Power electronics for a pulse inverter

Abstract

The invention relates to power electronics for a pulse inverter, comprising at least one power module (1) having at least one semiconductor element (3) and a substrate (9) on which the semiconductor element (3) is soldered or sintered, and a cooler (2) for dissipating heat from the power module (1), wherein the cooler (2) has a coolant-flowing free space (15) defined between the underside of the substrate (14) and a cooling element (17) that is clamped to it by friction, in particular a shell-shaped one. According to the invention, the friction-fit connection between the underside of the substrate (14) and the cooling element (17) comprises at least one rivet or screw connection (N; S), in which the underside of the substrate (14) is directly connected to the cooling element (17) by means of a rivet or screw bolt (35; 43), in particular without further auxiliary joining elements, such as a clamping or clamping frame (29).

Description

The invention relates to power electronics for a pulse inverter according to the preamble of claim 1.The power electronics for a pulse inverter must ensure adequate heat dissipation of the semiconductor elements of the power module. For this purpose, the semiconductor elements of the power module are in thermal connection with a cooler through which coolant flows, for example.In power electronics of the generic type, the cooler has a free space through which coolant flows, which free space is defined between a substrate underside of the power module and a cooler element. In the prior art, the substrate underside is braced with the shell-shaped cooler element via a frame-shaped clamping unit. The frame-shaped clamping unit can have a clamping frame with an angle profile, in which a clamping leg presses the substrate against the cooler element, and a mounting leg at right angles thereto is screwed to the cooler element via a screw connection. In this case, the substrate or its substrate underside is clamped between the clamping leg of the clamping frame and the cooler element.Such a clamping connection via a clamping or clamping frame is relatively component-intensive and space-intensive. In addition, a thermomechanical stress can occur in the component arrangement due to different thermal expansion coefficients of the components involved.DE 10 2019 114 001 A1 discloses a power electronics unit for an electric motor of a motor vehicle drive, having a plate-shaped heat sink, at least one semiconductor module and a module holder which consists of a plastic and fixes the at least one semiconductor module relative to the heat sink, wherein the module holder is fixed to the heat sink via a positive snap connection. DE 10 2020 207 947 A1 discloses a cooling arrangement for electronic components of a motor vehicle. This is distinguished in that a base box is designed as a trough formed from a sheet metal with a longitudinal web inserted in a fluid-tight manner in a materially bonded manner, by means of which the trough is divided into the inlet longitudinal chamber and the outlet longitudinal chamber.The object of the invention is to provide power electronics for a pulse inverter in which the connection between the substrate underside and the cooler element is implemented in a structurally simpler manner compared to the prior art.The object is achieved by the features of claim 1. Preferred developments of the invention are disclosed in the dependent claims.The invention relates to power electronics for a pulse inverter. This is composed of at least one power module, which has at least one semiconductor element and a substrate on which the semiconductor element is soldered or sintered, and a cooler for heat dissipation of the power module. The cooler has a free space through which coolant flows, which is defined between the substrate bottom side and an in particular shell-shaped cooler element which is clamped thereto in a force-fitting manner. According to the characterizing part of claim 1, the following measures are taken to achieve a structurally simple connection of the power module to the cooler which is subject to low thermomechanical stress: the force-locking connection between the substrate underside and the cooler element thus has at least one rivet or screw connection, in which the substrate underside is connected directly to the cooler element by means of a rivet or screw bolt, in particular without further auxiliary joining elements, for example a clamping or clamping frame. By means of the invention, the connection can be realized with reduced component complexity. In addition, by means of the direct rivet or screw connection according to the invention, a sufficient relative movement between the joining partners