WO2020084256A1

WO2020084256A1 - Power electronic module housing and method for manufacturing such a housing

Info

Publication number: WO2020084256A1
Application number: PCT/FR2019/052532
Authority: WO
Inventors: Rabih KHAZAKA; Stéphane Joseph AZZOPARDI; Donatien Henri Edouard MARTINEAU; Toni Youssef; Thanh Long LE
Original assignee: Safran
Priority date: 2018-10-23
Filing date: 2019-10-23
Publication date: 2020-04-30
Also published as: FR3087578A1; FR3087578B1

Abstract

The invention relates to a housing (1) for a power electronic module, characterised in that it comprises an electrically conductive inner wall (2a) and an electrically conductive outer wall (2b), between which is provided a space configured to receive a dielectric resin, each wall (2a, 2b) of the housing (1) comprising an upper closure cap (3a, 3b); and in that the inner (2a) and outer (2b) walls of the housing (1) are mechanically and electrically connected to a metallised substrate (5), and form electrodes of a capacitor.

Description

HOUSING FOR ELECTRONIC POWER MODULE AND METHOD FOR MANUFACTURING SUCH A HOUSING

TECHNICAL AREA

The present invention relates to the field of power electronics. It relates to housings for electronic power modules.

STATE OF THE ART

Document US-A1 -8 1 12 853 describes an inverter comprising six semiconductor components of controlled power and a decoupling capacity. These power semiconductor components are generally controlled from the on state and the blocked state and vice versa by signals distributed by command and control circuits (not shown). Busbars are used to provide the electrical connection between capacitors and input connectors of the power module device.

One of the major drawbacks of such a power electronics device lies in the fact that the parasitic inductances of the power loop are linked in part to physical constraints such as the size of the capacitors, their connections, and the interconnection between decoupling capacitors and power semiconductor components. These inductances are at the origin of the appearance of overvoltage at the terminals of the power semiconductor components during a large current variation and can lead to the destruction of the power semiconductor components forming the semiconductor components. of power if their safety margin in voltage withstand is not sufficient. Indeed, parasitic inductance values of the order of a hundred nano henry strongly impact the performance of power semiconductor components, in particular for functions requiring a large variation in current as a function of time when they are ordered between l 'blocked state in passing state and vice versa.

Thus, in order to reduce the inductances between the decoupling capacitors and the power electronics modules, the capacitors decoupling are positioned closest to the power semiconductor components.

Electrolytic capacitors or film capacitors are usually connected to metal connectors or to the metallization of a busbar by soldering or screwing. However, these fixing techniques have several drawbacks. Indeed, an assembly by screwing of each capacitor on the metal connectors is a long process and, consequently, expensive. Connections fixed by soldering present reliability problems during thermal shocks or when they are subjected to vibrations. In addition, with these techniques for fixing the capacitors, the heat transfer is also not optimal due to the absence of an efficient interface between the capacitors and a cooler.

To overcome these drawbacks, several solutions have been proposed.

Document US-A1 -9 615 490 proposes to remedy the problem of cooling the capacitors and reliability of the connectors. For this, this document describes a module having a cold plate on which the module is placed and having a pocket sized to receive a decoupling capacitor thus allowing the physical integration of the decoupling capacitor directly in the cold plate.

This module thus makes it possible to increase the reliability in terms of vibrations and thermal shocks of the connectors and to ensure the cooling of the capacitors on the cold plate of the modules.

Document US-A1 -8,787,003 describes a module comprising capacitors connected together, to form a capacitive block, and with the outside. This module is then mechanically and thermally connected to a cold plate close to a power module. A bus bar (or metal plates) then electrically connects the capacitor and the power module. The capacitor module includes a substrate having a metallization on a first side of the substrate, a plurality of connectors electrically coupled to the metallization and a plurality of capacitors disposed on the metallization. The plurality of capacitors includes a first set of capacitors electrically connected in parallel between a first set of connectors and a second set of connectors. The capacitor module further includes a housing enclosing the plurality of capacitors within the capacitor module.

