the second connecting layer  72 . Cracking can thereby commence in the second connecting layer  72  depending on the number of temperature cycles undergone and on the temperature differences that occur, whereby the heat dissipation from the semiconductor chip  6  in the direction of the heat sink  4  is impaired. This in turn brings about an increase in the temperature in the semiconductor chip  6 , whereby the second connecting layer  72  is loaded to an even greater extent. 
     Further loading of the second connecting layer  72  arises as a result of mechanical stresses which occur at fixing locations  3  for fixing the baseplate  2  and hence the power semiconductor module  1  at a heat sink  4 . 
       FIG. 2  illustrates a perspective view of a quarter model of a baseplate  2 , which is equipped with 3 circuit carriers in this example, to which baseplate a circuit carrier  5  is fixedly connected by means of a connecting layer  72 . 
     A fixing location  3  formed as a continuous opening is provided in the region of an outer corner of the baseplate  2 , by means of which fixing location the baseplate  2  may be fixed at a heat sink. 
     What is problematic in this case is the stability of the connecting layer  72  in its portions  72   a  located in the region of the outer corners  5   a  of the circuit carriers  5 . In this case, an outer corner  5   a  of the circuit carrier  5  is understood to mean a corner adjacent to which no other circuit carrier is arranged. Likewise problematic is the thermal cycling stability of the second connecting layer  72  in its portions  72   b  arranged in the region of the inner corners  5   b  of the circuit carrier  5 . In this case, an inner corner  5   b  of the circuit carrier  5  is understood to mean a corner in the vicinity of which another circuit carrier  5  is arranged. 
       FIGS. 3A and 3B  illustrate the von-Mises stresses—on that side of the second connecting layer  72  in accordance with  FIGS. 1 and 2  which faces the baseplate  2  ( FIG. 3A ) and the substrate  5  ( FIG. 3B ). 
     It can be seen therefrom that peaks of the von-Mises stresses occur below the outer corners  5   a  in regions  72   a  of the second connecting layer  72  and below the inner corners  5   b  in regions  72   b  of the second connecting layer  72 . 
     On account of the cracking associated therewith, progressive delamination of the circuit carrier  5  from the baseplate  2  occurs during operation of the power semiconductor module  1 . The delamination begins in the region of the portions  72   a ,  72   b  of the second connecting layer  72  owing to the peak values of the von-Mises stresses that occur there. 
       FIG. 4  illustrates such delamination effects on the basis of ultrasound examinations using the example of a power semiconductor module onto whose baseplate four circuit carriers are soldered, after  200  ( FIG. 4A ),  1000  ( FIG. 4B ),  2000  ( FIG. 4C) and 4000  ( FIG. 4D ) temperature cycles. The locations at which the delamination occurs are represented dark in  FIGS. 4A to 4D  and identified by the reference symbol  72   c.    
       FIG. 4  reveals that the delamination commences in the corner regions  72   a ,  72   b  (see  FIG. 4B ) and propagates toward the center of the respective circuit carriers as the number of temperature cycles increases. 
       FIG. 5  illustrates the profile of the von-Mises stresses σ on that side of the second connecting layer which faces the baseplate in the region of an outer corner  72   a , at which the von-Mises stresses including a maximum value of 26.7 MPa. 
       FIG. 6  illustrates a cross section through a power semiconductor module in the region of the interface between the second metallization layer  52  of the dielectric carrier and the second connecting layer  72  in cross section. It can be seen therefrom that the second connecting layer  72  includes a crack  72   c  in the region of its side facing the second metallization layer  52 . 
     SUMMARY 
     A power semiconductor module according to one embodiment includes a baseplate and a circuit carrier, which is fixedly connected to the baseplate by means of a connecting layer. The baseplate includes a connecting area given by a common interface between the connecting layer and the baseplate, and also a fixing location, by means of which the baseplate may be connected to a heat sink. In order to reduce the von-Mises stresses acting in the connecting layer, a recess is provided, which is arranged in a lateral direction between the fixing location and the connecting area and which extends into the baseplate proceeding from that side of the baseplate which faces the circuit carrier. 
