Multistage sealed power-electronic module

Abstract

The invention relates to a power-electronic module (1) comprising: - a substrate (10); - a first power-electronic component (11a) arranged on a first face (10a) of the substrate (10); - a first cover (15a) which defines, together with the substrate, a first cavity (17a) in which the first power-electronic component (11a) is housed; - a second power-electronic component (11b) arranged on a second face (10b) of the substrate (10); and - a second cover (15b) which defines, together with the substrate, a second cavity (17b) in which the second power-electronic component (11b) is housed; - a first ring seal (16a) which seals the first cavity (17a); - a second ring seal (16b) which seals the second cavity (17b); wherein the first and second ring seals (16a, 16b) are formed from a sintered material and wherein the first and second cavities (17a, 17b) hold a gas or a mixture of gases.

Description

DESCRIPTION TITLE: MULTI-STAGE AND HERMETIC POWER ELECTRONIC MODULE TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of electronic power modules.

[0002] The present invention relates more particularly to an electronic power module comprising several electronic power components distributed over several levels or stages. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Power electronic modules enable the implementation of basic functions such as switching, rectification, voltage division, etc.

[0004] A so-called "2D" or "single-stage" power module generally comprises one or more power electronic components soldered onto a ceramic substrate with metal tracks. The ceramic substrate is fixed on a copper base plate which serves as a mechanical support and transfers the heat generated by the components to a cooling device, typically a heat sink. The electrical connections inside the power module, between the components and the metal tracks of the substrate, are partly provided by bonding wires. The components are enclosed in a housing filled with an encapsulating material.

[0005] The purpose of the encapsulation material is to ensure the dielectric strength of the power module and to protect the components from external aggressions (humidity, contamination, etc.). In addition, it reinforces the electrical insulation between the conductors and improves resistance to partial discharges due in particular to defects in the metallization of the ceramic substrate.

[0006] Power electronic components can be transistors, thyristors, and diodes. These components are made from a semiconductor material. Wide bandgap semiconductor materials, such as gallium nitride (GaN), gallium arsenide (GaAs), silicon carbide (SiC), and diamond, are tending to replace silicon, due to their better performance in terms of current density, operating frequency and voltage withstand.

[0007] There are also so-called "3D" or "multi-stage" power electronic modules comprising several electronic components distributed over different levels (also called "stages"). The electronic components are typically arranged on either side of a substrate, or even between several stacked substrates.

[0008] The operation of a power electronic module (single-stage or multi-stage) generates temperature cycles that can be relatively severe. These temperature cycles produce significant mechanical stresses in the substrate(s) and at the interfaces between the electronic components and the substrate(s). These mechanical stresses are the cause of multiple failure modes of the power electronic module.

[0009] Document W02019 / 101634A1 describes a multi-stage power electronic module designed to reduce the risk of failure. This power electronic module comprises metal supports and power electronic components arranged on or between the metal supports. The metal supports are assembled together so that the power electronic module has a generally tubular external shape of circular cross-section. The supports have a T-shaped, F-shaped or right-angled cross-section.

[0010] Metal substrates, through which electrical power currents flow to or from electronic components, allow for efficient heat dissipation, through simultaneous conduction, convection, and radiation. Metal substrates constitute a substrate without a ceramic layer that could be weakened by thermal cycles.

[0011] The electrical power module further comprises a tubular, sealed cover made of plastic. This cover is attached to a portion of the metal supports. The metal supports and the cover together define an inner channel, in which a cooling fluid, for example a gas or a heat transfer liquid, circulates. The circulation of the cooling fluid in the inner channel allows the module to be cooled. The cooling fluid also provides electrical insulation for the module.

[0012] The power electronic module described by document W02019 / 101634A1 is however difficult to integrate into an electromechanical actuator, such as an electric motor, because of the circulation of the cooling fluid. SUMMARY OF THE INVENTION

[0013] There is therefore a need to provide a multi-stage power electronic module that has good electrical insulation performance and is easy to integrate.

[0014] According to a first aspect of the invention, this need is met by providing a power electronic module comprising: a substrate having a first face and a second face opposite the first face; a first power electronic component arranged on the first face of the substrate; a first cover arranged on the first face of the substrate and delimiting with the substrate a first cavity in which the first power electronic component is housed; a second power electronic component arranged on the second face of the substrate; a second cover arranged on the second face of the substrate and delimiting with the substrate a second cavity in which the second power electronic component is housed.a first annular seal disposed between the substrate and the first cover, the first annular seal sealing the first cavity; and a second annular seal disposed between the substrate and the second cover, the second annular seal sealing the second cavity.

[0015] The first and second annular seals are formed from a sintered material, preferably silver-based, and the first and second cavities contain a gas or a mixture of gases.

