Patent Publication Number: US-9907199-B2

Title: High-power electronic module and method for making such a module

Description:
TECHNICAL FIELD 
     The invention relates to the field of power electronic devices and more particularly power electronic modules. 
     STATE OF PRIOR ART 
     For the performance of some functions such as interrupting an electrical signal, it is known that medium and low voltage circuits can be fitted with power electronic devices such as power electronic modules. Each such power module may comprise a plurality of power electrical components such as diodes or insulated gate bipolar transistors (IGBT) arranged together to form an electrical sub-circuit of the equipped electrical circuit. 
     More precisely, such a power electronic module comprises a support to support components and to connect one of their power contacts and a connection plate to connect the other power contact of components and at least one of their control contacts when they have any, in addition to the plurality of components. In this way, components are integrated into a single module with two heat exchange surfaces to evacuate heat released by the components in operation, namely surfaces of the support and the connection plate. 
     Nevertheless, in such a configuration, most of the heat is evacuated through the support. The surface area of thermal contacts at connections between each component and the connection plate is much smaller than the surface area between each component and the support. The result is that the efficiency of heat removal is reduced and mechanical problems arise related to the temperature difference between the support and the connection plate and the resulting differential thermal expansion. 
     Document US2013/020694 A1 discloses how to produce a module comprising a first and a second support on which the electronic components are laid out in order to improve the temperature distribution and to optimise evacuation of heat released by components of electronic modules. In the layout of modules disclosed in this document, each component has a first face on which a first power contact is located and through which it is supported by one of the supports, and a second face on which a second power contact is located and through which it is connected to the other support. In such a module, components of the same type are connected in series with a first component supported on the first support and a second component supported on the second support. With this procedure, the first component has a preponderant thermal contact with the second support and the second component has a preponderant thermal contact with the second support. 
     The result is that such a module has two heat exchange surfaces to evacuate heat released by the components in operation with a relatively balanced heat distribution between the first and the second support. 
     Nevertheless, such a module has a number of disadvantages concerning the thermal distribution between the supports and allowable connections between components. The thermal distribution of such a module is not always genuinely balanced because there are often cases in which the two components do not operate symmetrically or in a balanced manner, which can cause a thermal unbalance. Furthermore, according to the principle presented in document US2013/020694 A1 there are tight constraints regarding the allowable electrical circuit because components necessarily have to be mounted in series in order to create a balanced heat distribution. 
     PRESENTATION OF THE INVENTION 
     The invention aims at solving these disadvantages and thus at supplying a power electronic module that does not restrict allowable electrical circuits, while having a configuration that facilitates balanced removal of heat regardless of the operating configuration. 
     The invention relates to a power electronic module comprising:
         a plurality of power electronic components, each component comprising a first face attempt to be supported on a support in electrical contact with an electrical circuit of the support, and a second face that attempt to be electrically connected to another electrical circuit with a smaller thermal contact area than the contact area between the first face and the support,   a first and a second support arranged approximately parallel to each other and that comprise a first and a second electrical circuit respectively,       

