POWER MODULE WITH OVERMOLD AND SYSTEMS INCLUDING SUCH A POWER MODULE

Abstract

The invention relates to a power module comprising: a first and a second electrical connection piece, each having a main plate, the main plates extending along the same principal plane so as to be substantially coplanar; a transistor mounted on an upper face of the main plate of the first electrical connection piece, said transistor being electrically connected by at least one ribbon or by at least one wire to the upper face of the main plate of the second electrical connection piece; and an electrically insulating overmolding, covering said transistor and at least a portion of the upper face of the main plate of the first and second electrical connection pieces, the upper face of the electrically insulating overmolding having a cavity situated at least partially above the ribbon or wire; Figure for the abstract: Fig. 6

Description

Title of the invention: POWER MODULE WITH OVERMOLD AND SYSTEMS INCLUDING SUCH A POWER MODULE

[0001] The present invention relates to a power module with overmolding, an electrical system and a voltage converter comprising such a power module.

[0002] A power module is an electronic module, most often containing semiconductor chips (for example, so-called power transistors), designed to carry out energy conversion circuits, such as those for example of a switching cell, an inverter or a rectifier bridge.

[0003] It is known from the prior art of power modules comprising: - a first and a second electrical connection piece, preferably made of metal, each having a main plate, the main plates extending along the same main plane so as to be substantially coplanar; - a transistor mounted on the upper face of the main plate of the first electrical connection piece, the upper face of the transistor defining a reference plane, said transistor being electrically connected by at least one ribbon or by at least one wire to the upper face of the main plate of the second electrical connection piece; and - an electrical insulating overmolding, for example of resin, covering said transistor and at least part of the upper face of the main plate of the first and second electrical connection pieces, the upper face of the electrical insulating overmolding having a cavity situated at least partially above the ribbon or wire.

[0004] However, in the event of overheating of the transistor, for example in the event of a short circuit, the heat diffuses into the electrical insulator so that the latter risks catching fire, endangering the surrounding elements.

[0005] The invention aims to alleviate at least part of the aforementioned problem.

[0006] According to a first aspect of the invention, a power module comprising: - a first and a second electrical connection piece, preferably made of metal, each having a main plate, the main plates extending along the same main plane so as to be substantially coplanar; - a transistor mounted on the upper face of the main plate of the first electrical connection piece, the upper face of the transistor defining a reference plane, said transistor being electrically connected by at least one ribbon or by at least one wire to the upper face of the main plate of the second electrical connection piece; and - an electrically insulating overmolding, for example made of resin, covering said transistor and at least part of the upper face of the main plate of the first and second electrical connection pieces, the upper face of the electrically insulating overmolding having a cavity situated at least partially above the ribbon or wire,

[0007] this power module being characterized in that the difference between the distance D3 between the plane parallel to the reference plane passing through said highest point of the electrical insulating overmolding and the reference plane and the distance D2 between the plane parallel to the reference plane passing through the highest point of the electrical insulating overmolding and the plane parallel to the reference plane passing through the lowest point of said cavity is greater than or equal to twice the thickness of the ribbon or wire.

[0008] The fact that the cavity is located at least partially above the ribbon or wire means geometrically that the intersection between the orthogonal projection of the ribbon or wire onto the principal plane and the orthogonal projection of the cavity onto this same principal plane is non-empty.

[0009] Thanks to this technical feature, the thickness of the electrical insulating overmolding is adjusted according to the arrangement of the ribbon or wire so that this thickness is less, or even zero, above the ribbon or wire.

[0010] In this way, the holding force of the electrical insulating overmolding exerted on the ribbon or wire is reduced, which allows for easier breakage of this ribbon or wire when it heats up.

[0011] Thus, the ribbon or wire in the power module according to the invention breaks at a lower temperature than that in the power module according to the prior art. Thanks to this break at a lower temperature, the heating of the transistor is limited.

[0012] In other words, thanks to the cavity located above the ribbon or wire, the temperature of the electrical insulating overmolding of the power module according to the invention remains lower in the event of a malfunction of the transistor than in the power module according to the prior art so that the power module according to the invention is less likely to catch fire.

[0013] In addition, the relationship between the distances D2, D3 and the thickness of the ribbon or wire makes it possible to guarantee the existence of a minimum thickness of resin above the transistor so that the transistor is properly protected by the resin.

[0014] A power module according to the invention may further include one or more of the following optional features, taken individually or in any technically possible combination.

[0015] According to a first characteristic, the cavity has a flat bottom and the power module is characterized in that the orthogonal projection of the highest point of the ribbon or wire onto the reference plane is included in the orthogonal projection of the flat bottom onto the reference plane and in that the difference between the distance DI between the highest point of the ribbon or wire with respect to the reference plane and the thickness of the ribbon or wire is greater than or equal to the difference between the distance D3 and the distance D2.

