Connecting element for thermally contacting a component to be cooled and a heat sink

Abstract

The invention relates to a connecting element (600) for thermally contacting an electrical connecting component (3041) of a power module (110) and a heat sink (206), comprising at least two dielectric layers (601, 603) and a metal layer (602), wherein the metal layer (602) is arranged between the two dielectric layers (601, 603) and comprises an aluminium sheet or plate.

Description

Description TITLE: CONNECTION ELEMENT INTENDED TO BRING A PART TO BE COOLED AND A HEAT SINK INTO THERMAL CONTACT

[0001] The present invention relates to a connecting element intended to bring a part to be cooled into thermal contact, for example an electrical connection part of a power module, and a heat sink as well as an electronic system comprising a power module and a heat sink in thermal contact by such a connecting element.

[0002] The present invention also relates to a voltage converter comprising such a system and a vehicle comprising such a voltage converter.

[0003] A power module is an electronic module, most often containing semiconductor chips (for example, so-called power transistors), designed to create energy conversion circuits, such as those of a switching cell, a voltage converter, an inverter or even a rectifier bridge.

[0004] Known from the prior art is a connecting element intended to bring into thermal contact an electrical connection part of a power module and a heat sink and consisting of an insulating thermal glue more or less loaded with ceramic particles to reduce the thermal resistance of the glue.

[0005] When using such a bonding element, a polymerization reaction occurs and gas bubbles may appear in the adhesive layer. These gas bubbles are detrimental to the path of heat flow to the heat sink, which leads to greater thermal resistance of the bonding element.

[0006] Another disadvantage of glue-based connecting elements is their significant thickness, which helps to ensure the dielectric requirements between the power module and the heat sink but increases the thermal resistance of the connecting element.

[0007] Finally, surface irregularities, particularly those of the heat sink, can pierce the connecting element or cause electric arcs. and thus lead to a loss of electrical insulation between the power module and the heat sink.

[0008] It may therefore be desirable to provide a connecting element which makes it possible to overcome at least some of the aforementioned problems and constraints.

[0009] There is therefore proposed, according to a first aspect of the invention, a connecting element intended to bring into thermal contact an electrical connection part of a power module and a heat sink and comprising at least two dielectric layers and a metal layer, the metal layer being arranged between said two dielectric layers, said metal layer comprising an aluminum sheet or plate.

[0010] Thus, the two dielectric layers ensure the electrical insulation of the power module while ensuring efficient heat transfer, while the metal layer prevents perforation of the dielectric layers.

[0011] On the other hand, the existence of a metallic layer in aluminum allows the creation of an electrically conductive plane which makes it possible to reduce the capacitive coupling which naturally exists between the metallic substrate of the power module and the heat sink.

[0012] The connecting element according to the invention may further comprise one or more of the following optional features, taken individually or in any technically possible combination.

[0013] According to a first characteristic, the metal layer has a thickness of between 10 pm and 200 pm.

[0014] According to another feature, the connecting element is intended to fix the power module and the heat sink.

[0015] According to another feature the connecting element is a separate part from the power module.

[0016] According to another characteristic the connecting element is intended to be positioned between the heat sink and the power module.

[0017] According to another feature, the metal layer is an aluminum foil or plate.

[0018] According to another characteristic, at least one of the faces of said aluminum sheet or plate is anodized.

[0019] According to another characteristic, the anodized face bears a deposit of aluminum oxide or aluminum nitride.

[0020] According to another characteristic, the metal sheet or plate is made of aluminum, at least one of the faces of which bears a deposit of aluminum oxide or aluminum nitride obtained for example by anodization.

[0021] According to another characteristic, the deposit has a thickness between 5 pm and 50 pm.

[0022] According to another characteristic, the metal sheet or plate is made of aluminum, the two faces of the aluminum sheet each carry a deposit of aluminum oxide or aluminum nitride obtained for example by anodization.

