Cooling of a power semiconductor module

Abstract

The present invention relates to a device (14) for cooling an electrical power semiconductor module (12), comprising: a base plate (26) for applying the device (14) to the power semiconductor module (12); and at least two elongated cooling fins (28) which extend away from the base plate (26) and are connected to the base plate (26), wherein at least one of the two cooling fins (28) has at least one bulge (36) in order to interrupt a thermal boundary layer building up on the wall of the cooling fin (28) and to improve heat transfer into a cooling fluid. The present invention further relates to a system (10) for cooling an electrical power semiconductor module (12).

Description

[0001] The present invention relates to a device for cooling an electrical power semiconductor module. The present invention further relates to a system for cooling an electrical power semiconductor module.

[0002] The power electronics of electric and hybrid vehicles transfer the traction energy from the battery to the electric motor, converting direct current into alternating current. An AC converter, also known as an inverter, or traction converter, is used for this purpose. Typically, several transistors or other power semiconductors are used, combined to form a power semiconductor module that switches at short, regular intervals. MOSFETs (metal oxide semiconductor field-effect transistors) and IGBTs (insulated gate bipolar transistors) are used as switches in this context. When switched on, the battery current is transferred to the motor (conduction phase). These high-frequency switching processes create an alternating voltage profile, which can then be converted into traction energy in the electric motor.To increase the current carrying capacity, several power semiconductors are usually connected in parallel.

[0003] Such power semiconductor modules or power semiconductors in this or other applications switch comparatively high currents, and the switching power semiconductors generate high temperatures. Active cooling systems are often used to dissipate switching and power losses. This places high demands on the space requirements and efficiency of such cooling systems.

[0004] Challenges in cooling include, in particular, a pressure loss that can occur when conveying a cooling fluid, as well as a system-related maximum pressure with which the cooling fluid can be conveyed.

[0005] Based on this, the present invention aims to provide an approach for cooling a semiconductor module. In particular, an effective and space-efficient cooling option is to be provided, preferably allowing cooling at a cooling fluid pressure above a predefined minimum pressure. During operation, a cooling fluid is to be guided with a low pressure loss, in particular a pressure loss below a maximum pressure loss.

[0006] The above task is solved by a device for cooling an electrical power semiconductor module, with: a base plate for applying the device to the power semiconductor module; and at least two elongated cooling fins extending from the base plate and connected to the base plate, wherein at least one of the two cooling fins has at least one bulge to interrupt a thermal boundary layer building up on the wall of the cooling fin and to improve heat transfer into a cooling fluid.

[0007] The above object is further achieved by a system for cooling an electrical power semiconductor module, comprising: an electrical power semiconductor module; a device as defined above, which is arranged with the base plate on the power semiconductor module and is attached to the power semiconductor module by means of a bent structure, preferably by means of a copper sheet, wherein the structure runs parallel to the base plate at least in the region of the cooling fins and forms at least one cooling channel together with the base plate and the cooling fins; and a fluid conveying device that conveys cooling fluid through the at least one cooling channel.

[0008] Preferred embodiments of the invention are described in the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the present invention. In particular, the system can be designed according to the embodiments described in the dependent claims.

[0009] The cooling fins are basically cuboid-shaped or plate-shaped and elongated, with a thin wall compared to their length. At least one cooling fin is formed integrally with this basic shape and has at least one bulge. A bulge is understood to mean, in particular, a thickening of the wall thickness of the cooling fin. The bulge preferably extends symmetrically on a front and rear side of the base body of the cooling fin and in particular in a direction perpendicular to the height and perpendicular to the longitudinal extent of the cooling fin. The longitudinal extent is understood to mean, in particular, the extent of the cooling fin with the greatest value. Improved cooling can be achieved by means of two elongated cooling fins, which, in conjunction with a support structure, form a fluid channel. In particular, cooling channels enable cooling by means of a cooling fluid with minimal fluid pressure loss.By arranging bulges in the resulting fluid channel, heat transfer to the cooling fluid can be improved. The combination of cooling channels with bulges on the walls of the cooling channels represents a preferred compromise between pressure loss and heat input into the cooling fluid.