     The recess may be formed as a non-continuous trench or as a continuous opening of the baseplate and amount to a depth of 1 mm or more. In the case of a non-continuous trench, the recess may include, for example, a depth of at least 30% of the thickness of the baseplate. 
     Such a recess includes an effect when it is arranged between a fixing location and a location at which the edge of the connecting area falls below a predetermined radius of curvature, for example between 0 mm and 10 mm. 
     The width of the recess may be, for example, 10% to 100% of the thickness of the baseplate or 0.5 mm to 5 mm. 
     In accordance with one embodiment, such a recess may be arranged in ring-shapedly closed fashion around the connecting area. 
     In order to reliably reduce the mechanical stresses that occur, the distance between the connecting area and the recess in the lateral direction is chosen to be less than or equal to a predetermined value, for example less than or equal to 3 mm. 
     On account of the reduction of the thermomechanical stresses that is associated with the recess, the distance between the fixing location and the connecting area in the lateral direction may be chosen to be relatively small, for example, less than or equal to 3 mm. 
     In order to reduce the thermomechanical stresses of the fixing location between the circuit carrier and the baseplate, in addition or as an alternative provision may be made for arranging a fixing location of the baseplate below the circuit carrier. In this case, the fixing location may be arranged in a region in which the baseplate includes a concave precurvature on its side remote from the circuit carrier. 
     Furthermore, in addition or as an alternative the baseplate may also include a convex precurvature on its side remote from the circuit carrier. 
     In power semiconductor modules according to embodiments, the fixing location may be formed as a continuous opening of the baseplate. 
     A fixing location may likewise be given by a location at which the baseplate is connected to a bolt in a releasable or non-releasable manner or at which it includes a projection formed as a fixing element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. 
       The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, instead emphasis being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts. In the drawings: 
         FIG. 1  illustrates a cross section through a power semiconductor module fixed at a heat sink. 
         FIG. 2  illustrates a perspective view of a quarter model of a baseplate which is fixedly connected to a circuit carrier by means of a connecting layer. 
         FIG. 3  illustrates a diagram of forces with von-Mises forces such as occur in the region of that interface of the second connecting layer of the arrangement in accordance with  FIG. 2  which faces the baseplate and the circuit carrier, respectively. 
         FIGS. 4A-4D  illustrate the course of a delamination process in a power semiconductor module depending on the number of temperature change cycles undergone on the basis of ultrasound examinations. 
         FIG. 5  illustrates the profile of the von-Mises stresses at that side of the second connecting layer which faces the baseplate in the region of an outer corner of a circuit carrier. 
         FIG. 6  illustrates a cross section through an edge-side portion of the second metallization layer of a circuit carrier with adjoining connecting layer with incipient cracking in a power semiconductor module. 
         FIG. 7  illustrates a cross section through a power semiconductor module, which is connected to a heat sink and in which a recess is provided between a connecting area formed between a connecting layer and the baseplate and a fixing location for fixing the baseplate at a heat sink, said recess extending into the baseplate proceeding from that side of the baseplate which faces the circuit carrier, wherein the fixing location is fixedly established by a screw that is screwed into a blind hole provided with an internal thread in the heat sink. 
         FIG. 8  illustrates an enlarged excerpt from the arrangement in accordance with  FIG. 7 , with the difference that the screw is screwed into a blind hole provided with an internal thread in the heat sink. 
         FIG. 9  illustrates an enlarged excerpt from a power semiconductor module according to the embodiment in accordance with  FIG. 8  with the difference that instead of the blind hole a continuous opening is provided in the heat sink. 
         FIG. 10  illustrates an enlarged excerpt from the arrangement in accordance with  FIG. 8  with the difference that the recess is formed as a continuous opening in the baseplate. 
         FIG. 11  illustrates an enlarged excerpt from the arrangement in accordance with  FIG. 9  with the difference that the recess is formed as a continuous opening in the baseplate. 
         FIG. 12  illustrates a plan view of the front side of a baseplate of a power semiconductor module on which four circuit carriers are arranged and which includes four fixing holes, wherein a recess is arranged in the baseplate between in each case an outer corner of a circuit carrier and a fixing location. 
