Capacitive element, assembly for a power module and associated manufacturing method

Abstract

The invention relates to a capacitive element (1) comprising: - a cylindrical casing (10) extending along a longitudinal axis (X); - a core (3) extending along the longitudinal axis (X) between an upper end (31) and a lower end (32); - a roll (2), housed inside the casing (10) and formed: o of a first film (20) provided with a first insulating portion (200) extended by a first conductive portion (201), and o of a second film (21) provided with a second insulating portion (210) extended by a second conductive portion (211), the two films (20, 21) being stacked and wound around the core (3) so that the first insulating portion (200) is in contact with the second insulating portion (210) and so that the first conductive portion (201) and the second conductive portion (211) are opposite along a longitudinal axis of the capacitive element (1), the first conductive portion (201) forming a first end of the roll, the second conductive portion (211) forming a second end of the roll, - a first metallized layer (40) formed on an upper surface of the roll at the location of the first end of the roll; - a second metallized layer (41) formed on a lower surface of the roll at the location of the second end of the roll; - two radial outlets (50, 51), one of the two radial outlets (50) being in electrical connection with the first metallized layer (40), the other of the two radial outlets (51) being in electrical connection with the second metallized layer (41), the two radial outlets (50, 51) being mounted at least partially projecting from an upper surface (100) of the casing (10), characterized in that the core (3) is made at least partially from a metal material, and has an outer surface at least partially covered with a layer of insulating material (30).

Description

[0001] DESCRIPTION

[0002] TITLE: CAPACITIVE ELEMENT, POWER MODULE ASSEMBLY, AND CORRESPONDING MANUFACTURING METHOD.

[0003] Scope of the invention

[0004] The present invention relates to the field of power electronics, and more specifically to the context of a DC voltage distribution and the capacitive interface between this distribution and the switching elements of a power converter.

[0005] More particularly, the invention relates to a capacitive element such as a power film capacitor allowing to limit the phenomena of self-induction, or inductive phenomena in English.

[0006] The invention could, for example, find an application in the aeronautical field, and could be used within aircraft electronics.

[0007] Prior art

[0008] Among the various electronic components used in the field of microelectronics, capacitive elements are among the most widely used.

[0009] A capacitor is a basic electronic component consisting of two conductive plates, also called electrodes, in total influence and separated by a polarizable insulator, also called a dielectric. Its main property is its ability to store opposite electrical charges on its plates.

[0010] Among the different types of capacitors, film capacitors are the most commonly used passive components, such as coupling capacitors, to keep unwanted DC voltage parts away, or in frequency and oscillator circuits.

[0011] These capacitors are usually made in three stages, with the coil being made by superimposing and winding two dielectric films around a plastic mandrel, then the projection of metallic particles onto the ends of the dielectric films, and finally the formation of electrical bonds between the projections of metallic particles and radial leads allowing subsequent connection with other components.

[0012] However, a drawback of such film capacitors is that they are subject to self-induction phenomena, and therefore each generates parasitic inductances. Each parasitic inductance induces an overvoltage that is detrimental to the integrity and operation of this type of switching component.

[0013] Furthermore, the power capacitor dissipates power, which is related to the metallization resistance of the two dielectric films and the effective current flowing through these metallizations. The temperature rise limits the capacitor's use in relation to the class of the dielectric used (85°C, 105°C, 125°C, 150°C...).

[0014] Therefore, there is a need to provide a solution to improve the operation of these switching components and reduce the heating of the power capacitor.

[0015] Description of the invention

[0016] The invention aims to remedy at least in part the aforementioned drawbacks relating to prior art techniques.

[0017] To this end, the invention relates to a capacitive element comprising: a cylindrical housing extending along a longitudinal axis X; a mandrel extending along said longitudinal axis X between an upper end and a lower end;a coil, housed inside said casing and formed of: o a first film having a first insulating portion extended by a first conductive portion, and o a second film having a second insulating portion extended by a second conductive portion, the two films being superimposed and wound around said mandrel so that said first insulating portion is in contact with said second insulating portion and that said first conductive portion and said second conductive portion are opposite along a longitudinal axis of said capacitive element, the first conductive portion forming a first end of said coil, the second conductive portion forming a second end of said coil, a first metallized layer formed on a superior surface of said coil at the location of said first end of said coil;a second metallized layer formed on a lower surface of said coil at the location of said second end of said coil; two radial outputs, one of said two radial outputs being electrically connected to said first metallized layer, the other of said two radial outputs being electrically connected to said second metallized layer, said two radial outputs being mounted at least partially projecting from an upper surface of said housing. According to the invention, said chuck is made at least partially from a metallic material, and has an outer surface at least partially covered with a layer of insulating material.