This solution makes it possible to cool the capacitors, improve reliability at the connection of the capacitors and reduce parasitic inductances.

Finally, document US-A-5,142,439 describes a high-voltage, low-volume ceramic capacitor module, comprising surface-mounted chip capacitors, and which can be integrated into various electrical systems so as to minimize the parasitic inductance. This module makes it possible to reduce parasitic inductances, to increase resistance to vibrations and thermal shocks.

These different solutions of the prior art, although acceptable, are complex, expensive and do not give complete satisfaction with respect to compactness.

An object of the present invention is to provide a simple and effective solution free from the aforementioned drawbacks.

STATEMENT OF THE INVENTION

To this end, the invention relates to a housing for an electronic power module, the housing comprising an electrically conductive inner wall and an electrically conductive outer wall between which is formed a space configured to receive a dielectric resin, each wall of the housing. comprising an upper closure cover, and in that the inner and outer walls of the housing are mechanically and electrically connected to a metallized substrate and forming electrodes of a capacitor. The housing being characterized in that the upper outer cover of the outer wall has an orifice for the passage of the dielectric resin.

The housing according to the invention has several interesting advantages. Especially :

- the functionalization of the housing of the electronic power module which serves as an electrode for a capacitor, the walls of the case forming the electrodes of a capacitor, for example of decoupling, allows the latter to be as close as possible to the power components of the power module,

- the case thus formed can benefit from the cooling of the substrate so that it does not require an additional cooling system,

- better reliability of the decoupling capacitor in the face of thermal shock and vibration.

Advantageously, an inner face of the outer wall of the housing is provided with first fins and an outer face of the inner wall of the housing is provided with second fins, the inner and outer walls of the housing being arranged so as to obtain alternation first fins and second fins in the space formed between the inner and outer walls.

Thus, the surface between the two walls of the housing forming the electrodes of the capacitor is increased, as is the capacity of said capacitor.

Preferably and advantageously, the space provided between the inner wall and the outer wall has a width of between a few micrometers and a few millimeters.

Thus, the thickness of the dielectric is controlled, as well as the capacity of the capacitor.

Preferably and advantageously, the metallized substrate is a multilayer substrate which allows the production of complex cabling while ensuring airtightness of the housing.

Advantageously, the dielectric resin is a pure resin, for example poly (vinylidene fluoride) having a high permittivity.

Advantageously, the dielectric resin is a composite resin loaded with ceramic particles or loaded with metal particles in order to improve the permittivity.

According to an exemplary embodiment, the housing is produced by additive manufacturing directly on the metallized substrate.

According to another embodiment, the housing is attached and fixed to the metallized substrate by brazing or sintering. The present invention also relates to an electronic power module characterized in that it comprises a housing having any of the above characteristics and forming a decoupling capacitor.

Such a module has several interesting advantages, namely:

- the functionalization of the box which allows a strong integration of the capacitors, in particular of decoupling,

the walls of the housing forming the electrodes of the capacitor allow a reduction of the parasitic inductances generated by the connection wires of the capacitors,

- direct cooling of the capacitor by the same cooling system as the substrate,

- improved reliability of the power module to thermal shock and vibration.

The invention also relates to a method for producing a housing having any of the above characteristics, characterized in that it comprises the following steps:

the interior and exterior walls of the housing are arranged on the metallized substrate so as to provide a space;

each of the walls is closed using the respective upper cover;

the dielectric resin is injected under vacuum into the interior of the housing through the orifice provided in the outer top cover of the exterior wall; the casing is annealed in order to stiffen the dielectric resin.

DESCRIPTION OF THE FIGURES

The present invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description of a nonlimiting example which follows, with reference to the attached drawings in which:

- Figure 1 is an exploded perspective view of the housing according to the invention;

- Figure 2 is a detail and perspective view of the walls of the housing according to the invention; - Figure 3 is a top view of the walls of the housing according to the invention illustrated in Figure 1;

- Figure 4 is a schematic sectional view of the housing according to the invention.

