Power switching device with optimized pressure plate

Abstract

Switching device - wherein the switching device has a substrate (1) with a top (2) and a bottom (3), - wherein electronic power components (5) are arranged on the top surface (2) of the substrate (1), - wherein a heat sink (8) is directly or via an intermediate body (9) arranged between the substrate (1) and the heat sink (8) rests on the underside (3) of the substrate (1), - wherein the switching device has a pressure device (11) which is pressed against the power components (5) by means of at least one pressure element (16), - wherein the pressure device (11) has a plate-shaped pressure body (12) with a bottom surface (13) facing the substrate (1) and a top surface (14) facing away from the substrate (1), - wherein deformable pressure elements (15) are arranged on the underside (13) of the pressure body (12) in the area of ​​the electronic power components (5), - wherein recesses (17, 19) are provided into the pressure body (12) from the top (14) and the bottom (13) of the pressure body (12), so that the pressure body (12) has corresponding bulges (18, 20) at the corresponding locations of its opposite side (13, 14), and - wherein the recesses (17, 19) are provided in areas of the pressure body (12) where the pressure elements (15) are located.

Description

[0001] The present invention relates to a switching device, - wherein the switching device has a substrate with a top and a bottom, - wherein electronic power components are arranged on the top side of the substrate, - wherein a heat sink is directly attached to the underside of the substrate or via an intermediate body arranged between the substrate and the heat sink, - wherein the switching device has a pressure device which is pressed against the power components by means of at least one pressure element, - wherein the pressure device has a plate-shaped pressure body with a bottom facing the substrate and a top facing away from the substrate, - wherein deformable pressure elements are arranged on the underside of the pressure body in the area of ​​the electronic power components.

[0002] Such switching devices are generally known. By way of example, reference can be made to DE 10 2013 104 949 B3 or DE 10 2014 106 570 A1. Furthermore, DE 10 2016 123 697 A1 and DE 10 2017 126 716 A1 can be mentioned.

[0003] Such switching devices are often used in inverters. The voltages switched by these devices can be several hundred volts, sometimes even slightly over 1 kV. The switched currents can be several hundred amps. Consequently, high power losses (often 100 W and more) occur in the electronic power components, which must be quickly dissipated from the power components to the heat sink. Therefore, good thermal coupling between the power components and the substrate to the heat sink is essential.

[0004] Thermal coupling is facilitated in particular by pressing the substrate against the heat sink via the power components. This is achieved using a pressure device. Despite all efforts in the prior art, it has not yet been possible to press the power components against the substrate with a substantially uniform pressure. Specifically, the plate-shaped pressure body is typically pressed against the power components either by means of a centrally located screw or by externally arranged clamps. In one case, the pressure body is deflected due to the central force, so that the pressure force is greatest in the central area of ​​the pressure body and decreases towards the edges.In another case, the pressure body also deflects, but in this case the compressive force is greatest in the area of ​​the clamps and decreases with increasing distance from the clamps – especially towards the central area of ​​the pressure body. This results in a location-dependent thermal coupling of the power components to the substrate and of the substrate to the heat sink.

[0005] From DE 10 2009 057 145 A1, a power semiconductor module is known that can be connected to a cooling element and has an electrically insulating substrate. Conductive traces are arranged on one side of the substrate, and power semiconductor devices are mounted on these traces. A copper layer is applied to the other side of the substrate, via which the heat sink is contacted. Furthermore, a pressure device is provided that serves for the thermal connection of the power semiconductor module to the cooling element and simultaneously for the electrical contact of the contact feet of load connection elements to the conductive traces of the substrate. The pressure device includes a pressure element, which can, for example, be designed as a cover for the power semiconductor module. A spring-loaded cushion element can be arranged between the pressure element and the ribbon-like sections of the load connection elements.The ribbon-like sections can be arranged one above the other. To transfer pressure from one ribbon-like section to the next, plastic molded bodies are arranged between the ribbon-like sections; these bodies may have several rotationally symmetrical pressure studs.

[0006] From US patent 2005 / 0 135 065 A1, a switching device is known in which individual, discrete semiconductor switches, each in its own package, are arranged on a heat sink. The terminal pins of the semiconductor switches are bent so that they point away from the heat sink. The packages are pressed against the heat sink by means of metal plates. A layer with low elasticity can be placed between the package and the heat sink. Furthermore, a resin layer with low elasticity can be placed between the metal plate used to press the packages against the heat sink and the packages themselves.

