POWER MODULE WITH COOLING STRUCTURE AND SEALING DIAPHRAGM TO PROTECT THE POWER MODULE FROM FAILURE CAUSED BY CORROSION

Abstract

Power module (1) with a cooling structure (3) for mounting on a surface of a housing (2), wherein a seal (5) is provided as an intermediate layer between the power module (1) and the housing (2), which is designed to prevent an unwanted flow of coolant, the seal (5) has a membrane (6) which is intended to serve as an intermediate layer between the housing (2) and the cooling structure (3), and the membrane (6) has a raised structure (10, 11) by means of which an interface of the membrane (6) facing the cooling structure (3) or an interface of the membrane (6) facing the housing (2) is spaced away from the housing (2).

Description

field of technology

[0001] The invention relates to a power module with a cooling structure for mounting on a housing surface, wherein a seal is provided as an intermediate layer between the power module and the housing, which prevents the unwanted flow of coolant. State of the art

[0002] Power modules are key performance components in the inverters of electric vehicles (cars, trucks, and other commercial vehicles). Inverters form the central unit between the motor (generator) and the battery, performing regulatory and control functions as well as voltage conversion. The latter includes, in particular, the conversion of the alternating current (AC) transmitted by the motor to direct current (DC) during braking, a necessary step for storing energy in the battery, and the reverse conversion back to DC when driving the electric motor. Power modules contain transistors for an inverter circuit as power electronic components. These include, in particular, metal-oxide-semiconductor field-effect transistors (MEFTs)."Metal-Oxide-Semiconductor-Field-Effect-Transistor," or MOSFET for short, are widely used in numerous technical applications. Due to the central function of MOSFETs in inverter circuits, ensuring their longevity is of paramount importance.

[0003] The technical efficiency of semiconductor devices, such as MOSFETs, is generally limited due to conversion losses. Thermal energy losses (heat dissipation) are a major factor in power dissipation. The heat generated at the MOSFETs, and thus in the power module, must be dissipated because the maximum operating temperature of the MOSFETs is limited (by material physics, specifically by the maximum permissible junction temperature). If the permissible operating temperature is exceeded, either briefly or for an extended period, the MOSFET can be destroyed. The junction temperature refers to the temperature of the semiconductor material inside the MOSFET and depends on the specific power dissipation of the MOSFET. An increase in the junction temperature is directly proportional to the dissipated heat and the thermal resistance. As soon as the MOSFET is driven with current, its junction temperature increases.

[0004] An industrial solution for dissipating the heat generated by MOSFETs involves cooling structures on power modules. These structures come in various designs and initially conduct the heat from the MOSFETs, typically using materials with high thermal conductivity, such as copper. In automotive applications, heat is often transferred from the conductive cooling structure of the power module via a cooling circuit that uses coolant to convectively remove the heat. The cooling circuit is usually located on the underside of the power module and, if necessary, also on the top side. It is sealed around the cooling structure with a gasket. The housing on which the power module is mounted is generally made of aluminum.

[0005] Due to the good thermal conductivity of water compared to, for example, ambient air, water cooling of the cooling structure represents an industrial standard for cooling, whereby in the context of cars / trucks, despite a lower thermal conductivity coefficient, water-glycol mixtures with various additives are used as coolants in the cooling circuits, particularly for frost protection reasons.

[0006] The copper cooling structure of the power module is designed with a typically small gap of approximately 0.05 to 0.3 mm between it and the aluminum housing. Due to the different electrochemical potentials of copper and aluminum (the potential difference), electrochemical / electrolytic corrosion occurs in the gap, caused by the coolant connecting the surfaces. This coolant acts as an electrolyte, facilitating ion transport between the surfaces. Because aluminum has a lower electrochemical potential than copper, the surface of the aluminum housing corrodes, releasing ions. This process locally degrades the aluminum housing. Typically, the structure of the cooling channels becomes visible as a corroded surface on the corresponding surface of the housing.The additives in the coolant cause gel to precipitate at corroded areas. This deposition mechanism can lead to clogging of the power module's cooling structure (so-called power module / inverter gelation) and ultimately to overheating of the power module due to the complete or partial obstruction of coolant flow around the cooling structure, resulting in power module failure. Given the central importance of the power module and its integrated inverters for the propulsion of electric vehicles in particular, a solution must be found for the interconnected problems of corrosive housing deterioration and clogging of the cooling structure due to gelation in the corroded housing area.