     at least some of the components are arranged in pairs each comprising a first and a second approximately identical component. 
     The two components in a pair have a redundant arrangement, the first component in the pair being supported by the first support and connected to the second electrical circuit, the second component being supported by the second support and being connected to the first electrical circuit so as to operate in parallel with the first component in said pair. 
     Such a module is capable of good removal of heat released during operation with a balanced thermal distribution between the first and the second support while leaving it possible to make a relatively complex connection between its different components. For each pair of components, the heat exchange surface area between the first component and the first support is practically identical to the heat exchange area between the second component and the second support, to provide a balanced distribution between the two supports considering that the first and second components are redundant and function in parallel. Furthermore, such a set up in no way limits circuits that can be used with such a module, since every component can be replaced by an equivalent pair of components operating in parallel. 
     In the above and throughout the remainder of this document, the expression “the first and second components have a redundant layout” means that the first component and the second component have an equivalent layout in which they operate in parallel and under practically identical conditions. 
     In the following and throughout the remainder of this document, the expression “so as to operate in parallel” means that the first component and the second component are mounted either directly in parallel with each other or in a circuit in which the first component and the second component are included in two equivalent branches of the circuit parallel to each other. Thus, such a configuration for example includes a circuit with two pairs of components in which the first components of the two pairs are in series with each other in parallel with the second components of the two pairs also in series with each other. 
     In the above and throughout the remainder of this document, the expression “approximately identical components” means that the components have identical characteristics within tolerances. 
     The first and the second component may be installed in parallel with each other. 
     Each component may be connected to the electrical circuit of the support that is not supporting them by means of solder bridges, for example such as can be obtained by ball soldering or brazing. 
     The first face of each component may be fixed to the support supporting it by solder or brazing material. 
     Such connection and attachment means enable a fast and reliable electrical connection of components to the conducting tracks and a firm mechanical attachment of components. A module comprising these two types of means can thus be easily manufactured and may have reliable electrical and thermal connections. 
     Each component of at least one pair may comprise at least one control contact and at least two power contacts, the control contact being located on the second face and at least one first power contact being located on the first face, the electrical circuit of each of the first and the second supports may include at least one first high power circuit conducting track called the power track and a control conducting track called the control track, 
     and the components of the at least one pair may be arranged on the corresponding support with the power contact of the first face in contact with a high power track and with the control contact connected to a control track of the support on which the component is not supported. 
     With such a module configuration, the connection of one pair of components comprising a control contact, such as a controlled switch, is facilitated. 
     The control track of the first support may have a track portion facing the first power track of the second support and the control track of the second support may have a track portion facing the first power track of the first support. 
     With such a configuration, placement of a component which comprises a control contact on its second face, regrading the power and control tracks of the first and the second supports, is optimised. 
     The second power contact of each of the components which comprise a control contact may be arranged on the second face of the component, each of the first and second supports comprising at least one second power track, the components which comprise a control contact may have each the second control contact connected to the second power track of the support on which the component is not supported. 
     The second power track of the first support may comprise a track portion facing the first power track of the second support, the second power track of the second support comprising a track portion facing the first power track of the first support. 
     The invention also relates to a method of manufacturing an electronic power module comprising the following steps:
         supply a first and a second support comprising a first and a second electrical circuit respectively,   supply a plurality of power electronic components each component comprising a first and a second face, at least part of the components being designed to be arranged in pairs, each comprising a first and a second approximately identical component,   installation of each first component on the first support so that its first face supported by the first support is in electrical contact with the first electrical circuit,   install each second component on the second support such that its first face supported by the second support is in electrical contact with the second electrical circuit,   assemble the first and the second support by electrically connecting the second face of each first component to a second electrical circuit of the second support and electrically connecting the second face of each second component to a first electrical circuit of the first support so as to operate in parallel with the corresponding first component, the two components in the same pair having a redundant layout.       

     The assembly steps of each first and second component on the first and second supports respectively may be a step to solder or braze each of said first and second components. 
     During the assembly step of the first and the second components, there may be a sub-step to install solder balls and a heating sub-step for ball soldering with said soldering balls. 
     Such methods can be used for the manufacture of modules according to the invention and therefore that benefit from the corresponding advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention will be better understood after reading the description of example embodiments given for guidance only and in no way limitative, with reference to the appended drawings in which: 
         FIG. 1  shows an example of a high power module according to the invention, in which a first and a second support are separated to show high power components mounted on each support, 
         FIG. 2  diagrammatically shows the equivalent circuit of the module shown in  FIG. 1 , 
         FIGS. 3A and 3B  show the electrical circuit of a first and a second support of the module shown in  FIG. 2  with the components that it supports, respectively, the components to which they are connected being represented by their contour, 
         FIG. 4  diagrammatically shows the heat distribution during operation of the module shown in  FIG. 1 , 
         FIGS. 5A to 5D  show the main steps for manufacturing a module as shown  FIG. 1 , 
     
    
    