[0010] In a preferred embodiment, at least one bulge has a lower height than the height of the cooling fins. The height of the cooling fins refers in particular to the distance from a free end of the cooling fin to the base plate. In particular, the height relates to the direction in which the cooling fins extend away from the base plate. Because the bulges do not extend over the entire height of a cooling fin, the pressure loss of the cooling fluid can be kept low, while still achieving a high heat transfer to the cooling fluid. Consequently, efficient cooling can be achieved. It is understood that bulges of different heights can be provided depending on requirements. In particular, it is conceivable to provide a heat sink tailored to the power semiconductor module to be cooled.

[0011] The cooling fins preferably extend perpendicular to the base plate and are aligned parallel to one another. Due to the parallel alignment to one another and the perpendicular alignment with respect to a surface of the base plate, the device can create cooling channels with a large cross-section using minimal material. A weight- and cost-optimized cooling device can be created that has high cooling performance. Arranged parallel to one another means, in particular, that a longitudinal axis of the cooling fins points in the same direction. The longitudinal axis is the axis that runs through the center of gravity of a cooling fin and is aligned parallel to its longitudinal direction.

[0012] In an advantageous embodiment, the cooling fins have several symmetrically distributed bulges. This allows the heat input into the cooling fluid to be further increased. In particular, a symmetrical distribution of the bulges can simplify the production of the cooling device. Particularly preferably, the cooling device also has symmetry. This simplifies assembly, since there is no need to orient the cooling device in at least one direction.

[0013] Particularly preferably, the bulges have an elliptical, circular, diamond-shaped, and / or square shape in plan view. It is understood that various geometries can be present in a cooling fin as required. A plan view is understood, in particular, to mean a view perpendicular to the base plate, i.e., along the height of the cooling fins. The above-mentioned geometries enable, on the one hand, efficient production of the cooling device. On the other hand, these shapes can advantageously interrupt the thermal boundary layer without having to accept excessive pressure loss, for example, due to turbulence.

[0014] In a particularly preferred embodiment, the cooling fins have bulges, preferably exclusively in the vicinity of a hotspot of the power semiconductor module to be cooled. This makes it possible to create a customized cooling solution. In particular, it can be ensured that no or only minimal pressure loss occurs in regions with lower heat generation. The cooling performance can generally be improved because, within the range of the permissible cooling fluid pressure, heat input into the cooling fluid is achieved with pressure loss only specifically in regions where cooling performance is required. By providing bulges in specific regions, a temperature profile of the cooling fluid in the device can be adjusted. Depending on the application, cooling fluid can be transported to a hotspot at high pressure and with low heat input, thus enabling more effective cooling of the hotspot.Furthermore, based on a temperature of the cooling fluid, sufficient cooling can be ensured even with already heated cooling fluid by providing a corresponding density of bulges.

[0015] A hotspot is specifically defined as a region on a module with a high heat buildup. It is understood that a hotspot can also be extensive. Furthermore, a module can have multiple hotspots. In particular, a hotspot can also arise if a module is to be cooled using preheated cooling fluid, for example, if it is the last module in a serial cooling chain.

[0016] Particularly preferably, the bulges of adjacent cooling fins are arranged offset from one another. This means, in particular, that with respect to a direction perpendicular to the longitudinal extent, i.e., parallel to a surface of the base plate, no bulge of a first cooling fin is present if a bulge is present on an adjacent second cooling fin. This offset arrangement is to be understood, in particular, with respect to a maximum transverse extent of the bulge. By arranging the bulges offset, a large average cross-section of the cooling channels can be achieved, on the one hand. On the other hand, preferred cooling can be achieved together with a low pressure loss.

[0017] In a further preferred embodiment, the bulges of adjacent cooling fins are arranged opposite one another to create a bottleneck where a particularly high heat transfer occurs. By forming a bottleneck using the bulges, a high heat input into the cooling fluid can be achieved specifically at the bottleneck. However, this results in a comparatively high pressure loss. Such an arrangement is therefore preferably used at hotspots where a high heat input into the cooling fluid is desired and a corresponding pressure loss can be accepted.