         FIG. 13  illustrates the plan view of the baseplate of a power semiconductor module in accordance with  FIG. 10  in which the baseplate includes additional recesses arranged in the region of the inner corners of the circuit carriers. 
         FIG. 14  illustrates a plan view of a baseplate of a power semiconductor module with three circuit carriers connected to a baseplate, in which a plurality of recesses are arranged in a manner spaced distant from one another in the region of an inner corner and in the region of an outer corner. 
         FIG. 15  illustrates an arrangement in accordance with  FIG. 14  in which the fixing locations are arranged beside the center of the side areas of a circuit carrier. 
         FIG. 16  illustrates the profile of the von-Mises stresses at that side of the second connecting layer which faces the baseplate in the region of an outer corner of a circuit carrier corresponding to  FIG. 5 , but in a power semiconductor module according to the embodiment whose baseplate is provided with a recess according to the arrangement in accordance with  FIG. 12 . 
         FIG. 17  illustrates a plan view of the baseplate of a power semiconductor module corresponding to  FIG. 12  in which the recesses are formed in elongate and straight fashion and run at angles of greater of 0° and less than 90° with respect to the outer edges of the circuit carriers. 
         FIG. 18  illustrates a plan view of the baseplate of a power semiconductor module with a plurality of circuit carriers fixed on a baseplate, in which the recess is formed in ring-shaped fashion in the baseplate and arranged around the circuit carriers. 
         FIG. 19  illustrates a perspective view of a portion of a baseplate according to an embodiment, provided with equipped circuit carriers, corresponding to  FIG. 18 . 
         FIG. 20  illustrates a plan view of the baseplate of a power semiconductor module in accordance with  FIG. 18  in which recesses arranged between adjacent circuit carriers are additionally arranged in the baseplate, such that individual circuit carriers are in each case surrounded by a ring-shapedly closed recess. 
         FIG. 21  illustrates a plan view of a portion of a baseplate of a power semiconductor module according to the embodiment which includes a connecting area including an edge whose radius of curvature at least one edge point falls below a predetermined value, wherein, at a distance from the connecting area, a recess is arranged in the baseplate in such a way that a straight line through the edge point and the centre of curvature assigned to said edge point crosses the recess in the plan view of the front side of the baseplate. 
         FIG. 22  illustrates a plan view of a portion of a baseplate of a power semiconductor module according to an embodiment which includes a connecting area, a fixing location spaced distant from the latter, and also a recess arranged between the connecting area and the fixing location, wherein the fixing location, in the plan view of the front side of the baseplate, proceeding from the center of curvature of a location at which the radius of curvature of the edge of the connecting area falls below a predetermined value, appears under an angular range which is arranged completely within the angular range under which the recess appears from the same center of curvature. 
         FIG. 23  illustrates a vertical section through a potted power semiconductor module according to an embodiment which is provided with a housing and whose baseplate is provided with recesses and also with fixing locations and which includes a busbar arrangement for its internal interconnection. 
         FIG. 24  illustrates a vertical section through a portion of a power semiconductor module according to an embodiment whose baseplate includes recesses and fixing locations and which is provided with a housing on whose inner wall guide rails are integrally formed, into which connection lugs are inserted or latched for the external connection of the module. 
     
    
    
     In the figures, identical reference symbols designate identical elements including an identical function. For the sake of better illustration, the exemplary embodiments are not reproduced true to scale. 
     DETAILED DESCRIPTION 
     In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise. 
       FIG. 7  illustrates a cross section through a power semiconductor module  1  according to the embodiment, which is mounted at a heat sink  4  by means of fixing screws  8 . The power semiconductor module  1  includes a circuit carrier  5  including a dielectric carrier  50  including a structured first metallization layer  51  and a second metallization layer  52 , which are arranged on mutually opposite sides of the dielectric carrier  50 . The dielectric carrier  50  may be formed, for example, from ceramic or plastic. The circuit carrier  5  may be for example a DCB substrate, a DAB substrate or an AMB substrate. 