[0023] According to another characteristic, at least one of the two dielectric layers (601, 603), preferably both, has a thickness of between 10 pm and 200 pm and / or a dielectric strength of between 40 kV / mm and 100 kV / mm and / or a thermal conductivity of between 1 and 20 W / mK

[0024] There is also provided, according to a second aspect of the invention, a system comprising: • a power module comprising o an electrical connection part made of metal and having a main plate extending along a main plane; o a switch mounted on an upper face of the main plate of the electrical connection part; and • a heat sink in thermal contact via a connecting element with the lower face of the main plate of the electrical connection part; said system being characterized in that said connecting element is a connecting element according to the first aspect of the invention.

[0025] The system according to the second aspect of the invention may further comprise one or more of the following optional features, taken individually or in any technically possible combination.

[0026] According to a first characteristic, the switch has one of its terminals electrically connected to the upper face of the main plate of the electrical connection part.

[0027] According to another characteristic, said system comprises the connecting element.

[0028] According to another feature, the power module and the connecting element are two separate parts. In other words, the connecting element is not part of the power module.

[0029] According to another feature, the connecting element fixes the power module to the heat sink.

[0030] Thus, the power module is mechanically attached to the heat sink by means of the connecting element. In other words, the connecting element is an element not belonging to the power module and allowing the latter to be attached to the heat sink.

[0031] According to another characteristic, the power module further comprises an electrically insulating overmolding, for example made of resin, covering said switch and at least part of the upper face of the main plate of the electrical connection part.

[0032] According to another characteristic, the overmolding leaves at least part of the lower face of the main plate of the electrical connection part visible, this part left visible being fixed to the heat sink by means of the connecting element.

[0033] According to another feature, at least a portion of the lower face of the main plate of the electrical connection part is exposed outside the power module, this exposed portion being fixed to the heat sink via the connecting element.

[0034] According to another feature, the switch is made in the form of one or more transistors connected in parallel.

[0035] According to another characteristic, the transistor(s) are of the FET type (from the English “Field-Effect Transistor”) or of the IGBT type (from the English “Insulated-Gate Bipolar Transistor”).

[0036] According to another characteristic, the FET type transistor(s) are MOSFETs with silicon substrate (Si-MOSFET) or silicon carbide (SiC-MOSFET) or are gallium nitride FET transistors (GaN-FET).

[0037] According to another characteristic, the transistor(s) are HEMT (high-electron-mobility transistor) transistors, for example made of gallium nitride.

[0038] According to another feature, one of the dielectric layers is fixed by heat-pressing with the underside of the electrical connection part.

[0039] According to another feature, one of the dielectric layers is fixed by heat pressing with the heat sink.

[0040] According to another characteristic, one of the electrical layers is electrically connected to the power module, for example via a capacitor.

[0041] There is also provided, according to a third aspect of the invention, a voltage converter comprising a system according to the second aspect of the invention.

[0042] There is also provided, according to a fourth aspect of the invention, a mobility device comprising a voltage converter according to the third aspect of the invention or an electrical system according to the second aspect of the invention.

[0043] A mobility device is, for example, a motorized land vehicle, an aircraft or a drone.

[0044] A motorized land vehicle is, for example, a motor vehicle, a motorcycle, a motorized bicycle or a motorized wheelchair.

[0045] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which:

[0046] [Fig. 1] Figure 1 schematically represents an electrical system comprising a voltage converter implementing the invention in one embodiment of the invention,

[0047] [Fig. 2] Figure 2 is a section along axis AA shown in Figure 3 of a power module of the voltage converter of Figure 1 assembled on a heat sink by means of a connecting element according to a first embodiment of the invention,

[0048] [Fig.3] Figure 3 is a top view of a power module of the voltage converter of Figure 1, without overmolding,

[0049] With reference to FIG. 1, an electrical system 100 implementing the invention in a first embodiment of the invention will now be described.

[0050] The electrical system 100 is for example intended to be installed in a mobility device such as a motor vehicle.