[0016] The gas (or gas mixture) contained in the first and second sealed cavities ensures a high degree of electrical insulation between the internal elements of the power electronic module. The power module is thus devoid of encapsulation material (generally a polymer material), which tends to degrade over the course of partial discharges in the 2D module of the prior art (in particular in the so-called triple point zone, between the ceramic substrate, the metal track carrying the electric current and the encapsulation material).

[0017] The integration of the power electronics module, for example in an electromechanical actuator, is also facilitated, as it does not require any fluid circulation. Instead, the electrically insulating gas is enclosed here. Furthermore, sintering is a technique that makes it easy to form the annular seals that seal the covers to the substrate and close the cavities.

[0018] In a first embodiment of the power electronic module, the first cover comprises: a first substrate formed from a first electrically insulating ceramic material; and at least one first conductive element passing through the first substrate and electrically connected to the first power electronic component; and the second cover comprises: a second substrate formed from a second electrically insulating ceramic material; and at least one second conductive element passing through the second substrate and electrically connected to the second power electronic component.

[0019] According to a development of this first embodiment, the first and second substrates are made of aluminum nitride.

[0020] In a second embodiment, the first and second covers each comprise a metal layer and an electrically insulating layer disposed on an outer face of the metal layer.

[0021] The power electronic module may further include: a third power electronic component disposed on the first face of the substrate and housed in the first cavity; and a fourth power electronic component disposed on the second face of the substrate and housed in the second cavity.

[0022] For example, the first power electronic component is connected in parallel with the third power electronic component, the second power electronic component is connected in parallel with the fourth power electronic component, the first power electronic component is a transistor, the second power electronic component is a transistor, the third power electronic component is a diode, and the fourth power electronic component is a diode.

[0023] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the power electronic module according to the first aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations: the substrate is made of metal; the first power electronic component comprises a first terminal electrically connected to the substrate and a second terminal electrically connected to a conductive portion of the first cover; the second power electronic component comprises a first terminal electrically connected to the substrate and a second terminal electrically connected to a conductive portion of the second cover; each of the first and second power electronic components is electrically connected to the substrate via a conductive track and a conductive joint formed from the sintered material;the first power electronic component is electrically connected to the conductive portion of the first cover via a conductive track and a conductive joint formed from the sintered material; and; the second electronic power component is electrically connected to the conductive portion of the second cover via a conductive track and a conductive seal formed from the sintered material.

[0024] A second aspect of the invention relates to an electromechanical actuator comprising at least one electronic power module according to the first aspect of the invention.

[0025] The electromechanical actuator preferably comprises a three-phase motor and a circuit for controlling and supplying the three-phase motor, the circuit for controlling and supplying the three-phase motor comprising a plurality of electronic power modules according to the first aspect of the invention for generating phase currents of the three-phase motor.

[0026] Each electronic power module is advantageously arranged opposite a coil head of the three-phase motor.

[0027] A third aspect of the invention relates to a method for manufacturing a power electronic module, comprising the following steps: providing a substrate, a first cover and a second cover; fixing a first power electronic component on the first cover; depositing a sintering material on the first cover so as to form a first bead around the first power electronic component; fixing a second power electronic component on the second cover; depositing the sintering material on the second cover so as to form a second bead around the second power electronic component; transferring the first cover onto a first face of the substrate and the second cover onto a second opposite face of the substrate, by arranging the first and second beads of sintering material in contact with the substrate;and sintering the sintering material to form first and second annular seals, the first annular seal closing; sealingly a first cavity delimited by the first cover and the substrate and the second annular seal sealingly closing a second cavity delimited by the second cover and the substrate, the first and second cavities containing a gas or a mixture of gases.

[0028] Preferably, the substrate is made of aluminum and the method further comprises, before the step of transferring the covers, a step of forming silver-based conductive tracks on the first face and the second face of the substrate, the step of forming the silver-based conductive tracks comprising the following operations: deposition by screen printing of a paste comprising silver particles; drying of the paste; and annealing of the paste at a temperature greater than or equal to 570°C. BRIEF DESCRIPTION OF THE FIGURES

[0029] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which: Figure 1 is a schematic sectional view of an electronic power module according to a first embodiment; Figure 2 is a schematic sectional view of an electronic power module according to a second embodiment; Figure 3 is a partial perspective view of a three-phase motor in which several electronic power modules are integrated; and Figures 4A to 4E schematically represent steps of a method of manufacturing the electronic power module; and Figure 5 represents an aluminum-silver phase diagram.

[0030] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION

[0031] Figure 1 schematically represents an electronic power module 1 according to a first embodiment. The electronic power module power 1 can have the function of converting an alternating voltage into a direct voltage (function of a rectifier), converting a direct voltage into an alternating voltage (inverter), modifying the effective value of an alternating voltage (dimmer), modifying the average value of a direct voltage (chopper) or modifying the frequency of an alternating voltage (cycloconverter) or dissipating a current (active resistance).