DETAILED DESCRIPTION

In the present description, the terms "internal", "external", "interior", "exterior", "upper" and "lower" are used with reference to the positioning during use of the components of the housing according to the invention.

The box 1 for an electronic power module according to the invention comprises:

a first interior assembly comprising an interior wall 2a capable of being closed by an interior top cover 3a;

a second exterior assembly comprising an exterior wall 2b capable of being closed by an exterior top cover 3b;

the first set being placed inside the second set.

The inner 2a and outer 2b walls, for example of rectangular or square section, are dimensioned so as to provide a space E between an outer face 2a 'of the inner wall 2a and an inner face 2b' of the outer wall 2b , the inner wall 2a having a perimeter and a height less, respectively, than the perimeter and the height of the outer wall 2b.

A seal 4a, 4b is advantageously disposed, respectively, between the inner wall 2a and the inner upper cover 3a, and between the outer wall 2b and the outer upper cover 3b.

The inner 2a and outer 2b walls are electrically conductive. Preferably and advantageously, the inner 2a and outer 2b walls and their respective upper covers 3a and 3b are made of metal. The metal housing 1 thus formed can then serve as mechanical protection allowing the electronics to operate in harsh environments. In addition, the metal housing 1 also has a diffusion barrier and electromagnetic shielding function of the power module.

Referring to Figure 4, the inner wall 2a and the outer wall 2b of the housing 1 are mechanically and electrically connected, in a manner known per se, to a metallized substrate 5. The space E formed between the inner wall 2a and the outer wall 2b makes it possible to prevent any electrical connection being made between the inner 2a and outer 2b walls. Thus, the inner wall 2a and the outer wall 2b of the housing 1 form the electrodes of a capacitor integrated in the power module, as close as possible to the switching cells of the power module. The box 1 is then functionalized and does not only serve as mechanical protection for the power module.

The metallized substrate 5 is preferably a multilayer substrate, for example a double-layer substrate with a layer of silicon nitride and a layer of copper, thus ensuring hermeticity of the housing 1. The electronic connections are then provided outside the housing 1 through metallized vias in a first layer of the metallized substrate 5, making it possible to make an electrical connection between the two layers.

According to another embodiment, the metallization of the substrate is aluminum and the inner walls 2a and outer 2b of the housing 1 are made of an alloy of aluminum, silicon and magnesium.

In an embodiment not shown in which the hermeticity of the housing 1 is not sought, holes made in the upper inner cover 3a and outer 3b for the passage of the electrical connections linked to the metallized substrate 5.

The space E formed between the inner wall 2a and the outer wall 2b has a width between a few micrometers and a few millimeters. This width in fact depends on the value of the desired capacity for the capacitor formed by the casing 1, on its voltage resistance and on the electrical properties of the materials that compose it, such as its permittivity, the value of this capacity being inversely proportional. to this width. In order to further vary the capacitance of the capacitor, the inner face 2b 'of the outer wall 2b and the outer face 2a' of the inner wall 2a of the housing 1 are provided with fins, respectively the first fins 6b and second fins 6a. Referring to Figure 3, the first fins 6b and second fins 6a are arranged, respectively, on the inner face 2b 'of the outer wall 2b and on the outer face 2a' of the inner wall 2a so as to define an alternation first fins 6b and second fins 6a in the space E formed between the inner wall 2a and the outer wall 2b. These fins 6a, 6b thus make it possible to increase the surface between the interior wall 2a and the exterior wall 2b and, consequently, the value of the capacitor capacity.

The space E formed between the inner wall 2a and the outer wall 2b is configured to receive a dielectric resin. This resin can be injected into the housing 1, in a volume V having an inverted U-shaped section delimited by the metallized substrate 5, the internal face 2b 'of the external wall 2b, the external face 2a' of the internal wall 2a , the inner top cover 3a and the top exterior cover 3b.

The dielectric resin is for example injected through a passage orifice 7 formed in the upper outer cover 3b and flows into the volume V defined above.