[0051] The electrical system 100 firstly comprises an electrical power source 102 designed to deliver a direct voltage U, for example between 800 V and 1000 V, for example 850 V.

[0052] The electrical power source 102 is therefore a direct voltage source. This electrical power source comprises, for example, a battery.

[0053] The electrical system 100 further comprises an electrical machine 130 comprising several phases (not shown) intended to have respective phase voltages.

[0054] The electrical system 100 further comprises a voltage converter 104 connected between the electrical power source 102 and the electrical machine 130 to perform a conversion between the direct voltage U and the phase voltages.

[0055] The voltage converter 104 firstly comprises a positive bus bar 106 and a negative bus bar 108 intended to be connected to the electrical power source 102 to receive the direct voltage U, the positive bus bar 106 receiving a high electrical potential and the negative bus bar 108 receiving a low electrical potential.

[0056] The voltage converter 104 further comprises at least one electrical module 110. This electrical module 110 is a power module. The power module 110 comprises a phase bus bar intended to be respectively connected to a phase of the electrical machine 130, to provide their respective phase voltages.

[0057] In the example described, the voltage converter 104 comprises three power modules 110 each comprising a phase bus bar 122 connected to a phase of the electrical machine 130.

[0058] More specifically, in the example described, the electrical machine 130 comprises a three-phase system comprising three phases. The phase bus bars 122 of the three power modules 110 are connected to the three phases of the three-phase system.

[0059] Each power module 110 comprises, for each phase bus bar 122, a first electrical component (here a high side switch 112) connected between the positive bus bar 106 and the phase bus bar 122 and a second electrical component (here a low side switch 114), connected between the phase bus bar 122 and the negative bus bar 108. Thus, the switches 112, 114 are arranged to form a switching arm, in which the phase bus bar 122 forms a midpoint.

[0060] Each switch 112, 114 has first and second main terminals 116, 118 and a control terminal 120 for selectively opening and closing the switch 112, 114 between its two main terminals 116, 118 depending on a control signal applied thereto.

[0061] The switches 112, 114 are preferably made by means of one or more transistors connected in parallel. The transistors are for example metal-oxide-semiconductor field effect transistors (MOSFETs) with a silicon or silicon carbide substrate having a gate forming the control terminal 120, and a drain and a source respectively forming the main terminals 116, 118. Alternatively, the switches 112, 114 could be insulated gate bipolar transistors (IGBTs) or gallium nitride field effect transistors.

[0062] In the example described, the switches 112, 114 each have the shape of a plate, for example substantially rectangular, having an upper face and a lower face. The first main terminal 116 extends on the lower face, while the second main terminal 118 extends on the upper face. The switches 112, 114 are intended to be crossed, between their main terminals 116, 118, by a current greater than 1 A.

[0063] It will be appreciated that the positive bus bar 106, the negative bus bar 108 and the phase bus bars 122 are rigid electrical conductors. They preferably have a thickness of between 0.3 mm and 1.5 mm, preferably less than 1.2 mm.

[0064] Furthermore, in the example described, the positive bus bar 106 firstly comprises a positive common bus bar 106A connecting the power modules 110 and, in each power module 110, a positive local bus bar 106B connected to the positive common bus bar 106A. Similarly, the negative bus bar 108 comprises a common bus bar negative 108A connecting the power modules 110 and, in each power module 110, a negative local bus bar 108B connected to the negative common bus bar 108A. The connections are shown in Figure 1 by diamonds.

[0065] Further, in the described example, the positive common bus bar 106A and the negative common bus bar 108A are each formed from a single conductive piece.

[0066] Furthermore, in the example described, the electric machine 130 is a rotating electric machine having an electric motor function intended to drive wheels of the motor vehicle via its output shaft. Thus, when operating as an alternator, the electric machine 130 supplies electrical energy towards the electrical power source 102 from the rotation of the output shaft. The voltage converter 104 then operates as a rectifier. When operating as an electric motor, the electric machine drives the output shaft. The voltage converter 104 then operates as an inverter.

