POWER MODULE WITH OVERMOLD AND SYSTEMS INCLUDING SUCH A POWER MODULE
Patent Information
- Application Number
- FR2020013916
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2020-12-22
- Publication Date
- 2025-01-17
- Estimated Expiration
- 2040-12-22
Smart Images
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Abstract
Description
Title of the invention: POWER MODULE WITH OVERMOLDING AND SYSTEMS COMPRISING 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 produce energy conversion circuits, such as those of a switching cell, an inverter or even a rectifier bridge.
[0003] Power modules comprising: - a first and a second electrical connection part, 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 an upper face of the main plate of the first electrical connection part, the upper face of the transistor defining a reference plane, said transistor being electrically connected by at least one strip or by at least one wire to the upper face of the main plate of the second electrical connection part; 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 parts, the upper face of the electrically insulating overmolding having a cavity located 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 insulation so that it risks catching fire, endangering the surrounding elements.
[0005] The invention aims to at least partially overcome the aforementioned problem.
[0006] According to a first aspect of the invention, there is therefore proposed a power module comprising: - a first and a second electrical connection part, 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 an upper face of the main plate of the first electrical connection part, the upper face of the transistor defining a reference plane, said transistor being electrically connected by at least one strip or by at least one wire to the upper face of the main plate of the second electrical connection part; 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 parts, the upper face of the electrically insulating overmolding having a cavity located at least partially above the ribbon or wire.
[0007] This power module is characterized in that said cavity has a flat bottom, in that the ribbon or wire forms a first bridge whose two ends rest flat on the upper face of the transistor,in that the orthogonal projection of the highest point of the first bridge onto the reference plane is included in the orthogonal projection of said flat bottom of the cavity onto the reference plane and in which the difference between the distance D5 between the highest point of the first bridge relative to the reference plane and the thickness of the tape or wire is greater than or equal to the difference between the distance D3 between the plane parallel to the reference plane passing through said highest point of the electrically 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 electrically insulating overmolding and the plane parallel to the reference plane passing through the lowest point of said cavity.
[0008] The fact that the cavity is located at least partially above the ribbon or wire geometrically means that the intersection between the orthogonal projection of the ribbon or wire on the principal plane and the orthogonal projection of the cavity on this same principal plane is non-empty.
[0009] Thanks to this technical characteristic, the thickness of the electrically insulating overmolding is adjusted according to the arrangement of the tape or wire so that this thickness is less, or even zero above the tape or wire.
[0010] Furthermore, the relationship between the distances D5, D2, D3 and the thickness of the ribbon or wire ensures that the upper end of the first bridge formed by the ribbon or wire is located in the cavity so that the electrically insulating overmolding exerts little or no holding force on this upper end.
[0011] In this way, the holding force of the electrically insulating overmolding exerted on the tape or wire, and in particular on the upper end, is reduced, which allows easier breaking of this tape or wire when it heats up.
[0012] 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 breakdown at a lower temperature, heating of the transistor is limited.
[0013] In other words, the temperature of the electrically insulating overmolding of the power module according to the invention remains lower in the event of a transistor malfunction 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.
[0014] A power module according to the invention may further comprise one or more of the following optional features, taken individually or in any technically possible combination.
[0015] According to another characteristic, the difference between the distance D3 and the distance D2 is greater than or equal to the thickness of the ribbon or wire, preferably greater than or equal to twice the thickness of the ribbon or wire.
[0016] 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 correctly protected by the resin.
[0017] According to another 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 on the reference plane is included in the orthogonal projection of the flat bottom on the reference plane and in that the difference between the distance DI between the highest point of the ribbon or wire relative 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 characteristic, the ribbon or wire forms a second bridge, one end of which rests flat on the upper face of the transistor and the other end of which rests flat on the upper face of the main plate of the second electrical connection part, the orthogonal projection of the highest point of the second bridge on the reference plane is included in the orthogonal projection of the flat bottom of the cavity on the reference plane and the difference between the distance D6 between the highest point of the second bridge relative 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.
