Cooling for a power converter

Abstract

Cooling element (150) for a printed circuit board (135) with a semiconductor (140) mounted on the printed circuit board (135); wherein the cooling element (150) - a mounting area (155) for the semiconductor (140) and - includes a screw boss (165) located next to the mounting surface (155), into which a screw (175) can be screwed to attach the circuit board (135) to the cooling element (150); - wherein a channel (180) is formed in an area between the mounting surface (155) and the screw dome (165) to drain a thermal transition material, for example in liquid, viscous or pasty form, and / or a pasty mass (160) from an area between the mounting surface (155) and the semiconductor (140); - wherein the channel (180) comprises a first channel or channel section that annularly surrounds the screw boss (165) and / or is a groove circumferential to the screw boss (165); characterized in that, - that the channel (180) continues to include a second channel or channel section extending radially away from the screw dome (165).

Description

[0001] The present invention relates to the cooling of a power converter. In particular, the invention relates to the cooling of a semiconductor on a printed circuit board of a power converter.

[0002] A motor vehicle comprises a powertrain with an electric motor. An inverter is provided to control the electric motor, converting a direct current (DC) voltage supplied by a battery into phase-shifted alternating current (AC) voltages for the motor. The frequency and voltage of the AC voltages can be controlled by the inverter so that the electric motor delivers a predetermined torque and / or maintains a predetermined speed.

[0003] The power converter comprises a number of semiconductors through which alternating voltages flow and which can heat up during operation. A cooling element with a contact surface is provided to dissipate this heat. To improve thermal coupling, a thermal interface material (TIM) can be applied between a semiconductor and the contact surface. The printed circuit board (PCB) can be attached to the cooling element using screws. The TIM can be applied in paste form between the PCB and the contact surface before the PCB is screwed in place. The TIM can also be called a gap filler.

[0004] If too little TIM is used, one of the semiconductors may not be sufficiently thermally bonded to the cooling element, potentially leading to thermal damage. If too much TIM is used, there is a risk that the pasty material will seep into a screw hole. If a screw is then inserted, the incompressible TIM can prevent it from being screwed in. This can cause the cooling element to burst or the screw to break off.

[0005] DE 10 2020 216 057 A1 shows a cooling element in which a TIM material has free access to four screw bosses and no protective measures are provided against this.

[0006] DE 10 2014 110 008 A1 shows a cooling element with radial channels for receiving TIM material. Screw bosses are not described, but would be accessible despite the channels through the TIM material.

[0007] US 2016 / 0 185 232 A1 shows a power converter housing without going into details about screw bosses or their protection from TIM material or pasty masses.

[0008] DE 10 2018 221 889 A1 shows a cooling element according to the preamble of claim 1.

[0009] One object of the invention is to provide an improved technique for attaching a printed circuit board to a cooling element, in particular with regard to improved protection of screw bosses against the ingress of TIM material or pasty masses.

[0010] The invention solves this problem by means of the subject matter of the independent claims. Dependent claims describe preferred embodiments.

[0011] A semiconductor is mounted on a printed circuit board (PCB). A cooling element for the PCB comprises a mounting surface for the semiconductor and a screw boss located next to the mounting surface, into which a screw can be inserted to attach the PCB to the cooling element. A channel is formed in the area between the mounting surface and the screw boss to drain any thermal interface material, for example, in liquid, viscous, or pasty form, and / or a pasty mass from the area between the mounting surface and the semiconductor.

[0012] The pasty mass can be used, in particular, to compensate for play and fill a gap between the semiconductor and the mounting surface. Preferably, the mass is designed to conduct heat well, thus improving the thermal bond between the semiconductor and the mounting surface. The mass can, in particular, comprise TIM. In one embodiment, the TIM remains pasty after application; in another, its viscosity can subsequently increase or it can harden.

[0013] The channel is preferably provided as a groove in a surface of the cooling element facing the circuit board. The cooling element can, for example, be manufactured as a casting made of a light metal. The contact surface is preferably flat, and a surface of the cooling element from which the screw boss rises is further preferably also flat and can encompass the contact surface or lie parallel to it.

[0014] The channel allows the mass to be diverted away from the screw boss as it approaches it laterally, thus reducing the risk of the mass penetrating the screw hole. This allows a screw to be driven into the screw hole without having to compress any mass that has entered the hole. This prevents the screw from being blocked or from being damaged during installation.

[0015] The compound can be forced towards the screw boss, particularly if it is compressed between the mounting surface and the semiconductor during installation of the circuit board on the cooling element. The channel also prevents the compound from becoming trapped between one end of the screw boss and the circuit board, thus preventing distortion of the board. Furthermore, it prevents the compound from reaching the screw and becoming trapped between the screw and the threads in the screw boss, where it could negatively affect the screw's retention in the screw hole.