     Identical, similar or equivalent parts of the different figures have the same numeric references to facilitate comparison between the different figures. 
     The different parts shown in the figures are not necessarily all shown at the same scale to make the figures more easily readable. 
     DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS 
       FIG. 1  shows a perspective view of an electronic power module  1  according to the invention in which a first and a second support  10 ,  20  are separated in order to show the electronic power components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  that are arranged on these two supports  10 ,  20 . 
     With reference to  FIGS. 3A and 3B , such a module  1  comprises:
         a first and a second support  10 ,  20  each comprising an electrical circuit on their inner face, in other words the face facing the other support  20 ,  10 .   a plurality of pairs  30 ,  35 ,  40 ,  45  of components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47 , each of the pairs  30 ,  35 ,  40 ,  45  comprising a first and a second approximately identical component  31 ,  36 ,  41 ,  46 ,  32 ,  37 ,  42 ,  47  and each of the components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  comprising a first face  31   a ,  32   a ,  36   a ,  37   a ,  41   a , 42   a ,  46   a ,  47   a  supported on the first support  10  for some  31 ,  36 ,  41 ,  46  and on the second support  20  for the others  32 ,  37 ,  42 ,  47 , and a second face  31   b ,  32   b ,  36   b ,  37   b  connected to an electrical circuit of the second support  20  for the some and of the first support  10  for the others.       

     The two components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  of one pair  30 ,  35 ,  40 ,  45  have a redundant arrangement, the first component  31 ,  36 ,  41 ,  46  of said pair  30 ,  35 ,  40 ,  45  being supported by the first support  10  and connected to the second electrical circuit, the second component  32 ,  37 ,  42 ,  47  being supported by the second support  20  and connected to the first electrical circuit so as to operate in parallel with the first component  31 ,  36 ,  41 ,  46  of said pair  30 ,  35 ,  40 ,  45 . 
       FIG. 2  diagrammatically shows the sub-circuit formed by the module  1  that reproduces a conventional configuration in which two switches are put in series, better known under its name “dual switch”, in which each switch has been doubled up by two switches installed in parallel. Thus more precisely, the module  1  comprises:
         a first and a second pair  30 ,  40  of IGBTs,   a first and a second pair  35 ,  45  of diodes associated with the first and the second pair  30 , 40  of IGBTs respectively.       

     The first face  31   a ,  32   a ,  41   a ,  42   a  of each IGBT  31 ,  32 ,  41 ,  42  comprises a first power contact  31 C,  32 C,  41 C,  42 C corresponding to the IGBT collector  31 ,  32 ,  41 ,  42 . The first power contact  31 C,  32 C,  41 C,  42 C represents the largest part of the surface of the first face  31   a ,  32   a ,  41   a ,  42   a  of the IGBT  31 ,  32 ,  41 ,  42 . The second face  31   b ,  32   b ,  41   b ,  42   b  of each IGBT  31 ,  32 ,  41 ,  42  comprises a second power contact  31 E,  32 E,  41 E,  42 E corresponding to the IGBT emitter and a control contact  31 G,  32 G,  41 G,  42 G corresponding to the IGBT gate. The control contact  31 G,  32 G,  41 G,  42 G is arranged on the second face  31   b ,  32   b ,  41   b ,  42   b  of each IGBT  31 ,  32 ,  41 ,  42  in the form of a single central contact pad. The second power contact  31 E,  32 E,  41 E,  42 E is arranged on the second face  31   b ,  32   b ,  41   b ,  42   b  of each IGBT  31 ,  32 ,  41 ,  42  in the form of peripheral contact pads. Thus,  FIGS. 3A and 3B  show that each IGBT  31 ,  32 ,  41 ,  42  comprises 8 power contact pads  31 E,  32 E,  41 E,  42 E surrounding the single control contact pad  31 G,  32 G,  41 G,  42 G. 
     The first face  36   a ,  37   a ,  46   a ,  47   a  of each diode  36 ,  37 ,  46 ,  47  comprises a first power contact  36 K,  37 K,  46 K,  47 K forming a cathode. The first power contact  36 K,  37 K,  46 K,  47 K represents most of the surface of the first face  36   a ,  37   a ,  46   a ,  47   a  of the diode  36 ,  37 ,  46 ,  47 . The second face  36   b ,  37   b ,  46   b ,  47   b  of each diode  36 ,  37 ,  46 ,  47  comprises a second power contact  36 A,  37 A,  46 A,  47 A forming an anode. The second power contact  36 A,  37 A,  46 A,  47 A represents most of the surface of the second face  36   b ,  37   b ,  46   b ,  47   b  of the diode  36 ,  37 ,  46 ,  47 . 
     The layout of the first and second pairs  30 ,  40 ,  35 ,  45  of IGBTs and diodes is shown in  FIGS. 1 and 2 . 
     Thus,  FIGS. 1 and 2  show that for the first pairs  30 ,  35  of IGBTs and diodes:
         the first power contacts  31 C,  36 K of the first IGBT  31  and the first diode  36  are electrically connected together by a first power track  11 ,   the second power contacts  31 E,  36 A of the first IGBT  31  and the first diode  36  are electrically connected together by a second power track  22 ,   the control contact  31 G of the first IGBT  31  is connected to a first control track  25 ,   the first power contacts  32 C,  37 K of the second IGBT  32  and the second diode  37  are connected together by a third power track  21 ,   the second power contacts  32 E,  37 A of the second IGBT  32  and the second diode  37  are electrically connected together by a fourth power track  12 ,   the control contact  32 G of the first IGBT  32  is connected to a second control track  15 .       