[0007] From DE 197 12 099 A1, an electrical circuit is known which has a printed circuit board with a top and a bottom, wherein power components are arranged on the top. Heat-dissipating areas are present, which are partially in contact with the printed circuit board and partially with the power components. The circuit has a housing top part, which is pressed against a housing bottom part, the printed circuit board, and the power components by means of fasteners. The housing top part has downward-projecting protrusions, with at least one of the protrusions pressing against a power component, and an elastomer layer is arranged between this protrusion and the power component.

[0008] From DE 10 2013 104 950 B3, a switching device is known which has a substrate with a top and a bottom. Electronic power components are arranged on the top of the substrate. A heat sink is located on the bottom of the substrate. The switching device has a pressure device which is pressed against the power components by means of a pressure element. The pressure device has a plate-shaped pressure body with a bottom facing the substrate and a top facing away from the substrate. Deformable pressure elements are arranged on the bottom of the pressure body in the area of ​​the electronic power components. Recesses are formed in the pressure body from the top and bottom. Pressure elements are located in the recesses.

[0009] The object of the present invention is to create possibilities by means of which the pressure forces acting on the individual power components can be standardized as far as possible.

[0010] The problem is solved by a switching device with the features of claim 1. Advantageous embodiments of the switching device according to the invention are the subject of dependent claims 2 to 10.

[0011] According to the invention, a switching device of the type mentioned above is designed by: - that depressions are made into the pressure body from the top and bottom, so that the pressure body has corresponding bulges at the corresponding points on its opposite side, and - that the indentations are placed in areas of the pressure body where the pressure elements are located.

[0012] This allows the compressive forces acting on the individual power components to be adjusted as needed. An additional positive side effect is a stiffening of the pressure body.

[0013] Preferably, the depressions are conical or semi-spherical. This design is simple and reliable.

[0014] It is possible for the indentations in the pressure body to have a uniform depth and / or the corresponding bulges to have a uniform height. Even in this case, there is still considerable flexibility in adjusting the pressure forces, because some of the indentations are formed from the top of the pressure body and some from the bottom. However, even better results are achieved if the indentations in the pressure body have different depths and / or the corresponding bulges have different heights. This allows the pressure forces acting on the individual power components to be adjusted almost individually. Often, the depths of the indentations and / or the heights of the bulges will be greater at a greater distance from the pressure element than at a smaller distance.However, this is not absolutely necessary.

[0015] In many cases, the pressure element is designed as a threaded screw. In this case, the pressure element can alternatively be screwed into the heat sink or the intermediate body.

[0016] In the case of a pressure element designed as a threaded screw, the pressure body has a recess for the threaded screw to pass through it. Preferably, a depression is also formed in the pressure body in the area of ​​the recess, either from the top or bottom, so that the pressure body has a corresponding bulge on its opposite side. This design improves the stiffness of the pressure body.

[0017] It is possible for the printing elements to be separate from one another. Preferably, however, at least some of the printing elements are connected to each other via a connecting structure. This offers particular advantages in terms of manufacturing. The connecting structure can be net-like, grid-like, or planar, as required. It is generally made of the same material as the printing elements themselves.

[0018] In the case of the interconnection structure, the interconnection structure has a thinner profile in the areas between the pressure elements than the pressure elements themselves. As the name suggests, the interconnection structure serves solely to connect the pressure elements to one another. No pressure is exerted on the substrate via the interconnection structure. The pressure elements thus protrude from the interconnection structure. Typically, the pressure elements protrude from the interconnection structure in the direction of the power components. However, in specific cases—particularly if the interconnection structure is sufficiently flexible—the opposite can also be true.

[0019] It is possible for the printing elements to have a uniform thickness. Alternatively, at least some of the printing elements can have different thicknesses. This allows for a very flexible adjustment of the locally applied pressure, especially in combination with individual depths of the indentations and / or individual heights of the bulges. Often, the thickness of the printing elements will be greater at a greater distance from the pressure element than at a smaller distance. However, this is not mandatory.

[0020] Preferably, the pressure body comprises a plate-shaped main part and a plate-shaped reinforcement part, wherein the main part is made of plastic and the reinforcement part of metal, in particular steel. This allows the pressure body to be manufactured cost-effectively while still exhibiting high rigidity. Typically, in this case, the reinforcement part is arranged on the side of the main part facing away from the power components.

[0021] As a rule, the indentations are positioned exactly or approximately in the center of the respective printed element.