     A semiconductor chip  6  is connected to a portion of the first metallization layer  51  by means of a first connecting layer  71 , for example composed of a solder or composed of an electrically conductive adhesive. The semiconductor chip  6  includes a semiconductor body  60  and also a first metallization  61  and a second metallization  62 , which are arranged on mutually opposite sides of the semiconductor body  60 . The semiconductor chip  6  is connected at its first metallization layer  61  to a further portion of the structured first metallization layer  51  by means of a bonding wire  7 . 
     The circuit carrier  5  equipped with the semiconductor chip  6  is connected via its second metallization layer  52  to a connecting area  2   b  of a baseplate  2  by means of a second connecting layer  72 . The connecting area  2   b  is a partial area of that side of the baseplate  2  which is also referred to hereinafter as front side  2   a , on which the circuit carrier  5  is fixed. Since the heat loss arising in the semiconductor chip  6  is dissipated via the connecting area  2   b , the connecting area is chosen to include the largest possible area. 
     The connection between the circuit carrier  5  and the baseplate  2  may be produced, for example, by soldering, by means of a thermally conductive adhesive, or by means of a low-temperature connection method. 
     The baseplate  2  may consist of, for example, copper and/or aluminum silicon carbide (AlSiC), or may include at least one of said materials. Furthermore, the baseplate  2  includes fixing locations  3 , by means of which the baseplate and hence the entire power semiconductor module  1  may be fixed at a heat sink  4 . 
     Fixing location in the sense of the present embodiment is understood to mean any location of the baseplate  2  which is provided for allowing a force for pressing the baseplate  2  onto the heat sink  4  to act on the baseplate  2 . In the exemplary embodiment in accordance with  FIG. 7 , the fixing locations  3  are formed as continuous openings of the baseplate  2  and are spaced distant from the second connecting layer  72  in a first lateral direction r 1 , which is perpendicular to a direction of the normal n to the front side  2   a.    
     A recess  9  is provided in the first lateral direction r 1  between the fixing location  3  and the second metallization layer  52 , said recess extending into the baseplate  2  proceeding from the front side  2   a  of the baseplate  2 . The recess  9  may be formed, as illustrated in  FIG. 7 , as a non-continuous trench or else—as not illustrated in FIG.  7 —as a continuous opening in the baseplate  2 . 
     An enlarged excerpt from the arrangement in accordance with  FIG. 7  is illustrated in  FIG. 8 . It can be seen therefrom that the recess  9  extends right into a depth t proceeding from the front side  2   a  of the baseplate  2 . The recess  9  includes a width b and is at a distance d 1  from the connecting area  2   b  in the first lateral direction r 1 . Furthermore, the baseplate  2  includes a thickness d 0 . 
     As can be seen from  FIG. 8 , the heat sink  4  may be fixed to the baseplate  2  and hence to the entire power semiconductor module  1  by means of a fixing means  8 , which is formed as a screw, by way of example, which engages into the internal thread of a blind hole formed in the heat sink  4 . Since the force with which the baseplate  2  is pressed onto the heat sink  4  proceeds from the head of the screw, the fixing location is given by that region of the baseplate  2  which is given within the lateral boundary of the bearing area  3   a  of the screw head on the baseplate  2 . In this case, the fixing location  3  extends over the entire thickness of the baseplate  2  in the direction of the normal n. 
       FIG. 8  furthermore illustrates that the second metallization layer  52  and the second connecting layer  72  may be spaced distant from the lateral edge of the dielectric carrier  50  in the lateral direction. 
       FIG. 9  illustrates an enlarged excerpt from an arrangement corresponding to  FIGS. 7 and 8  with the difference that instead of the blind hole a continuous opening with an internal thread is provided in the heat sink  4 . 
       FIG. 10  corresponds to the arrangement in accordance with  FIG. 8 , and  FIG. 11  corresponds to the arrangement in accordance with  FIG. 9 , in each case with the difference that the recess  9  is not formed as a non-continuous trench but rather as a continuous opening in the baseplate  2 . 