[0019] According to another characteristic, the transistor is connected by a plurality of strips and / or wires to the upper face of the main plate of the second electrical connection part and the cavity has a flat bottom, the power module being further characterized in that the orthogonal projection of the highest point of each strip and / or wire on the reference plane is included in the orthogonal projection of the flat bottom of the cavity on the reference plane and in that for each strip and / or wire, the difference between the distance between the highest point of this strip and / or wire relative to the reference plane and the thickness of this strip or wire is greater than or equal to the difference between the distance D3 and the distance D2
[0020] According to another characteristic, the cavity is located at least partially above the highest part of the ribbon or wire.
[0021] According to another characteristic, the cavity is located at least partially above the first bridge.
[0022] According to another characteristic, the cavity is located at least partially above the second bridge.
[0023] According to another characteristic, the first electrical connection part is intended to be connected to a positive terminal of a direct voltage source.
[0024] According to another characteristic, the second electrical connection part is intended to be connected to a phase of a rotating electrical machine.
[0025] According to another characteristic, the first electrical connection part comprises at least one electrical connector projecting from its main plate.
[0026] According to another characteristic, the electrical connector of the first electrical connection part projects from the main plate of the first electrical connection part in the main plane.
[0027] According to another characteristic, the electrical connector and the main plate of the first electrical connection part carrying it are made in a single piece by continuity of material.
[0028] According to another characteristic, the second electrical connection part comprises at least one electrical connector projecting from its main plate.
[0029] According to another characteristic, the electrical connector of the second electrical connection part projects from the main plate of the second electrical connection part into the main plane.
[0030] According to another characteristic, the electrical connector and the main plate of the second electrical connection part carrying it are made in a single piece by continuity of material.
[0031] According to another characteristic, the transistor is electrically connected to the upper face of the main plate of the first electrical connection part.
[0032] According to another characteristic, the electrically insulating overmolding is integral in a single piece.
[0033] According to another characteristic, the cavity is filled with gel or a resin having a lesser hardness than that of the electrically insulating overmolding.
[0034] According to another characteristic, the transistor is a FET type transistor (from the English “Field-Effect Transistor”) or an IGBT type transistor (from the English “Insulated-Gate Bipolar Transistor”).
[0035] According to another characteristic, the FET type transistor is a silicon MOSFET (Si-MOSFET) or silicon carbide MOSFET (SiC-MOSFET) or is a gallium nitride FET transistor (GaN-FET).
[0036] According to another characteristic, the transistor is a HEMT transistor (from the English “high-electron-mobility transistor”) for example made of gallium nitride.
[0037] According to another characteristic, the transistor has the shape of a plate, for example substantially rectangular, having an upper face and a lower face.
[0038] According to another characteristic, the transistor has a lower face pressed against the upper face of the main plate of the first electrical connection part on which the transistor is mounted.
[0039] According to another characteristic, the transistor is electrically connected to the upper face of the main plate of the first electrical connection part via its lower face.
[0040] According to another characteristic, the overmolding has a resin pad projecting downwards.
[0041] According to another characteristic, the main plates are separated from each other along the main plane by at least one gap and the overmolding fills each gap and has, in each gap, a lower face flush with the lower faces of the main plates.
[0042] According to another characteristic, the resin pad projects from the lower face of the overmolding present in the gap.
[0043] According to another characteristic, the electrical connection parts are obtained by cutting out a single metal plate.
[0044] According to another characteristic, the overmolding leaves visible at least a part of the lower face of the main plate of at least one of the electrical connection parts, this part left visible being designed to be pressed against a heat sink.
[0045] According to another characteristic, the cavity is at least partially cut by laser ablation in the upper face of the electrically insulating overmolding.
[0046] It should be noted that the relationship between the distances D2, D3 and D4 also ensures that a sufficient layer of resin is located between the bottom of the cavity and the transistor so that the transistor is not damaged during laser ablation of the cavity.
[0047] According to another characteristic, the cavity has a flat bottom.