[0007] From DE 102 22 443 C1, an electronic module with a cooling structure for mounting on a surface of a housing is known, wherein a seal is provided for an intermediate layer between the module and the housing, which is intended to prevent an unwanted flow of coolant, and wherein the seal has a membrane which is intended for an intermediate layer between the housing and the cooling structure.

[0008] Regarding further state of the art, reference is made to DE 11 2019 007 407 T5. Summary of the invention; Technical task

[0009] The object of the present invention is therefore to avoid or at least mitigate the disadvantages known from the prior art. Technical solution

[0010] This problem is solved according to the invention by the measures specified in claim 1.

[0011] In a power module, in addition to a seal intended as an intermediate layer between the power module and the housing, a membrane is provided which is intended as an intermediate layer between the housing and the power module cooling structure.

[0012] The inverter / power module including the provided cooling structure and the aluminum housing is protected from destruction and at the same time (via heat dissipation from the cooling structure) long operating times with full functionality are ensured.

[0013] One could also say that the corrosion processes (across the gap) between the cooling structure and the aluminum housing are prevented by the membrane when installed, thus preventing corrosion of the aluminum housing. Despite the continuous possibility of heat dissipation from the cooling structure, the surfaces of the cooling structure and the housing, with their differing electrochemical potentials, are no longer, or only partially, connected via the coolant through the intervening membrane. Due to the complete or near-complete shielding of the aluminum housing, no gel precipitates or deposits form on the aluminum housing in the area of ​​the cooling structure as a result of the additives in the coolant.The membrane thus ultimately prevents overheating, failure and malfunctions of the power module due to the coolant flow around the cooling structure being completely or partially blocked by gel deposits, according to the invention.

[0014] Advantageous embodiments are claimed in the dependent claims and are explained in more detail below.

[0015] It is advantageous that a membrane interface facing the cooling structure is in predominantly or entirely contact with the cooling structure. This arrangement allows the housing to be separated from the coolant, with the coolant only coming into contact with the housing in areas where it is required for the cooling circuit to supply or remove the coolant from the cooling structure. Sealing the housing against the coolant enables improved utilization of the coolant flow. A recess of approximately 1 mm should be provided in the area of ​​the housing-side contact surface of the seal to ensure reliable positioning during assembly and prevent slippage during operation.For the longevity of the seal, it is also advantageous that the cooling structure of the power module is rounded or at least not sharp-edged in order to counteract damage to the seal during operation at the transition of / the seam between the membrane and the frame / ring.

[0016] Furthermore, it is advantageous that the seal has a frame / ring within which the diaphragm is positioned. This ensures that the diaphragm's position is fixed both during assembly and operation. Additionally, the diaphragm can be easily integrated into the injection mold during seal manufacturing. This significantly reduces the additional manufacturing costs. From a manufacturing perspective, it is also advantageous to widen the seal compared to the prior art. The wider seal allows the diaphragm to transition into one of the sealing lips, thus ensuring improved manufacturability. The design with an additional sealing lip, separate from the diaphragm, maintains the sealing function. The support provided by the two upper sealing lips, the lower sealing lip, and the diaphragm prevents the seal from twisting under load.This proves advantageous in that it allows the seal to fulfill its intended function in the long term.

[0017] Another advantageous embodiment provides that the rectangular frame / ring has four legs, at least two of which are connected via the diaphragm. This design allows for an advantageous seal of the housing against the coolant, since there are no free transitions between the diaphragm and the frame / ring of the seal in the area between the at least two legs.

