Power electronic switching device and assembly

A switching device having a substrate, a power semiconductor component, a connecting device, load connection devices and a pressure device. Substrate has electrically insulated conductor tracks. A power semiconductor component is arranged on a conductor track. Connecting device is formed as a film composite having an electrically conductive film and an electrically insulating film, and has first and second main surfaces. Switching device is connected in an internally circuit-conforming manner by connecting device. The pressure device has a pressure body with a first recess, a pressure element being arranged so that it projects out of the recess, wherein the pressure element presses onto a section of the second main surface of film composite and, in this case, the section is arranged within the surface of the power semiconductor component in projection along the normal direction of the power semiconductor component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a power electronics switching device which can form a base cell of a power semiconductor module or of a power electronics system by the power electronics switching device alone or in combination with further, preferably identical, base cells forming the basic power electronics building block of the power semiconductor module or of the power electronics system.

2. Description of the Related Art

Known power semiconductor modules are shown, for example, in German Patent Application DE 10 2010 62 556 A1, in the form of a power semiconductor module in which a housing has pressure elements with a pressure body, wherein the pressure body presses either directly onto a portion of a semiconductor component or onto a section of a substrate. U.S. Pat. No. 7,808,100 B2 likewise discloses pressing directly onto power semiconductor components by a pressing ram. One disadvantage of these two devices is that direct pressure can be applied to a power semiconductor component, which is connected in an internally circuit-conforming manner by wire bonded connections, only in a highly selective manner due to the limited area available in real-world applications. Therefore, the current-carrying capacity of the internal connection is reduced, since no bonding connections can be established at the pressure point.

German Patent Application DE 10 2007 006 706 A1 describes a circuit arrangement having a substrate and conductor tracks arranged on the substrate, with semiconductor components arranged on the conductor tracks. According to this disclosure, an internal connecting device is formed as a film composite which connects a power semiconductor component to a contact area of a conductor track. In this case, an insulating material is arranged at the edge of the semiconductor component.

By way of further example, German Patent Application DE 10 2006 006 425 A1 discloses forming a power semiconductor module so that pressure devices, formed as load connection elements with a plurality of contact feet in each case, exert pressure on contact points of a substrate to establish thermally conductive contact between the substrate and a cooling device. However, one disadvantage of this arrangement is that, in spite of a plurality of contact feet which exert pressure, the thermal connection is not optimal since the thermal connection of the power semiconductor component which generates waste heat is made only indirectly.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved power electronics switching device which overcomes the drawbacks of the prior art.

It is a further object of the invention to provide a power electronics switching device and an arrangement comprising the same, wherein the switching device can be used in a versatile manner and, as a base cell, thereby offering improved and, preferably, optimal thermal pressure connection to a cooling device.

The inventive switching device is a power electronics switching device having a substrate, a power semiconductor component is arranged on the substrate, a connecting device, load connection devices and a pressure device, wherein the substrate has conductor tracks which are electrically insulated from one another and a power semiconductor component is arranged on a conductor track and is cohesively connected to the conductor track, wherein the connecting device is formed as a film composite having an electrically conductive film and an electrically insulating film, and therefore forms a first and a second main surface, and wherein the switching device is connected in an internally circuit-conforming manner by a connecting device, wherein the pressure device has a pressure body with a first recess, a pressure element being arranged such that it projects out of the recess, and wherein the pressure element presses onto a section of the second main surface of film composite and, in this case, the section is arranged within the surface of the power semiconductor component in projection along the normal direction of the power semiconductor component.

It goes without saying that the term “power semiconductor component” as used herein would be understood to include at least one power semiconductor component, wherein a plurality of power semiconductor components can be arranged on one or more conductor tracks.

In the inventive device, it is preferred that the recess in the pressure body is formed exclusively as a depression starting from a first main surface or as a depression starting from the first main surface with a cutout, which passes through the pressure body to the second main surface, with an opening arranged there. In this case, the pressure element can substantially completely fill the recess in the pressure body. As an alternative, at the same time or in addition, the pressure element can project out of the cutout in the pressure body at its second main surface.