[0048] According to another characteristic, the flat bottom of the cavity is made up of several steps located at different levels.
[0049] According to another characteristic, the bottom of the cavity is flat except for a projecting portion located under the ribbon or wire.
[0050] According to another characteristic, the bottom of the cavity is flat with the exception of a projecting portion located under each ribbon and / or each wire.
[0051] According to another characteristic, the projecting portion rises from the flat bottom of the cavity.
[0052] According to a second aspect of the invention, there is also provided an electrical system 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 visible by the overmolding.
[0053] According to a third aspect of the invention, there is also provided a voltage converter comprising a power module according to the first aspect of the invention or an electrical system according to the second aspect of the invention.
[0054] This voltage converter is intended to be connected between an electrical power source delivering a direct voltage and a rotating electrical machine to perform a conversion between the direct voltage of the electrical power source and at least one phase voltage of the rotating electrical machine.
[0055] 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:
[0056] [fig. 1] [fig.l] schematically represents an electrical system comprising a voltage converter implementing the invention in a first embodiment of the invention,
[0057] [fig.2] [fig.2] is a three-dimensional exploded view of the voltage converter of [fig.l] in a first embodiment of the invention,
[0058] [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,
[0059] [fig.4] [fig.4] is a view similar to that of [fig.3], with overmolding,
[0060] [fig.5] [fig.5] is a three-dimensional view from below of the power module figures 3 and 4, with overmolding,
[0061] [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
[0062] [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.
[0063] [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.
[0064] With reference to [fig.l], an electrical system 100 implementing the invention in a first embodiment of the invention will now be described.
[0065] The electrical system 100 is for example intended to be installed in a vehicle automobile.
[0066] The electrical system 100 firstly comprises an electrical power source 102 designed to deliver a direct voltage U, for example between 10 V and 100 V, for example 48 V or 12 V.
[0067] The electrical power source 102 is therefore a direct voltage source. This electrical power source comprises, for example, a battery.
[0068] The electrical system 100 further comprises an electrical machine 130 comprising several phases (not shown) intended to have respective phase voltages.
[0069] 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.
[0070] 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.
[0071] The voltage converter 104 further comprises at least one power module 110. The power module 110 comprises one or more phase bus bars intended to be respectively connected to one or more phases of the electrical machine 130, to provide their respective phase voltages.
[0072] In the example described, the voltage converter 104 comprises three power modules 110 each comprising two phase bus bars 122b 1222 connected to two phases of the electrical machine 130.
[0073] More specifically, in the example described, the electrical machine 130 comprises two three-phase systems each comprising three phases, and intended to be electrically phase-shifted by 120° relative to each other. Preferably, the first phase bus bars 122i of the power modules 110 are respectively connected to the three phases of the first three-phase system, while the second phase bus bars 1222 of the power modules 110 are respectively connected to the three phases of the second three-phase system.
[0074] Each power module 110 comprises, for each phase bus bar 122i, a first electrical component, (here a high side switch 112J connected between the positive bus bar 106 and the phase bus bar 122i and a second electrical component (here a low side switch 114i), connected between the phase bus bar 122i and the negative bus bar 108. Thus, the switches 112b 114i are arranged so as to form a switching arm, in which the phase bus bar 122i forms a midpoint.
[0075] Each power module 110 also comprises, for each phase bus bar 1222, a third electrical component (here a high side switch 1122) connected between the positive bus bar 106 and the phase bus bar 1222 and a fourth electrical component (here a low side switch 1142) connected between the phase bus bar 1222 and the negative bus bar 108. Thus, the switches 1122, 1142 are arranged so as to form a switching arm, in which the phase bus bar 1222 forms a midpoint.
[0076] Each switch 112b 114b 1122, 1142 comprises 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 as a function of a control signal applied thereto. The switches 112b 114b 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 respectively forming the main terminals 116, 118. Alternatively, the switches 112b 114b 1122, 1142 could be insulated gate bipolar transistors (IGBTs).