is made possible on account of different thermal expansion coefficients. Such a relative movement would not be possible, for example, in the case of a large-surface, materially bonded connection.The invention is therefore an integrated substrate which is mounted on a plastic heat sink shell by means of at least one direct screw connection. In this case, a force-fit connection between integrated substrate and the cooler element is preferably produced by threaded inserts already introduced into the cooler element during the production process, which connection resists the pressure of the cooling circuit. The sealing function is realized in this construction by sealing elements between the cooler element and the module substrate. The sealing elements can be embodied as separate O-rings or as rubber lips injection-molded onto the cooler by 2k injection molding. The mechanical stress to be expected is absorbed by inserts in the screw holes or mounting holes of the integrated substrate.An important advantage of the invention is that a clamping frame or other hold-down clamps can be dispensed with. According to the invention, the integrated module is screwed directly onto the open shell-shaped cooler element. The threads required for this purpose in the cooling body shell are already introduced in the manufacturing process of the cooling body shell. Screw holes in the substrate are already provided in the production of the integrated substrate and are subsequently reinforced by means of metallic inserts for absorbing mechanical stress.In one technical implementation, the substrate can have a three-layer structure consisting of a middle ceramic layer and of substrate metal layers coated on both sides on the ceramic layer. On an upper substrate metal layer, this can be soldered or sintered, while on a lower substrate metal layer, the substrate underside forms, against which the cooler element is braced.With regard to a simple joining process from a manufacturing standpoint, it is preferred if the lower substrate metal layer protrudes laterally beyond the middle ceramic layer and the upper substrate metal layer by a free layer protrusion. In this case, the rivet or screw connection can be realized in a simple manner accessible between the free layer protrusion and the cooler element.The substrate underside is braced against a laterally raised shell wall of the shell-shaped cooler element, so that a cooler which is completely closed toward the outside is formed, in which the shell-shaped cooler element is covered by the power module forming the cover. The power module with its components (i.e. semiconductor elements and substrate) can be prefabricated as a single-piece pre-assembly unit in a first assembly step. In a subsequent joining step, the pre-assembly unit can be joined to the shell-shaped cooler element.In a specific embodiment, the screw bolt or rivet bolt is guided through a mounting hole of the lower substrate metal layer and brought into riveting or threaded engagement with the cooler element. The rivet or screw bolt can preferably be laterally offset by a transverse offset with respect to the shell wall of the cooler element in riveting or threaded engagement with the shell base of the cooler element. In this case, not the laterally encircling shell wall, but rather the shell base of the shell-shaped cooler element forms a supporting structure in which the threaded or rivet engagement takes place. In the case of the screw connection, the lower substrate metal layer is braced between a bolt head supported on the opening edge region of the mounting hole of the lower substrate metal layer and the cooler element.In order to reduce force peaks acting on the lower substrate metal layer, a metal sleeve which delimits the mounting hole can be embedded in the material of the lower substrate metal layer. In the same way, in order to reduce force peaks acting on the cooler element in the cooler element material, a metal insert, i.e. a threaded sleeve, with an internal thread can be embedded, into which the screw bolt can be screwed. In the above embodiment, the integrated substrate is mounted on the cup-shaped cooler element with threaded sleeves inserted. Reinforcing inserts in the screw holes or mounting holes of the integrated substrate are already introduced at the manufacturer's manufacturing of the integrated substrate.The screw connection into inserted threaded inserts in the shell-shaped cooler element offers the advantage that in the event of a module failure, it can be replaced without replacing the shell-shaped cooler element (i.e. cooler half shell) and the further components connected thereto. The introduction of the reinforcing inserts directly in the manufacturing process of the integrated