[0016] According to another feature, the cavity has a flat bottom, the ribbon or wire forms a first bridge whose two ends rest flat on the top face of the transistor, the orthogonal projection of the highest point of the first bridge on the reference plane is included in the orthogonal projection of the flat bottom of the cavity on the reference plane and in which the difference between the distance D5 between the highest point of the first bridge with respect to the reference plane and the thickness of the ribbon or wire is greater than or equal to the difference between the distance D3 and the distance D2.

[0017] According to another feature, the ribbon or wire forms a second bridge, one end of which rests flat on the top face of the transistor and the other end of which rests flat on the top face of the main plate of the second electrical connection piece, the orthogonal projection of the highest point of the second bridge onto the reference plane is included in the orthogonal projection of the flat bottom of the cavity onto the reference plane and the difference between the distance D6 between the highest point of the second bridge with respect to the reference plane and the thickness of the ribbon or wire is greater than or equal to the difference between the distance D3 and the distance D2.

[0018] According to another feature, the transistor is connected by a plurality of ribbons and / or wires to the upper face of the main plate of the second electrical connection piece, and the cavity has a flat bottom. The power module is further characterized in that the orthogonal projection of the highest point of each ribbon and / or wire onto the reference plane is included in the orthogonal projection of the flat bottom of the cavity onto the reference plane, and in that, for each ribbon and / or wire, the difference between the distance from the highest point of that ribbon and / or wire to the reference plane and the thickness of that ribbon or wire is greater than or equal to the difference between distance D3 and distance D2.

[0019] According to another feature, the cavity is located at least partially above the highest part of the ribbon or wire.

[0020] According to another feature, the cavity is located at least partially above the first bridge.

[0021] According to another feature, the cavity is located at least partially above the second bridge.

[0022] According to another feature, the first electrical connection piece is intended to be connected to a positive terminal of a DC voltage source.

[0023] According to another feature, the second electrical connection piece is intended to be connected to a phase of a rotating electrical machine.

[0024] According to another feature, the first electrical connection piece includes at least one electrical connector projecting from its main plate.

[0025] According to another feature, the electrical connector of the first electrical connection piece projects from the main plate of the first electrical connection piece into the main plane.

[0026] According to another feature, the electrical connector and the main plate of the first electrical connection piece bearing it are made in one piece by continuity of material.

[0027] According to another feature, the second electrical connection piece includes at least one electrical connector projecting from its main plate.

[0028] According to another feature, the electrical connector of the second electrical connection piece projects from the main plate of the second electrical connection piece into the main plane.

[0029] According to another feature, the electrical connector and the main plate of the second electrical connection piece bearing it are made in one piece by continuity of material.

[0030] According to another feature, the transistor is electrically connected to the upper face of the main plate of the first electrical connection piece.

[0031] According to another feature, the electrical insulating overmolding is integral in one piece.

[0032] According to another feature, the cavity is filled with a gel or resin having a lower hardness than that of the electrically insulating overmolding

[0033] According to another characteristic, the transistor is a FET (Field-Effect Transistor) type transistor or an IGBT (Insulated-Gate Bipolar Transistor) type transistor.

[0034] According to another characteristic, the FET type transistor is a silicon MOSFET (Si-MOSFET) or a silicon carbide MOSFET (SiC-MOSFET) or is a gallium nitride FET (GaN-FET).

[0035] According to another characteristic, the transistor is a HEMT transistor (from the English "high-electron-mobility transistor") for example made of gallium nitride.

[0036] According to another characteristic, the transistor has the shape of a plate, for example substantially rectangular, having an upper face and a lower face.

[0037] According to another feature, the transistor has a lower face plated against the upper face of the main plate of the first electrical connection piece on which the transistor is mounted.

[0038] According to another feature, the transistor is electrically connected to the upper face of the main plate of the first electrical connection piece via its lower face.

[0039] According to another feature, the overmolding has a downward-projecting resin blob

[0040] According to another feature, the main plates are separated from each other along the main plane by at least one gap and the overmolding fills each gap and presents, in each gap, a lower face flush with the lower faces of the main plates.

[0041] According to another feature, the resin pellet is projected from the underside of the overmolding present in the gap.

[0042] According to another feature, the electrical connection parts are obtained by cutting from a single metal plate.

[0043] According to another feature, the overmolding leaves at least a portion of the underside of the main plate of at least one of the electrical connection parts exposed, this exposed portion being designed to be pressed against a heat sink.

[0044] According to another feature, the cavity is at least partially cut by laser ablation in the upper face of the electrically insulating overmolding.

[0045] It should be noted that the relationship between the distances D2, D3 and D4 also ensures that a sufficient layer of resin is between the bottom of the cavity and the transistor so that the transistor is not damaged during laser ablation of the cavity.

[0046] According to another feature, the cavity has a flat bottom.

[0047] According to another feature, the flat bottom of the cavity is made up of several steps located at different levels.

[0048] According to another feature, the bottom of the cavity is flat except for a protruding portion located under the ribbon or wire.

[0049] According to another feature, the bottom of the cavity is flat except for a protruding portion located under each ribbon and / or each wire.

[0050] According to another feature, the projecting portion rises from the flat bottom of the cavity.