[0016] According to the invention, the channel comprises a first channel or channel section that surrounds the screw boss. This allows the mass to be absorbed at the screw boss from all radial directions. The volume of mass that can be absorbed by the channel can be maximized while minimizing the channel's space requirements.

[0017] According to the invention, a second channel or channel section is further provided, which extends radially away from the screw boss. The channel can, in particular, extend in a direction away from the semiconductor. This allows a larger quantity of the pasty mass to be drained from the area of ​​the screw boss. This embodiment can advantageously be combined with the circumferential groove to potentially capture mass from all directions and drain it in a predetermined direction.

[0018] Preferably, several screw bosses are arranged in a region of the cooling element that encompasses the contact surface. Each screw boss can have a dedicated channel. Screw bosses can be arranged around a region where one or more semiconductors can be thermally connected to the contact surface.

[0019] In one embodiment, a connecting line can be specified that runs across the screw bosses and encircles the contact surface. Two or more channels of different screw bosses can be connected to each other or merge into one another. All channels or sections of channels can be designed in the same way, i.e., with the same shape and cross-section. In another embodiment, shapes and / or cross-sections can also be dimensioned differently. In an area where a larger quantity of pasty material is expected to be received, a channel can be dimensioned larger than in an area where only a smaller quantity of material is expected to be received or conveyed.

[0020] Preferably, a cooling channel for a fluid cooling medium is formed in the cooling element. The cooling channel can be located on the side facing the contact surface. In one embodiment, the cooling channel is open on one side and can be closed by attaching the cooling element to another element, in particular a housing part. The cooling channel can also be embedded in a material of the cooling element.

[0021] Preferably, several semiconductors of a power converter are mounted on the circuit board. The semiconductors can function as current valves through which a controlled current can flow. Two semiconductors can be connected to form a half-bridge. The half-bridge comprises an upper semiconductor (high-side switch) and a lower semiconductor (low-side switch) and is configured to generate a predetermined voltage from a DC voltage by appropriately alternating the two semiconductors. The half-bridge can also include several upper and / or several lower semiconductors to increase the maximum controllable current. The power converter can comprise multiple half-bridges. In a preferred embodiment, three half-bridges, each with at least two semiconductors, are provided. Any number, preferably all, of the semiconductors can be thermally connected to the contact surface of the cooling element.

[0022] A housing for an electric machine includes a cooling element as described herein. The housing further preferably includes a power converter with semiconductors for controlling the electric machine.

[0023] The housing can further include a transmission for coupling the electric machine to a drive shaft of a motor vehicle. Preferably, the transmission is configured to couple an output shaft of an internal combustion engine with the output shaft of the electric motor. The transmission can couple torques from the internal combustion engine and / or the electric machine to the output shaft, similar to a hybrid drive. Depending on the relative power output of the electric machine compared to the internal combustion engine, this can be referred to as a mild hybrid drive or a full hybrid drive.

[0024] An assembly consisting of a housing and a printed circuit board can be part of a control device for an electric drive motor or an electric axle drive. The printed circuit board can, in particular, include a power converter. The power converter is preferably configured to convert a direct current, which can be supplied by a battery, into one or more alternating currents to drive the motor. The current flows from the battery through one of the semiconductors, then through the motor, through another semiconductor, and back to the battery. The semiconductors can advantageously be cooled by the housing. The assembly can form a separately handleable unit.

[0025] An electric axle drive comprises a housing containing a power converter as described herein and an electric drive motor. The power converter is configured to control the electric drive motor. The drive motor can be configured to drive a motor vehicle directly or via a gearbox.

[0026] The circuit board can include components for controlling the semiconductors, for example, to provide a predetermined torque or to assume a predetermined speed, depending on a driver request. In one embodiment, the electric drive motor is controlled by the control device using vector control, in particular by field-oriented control.

[0027] A vehicle comprises a powertrain with a hybrid transmission, which includes a housing as described herein. The vehicle is preferably designed as a motor vehicle, more preferably as a passenger car, a motorcycle, a truck, or a bus.

[0028] The invention will now be described in more detail with reference to the attached figures, in which: Fig. 1 a power converter; Fig. 2 views of a screw boss on a housing element; Fig. 3. A top view of a printed circuit board with semiconductors; Fig. 4 a top view of a housing element for a power converter; and Fig. 5 shows a flowchart of a process.

[0029] Fig. Figure 1 shows a power converter 100 in a housing 105. The power converter 100 is configured to provide an alternating voltage for an electric machine 110 based on a direct current voltage. The housing 105 can accommodate not only the power converter 100 but also the electric machine 110 and, optionally, a gearbox 115. The gearbox 115 can be arranged in the drivetrain of a motor vehicle. The drivetrain can also include a further drive motor, in particular an internal combustion engine, wherein the gearbox can couple torques from the further drive motor and / or the electric machine 110 to an output shaft for connection to a drive wheel of the motor vehicle.

