MULTI-STAGE POWER ELECTRONIC MODULE

Abstract

MULTI-STAGE POWER ELECTRONIC MODULE The invention relates to a power electronic module (1) comprising: a substrate (10) having a first face (10a) and a second face (10b) opposite the first face; a first power electronic component (11a) disposed on the first face (10a) of the substrate (10); a first cover (15a) disposed on the first power electronic component (11a); a second power electronic component (11b) disposed on the second face (10b) of the substrate (10); and a second cover (15b) disposed on the second power electronic component (11b); an electrically insulating encapsulation material (16) enclosing the first and second power electronic components (11a and 11b) and extending from the substrate (10) to the first cover (15a) and from the substrate to the second cover (15b). Figure to be published with the abbreviation: Figure 1

Description

Title of the invention: MULTI-STAGE POWER ELECTRONIC MODULE TECHNICAL FIELD OF THE INVENTION

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

[0002] The present invention relates more particularly to a power electronic module comprising several power electronic 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...

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

[0005] The encapsulation material is intended 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 formed from a semiconductor material. Wide bandgap semiconductor materials, such as gallium nitride (GaN), gallium arsenide (GaAs), silicon carbide (SiC), and diamond, tend to replace silicon due to their superior 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 in the power electronic module.

[0009] Document WO2019 / 101634A1 describes a multistage power electronics module designed to reduce the risk of failure. This power electronics module comprises metal supports and power electronics components arranged on or between the metal supports. The metal supports are assembled so that the power electronics module has a generally tubular external shape with a circular cross-section. The supports have a T-shaped, F-shaped, or right-angled cross-section.

[0010] The metallic supports, through which the power currents flow to or from the electronic components, allow for efficient heat dissipation by conduction, convection, and radiation simultaneously. The metallic supports constitute a substrate without a ceramic layer that could be weakened by thermal cycling.

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

[0012] The electronic power module described in document WO2019 / 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 exhibits 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 to the first face; • a first power electronic component arranged on the first face of the substrate; • a first cover placed on the first power electronic component; • a second power electronic component arranged on the second face of the substrate; • a second cover placed over the second power electronic component; and • an electrically insulating encapsulation material surrounding the first and second power electronic components and extending from the substrate to the first hood and from the substrate to the second hood.

[0015] Thus, the encapsulation material provides electrical insulation between the power electronic components, while also contributing to the cohesion of the power module by mechanically connecting the hoods to the substrate.

[0016] The integration of the electronic power module, for example in an electromechanical actuator, is further facilitated, since the latter does not require any fluid circulation.

[0017] In a first embodiment of the power electronic module, the first cover comprises: • a first substrate made of 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 hood includes: • a second substrate made of 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.

[0018] According to a development of this first embodiment, the first and second substrates are made of aluminum nitride.

[0019] In a second embodiment, the first and second hoods each comprise a metal layer and an electrically insulating layer disposed on an outer face of the metal layer.

[0020] The power electronic module may further comprise: • a third power electronic component disposed on the first face of the substrate and encapsulated by the encapsulation material; and • a fourth power electronic component disposed on the second face of the substrate and coated by the encapsulation material.

[0021] For example, the first power electronic component is connected in parallel to the third power electronic component, the second power electronic component is connected in parallel to 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.

[0022] In addition to the characteristics mentioned in the preceding paragraphs, the power electronic module according to the first aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • the encapsulation material occupies all the available space between the substrate and the first hood and all the available space between the substrate and the second hood; • the encapsulation material also coats an inner portion of the first cap and an inner portion of the second cap; • the substrate is made of metal; • the first power electronic component includes a first terminal electrically connected to the substrate and a second terminal electrically connected to a conductive portion of the first hood; • the second power electronic component includes a first terminal electrically connected to the substrate and a second terminal electrically connected to a conductive portion of the second hood; • each of the first and second power electronic components is electrically connected to the substrate via a conductive track and a conductive joint made of a sintered material, preferably silver-based; • The first power electronic component is electrically connected to the conductive portion of the first hood via a conductive track and a conductive joint formed from the sintered material; and • The second power electronic component is electrically connected to the conductive portion of the second hood via a conductive track and a conductive joint formed from the sintered material.