[0032] The power module 1 comprises a substrate 10 and at least two power electronic components: a first component 11a arranged on a first face 10a of the substrate 10 and a second component 11b arranged on a second face 10b of the substrate 10, opposite the first face 10a.

[0033] Thus, the power module 1 comprises two component stages, a first stage comprising (at least) the first component 11 a and a second stage comprising (at least) the second component 11 b.

[0034] The substrate 10 is preferably metallic. It may be formed from a single metal layer, for example aluminum or copper, or from several stacked metal layers formed from different metals. It has, for example, the shape of a rectangular plate. Its thickness is preferably between 0.2 mm and 2 mm. It may have recesses, bosses (preferably with a width to height ratio of between 1 and 3) and excess thicknesses, in other words be textured. Thus, its faces 10a-10b are not necessarily flat, as is shown schematically in FIG. 1. They may also be rough and / or porous.

[0035] The substrate 10 advantageously forms a power conductor which carries one or more electrical outputs of the power module 1. It is capable of conducting a high electrical current, typically greater than 20 A.

[0036] One or more additional conductors 12 may be attached to the substrate 10, in order to facilitate the connection of the power module 1 to one or more electrical devices (an electric motor and a current sensor in the example below). For example, the power module 1 of FIG. 1 comprises two additional conductors 12 attached to two opposite side faces of the substrate 10. These additional conductors 12 then constitute output terminals of the power module 1. Each additional conductor 12 preferably extends perpendicular to the substrate 10.

[0037] The substrate 10 thus serves as an electrical bridge (or common point) between the two component stages. During operation of the power module 1, the temperature at the substrate 10 is substantially constant due to the fact that it is entirely metallic. Sudden temperature variations called transients are suppressed, which has the effect of reducing the (thermal) noise on the electrical output(s) of the power module 1 and improving reliability from the point of view of thermomechanical constraints.

[0038] The substrate 10 is advantageously covered, on each of its faces 10a-10b, with one or more electrically conductive tracks 13 commonly called finishes. These conductive tracks 13 are preferably made of a silver-based conductive material, which has the advantage of being stainless.

[0039] The first and second components 11 a-11 b are each electrically connected to the substrate 10, preferably via one of the conductive tracks 13 and a conductive joint 14 formed of sintered material. The conductive joint 14 is arranged on the conductive track 13.

[0040] The sintered material of the conductive joints 14 is advantageously based on silver or copper. In particular, a silver-based conductive joint 14 and a conductive track 13 based on the same metal form a high-performance electrical and mechanical connection, particularly in terms of resistance and electrical and thermal conductivity. This type of connection can withstand high operating temperatures, which are common in power electronic modules.

[0041] Alternatively, the conductive joints 14 based on silver or copper are formed on conductive tracks or finishes of the ENIG (“Electroless nickel immersion gold”) or ENEPIG (“Electroless Nickel Electroless Palladium Immersion Gold”) type.

[0042] The power module 1 further comprises: a first cover 15a arranged on the first face 10a of the substrate 10; a second cover 15b arranged on the second face of the substrate 10; a first annular seal 16a disposed between the substrate 10 and the first cover 15a; and a second annular seal 16b disposed between the substrate 10 and the second cover 15b.

[0043] The first cover 15a delimits with the substrate 10 a first cavity 17a in which the first component 11a is housed, while the second cover 15b delimits with the substrate 10 a second cavity 17b in which the second component 11b is housed.

[0044] Preferably, the first component 11 a is electrically connected to the first cover 15 a and the second component 11 b is electrically connected to the second cover 15 b. The components 11 a-11 b are advantageously connected to the covers 15 a-15 b in the same way as to the substrate 10, by means of conductive tracks 13 (here arranged on the inner faces of the covers 15 a-15 b) and conductive joints 14.

[0045] The first annular seal 16a and the second annular seal 16b respectively seal the first cavity 17a and the second cavity 17b. They are formed from a sintered material, preferably silver-based. This sintered material is advantageously the same as that of the conductive seals 14. Using the same sintered material to form the conductive seals 14 and the annular seals 16a-16b greatly simplifies the manufacture of the power module 1.

[0046] In order to reduce the risks of the covers 15a-15b coming off, each annular seal 16a, 16b is advantageously arranged in contact with a conductive track 13 arranged on the substrate 10.

[0047] The substrate 10 extends beyond the annular seals 16a-16b to be able to make the electrical connection of the power module 1 (directly or via the additional conductors 12).