[0051] According to a second aspect of the invention, an electrical system is also proposed comprising a heat sink and a power module according to the first aspect of the invention, and in which the heat sink is in thermal contact with the lower face left exposed by the overmolding.

[0052] According to a third aspect of the invention, a voltage converter is also proposed comprising a power module according to the first aspect of the invention or an electrical system according to the second aspect of the invention.

[0053] This voltage converter is intended to be connected between a power supply delivering a direct current voltage and a rotating electrical machine to perform a conversion between the direct current voltage of the power supply and at least one phase voltage of the rotating electrical machine.

[0054] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which:

[0055] [Fig-1] [Fig.1] schematically represents an electrical system comprising a voltage converter implementing the invention in a first embodiment of the invention,

[0056] [Fig.2] [Fig.2] is a three-dimensional exploded view of the voltage converter of [Fig.1] in a first embodiment of the invention,

[0057] [Fig.3] [Fig.3] is a three-dimensional top view of a power module of the voltage converter of [Fig.2], without overmolding in the first embodiment of the invention,

[0058] [Fig.4] [Fig.4] is a view similar to that of [Fig.3], with overmolding,

[0059] [Fig. 5] [Fig. 5] is a three-dimensional view from below of the power module Figures 3 and 4, with overmolding,

[0060] [Fig.6] [Fig.6] is a schematic view describing the relationships existing between certain physical dimensions of a power module in the first embodiment of the invention, and

[0061] [Fig.7] [Fig.7] is a schematic view describing the relationships existing between certain physical dimensions of a power module in a second embodiment of the invention.

[0062] [Fig.8] [Fig.8] is a schematic view describing the relationships existing between certain physical dimensions of a power module in a third embodiment of the invention.

[0063] With reference to [Fig.1], an electrical system 100 implementing the invention in a first embodiment of the invention will now be described.

[0064] The electrical system 100 is, for example, intended to be installed in a motor vehicle.

[0065] The electrical system 100 first includes an electrical power supply 102 designed to deliver a direct voltage U, for example between 10 V and 100 V, for example 48 V or 12 V.

[0066] The power supply 102 is therefore a DC voltage source. This power supply includes, for example, a battery.

[0067] The electrical system 100 further comprises an electrical machine 130 having several phases (not shown) intended to present respective phase voltages.

[0068] The electrical system 100 further includes a voltage converter 104 connected between the power supply 102 and the electrical machine 130 to perform a conversion between the direct voltage U and the phase voltages.

[0069] The voltage converter 104 first includes a positive busbar 106 and a negative busbar 108 intended to be connected to the power supply 102 to receive the DC voltage U, the positive busbar 106 receiving a high electrical potential and the negative busbar 108 receiving a low electrical potential.

[0070] The voltage converter 104 further comprises at least one power module 110. The power module 110 comprises one or more phase busbars intended to be connected respectively to one or more phases of the electrical machine 130, to supply their respective phase voltages.

[0071] In the example described, the voltage converter 104 comprises three power modules 110 each comprising two phase busbars 122b 1222 connected to two phases of the electrical machine 130.

[0072] More specifically, in the example described, the electric machine 130 comprises two three-phase systems, each with three phases, and intended to be electrically phase-shifted by 120° relative to each other. Preferably, the first phase busbars 122i of the power modules 110 are respectively connected to the three phases of the first three-phase system, while the second phase busbars 1222 of the power modules 110 are respectively connected to the three phases of the second three-phase system.

[0073] Each power module 110 comprises, for each phase busbar 122i, a first electrical component, (here a top side switch 112i) connected between the positive busbar 106 and the phase busbar 122i and a second electrical component (here a bottom side switch 1140), connected between the phase busbar 122i and the negative busbar 108. Thus, the switches 112b 114i are arranged to form a switching arm, in which the phase busbar 122i forms a midpoint.

[0074] Each power module 110 also includes, for each phase busbar 1222, a third electrical component (here a top side switch 1122) connected between the positive busbar 106 and the phase busbar 1222 and a fourth electrical component (here a bottom side switch 1142) connected between the phase busbar 1222 and the negative busbar 108. Thus, the switches 1122, 1142 are arranged to form a switching arm, in which the phase busbar 1222 forms a midpoint.

[0075] Each switch 112b 114b 1122, 1142 has first and second main terminals 116, 118 and a control terminal 120 intended to selectively open and close the switch 112b 114b 1122, 1142 between its two main terminals 116, 118 according to a control signal which is applied to it. The switches 112i, 114i, 1122, 1142 are preferably transistors, for example metal-oxide-semiconductor field-effect transistors (MOSFETs) having a gate forming the control terminal 120, and a drain and a source forming the main terminals 116, 118 respectively. Alternatively, the switches 112b, 114b, 1122, 1142 could be insulated-gate bipolar transistors (IGBTs).

[0076] In the described example, the switches 112b, 114b, 1122, and 1142 each have the shape of a plate, for example, substantially rectangular, having an upper and a lower face. The first main terminal 116 extends over the lower face, while the second main terminal 118 extends over the upper face. The switches 112b, 114b, 1122, and 1142 are intended to carry, between their main terminals 116 and 118, a current exceeding 1 A.