[0023] 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.

[0024] The electromechanical actuator preferably comprises a three-phase motor and a three-phase motor control and power supply circuit, the control circuit and power supply for the three-phase motor comprising a plurality of electronic power modules according to the first aspect of the invention for generating phase currents for the three-phase motor.

[0025] Each electronic power module is advantageously arranged opposite a coil head of the three-phase motor.

[0026] A third aspect of the invention relates to a method for manufacturing a power electronic module, comprising the following steps: • provide a substrate, a first hood and a second hood; • attach a first power electronic component to the first hood; • attach a second power electronic component to the second hood; • Place the first cover on one face of the substrate and the second cover on the opposite face of the substrate, so that the first power electronic component is positioned between the substrate and the first cover, and the second power electronic component is positioned between the substrate and the second cover; and • Encase the first power electronic component and the second power electronic component in an electrically insulating encapsulation material, the encapsulation material extending from the substrate to the first hood and from the substrate to the second hood.

[0027] Preferably, the substrate is made of aluminum and the process further comprises, before the step of transferring the caps, a step of forming silver-based conductive tracks on the first and second faces 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; • dough drying; and • annealing of the dough at a temperature greater than or equal to 570 °C. BRIEF DESCRIPTION OF THE FIGURES

[0028] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying figures, among which: • Fig. 1 is a schematic cross-sectional view of a power electronic module according to a first embodiment; • [Fig.2] is a schematic cross-sectional view of a power electronic 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 • [Fig.4] is an exploded and schematic view of a power electronic module according to a third embodiment; • Figures 5A to 5E schematically represent steps in a manufacturing process for the power electronic module; and • [Fig.6] represents an aluminium-silver phase diagram.

[0029] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION

[0030] Figure 1 schematically represents a power electronic module 1 according to a first embodiment. The power electronic module 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 RMS value of an alternating voltage (dimmer), modifying the average value of a direct voltage (chopper), modifying the frequency of an alternating voltage (cycloconverter) or dissipating a current (active resistor).

[0031] The power module 1 comprises a substrate 10 and at least two power electronic components: a first component 11 disposed on a first face 10a of the substrate 10 and a second component 11b disposed on a second face 10b of the substrate 10, opposite to the first face 10a.

[0032] Thus, the power module 1 comprises two component stages, a first stage comprising (at least) the first component 1la and a second stage comprising (at least) the second component 11b.

[0033] The substrate 10 is preferably metallic. It can be formed of a single metallic layer, for example of aluminum or copper, or of several stacked metallic layers made of different metals. It may, for example, have 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 between 1 and 3), and raised areas, in other words, be textured. Thus, its faces 10a-10b are not necessarily flat, as schematically represented in [Fig. 1]. They may also be rough and / or porous.

[0034] 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 electric current, typically greater than 20 A.

[0035] 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). By For example, the power module 1 of [Fig.1] includes two additional conductors 12 fixed on two opposite lateral faces of the substrate 10. These additional conductors 12 then constitute output terminals of the power module 1. Each additional conductor 12 preferably extends perpendicularly to the substrate 10.

[0036] 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 essentially constant due to its all-metal construction. Sudden temperature variations, known as transients, are eliminated, which reduces (thermal) noise on the electrical output(s) of the power module 1 and improves reliability from a thermomechanical stress perspective.

[0037] 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 rustproof.

[0038] The first and second components 1la-11b 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 disposed on the conductive track 13.

[0039] The sintered material of the conductive joints 14 is advantageously silver- or copper-based. In particular, a silver-based conductive joint 14 and a conductive track 13 made of the same metal form a high-performance electrical and mechanical connection, especially in terms of electrical and thermal resistance and conductivity. This type of connection is particularly suited to high operating temperatures, which are common in power electronic modules.