[0077] In the example described, the switches 112b 114b 1122, 1142 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 112b H4b 1122, 1142 are intended to be crossed, between their main terminals 116, 118, by a current greater than 1 A.
[0078] It will be appreciated that the positive bus bar 106, the negative bus bar 108 and the phase bus bars 122b 1222 are rigid electrical conductors designed to carry electrical currents of at least 1 A intended to pass through the switches 112b H4b 1122, 1142. They preferably have a thickness of at least 1 mm.
[0079] 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 negative common bus bar 108A connecting the power modules 110 and, in each power module 110, a negative local bus bar 108B1, 108B2 for each low side switch 114b 1142, the negative local bus bars 108B1, 108B2 being connected to the negative common bus bar 108A. The connections are shown in the figure by diamonds.
[0080] 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.
[0081] Furthermore, in the example described, the electrical machine 130 is a rotating electrical machine having both an alternator and an electric motor function. More specifically, the motor vehicle further comprises a heat engine (not shown) having an output shaft to which the electrical machine 130 is connected by a belt (not shown). The heat engine is intended to drive wheels of the motor vehicle via its output shaft. Thus, when operating as an alternator, the electrical machine 130 supplies electrical energy to 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 (in addition to or instead of the heat engine). The voltage converter 104 then operates as an inverter.
[0082] The electrical machine 130 is for example located in a gearbox or in a clutch of the motor vehicle or in place of the alternator.
[0083] In the remainder of the 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, “H” representing the top and “B” representing the bottom. This vertical direction HB being denoted in the figures by the reference V.
[0084] With reference to [fig.2], the voltage converter 104 comprises a heat sink 206, also called a heat sink, having heat exchange surfaces 204 on which the power modules 110 are respectively mounted (a single 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 means of contact, direct or via a thermally conductive paste, between the heat exchange surface 204 of the heat sink 206 and the power module 110.
[0085] The voltage converter 104 also comprises a support housing 208 on which a secondary electronic module such as a control module 210 is fixed. In the example of [fig.l], the control module 210 is a control card. In addition and optionally, the support housing 208 is mounted on the heat sink 206.
[0086] With reference to [fig.3], we will now describe the power module 110.
[0087] This power module 110 comprises several electrical connection parts 304, 304i, 3042, 3043 preferably in metal.
[0088] Each electrical connection part 304, 304b 3042, 3043 has a main plate 306, 306b 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, 3081, 3082, 3083 extending at the same level. For the sake of clarity, the upper faces 308, 308 b 3082, 3083 are only indicated in the figure for the largest main plates 306, 3063, 3062, 3063.
[0089] In particular, the power module 110 comprises a first electrical connection part 304i having a main plate 3063 having an upper face 308i, a second electrical connection part 3042 having a main plate 3062 having an upper face 3082 and a third electrical connection part 3043 having a main plate 3063 having an upper face 3083.
[0090] Furthermore, the main plates 306, 306i, 3062, 3063 are separated from each other along the main 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 at most five millimeters apart along this gap 310.
[0091] Generally, at least one of the electrical connection parts 304 (all in the example described) further has at least one electrical connector projecting from its main plate 306, 3063, 3062, 3063. Each electrical connector is for example either in the form of a pin 312b or in the form of a folded tab 3122, 3123, or even in the form of a straight tab 3124.
[0092] In the example described here, the straight tabs 3124 form with their main plates 3062, 306 the phase bus bars 122b 1222, the bent tab 3123 forms with its main plate 3063 the positive local bus bar 106B and the bent tabs 3122 form with their main plates 3063, 306 the negative local bus bars 108B1, 108B2.
[0093] Each electrical connector 312b 3122, 3123 has a fixed end 314 fixed to the main plate 306, 3062, 3063, 306b 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. For the sake of clarity, these different elements of the electrical connectors 312b 3122, 3123 are only indicated in the figure for two electrical connectors 312b 3122, one in the form of a pin, the other in the form of a tab.