[0077] It will be appreciated if the positive busbar 106, the negative busbar 108 and the phase busbars 122b 1222 are rigid electrical conductors designed to support electric currents of at least 1 A intended to pass through the switches 112b 114b 1122, 1142. They preferably have a thickness of at least 1 mm.

[0078] Furthermore, in the described example, the positive busbar 106 first comprises a common positive busbar 106A connecting the power modules 110 and, in each power module 110, a local positive busbar 106B connected to the common positive busbar 106A. Similarly, the negative busbar 108 comprises a common negative busbar 108A connecting the power modules 110 and, in each power module 110, a local negative busbar 108B1, 108B2 for each bottom-side switch 114b 1142, the local negative busbars 108B1, 108B2 being connected to the busbar Negative common omnibus 108A. The connections are represented on [Fig.1] by diamonds.

[0079] Furthermore, in the example described, the positive common busbar 106A and the negative common busbar 108A are each formed from a single conductive piece.

[0080] Furthermore, in the described example, the electric machine 130 is a rotating electric machine that functions as both an alternator and an electric motor. More specifically, the motor vehicle also includes a heat engine (not shown) with an output shaft to which the electric machine 130 is connected by a belt (not shown). The heat engine is designed to drive the wheels of the motor vehicle via its output shaft. Thus, when operating as an alternator, the electric machine 130 supplies electrical energy to the power supply 102 from the rotation of the output shaft. The voltage converter 104 then functions as a rectifier. When operating as an electric motor, the electric machine drives the output shaft (either in addition to or instead of the heat engine). The voltage converter 104 then functions as an inverter.

[0081] The electric machine 130 is for example located in a gearbox or in a clutch of the motor vehicle or in place of the alternator.

[0082] In the following description, the structure and arrangement of the elements of the voltage converter 104 will be described in more detail, with reference to a vertical direction HB, where "H" represents the top and "B" represents the bottom. This vertical direction HB is denoted in the figures by the reference numeral V.

[0083] With reference to [Fig. 2], the voltage converter 104 includes a heat sink 206, also called a heat dissipator, having heat exchange surfaces 204 on which the power modules 110 are respectively mounted (only one power module 110 is shown in [Fig. 2]). The heat exchange between the heat exchange surface 204 of the heat sink 206 and the power module 110 is achieved, for example, by direct contact or contact via a thermally conductive paste between the heat exchange surface 204 of the heat sink 206 and the power module 110.

[0084] The voltage converter 104 also includes a mounting housing 208 on which a secondary electronic module, such as a control module 210, is attached. In the example of [Fig. 1], the control module 210 is a control board. Optionally, the mounting housing 208 is also mounted on the heat sink 206.

[0085] With reference to [Fig.3], we will now describe the power module 110.

[0086] The power module 110 includes several electrical connection parts 304, 304i, 3042, 3043 preferably made of metal.

[0087] Each electrical connection piece 304, 304b, 3042, 3043 has a main plate 306, 306b, 3062, 3063 extending along a horizontal principal plane PP, the same for all the main plates 306, 306b, 3062, 3063, such that the main plates 306, 306b, 3062, 3063 are substantially coplanar. In particular, in the example described, the main plates 306, 306b, 3062, 3063 have respective horizontal upper faces 308, 308i, 3082, 3083 extending at the same level. For clarity, the upper faces 308, 308b 3082, 3083 are indicated in the figure only for the largest main plates 306, 306b 3062, 3063.

[0088] In particular, the power module 110 comprises a first electrical connection piece 304i having a main plate 306i presenting an upper face 308b, a second electrical connection piece 3042 having a main plate 3062 presenting an upper face 3082, and a third electrical connection piece 3043 having a main plate 3063 presenting an upper face 3083.

[0089] Furthermore, the main plates 306, 306b, 3062, 3063 are separated from each other along the principal plane PP by at least one gap 310. In the example described, each gap 310 has a width less than or equal to five millimeters. This means that the two main plates delimiting the gap 310 are separated by a distance of at most five millimeters along this gap 310.

[0090] Generally, at least one of the electrical connection pieces 304 (all in the described example) also has at least one electrical connector projecting from its main plate 306, 306b 3062, 3063. Each electrical connector is, for example, either in the form of a pin 312b or in the form of a bent tab 3122, 3123, or even in the form of a straight tab 3124.

[0091] In the example described here, the straight tabs 3124 form with their main plates 3062, 306 the phase omnibus bars 122b 1222, the bent tab 3123 forms with its main plate 3061 the positive local omnibus bar 106B and the bent tabs 3122 form with their main plates 3063, 306 the negative local omnibus bars 108B1, 108B2.