[0040] Alternatively, the silver- or copper-based conductive joints 14 are formed on conductive tracks or finishes of the ENIG (“Electroless nickel immersion gold”) or ENEPIG (“Electroless Nickel Electroless Palladium Immersion Gold”) type.

[0041] Power module 1 further comprises: • a first cover 15a placed on the first component 1 la; • a second cover 15b arranged on the second component 11b; and • an encapsulation material 16 enclosing the first component lia (located between substrate 10 and first hood 15a) and second component 11b (located between substrate 10 and second hood 15b).

[0042] The encapsulation material 16 extends from the substrate 10 to the first cap 15a and from the substrate 10 to the second cap 15b. In other words, it mechanically connects the substrate 10 to the caps 15a-15b and contributes to the cohesion of the power module 1.

[0043] The encapsulation material 16 is electrically insulating and therefore provides electrical insulation between the electronic components of the power module 1. Thus, 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 prior art module, which facilitates its integration.

[0044] The encapsulation material 16 is also impermeable to liquids, gases and solid particles (dust). Thus, it protects the electronic components from any contamination.

[0045] The encapsulation material 16 is preferably a polymer material, for example a silicone elastomer, a (crosslinked) epoxy resin, a liquid crystal polymer (LCP) material, or parylene. In the case of an epoxy resin, it is advantageously loaded with thermally conductive particles to dissipate heat.

[0046] The encapsulation material 16 preferably fills all the available space between the substrate 10 and the first cover 15a and all the available space between the substrate 10 and the second cover 15b. Only the electrical output(s) of the power module 1 (each formed by one end of the substrate 10 and / or an additional conductor 12) protrude from the encapsulation material 16. The power module 1 is thus compact and sealed, which gives it high strength. Preferably, the outer face of the covers 15a-15b is not covered by the encapsulation material 16.

[0047] In order to reduce the risk of the covers 15a-15b detaching, the encapsulation material 16 can further coat an inner portion of the first cover 15a and an inner portion of the second cover 15b. In other words, the encapsulation material 16 extends over at least part of the side walls of the covers 15a-15b.

[0048] Like the substrate 10, the covers 15a-15b preferably have a general parallelepiped shape. Each of the covers 15a-15b advantageously has a thickness between 0.2 mm and 2 mm. Thus, the power module 1 is compact, unlike the prior art power module whose metal supports have right angles. The thickness of the covers 15a-15b is preferably constant or substantially constant (thickness variation less than 100 µm).

[0049] Preferably, the hoods 15a and 15b are made using the same material or materials and have identical dimensions, making the power module 1 globally symmetrical with respect to the substrate 10. This symmetry reduces mechanical stresses within the power module 1, in particular bending stresses (by locating the neutral plane of the module in the substrate 10).

[0050] The first and second components 11a-11b are preferably components 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 11a-11b are electrically connected to the substrate 10, the second terminal of the first component 1a is electrically connected to a conductive portion of the first cover 15a, and the second terminal of the second component 11b is electrically connected to a conductive portion of the second cover 15b. Thus, the covers are functionalized in that they serve to transmit electrical signals between the outside and the inside of the power module 1.

[0051] The electrical connection of the power electronic module 1 is advantageously made on the outer faces of the covers 15a-15b and at least one end of the central substrate 10, which further facilitates its integration, particularly in electrical devices where space is limited. The outer faces of the covers 15a-15b are preferably flat or substantially flat (thickness variation less than 100 µm).

[0052] In this first embodiment, the hoods 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 preferably hermetic, that is to say they prevent any exchange of fluid (such as water vapor) between the outside and the inside of the power module 1. They serve to conduct electric currents between the outside and the inside of the module, to or from the power electronic components.

[0053] Thus, at least one conductive element 152 of the first hood 15a is electrically connected to the second terminal of the first component 1a and at least one conductive element 152 of the second hood 15b is electrically connected to the second terminal of the second component 11b. The components 1a-11b are advantageously connected to the conductive elements 152 of the hoods 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 hoods 15a-15b) and conductive joints 14.

[0054] The conductive elements 152 can also be used to dissipate the heat generated by the components 1 la-11b (electrically and thermally conductive elements).