[0067] With reference to Figure 2, the voltage converter 104 comprises a system 900 according to the invention. This system comprises a heat sink 206, also called a heat sink, having heat exchange surfaces 204 on which a power module 110 is respectively mounted. The heat exchange between the heat exchange surface 204 of the heat sink 206 and the power module 110 is achieved by means of thermal contact via a connecting element 600 positioned between the heat exchange surface 204 of the heat sink 206 and the power module 110.

[0068] The power module 110 comprises several electrical connection parts 304, 304i, 3042, 3043, preferably made of metal.

[0069] Each electrical connection part 304, 304i, 3042, 3043 has a main plate 306, 306i, 3062, 3063 extending along a horizontal main plane PP, the same for all the main plates 306, 306i, 3062, 3063 so that the main plates 306, 306i, 3062, 3063 are substantially coplanar. In particular, in the example described, the main plates 306, 306i, 3062, 3063 have respective horizontal upper faces 308, 308i, 3082, 3083 extending at the same level.

[0070] Furthermore, the main plates 306, 306i, 3062, 306s are separated from each other along the main plane PP by at least one gap 310.

[0071] Generally, at least one of the electrical connection parts 304, 304i, 3042, 3043 (all in the example described) further has at least one electrical connector projecting from its main plate 306, 306i, 3062, 3063. Each electrical connector is for example either in the form of a pin 312i, or in the form of a straight tab 3122.

[0072] In the example described here, the straight tab 3122 forms with the main plate 3062 the phase bus bar 122, the main plate 306i with the pin 312i associated with it forms the positive local bus bar 106B and the main plate 3063 forms with one of the bent tabs 312i associated with it (the lower one in Figure 3) the negative local bus bar 108B.

[0073] Each pin 312i has a fixed end 314 fixed to the main plate 306, 306i 3063, a main portion 316 extending vertically in the example described and ending in a free end 318 and an elbow 320 connecting the fixed end 314 to the main portion 316.

[0074] In the case of a straight tab, the electrical connector 3122 projects into the main plane PP. In addition, the electrical connector 3122 has a fixed end 314 fixed to the main plate 3062.

[0075] The electrical connection parts 304 are obtained in the example described by cutting a metal plate.

[0076] In the example described here, the metal plate is copper. Alternatively, the metal plate could be aluminum or even gold.

[0077] Furthermore, as explained previously, the power module 110 comprises the switches 112, 114 each electrically connected between two upper faces 308i, 3082, 3083 of respectively two of the main plates 306i, 3062, 3063 for example to pass and interrupt on command a power current between these two main plates 306i, 3062, 3063. In the example described here, each switch 112, 114 is produced by a single MOSFET transistor with a silicon carbide substrate. Thus, the first main terminal 116 and the second main terminal 118 correspond respectively to the drain and the source of the MOSFETs producing the switch. Alternatively, each switch 112, 114 is produced by a plurality of MOSFET transistors with a silicon carbide substrate. silicon connected in parallel, that is, their sources are electrically connected together as well as their drains.

[0078] Each switch 112, 114 firstly has a lower face pressed against one of the two upper faces 308i, 3082, 308s to which this switch is electrically connected. Each switch 112, 114 further has an upper face, a portion of which is electrically connected to the other of the two upper faces. In the example described, the upper face of the switch 112, 114 further comprises a control portion of the switch 112, 114 electrically connected to an upper face of a main plate 306 different from the main plates 306i, 3062, 3063, for example by a wire 328 in the example described.

[0079] In other words, the switch 1 12 is mounted on, and electrically connected to, the upper face 308i of the main plate 306i of the electrical connection part 304i and a first electrical connection element electrically connects the switch 1 12 to the upper face 3082 of the main plate 3062 of the electrical connection part 3042.