     Thus, the first and the second IGBT  31 ,  32  of the first pair of IGBTs  30  are installed in parallel in a redundant layout so that they operate in parallel with each other. In the same way, the first and the second diode  36 ,  37  of the first pair of diodes  35  are installed in parallel with a redundant layout so as to operate in parallel with each other. 
     Similarly as can be seen in  FIGS. 1 and 2 , for the second pairs  40 ,  45  of IGBTs  41 ,  42  and diodes  46 ,  47 :
         the first power contacts  41 C,  46 K of the first IGBT  41  and the first diode  46  are electrically connected together by a fifth power track  13 ,   the second power contacts  41 E,  46 A of the first IGBT  41  and of the first diode  46  are electrically connected together by a sixth power track  24 ,   the control contact  41 G of the first IGBT  41  is connected to a third control track  26 ,   the first power contacts  42 C,  47 K of the second IGBT  42  and the second diode  47  are connected together by a seventh power track  23 ,   the second power contacts  42 E,  47 A of the second IGBT  42  and the second diode  47  are electrically connected together by an eighth power track  14 ,   the control contact  42 G of the first IGBT  42  is connected to a fourth control track  16 .       

     In this way, the first and the second IGBT  41 ,  42  of the second pair of IGBTs  40  are mounted in parallel in a redundant layout so that they operate in parallel with each other. In the same way, the first and the second diode  46 ,  47  of the second pair of diodes  45  are mounted in parallel with a redundant layout so as to operate in parallel with each other. 
     Such layouts of the first and second pairs  30 ,  40 ,  35 ,  45  of IGBTs  31 ,  32 ,  41 ,  42  and diodes  36 ,  37 ,  46 ,  47  are made using the first and the second electrical circuit of the first and second support  10 ,  20  respectively. 
     To achieve this and with reference to  FIGS. 1 and 3A , the first electrical circuit of the first support  10  comprises first, fourth, fifth and eighth power tracks  11 ,  12 ,  13 ,  14  and the first and third control tracks  15 ,  16 , on its inner face. The second circuit of the second support  12  comprises the second, third, sixth, seventh power tracks  21 ,  22 ,  23 ,  24  and the second and fourth control tracks  25 ,  26 , as shown in  FIGS. 1 and 3B . 
     Note that the first and eighth power tracks  11 ,  14  are connected to each other and are coincident to form a single track. Similarly, the second and seventh power tracks  21 ,  24  are connected to each other and are coincident to form a single track. 
     The first and fifth power tracks  11 ,  13  are arranged on the first support  10  such that an IGBT  31 ,  41  and a diode  36 ,  46  supported by their first face  31   a ,  41   a  electrically connected to them, the IGBT  31 ,  41  and the diode  36 ,  46  have their second power contact  31 E,  41 E,  36 A,  46 A facing a power track  22 ,  24  of the second support  20 , and such that the IGBT  31 ,  41  has its control contact  31 G,  41 G facing a control track  25 , 26  of the second support  20 . In other words, the first power track  11  faces the second power track  22  and the first control track  25  and the fifth power track  13  faces the sixth power track  24  and the third control track  26 . 
     Thus, the first IGBTs  31 ,  41  and diodes  36 ,  46  of the first and second pairs of IGBTs  30 ,  40  and diodes  35 ,  45  by being supported by their first face  31   a ,  41   a ,  36   a ,  46   a  on the first support  10  connected to power tracks  21 ,  23  of this support, can easily be connected through their second face  31   b ,  41   b ,  36   b ,  46   b  to the electrical circuit of the second support  20 . Such a connection may be provided by ball soldering  19 , as shown in  FIG. 1 . 