In a particularly preferred embodiment, the pressure body can be composed of a high-temperature-resistant thermoplastic material, in particular polyphenylene sulphide, and the pressure element can be composed of a silicone rubber, in particular liquid silicone.

In order to form an efficient pressure device which, when it is loaded for the power semiconductor component, does not lead to destruction of the power semiconductor component, it is particularly advantageous when the surface area of the section is at least about 20%, most preferably at least about 50%, of the surface of the power semiconductor component.

Within the meaning of a base cell, it is further preferred when the lateral extent of the pressure device in the two orthogonal directions parallel to the substrate plane is smaller than the lateral extent of the substrate as such.

In order to provide particular protection against environmental influences, it may also be preferred that the top face of the substrate, including the conductor tracks of the substrate, the power semiconductor component and connecting device, be encapsulated in a moisture-tight manner by an encapsulation compound.

An arrangement having an above-described electronic switching device, having a cooling device and having a pressure introduction device is formed according to the invention, wherein the pressure introduction device is supported indirectly or directly against the cooling device, introduces pressure centrally onto the pressure device and, as a result, the switching device is connected in a force-fitting manner to the cooling device. In this case, a cooling device can be understood to mean, in particular, a base plate or preferably a heat sink.

Similarly, on account of the particularly effective introduction of pressure, it is possible for a thermally conductive paste to be arranged between the substrate, in particular that part of the substrate on which the power semiconductor components are arranged, and the cooling device. The paste preferably has a thickness of less than about 20 μm, more preferably of less than about 10 μm, and most preferably of less than about 5 μm.

It is particularly preferred when the ratio of the lateral extent to the vertical extent of the pressure body before the arrangement with a cooling device has a ratio of at least about 2 to 1, and more preferably of at least about 4 to 1, and after this arrangement, together with the accompanying application of pressure, has a ratio of at least about 3 to 1, and more preferably of at least about 5 to 1.

It goes without saying that the various embodiments of the invention can be realized individually or in any desired combinations in order to achieve improvements. In particular, the features mentioned and explained above can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1shows a first embodiment of a power electronics switching device1according to the invention.FIG. 1shows a substrate2which is formed in a manner which is fundamentally routine in the art, having an insulating material body20and conductor tracks22which are arranged on insulating material body20, are each electrically insulated from one another and have different potentials, in particular load potentials, but also auxiliary, in particular switching and measurement, potentials, of the switching device. Specifically, three conductor tracks22with load potentials as are typical for a half-bridge topology are illustrated here.

A respective power switch24, which may be formed conventionally as an individual switch, for example as a MOSFET or as an IGBT with a power diode which is connected back-to-back in parallel, is arranged on two conductor tracks22, the power switches being illustrated here. Power switches24are electrically conductively connected to conductor tracks22in conventional fashion, preferably by a sintered connection.

The internal connections of switching device1are formed by a connecting device3from a film composite which has, in an alternating manner, electrically conductive films30,34and one or more electrically insulating films32. In this case, film composite3has exactly two conductive films and one insulating film which is arranged between the conductive films. In this case, that surface of film composite3which faces substrate2forms a first main surface300, whereas the surface opposite the substrate forms a second main surface340. In particular, the conductive films30,34of connecting device3are inherently patterned and therefore form conductor track sections which are electrically insulated from one another. These conductor track sections connect, in particular, the respective power semiconductor component24, more precisely the contact areas of the power semiconductor component on that side which is averted from substrate2, to conductor tracks22of substrate2. In a preferred embodiment, the conductor track sections are cohesively connected to the contact areas by a sintered connection.

The connections between power semiconductor components24and between conductor tracks22of substrate2can also be formed in the same way. Particularly in the case of pressure-sintered connections, it is advantageous, as illustrated, to arrange an insulating compound28at the edge region of power semiconductor component24. This insulating compound28can also be arranged in the intermediate spaces between conductor tracks22.

For the purpose of electrical connection, power electronics switching device1has load connection elements4and auxiliary connection elements (not shown). Load connection element4are formed, purely by way of example, as shaped metal bodies which are cohesively connected, advantageously likewise connected by a sintered connection, to a conductor track22of substrate2by a contact foot. In principle, parts of connecting device3itself can also be formed as load connection elements or auxiliary connection elements. The auxiliary connection elements, such as gate or sensor connections, can otherwise be formed in any known manner.