[0018] In a particularly preferred embodiment, a ratio of a distance between two adjacent cooling fins to a thickness of a cooling fin is in the range from 2:1 to 4:1 and is particularly preferably substantially 3:1. Additionally or alternatively, a ratio of a thickness of a bulge to a thickness of the cooling fins is in the range from 4:1 to 1:1 and particularly preferably substantially 2:1. Further additionally or alternatively, a ratio of a thickness of a bulge to a vertical distance between two adjacent bulges is in the range from 3:1 to 0.5:1 and particularly preferably substantially 1:1. The dimensions mentioned above can be used to find a preferred compromise between material usage and cooling performance. It should be noted here that heat should be absorbed quickly in the device and also quickly released from the device into the cooling fluid.By changing the previously described conditions, inertia can be introduced into the cooling system. The above-mentioned ranges enable rapid heat dissipation from the power semiconductor module using the device.

[0019] In current inverter designs, the switching semiconductors, i.e., the power semiconductor modules, must be actively cooled to dissipate switching and conduction losses. To dissipate these losses, a heat conduction path is constructed from the semiconductor into a cooling medium, which should have the lowest possible thermal resistance.

[0020] It has been shown that structures with cooling pins, so-called pin-fin structures, can transfer heat quickly into a cooling medium, but they suffer from a high pressure loss of the cooling medium.

[0021] A low pressure drop of a cooling medium can be achieved using so-called microchannel coolers, in which the cooling fluid is guided through parallel, smooth microchannels. However, the heat transfer from a heat sink to the cooling fluid is low.

[0022] Within the scope of the present invention, it was recognized that a thermal boundary layer develops in microchannels, which can reduce the heat input into the cooling fluid. This thermal boundary layer can be penetrated by bulges, allowing increased heat input into the cooling fluid, whereby the pressure losses caused by the bulge are less pronounced than in so-called pin-fin cooling structures.

[0023] Herein, a power semiconductor module is understood to be, in particular, an assembly for use in an inverter configuration. A power semiconductor module typically comprises several individual power semiconductors or chips. A power semiconductor is, in particular, an electronic chip that has one or more integrated circuit components. For example, insulated-gate bipolar transistors or other semiconductors can be used.

[0024] The power semiconductor module can in particular be designed to be flat and comprise a plurality of power semiconductors which are also designed to be flat.

[0025] The invention is described and explained in more detail below using selected embodiments in conjunction with the accompanying drawings. They show: Fig. 1 a schematically simplified representation of a system for cooling an electrical power semiconductor module; Fig. 2 a schematic plan view of a device for cooling an electrical power semiconductor module with cooling fins and bulges; Fig. 3 an alternative embodiment of a device in plan view; Fig. 4 a and Fig. 4 b schematically shows different geometries for bulges on a cooling fin; and Fig. 5 a schematic perspective view of a device for cooling a power semiconductor module.

[0026] In Fig. Figure 1 schematically shows a system 10 for cooling an electrical power semiconductor module 12. A device 14, particularly in the form of a heat sink, is arranged on the power semiconductor module 12.

[0027] For cooling, the device 14 is surrounded by a cooling fluid which is conveyed by a fluid conveying device 16.

[0028] The power semiconductor module 12 has a layered structure, with the bottom layer, on which the device 14 is arranged, comprising a copper plate 18. This copper plate 18 is followed by a ceramic plate 20 and another copper plate 18, on which a semiconductor, in particular a power semiconductor 22, is arranged. The aforementioned layers or plates are housed in a package 24 and form a DCB, a direct copper bonded structure.

[0029] The device 14 comprises a base plate 26, preferably in the shape of a square or cuboid, with cooling fins 28 extending perpendicularly from the base surface or base plate 26. It is understood that the base plate 26 does not have to be exactly flat in order to maintain clearance and creepage distances. The simpler representation chosen here serves to better understand the invention.

[0030] The device 14 is connected to the power semiconductor module 12 by means of a structure 30. The structure 30 can, for example, be a copper sheet that surrounds both the device 14 and the power semiconductor module 12, thus securing the device 14 to the power semiconductor module. It is understood that a clamping technique or other options for securing the device 14 to the power semiconductor module 12 can also be provided.

[0031] The fluid conveying device 16 is connected to the structure 30 by means of lines 32. The structure 30, in cooperation with the device 14, forms a fluid circuit, wherein cooling channels through which cooling fluid can flow are formed by the substantially planar contact of the structure 30 with the cooling fins 28.

[0032] In the example shown, a cooling fluid circuit is shown in a simplified schematic. It is understood that this representation is only schematic to enhance understanding of the invention.

