Abstract:
An electric sub-assembly has an integrated circuit, which contains at least one power semi-conductor component and additional electronic components, the latter being interconnected and linked to connections by the conductors of a lead frame ( 1, 2, 3 ). The lead frame ( 1, 2, 3 ) has at least one cooling surface ( 3 ), which is connected in a thermally conductive manner to a thermal contact ( 4 ) of the integrated circuit or circuits. The cooling surface has a greater surface area than the thermal contact surface ( 4 ) of the integrated circuit or circuits and is wider than the parts ( 1 ) of the lead frame that are used as electric conductors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application of International Application No. PCT/EP2005/054189 filed Aug. 25, 2005, which designates the United States of America, and claims priority to German application number DE 10 2004 042 488.8 filed Aug. 31, 2004, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The invention relates to an electrical assembly comprising an integrated circuit, which has at least one power semiconductor element and further electronic components, which are connected to one another and to connections by conductors formed by a leadframe. 
     BACKGROUND 
     Electrical assemblies, which are to operate reliably and must be robust in relation to ambient influences, are often realized with the aid of leadframe structures to which active and passive electrical and electronic components are applied by welding. The assemblies are encapsulated with electrically insulating materials, so that they are hermetically sealed in relation to ambient influences and can withstand even large mechanical loadings (impact, vibration). Examples of such assemblies are rotational speed sensors or position sensors in motor vehicles. 
     When using power semiconductor elements, in particular field effect transistors, occasionally large power losses arise, however, which are difficult to dissipate in the case of the assemblies described. 
     SUMMARY 
     It is an object of the present invention to configure an electrical assembly according to the preamble in such a way that, whilst maintaining the positive properties and with minimum additional costs, good heat dissipation is possible and a construction by way of printed circuit board assemblies (epoxy printed circuit boards or ceramic boards using SO technology) with separate cooling elements is avoided. 
     In the case of the assembly according to an embodiment, this object is achieved by virtue of the fact that the leadframe has at least one cooling area, which is thermally conductively connected to a thermal contact area of the at least one integrated circuit, which has a larger area than the thermal contact area of the at least one integrated circuit and which is wider than the parts of the leadframe which are used for electrical conduction. 
     Thus, according to an embodiment, an electrical assembly may comprise an integrated circuit, which has at least one power semiconductor element and further electronic components, which are connected to one another and to connections by conductors formed by a leadframe, wherein the leadframe has at least one cooling area, which is thermally conductively connected to a thermal contact area of the at least one integrated circuit, which has a larger area than the thermal contact area of the at least one integrated circuit and which is wider than the parts of the leadframe which are used for electrical conduction, and wherein the cooling area is formed as a thermal contact plate with a connection lug, which is bent away from its plane at its end remote from the integrated circuit and at which one end of the contact area bears and is thermally conductively connected, wherein the thermal contact plate is injection-molded or cast into a component composed of an electrically insulating material, wherein the component has a receptacle, into which the integrated circuit can be inserted in a manner positioned in such a way that connection lug and mating connection lug bear on one another and signal connection lugs and signal mating connection lugs bear on one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention permits numerous embodiments. A plurality of these embodiments are illustrated schematically in the drawing on the basis of a plurality of figures and are described below. In the figures: 
         FIG. 1  shows a first view of an exemplary embodiment, 
         FIG. 2  shows a second view of parts of the exemplary embodiment according to  FIG. 1 , 
         FIG. 3  and  FIG. 4  each show a cross section through a part of an exemplary embodiment in which, as a result of prior bending of the cooling area, a good thermal contact is obtained in a first phase during production and in the finished state, 
         FIG. 5  shows an exemplary embodiment with an encapsulation composed of plastic, 
         FIG. 6  shows a further exemplary embodiment with an encapsulation. 
         FIG. 7  shows a perspective view of a further exemplary embodiment, 
         FIG. 8  shows a perspective view of a further exemplary embodiment, and 
         FIG. 9  shows a perspective view of a further exemplary embodiment, 
         FIG. 10  shows a stylized plan view of a leadframe with connected circuit, motor and sensor. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, the leadframe is preferably stamped out in one piece from a metal sheet. Parts of the leadframe serve for electrical connection, and other parts serve for cooling. According to an embodiment, the thermal connection between the contact area and the cooling area can be effected in various ways, for example by conductive adhesive, by welding or soldering. However, it is also possible for a spring-elastic clamping to be provided. According to an embodiment, the cooling area may in particular cases be connected to the ground or the negative pole of the operating voltage source. 
     In order to obtain a good thermal contact, in one embodiment of the assembly it is provided that the cooling area is fixedly connected to the contact area at least two opposite edges, and that the area region of the cooling area that bears on the contact area is prestressed against the contact area. It is assumed in this case that the thickness of the cooling plate is smaller than the thickness of the metal body of the integrated circuit that forms the contact area. 