     Similarly, the third and seventh power tracks  21 ,  23 , are laid out on the second support  20  such that when an IGBT  32 ,  42  and a diode  37 ,  47  are supported by their first face electrically connected to the latter, the IGBT  32 ,  42  and the diode  37 ,  47  have their second power contact  32 E,  42 E,  37 A,  47 A facing the same power track  12 ,  13  of the first support  10  and the IGBT  32 ,  42  has its control contact  32 G,  42 G facing a control track  15 ,  16  of the first support  10 . In other words, the third power track  21  has a track portion facing the fourth power track  12  and the second control track  15  and the seventh power track  23  has a track portion facing the eighth power track  14  and the fourth control track  16 . 
     Thus, the second IGBTs  32 ,  42  and diodes  37 ,  47  of the first and second pairs of IGBTs  30 ,  40  and diodes  35 ,  45  being supported by their first face  32   a ,  42   a ,  37   a ,  47   a  on the second support  20  connected to the power tracks  21 ,  23  of this support can easily be connected by their second face  32   b ,  42   b ,  37   b ,  47   b  to the electrical circuit of the first support  10 . 
     Note that the first and the eighth power tracks  11 ,  14  comprise a track portion facing the third and sixth power tracks  21 ,  24  respectively, to enable connection of the first and eighth power tracks  11 ,  14  of the first support  10  with the third et sixth power tracks  21 ,  24  of the second support  20 . Similarly the fourth and the fifth power tracks  12 ,  13  comprise a track portion facing the second and seventh power tracks  22 ,  23  respectively, to enable a connection between the fourth and fifth power tracks  12 ,  13  of the first support  10  with the second and seventh power tracks  22 ,  23  respectively of the second support. 
     Thus, connections between the power tracks  11 ,  12 ,  13 ,  14 ,  21 ,  22 ,  23 ,  24  of the first and of the second support  10   20  may be made using a simple connection method such as ball soldering  19  as shown in  FIG. 1 . 
     Similarly, to enable simultaneous control of the first and second IGBTs  31 ,  41 ,  32 ,  42  of a single pair of IGBTs  30 ,  40 , the first and the third control tracks  15 ,  16  each comprises a track portion facing the second and the fourth control track  25 ,  26  respectively. In this way, the first and the third control tracks  15 ,  16  may be connected to the second and fourth control tracks  25 ,  26  respectively by a simple connection method such as ball soldering as shown in  FIG. 1 . 
     Therefore with such a module, as shown in  FIG. 1 , the thermal contact area between the first component  31 ,  36 ,  41 ,  46  of each of the pairs  30 ,  35 ,  40 ,  45  and the first support  10  is larger than the thermal contact area with the second support  20 . The thermal contact area on the first support  10  is provided by an attachment of the first face  31   a ,  36   a ,  41   a ,  46   a  of the first component  31 ,  37 ,  41 ,  47  on a power track of the first  11 ,  13  support  10  while it is provided by the thermal contact with the second support  20  by simple electrical connections such as solder balls  19 . The result is that the thermal contact area of the first component  31 ,  36 ,  41 ,  46  of each pair  30 ,  35 ,  40 ,  45  with the first support  10  is generally 5 times or even 10 or more times larger than with the second support  20 . 
     Conversely, and in the same manner, the second component  32 ,  37 ,  42 ,  47  of each pair  30 ,  35 ,  40 ,  45  has a larger thermal contact surface area with the second support  20  than the thermal contact surface area with the first support  10 . Thus, the second component  32 ,  36 ,  42 ,  47  of each pair  30 ,  35 ,  40 ,  45  has a thermal contact surface area with the second support  20  that is generally 5 times or even 10 times larger than with the second support  10 . 