[0018] Furthermore, it is advantageous that an elongated hole exists between the frame / ring and the diaphragm, or that two identically oriented and designed elongated holes exist between two legs of the frame / ring and the diaphragm. The elongated holes allow for the reliable supply of coolant from the cooling channels in the aluminum housing to the cooling structure of the power module during operation. A continuous flow of coolant in and out is possible. This is advantageous with regard to the continuous heat dissipation necessary to maintain the operating temperature of the MOSFETs within a range that enables long-term operation of the power module. For tolerance reasons, it is advantageous that the elongated holes in the seal are slightly larger than the coolant openings, thus providing some clearance around the edges of the coolant openings.This advantage outweighs the disadvantage that a small part of the housing surface is not protected against corrosion.

[0019] Furthermore, the elongated holes and the advantageously rectangular shape of the seal(s) with sides of approximately equal length significantly simplify assembly. This is because the positioning and alignment of the rectangular seals can be reliably detected during assembly, either by camera inspection or manually.

[0020] Furthermore, it is advantageous that the seal is made of elastic and / or compliant material. The high deformation capacity of elastic and therefore compliant materials allows for the compensation of height tolerances in the gap between the cooling structure and the housing to a certain extent. This allows for better utilization of the coolant flow, as any potential bypass via the end face of the cooling structure is sealed. Alternatively, the tolerances of the housing can be refined or expanded, resulting in shorter cycle times during the machining of the aluminum housing.

[0021] Another advantageous embodiment provides that the seal is made entirely or partially of plastic, preferably ethylene propylene diene monomer rubber (EPDM). Due to EPDM's high flexibility and elasticity, combined with its low tendency to absorb water and thus its high sealing capacity against water, EPDM promises a long service life for the seal. A further advantageous property of EPDM is its good resistance to acidic and especially alkaline media, such as coolants. Due to EPDM's temperature resistance (from approximately -40°C to 100°C) and thus its suitability for a wide range of operating temperatures in cars and trucks, as well as its ability to absorb vibrations, EPDM is particularly suitable for use under the dynamic conditions found in cars and trucks.The option of reinforcement / non-reinforcement, and thus strengthening / non-strengthening of the seal, makes it advantageous to adapt the sealing material to higher loads that occur during the operation of cars / trucks, also as a result of the coolant flow / assembly / operational forces / moments / vibrations.

[0022] Furthermore, it is advantageous that the power module has power units such as transistors and, in particular, metal oxide semiconductor field-effect transistors (MOSFETs) that can perform the function of the inverter circuit.

[0023] The housing and cooling structure can advantageously be manufactured from materials with different electrochemical potentials to leverage lightweight construction potential. In such a case, the invention particularly demonstrates its advantages. The corrosion that would otherwise occur is avoided by preventing ion exchange between the materials with different electrochemical potentials.

[0024] The use of lightweight metals such as aluminum, which has a density approximately two-thirds lower than that of steel, for the housing is advantageous for lightweight vehicle construction, not least from the perspective of reducing the overall vehicle weight and the resulting fuel savings during operation, thus contributing to sustainability. The use of copper for the cooling structure offers advantages due to its high thermal conductivity (approximately 300 W / (mK)) compared to other materials, enabling rapid heat dissipation from the MOSFET(s) of the inverter circuit.

[0025] The membrane has a raised structure by means of which a surface of the membrane facing the cooling structure or a surface of the membrane facing the housing is spaced away from the housing.

[0026] The structure advantageously features several bumps.

[0027] The structure advantageously features a web structure.

[0028] Advantageously, the bridge structure meanders along one side of the membrane.

[0029] It is advantageous that a gap is formed between parts of the bridge structure.

[0030] Advantageously, the shape of the structure along the interface of the membrane follows the shape of the cooling structure in such a way that a surface of the structure facing the cooling structure is directly adjacent to a surface of the cooling structure facing the structure.