[0022] Further advantages and details will become apparent from the following description of exemplary embodiments in conjunction with the drawings. These show, in schematic principle representation: Fig. 1 a circuit arrangement, Fig. 2 a top view of a pressure vessel, Fig. 3 a section through the pressure body of Fig. 2 along a line III-III in Fig. 2, Fig. 4 a perspective view of a section through the pressure body of Fig. 2 and Fig. 5 a detail of a printing plate.

[0023] The drawings in each case show only partial aspects of the subject matter according to claim 1.

[0024] According to Fig. A switching device comprises a substrate 1 with a top surface 2 and a bottom surface 3. The substrate 1 is made of ceramic and is arranged in a housing 4. Electronic power components 5 are arranged on the top surface 2 of the substrate 1. These electronic power components 5 can include, in particular, switching elements (e.g., IGBTs or MOSFETs) and rectifying elements (especially diodes). The power components 5 are electrically connected to each other and / or to external terminals 6, at least partially, via conductive traces 7 arranged on the top surface 2 of the substrate 1. These conductive traces 7 can be applied to the substrate 1, for example, by direct copper bonding (DCB) or active metal brazing (AMB).

[0025] A heat sink 8 is located on the underside 3 of the substrate 1. In some embodiments, the heat sink 8 can be in direct contact with the underside 3 of the substrate 1. According to the embodiment of Fig. An intermediate body 9 is arranged between the substrate 1 and the heat sink 8. The intermediate body 9 is usually plate-shaped. To optimize the thermal connection of the heat sink 8 to the substrate 1, a thin layer (usually only about 10 µm thick) of thermal paste 10 can be arranged between the heat sink 8 and the intermediate body 9 and / or the intermediate body 9 and the substrate 1, or (in the case of direct connection of the heat sink 8 to the underside 3 of the substrate 1) between the heat sink 8 and the substrate 1.

[0026] To optimize the thermal connection of the power components 5 to the substrate 1, a pressure device 11 is provided. The pressure device 11 has a plate-shaped pressure body 12 with a bottom surface 13 facing the substrate 1 and a top surface 14 facing away from the substrate 1. The pressure body 12 can be made, for example, of metal (especially steel or aluminum) or of a sufficiently temperature-resistant plastic. Polyphenylene sulfide is one example of a suitable plastic. It is also suitable as shown in the illustration in Fig. 1. The pressure body 12 may comprise a main part 12' ("the main plate") and a reinforcing part 12" ("the additional plate"), wherein the main part 12' is made of plastic and the reinforcing part 12" is made of metal (especially steel).

[0027] On the underside 13 of the pressure body 12, deformable pressure elements 15 are arranged in the area of ​​the electronic power components 5. The pressure elements 15 can be made, for example, of silicone rubber, in particular of so-called liquid silicone. They can alternatively have a uniform thickness or, if required, different thicknesses from one another. Furthermore, they can be connected to each other via a connection structure (without reference numeral) if required. If present, the connection structure has a smaller thickness in the areas between the pressure elements 15 than the pressure elements 15 themselves. The connection structure thus serves only to connect the pressure elements 15 to each other, but not to exert pressure on the substrate 1.

[0028] The pressure device 11 is pressed against the power components 5 by means of (at least) one pressure element 16. As a result, the corresponding areas of the substrate 1 are pressed against the heat sink 8 via the power components 5. The pressure element 16 can be configured as shown in the illustration. Fig. 1 in particular shall be designed as a threaded screw which is screwed into the heat sink 8 (alternatively the intermediate body 9).

[0029] The core subject of the present invention is the design of the pressure body 12. It is described below in conjunction with the Fig. 2, Fig. 3 to Fig. 4 explained in more detail.

[0030] According to the Fig. 2, Fig. 3 to Fig. Recesses 17 are formed into the pressure body 12 from the upper surface 14 of the pressure body 12. As a result, the pressure body 12 has corresponding bulges 18 at the corresponding locations on its underside 13. Additionally, recesses 19 are formed into the pressure body 12 from the underside 13 of the pressure body 12. As a result, the pressure body 12 has corresponding bulges 20 at the corresponding locations on its upper surface 14. In both cases, the recesses 17, 19 are formed in areas of the pressure body 12 where pressure elements 15 are located. The recesses 17, 19 are generally positioned exactly or approximately in the center of the respective pressure element 15. Of the recesses 17, 19 and the bulges 18, 20, the Fig. 2, Fig. 3 to Fig. For the sake of clarity, only some are listed with their reference symbol.