     Since the first and the second components  31 ,  36 ,  41 ,  46 ,  32 ,  37 ,  42 ,  47  of a single pair  30 ,  35 ,  40 ,  45  operate in parallel as shown in  FIG. 2 , therefore as shown in  FIG. 4 , during operation, the quantity of heat transmitted through the first and second components  31 ,  36 ,  41 ,  46 ,  32 ,  37 ,  42 ,  47  to the first or the second support  10 ,  20  balances the quantity of heat transmitted by the other of the first and second components  31 ,  36 ,  41 ,  46 ,  32 ,  37 ,  42 ,  47  to the other of the first and second supports  10 ,  20 . Thus, as shown in  FIG. 4 , the first and the second supports  10 ,  20  receive the same quantity of thermal energy. The result is that heat dissipation is approximately identical to heat dissipation in modules in which the components are thermally connected to the two supports  10 ,  20 . 
     Such a module may be manufactured using a method comprising the following steps:
         supply the first and the second supports  10 ,  20 , each comprising a conducting face like that shown in  FIG. 5A , in which conducting tracks such as power or control tracks may be formed,   supply of power components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  in pairs  30 ,  35 ,  40 ,  45 ,   attachment of the first face  31   a ,  32   a ,  36   a ,  37   a ,  41   a ,  42   a ,  46   a ,  47   a  of components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  onto the conducting face of supports  10 ,  20 , with the first component  31 ,  36 ,  41 ,  46  of each pair  30 ,  35 ,  40 ,  45  attached to the first support  10  and the second component  32 ,  37 ,  42 ,  47  of each pair  30 ,  35 ,  40 ,  45  attached to the second support, as shown in  FIG. 5B  for the first support  10 ,   formation of power and control tracks  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  21 ,  22 ,  23 ,  24 ,  25 ,  26  on the conducting face of each support  10 ,  20 , as shown in  FIG. 5C  for the second support  20 ,   formation of balls  19  for ball soldering, onto the second faces of the components and onto power and control tracks of supports, as shown in  FIG. 5D ,   assembly of the first and the second support so as to bring the power and control tracks of the first support and the second support to face each other as can be seen in  FIG. 1  before closing the module  1 ,   heating to achieve ball soldering of components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  onto the power and control tracks  11 ,  12 ,  13 ,  14 ,  21 ,  22 ,  23 ,  24 ,  15 ,  16 ,  25 ,  26  of the support  10 ,  20  on which the components  31 ,  32 ,  36 ,  37 ,  41 ,  42 ,  46 ,  47  are not supported.       

     During the step to fasten the components through their first face onto the conducting face of the corresponding support, this attachment may be made equally well by brazing or by soldering. Thus, each component may be fixed to the support supporting it either by brazing material or by solder material. 
     Similarly, the method includes a step to position solder balls, to assemble the supports, and a heating step in which ball soldering is done. Nevertheless, without going outside the scope of the invention, it would also be possible to connect the components to the support that is not supporting them using a different method such as the use of solder bridges other than solder balls. 
     Note also that in the embodiment described above, although two pairs of IGBTs and two pairs of diodes are described, the principle of the invention can be applied to other types of modules comprising an arbitrary number of switches, with different components distributed in a different number of pairs. Thus, the invention can be applied to a module comprising a single pair of IGBTs or to modules with much more complex structures.