[0055] The conductive elements 152 may in particular be vias or heat sinks. They are preferably made of one or more metals, for example chosen from copper, aluminium, tungsten, gold, titanium, silver, palladium and their alloys.

[0056] The substrates 151 of the hoods 15a-15b are preferably formed of the same ceramic material, for example aluminium nitride (AIN), aluminium oxide (Al2O3 ), silicon carbide (SiC), aluminum silicon carbide (AlSiC), or silicon nitride (Si3N4). Aluminum nitride is particularly advantageous because it exhibits high thermal conductivity, high electrical resistivity, and can be easily integrated into hermetic inserts. Compared to metals, it also has a coefficient of thermal expansion closer to that of the semiconductor materials forming the basis of components 11a-11b. Therefore, 15a-15b covers incorporating aluminum nitride offer the advantage of significantly reducing thermomechanical stresses within power module 1.

[0057] As shown in [Fig.1], the power module 1 may include more than two power electronic components, for example two per stage, i.e. four in total.

[0058] The power module 1 may thus comprise: • a third component 1 disposed on the first face 10a of the substrate 10 and coated by the encapsulation material 16; • a fourth component 1 Id disposed on the second face 10b of the substrate 10 and coated by the encapsulation material 16.

[0059] Like the first and second components 1 la-11b, each of the third and fourth components 1 lc-1 Id is connected to the substrate 10 and to at least one conductive element 152 of the hoods 15a-15b, preferably via a conductive track 13 and a conductive joint 14 made of sintered material.

[0060] The electronic power module 1 can be (easily) integrated into an electromechanical actuator. By way of 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 has inductors or coils. Each power module 1 serves to supply the motor by generating one of the motor's phase currents.

[0061] Figure 3 shows a portion of the three-phase motor 40. Only three coils are shown, and the motor shaft has been intentionally 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).

[0062] In this application example, the power module 1 is in a four-component configuration. The components 1a-1Id are connected to each other to form a bridge arm of an inverter assembly. The first component 1a is a transistor (preferably a metal-oxide-semiconductor 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 1Id is a diode.

[0063] Again with reference to [Fig. 1], the first component 1a (transistor) and the third component 11c (diode) are connected in parallel, between a positive supply voltage V+, carried by a conductive element 152 of the first hood 15a (for example a heat sink made of copper-tungsten alloy), and a first electrical output Vs of the power module 1, carried by the substrate 10. The second component 11b (transistor) and the fourth component 1 Id (diode) are connected in parallel, between a negative supply voltage V-, carried by a conductive element 152 of the second hood 15b (for example a heat sink made of copper-tungsten alloy), and the electrical output Vs of the power module 1.

[0064] A first control signal G1 is routed to the gate electrode of the transistor lia, here via a via 152 (for example in tungsten) passing through the first hood 15a, a conductive joint 14 of sintered material and a conductive track 13 disposed on the first face 10a of the substrate 10 but electrically isolated from it by a first dielectric layer 18.

[0065] Similarly, a second control signal G2 is routed to the gate electrode of the transistor 11b, here via a via 152 (for example tungsten) passing through the second hood 15b and a conductive track 13 disposed on the inner face of the second hood 15b (optionally covered with a second dielectric layer 18 to relieve the encapsulation material 16).

[0066] The power module 1 includes a second electrical output VHaii, 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, in this example, the power module 1 is a bridge arm of an inverter incorporating a current measurement.

[0067] Figure 2 represents a power electronic 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 disposed on the outer face of the metal layer 153. The insulating layers 154 limit partial discharges between the metal layers 153 of the covers 15a-15b and adjacent 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.

[0068] 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, except for a portion necessary for electrical contact. The control signal G1 of transistor 1 is here routed by a metal rod 19 passing through the encapsulation material 16 from a lateral face of the power module 1 and by a conductive track 13, disposed 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 metal rod 19 passing through the encapsulation material 16 from a lateral face (preferably opposite) of the power module 1 and by a conductive track 13, deposited on the inner face of the second cover 15b and separated from the metal layer 153 of this same cover by a second dielectric layer 18.