[0092] Each electrical connector 312b, 3122, 3123 has a fixed end 314 attached to the main plate 306, 3062, 3063, 306b, a main portion 316 extending vertically in the described example and terminating in a free end 318, and an elbow 320 connecting the fixed end 314 to the main portion 316. For clarity, these different elements of the electrical connectors 312b, 3122, 3123 are not indicated in the figure that for two electrical connectors 312b 3122, one in the shape of a pin, the other in the shape of a tab.

[0093] In the case of a straight tab, the electrical connector 3124 projects into the main plane PP over a considerable length to allow for its connection, for example, at least one centimeter. Furthermore, the electrical connector 3124 has a fixed end 314 attached to the main plate 306, this fixed end 314 having a considerable width to allow the passage of current, for example, at least one centimeter.

[0094] The electrical connection parts 304 are obtained in the example described by cutting a metal plate.

[0095] In the example described here, the metal plate is made of copper. Alternatively, the metal plate could be made of aluminum or even gold.

[0096] Furthermore, as explained previously, the power module 110 includes transistors 112b, 1122, 114b, 1142, each electrically connected between two upper faces 308, 308b, 3082, 3083 of respectively two of the main plates 306, 306i, 3062, 3063, for example, to pass and interrupt on command a power current, which may, for example, be greater than one ampere between these two main plates 306, 306b, 3062, 3063. Each transistor 112b, 1122, 114b, 1142 has first of all a lower face pressed against one of the two upper faces 308, 308b, 3082 to which this transistor is electrically connected. Each transistor 112b 1122, 114b 1142 also has a top face, part of which is electrically connected to the other of the two top faces.In the example described, the upper face of the transistor 112b 1122, 114b 1142 further comprises a control portion of the transistor 112b 1122, 114b 1142, electrically connected to an upper face of a third main plate 306, for example by a wire 328 in the example described.

[0097] In other words, the transistor 112i is mounted on, and electrically connected to the top face 3081 of the main plate 3061 of the first electrical connection piece 304i and a first electrical linking element electrically connects the transistor 112i to the top face 3082 of the main plate 3062 of the second electrical connection piece 3042.

[0098] The first electrical connection element comprises two metal ribbons 326b. One end of each metal ribbon 326i is welded to the upper face 3082 of the main plate 3062 of the second electrical connection piece 3042 by a welding process. The other end of each metal ribbon 3261 is welded directly to the transistor 112i by a welding process. The welding processes used are, for example, ultrasonic or friction welding processes.

[0099] In the example described here, the two 326i ribbons have substantially the same shape.

[0100] Similarly, the transistor 114i is mounted on, and electrically connected to the upper face 3082 of the main plate 3062 of the second electrical connecting piece 3042 and a second electrical connecting element electrically connects the transistor 114i to the upper face 3083 of the main plate 3063 of the third electrical connecting piece 3043.

[0101] The second electrical connection element comprises two ribbons 3262. One end of each metal ribbon 3262 is welded to the upper face 3083 of the main plate 3063 of the third electrical connection piece 3043 by a welding process. The other end of each metal ribbon 3262 is welded directly to the transistor 114i by a welding process. The welding processes used are, for example, ultrasonic or friction welding processes.

[0102] Similarly, transistors 1122 and 1142 are mounted on, and electrically connected to the upper face 308, 3081 of the main plate 306, 306i of an electrical connection piece 304, 304i and have their upper face electrically connected to an upper face of another main plate 306 by means of two identically shaped ribbons 326.

[0103] In the example described, the ribbons 326, 326i, 3262 are made of aluminum and have, for example, a cross-section of 2 mm x 0.3 mm. In an alternative embodiment, the ribbons 326, 326i, 3262 are made of gold.

[0104] In the example described, wire 328 is made of aluminium and has a diameter of 0.2mm. In an alternative embodiment, wire 328 is made of gold.

[0105] In the example described, the pin-shaped electrical connectors 312t are used to connect the power module 110 to the control module 210, in order to take measurements of electrical quantities and to control the transistors 112b 1122, 114b 1142.

[0106] Furthermore, still in the example described, the electrical connectors 3122 are connected to the common negative busbar 108A and the electrical connector 3123 is connected to the common positive busbar 106A.

[0107] Furthermore, still in the example described, the two electrical connectors 3124 in the form of a straight tab respectively form the two phase omnibus bars 122i, 1222 of the power module 110.

[0108] With reference to [Fig.4], the overmolding of the power module 110 is shown and bears the reference 402.

[0109] The overmolding 402 is an electrical insulator and completely covers each transistor 112i, 1122, 114i, 1142 and at least part of the upper faces 308i, 3082, 3083, 308 of the main plates 306i, 3062, 3063, 306.

[0110] In the example described here, the overmolding 402 also completely covers each wire 328.

[0111] In addition, the upper face of the electrical insulating overmolding 402 has a first cavity Cl located at least partially above the highest part of the first electrical bonding element.

[0112] This first cavity Cl is for example at least partially cut by laser ablation in the upper face of the electrical insulating overmold 402. By its realization, the bottom of the first cavity Cl is flat, for example made up of several steps located at different levels, with the exception of a projecting portion, rising from the flat bottom of the first cavity, located under each of the two ribbons 3261.