[0030] In this example, the power converter 100 comprises an electrical connection element 120, a control assembly 125, and a power assembly 130. The power assembly 130 comprises a printed circuit board 135 on the surface of which one or more semiconductors 140 are mounted. An optional carrier 145 is designed to be positioned between elements of the power converter 100 in order to mount them together as an assembly or to another element.

[0031] A further element, a cooling element 150, is provided, which can simultaneously be part of the housing 105. The cooling element 150 comprises a cooling channel 152 for a cooling fluid and a contact surface 155, which is configured to be thermally coupled to the surfaces of the semiconductors 140. For this purpose, surfaces of the semiconductors 140 can be in contact with the contact surface 155, or a thermal interface material (TIM) 160 can be provided between them. The TIM 160 can be applied in liquid, viscous, or preferably paste-like form between the power assembly 130 and the cooling element 150.

[0032] Preferably, a screw boss 165 is formed on the cooling element 150. This boss extends from a plane in which the mounting surface 155 lies towards the circuit board 135 and has a screw hole 170 with an internal thread. A screw 175 is inserted through recesses in the power converter 100 and screwed into the screw hole 170. It is proposed to form a channel 180 in the cooling element 150 in the area of ​​the screw boss 165. This channel is designed to receive excess TIM 160 and prevent it from rising up the screw boss 165 and, for example, entering the screw hole 170.

[0033] Fig. Figure 2 shows a schematic representation of a cooling element 150 in a further embodiment. In an upper area, a longitudinal section through a screw boss 165 with a screw 175 is shown, and in a lower area, an axial view of a screw boss 165 on a cooling element 150 is shown.

[0034] The channel 180 shown as an example is designed as a groove-shaped recess in the material of the cooling element 150. A cross-section of the channel 180 is, for example, semicircular. The channel 180 preferably extends in a region located between the screw boss 165 and the semiconductor 140. More preferably, the channel 180 is configured to receive TIM 160 and discharge it around the screw boss 165. For example, the channel 180 can extend in a ring shape around the screw boss 165. The channel 180 can also extend radially away from the screw boss 165, particularly in a direction away from the semiconductor 140.

[0035] The lower illustration shows an exemplary combination according to the invention of an annular channel 180, which is referred to here as the first channel or as the first channel section, with a radially extending channel 180, which is referred to here as the second channel or as the second channel section.

[0036] During the assembly of the printed circuit board 135 onto the cooling element 150, paste-like TIM 160 is typically applied manually or automatically either in the area of ​​the semiconductor 140 or on the cooling element 150. When the printed circuit board 135 is placed onto the cooling element 150, there may initially be more TIM 160 between the elements than is required to compensate for any play or to improve heat transfer between the semiconductor 140 and the cooling element 150. This situation is illustrated in the diagram above.

[0037] When the circuit board 135 with the semiconductor 140 is brought close to the contact surface 155 of the cooling element, the TIM 160 is displaced and distributed laterally. At this point, the screw 175 may not yet be inserted into the screw hole 170, or may only be loosely inserted. The channel 180 facilitates the channeling of laterally approaching TIMs 160, thus preventing them from rising up the screw boss 165 and penetrating the screw hole 170.

[0038] Fig. Figure 3 shows a top view of a power converter 100. One side of the power converter 100 faces the viewer, on which the circuit board 135 and several semiconductors 140 are located. In the exemplary embodiment shown, the power converter 100 has three groups of 12 semiconductors 140 each for three phases of the electric machine 100, with each group being comprised of a half-bridge and including an equal number of high-side and low-side switches (current valves).

[0039] Fig. Figure 4 shows a view of the cooling element 150. One side, which encompasses the mounting surface 155, faces the viewer. The cooling element 150 shown corresponds to the power converter 100 of Fig. 3; the two elements may have been attached to each other and then separated again. The illustrated cooling element 150 is coated with TIM 160 in the area of ​​contact surfaces 155 for semiconductors 140. One contact surface 155 of the cooling element 150 for one of the semiconductors 140 is highlighted as an example.

[0040] An area in which the semiconductors 140 are located after mounting the power converter 100 on the cooling element 150 is preferably surrounded by screw bosses 165. Optionally, a screw boss 165 can also be provided within this area. A channel 180 is provided in the area of ​​a screw boss 175, which concentrically surrounds the screw boss 165 in this case; however, other configurations of the channel 180 are also conceivable. At some channels 180 in Fig. Figure 4 shows TIM 160, which was derived from an associated screw boss 165. Part of the TIM 160 has been displaced beyond the mounting areas 155 for semiconductors 140 and has spread along the surface of the cooling element 150.