substrates additionally offers the advantage that handling of the inserts during the assembly of the power boxes is not required.Alternatively to the above embodiment variant, the screw bolt can have a self-grooving thread. In this case, the screw bolt is brought into threaded engagement with the cooler element during the joining process, namely without a prefabricated internal threaded bore in the cooler element. Self-tapping screws can save the costs of the threaded inserts here.It is preferred if the rivet or screw connection is not positioned in the wet region, i.e. in the free space through which coolant flows, but rather in a dry region. Against this background, the free space between the substrate underside and the cooler element can be divided by means of a sealing element into a coolant-throughflow region and a dry mounting space. The sealing element can be spaced apart from the shell wall of the shell-shaped cooler element by a transverse offset, forming a dry mounting space. The rivet bolt or screw bolt can preferably be guided through the dry mounting space.The rivet connection can preferably be realized as follows: Thus, the rivet bolt can be guided outwards through a mounting hole formed in the cooler element. In the rivet connection, the lower substrate metal layer and the cooler element can be braced between a first bolt head, which is supported on the opening edge region of the mounting hole of the substrate metal layer, and a second bolt head, which is supported on the opening edge region of the mounting hole of the cooler element, of the rivet bolt.Exemplary embodiments of the invention and comparative examples not encompassed by the invention are described below with reference to the appended figures. The following are shown: FIGS. 1, 2 to 3 are views of power electronics according to different exemplary embodiments; and FIGS. 4 and 5 each show a comparative example not included in the invention in a view corresponding to FIGS. 1, 2 to 3.For a simpler understanding of the invention, reference is first made to the comparative example shown in FIG. 4 and not comprised by the invention. FIG. 4 shows a power module 1 of power electronics for a pulse inverter. The power electronics unit forms, in addition to further assemblies, for example a control board, an intermediate circuit capacitor and an EMC unit, a component of the pulse inverter. In an actual application (but not shown), the power electronics system is constructed by way of example for three phases with correspondingly three power modules 1 and a cooler 2. Each of these three power modules 1 has, by way of example, a half bridge consisting of two semiconductor components 3, of which only one semiconductor component 3 is shown in FIG. 4. The semiconductor component 3 is encapsulated in a potting compound 5, which is indicated only by an outline in FIG. 4. In the figures, further components of the pulse inverter are omitted for reasons of clarity. In addition, the semiconductor element 3 is applied to a substrate 9 via a sintering layer 7. The substrate 9 in FIG. 4 has a three-layer structure, consisting of an upper aluminum layer 13, a middle ceramic layer 11 and a lower aluminum layer 14, which forms the substrate bottom side.As can be further seen from FIG. 4, the cooler 2 has a free space 15 through which coolant flows, which is defined between the substrate underside (i.e. the lower aluminum layer 14) and a shell-shaped cooler element 17 which is braced in a force-fitting manner therewith. On the side of the lower aluminum layer 14 facing away from the semiconductor element 3, cooler ribs 18 are formed on, which are supported on a shell base 19 of the shell-shaped cooler element 17. In addition, a sealing element 23 is arranged offset inward from a lateral shell wall 21 of the cooler element 17 by a transverse offset. The sealing element 23 is pressed between the substrate underside (i.e. the lower aluminum layer 14) and the shell base 19 of the cooler element 17 and separates the coolant-throughflow free space 15 from an outer dry mounting space 25.In FIG. 4, the substrate underside (i.e. the lower aluminum layer 14) is braced with the shell-shaped cooler element 14 via a frame-shaped clamping unit. In FIG. 4, the frame-shaped clamping unit has a clamping frame 29 which is formed in cross section as an angle profile, in which a horizontal clamping leg 31 presses a layer protrusion 32 of the lower aluminum layer 14 against the shell base 19 of the cooler element 17 with the sealing element 23 interposed, and a vertical mounting leg 33 at right angles thereto is screwed to the cooler element 17 via a screw connection S. Accordingly, the lower aluminum sheet 14 of the substrate 9 of the power module 1 is clamped between