[0033] In Fig. Figure 2 shows a schematic plan view of a device 14. A plan view is understood in particular to mean a view from above, i.e., perpendicular to a surface of the base plate 26.

[0034] In the embodiment shown, the device 14 has a total of nine cooling fins 28, which are arranged alternately offset from one another. All cooling fins 28 are arranged parallel to one another. Two adjacent cooling fins are arranged offset from one another in the direction of their elongated extension. The next but one neighbors are arranged flush with one another.

[0035] The cooling fins 28 have a base body 34 with protrusions 36. The base body 34 essentially has a cuboidal geometry. In the example shown, the protrusions 36 are elliptical in plan view.

[0036] For a better understanding of the invention, different distances and thicknesses are shown in the Fig. 2 marked.

[0037] A width or thickness of the base body 34 or the cooling fins 28 is designated by 40. A distance between two adjacent cooling fins 28 is defined with respect to the thickness 40 of the base body 34 and is designated by 38.

[0038] A strength or thickness of the bulge 36 is to be understood as the maximum extent of the bulge 36 in plan view and is marked with 44.

[0039] A distance between two bulges 36 is to be understood as the smallest distance perpendicular to the longitudinal alignment of the cooling fins 28 between two bulges 36 and is designated by 42.

[0040] In the embodiment shown, two bulges 36 of a cooling fin 28 are spaced apart from one another, so that the base body 34 forms flat walls at least in sections.

[0041] Furthermore, the bulges 36 are distributed symmetrically over the individual cooling fins 28 such that on adjacent cooling fins 28 the bulges 36 are not directly opposite each other.

[0042] It is understood that the Fig. 2 The representation chosen is schematic and serves to provide a better overview.

[0043] A ratio of the distance between two adjacent cooling fins 28 to a thickness 40 of the cooling fins 28 is preferably 3:1. A ratio of the thickness 44 of the bulges 36 to a thickness 40 of the cooling fins 28 is in the range of 2:1. A ratio of the thickness 44 of the bulges 36 to a vertical distance 42 between two bulges 36 of adjacent cooling fins 28 is preferably 1:1.

[0044] In Fig. 3 is analogous to the Fig. 2 shows an alternative embodiment of a device 14. In contrast to the device shown in Fig. In the embodiment shown in Figure 2, the bulges 36 overlap.

[0045] For better understanding, the shape of a base body 34 of a cooling fin 28 is shown in dashed lines. The overlap of the bulges 36 allows for increased heat transfer into the cooling fluid.

[0046] In Fig. Figure 4a shows an alternative configuration of the geometry of the bulges 36. In the illustrated embodiment, the bulges 36 are circular in plan view.

[0047] In Fig. Figure 4b illustrates another alternative geometry of the protrusions 36. In plan view, the protrusions 36 have a diamond-shaped geometry.

[0048] It goes without saying that other geometries are conceivable. In particular, the geometries can be designed according to the specific application. For example, a rounded, circular or elliptical geometry can contribute to reducing pressure loss, whereas a chamfered geometry can increase heat transfer to the cooling fluid.

[0049] It goes without saying that different bulge geometries can also be combined. In particular, it is conceivable to provide the device 14 with corresponding bulges only at so-called hotspots.

[0050] In Fig.Figure 5 shows a perspective schematic representation of a portion of a device 14. In the embodiment shown, the protrusions 36 have an elliptical geometry in plan view, extending from the base plate 26 to approximately 2 / 3 of the height of a cooling fin 28. In other words, the cooling fins 28 have the shape of the base body at ends spaced from the base plate 26, with the protrusions 36 being formed only up to a certain height.

[0051] It is understood that the bulges 36 can also have a shape and, in particular, can become narrower towards the top.

[0052] The invention has been described in detail and illustrated by several embodiments. One skilled in the art will recognize that at least one of the following advantages can be achieved with the disclosed teachings, or the teachings can be embodied in one of the following embodiments: The bulges can only be arranged in places where the greatest effect is expected, for example directly under the chips of the power semiconductor module.

[0053] The bulges can be used to compensate for fluid heating through improved heat transfer. This allows for homogeneous chip temperatures to be achieved across the entire cooler. In other words, heat transfer can occur from warm regions to cold regions. It is understood that in addition to elliptical bulges, circular, diamond-shaped, or square shapes can also be used.