[0080] The first electrical connection element comprises two metal strips 3261, one end of each metal strip 326i is connected directly to the upper face 3082 of the main plate 3062 of the electrical connection part 3042 by a welding process or a sintering process. The second end of each metal strip 326i is connected directly to the switch 112 by a welding process or a sintering process. The welding processes used are, for example, ultrasonic or friction welding processes. Thus, each metal strip forms a bridge, one end of which lies flat on the upper face of the switch 112 and the other end of which lies flat on the upper face 3082 of the main plate 3062 of the electrical connection part 3042.

[0081] Similarly, the switch 114 is mounted on, and electrically connected to, the upper face 3082 of the main plate 3062 of the electrical connection part 3042 and a second electrical connection element electrically connects the switch 114 to the upper face 3083 of the main plate 306s of the electrical connection part 3043.

[0082] The second electrical connection element comprises two metal strips 3262, one end of each metal ribbon 3262 is connected directly to the upper face 308s of the main plate 306s of the electrical connection part 3043 by a welding or sintering process. The second end of each metal strip 3262 is connected directly to the switch 114 by a welding or sintering process. The welding processes used are, for example, ultrasonic or friction welding processes. Thus, each metal strip forms a bridge, one end of which lies flat on the upper face of the switch 114 and the other end of which lies flat on the upper face 3083 of the main plate 3063 of the electrical connection part 3043.

[0083] In the example described, the ribbons 326i, 3262 are made of aluminum. In an alternative embodiment, the ribbons 326i, 3262 are made of gold. Alternatively, the ribbons 326i, 3262 may be made of copper.

[0084] In the example described, wire 328 is made of aluminum. In an alternative embodiment, wire 328 is made of gold. Alternatively, wire 328 may be made of copper.

[0085] In the example described, the ribbons 326i, 3262 have, when viewed from above, a substantially rectangular shape.

[0086] In the example described, the pin-shaped electrical connectors 312i associated with the electrical connection parts 304 serve to connect the power module 110 to a control module 210, in order to control the switches 112, 114.

[0087] In addition, one of the electrical connectors 312i associated with the electrical connection part 3043 (the top one in Figure 3) is also intended to be connected to the control module 210 to make a measurement of the electrical current passing through this electrical connection part 3043.

[0088] The power module 110 has an overmolding 402. The overmolding 402 is an electrical insulator and covers each switch 112, 114 and at least a portion of the upper faces 308, 308i, 3082, 3083 of the main plates 306, 306i, 3062, 3063.

[0089] In the example described here, the overmold 402 also covers each wire 328 and the metal ribbons 326i, 3262.

[0090] The overmolding 402 is for example made of resin, for example still made of epoxy containing elements, preferably spherical, of silica representing for example by mass between 80 and 90% of the epoxy / silica assembly.

[0091] Preferably, the overmold 402 is integral in a single piece.

[0092] The overmolding 402 leaves the lower face 502i of the main plate 306i of the electrical connection part 304i visible. This part left visible is designed to be pressed against the heat sink 206. Thus, the heat sink 206 is in thermal contact with the lower face 502i left visible by the overmolding 402. This thermal contact is here made via an insulating and thermally conductive connecting element 600.

[0093] Likewise, the overmolding 402 leaves the lower faces 502, 5022, 5023 of the main plates 306, 3062, 3063 of each of the other electrical connection parts 304, 3042, 3043 visible. These parts left visible are designed to be pressed against the heat sink 206. Thus, the heat sink 206 is in thermal contact with the lower faces 502, 5022, 5023 left visible by the overmolding 402. This thermal contact is here achieved via the insulating and thermally conductive electrical connection element 600.

[0094] Furthermore, the overmolding 402 fills each gap 310 and has, in each gap 310, a lower face flush with the lower faces 502 of the main plates 206.

[0095] The connecting element 600 is in this example a laminated film comprising two dielectric layers 601, 603 and a metal layer 602, the metal layer 602 being arranged between the two dielectric layers 601, 603.

[0096] The so-called upper dielectric layer 601 is intended to be in contact with the power module and the so-called lower dielectric layer 603 is intended to be in contact with the heat dissipation surface of the heat sink.