[0048] The cavities 17a-17b contain a gas, preferably a neutral gas such as argon, nitrogen or helium. Alternatively, they may contain a mixture of gases, for example air. The pressure of the gas (or gas mixture) may be atmospheric pressure (at the time the cavities 17a-17b are sealed) or a much lower pressure, typically less than 133.3x10' 3 Pa (or 10' 3 Torr), of so as to obtain a primary vacuum configuration. The gas pressure is advantageously between 133.3x1 O' 6 Pa (10 -6 Torr) and 133.3x1 O' 7 Pa (10 -7 Torr), or a secondary vacuum configuration, to avoid partial discharges that can occur in primary vacuum. Cavities 17a-17b do not contain water vapor.

[0049] The gas contained in the cavities 17a-17b provides electrical insulation between the internal elements of the power module 1. The annular seals 16a-16b prevent, in particular, moisture from penetrating into the cavities 17a-17b, which could cause partial discharges. This contributes to increasing the reliability of the components and their electrical connections. In addition, the electrical insulation of the power electronic module 1 is independent of cooling and does not require the circulation of a fluid as in the module of the prior art, which facilitates its integration.

[0050] The annular seals 16a-16b make it possible to obtain a RJC junction-to-case thermal resistance of less than 0.3°C / W. They also make it possible to obtain a more compact module than those of the prior art with an encapsulation (or coating) material.

[0051] Like the substrate 10, the covers 15a-15b preferably have a generally parallelepiped shape. Each of the covers 15a-15b advantageously has a thickness of between 0.2 mm and 2 mm. Thus, the power module 1 is compact, unlike the power module of the prior art whose metal supports have right angles.

[0052] The thickness of the covers 15a-15b may be constant or substantially constant (thickness variation less than 100 μm). One or both covers 15a-15b may alternatively have a peripheral rim, which extends towards the substrate 10, in order to increase the volume of the first cavity 17a and / or of the second cavity 17b (in particular depending on the thickness of the components which they contain).

[0053] Preferably, the covers 15a and 15b are manufactured using the same material(s) and have identical dimensions, making the power module 1 generally symmetrical with respect to the substrate 10. This symmetry reduces the mechanical constraints within the power module 1, in particular the bending constraints (by locating the neutral plane of the module in the substrate 10).

[0054] The first and second components 11 a-11 b are preferably active components, for example of the transistor, diode or thyristor type. They comprise at least two terminals or electrodes (not shown in the figure). Advantageously, the first terminals of the first and second components 11 a-11 b are electrically connected to the substrate 10, the second terminal of the first component 11 a is electrically connected to a conductive portion of the first cover 15 a and the second terminal of the second component 11 b is electrically connected to a conductive portion of the second cover 15 b. Thus, the covers are functionalized in the sense that they are used to transmit electrical signals between the exterior and the interior of the power module 1.

[0055] The electrical connection of the electronic power module 1 is advantageously carried out on the outer faces of the covers 15a-15b and at least one of the ends of the central substrate 10, which further facilitates its integration, in particular in electrical devices where the available space is limited. The outer faces of the covers 15a-15b are preferably flat or substantially flat (thickness variation less than 100 μm).

[0056] In this first embodiment, the covers 15a-15b each comprise a substrate 151 made of an electrically insulating ceramic material and one or more electrically conductive elements 152 passing through the substrate 151. The conductive elements 152, also called inserts, are hermetic, that is to say they prevent any exchange of fluid (such as water vapor) between the exterior and the interior of the power module 1. They are used to conduct electric currents between the exterior and the interior of the module, to or from the electronic power components.

[0057] Thus, at least one conductive element 152 of the first cover 15a is electrically connected to the second terminal of the first component 11a and at least one conductive element 152 of the second cover 15b is electrically connected to the second terminal of the second component 11b. The components 11a-11b are advantageously connected to the conductive elements 152 of the covers 15a-15b in the same way as to the substrate 10, by means of conductive tracks 13 (here arranged on the inner faces of the covers 15a-15b) and conductive joints 14.

[0058] The conductive elements 152 can also serve to dissipate the heat generated by the components 11 a-11 b (electrically and thermally conductive elements).

[0059] The conductive elements 152 may in particular be vias or heat sinks. They are preferably formed from one or more metals, for example chosen from copper, aluminum, tungsten, gold, titanium, silver, palladium and their alloys.

[0060] The substrates 151 of the covers 15a-15b are preferably formed from the same ceramic material, for example aluminum nitride (AIN), aluminum oxide (AI2O3), silicon carbide (SiC), aluminum-silicon carbide (AlSiC) or silicon nitride (SisN4). Aluminum nitride is particularly advantageous because it has high thermal conductivity, high electrical resistivity and can easily integrate hermetic inserts. Compared to metals, it also has a coefficient of thermal expansion closer to that of the semiconductor materials constituting the basis of the components 11a-11b. Covers 15a-15b comprising aluminum nitride therefore have the advantage of considerably reducing the thermomechanical stresses within the power module 1.