[0054] The bulges can be offset or arranged directly opposite each other to create a bottleneck where particularly high heat transfer occurs. It goes without saying that the bulges do not need to be as high as the cooling fins or walls of the microchannels. The microchannels can extend through the entire cooler, i.e., the entire device 14, or be interrupted, for example, between individual phases to reduce pressure loss.

[0055] In particular, the walls of the microchannels can be connected to the bottom of the cooler. It goes without saying that individual bulges can overlap.

[0056] The invention has been comprehensively described and explained with reference to the drawings and the description. The description and explanation are to be understood as exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other embodiments or variations will become apparent to those skilled in the art upon use of the present invention and upon careful analysis of the drawings, the disclosure, and the following claims.

[0057] In the claims, the words "comprising" and "having" do not exclude the presence of further elements or steps. The undefined article "a" or "an" does not exclude the presence of a plurality. A single element or unit can perform the functions of several of the units recited in the claims. An element, unit, interface, device, and system can be partially or completely implemented in hardware and / or software. The mere mention of some measures in several different dependent claims should not be understood to mean that a combination of these measures cannot also be used advantageously. Reference signs in the claims are not to be understood as limiting. Reference symbol 10 systems 12 power semiconductor modules 14 Device 16 Fluid conveying device 18 copper plate 20 ceramic plates 22 power semiconductors 24 Package 26 Base plate 28 cooling fins 30 Structure 32 Line 34 basic bodies 36 bulge 38 Distance cooling fins 40 thick cooling fins 42 Distance bulges 44 Thick bulges

Claims

[1] Device (14) for cooling an electrical power semiconductor module (12), comprising: a base plate (26) for applying the device (14) to the power semiconductor module (12); and at least two elongated cooling fins (28) extending away from the base plate (26) and connected to the base plate (26), wherein at least one of the two cooling fins (28) has at least one bulge (36) to interrupt a thermal boundary layer building up on the wall of the cooling fin (28) and to improve heat transfer into a cooling fluid. [2] Device (14) according to claim 1, wherein the bulge (36) has a lower height than a height of the cooling fins (28). [3] Device (14) according to one of the preceding claims, wherein the cooling fins (28) extend perpendicular to the base plate (26) and are aligned parallel to one another. [4] Device (14) according to one of the preceding claims, wherein the cooling fins (28) have a plurality of symmetrically distributed bulges (36). [5] Device (14) according to one of the preceding claims, wherein the bulge (36) has an elliptical, circular, diamond-shaped and / or square shape in plan view. [6] Device (14) according to one of the preceding claims, wherein the cooling fins (28) have the bulge (36), preferably exclusively, in an environment of a hotspot of the power semiconductor module (12) to be cooled. [7] Device (14) according to one of the preceding claims, wherein the cooling fins (28) have a plurality of bulges (36) and the bulges (36) of adjacent cooling fins (28) are each arranged offset. [8] Device (14) according to one of the preceding claims, wherein the cooling fins (28) have a plurality of bulges (36) and the bulges (36) of adjacent cooling fins (28) are each arranged opposite one another in order to create a bottleneck at which a particularly high heat transfer takes place. [9] Device (14) according to one of the preceding claims, wherein a ratio of a distance (38) between two adjacent cooling fins (28) to a thickness (40) of a cooling fin (28) is in the range from 2:1 to 4:1 and is preferably 3:1; a ratio of a thickness (44) of a bulge (36) to a thickness (40) of the cooling fin (28) is in the range from 4:1 to 1:1 and is preferably 2:1; and / or a ratio of a thickness (44) of a bulge (36) to a vertical distance (42) between two adjacent bulges (36) is in the range from 3:1 to 0.5:1 and is preferably 1:

1. [10] System (10) for cooling an electrical power semiconductor module (12), comprising: an electrical power semiconductor module (12); a device (14) according to one of the preceding claims, which is arranged with the base plate (26) on the power semiconductor module (12) and is fastened to the power semiconductor module (12) by means of a curved structure (30), wherein the structure (30) runs parallel to the base plate (26) at least in the region of the cooling fins (28) and forms cooling channels together with the base plate (26) and the cooling fins (28); and a fluid conveying device (16) which conveys cooling fluid through the cooling channels.

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