[0094] In the case of a straight tab, the electrical connector 3124 projects into the main plane PP over a large length to allow its connection, for example at least one centimeter. In addition, the electrical connector 3124 has a fixed end 314 fixed to the main plate 306, this fixed end 314 having a large width to allow the passage of current, for example at least one centimeter.
[0095] The electrical connection parts 304 are obtained in the example described by cutting out a metal plate.
[0096] In the example described here, the metal plate is made of copper. Alternatively, the metal plate could be made of aluminum or even gold.
[0097] Furthermore, as explained previously, the power module 110 comprises transistors 112b 1122, 114b 1142 each electrically connected between two upper faces 308, 3081, 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, 306i, 3062, 3063. Each transistor 112b 1122, 114b 1142 firstly has a lower face pressed against one of the two upper faces 308, 308i, 3082 to which this transistor is electrically connected. Each transistor 112b 1122, 114b 1142 further has an upper face, a part of which is electrically connected to the other of the two upper faces.In the example described, the upper face of the transistor 112b 1122, 114b 1142 further comprises a control part 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.
[0098] In other words, the transistor 112i is mounted on, and electrically connected to, the upper face 3081 of the main plate 3061 of the first electrical connection part 304i and a first electrical connection element electrically connects the transistor 112i to the upper face 3082 of the main plate 3062 of the second electrical connection part 3042.
[0099] The first electrical connection element comprises two strips 326b one end of each metal strip 326i is welded to the upper face 3082 of the main plate 3062 of the second electrical connection part 3042 by a welding method. The second end of each metal strip 3261 is welded directly to the transistor 112i by a welding method. The welding methods used are for example ultrasonic or friction welding methods.
[0100] In the example described here, the two strips 326i have substantially the same shape.
[0101] Similarly, the transistor 114i is mounted on, and electrically connected to, the upper face 3082 of the main plate 3062 of the second electrical connection part 3042 and a second electrical connection element electrically connects the transistor 114i to the upper face 3083 of the main plate 3063 of the third electrical connection part 3043.
[0102] The second electrical connection element comprises two strips 3262, one end of each metal strip 3262 is welded to the upper face 3083 of the main plate 3063 of the third electrical connection part 3043 by a welding method. The second end of each metal strip 3262 is welded directly to the transistor 114i by a welding method. The welding methods used are, for example, ultrasonic or friction welding methods.
[0103] Similarly, transistors 1122 and 1142 are mounted on, and electrically connected to, the upper face 308, 3083 of the main plate 306, 3063 of an electrical connection part 304, 304i and have their upper face electrically connected to an upper face of another main plate 306 by means of two identically shaped strips 326.
[0104] In the example described, the ribbons 326, 326b 3262 are made of aluminum and have, for example, a section of 2mmx0.3mm. In an alternative embodiment, the ribbons 326, 326i, 3262 are made of gold.
[0105] In the example described, the wire 328 is made of aluminum and has a diameter of 0.2 mm. In an alternative embodiment, the wire 328 is made of gold.
[0106] In the example described, the pin-shaped electrical connectors 312i are used to connect the power module 110 to the control module 210, in order to make measurements of electrical quantities and to control the transistors 112b 1122, 114b 114 2*
[0107] Further, still in the described example, electrical connectors 3122 are connected to negative common bus bar 108A and electrical connector 3123 is connected to positive common bus bar 106A.
[0108] Furthermore, still in the example described, the two electrical connectors 3124 in the form of a straight tab respectively form the two phase bus bars 122i, 1222 of the power module 110.
[0109] With reference to [fig.4], the overmolding of the power module 110 is shown and bears the reference 402.
[0110] The overmolding 402 is an electrical insulator and completely covers each transistor 112i, 1122, 114i, 1142 and at least a portion of the upper faces 308i, 3082, 3083, 308 of the main plates 306i, 3062, 3063, 306.
[0111] In the example described here, the overmolding 402 also completely covers each wire 328.
[0112] Furthermore, the upper face of the electrically insulating overmolding 402 has a first cavity C1 located at least partially above the highest part of the first electrical connection element.