[0061] As shown in Figure 1, the power module 1 may comprise more than two power electronic components, for example two per stage, or four in total.

[0062] The power module 1 can thus comprise: a third component 11c arranged on the first face 10a of the substrate 10 and housed in the first cavity 17a; a fourth component 11d arranged on the second face 10b of the substrate 10 and housed in the second cavity 17b.

[0063] Like the first and second components 11 a-11 b, each of the third and fourth components 11 c-11 d is connected to the substrate 10 and to at least one conductive element 152 of the covers 15a-15b, preferably by means of a conductive track 13 and a conductive seal 14 made of sintered material.

[0064] The electronic power module 1 can be (easily) integrated into an electromechanical actuator. For example, the electromechanical actuator comprises a three-phase motor and a power supply and control circuit for the three-phase motor. This electrical circuit comprises a plurality of power modules 1, preferably as many power modules 1 as the three-phase motor comprises inductors or coils. Each power module 1 is used to power the motor, by generating one of the phase currents of the motor.

[0065] Figure 3 shows a part of the three-phase motor 40. Only three coils are shown and the motor shaft has been deliberately omitted. The power modules 1 are advantageously arranged inside the motor 40, preferably opposite the coil heads 41 of the motor 40 (one module per coil).

[0066] In this application example, the power module 1 is in a four-component configuration. The components 11a-11d are connected together to form a bridge arm of an inverter assembly. The first component 11a is a transistor (preferably a metal-oxide-gate field-effect transistor, or MOSFET, or an insulated-gate bipolar transistor, or IGBT), the second component 11b is a transistor (preferably a MOSFET or IGBT), the third component 11c is a diode, and the fourth component 11d is a diode.

[0067] Again with reference to FIG. 1, the first component 11 a (transistor) and the third component 11 c (diode) are connected in parallel, between a positive supply voltage V+, carried by a conductive element 152 of the first cover 15 a (for example a copper-tungsten alloy heat sink), and a first electrical output Vs of the power module 1, carried by the substrate 10. The second component 11 b (transistor) and the fourth component 11 d (diode) are connected in parallel, between a negative supply voltage V-, carried by a conductive element 152 of the second cover 15 b (for example a copper-tungsten alloy heat sink), and the electrical output Vs of the power module 1.

[0068] A first control signal G1 is routed to the gate electrode of transistor 11a, here via a via 152 (e.g. tungsten) passing through the first cover 15a, of a conductive seal 14 of sintered material and of a conductive track 13 arranged on the first face 10a of the substrate 10 but electrically insulated from the latter by a first dielectric layer 18.

[0069] Similarly, a second control signal G2 is routed to the gate electrode of the transistor 11b, here via a via 152 (for example made of tungsten) passing through the second cover 15b and a conductive track 13 arranged on the inner face of the second cover 15b (possibly covered with a second dielectric layer 18 to reinforce the electrical insulation).

[0070] The power module 1 comprises a second electrical output Vnaii, carried by the substrate 10 and connected to a current sensor, for example a Hall effect sensor. This current sensor measures the phase current delivered to the motor. Thus, the power module 1 is in this example a bridge arm of an inverter integrating a current measurement.

[0071] Figure 2 shows an electronic power module 1 according to a second embodiment. This second embodiment differs from the first embodiment essentially in the construction of the covers 15-15b. Here, the covers 15-15b each comprise a metal layer 153 rather than a ceramic substrate. Advantageously, they further comprise an electrically insulating layer 154 arranged on the outer face of the metal layer 153. The insulating layers 154 limit the partial discharges between the metal layers 153 of the covers 15a-15b and neighboring conductive parts, for example those of the motor in which the power module 1 is integrated. They are for example made of AIN and have a thickness of 100 μm.

[0072] The metal layer 153 of the first cover 15a and the metal layer 153 of the second cover 15b respectively carry the positive supply voltage V+ and the negative supply voltage V-. The insulating layer 154 completely covers the outer face of the metal layer 153, with the exception of a portion necessary for making electrical contact. The control signal G1 of the transistor 11a is here carried by a conductive track 13 arranged on the substrate 10 and separated from the substrate 10 by a first dielectric layer 18. The control signal G2 of the transistor 11b is here carried by a conductive track 13 deposited on the face interior of the second cover 15b and separated from the metal layer 153 of this same cover by a second dielectric layer 18.

[0073] To avoid short circuits between the substrate 10 (metal) and the covers 15a-15b, the annular seals 16a-16b are separated from the substrate 10 and the covers 15a-15b by other dielectric layers 18.