     One advantageous configuration of the assembly consists in the fact that the assembly including the leadframe is encapsulated with an electrically insulating material. According to an embodiment, the assembly can be brought into contact with cooling air. 
     In order in this case to ensure a good heat dissipation from the cooling area to the surrounding medium, however, in this configuration it may be provided that the cooling area is at least partially not encapsulated, or that the cooling area is at least partially encapsulated with a thinner layer than the remaining parts of the assembly. 
     Another embodiment enables a universal use of the assembly by virtue of the fact that the further electronic components form an application specific integrated circuit. 
     Moreover, in the case of the assembly according to an embodiment it may be provided that a sensor, in particular a position detecting sensor, is connected with the aid of the conductors formed by the leadframe. 
     According to an embodiment, a particularly compact assembly is obtained by the application specific integrated circuit and the integrated circuits being integrated in a common housing. 
     Furthermore, the fact that the leadframe is mounted in an electrically insulating holding frame contributes to the stability in the manufacturing process, according to an embodiment. 
     For electrical connection to other assemblies and apparatuses, in accordance with one embodiment, it may be provided that parts of the leadframe are embodied as electrical plug connections. 
     In order to improve the heat dissipation, it may furthermore be provided that a thermally conductive intermediate layer is applied between the contact area and the region of the leadframe that touches said contact area, according to an embodiment. 
     If the cooling area is formed as a thermal contact plate with a connection lug, which is bent away from its plane at its end remote from the integrated circuit and at which one end of the contact area bears and is thermally conductively connected, then both simple mountability of the integrated circuit and simple diagnosis in the event of a defect of the assembly are possible. 
     Said simple mountability is also improved if the contact area has a mating connection lug, which bears on the connection lug of the thermal contact plate and is thermally conductively connected to the connection lug, according to an embodiment. 
     A welding may be effected e.g. in a simple manner after the completion of the component of the assembly, according to an embodiment. 
     According to an embodiment, the same advantages are furthermore achieved if the leadframe has signal-carrying conductors having signal connection lugs, which are bent away from their plane at their ends facing the integrated circuit and at which ends the signal-carrying conductors bear and are electrically conductively connected, and if the ends of the signal-carrying conductors have signal mating connection lugs, which bear and are electrically conductively connected at the signal connection lugs. 
     Both good thermal conduction and good electrical conduction are achieved by virtue of the fact that the connection lug is connected to the mating connection lug and/or the signal connection lugs are connected to the signal mating connection lugs by welding such as electrical resistance welding or laser welding or by soldering, according to an embodiment. 
     Good thermal conduction can be achieved in a simple manner also by virtue of the fact that the connection lug is connected to the mating connection lug by means of electrically and/or thermally conductive adhesive, according to an embodiment. 
     For good electrical conduction, in a simple manner, the signal connection lugs may be connected to the signal mating connection lugs by means of an electrically conductive adhesive, according to an embodiment. 
     If the thermal contact plate is injection-molded or cast into a component composed of an electrically insulating material, wherein the component has a receptacle, into which the integrated circuit can be inserted in a manner positioned in such a way that connection lug and mating connection lug bear on one another and signal connection lugs and signal mating connection lugs bear on one another, then as a result of the integrated circuit being inserted into the receptacle, at the same time connection lugs and mating connection lugs and also signal connection lugs and signal mating connection lugs bear on one another in a correctly assigned manner, which significantly simplifies the mounting operation, according to an embodiment. 
     For conductive connection, a good accessibility e.g. for welding is achieved if connection lug and mating connection lug and/or signal connection lugs and signal mating connection lugs are bent away in a manner directed away from the plane of a bottom of the receptacle, according to an embodiment. 
     If the thermal contact plate is injection-molded or cast into the component composed of electrically insulating material in such a way that at least 50% of the area of the contact plate is covered with a wall thickness of the electrically insulating material of &lt;3 mm, in particular of &lt;1.5 mm, then good heat dissipation from the thermal contact plate via the component composed of electrically insulating material is achieved in conjunction with good stability of the assembly, according to an embodiment. 
     If the signal-carrying conductors of the leadframe are injection-molded or cast into the component composed of electrically insulating material, and the integrated circuit can be inserted into the receptacle in a manner positioned in such a way that mutually assigned signal connection lugs and signal mating connection lugs bear on one another, then a simple exact positioning of the signal connection lugs with respect to the signal mating connection lugs during mounting is possible in this case, too, according to an embodiment. 