[0113] This first cavity Cl is for example at least partially cut by laser ablation in the upper face of the electrically insulating overmolding 402. By virtue of its construction, the bottom of the first cavity C1 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.
[0114] A portion of the ribbons 3261 is thus located in the first cavity Cl and the electrically insulating overmolding 402 covers the remainder of the ribbons 326b. In other words, the electrically insulating overmolding 402 partially covers the ribbons 326i so that only the highest portion, relative to the top-bottom direction, of the ribbons 326i is not covered by the electrically insulating overmolding 402 and is furthermore located in the first cavity Cl.
[0115] In this way, the electrically insulating overmolding exerts little or no holding force on the uppermost portion of the ribbons 3261, which allows for easy rupture of these ribbons when these ribbons heat up.
[0116] Similarly, the upper face of the electrically insulating overmolding 402 has a second cavity C2 located at least partially above the highest part of the second electrical connection element 3262.
[0117] A portion of the ribbons 3262 is thus located in the second cavity C2 and the electrically insulating overmolding 402 covers the remainder of the ribbons 3262. In other words, the electrically insulating overmolding 402 partially covers the ribbons 3262 so that only the highest portion, relative to the top-bottom direction, of the ribbons 3262 is not covered by the electrically insulating overmolding 402 and is furthermore located in the second cavity C2.
[0118] For the same reasons as previously, the electrically insulating overmolding 402 exerts little or no holding force on the highest part of the ribbons 3262, which allows easy rupture of these ribbons when these ribbons heat up.
[0119] 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 strips 326 of the transistor 1122 and of the transistor 1142 and sufficiently deep so that only the upper part of the strips 326 of the transistor 1122 and the upper part of the strips 326 of the transistor 1142 are located respectively in the third cavity C3 and in the fourth cavity C4 and so that the electrically insulating overmolding 402 covers the rest of the strips 326.
[0120] The overmolding 402 is for example made of resin, for example still made of epoxy. Preferably, the overmolding 402 is integral in a single piece.
[0121] In the embodiment described herein, the cavities are free of material. Alternatively, the cavities are filled with a gel, for example dielectric and / or silicone. The gel may also have a viscosity of 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 180g, preferably between 110 and 160g, for example 123g or 154g.
[0122] In another variant, the cavities are filled with a resin different from the resin forming the electrically insulating overmolding 402. In particular, the resin filling the cavities has a lesser hardness than that forming the electrically insulating overmolding 402. For example, the electrically insulating overmolding 402 is formed from an epoxy resin, for example having a hardness between 70 and 90 shore and the cavities are filled with an elastomeric resin, for example having a hardness between 20 and 40 shore. The resin filling the cavities may also belong to the UL 94 V-0 fire class, as defined by the certification company Underwriters Laboratories.
[0123] [Fig.5] is a bottom view of the power module 110.
[0124] 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 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 can be direct contact or via an insulating and thermally conductive electrical connection element.
[0125] Likewise, 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 can be direct contact or via an insulating and thermally conductive electrical connection element.
[0126] 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.
[0127] The overmolding 402 has at least one resin pad 506 projecting downwards and designed to come into direct contact with the heat sink 206 in order to define a predefined spacing between the lower faces 502, 502i, 5022, 5023 of the main plates 306, 3063, 3062, 3063 and the heat sink 206, and thus the thickness of the thermally conductive element filling this spacing. In the example described, each resin pad 506 projects from the lower face of the overmolding present in one of the gaps 310 between the main plates 306, 306i, 3062, 3063.
[0128] [fig.6] shows a partial view of the power module 110 along a section plane perpendicular to the main plane PP and passing through the main axis of one of the ribbons of the first electrical connection element.
[0129] First of all, note that the upper face of the first transistor 112i defines a reference plane P.
[0130] The two identical ribbons 326i each form a first bridge POi and a second bridge PO2.