[0113] A portion of the 326i ribbons is thus located in the first cavity Cl and the electrical insulating overmolding 402 covers the rest of the 326i ribbons. In other words, the electrical insulating overmolding 402 partially covers the 326ide ribbons so that only the highest part, relative to the top-down direction, of the 326in ribbons is not covered by the electrical insulating overmolding 402 and is further located in the first cavity Cl.

[0114] In this way, the electrically insulating overmolding exerts little or no holding force on the highest part of the 326i ribbons, which allows these ribbons to break easily when they heat up.

[0115] Similarly, the upper face of the electrical insulating overmolding 402 has a second cavity C2 located at least partially above the highest part of the second electrical connecting element 3262.

[0116] Part of the ribbons 3262 is thus located in the second cavity C2 and the electrical insulating overmold 402 covers the rest of the ribbons 3262. In other words, the electrical insulating overmold 402 partially covers the ribbons 3262 so that only the highest part, with respect to the top-bottom direction, of the ribbons 3262 is not covered by the electrical insulating overmold 402 and is further located in the second cavity C2.

[0117] For the same reasons as before, the electrical insulating overmolding 402 exerts little or no holding force on the highest part of the ribbons 3262, which allows these ribbons to break easily when they heat up.

[0118] Finally, the upper face of the electrically insulating overmolding 402 also has a third cavity C3 and a fourth cavity C4 located respectively at least partially above the ribbons 326 of transistor 1122 and transistor 1142 and sufficiently deep so that only the upper part of the ribbons 326 of transistor 1122 and the upper part of the ribbons 326 of transistor 1142 are located respectively in the third cavity C3 and in the fourth cavity C4 and so that the electrical insulating overmolding 402 covers the rest of the tapes 326.

[0119] The overmolding 402 is, for example, made of resin, or even epoxy. Preferably, the overmolding 402 is integral in one piece.

[0120] In the embodiment described here, the cavities are devoid of material. Alternatively, the cavities are filled with a gel, for example dielectric and / or silicone. The gel may also have a viscosity between 230 and 600 mPa-s, preferably between 400 and 500 mPa-s, for example 465 mPa-s, and / or a hardness between 65 and 180 g, preferably between 110 and 160 g, for example 123 g or 154 g.

[0121] In another embodiment, the cavities are filled with a resin different from that used in the electrical insulating overmolding 402. In particular, the resin filling the cavities has a lower hardness than that used in the electrical insulating overmolding 402. For example, the electrical insulating overmolding 402 is made of an epoxy resin, having, for example, a hardness between 70 and 90 Shore A, and the cavities are filled with an elastomeric resin, having, for example, a hardness between 20 and 40 Shore A. The resin filling the cavities may also belong to the UL 94 V-0 fire class, as defined by the certification company Underwriters Laboratories.

[0122] The [Fig.5] is a bottom view of the power module 110.

[0123] As can be seen in this figure, the overmolding 402 leaves the lower face 502i of the main plate 306i of the first electrical connection piece 304p exposed. This exposed portion is designed to be pressed against the heat sink 206. Thus, the heat sink 206 is in thermal contact with the lower face 502i exposed by the overmolding 402. This thermal contact can be direct contact or via an electrically insulating and thermally conductive connecting element.

[0124] Similarly, 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 exposed. These exposed parts 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 exposed by the overmolding 402. This thermal contact can be direct contact or via an insulating and thermally conductive electrical connecting element.

[0125] In addition, 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.

[0126] The overmolding 402 has at least one downward-projecting resin pad 506 designed to make direct contact with the heat sink 206 in order to define a predefined gap between the lower faces 502, 502i, 5022, 5023 of the main plates 306, 306i, 3062, 3063 and the heat sink 206, and thus the thickness of the thermally conductive element filling this gap. In the example described, each resin pad 506 is projected from the lower face of the overmolding into one of the gaps 310 between the main plates 306, 306i, 3062, 3063.

[0127] Fig. 6 presents a partial view of the power module 110 along a cutting plane perpendicular to the main plane PP and passing through the main axis of one of the ribbons of the first electrical linking element.

[0128] First of all, let us note that the upper face of the first transistor 112i defines a reference plane P.

[0129] The two identical 326i ribbons each form a first bridge PO1 and a second bridge PO2.

[0130] The two ends of the first POi bridge rest flat on the upper face of the first transistor 112b. The orthogonal projection of the highest point of the first POi bridge onto the reference plane P is included in the orthogonal projection of the flat bottom of the first cavity Cl onto the reference plane P.

[0131] One end of the second bridge PO2 rests flat on the upper face of the first transistor 112i and the other end of the second bridge PO2 rests flat on the upper face of the main plate 3062 of the second electrical connection piece 3042. The orthogonal projection of the highest point of the second bridge PO2 onto the reference plane P is included in the orthogonal projection of the flat bottom of the first cavity Cl onto the reference plane P.