[0097] In the example described here, the metal layer is not in electrical contact with the power module 110. Alternatively, this metal layer is electrically connected, for example by a capacitor, to the power module 110.

[0098] In the example described here, the metal layer is made from an aluminum sheet with a thickness between 10 pm and 200 pm.

[0099] Preferably, at least one of the faces of the aluminum layer has been treated by anodization in order to deposit thereon a deposit of aluminum oxide or aluminum nitride. In the example described, this deposit has a thickness of between 5 μm and 50 μm.

[0100] In the example described here, each of the two dielectric layers is made by a resin sheet with a thickness of between 10 μm and 200 μm. The resin sheet is for example made in the form of epoxy containing ceramic and / or silica beads.

[0101] Each of the dielectric layers further has a dielectric strength between 40kV / mm and 100kV / mm and a thermal conductivity between 1 and 20W / mK

[0102] In the example described here, the upper layer 601 of the connecting element 600 is positioned on the lower face 502, 502i, 5022, 5023 of the electrical connection parts and the lower layer 603 of the connecting element 600 is positioned on the heat dissipation face 204 of the heat sink 206. A thermo-pressing operation of the stack thus produced is then carried out to ensure the mechanical assembly of the power module 110 with the heat sink 206 via the connecting element 600.

[0103] It will also be noted that in the embodiments described previously, the connecting element 600 is a separate part from the power module 110, this connecting element 600 being positioned between the heat sink 206 and the power module 110 so as to mechanically fix the power module 110 to the heat sink 206.

[0104] Similarly, in the embodiments described above, the lower face 502i of the main plate 306i of the electrical connection part 304i is exposed outside the power module 110, this exposed portion being fixed to the heat sink 206 via the connecting element 600.

[0105] It will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0106] For example, the two metal layers can be made as a metal plate instead of metal sheets.

[0107] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents the foreseeability of which is within the reach of those skilled in the art. by applying his general knowledge to the implementation of the teaching which has just been disclosed to him.

Claims

Claims [1] Connecting element (600) intended to bring into thermal contact an electrical connection part (304i) of a power module (110) and a heat sink (206) and comprising at least two dielectric layers (601, 603) and a metal layer (602), the metal layer (602) being arranged between said two dielectric layers (601, 603), said metal layer comprising an aluminum foil or plate. [2] Element (600) according to the preceding claim wherein said metal layer (602) has a thickness of between 10 pm and 200 pm. [3] Element (600) according to any one of the two preceding claims in which at least one of the faces of said aluminum sheet or plate is anodized. [4] Element (600) according to the preceding claim in which the anodized face carries a deposit of aluminum oxide or aluminum nitride. [5] Element (600) according to any one of the preceding claims wherein at least one of the two dielectric layers (601, 603), preferably both, has a thickness of between 10 pm and 200 pm and / or a dielectric strength of between 40 kV / mm and 100 kV / mm and / or a thermal conductivity of between 1 and 20 W / mK [6] System (900) comprising: • a power module (110) comprising o an electrical connection part (304i) made of metal and having a main plate extending along a main plane; o a switch (112) mounted on an upper face of the main plate of the electrical connection part (304i); and • a heat sink (206) in thermal contact via a connecting element (600) with the lower face of the electrical connection part; said system being characterized in that said connecting element (600) is a connecting element according to any one of claims 1 to 5. [7] System according to the preceding claim in which at least a part of a lower face of the main plate of the electrical connection part is exposed outside the power module (110), this exposed part being fixed to the heat sink (206) via the connecting element (600). [8] System according to claim 6 or 7 in which one of the dielectric layers (601) is fixed by heat-pressing with the lower face of the main plate of the electrical connection part. [9] System according to any one of claims 6 to 8 in which one of the dielectric layers (601) is fixed by heat-pressing with the heat sink (206). [10] A voltage converter (104) comprising a system according to any one of claims 6 to 9. [11] Mobility device comprising a voltage converter (104) according to the preceding claim or a system according to any one of the claims 6 to 9.

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