As shown, a pressure device5has a first main surface500which faces substrate2, and a second main surface502, which is averted from substrate2, and in this case is illustrated in a manner spaced apart from connecting device3for clarity of illustration. Pressure device5is composed of a pressure body50and a plurality of pressure elements52, two of which are illustrated. Pressure body50is preferably of particularly rigid form so as to pass pressure which is thereto to pressure elements52in a homogeneous manner. To this end, and against the background of thermal loading during operation of switching device1, pressure body50is composed of a high-temperature-resistant thermoplastic material, in particular of polyphenylene sulphide. Pressure elements52have to be able to exert a substantially constant pressure during operation and, in this case, in particular at different temperatures. To this end, pressure elements52are composed of a silicone rubber, preferably of a so-called liquid silicone.

In the two orthogonal directions parallel to the plane of substrate1, pressure device5has a lateral extent540which is smaller than the associated lateral extent200of substrate2itself.

FIG. 2shows this first embodiment of an arrangement100according to the invention. Arrangement100has a first power electronics switching device1according toFIG. 1, and also a heat sink, which forms a cooling device7, and a schematically indicated pressure introduction device6.

Pressure introduction device6is supported, in a manner not illustrated, against the cooling device7. This support can be performed either directly or indirectly, for example by a screw connection between pressure introduction device6and a housing which is attached to the cooling device.

In this case, the pressure introduction device6presses centrally onto pressure device5of switching device1. Pressure body50of pressure device5distributes the applied pressure uniformly between pressure elements52which, for their part, press on sections342of second main surface340of connecting device3. Sections342of connecting device3, to which pressure is applied, are selected according to the invention so that they, and therefore the areas of extent thereof, are arranged, as viewed in the normal direction of the associated power semiconductor component24, within the surface of the power semiconductor component24. Therefore, pressure element52presses onto the power semiconductor component24by connecting device3so that the power semiconductor component, more precisely substrate2which is located beneath power semiconductor component24, is pressed onto heat sink7and therefore the thermal contact from the power semiconductor component24to heat sink7is optimized.

Owing to this introduction of pressure onto pressure elements52, pressure elements52deform, wherein it is also possible in this case for the lateral extent342of pressure elements52to increase. In the load-free state, that is to say, without pressure being introduced, cf.FIG. 1, pressure body52has a ratio of its lateral extent520to its vertical extent522of at least about 4 to 1, cf. the information given in relation to the dimensions inFIG. 4. This ratio changes to at least about 5 to 1 in the loaded state, that is to say in the state in which pressure is applied, and owing to the resulting deformation of the pressure body52according toFIG. 2.

A thermally conductive paste70may preferably be arranged between substrate2and heat sink7with a thickness of less than about 10 μm, preferably less than about 5 μm. A thin thermally conductive paste layer70of this kind is possible, taking into account latent local sagging of substrate2, in particular owing to the pressure being introduced onto the power semiconductor component24in the normal direction, and therefore power semiconductor component24, and not a surrounding area, being in optimal thermal contact with heat sink7.

In this embodiment, the cooling device is illustrated as a heat sink7for air cooling, but can equally be formed as a base plate of a power semiconductor module or as a heat sink for liquid cooling.

FIG. 3shows a pressure device5of a second embodiment of a power electronics switching device. The pressure body50of pressure device5additionally has a metal insert510which in this case is arranged, without restricting the generality, in a second recess506in the second main surface504of pressure device5. In this case, the base of second recess506forms an auxiliary surface508which delimits pressure body50.

FIGS. 4 to 6show different embodiments of parts of the pressure device, in particular a section of the pressure body with a pressure element, or, in the case ofFIG. 6, with two pressure elements.

FIG. 4shows a pressure body50with a first recess504which starts from the first main surface500and which is formed not only as a depression, as in the case of the pressure device according toFIG. 1, but also as a depression with a cutout504and an opening in the second main surface502of pressure body50, which opening extends from the first main surface500to second main surface502. In this case, it is true for this and all other cutouts504of this kind that, in each case viewed one-dimensionally, their clear width at the first main surface500corresponds to at least five times, usually at least ten times, the clear width at the second main surface502, even if this is not shown in the schematic illustration.