     For further dissipation of the heat generated by the integrated circuit, according to an embodiment, the integrated circuit may bear with a boundary wall on the bottom of the receptacle, in which case preferably the component composed of electrically insulating material has a wall thickness of &lt;4 mm, in particular of &lt;2 mm, in the region of the bottom of the receptacle. The smaller the wall thickness, the better the heat dissipation capability to the ambient air. 
     In this case, according to an embodiment, the integrated circuit may bear on the bottom of the receptacle via an intermediate layer. 
     For good heat transfer, it is possible for the intermediate layer to comprise a thermally conductive adhesive, a thermally conductive adhesive film or a thermally conductive paste, according to an embodiment. 
     If the thermal contact plate is provided with a cutout or a plurality, in particular a multiplicity of continuous cutouts in its region enclosed by the electrically insulating material, according to an embodiment, then an at least largely reliable bearing of the contact plate on the plastic is achieved, even in the event of temperature change, by means of the electrically insulating material filling the cutouts. Delaminations between these parts which might occur after a temperature change and might lead to an insulating layer of air between said parts are thus avoided in a simple manner. 
     According to an embodiment, the integrated circuit may be a plastic-encapsulated power semiconductor element or a hybrid circuit that is arranged on a substrate and has power semiconductor elements. 
     In this case, according to an embodiment, the substrate is preferably a ceramic substrate or an insulated metal substrate or an epoxy printed circuit board, on which the power semiconductor element and electronic components are arranged, in particular soldered or in particular thermally conductively adhesively bonded. 
     In the exemplary embodiment according to  FIGS. 1 and 2 , conductors  1  of a leadframe connect a structural unit which is formed as an integrated circuit and comprises a plurality of power semiconductor elements  2  to an application specific integrated circuit  7  and a sensor  6 . Further conductors of the leadframe are led out from the assembly and serve as connection pins  9 ,  9 ′. A wider conductor of the leadframe is extended areally and forms a cooling area  3 , which is in thermal contact with a thermal contact area  4  of the integrated circuit  2 . The connection pins  9  serve for connection to a motor, preferably via interference-suppression inductors, which are not illustrated in  FIG. 1 . The conductors  1 ′ illustrated as broken off are intended to show that other components may additionally be present in the assembly according to an embodiment. 
     During production, a leadframe is firstly produced as one piece. Bridges present between the individual conductors  1 ,  1 ′ are separated later. As a result, the leadframe can be handled as one piece up to a definition of the conductors. The separation is effected only when the individual conductors have been fixed, which is effected by a holding frame  8  in the exemplary embodiment according to  FIG. 1 . A final fixing is effected when the entire assembly is encapsulated with electrically insulated material. 
     In the exemplary embodiment according to  FIG. 3 , an area region  5  of a conductor of the leadframe is pre-bent on that area which is intended to touch the contact area  4  of the power semiconductor element  2 . During mounting, the area region  5  is pressed onto the contact area  4  and fixed there for example by means of a soldering or welding seam  10  or by suitable clips. By means of the prestress, the conductor bears fixedly on the entire contact area  4  in the area region  5 . 
     The exemplary embodiment according to  FIG. 5  has an encapsulation  11 , which also encompasses the cooling area  3  and is illustrated in transparent fashion in order to provide a clear view of the components and conductors. In order to obtain higher heat dissipation, the cooling areas  3  are not enclosed by the encapsulation  12  in the case of the exemplary embodiment according to  FIG. 6 . 
     The exemplary embodiments illustrated in  FIGS. 7 to 9  show an approximately pot-like component  13  composed of an electrically insulating material, which is a plastic and may be an epoxy resin, a filler plastic or a thermosetting plastic. 
     The housing part  13  may be a housing cover of a housing of a butterfly valve for a motor vehicle. 
     A recessed cutout  15  having a rectangular cross section is formed at the base of the pot-like depression  14  of the component  13 . 
     A leadframe comprising thermal contact plates  16 ,  16 ′ and signal-carrying conductors  17 ,  17 ′ is concomitantly injection-molded into the plastic. 
     In the case of the exemplary embodiment in  FIG. 9 , the leadframe was firstly provided with a preencapsulation  18  composed of plastic so as then to be encapsulated by injection-molding once again in a further work operation to form the component  13 . 
     In each case two contact plates  16  and two conductors  17  project in a manner lying alongside one another from the side wall of the depression  14  of the component  13 . 
     Opposite said two contact plates  16  and conductors  17 , likewise two contact plates  16 ′ and two conductors  17 ′ project from a side wall of the depression  14  of the component  13 . 
     The free ends of the contact plates  16 ,  16 ′ which project into the depression  14  are bent away at right angles from the plane of the contact plates  16 ,  16 ′ to form connection lugs  19 ,  19 ′. 