     In power semiconductor modules  1  according to the embodiment, the depth t of the recess  9  may be for example at least 30% of the thickness d 0  of the baseplate  2  or at least 1 mm. Moreover, the recess  9  may include, for example, a width of 10% to 100% of the thickness d 0  of the baseplate  2 . The distance d 1  may be chosen to be, for example, less than or equal to 3 mm. 
     Instead of or in addition to a screw connection, the connection between the baseplate  2  and the heat sink  4  may, for example, also be produced by means of a spring clip or by means of any other connecting element. 
       FIG. 12  illustrates a plan view of a baseplate  2  of a power semiconductor module  1  in accordance with an embodiment which is equipped with circuit carriers  5 . The baseplate  2  includes an essentially rectangular basic area and includes a fixing location  3  in each corner region. The circuit carriers  5  are fixed in two rows and two columns next to one another on the baseplate  2 . 
     The circuit carriers  5  also include essentially rectangular basic areas. Each of the circuit carriers  5  includes one outer corner  5   a  and also three inner corners  5   b.    
     The connecting areas  2   b  situated below the circuit carriers  5  are illustrated by broken lines. Each connecting area  2   b  includes an outer corner  2   c  corresponding to the outer corner  5   a  of the circuit carrier  5  connected to it. Moreover, each connecting area  2   b  includes inner corners  2   d  corresponding to the inner corners  5   b  of the circuit carrier  5  connected to it. 
     In the region of each of the outer corners  5   a  of the circuit carriers  5  a recess  9  is provided in the baseplate  2 , said recess being arranged between an outer corner  2   c  of the connecting area  2   b  and a fixing location  3  situated closest to the relevant outer corner  2   c . The recesses  9  are spaced distant from the second connecting layer  72  in the first lateral direction r 1  and in a second lateral direction r 2 , which is perpendicular to the first lateral direction r 1  and to the direction of the normal n. As an alternative to this, a recess  9  may also adjoin a connecting area  2   b.    
     Each of the recesses  9  runs in a predetermined angular range continuously around the outer corner  2   c  situated closest to it of the connecting area  2   b  situated closest to it. 
     The exemplary embodiment in accordance with  FIG. 13  corresponds to the exemplary embodiment in accordance with  FIG. 12  with the difference that in addition to the recesses  9  in the region of the outer corners  2   c  of the connecting areas  2   b , recesses  9  are also provided which are arranged around inner corners  2   d  of the respective connecting area  2   b  which correspond to the inner corners  5   b  of the circuit carriers  5 . 
     The recesses  9  of the baseplate  2  which are arranged in the region of the outer corners  2   c  may be formed in angular fashion in the plan view of the baseplate  2  as illustrated and include two limbs running perpendicular to one another. Depending on the concrete arrangement of the circuit carriers  5  on the baseplate  2 , the recesses  9  of the baseplate  2  which are arranged in the region of the inner corners  5   b  may be formed in T-shaped or cruciform fashion in the plan view of the baseplate  2  as illustrated by way of example. 
       FIG. 14  illustrates a plan view of a baseplate  2  of a power semiconductor module according to an embodiment on which three circuit carriers  5  arranged next to one another in a row are fixed. 
     The left-hand half of  FIG. 14  illustrates by way of example that instead of one recess  9  arranged in the region of an outer corner  2   c  or an inner corner  2   d , it is also possible for a plurality of recesses  9  to be arranged in a manner spaced distant from one another in the baseplate  2 . 
     While the fixing locations  3  are arranged in the region of the corners of the baseplate  2  in the exemplary embodiment in accordance with  FIG. 14 , they are situated centrally between the longitudinal sides  2   e  of the baseplate  2  in the exemplary embodiment in accordance with  FIG. 15 . 
     In order to reduce the von-Mises stresses proceeding from the fixing locations  3  in the case of fixing at a heat sink, a recess  9  is provided in the baseplate  2  between each of the fixing locations  3  and the circuit carrier  5  situated closest to the relevant fixing location  3 . 
     The von-Mises stresses acting on the second connecting layer may be effectively reduced by the recesses  9  in the baseplate  2 . 