[0131] The two ends of the first bridge POi lie flat on the upper face of the first transistor 112b. The orthogonal projection of the highest point of the first bridge POi on the reference plane P is included in the orthogonal projection of the flat bottom of the first cavity Cl on the reference plane P.
[0132] One end of the second bridge PO2 lies flat on the upper face of the first transistor 112i and the other end of the second bridge PO2 lies flat on the upper face of the main plate 3062 of the second electrical connection part 304 2. The orthogonal projection of the highest point of the second bridge PO2 on the reference plane P is included in the orthogonal projection of the flat bottom of the first cavity Cl on the reference plane P.
[0133] 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 on the reference plane is included in the orthogonal projection of the flat bottom of the cavity on the reference plane (P).
[0134] We will now highlight the relationships existing between the physical dimensions of the ribbons 326b of the overmolding 402 and of the first cavity CL
[0135] In the following description, elevations are defined relative to the previously described top-bottom dimension.
[0136] 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
[0137] The distance D3 is the distance between the plane parallel to the reference plane P passing through the highest point of the electrically insulating overmolding 402 and the reference plane P.
[0138] The distance D4 corresponds to the identical thickness of each of the two 326p ribbons
[0139] These distances D2, D3 and D4 are configured so 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:
[0140] [Math.l] D3-D2 £ 2D4
[0141] 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 correctly protected by the resin.
[0142] Furthermore, this minimum resin thickness also ensures that the first transistor 112i is not likely to be damaged during the laser ablation of the first cavity Cl.
[0143] Furthermore, if the distance D5 is defined as the distance between the highest point of the first bridge POi relative 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.
[0144] In other words, the distances D2, D3, D4 and D5 verify the equation:
[0145] [Math.2] D5-D4 > D3-D2
[0146] Similarly, if the distance D6 is defined as the distance between the highest point of the second bridge PO2 relative 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.
[0147] In other words, the distances D2, D3, D4 and D6 verify the equation:
[0148] [Math.3] D6-D4 > D3-D2
[0149] Thanks to these mathematical relationships, the upper ends of the two bridges POi and PO2 are located in the first cavity Cl so that the overmolding 402 exerts little or no pressure on these upper ends.
[0150] In the example described, the two bridges POi and PO2 have the same elevation so that 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 relative to the reference plane P.
[0151] In other words, the distances Dl, D3, D2 and D4 verify the equation:
[0152] [Math.4] Dl -D4 > D3-D2
[0153] 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.
[0154] With reference to [fig.7], we will now describe a second embodiment of the invention. Elements identical to, or similar to, those of the first embodiment bear the same numerical reference in the description of the second embodiment.
[0155] This second embodiment differs from the first by the shape of the ribbons 326i and by the dimensions of the first cavity CL
[0156] More precisely, for the two ribbons 326b the second bridge PO2 has an elevation greater than that of the first bridge POi and the first cavity Cl is made so that the first bridge POi is entirely covered with resin.
[0157] As for the first embodiment, the distances D2, D3 and D4 are configured so 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
[0158] Furthermore, the distances D2, D3, D4 and D6 verify the equation Math. 3.
[0159] 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.
[0160] With reference to [fig.8], we will now describe a third embodiment of the invention. Elements identical to, or similar to, those of the first or second embodiment bear the same numerical reference in the description of this third embodiment.
[0161] This third embodiment differs from the first in that the two ribbons are not identical.
[0162] Thus, the second bridge PO'2 of one of the two ribbons 326'i has an elevation greater than that of the second bridge PO2 of the other ribbon 326i.
[0163] As can be seen in the figure, the orthogonal projection of the highest point of each strip 3261, 326'i on the reference plane P is included in the orthogonal projection of the flat bottom of the first cavity Cl on the reference plane P and for each strip 326i, 326'b the difference between the distance between the highest point D6, D6- of this strip relative to the reference plane P and the thickness D4 of this strip is greater than or equal to the difference between the distance D3 and the distance D2.
[0164] 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.
[0165] For example, all or some of the ribbons 326, 326b 3262 could be replaced with wires and / or fuses.