[0018] Thus, the proposed solution makes it possible to resolve at least some of the drawbacks of the previous art.

[0019] Indeed, thanks to the chuck, the simplified surface area of ​​the current paths flowing from one power terminal to the other is reduced, with a parasitic inductance that is reduced accordingly.

[0020] This simplified surface area can, for example, be reduced by 20%.

[0021] Furthermore, the power dissipated by the capacitive element, and therefore the excess heat, is removed along the axis of the capacitor with the highest thermal conductivity. This limits heating, as the mandrel acts as a thermal conductor, thus allowing heat to be removed along the longitudinal axis away from the capacitive element.

[0022] According to a particular aspect of at least one embodiment of the invention, said chuck is made entirely from a metallic material.

[0023] According to a particular aspect of at least one embodiment of the invention, said chuck has a hollow tubular wall.

[0024] This facilitates heat exchange and thus promotes the thermal function of the chuck.

[0025] According to a particular aspect of at least one embodiment of the invention, said hollow tubular wall has a regular thickness of between 0.5mm and 1mm, preferably substantially equal to 0.7mm.

[0026] According to a particular aspect of at least one embodiment of the invention, at least one of said upper end and said lower end is covered by said layer of insulating material.

[0027] According to a particular aspect of at least one embodiment of the invention, said layer of insulating material has a regular thickness of between 50pm and 200pm, preferably substantially equal to 100pm.

[0028] According to a particular aspect of at least one embodiment of the invention, said mandrel extends over at least the entire length of said coil along said longitudinal axis X.

[0029] According to a particular aspect of at least one embodiment of the invention, said metallic material belongs to the group comprising electrically and thermally conductive materials.

[0030] According to a particular aspect of at least one embodiment of the invention, this metallic material may be copper or aluminum. According to a particular aspect of at least one embodiment of the invention, said capacitive element is a power capacitor.

[0031] According to a particular aspect of at least one embodiment of the invention, the power capacitor is of the polypropylene film, polyester film, polyethylene film, or polycarbonate film type. According to a particular aspect of at least one embodiment of the invention, said capacitive element is adapted to be subjected to a current intensity ranging from a few amperes to a few hundred amperes.

[0032] According to a particular aspect of at least one embodiment of the invention, said capacitive element further comprises a thermal conduction element arranged orthogonally with respect to said mandrel and connected to said mandrel at one of said upper and lower ends, said thermal conduction element being configured to be in contact with an external cold source.

[0033] According to a particular aspect of at least one embodiment of the invention, said capacitive element further comprises an external insulating layer surrounding said coil and said thermal conduction element so as to electrically isolate said thermal conduction element from said external cold source.

[0034] The invention also relates to a power module assembly comprising at least one capacitive element according to any one of the preceding claims.

[0035] The invention further relates to a method of manufacturing a capacitive element according to one of the aforementioned embodiments, the method comprising the following successive steps: formation of the coil by superimposing and winding said first film and second film around said mandrel so that said first insulating portion is against said second insulating portion and that said first conductive portion and said second conductive portion are opposed along a longitudinal axis X of said capacitive element; projection of metallic particles at said first end of said coil so as to form a first metallized layer, and at said second end of said coil so as to form a second metallized layer;formation of a first electrical bond between one of the two radial outputs and the first metallized layer, and of a second electrical bond between the other of the two radial outputs and the second metallized layer.

[0036] Presentation of the figures

[0037] The invention, as well as the various advantages it presents, will be more easily understood in the light of the following description of an illustrative and non-limiting embodiment thereof, and the accompanying drawings among which: [Fig. 1A], [Fig. IB] and [Fig. IC] are schematic views respectively in perspective, in partially exploded perspective, and in partial section of a capacitive element according to a first embodiment of the invention;

[0038] [Fig. 2A] and [Fig. 2B] are schematic views respectively in partial section and in lateral section of a part of a capacitive element, according to the first embodiment, illustrating the chuck;

[0039] [Fig. 3A] and [Fig. 3B] are schematic views respectively in partial section and in lateral section of a part of a capacitive element, according to the first embodiment, after the coil formation step;

[0040] [Fig. 4A], [Fig. 4B] and [Fig. 4C] are schematic views respectively in partial top section, in lateral section, and in partial bottom section of a part of a capacitive element, according to the first, after the metallic particle projection step;

[0041] [Fig. 5A], [Fig. 5B] and [Fig. 5C] are schematic views respectively in partial top section, in side section, and in partial bottom section of a part of a capacitive element, according to the first embodiment, after the step of forming the electrical bonds;