     In the same way, the free ends of the conductors  17 ,  17 ′ which project into the depression  14  are also bent away at right angles from the plane of the conductors  17 ,  17 ′ to form signal connection lugs  20 ,  20 ′. 
     Both the connection lugs  19 ,  19 ′ and the signal connection lugs  20 ,  20 ′ are directed toward the opening of the depression  14 . 
     An integrated circuit having approximately the same cross-sectional contour as the receptacle  15  is inserted into the receptacle  15 , and is connected to the bottom  27  of the receptacle  15  by means of a thermally conductive adhesive  26  in  FIG. 9 . 
     In the case of the exemplary embodiments of  FIGS. 7 and 9 , plate-like contact areas  4  are led out, parallel to the contact plates  16 ,  16 ′, from the sides of the encapsulated integrated circuit  21  which face the contact plates  16 ,  16 ′ and are bent away at right angles at their free ends in a manner directed toward the opening of the depression  14  to form mating connection lugs  22 ,  22 ′. 
     Each connection lug  19 ,  19 ′ is assigned a mating connection lug  22 ,  22 ′. In this case, mutually assigned connection lugs  19 ,  19 ′ and mating connection lugs  22 ,  22 ′ have the same width, are directed in the same direction and bear on one another. 
     The mutually assigned connection lugs  19 ,  19 ′ and mating connection lugs  22 ,  22 ′ are electrically and thermally conductively connected to one another by a plurality of welding points  23 . 
     In the same way as the mating connection lugs  22 ,  22 ′, plate-like signal conductors  24 ,  24 ′ are also led out from the integrated circuit and bent away to form signal mating connection lugs  25 ,  25 ′, which bear on the signal connection lugs  20 ,  20 ′ and are electrically conductively connected thereto by welding points  23 ′. 
     In the case of the exemplary embodiment in  FIG. 8 , plate-like contact areas  4 ′ are present, which are bent to form a “U” in a manner corresponding to the receptacle  15  and are inserted into the receptacle  15 . 
     The contact areas  4 ′ are fixed to the bottom  27  of the receptacle  15  by means of a thermally conductive adhesive  26 , a substrate  29  of the integrated circuit  21 ′ likewise being fixed on the inner side of the “U” of the contact area  4 ′ by means of a thermally conductive adhesive  28 . 
     In this case, that part of the contact area  4 ′ which bears on the bottom  27  forms an intermediate layer  30 . 
     The two parallel limbs of the contact areas  4 ′ form mating connection lugs  22 ,  22 ′ which, as in the exemplary embodiments in  FIGS. 7 and 9 , bear on the connection lugs  19 ,  19 ′ and are thermally conductively connected thereto by welding points  23 ,  23 ′. 
     Arranged on the substrate  29  is an integrated circuit  21 ′ in the form of a hybrid circuit with conductor tracks (not illustrated), which also has a power semiconductor element alongside further electronic components. 
     Some of the conductor tracks (not illustrated) lead to the edge regions of the substrate  29  which are opposite the signal connection lugs  20 ,  20 ′. Plate-like signal conductors  24 ,  24 ′ are soldered by one end thereof onto the ends of the conductor tracks of the substrate  29  which are respectively assigned to them. 
     The other ends of the signal conductors  24 ,  24 ′ are bent away at right angles to form signal connection lugs  20 ,  20 ′ and bear on the signal mating connection lugs  25 ,  25 ′ which are respectively assigned to them and to which they are electrically conductively connected by welding points  23 ,  23 ′. 
     In the case of the exemplary embodiments in  FIGS. 7 to 9 , the regions of the contact plates  16 ,  16 ′ which are arranged in the component  13  extend near the outer wall of the component  13 , with the result that the majority of their area is covered by the electrically insulating material having only a small wall thickness  32  of approximately 1 to 1.5 mm. Good heat emission toward the outside is thereby possible. 
     For good connection of the contact plates  16 ,  16 ′ to the electrically insulating material, a multiplicity of continuous cutouts  31  which are filled by the electrically insulating material are formed in the contact plates  16 ,  16 ′. 
     In the case of the exemplary embodiments in  FIGS. 7 and 9 , the contact plates  16 ,  16 ′ serve both for heat dissipation and as electrical connection to plug pins (not illustrated), while in the case of the exemplary embodiment in  FIG. 8 , the contact plates  16 ,  16 ′ serve only for heat dissipation. 
       FIG. 10  reveals the stylized plan view of a leadframe such as is used in the case of the exemplary embodiments in  FIGS. 7 and 9 . 
     In this case, the contact plates  16  have plug pins  33  and one of the conductors  17  leads to a position detection sensor  34 . 
     A further conductor  17  leads to the voltage supply  35 . 
     A DC motor  36  can be driven by the integrated circuit via the contact plates  16 ′.