[0166] For example, the transistors 112b 114b 1122, 1142 could be gallium nitride FET or HEMT transistors.
[0167] Furthermore, in the previously described embodiments, the electrical connection elements each have strips. Alternatively, these electrical connection elements could have only one strip. In another alternative, these electrical connection elements could have at least three strips.
[0168] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.
Claims
1. Claims Power module (110) comprising: - a first (3040) and a second (3042) electrical connection part, preferably made of metal, each having a main plate (306i, 3062), the main plates (3061, 3062) extending along the same main plane (PP) so as to be substantially coplanar; - a transistor (112x) mounted on an upper face of the main plate (3060) of the first electrical connection part (304i), the upper face of the transistor (112x) defining a reference plane (P), said transistor (1120) being electrically connected by at least one strip (3260) or by at least one wire to the upper face of the main plate (3062) of the second electrical connection part (3042); and - an electrically insulating overmolding (402), for example made of resin, covering said transistor (1120) and at least a portion of the upper face of the main plate (306i, 3062) of the first (3040) and second (3042) electrical connection parts, the upper face of the electrically insulating overmolding (402) having a cavity (Cl) located at least partially above the ribbon (3260) or wire; said power module (110) being characterized in that said cavity (Cl) has a flat bottom, in that the ribbon (3260 or the wire forms a first bridge (PO0 whose two ends rest flat on the upper face of the transistor (1120,in that the orthogonal projection of the highest point of the first bridge (PO0) 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 which the difference between the distance D5 between the highest point of the first bridge (PO0) relative to the reference plane (P) and the thickness (D4) of the ribbon (3260) or wire is greater than or equal to 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 plane of, reference passing through the lowest point of said cavity (Cl).
2. Power module (110) according to the preceding claim wherein the difference between the distance D3 and the distance D2 is greater than or equal to the thickness (D4) of the ribbon or wire, preferably greater than or equal to twice the thickness of the ribbon or wire.
3. Power module (110) according to one of the preceding claims wherein 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 (326J or wire on the reference plane (P) is included in the orthogonal projection of said flat bottom on the reference plane (P) and in that the difference between the distance DI between the highest point of the ribbon (3260 or wire relative 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.
4. Power module (110) according to one of the preceding claims wherein said ribbon (3260 or wire forms a second bridge (PO2) one end of which lies flat on the upper face of the transistor (1120 and the other end of which lies flat on the upper face of the main plate (3062) of the second electrical connection part (3042), wherein the orthogonal projection of the highest point of the second bridge (PO2) 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 wherein the difference between the distance D6 between the highest point of the second bridge (PO2) relative to 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.
5. Power module (110) according to one of the preceding claims wherein said transistor (1120) is connected by a plurality of strips (3261) and / or wires to the upper face of the main plate (3062) of the second electrical connection part (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 strip (3260) and / or wire on the reference plane (P) is included in the orthogonal projection of the flat bottom of the cavity (Cl) on the reference plane (P) and in that for each strip (3260) and / or wire, the difference between the distance (D6i, D62) between the highest point of this strip and / or wire relative to the reference plane (P) and the thickness (D4) of this strip (3260) or wire is greater than or equal to the difference between the distance D3 and distance D2
6. Power module (110) according to one of the preceding claims in which said cavity (Cl) has been at least partially cut by laser ablation in the upper face of the electrically insulating overmolding (402).
7. Power module (110) according to one of the preceding claims in which the overmolding (402) leaves visible at least a part of the lower face (502i, 5022) of the main plate (306b 3062) of at least one of the electrical connection parts (304b 3042), this part left visible being designed to be pressed against a heat sink (206).
8. Electrical system (100) comprising a heat sink (206) and a power module according to the preceding claim, and in which the heat sink (206) is in thermal contact with the lower face left visible by the overmolding (402).
9. A voltage converter (104) comprising a power module (110) according to any one of claims 1 to 7 or an electrical system (100) according to claim 8.