[0042] [Fig. 6A], [Fig. 6B] and [Fig. 6C] are schematic views respectively in partial top section, in side section, and in partial bottom section of a part of a capacitive element, according to the first embodiment, with the additional insulating layer;

[0043] [Fig. 7A], [Fig. 7B] and [Fig. 7C] are schematic views respectively in partial top section, in side section, and in partial bottom section of a part of a capacitive element, according to the first embodiment, the second electrical connection being extended so as to be connected to the second radial output;

[0044] [Fig. 8A], [Fig. 8B] and [Fig. 8C] are schematic views respectively in top section, in side section, and in bottom section of a capacitive element, according to the first embodiment;

[0045] [Fig. 9A], [Fig. 9B] and [Fig. 9C] are schematic views respectively in top section, in side section, and in bottom section of a capacitive element, according to a second embodiment of the invention, the capacitive element comprising a thermal conduction element connected to a cold source;

[0046] [Fig. 10A], [Fig. 10B] and [Fig. 10C] are schematic views respectively in top section, in side section, and in bottom section of a capacitive element according to a third embodiment of the invention, the capacitive element comprising a thermal conduction element and being surrounded by a peripheral insulating layer;

[0047] [Fig. 11A] and [Fig. 11B] are schematic top and side section views respectively of a capacitive element according to a fourth embodiment of the invention, [Fig. 12A] and [Fig. 12B] are simplified side section views of a capacitive element respectively according to the invention and the prior art, detailing the current paths flowing from one radial output to the other.

[0048] Detailed description of an embodiment of the invention

[0049] It should be noted that the invention applies to any type of capacitive element such as a power film capacitor allowing to limit the phenomena of self-induction, or inductive phenomena in English, which could for example find an application in the aeronautical field, and could be used within aircraft electronics, in particular in an assembly for power module comprising at least one capacitive element 1.

[0050] Such a power capacitor can be of the polypropylene film type, polyester film, polyethylene film, or polycarbonate film.

[0051] More specifically, such a power capacitor can be particularly well-suited for use with currents ranging from a few amperes to a few hundred amperes. A first embodiment of the invention is now presented with reference to Figures IA to 8C.

[0052] As illustrated, the capacitive element 1 comprises: a cylindrical housing 10 extending along a longitudinal axis X; a mandrel 3 extending along the longitudinal axis X between an upper end 31 and a lower end 32, and a coil 2, housed inside said housing 10.

[0053] It should be noted that the casing 10 can, for example, be made from a material that is at least partially insulating.

[0054] According to the invention, the chuck 3 is made at least partially from a metallic material. In various embodiments, this metallic material belongs to the group comprising electrically and thermally conductive materials.

[0055] These electrically and thermally conductive materials can include copper or aluminum.

[0056] In the first illustrated embodiment, the mandrel 3 has a hollow tubular wall. This hollow tubular wall has a regular thickness between 0.2 mm and 1 mm, preferably approximately 0.7 mm.

[0057] Furthermore, according to the invention, the mandrel 3 has an outer surface at least partially covered with a layer of insulating material.

[0058] Thus, thanks to such a chuck made at least partially from a metallic material and having an outer surface at least partially covered with a layer of insulating material, the simplified surface of the current paths flowing from one power terminal to the other is reduced, with a parasitic inductance that is reduced accordingly.

[0059] As can be seen in particular in figure 12A, this simplified surface according to the invention, corresponding to a volume, can for example be reduced by 20% compared to a prior art solution as illustrated in figure 12B.

[0060] In the illustrated embodiment, the upper end 31 is covered by a layer of insulating material 30.

[0061] According to other alternatives, at least one of the upper end 31 and the lower end 32 is covered by the layer of insulating material.

[0062] This layer of insulating material 30 has a thickness between 50pm and 200pm, preferably approximately equal to 100pm.

[0063] This layer of insulating material 30 preferably has a regular and constant thickness over its entire length.

[0064] However, embodiments could also be envisaged in which this layer of insulating material would have irregularities, such as grooves or protrusions.

[0065] On this outer surface is wound the reel 2. This reel 2 is formed of a first film 20 having a first insulating portion 200 extended by a first conductive portion 201, and of a second film 21 having a second insulating portion 210 extended by a second conductive portion 211.

[0066] The two films 20, 21 are superimposed and wound around the mandrel 3 so that the first insulating portion 200 is in contact with the second insulating portion 210 and the first conductive portion 201 and the second conductive portion 211 are opposite along a longitudinal axis of the capacitive element 1.