[0031] Advantageously, an inverter has the power module described above, which is attached to the surface of the housing with the membrane of the seal in between. Brief description of the drawings

[0032] The invention is explained in more detail below with the aid of a drawing. The drawing shows: Fig. 1 a power module with cooling structure mounted on an aluminium housing with an intermediate seal according to a non-inventive embodiment. Fig. 2 the seal with elongated holes and membrane according to the non-inventive design. Fig. 3 the seal in partial and cross-section according to the non-inventive design. Fig. 4 a top surface of a seal with elongated holes and membrane in a perspective view according to an embodiment of the invention. Fig. 5 an underside of the seal with elongated holes and membrane in a perspective view according to the embodiment of the invention. Fig. 6 an enlarged view of one in Fig. 5 encircled area of ​​the seal according to the embodiment of the invention. Fig. 7 the seal in cross-section according to the embodiment of the invention. Fig. 8 an enlarged view of one in Fig. 7 encircled area of ​​the seal according to the embodiment of the invention. Fig. 9 a bottom view of the seal according to the embodiment of the invention. Fig. 10 an enlarged view of one in Fig. 9 encircled area of ​​the seal according to the embodiment of the invention.

[0033] The figures are purely schematic and serve only to illustrate the invention. The same elements are identified by the same reference symbols.

[0034] The following is a description of a non-inventive embodiment.

[0035] In the Fig. Figure 1 shows a power module 1 mounted on a housing 2 with a cooling structure 3. Heat dissipation is achieved via a coolant flow 4, comprising a coolant, preferably a liquid such as an aqueous solution with application-specific additives (antifreeze additives). The seal 5 separates the cooling structure 3 from the aluminum housing 2 via a membrane 6. The surfaces of the housing 2 and the cooling structure 3 thus do not come into direct contact and are not conductively connected by a coolant acting as an intermediate medium, which, due to its composition, is an electrolyte. The intervening membrane 6 prevents ion transport, and therefore corrosion, between the copper surface of the cooling structure 3 and the aluminum surface of the housing 2 due to an electrochemical potential difference.On the housing and seal side, coolant openings / elongated holes 7 are provided in the seal 5, through which the coolant flow 4 can be directed to and from the cooling structure 3.

[0036] In the Fig. Figure 2 shows a rectangular seal 5 with an internal membrane 6. Geometries other than a rectangular shape are also conceivable. The membrane 6 has recesses in the form of, for example, two elongated holes 7. Sealing lips 8 are located on a frame / ring 9 of the seal 5. There is a continuous transition from the frame 9 of the seal 5 to the membrane 6. No seams occur, as the entire seal 5, including the membrane 6, can be manufactured in a single operation using injection molding. The area of ​​the membrane 6 should be as large as possible relative to the area of ​​the elongated holes 7 in order to cover as much of the area between the cooling structure 3 and the housing 2 as possible with the membrane 6 and protect it from corrosion.However, the elongated holes 7 must be chosen to be large enough that the coolant openings 7 and an area around the coolant openings 7 that must be left uncovered for manufacturing reasons are not covered by the membrane 6.

[0037] In the Fig. Figure 3 shows a seal 5 in partial and cross-sectional view. The seal 5 has sealing lips 8 in its upper and lower areas, which are connected to the diaphragm 6. The coolant opening / elongated hole 7 is also shown in cross-section.

[0038] Two sealing lips 8 are provided at the upper edge of the frame 9. At the lower edge of the frame 9, there is one sealing lip 8, which is provided in this embodiment. Other embodiments and numbers of sealing lips are conceivable in principle. Depending on the application, the material for the seal 5 and the membrane 6 can also be reinforced. Reinforced plastics are particularly suitable for this purpose, as they give the frame of the seal 9 made from them greater strength against stress, especially compared to the use of unreinforced plastics. The following is a description of one embodiment.

[0039] The embodiment is identical to the non-inventive embodiment except for the differences described below, so that only the differences of the embodiment compared to the non-inventive embodiment are described and reference is made to the previously given description of the non-inventive embodiment with regard to further features of the second embodiment.

[0040] In the figures described below relating to the embodiment, the same reference numerals as in the figures described above relating to the non-inventive embodiment denote the same or corresponding parts, so that a further description thereof is omitted.

[0041] Fig. Figure 4 shows a top side of a seal 5 with elongated holes 7 and membrane 6 in a perspective view according to the embodiment of the invention.

[0042] The top side is understood to be the side on which the (not shown) power module is located when the seal 5 is installed.