[0031] The recesses 17, 19 can be found - see especially Fig. 3 - for example, cone-shaped. Alternatively, the depressions 17, 19 can be semi-spherical. Furthermore, the depressions 17, 19 (in Fig. 3. The indentations 17, which are only visible from the upper surface 14, preferably have different depths. Likewise, the corresponding bulges 18, 20 preferably have different heights.

[0032] The pressure vessel 12 exhibits according to the Fig. 2 and Fig.4. A recess 21 is provided for the passage of the pressure element 16 (the threaded screw) through the pressure body 12. For additional stiffening of the pressure body 12, the pressure body 12 can also have a further depression 22 in the area of ​​the recess 21. This further depression 22 can be formed in the pressure body 12 from either the top 14 or the bottom 13, as required. In both cases, however, the pressure body 12 has a corresponding bulge 23 at the corresponding location on its opposite side 13, 14. Here, too, the depression 22 can be, in particular, conical or semi-spherical.

[0033] The present invention has many advantages. In particular, the pressure exerted on the power components 5 by means of the pressure device 11 can be easily adjusted as required, for example, to even it out. Deflection of the pressure body 12 can be reduced by the additional stiffening of the pressure body, and any remaining deflection can be compensated for. Reference symbol list 1 substrate 2, 14 top sides 3.13 subpages 4 cases 5 power components 6 connections 7 conductor tracks 8 heat sinks 9 Intermediate Bodies 10 Thermal paste 11 Pressure device 12 pressure bodies 15 printing elements 16 Pressure element 17, 19, 22 indentations 18, 20, 23 bulges 21 Exclusion

Claims

[1] Switching device, - wherein the switching device has a substrate (1) with a top (2) and a bottom (3), - wherein electronic power components (5) are arranged on the top surface (2) of the substrate (1), - wherein a heat sink (8) is directly or via an intermediate body (9) arranged between the substrate (1) and the heat sink (8) rests on the underside (3) of the substrate (1), - wherein the switching device has a pressure device (11) which is pressed against the power components (5) by means of at least one pressure element (16), - wherein the pressure device (11) has a plate-shaped pressure body (12) with a bottom surface (13) facing the substrate (1) and a top surface (14) facing away from the substrate (1), - wherein deformable pressure elements (15) are arranged on the underside (13) of the pressure body (12) in the area of ​​the electronic power components (5), - wherein recesses (17, 19) are provided into the pressure body (12) from the top (14) and the bottom (13) of the pressure body (12), so that the pressure body (12) has corresponding bulges (18, 20) at the corresponding locations of its opposite side (13, 14), and - wherein the recesses (17, 19) are provided in areas of the pressure body (12) where the pressure elements (15) are located. [2] Switching device according to claim 1, characterized by , that the depressions (17, 19) are cone-shaped or semi-spherical. [3] Switching device according to claim 1 or 2, characterized by, that the depressions (17, 19) introduced into the pressure body (12) have different depths and / or the corresponding bulges (18, 20) have different heights. [4] Switching device according to claim 1, 2 or 3, characterized by , that the pressure element (16) is designed as a threaded screw and that the pressure element (16) is screwed into the heat sink (8) or the intermediate body (9). [5] Switching device according to claim 4, characterized by , that the pressure body (12) has a recess (21) for the passage of the threaded screw through the pressure body (12) and that a depression (22) is also provided in the pressure body (12) in the area of ​​the recess (21) from the top (14) or the bottom (13) of the pressure body (12), so that the pressure body (12) has a corresponding bulge (23) at the corresponding location on its opposite side (13, 14). [6] Switching device according to any one of the above claims, characterized by , that at least some of the printing elements (15) are connected to each other via a net-like, grid-like or planar connecting structure. [7] Switching device according to any one of the above claims, characterized by , that at least some of the printing elements (15) have different thicknesses from each other. [8] Switching device according to any one of the above claims, characterized by , that the pressure body (12) comprises a plate-shaped main part (12') and a plate-shaped reinforcing part (12") and that the main part (12') is made of plastic and the reinforcing part (12") is made of metal, in particular steel. [9] Switching device according to claim 8, characterized by , that the reinforcement part (12") is arranged on the side of the main part (12') facing away from the power components (5). [10] Switching device according to any one of the above claims, characterized bythat the depressions (17, 19) are arranged exactly or approximately in the center of the respective printing element (15).

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