       FIG. 16  illustrates by way of example the profile of the von-Mises stresses σ in the second connecting layer  72  corresponding to  FIG. 5  in the region of an outer corner  72   a , a recess according to an embodiment additionally being provided in the baseplate around the outer corner  5   a . It can be seen therefrom that the maximum value of the von-Mises stresses σ includes decreased relative to the corresponding maximum value from 26.7 MPa to 26.0 MPa, that is, by more than 2.6%. Moreover, it can be seen that a reduction of the von-Mises stresses σ also occurs in the inner region of the second connecting layer. 
     While the recesses  9  in the exemplary embodiments in accordance with  FIGS. 12 to 15  run at least in portions parallel to one of the sides of the circuit carriers, in the exemplary embodiment in accordance with  FIG. 17  in the plan view they run at an angle of greater than 0° and less than 90° with respect to each side of the circuit carrier  5  situated closest to the relevant recess  9  which form the outer corner  5   a  facing the relevant recess  9 . In this exemplary embodiment, the recess  9  is arranged, in the plan view of the front side  2   a  of the baseplate  2 , between an outer corner  5   a  of a circuit carrier  5  and the fixing location  3  situated closest to the relevant outer corner  5   a.    
     In accordance with an exemplary embodiment illustrated in  FIG. 18 , a recess  9  may also be formed in ring-shapedly closed fashion and be arranged around the connecting areas  2   b  of the baseplate  2  of a plurality of circuit carriers  5 .  FIG. 19  illustrates a portion of such an arrangement in a perspective view. 
     As can be seen from  FIG. 20 , in the case of a plurality of circuit carriers  5  connected to the same baseplate  2 , the connecting areas  2   b  of individual circuit carriers  5  may in each case be surrounded by a ring-shapedly closed recess  9 . In this case, ring-shapedly closed recesses  9  around adjacent circuit carriers  5  may be utilized jointly in portions. It is likewise possible for a plurality of recesses  9  formed in ring-shaped fashion also to be arranged in a manner spaced distant from one another. 
     The profile and intensity of the von-Mises stresses within a second connecting layer are determined by the geometry thereof. Peak values of the von Misses stresses occur primarily at the locations at which the second connecting layer and hence also the connecting area include a small edge curvature. 
     Therefore, one embodiment provides recesses in the baseplate primarily in the region of the locations at which the radius of curvature of the edge of the connecting area falls below a predetermined value. 
     An exemplary embodiment in this respect is illustrated in  FIG. 21 . An outer corner  2   c  of a connecting area  2   b  is arranged near an outer corner of a baseplate  2 . Each edge point R of the edge of the connecting area  2   b  may be individually assigned a radius r of curvature and a center M of curvature. In the limiting case, a radius r of curvature may also become infinite. 
       FIG. 21  illustrates the special case in which the edge is formed in portions as a quarter circle, such that, in all the edge points R situated on this edge portion, the radii r of curvature and centers M of curvature assigned to said edge points are identical. 
     Independently of the special case mentioned, in the case in which the radius r of curvature assigned to an edge point R falls below a predetermined value, for example 0 mm to 10 mm, a recess  9  may be provided which is arranged outside the connecting area  2   b  and which, in the plan view of the front side  2   a  of the baseplate  2 , is situated behind the edge point R in a radial direction r 0  with respect to the relevant edge point R proceeding from the center M of curvature assigned to the relevant edge point R. 
     To put it another way, in the plan view, the straight line running through the edge point R and the associated center M of curvature intersects the recess  9 . 
     If all of the radii of curvature assigned to a continuous portion of the edge of the connecting area  2   b  exceed said predetermined value, then it follows from this that the recess  9  extends over a specific minimum angle φ 0  in the plan view of the front side  2   a . In this case, the vertex of the minimum angle φ 0  is given by the center M of curvature assigned to the smallest radius of curvature that occurs in the edge portion. 
     In the case where an edge portion includes the smallest radius of curvature at a plurality of locations, a minimum angle φ over which the recess  9  at least extends may be assigned to each of the centers M of curvature assigned to said locations. 
     The criteria described in  FIG. 21  using the example of an outer corner  2   c  of the connecting area  2   b  may be applied in the same way to any desired edge location or to any desired edge portion of the connecting area  2   b , to the region of inner corners  2   d , as illustrated by way of example in  FIGS. 12 to 15 ,  17 ,  18  and  20 . 