In the embodiment not shown in which holes are made in the upper inner cover 3a and outer 3b for the passage of the electrical connectors linked to the metallized substrate 5, seals are provided at the connectors to prevent the dielectric resin to flow into the power module during its injection.

The dielectric resin is advantageously a pure resin such as a ferroelectric polymer, for example poly (vinylidene fluoride) (known by the acronym PVDF) having a high permittivity or a ferroelectric copolymer P (VDF-TrFE).

The dielectric resin is preferably charged with ceramic particles and / or metal particles in order to increase the permittivity of the resin and therefore the value of the capacitance of the capacitor. In the case of these resins, the reduction in particle size on the nanometric scale makes it possible to have high permittivities with low loading rates. In fact, the smaller the particles, the lower the viscosity of the resin, allowing easier injection of the resin into the housing 1 and filling of the volume V without air bubbles. Indeed, the filling of the volume V between the two electrodes of the capacitor with the dielectric resin must be complete and without the presence of air, so that the dielectric resin preferably has a viscosity of less than 1000 cP.

The seals 4a, 4b for attaching the upper inner covers 3a and outer 3b, respectively on the inner walls 2a and outer 2b then also make it possible to seal the housing 1 during the insertion of the dielectric resin.

The method of making the housing 1 includes a step of arranging the inner wall 2a inside the outer wall 2b on the metallized substrate 5 so as to provide a space E between the inner face 2b 'of the outer wall 2b and the outer face 2a 'of the inner wall 2a. The interior upper cover 3a is applied to the interior wall 2a so as to define an interior volume Va and the exterior top cover 3b is applied to the exterior wall 2b so as to define an exterior volume Vb.

According to a first embodiment, the inner walls 2a and outer 2b housing 1 is produced by additive manufacturing directly on the metallized substrate 5, for example by SLM technology (acronym for "Selective Laser Melting" in English) additive manufacturing, which consists of fusing powder using a high energy beam such as a laser beam. In practice, a powder bed is deposited on a support plate, here directly on the metallized substrate 5 and is scanned by the laser beam to manufacture the interior walls 2a and exterior 2b housing 1, layer by layer, a third layer of fused powder being disposed above a second layer which is itself disposed above a first layer, thus ensuring mechanical attachment and electrical connection to the metallized substrate 5. The fins 6a, 6b are then manufactured in the same way time that the inner walls 2a and outer 2b. The upper inner 3a and outer 3b covers are either also directly manufactured, respectively, on the inner 2a and outer 2b walls by additive manufacturing, or manufactured separately by any method known per se of production of metal parts and attached and fixed, respectively on the inner 2a and outer 2b walls by any fixing method such as by brazing or sintering.

According to another exemplary embodiment:

a) the inner 2a and outer 2b walls are produced by any known method of producing metal parts, such as foundry, forging, machining;

b) the upper internal cover 3a and external cover 3b are also produced by any known method of producing metal parts; c) fixing, if necessary, the covers on the respective walls

d) the housing 1 is attached and it is fixed to the metallized substrate 5 by any known mechanical fixing and electrical connection methods, such as by soldering or sintering,

steps a) and b) can be carried out simultaneously and steps c) and d) can be reversed.

The inner wall 2a can be made in one piece with the inner upper cover 3a, and the outer wall 2b can be made in one piece with the outer upper cover 3b, steps a), b) and c) then corresponding to one and the same step.

The dielectric resin is then injected, under vacuum, through the orifice 7 formed in the outer top cover 3b in the volume V corresponding to the exterior volume Vb subtracted from the interior volume Va (V = Vb - Va) in order to avoid any presence of air between the electrodes formed by the inner 2a and outer 2b walls.

The assembly is then annealed, in a manner known per se, in order to stiffen the dielectric resin.

With a power module comprising such a functionalization of the housing 1 so as to form an integrated capacitor as close as possible to power components of the module, the estimated capacitor capacitance values for an epoxy polymer resin ("epoxy") are between 10nF and 100pF, depending on the permittivity of the resin, its thickness and the surface area of the electrodes of the capacitor. Indeed, composite resins have a lower breaking tension than pure resins so that it is necessary to increase the space between the interior walls 2a and exterior 2b (in other words the distance between the electrodes) for resins composites to maintain high voltages.