[0043] In Fig. Reference numeral 4 identifies, by way of example, one of several bumps arranged on the top of the membrane 6, reference numeral 11 identifies, by way of example, one of several ridge structures arranged on the top of the membrane 6, and reference numeral 12 identifies, by way of example, one of several gaps present on the top of the membrane 6 between respective ridge structures 11.

[0044] Fig. 5 similar to Fig. 4 an underside of the seal 5 with elongated holes 7 and membrane 6 in a perspective view according to the embodiment of the invention.

[0045] The underside is understood to be the side on which the (not shown) housing is located when the seal 5 is installed.

[0046] As it is in Fig. As shown in Figure 5, the underside has several studs 10, several ridge structures 11 and several columns 12, similar to the top side.

[0047] The bridge structures 11 run in a meandering pattern along one side of the membrane 6 and likewise along one longitudinal side of one of the elongated holes 7.

[0048] Fig. Figure 6 shows an enlarged view of one in Fig. 5 circled area A of the seal 5 according to the embodiment of the invention.

[0049] As it is in Fig. As can be seen more clearly in Figure 6, each web structure 11 is separated from the others by a gap 12 located between the web structures 11. The same applies to the web structures 11 and gap 12 provided on the upper side.

[0050] Fig. Figure 7 shows the seal in cross-section according to the embodiment of the invention and Fig. Figure 8 shows an enlarged view of one in Fig. 7 encircled area B of the seal according to the embodiment of the invention.

[0051] Fig. Figure 9 shows a bottom view of the seal according to the embodiment of the invention and Fig. Figure 10 shows an enlarged view of one in Fig. 9 encircled area C of the seal according to the embodiment of the invention, wherein in Fig. 9 and Fig. 10 also shows the cooling structure 3 to illustrate the relationship between the studs 10 and the ridge structures 11 to the cooling structure 3.

[0052] The difference between this embodiment and the non-inventive embodiment is essentially that, according to this embodiment, a special structure is formed on the membrane 3 with the knobs 10 and ridge structures 11, which sets a distance between the cooling structure 3 and the membrane 6 as precisely as possible.

[0053] More precisely, the distance achieved by the special structure under the cooling structure 3, which allows part of the coolant flow to bridge the cooling structure 3, is used to design a heat dissipation and a flow resistance of the coolant relative to each other.

[0054] Heat dissipation is optimal at a small or no distance, as in the first embodiment, because the flow of the coolant through the meandering cooling structure 3 is maximized. Conversely, the flow resistance of the coolant is optimal at a large distance, since flow over the meandering cooling structure 3 exhibits less resistance.

[0055] The in the Fig. The seal 5 shown in figures 4 to 10, with the membrane 6 having several studs 10 and several ridge structures 11, has several functions:

[0056] The multiple nubs 10 between the membrane 6 and the cooling structure 3 serve as spacers to fix the distance between the membrane 6 and the cooling structure 3 to a predetermined value, which is their central function. For this purpose, the multiple nubs 10 are designed to be so wide that the distance is kept as constant as possible under different compressions, i.e., different contact pressures, of the power module 1 against the housing 2, due to the high rigidity of the nubs 10.

[0057] The multiple nubs 10 between the membrane 6 and the housing 2 serve as tolerance compensation nubs, which compensate as much as possible for height tolerances between the cooling structure 3 and the housing 2 (defined by tolerances in the cooling structure 3, a pocket depth in the housing 2, and the seal 5). These nubs 10 are designed to be as flexible as possible without buckling, so that any deformation of the nubs 10 is as constant as possible and the nubs 10 also make secure contact.

[0058] The membrane 6 itself defines a distance to the cooling structure 3 and seals off a desired flow of the coolant in the cooling structure 3 against a parasitic flow under the membrane 6, which contributes practically nothing to cooling.

[0059] In summary, a desired distance can be set while maintaining the main function of the membrane 6, namely, insulation against galvanic corrosion. Height tolerances of the distance can be reduced by compensation, typically halved, so that a tolerance range comparable to that without the insulation, i.e., without the membrane 6 between the power module 1 and the housing 2, is achieved.