[0074] The metal layers 153, the substrate 10 and the annular seals 16a-16b thus form a structure similar to a Faraday cage, which protects the electronic components from electromagnetic fields and electrostatic discharges.

[0075] The power module 1 is not limited to the embodiments described in relation to figures 1 and 2. In particular, each stage of components may comprise several (two or more) electronic power components (preferably of the transistor, diode or thyristor type) connected in parallel or in series.

[0076] Figures 4A to 4E schematically represent steps S1 to S5 of a method for manufacturing the power module 1.

[0077] The first step S1 of this manufacturing process, illustrated by Figure 4A, consists of providing the substrate 10 and the covers 15a-15b, in anticipation of the transfer of the power electronic components (steps S2 and S3; Figs.4B-4C) and their assembly by sintering (steps S4 and S5; Figs.4D-4E).

[0078] The manufacturing method may further comprise the formation of one or more conductive tracks 13 on each of the faces 10a-10b of the substrate 10 and the deposition of one or more dielectric layers 18, on one or both faces 10a-10b.

[0079] The provision of the first cover 15a or the second cover 15b may comprise, in the case of the power module 1 according to the first embodiment (see Figs. 1 & 4A), the following operations: the provision of a ceramic substrate 151; and the formation of one or more conductive elements 152 (or inserts) in the ceramic substrate 151, for example by creating cavities and filling them with metal.

[0080] The manufacturing method may then comprise the formation of one or more conductive tracks 13 on the inner face of the cover 15a, 15b, and the deposition of one or more dielectric layers 18 on this same inner face.

[0081] The conductive tracks 13 are for example formed by screen printing, drying and annealing a silver paste, such as that marketed by the company Dupont™ under the reference AS300. The dielectric layers 18 can also be formed in this way, using a dielectric paste such as that marketed by the company Dupont™ under the reference AS100.

[0082] Silver paste, sometimes referred to as "ink", comprises silver particles dispersed in a matrix preferably comprising a metal oxide, for example aluminium oxide (AI2O3).

[0083] By default, the holding of conductive tracks 13 in silver on a substrate 10 or a layer of metal 153 (covers 15a-15b) in aluminum is poor, due to the presence on the surface of a layer of native oxide (AI2O3) which forms a barrier layer. To remedy this, it is possible to dissolve this layer of native oxide (and therefore to deoxidize the surface) before the deposition of the silver paste, for example by depositing a zincate there.

[0084] In a preferred embodiment of the manufacturing process, the silver paste is annealed at a temperature greater than or equal to 570 °C (rather than 450 °C according to the manufacturer's recommendations for AS300 paste). The phase diagram in Figure 5 shows that at 567 °C and above, the annealing forms a eutectic aluminum-silver alloy, rather than an intermetallic alloy (between 425 °C and 567 °C). However, it is estimated that the resistance of the eutectic alloy is four times greater than that of the intermetallic alloy while being more stable over time, at least in terms of tearing. In addition, annealing at such a temperature breaks the aluminum oxide barrier layer. It is therefore not necessary to perform a deoxidation step beforehand. The annealing time is preferably between 30 min and 300 min.

[0085] Step S2 of Figure 4B comprises: fixing the first component 11a on the inner face of the first cover 15a, and more particularly on a conductive track 13; depositing a first sintering material on the first cover 15a so as to form a first annular bead (or ribbon) 20a around the first component 11a or its location; and drying the first sintering material, for example for 40 min at 150°C.

[0086] Although represented by the same figure, these operations are carried out successively (the fixing of the first component 11a can be accomplished before or after the formation of the first annular bead 20a).

[0087] As shown in Figure 4B, the first annular bead 20a may be formed on a peripheral rim of the first cover 15a.

[0088] Attaching the first component 11a preferably comprises forming a first layer 21a of a second sintering material on the first cover 15a, depositing the first component 11a on the first layer 21a and drying the second sintering material of the first layer 21a. The first component 11a will thus be connected to the first cover 15a by a joint of sintered material rather than by soldering or brazing.

[0089] Step S2 may also comprise forming a second layer 22a made of the second sintering material on the first component 11a, to subsequently connect the first component 11a to the substrate 10 by a sintered material joint. Alternatively, the second layer 22a made of second sintering material is deposited on the substrate 10.

[0090] Sintering materials are in the form of a paste comprising metallic particles, preferably silver, and one or more organic elements intended to give cohesion to the paste and allow its application by screen printing (binder) and / or to separate the particles and prevent them from sintering before desired (dispersant). These organic elements are largely removed during the drying operation. The sintering paste may also include additives to accelerate the (further) sintering of the particles.

[0091] Any other power electronic components belonging to the same component stage, such as the third component 11c, are preferably fixed to the first cover 15a in the same way as the first component 11a.