[0041] In the upper part of the illustration, a meandering section of applied TIM 160 can be seen. This section comes from an automatic dosing system that automatically applies the TIM 160 to the cooling element 150 during assembly. The section is located outside a system area 155 and ensures that the TIM 160 is conveyed without bubbles and applied to the surface of the cooling element 150.

[0042] Fig.Figure 5 shows a flowchart of an exemplary process 500 for attaching a power converter 100 to a cooling element 150. In a first step 505, the cooling element 150 is provided. Subsequently, in a step 510, paste-like TIM 160 can be applied to the contact surface 155 of the cooling element 150. Alternatively or additionally, TIM 160 can be applied to a semiconductor 140 or a printed circuit board 135 of a power converter 100. The application is preferably automated, for example, by means of an industrial robot.

[0043] In step 515, the circuit board 135 can be placed on the cooling element 150, so that the TIM 160 is located between the semiconductor 140 and the mounting surface 155. Preferably, the circuit board 135 is already attached to other elements of the power converter 100 at this point. In particular, the power converter 100 can already be pre-assembled and available as a separately handleable unit.

[0044] In step 520, the circuit board 135 can be pressed onto the cooling element 150, so that the TIM 160 is distributed across the contact surface 155. This pressing action can be performed as a separate step before a screw 175 is inserted into a corresponding recess in the power converter 100 and into the screw hole 170. In another embodiment, the screw 175 is already inserted before pressing and can be screwed into the screw hole 170 to effect the pressing action. The tightening torque of the screw 175 can be controlled to prevent mechanical stress on the circuit board 135 against the cooling element 150.

[0045] In step 525, an electrical connection to the power converter 100 can be established and the housing 105, in which the power converter 100 is located, can be closed. Reference sign 100 power converters 105 cases 110 electric machine 115 gearbox 120 connection element 125 Control assembly 130 Power module 135 circuit board 140 semiconductors 145 carriers 150 cooling elements 152 Cooling channel 155 m² of installation area 160 thermal transition material, TIM 165 screw dome 170 screw holes 175 screw 180 channel 500 procedures 505 Provide cooling element Apply 510 TIM 515 Mounting circuit board 520 Screw the circuit board in place 525 Close case

Claims

[1] Cooling element (150) for a printed circuit board (135) with a semiconductor (140) mounted on the printed circuit board (135); wherein the cooling element (150) - a mounting area (155) for the semiconductor (140) and - includes a screw boss (165) located next to the mounting surface (155), into which a screw (175) can be screwed to attach the circuit board (135) to the cooling element (150); - wherein a channel (180) is formed in an area between the mounting surface (155) and the screw dome (165) to drain a thermal transition material, for example in liquid, viscous or pasty form, and / or a pasty mass (160) from an area between the mounting surface (155) and the semiconductor (140); - wherein the channel (180) comprises a first channel or channel section that annularly surrounds the screw dome (165) and / or is a groove circumferential to the screw dome (165); characterized by , - that the channel (180) continues to include a second channel or channel section extending radially away from the screw dome (165). [2] Cooling element (150) according to claim 1, wherein the second channel or channel section extends radially away from the screw dome (165) in a direction away from the semiconductor (140). [3] Cooling element (150) according to claim 1 or 2, wherein the second channel or channel section extends radially away from the screw dome (165) starting from the first channel or channel section. [4] Cooling element (150) according to one of the preceding claims, wherein the channel (180) - is embedded in a material of the cooling element (150) and / or - is designed as a groove-shaped depression in the material of the cooling element (150). [5] Cooling element (150) according to one of the preceding claims, wherein several screw bosses (165) are arranged in a region of the cooling element (150) which includes the contact surface (155). [6] Cooling element (150) according to claim 5, wherein a connecting line via the screw bosses (165) surrounds the contact surface (155). [7] Cooling element (150) according to one of the preceding claims, wherein a cooling channel (152) for a fluid cooling medium is formed in the cooling element (150). [8] Cooling element (150) according to one of the preceding claims, wherein several semiconductors (140) of a power converter (100) are attached to the circuit board (135). [9] Housing (105) for an electric machine (110), wherein the housing (105) comprises a cooling element (150) according to one of the preceding claims. [10] Housing (105) according to claim 9, further comprising - a transmission (115) for coupling the electric machine (110) and an output shaft of an internal combustion engine with a drive shaft of a motor vehicle and / or - a printed circuit board (135); wherein the printed circuit board (135) is encompassed by a power converter. [11] Electric axle drive comprising a housing (105) according to claim 10 and an electric drive motor, in particular for a vehicle; wherein the power converter is configured to control the electric drive motor. [12] vehicle comprising a powertrain with a hybrid transmission (115) - a cooling element (150) according to one of claims 1 to 8 and / or - comprising a housing (105) according to claim 9 or 10.

Images