[0060] The studs 10 are located on the membrane 6 at positions that correspond to positions of ribs of the meandering cooling structure 3 of the power module 1, thus following the positioning of the cooling structure 3.

[0061] In addition, there are barrier structures 11 to block a parasitic current under the membrane. The barrier structures 11 do not necessarily need to be tightly sealed in all tolerance positions. The barrier structures 11 are located at points on the meandering cooling structure 3 and are supported on an upper surface of the membrane 6 against the cooling structure 3. This design of the barrier structures 11 ensures that the flow of coolant over the meandering rib structures 11 is not blocked. Furthermore, the barrier structures 11 are perforated at certain points by gaps 12 to allow a small amount of parasitic flow to expel any air trapped during assembly. This is necessary because air negatively affects the corrosion inhibitors in the coolant and could thus trigger corrosion of the housing 2.

[0062] Furthermore, this largely equalizes the pressure between the top and bottom of the diaphragm 6, preventing the diaphragm 6 from being pressed against the housing side. The remaining pressure difference, typically in the range of <100 mbar, can be supported by the nubs 10 without functionally relevant deformation.

[0063] Although the present invention has been described above with reference to one embodiment, it is understood that various embodiments and modifications can be carried out without departing from the scope of the present invention as defined in the accompanying claims.

[0064] Regarding further features and advantages of the present invention, explicit reference is made to the disclosure of the drawing. Reference symbol list 1 Power module 2 Housings / Aluminum Housings 3 Cooling structure 4 Coolant flow 5 Seal 6 Membran 7 Coolant opening / elongated hole 8 Sealing lip 9 Frame / Ring of the seal 10 studs 11 Bridge structure 12 columns A first circled area B second circled area C third circled area

Claims

[1] Power module (1) with a cooling structure (3) for mounting on a surface of a housing (2), wherein a seal (5) is provided as an intermediate layer between the power module (1) and the housing (2), which is designed to prevent an unwanted flow of coolant, the seal (5) has a membrane (6) which is intended to serve as an intermediate layer between the housing (2) and the cooling structure (3), and the membrane (6) has a raised structure (10, 11) by means of which an interface of the membrane (6) facing the cooling structure (3) or an interface of the membrane (6) facing the housing (2) is spaced away from the housing (2). [2] Power module (1) according to claim 1, characterized by , that the seal (5) has a frame (9) within which the membrane (6) is arranged. [3] Power module (1) according to claim 2, characterized by, that the frame (9) has four legs, at least two of which are connected via the membrane (6). [4] Power module (1) according to claim 3, characterized by , that there is an elongated hole (7) between the frame (9) and the membrane (6) or that there are two elongated holes (7) of the same orientation and identical design between two legs of the frame (9) and the membrane (6). [5] Power module (1) according to any one of claims 1 to 4, characterized by , that the seal (5) is made of elastic or flexible material. [6] Power module (1) according to any one of claims 1 to 5, characterized by that the seal (5) is made entirely or partially of plastic. [7] Power module (1) according to any one of claims 1 to 6, characterized by , that the power module (1) comprises power units such as transistors and, in particular, metal oxide semiconductor field-effect transistors. [8] Power module (1) according to any one of claims 1 to 7, characterized by , that the housing (2) and the cooling structure (3) are made of materials with different electrochemical potentials. [9] Power module according to any one of claims 1 to 8, characterized by , that the structure (10, 11) has several studs (10). [10] Power module according to any one of claims 1 to 9, characterized by , that the structure (10, 11) has a web structure (11). [11] Power module according to claim 10, characterized by , that the bridge structure (11) runs in a meandering pattern along one side of the membrane (6). [12] Power module according to claim 10 or 11, characterized by , that a gap (12) is formed between parts of the bridge structure (11). [13] Power module according to any one of claims 1 to 12, characterized by, that a shaping of the structure (10, 11) along the interface of the membrane (6) follows a shaping of the cooling structure (3) such that a surface of the structure (10, 11) facing the cooling structure is directly adjacent to a surface of the cooling structure (3) facing the structure.

Images