[0132] In the example described here, the two bridges PO1 and PO2 of the two strips 326i have the same elevation. It follows that the orthogonal projection of the highest point of each strip 326i onto the reference plane is included in the orthogonal projection of the flat bottom of the cavity onto the reference plane (P).

[0133] We will now highlight the existing relationships between the physical dimensions of the 326i ribbons, the overmolding 402, and the first cavity CL

[0134] In the following description, the elevations are defined with respect to the previously described top-bottom dimension.

[0135] The distance D2 is the distance between the plane parallel to the reference plane passing through the highest point of the electrically insulating overmolding 402 and the plane parallel to the reference plane P passing through the lowest point of the first cavity CL

[0136] The distance D3 is the distance between the plane parallel to the reference plane P passing through the highest point of the electrical insulating overmolding 402 and the reference plane P.

[0137] The distance D4 corresponds to the identical thickness of each of the two 326p ribbons.

[0138] These distances D2, D3, and D4 are configured such that the difference between distances D3 and D2 is greater than or equal to twice the distance D4. In other words, the distances D3, D2, and D4 satisfy the equation:

[0139] [Math.l] D3-D2>2D4

[0140] Thanks to this mathematical relationship, the existence of a minimum resin thickness above the first transistor 112i is guaranteed so that the first transistor is properly protected by the resin.

[0141] In addition, this minimum resin thickness also guarantees that the first transistor 112ine is not at risk of being damaged during the laser ablation of the first cavity Cl.

[0142] Furthermore, if we define the distance D5 as the distance between the highest point of the first bridge POi with respect to the reference plane P, then the distances D5, D2, D3, D4 are further configured so that the difference between the distance D5 and the distance D4 is greater than or equal to the difference between the distance D3 and the distance D2.

[0143] In other words, the distances D2, D3, D4 and D5 satisfy the equation:

[0144] [Math.2] .D5-D4>D3-D2

[0145] Similarly, if we define the distance D6 as the distance between the highest point of the second bridge PO2 with respect to the reference plane P, then the distances D6, D2, D3, D4 are further configured so that the difference between the distance D6 and the distance D4 is greater than or equal to the difference between the distance D3 and the distance D2.

[0146] In other words, the distances D2, D3, D4 and D6 satisfy the equation:

[0147] [Math.3] D6-D4>D3-D2

[0148] Thanks to these mathematical relationships, the upper ends of the two bridges PO2 and PO2 are located in the first cavity Cl so that the overmolding 402 exerts little or no pressure on these upper ends.

[0149] In the example described, the two bridges PO1 and PO2 have the same elevation, so the distances D5 and D6 are equal. The distances D5 and D6 are also equal to the distance D1 between the highest point of each of the two identically shaped ribbons 326i with respect to the reference plane P.

[0150] In other words, the distances D1, D3, D2 and D4 satisfy the equation:

[0151] [Math.4] D1-D4>D3-D2

[0152] Obviously, identical relationships exist between the physical dimensions of the ribbons 3262, the overmolding 402 and the second cavity C2, as well as between the physical dimensions of the ribbons 326, the overmolding 402 and the cavities C3 and cavity C4.

[0153] With reference to [Fig. 7], we will now describe a second embodiment of the invention. Elements identical or analogous to those of the first embodiment bear the same numerical reference in the description of the second embodiment.

[0154] This second embodiment differs from the first by the shape of the ribbons 326i and by the dimensions of the first cavity Cl.

[0155] More precisely, for the two 326b ribbons the second bridge PO2 has a higher elevation than the first bridge POi and the first cavity Cl is made so that the first bridge POi is entirely covered with resin.

[0156] As in the first embodiment, the distances D2, D3, and D4 are configured such that the difference between the distances D3 and D2 is greater than or equal to twice the distance D4. In other words, the distances D3, D2, and D4 satisfy the equation Math. 1

[0157] In addition, the distances D2, D3, D4 and D6 satisfy the equation Math. 3.

[0158] Obviously, in this second embodiment, identical relationships exist between the physical dimensions of the ribbons 3262, the overmolding 402 and the second cavity C2, as well as between the physical dimensions of the ribbons 326, the overmolding 402 and the cavities C3 and C4.

[0159] With reference to [Fig. 8], we will now describe a third embodiment of the invention. Elements identical or analogous to those of the first or second embodiment bear the same numerical reference in the description of this third embodiment.

[0160] This third embodiment differs from the first in that the two ribbons are not identical.

[0161] Thus, the second bridge PO'2 of one of the two ribbons 326'i has a higher elevation than the second bridge PO2 of the other ribbon 326,.

[0162] As can be seen in the figure, the orthogonal projection of the highest point of each ribbon 326i 326'i onto the reference plane P is included in the orthogonal projection of the flat bottom of the first cavity Cl onto the reference plane P and for each ribbon 326i 326' b the difference between the distance between the highest point D6, D6- of this ribbon with respect to the reference plane P and the thickness D4 of this ribbon is greater than or equal to the difference between the distance D3 and the distance D2.

[0163] It should also be noted that the invention is not limited to the embodiments described above. It will indeed be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in light of the information just disclosed to them.