[0092] Similarly, step S3 of Figure 4C comprises fixing the second component 11b on the inner face of the second cover 15b (and more particularly on a conductive track 13), depositing the first sintering material on the second cover 15b so as to form a second annular bead 20b around the second component 11b (or its location) and drying the first sintering material. The second annular bead 20b is for example formed on a peripheral edge of the second cover 15b.

[0093] Attaching the second component 11 b preferably comprises forming a third layer 21 b of the second sintering material on the second cover 15 b, depositing the second component 11 b on the third layer 21 b and drying the second sintering material of the third layer 21 b.

[0094] Step S3 may also comprise forming a fourth layer 22b of second sintering material on the second component 11b, to subsequently connect the second component 11b to the substrate 10 by a sintered material joint. Alternatively, the fourth layer 22b of second sintering material is deposited on the substrate 10.

[0095] Any other power electronic components belonging to the same component stage, such as the fourth component 11d, are preferably fixed to the second cover 15b in the same way as the second component 11a.

[0096] Before the deposition of the sintering materials, an Ar / H2 plasma treatment can be carried out in order to clean the substrate of any organic pollution, to deoxidize it, to texture it with an arithmetic mean roughness (noted Ra) sought between 0.2 and 0.8 and to activate the surface before sintering. Furthermore, the drying of the first sintering material and the drying of the second sintering material can be carried out at the same time.

[0097] Advantageously, the second sintering material used to fix the components to the cover 15a, 15b or to the substrate 10 is identical to the first sintering material used to form the annular beads 20a-20b. The manufacturing method is then particularly simple to implement. The first annular bead 20a is advantageously deposited at the same time as the first layer 21a or the second layer 22a. The second annular bead 20b is advantageously deposited at the same time as the third layer 22a or the fourth layer 22b.

[0098] During a step S4 represented by FIG. 4D, the first cover 15a is transferred to the first face 10a of the substrate 10 and the second cover 15b is transferred to the second face 10b of the substrate 10. The annular cords 20a-20b are arranged in contact with the substrate 10. The transfers are for example carried out using “flip-chip” type equipment commonly used in the microelectronics industry.

[0099] Preferably, the covers 15a-15b are positioned relative to the substrate 10 such that the annular cords 20a-20b are located opposite each other. This arrangement tends to reduce mechanical stresses.

[0100] Finally, step S5 of Figure 4E consists of sintering the first sintering material to transform the annular beads 20a-20b into seals 16a-16b. The second sintering material is sintered simultaneously, forming the conductive seals 14 between the components 11a-11d and the substrate 10 and between the components 11a-11d and the covers 15a-15b. The sintering can be carried out under partial vacuum or in air (no oxidation of the silver conductive tracks). The air can be used to remove (calcine) the remaining organic elements in the sintering paste(s).

[0101] Sintering can be carried out under pressure, by means of a heating press, according to predetermined temperature and pressure profiles, for example according to the method described in international application WO2022 / 200749A2. The heating press preferably comprises a heating arm and a support, on which the substrate-components-covers assembly is arranged. Preferably, the sintering step S5 comprises the following phases: a first phase called creep phase, during which the support and the arm are brought to a creep temperature of between 165°C and 175°C and are maintained at this temperature for a period of between 30 s and 60 s, and during which a constant pressure of between 0.5 MPa and 1 MPa is applied for a period of between 15 s and 30 s after a rise of approximately 40 s; a second phase called sintering lasting between 60 s and 400 s, during which the temperatures of the arm and the support are maintained constant between 205 °C and 255 °C and a pressure between 10 MPa and 30 MPa is applied; a third phase called consolidation and cooling, during which the temperature decreases (for example until returning to room temperature) while maintaining the pressure applied during the second phase.

[0102] The duration of the third phase is, for example, between 1 minute and 10 minutes.

[0103] Alternatively, the sintering is carried out without pressure, for example according to the method described in application WO2017 / 046266A1.

[0104] The manufacturing method described in relation to FIGS. 4A to 4E is simple to implement, because steps S2 and S3 are so-called “2D” assembly steps which can be carried out on panels, in parallel with each other (in other words simultaneously), unlike step S4 of transferring the covers 1 Sa15b and the sintering step S5 (“3D” assembly steps). Similarly, the steps of forming the conductive tracks 13 and the dielectric layers 18 on the substrate 10 and the covers 15a-15b can be carried out in parallel.