The said clear width at first main surface500is identical to the lateral extent520of pressure element52, whereas the vertical extent522of pressure element52extends as far as the base514of first recess504, but not into the opening512to the second main surface502of the pressure body52.

The lateral extent520of pressure element52after pressure is applied corresponds to the lateral extent of that section342of connecting element3which is in contact with pressure element52, cf.FIG. 2.

In this case, pressure element52is composed of a so-called liquid silicone, also known as liquid silicone rubber (LSR), with a Shore A hardness of 20 to 70, preferably of from about 30 to about 40. This is arranged within pressure body50, which is composed of polyphenylene sulphide, by a two-component injection molding process. To this end, the liquid silicone can be introduced through opening512in second main surface502of pressure body50. In this embodiment of pressure device5, cutout504in pressure body50is not completely filled with liquid silicone, as a result of which it does not reach as far as the plane which is defined by the second main surface502of pressure device5.

FIG. 5shows a slightly modified embodiment of pressure device5according toFIG. 4. In this case, cutout504in pressure body50is completely filled with liquid silicone. The liquid silicone extends beyond the plane which is defined by second main surface502of pressure device5and protrudes therefrom.

FIG. 6shows a further modification of pressure device5, wherein pressure device5has a metal core510analogous to the embodiment shown inFIG. 3. In addition, cutouts504here in second pressure elements52, generally in a plurality of pressure elements, are connected to one another within pressure body50and have a common opening512which is directed toward auxiliary surface508in this case. Within the scope of the production method of pressure device5, the liquid silicone is introduced into pressure body50through opening512.

FIGS. 7a-dshows a plan view of a power electronics switching device1in different sectional planes. The sectional plane according toFIG. 7ashows two power semiconductor components24,26which are, however, typically arranged, in a manner not illustrated, on a common conductor track of a substrate. Without restricting the generality, the power semiconductor components are in this case a transistor26with a central gate connection area and emitter connection areas which surround the gate connection area, and a diode24with a cathode connection area.

FIG. 7bshows the first inherently patterned electrically conductive film30of connecting device3. Film30forms an electrically conductive connection between the emitter connection areas of transistor26and the cathode connection area of diode24. In this case, the gate connection area of the transistor26is cut out.

FIG. 7cshows the second inherently patterned electrically conductive film34of connecting device3. Film34forms an electrically conductive connection to the gate connection area of the transistor26.

FIG. 7dbranches, as it were, the footprint of the contact elements, which are associated with the power semiconductor components24,26, of the contact device, wherein only one contact element is associated with the transistor on account of its square basic shape, and two contact elements are associated with the diode on account of its rectangular basic shape. The respective footprint corresponds to those sections342,344on the second main surface304of connecting device3which are arranged in alignment in the normal direction to form the power semiconductor components, and in this case are projected onto the respective power semiconductor component. It is clear here that the area of the footprint, that is to say that area which is intended for introducing pressure, covers as large a portion of the area of the power semiconductor component as possible, without going beyond this.

FIG. 8shows a second embodiment of a power electronics switching device1according to the invention which is a development of the first embodiment according toFIG. 1. In this case, in order to meet the requirements for protecting against environmental influences, the top face of substrate2, including its conductor tracks22, the power semiconductor components24and connecting device3, is encapsulated in a moisture-tight manner by an encapsulation compound8, for example an epoxy resin. Protection with an IP54(International protection code according to IEC 60529) rating and higher can be achieved as a result. In this case, parts of the connection elements, in particular of load connection elements4, are advantageously also encapsulated.

In the preceding Detailed Description, reference was made to the accompanying drawings, which form a part of his disclosure, and in which are shown illustrative specific embodiments of the invention. In this regard, directional terminology, such as “top”, “bottom”, “left”, “right”, “front”, “back”, etc., is used with reference to the orientation of the Figure(s) with which such terms are used. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of ease of understanding and illustration only and is not to be considered limiting.