[0069] Figure 4 schematically represents a third embodiment of the module of power 1. In this third embodiment, the power module 1 comprises three metallic substrates 10, arranged between the first cover 15a and the second cover 15b. Each substrate 10 carries two power electronic components 1la-11b, 1lc-1Id, 1le-1If, one component per face, and includes an electrical output VI, V2, V3. The power module therefore comprises three components per stage, or six in total.

[0070] The substrates 10 and the components 1la-1 If are all coated with the encapsulation material (not shown). The encapsulation material can also coat the covers 15a-15b, except for a protruding portion for electrical contact.

[0071] The covers 15a-15b each comprise a metallic layer that electrically connects all the components of the stage (as in the second embodiment). The first cover 15a carries the positive supply voltage V+ and the second cover 15b carries the negative supply voltage V-. The six components 1a to 1If are, for example, diodes, connected in series in pairs. The three pairs of diodes are connected in parallel between the positive supply voltage V+ and the negative supply voltage V-. The power module 1 thus forms a three-phase rectifier bridge and can be coupled to a three-phase motor.

[0072] The power module 1 is not limited to the embodiments described in relation to Figures 1, 2 and 4. In particular, each component stage may comprise several (two or more) power electronic components (preferably of the transistor, diode or thyristor type) connected in parallel or in series.

[0073] Figures 5A to 5E schematically represent steps SI to S5 of a manufacturing process for the power module 1.

[0074] The first step SI of this manufacturing process, illustrated by [Fig.5A], consists of providing the substrate 10 and the hoods 15a-15b, in preparation for the transfer of the power electronic components (step S2 and S3; Figs.5B-5C) and their encapsulation (steps S4 and S5; Figs.5D-5E).

[0075] The manufacturing process may further include the formation of one or more conductive tracks 13 on each of the faces lOa-lOb of the substrate 10 and the deposition of a or several dielectric layers 18, on one or both faces 10a-10b.

[0076] The supply of the first hood 15a or the second hood 15b may include, in the case of the power module 1 according to the first embodiment (see Figs. 1 & 5A), the following operations: • the supply 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.

[0077] The manufacturing process may then include the formation of one or more conductive tracks 13 on the inner face of the hood 15a, 15b, and the deposition of one or more dielectric layers 18 on this same inner face.

[0078] The conductive tracks 13 are, for example, formed by screen printing, drying and annealing a silver paste, such as that marketed by 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 DuPont™ under the reference AS100.

[0079] Silver paste, sometimes called "ink", comprises silver particles dispersed in a matrix preferably comprising a metal oxide, for example aluminium oxide (Al2O3).

[0080] By default, the adhesion of conductive silver tracks 13 to a substrate 10 or a metal layer 153 (caps 15a-15b) made of aluminum is poor, due to the presence on the surface of a native oxide layer (Al₂O₃) which forms a barrier layer. To remedy this, it is possible to dissolve this native oxide layer (and thus deoxidize the surface) before the silver paste is deposited, for example by depositing a zincate.

[0081] In a preferred embodiment of the manufacturing process, the silver paste is annealed at a temperature of 570 °C or higher (rather than 450 °C as recommended by the manufacturer for AS300 paste). The phase diagram in [Fig. 6] shows that at 567 °C and above, the annealing process forms a eutectic aluminum-silver alloy, rather than an intermetallic alloy (between 425 °C and 567 °C). The eutectic alloy is estimated to be four times stronger than the intermetallic alloy and more stable over time, at least in terms of pull-out resistance. Furthermore, annealing at such a temperature breaks down the aluminum oxide barrier layer. Therefore, a preliminary deoxidation step is unnecessary. The annealing time is preferably between 30 and 300 minutes.