As an indication for a spacing between the electrodes of 400 pm, in other words for a width of the space E between the internal face 2b 'of the external wall 2b and the external face 2a' of the internal wall 2a of 400pm, for a composite polymer / ceramic or polymer / metal resin with a permittivity equal to 200 and an electrode area of 250 cm2 achievable on a housing 1 of 50 mm in width, 50 mm in length and 10 mm in height, the capacity calculated is of the order of 1 10 nF whereas for a capacity of 100nF, a film capacitor of the prior art measures 28.5 mm in width, 41.5 mm in length and 16 mm in height.

Such a power module makes it possible to limit the parasitic inductances compared to the power modules of the prior art, allows a marked improvement in the reliability of thermal shocks and vibrations due to the constitution of the integrated capacitor, as well as an increase in the overall power density of the power module due to the use of the same metallized substrate and the same cooling system for the power module and the integrated capacitor.

Such a hermetic power electronic module with a metal casing 1 including the decoupling capacitor between the inner 2a and outer 2b walls is particularly advantageous for applications of the intelligent motor type (from the English "Smart motor") and, more particularly in the aeronautical field, for power converters at the voltage source making it possible to convert the electrical energy of the main network (1 15V AC, 230V AC, 540V DC ...) in several forms (AC / DC, DC / AC, AC / AC and DC / DC).

Claims

1. Housing (1) for an electronic power module, the housing (1) comprising an electrically conductive inner wall (2a) and an electrically conductive outer wall (2b) between which is provided a space (E) configured to receive a dielectric resin, each wall (2a, 2b) of the housing (1) comprising an upper closing cover (3a, 3b), and in that the internal (2a) and external (2b) walls of the housing (1) are mechanically and electrically connected to a metallized substrate (5) and forming electrodes of a capacitor,

characterized in that the upper outer cover (3b) of the outer wall (2b) has an orifice (7) for the passage of the dielectric resin.

2. Housing (1) according to the preceding claim, characterized in that an internal face (2b ') of the external wall (2b) of the housing (1) is provided with first fins (6b) and in that a face outer (2a ') of the inner wall (2a) of the housing is provided with second fins (6a), the inner (2a) and outer (2b) walls of the housing (1) being arranged so as to obtain an alternation of first fins (6b) and second fins (6a) in the space (E) formed between the inner (2a) and outer (2b) walls.

3. Housing (1) according to one of the preceding claims, wherein the space (E) formed between the inner wall (2a) and the outer wall (2b) has a width between a few micrometers and a few millimeters.

4. Housing (1) according to one of the preceding claims, in which the metallized substrate (5) is a multilayer substrate.

5. Housing (1) according to one of the preceding claims, wherein the dielectric resin is a pure resin, for example poly (vinylidene fluoride).

6. Housing (1) according to one of the preceding claims, wherein the dielectric resin is a composite resin loaded with ceramic particles or loaded with metal particles.

7. Housing (1) according to one of claims 1 to 6, characterized in that it is produced by additive manufacturing directly on the metallized substrate (5).

8. Housing (1) according to one of claims 1 to 6, characterized in that it is attached and fixed to the metallized substrate (5) by brazing or sintering.

9. Electronic power module characterized in that it comprises a housing (1) according to any one of the preceding claims forming a decoupling capacitor.

10. Method for producing a housing (1) according to one of claims 1 to 8, characterized in that it comprises the following steps:

the inner (2a) and outer (2b) walls of the housing (1) are arranged on the metallized substrate (5) so as to provide a space (E);

each of the walls (2a, 2b) is closed using the respective upper cover (3a, 3b);

the dielectric resin is injected under vacuum into the interior of the housing (1) through the orifice (7) formed in the outer top cover (3b) of the exterior wall (2b);

the housing (1) is annealed in order to stiffen the dielectric resin.