the clamping frame 29 and the cooler member 17.In contrast, a first exemplary embodiment of the invention is shown in FIG. 1. Its construction and mode of operation substantially correspond to the construction and the operating method of the comparative example shown in FIG. 4. Reference is therefore made to the preceding description. In contrast to FIG. 4, the provision of the clamping frame 29 is omitted in FIG. 1. Instead, in FIG. 1, the lower aluminum layer 14 of the substrate 9 is in direct screw connection S with the shell base 19 of the cooler element 17 at its respective layer protrusion 33, The screw connection S has a screw bolt 35 which is guided through a mounting hole 37 in the layer protrusion 32 of the lower aluminum layer 14 and through the dry mounting space 25 of the cooler 2 as far as into threaded engagement with the shell base 19 of the cooler element 17. In FIG. 1, the lower aluminum layer 14 is supported on the edge side on an upper edge of the encircling shell wall 21 of the cooler element 17.In order to reduce force peaks acting on the lower aluminum layer 14, a metal sleeve 39 is embedded in the material of the lower aluminum layer 14, which limits the mounting hole 37. To further reduce force peaks acting on the shell-shaped cooler element 17, a metal insert 41 with an internal thread is embedded in the cooler element material, into which the screw bolt 35 can be screwed.FIG. 2 shows a second exemplary embodiment of the invention, namely in a view corresponding to FIG. 1. the structure and the mode of operation of the exemplary embodiment shown in FIG. 2 substantially correspond to the structure and the mode of operation of the exemplary embodiment shown in FIG. 1, so that reference is made to the description above. In contrast to FIG. 1, in FIG. 2 the screw bolt 35 is provided with a self-grooving external thread. During the joining process, the screw bolt 35 is therefore driven into the material of the shell base 19 of the cooler element 17, to be precise without a prefabricated internal threaded bore in the shell base 19.FIG. 3 shows a further exemplary embodiment in a view corresponding to the preceding figures. In contrast to the preceding figures, in FIG. 3 the force-fit connection between the power module 1 and the shell-shaped cooler element 17 is designed as a rivet connection N. In the rivet joint N, a rivet bolt 43 is passed through the mounting hole 37 of the lower aluminum sheet 14. The rivet bolt 43 passes through the dry mounting space 25 of the cooler 2 and is guided to the outside through a mounting hole 45 formed in the shell base 19. In the illustrated rivet connection N, the lower aluminum layer 14 of the substrate 9 and the shell-shaped cooler element 19 are braced between a first bolt head 47 supported on the opening edge region of the mounting hole 37 of the lower aluminum layer 14 and a second bolt head 49 of the rivet bolt 43 supported on the opening edge region of the mounting hole 45 in the cooler element 17.FIG. 5 shows a further comparative example in a view corresponding to the preceding figures. In contrast to the preceding figures, in FIG. 5, the substrate underside, i.e. the lower aluminum layer 14 of the substrate 9, is not braced in a force-fitting manner with the cooler 2, but rather is bonded in a material-fitting manner to a closed cooler 2 via a connecting layer, i.e. a brazing or sintering layer 51. In contrast to the invention, the substrate underside 14 is therefore connected to the cooler 2 over a large surface area in a materially bonded connection. Therefore, a significantly greater thermo-mechanical stress builds up in the bonding layer 51 as compared to the invention due to differences in the thermal expansion coefficients of the cooler 2 and the ceramic sheet 11. In contrast, in the case of the direct screw connection S according to the invention between the power module 1 and the cooler 2, sufficient clearance remains for deformations in order to ensure the different thermal expansions between the lower aluminum layer 14 and the shell-shaped cooler element 19 which is usually produced from plastic.List of reference characters1 Power module 2 Cooler 3 Semiconductor component 5 Casting compound 7 Sintered layer 9 Substrate 11 Middle ceramic layer 13 Upper aluminum layer 14 Lower aluminum layer 15 Free space 17 Cooler element 18 Cooler ribs 19 Shell base 21 Shell wall 23 Sealing element 25 Dry mounting space 29 Clamping frame 32 Layer protrusion 35 Screw bolt 37 Mounting hole 39 Metal sleeve 41 Metal insert with internal thread 43 Rivet bolt 45 Mounting hole 47 First bolt head 49 Second bolt head 51 Connecting layer N Rivet connection S Screw connectionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2019,114 001 A1