[0082] Step S2 of [Fig.5B] includes fixing the first component 1a to the inner face of the first hood 15a, and more particularly to a conductive track 13. The attachment of the first component 1a preferably includes forming a first layer 21a of a sintering material on the first cap 15a, depositing the first component 1a onto the first layer 21a, and drying the sintering material. The first component 1a will thus be connected to the first cap 15a by a sintered material joint rather than by welding or brazing. The drying of the sintering material is, for example, carried out by heating at 150 °C for 40 min.

[0083] Step S2 may also include forming a second layer 22a of the sintering material on the first component 1a, to subsequently connect the first component 1a to the substrate 10 by a sintered material joint. Alternatively, the second layer 22a of sintering material is deposited onto the substrate 10.

[0084] The sintering material is 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 prematurely (dispersant). These organic elements are largely eliminated during the drying operation. The sintering paste may also include additives to accelerate the (subsequent) sintering of the particles.

[0085] Any other power electronic components belonging to the same component stage, such as the third component 1 le, are preferably fixed to the first hood 25a in the same way as the first component 1 la.

[0086] Similarly, step S3 of [Fig.5C] includes fixing the second component 11b to the inner face of the second hood 15b (and more particularly to a conductive track 13).

[0087] The fixation of the second component 11b preferably includes the formation of a third layer 21b made of the sintering material on the second hood 15b, the deposition of the second component 11b on the third layer 21b and the drying of the sintering material of the third layer 21b.

[0088] Step S3 may also include the formation of a fourth layer 22b of sintering material on the second component 11b, to subsequently connect the second component 11b to the substrate 10 by means of a sintered material joint. Alternatively, the fourth layer 22b of sintering material is deposited on the substrate 10.

[0089] Any other power electronic components belonging to the same component stage, such as the fourth component 1 Id, are preferably fixed to the second hood 25b in the same way as the second component lia.

[0090] Before the sintering material is deposited, an Ar / H2 plasma treatment can be carried out to clean the substrate of any organic contaminants, to deoxidize, texture it with a desired average arithmetic roughness (noted Ra) between 0.2 and 0.8 and activate the surface before sintering.

[0091] During a step S4 represented by [Fig. 5D], the first cover 15a is transferred to the first face 10a of the substrate 10, inner face facing the first face 10a, and the second cover 15b is transferred to the second face 10b of the substrate 10, inner face facing the second face 10b. The transfers are carried out, for example, using a "flip-chip" type device commonly used in the microelectronics industry.

[0092] The sintering material is then sintered to form the conductive joints 14 between the components 1la-1 Id and the substrate 10 and between the components 1la-1 Id and the caps 15a-15b. Sintering can be carried out under partial vacuum or under air (no oxidation of the silver conductive tracks). Air can be used to remove (calcin) the remaining organic elements in the sintering paste.

[0093] Sintering can be carried out under pressure, using a heated press, according to predetermined temperature and pressure profiles, for example according to the process described in international application WO2022 / 200749A2. The heated press preferably comprises a heating arm and a support on which the substrate-component-hood assembly is placed. Preferably, the sintering step S5 comprises the following phases: • a first phase called the finishing phase, during which the support and the arm are brought to a finishing 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 about 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 kept constant between 205 °C and 255 °C and a pressure between 10 MPa and 30 MPa is applied; • a third phase known as consolidation and cooling, during which the temperature decreases (for example until it returns to ambient temperature) while maintaining the pressure applied during the second phase.

[0094] The duration of the third phase is, for example, between 1 minute and 10 minutes.

[0095] Alternatively, sintering is carried out without pressure, for example according to the process described in application WO2017 / 046266A1.

[0096] The additional conductors 12 can be fixed to the substrate 10, before or after the sintering operation.

[0097] Finally, step S5 of [Fig. 5E] is an encapsulation step of the power module, consisting of coating at least the components 1la-1Id with the encapsulation material 16, from the substrate 10 to the covers 15a-15b. The encapsulation step S5 may include the injection of a resin into a mold, in which the substrate-component-cover assembly is placed, and a resin curing step.