Claims

CLAIMS

1. Power electronic module (1) comprising: - a substrate (10) having a first face (10a) and a second face (10b) opposite the first face; - a first electronic power component (11 a) arranged on the first face (10a) of the substrate (10); - a first cover (15a) arranged on the first face (10a) of the substrate (10) and delimiting with the substrate a first cavity (17a) in which the first electronic power component (11a) is housed; - a second power electronic component (11 b) arranged on the second face (10 b) of the substrate (10); and - a second cover (15b) arranged on the second face (10b) of the substrate (10) and delimiting with the substrate a second cavity (17b) in which the second electronic power component (11b) is housed; characterized in that it further comprises: - a first annular seal (16a) disposed between the substrate (10) and the first cover (15a), the first annular seal closing the first cavity (17a) in a sealed manner; - a second annular seal (16b) arranged between the substrate (10) and the second cover (15b), the second annular seal sealing the second cavity (17b) in a sealed manner; in that the first and second annular seals (16a, 16b) are formed from a sintered material, preferably based on silver, and in that the first and second cavities (17a, 17b) contain a gas or a mixture of gases.

2. Module (1) according to claim 1, in which: - the substrate (10) is made of metal; - the first electronic power component (11 a) comprises a first terminal electrically connected to the substrate (10) and a second terminal electrically connected to a conductive portion (152, 153) of the first cover (15a); - the second electronic power component (11 b) comprises a first terminal electrically connected to the substrate (10) and a second terminal electrically connected to a conductive portion (152, 153) of the second cover (15 b). [Claim s] Module (1) according to claim 2, wherein each of the first and second power electronic components (11 a, 11 b) is electrically connected to the substrate (10) via a conductive track (13) and a conductive joint (14) formed from the sintered material.

4. Module (1) according to one of claims 2 and 3, in which: - the first electronic power component (11 a) is electrically connected to the conductive portion (152, 153) of the first cover (15a) via a conductive track (13) and a conductive seal (14) formed from the sintered material; - the second electronic power component (11 b) is electrically connected to the conductive portion (152, 153) of the second cover (15 b) via a conductive track (13) and a conductive seal (14) formed from the sintered material.

5. Module (1) according to any one of claims 1 to 4, wherein the first cover (15a) comprises: - a first substrate (151) formed from a first electrically insulating ceramic material; and - at least one first conductive element (152) passing through the first substrate (151) and electrically connected to the first electronic power component (11); and in which the second cover (15b) comprises: a second substrate (151) formed from a second electrically insulating ceramic material; and at least one second conductive element (152) passing through the second substrate (151) and electrically connected to the second power electronic component (11 b). [Claim s] Module (1) according to claim 5, wherein the first and second substrates (151) are made of aluminum nitride.

7. Module (1) according to any one of claims 1 to 4, wherein the first and second covers (15a, 15b) each comprise a metal layer (153) and an electrically insulating layer (154) arranged on an outer face of the metal layer (153).

8. Electromechanical actuator comprising at least one electronic power module (1) according to any one of claims 1 to 7.

9. Actuator according to claim 8, comprising a three-phase motor (40) and a circuit for controlling and supplying the three-phase motor, the circuit for controlling and supplying the three-phase motor comprising a plurality of electronic power modules (1) according to any one of claims 1 to 7 for generating phase currents of the three-phase motor (40).

10. Actuator according to claim 9, in which each electronic power module (1) is arranged opposite a coil head (41) of the three-phase motor (40).

11. Method of manufacturing an electronic module (1), comprising the following steps: - providing (S1) a substrate (10), a first cover (15a) and a second cover (15b); - fixing (S2) a first electronic power component (11 a) on the first cover (15 a); - depositing (S2) a sintering material on the first cover (15a) so as to form a first bead (20a) around the first electronic power component (11a); - fixing (S3) a second electronic power component (11 b) on the second cover (15 b); - depositing (S3) the sintering material on the second cover (15b) so as to form a second bead (20b) around the second electronic power component (11b); - transferring (S4) the first cover (15a) onto a first face (10a) of the substrate (10) and the second cover (15b) onto a second opposite face (10b) of the substrate, by arranging the first and second beads of sintering material (20a, 20b) in contact with the substrate; and - sintering (S5) the sintering material to form first and second annular seals (16a, 16b), the first annular seal (16a) sealingly closing a first cavity (17a) delimited by the first cover (15a) and the substrate (10) and the second annular seal (16b) sealingly closing a second cavity (17b) delimited by the second cover (15b) and the substrate (10), the first and second cavities containing a gas or a mixture of gases.

12. Method according to claim 11, in which the substrate (10) is made of aluminum, the method further comprising, before the step (S4) of transferring the covers (15a, 15b), a step of forming silver-based conductive tracks (13) on the first face (10a) and on the second face (10b) of the substrate (10), the step of forming the silver-based conductive tracks comprising the following operations: screen-printing deposition of a paste comprising silver particles; drying the paste; and annealing the paste at a temperature greater than or equal to 570°C.

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