[0005] DE 10 2020 207 947 A1

[0005]

Claims

Power electronics for a pulse inverter, having at least one power module (1) which has at least one semiconductor element (3) and a substrate (9) on which the semiconductor element (3) is soldered or sintered, and having a cooler (2) for heat dissipation of the power module (1), the cooler (2) having a free space (15) through which coolant flows, which free space is defined between the substrate underside (14) and an in particular shell-shaped cooler element (17) clamped in a force-fitting manner thereto, characterized in that the force-fitting connection between the substrate underside (14) and the cooler element (17) has at least one rivet or screw connection (N; S), in which the substrate underside (14) is defined by means of a rivet or screw bolt (35; 43), in particular without further auxiliary joining elements, for example a clamping or clamping frame (29), is directly connected to the cooler element (17).Power electronics according to Claim 1, characterized in that the substrate (9) has a three-layer structure comprising a central ceramic layer (11) and substrate metal layers (13, 14) coated on both sides on the ceramic layer (11), and in that, in particular, the power module (1) is soldered or sintered on an upper substrate metal layer (13), and / or in that a lower substrate metal layer (14) forms the substrate underside.Power electronics according to Claim 2, characterized in that the lower substrate metal layer (14) projects laterally beyond the ceramic layer (11) and the upper substrate metal layer (13) by means of a free layer projection (32), and in that the rivet or screw connection (N, S) is realized between the free layer projection (32) and the cooler element (17).Power electronics according to Claim 1, 2 or 3, characterized in that the substrate underside (14) is braced against a laterally raised shell wall (21) of the shell-shaped cooler element (17).Power electronics according to one of the preceding claims, characterized in that the screw bolt or rivet bolt (35; 43) is guided through a mounting hole (37) of the lower substrate metal layer (14) and is in riveting or threaded engagement with the cooler element (17), to be precise in particular laterally offset by a transverse offset with respect to the shell wall (21) of the cooler element (17) in riveting or threaded engagement with the shell base (19) of the cooler element (17), and / or in that, in the case of the screw connection (S), the lower substrate metal layer (14) is braced between a bolt head supported on the opening edge region of the mounting hole (37) of the lower substrate metal layer (14) and the cooler element (17).Power electronics according to one of Claims 2 to 5, characterized in that, in order to reduce force peaks acting on the lower substrate metal layer (14), a metal sleeve (39) which delimits the mounting hole (37) is embedded in the material of the lower substrate metal layer (14).Power electronics according to one of the preceding claims, characterized in that, in order to reduce force peaks acting on the cooler element (17), a metal insert (41) with an internal thread is embedded in the cooler element material, into which metal insert the screw bolt (35) can be screwed.Power electronics according to one of the preceding claims, characterized in that the screw bolt (35) has a self-grooving thread which can be brought into threaded engagement with the cooler element (17) during the joining process, to be precise without a prefabricated internal threaded bore in the cooler element (17).Power electronics according to one of the claims, characterized in that the free space (15) through which coolant flows is bounded between the substrate underside (14) and the cooler element (17) by means of at least one sealing element (23) which is pressed between the substrate underside (14) and the cooler element (17), and in that in particular the sealing element (23) is spaced apart from the shell wall (21) of the shell-shaped cooler element (17) by a transverse offset, namely to form a dry mounting space (25) through which the rivet bolt or screw bolt (35; 43) is guided.Power electronics according to one of the preceding claims, characterized in that, in the rivet connection (N), the rivet bolt (43) is led outwards through a mounting hole (45) formed in the cooler element (17), and in that, in the rivet connection (N), the lower substrate-substrate metal layer (14) and the cooler element (17) are braced between a first bolt head (47), which is supported on the opening edge region of the substrate metal layer (14), and a second bolt head (49), which is supported on the opening edge region of the cooler element (17), of the rivet bolt (43).

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