[0098] The manufacturing process described in relation to Figures 5A to 5E is simple to implement, since steps S2 and S3 are so-called "2D" assembly steps that can be carried out on panels, in parallel with each other (in other words, simultaneously), unlike step S4, which involves transferring the covers 15a-15b, and the encapsulation step S5 (which are "3D" assembly steps). Similarly, the steps for 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

Demands

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 power electronic component (1a) disposed on the first face (10a) of the substrate (10); - a first cover (15a) disposed on the first power electronic component (1a); - a second power electronic component (11b) disposed on the second face (10b) of the substrate (10); and - a second cover (15b) disposed on the second power electronic component (11b);- an electrically insulating encapsulation material (16) encasing the first and second power electronic components (liai 1b) and extending from the substrate (10) to the first hood (15a) and from the substrate to the second hood (15b), power electronic module (1) in which each of the first and second power electronic components (lia, 11b) is electrically connected to the substrate (10) via a conductive track (13) and a conductive joint (14) formed of a sintered material, each conductive track (13) and each conductive joint (14) being silver-based.;

2. Module (1) according to claim 1, wherein the encapsulation material occupies all the available space between the substrate (10) and the first hood (15a) and all the available space between the substrate (10) and the second hood (15a).

3. Module (1) according to any one of claims 1 and 2, wherein the encapsulating material further encases an inner portion of the first hood (15a) and an inner portion of the second hood (15b).

4. Module (1) according to any one of claims 1 to 3, wherein: - the substrate (10) is made of metal; - the first power electronic component (1a) 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 hood (15a); - the second power electronic component (11b) includes a first terminal electrically connected to the substrate (10) and a second terminal electrically connected to a conductive portion (152, 153) of the second hood (15b).

5. Module (1) according to any one of claims 1 to 4, wherein: - the first power electronic component (1a) is electrically connected to the conductive portion (152, 153) of the first hood (15a) via a conductive track (13) and a conductive joint (14) formed of the sintered material; - the second power electronic component (11b) is electrically connected to the conductive portion (152, 153) of the second hood (15b) via a conductive track (13) and a conductive joint (14) formed of the sintered material.

6. Module (1) according to any one of claims 1 to 5, wherein the first hood (15a) comprises: - a first substrate (151) formed of a first electrically insulating ceramic material; and - at least a first conductive element (152) passing through the first substrate (151) and electrically connected to the first power electronic component (11); and wherein the second hood (15b) comprises: - a second substrate (151) formed of a second electrically insulating ceramic material; and - at least a second conductive element (152) passing through the second substrate (151) and electrically connected to the second power electronic component (11b).

7. Module (1) according to claim 6, wherein the first and second substrates (151) are aluminum nitride.

8. Module (1) according to any one of claims 1 to 5, wherein the first and second hoods (15a, 15b) each comprise a metal layer (153) and an electrically insulating layer (154) disposed on an outer face of the metal layer (153).

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

10. O. Actuator according to claim 9, comprising a three-phase motor (40) and a control and supply circuit for the three-phase motor, the control and supply circuit for the three-phase motor comprising a plurality of electronic power modules (1) according to any one of claims 1 to 6 for generating phase currents for the three-phase motor (40).

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

12. 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 power electronic component (1a) on the first cover (15a); - fixing (S3) a second power electronic component (11b) on the second cover (15b); - 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, so as to place the first power electronic component (1a) between the substrate (10) and the first cover (15a) and the second power electronic component (11b) between the substrate (10) and the second cover (15b);and - to encase (S5) the first power electronic component (1a) and the second power electronic component (11b) with an electrically insulating encapsulation material (16), the encapsulation material extending from the substrate (10) to the first hood (15a) and from the substrate to the second; hood (15b), each of the first and second power electronic components (lia, 11b) being electrically connected to the substrate (10) via a conductive track (13) and a conductive joint (14) formed of a sintered material, each conductive track (13) and each conductive joint (14) being silver-based.

13. A method according to claim 12, wherein the substrate (10) is made of aluminum, the method further comprising, before the step (S4) of transferring the caps (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: - deposition by screen printing of a paste comprising silver particles; - drying of the dough; and - re-baking the dough at a temperature greater than or equal to 570

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