       FIG. 22  illustrates a plan view of a portion of a baseplate  2  of a power semiconductor module according to an embodiment which includes a connecting area  2   b , a fixing location  3  spaced distant from the latter, and also a recess  9  arranged between the connecting area  2   b  and the fixing location  3 . 
     A radius r of curvature and a center M of curvature may be assigned to each edge point of the connecting area  2   b . Proceeding from said center M of curvature, in the plan view of the front side  2   a , the fixing location  3  appears at an angle φ 1  and the recess  9  appears at an angle φ 2 . 
     For the case where the radius of curvature to which the center M of curvature is assigned falls below a predetermined value, for example 0 mm to 10 mm, the recess  9  may be chosen such that the range of the angle φ 1  does not lie outside the range of the angle φ 2 . This means that a location at which the edge of the connecting area  2   b  falls below a predetermined radius of curvature is shielded from the influences of the fixing location by the recess  9 . 
     The illustration of components present in the power semiconductor module was dispensed with in part in the previous figures for reasons of clarity. In  FIGS. 12 to 15 ,  17 ,  18  and  20 , this concerns the population and interconnection of the circuit carrier  5 , a housing of the power semiconductor module and also external connections. 
     Therefore,  FIG. 23  illustrates by way of example a vertical section through a power semiconductor module  1  with more details. 
     This cross-sectional view reveals two circuit carriers  5  fixed on a baseplate  2  by means of a second connecting layer  72 . The baseplate  2  includes recesses  9  which may be arranged in the manner described above. 
     Furthermore, various recesses  9  formed in each case as desired may be provided at different locations on the baseplate  2 . In individual geometries from among the geometries of the recess  9  which are illustrated in the various exemplary embodiments may be used in mixed fashion on the same baseplate  2 . 
     In order to ensure the mechanical stability, to prevent the penetration of dirt and moisture and to increase the insulation strength of the power semiconductor module  1 , it may include a housing  10  and/or be potted with a potting composition. 
     In the exemplary embodiment in accordance with  FIG. 23 , the baseplate  2  forms a component part of the housing  10 . The power semiconductor module  1  is additionally potted with a soft potting composition  12  and with a hard potting composition  13 . 
     In this case, the soft potting composition  12  extends from the front side  2   a  of the baseplate  2  to at least over the top sides of the semiconductor chips  6  or to at least over the bonding wires  7 . The hard potting composition  13  is arranged above the soft potting composition  12  on that side of the latter which is remote from the baseplate  2 . 
     A busbar arrangement  11  is provided for externally making contact with the power semiconductor module  1 , said busbar arrangement being electrically conductively connected at least to the first metallization layers  51  of the circuit carriers  5 , for example, by means of a soldering connection. Such a busbar arrangement  11  makes it possible, for the various equipped circuit carriers  5  of the power semiconductor module  1  to be electrically interconnected with one another. 
     Busbar arrangements  11  with external control connection lugs  11   b , and also load-current-carrying busbar arrangements  11  with external load connection lugs  11   a  are provided in this case. The electrical connection between the semiconductor chips  6  and the busbar arrangements  11  is effected by means of bonding wires  7  either directly or indirectly via portions of the first metallization layers  51 . 
     Instead of or in addition to such a busbar arrangement  11 , the external connection lugs  11   a  and/or  11   b  may also be provided as separate elements, as is illustrated by way of example in  FIG. 24  on the basis of a vertical section through a portion of a power semiconductor module  1  according to an embodiment. 
     The power semiconductor module  1  includes external load connection lugs  11   a  and also external control connection lugs  11   b , which are plugged and optionally latched into guide rails  10   a  formed on the inner wall of the housing  10 . At their lower end, the connection lugs  11   a ,  11   b  are angled by 90° in order to form base regions. The base regions bear on a projection of the housing  10  and may thereby be electrically conductively connected to a semiconductor chip or a portion of the first metallization  51  of a substrate  5  by means of a bonding connection. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.