[0067] This coil 2 is formed during the manufacturing process, during the coil 2 formation step by superimposing and winding the first film 20 and second film 21 around the mandrel 3 so that the first insulating portion 200 is against the second insulating portion 210 and that the first conductive portion 201 and the second conductive portion 211 are opposite along a longitudinal axis X of the capacitive element 1. Such a formed coil 2 is more particularly illustrated in figures 3A and 3B.

[0068] It should be noted that the first conductive portion 201 forms a first end of the coil, and that the second conductive portion 211 forms a second end of the coil.

[0069] In the first illustrated embodiment, the mandrel 3 extends over the entire length of the spool 2 along the longitudinal axis X, and protrudes at each end.

[0070] According to other alternatives, the mandrel 3 extends over at least one length of the reel 2 along the longitudinal axis X. The fact that, in this embodiment, the mandrel is metallic and has a hollow tubular wall allows the thermal effect of this mandrel to be amplified because it will allow heat exchange with the air circulating in the tubular wall and thus allow the heat released by the electrical exchanges between the two films to be evacuated.

[0071] The capacitive element further comprises: a first metallized layer 40 formed on an upper surface of the coil 2 at the location of the first end of the coil 2; a second metallized layer 41 formed on an lower surface of the coil 2 at the location of the second end of the coil 2.

[0072] These metallized layers are formed by shot peening. In other words, and as can be seen more particularly in figures 4A to 4C, they are formed during the manufacturing process by projecting metallic particles at the first end of the coil 2 so as to form a first metallized layer 40, and at the second end of the coil 2 so as to form a second metallized layer 41.

[0073] Furthermore, the capacitive element 1 comprises two radial outputs 50, 51, one of the two radial outputs 50 being electrically connected to said first metallized layer 40, the other of the two radial outputs 51 being electrically connected to the second metallized layer 41, the two radial outputs 50, 51 being mounted at least partially projecting from an upper surface 100 of the housing 10.

[0074] These electrical connections, illustrated more particularly in figures 5A to 5C, are formed during the manufacturing process, and more particularly during the step of forming a first electrical connection 60 between one of the two radial outlets 50 and the first metallized layer 40, and a second electrical connection 61 between the other of the two radial outlets 51 and the second metallized layer 41.

[0075] Thus, the first electrical connection 60 is provided here on an outer surface of the first metallized layer 40, in contact with this first metallized layer 40. For its part, the second electrical connection 61 is provided on an outer surface of the second metallized layer 41, in contact with this second metallized layer 41, ascends axially and also opposite the first electrical connection 60 so as to reach the second radial output 51, without however being in contact with the first electrical connection 60 to avoid short circuits.

[0076] In order to further limit the risk of short circuits, and because the two radial outputs 50, 51 are mounted at least partially protruding from a surface 100 above the housing 10, it is necessary to implement a first insulating layer 70 between the first electrical connection 60 and the second electrical connection 61 so as to electrically isolate the first electrical connection 60 from the second electrical connection 61. Furthermore, in this embodiment, and as can be seen more particularly in Figures 8A to 8C, in order to electrically isolate the second electrical connection 61 from the housing 10, the capacitive element includes a second insulating layer 71 surrounding the coil 2. Such a second insulating layer is more particularly illustrated in Figure 8B.As can be seen in this figure, the second insulating layer 71 completely surrounds the coil 2 and the various layers affixed, with the exception of a portion of the first electrical connection 60 and second electrical connection 61 which protrude from this second insulating layer 71.

[0077] Furthermore, in this embodiment, the first insulating layer 70 extends partly over the protruding portion of the first electrical connection 60 so as to electrically isolate the first electrical connection 60 from the second electrical connection 61 and to maintain a spacing to avoid electrical contact between these two electrical connections.

[0078] According to other embodiments of the invention, the first insulating layer can extend at least partially over one of the first or second electrical bonds from the upper surface so as to electrically isolate the first electrical bond from the second electrical bond.

[0079] We now present, in relation to figures 9A to 9C, a second embodiment of the invention.

[0080] The elements common to the first embodiment are not detailed again. In this embodiment, the capacitive element further comprises a thermal conduction element 8 arranged orthogonally with respect to the mandrel 3 and connected to the mandrel 3 at one of the upper ends 31 and lower ends 32. Here, and as more particularly visible in Figure 9B, the thermal conduction element 8 is arranged orthogonally with respect to the mandrel 3 and connected to the mandrel 3 at the lower end of this mandrel.

[0081] This thermal conduction element 8 is also configured to be in contact with an external cold source 80. To do this, the thermal conduction element 8 has a base 81 formed at one end, and forming an angle with the rest of the thermal conduction element, in order to facilitate the connection with the external cold source 80.

[0082] The thermal conduction element can, for example, be made from copper or aluminum.