[0164] For example, all or some of the 326, 326b 3262 ribbons could be replaced by wires and / or fuses.

[0165] For example, transistors 112b 114b 1122, 1142 could be gallium nitride FET or HEMT transistors.

[0166] Furthermore, in the embodiments described above, each electrical connection element has ribbons. Alternatively, these electrical connection elements could have only one ribbon. In another embodiment, these electrical connection elements could have at least three ribbons.

[0167] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiments set forth in this description, but shall be interpreted as including all equivalents which can be foreseen by a person skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Demands

1. Power module (110) comprising: - a first (3040) and a second (3042) electrical connection pieces, preferably made of metal, each having a main plate (306i, 3062), the main plates (3061, 3062) extending along the same principal plane (PP) so as to be substantially coplanar; - a transistor (1120) mounted on an upper face of the main plate (3060) of the first electrical connection piece (3040), the upper face of the transistor (1120) defining a reference plane (P), said transistor (1120) being electrically connected by at least one ribbon (3260) or by at least one wire to the upper face of the main plate (3062) of the second electrical connection piece (3042); and - an electrical insulating overmolding (402), for example of resin, covering said transistor (1120) and at least part of the upper face of the main plate (3061, 3062) of the first (3040) and second (3042) electrical connection pieces, the upper face of the electrical insulating overmolding (402) having a cavity (Cl) situated at least partially above the ribbon (3260) or wire; said power module (110) being characterized in that the difference between the distance D3 between the plane parallel to the reference plane passing through said highest point of the electrically insulating overmolding (402) and the reference plane (P) and the distance D2 between the plane parallel to the reference plane passing through the highest point of the electrically insulating overmolding (402) and the plane parallel to the reference plane passing through the lowest point of said cavity (Cl) is greater than or equal to twice the thickness of the ribbon or wire, said power module being further characterized in that said cavity (Cl) has a flat bottom, in that the ribbon (3260) or wire forms a first bridge (PO0) whose two ends rest flat on the upper face of the transistor (1120), in that the projection orthogonal of the highest point of the first bridge (POi) on the reference plane (P) is included in the orthogonal projection of said flat bottom of the cavity (Cl) on the reference plane (P) and in that the difference between the distance D5 between the highest point of the first bridge (POi) with respect to the reference plane (P) and the thickness of the tape (3260 or wire is greater than or equal to the difference between the distance D3 and the distance D2.

2. Power module (110) according to the preceding claim in which said cavity (Cl) has a flat bottom, said power module (110) being characterized in that the orthogonal projection of the highest point of the ribbon (326i) or wire onto the reference plane (P) is included in the orthogonal projection of said flat bottom onto the reference plane (P) and in that the difference between the distance DI between the highest point of the ribbon (326i) or wire with respect to the reference plane (P) and the thickness of the ribbon or wire (D4) is greater than or equal to the difference between the distance D3 and the distance D2.

3. Power module (110) according to any one of the preceding claims wherein said ribbon (3261) or wire forms a second bridge (PO2) one end of which lies flat on the top face of the transistor (1120) and the other end of which lies flat on the top of the main plate (3062) of the second electrical connection piece (3042), wherein the orthogonal projection of the highest point of the second bridge (PO2) onto the reference plane (P) is included in the orthogonal projection of said flat bottom of the cavity (Cl) onto the reference plane (P) and wherein the difference between the distance D6 between the highest point of the second bridge (PO2) from the reference plane (P) and the thickness (D4) of the ribbon or wire is greater than or equal to the difference between the distance D3 and the distance D2.

4. Power module (110) according to any one of the preceding claims, wherein said transistor (1120) is connected by a plurality of ribbons (3260) and / or wires to the upper face of the main plate (3062) of the second electrical connection piece (3042) and wherein said cavity (Cl) has a flat bottom, said power module (110) being characterized in that the orthogonal projection of the highest point of each ribbon (3260) and / or wire onto the reference plane (P) is included in the projection orthogonal to the flat bottom of the cavity (Cl) on the reference plane (P) and in that for each ribbon (3261) and / or wire, the difference between the distance (D6i, D62) between the highest point of this ribbon and / or wire with respect to the reference plane (P) and the thickness (D4) of this ribbon (326i) or wire is greater than or equal to the difference between the distance D3 and the distance D2

5. Power module (110) according to any one of the preceding claims in which said cavity (Cl) has been at least partially laser ablated into the upper face of the electrical insulating overmolding (402).

6. Power module (110) according to any one of the preceding claims in which the overmolding (402) leaves at least a portion of the underside (502i, 5022) of the main plate (306i, 3062) of at least one of the electrical connection pieces (304i, 3042) exposed, this portion being designed to be pressed against a heat sink (206).

7. Electrical system (100) comprising a heat sink (206) and a power module according to the preceding claim, and wherein the heat sink (206) is in thermal contact with the lower face left apparent by the overmolding (402).

8. Voltage converter (104) comprising a power module (110) according to any one of claims 1 to 6 or an electrical system (100) according to claim 7.

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