[0083] Such an arrangement allows heat to be extracted along the axial direction of coil 2 towards the external cold source by conduction with the thermal conduction element.

[0084] We now present, in relation to figures 10A to 10C, a third embodiment of the invention.

[0085] The common elements with the other embodiments presented are not detailed again. In this third embodiment, the capacitive element further comprises an external insulating layer 72 surrounding the coil 2 and the thermal conduction element 8 so as to electrically isolate the thermal conduction element 8 from the external cold source 80.

[0086] As can be seen in particular in figure 10B, the external insulating layer 72 completely surrounds the coil 2 and the thermal conduction element 8, with the exception of a portion of the first electrical connection 60 and second electrical connection 61 which protrude from this external insulating layer 72.

[0087] The thermal conduction element can, for example, be made from copper or aluminum.

[0088] Such an assembly makes it possible to electrically isolate the thermal conduction element from the external cold source, particularly in the case where such a thermal conduction element is made from an electrically conductive material such as copper or aluminum.

[0089] We now present, in relation to figures 11A and 11B, a fourth embodiment of the invention.

[0090] The elements common to the other embodiments presented are not detailed again.

[0091] In this embodiment, the mandrel 3' is made at least partially from a metallic material, and has an outer surface at least partially covered with a layer of insulating material 30.

[0092] This 3' mandrel extends along the longitudinal axis X between an upper end 31' and a lower end 32'.

[0093] As illustrated, in this embodiment, the mandrel 3' has a hollow tubular wall and is a heat pipe. In other words, this mandrel 3' is a hollow vacuum tube closed at its upper end 31' and lower end 32' and incorporates a fluid.

[0094] This heat pipe carries a current and thus becomes a cold source, allowing the capacitive element to be cooled.

Claims

DEMANDS

1. Capacitive element (1) comprising: a cylindrical housing (10) extending along a longitudinal axis (X); a mandrel (3, 3') extending along said longitudinal axis (X) between an upper end (31, 31') and a lower end (32, 32');a coil (2), housed inside said casing (10) and formed of: o a first film (20) having a first insulating portion (200) extended by a first conductive portion (201), and o a second film (21) having a second insulating portion (210) extended by a second conductive portion (211), the two films (20, 21) being superimposed and wound around said mandrel (3, 3') such that said first insulating portion (200) is in contact with said second insulating portion (210) and that said first conductive portion (201) and said second conductive portion (211) are opposite along a longitudinal axis of said capacitive element (1), the first conductive portion (201) forming a first end of said coil, the second conductive portion (211) forming a second end of said coil, a first metallized layer (40) formed on an upper surface of said coil at the location of the said first end of the said bobbin;a second metallized layer (41) formed on a lower surface of said coil at the location of said second end of said coil; two radial outlets (50, 51), one of said two radial outlets (50) being electrically connected to said first metallized layer (40), the other of said two radial outlets (51) being electrically connected to said second metallized layer (41), said two radial outlets (50, 51) being mounted at least partially projecting from an upper surface (100) of said housing (10), characterized in that said mandrel (3, 3') is made at least partially from a metallic material, and has an outer surface at least partially covered with a layer of insulating material (30).

2. Capacitive element according to claim 1, characterized in that said mandrel (3, 3') has a hollow tubular wall.

3. Capacitive element according to claim 2, characterized in that said hollow tubular wall has a regular thickness between 0.5mm and 1mm, preferably substantially equal to 0.7mm.

4. Capacitive element according to any one of the preceding claims, characterized in that at least one of said upper end (31) and said lower end (32) is covered by said layer of insulating material.

5. Capacitive element according to any one of the preceding claims, characterized in that said layer of insulating material has a regular thickness of between 50pm and 200pm, preferably substantially equal to 100pm.

6. Capacitive element according to any one of the preceding claims, characterized in that said mandrel (3) extends over at least one length of said coil (2) along said longitudinal axis (X).

7. Capacitive element according to any one of the preceding claims, characterized in that said metallic material belongs to the group comprising electrically and thermally conductive materials.

8. Capacitive element according to any one of the preceding claims, characterized in that it is a power capacitor.

9. Capacitive element according to the preceding claim, characterized in that the power capacitor is of the polypropylene film type, polyester film, polyethylene film, or polycarbonate film type.

10. Capacitive element according to any one of the preceding claims, characterized in that it is adapted to be subjected to a current of intensity between a few amperes and a few hundred amperes.

11. A capacitive element according to any one of the preceding claims, characterized in that it further comprises a thermal conduction element (8) arranged orthogonally with respect to said mandrel (3) and connected to said mandrel (3) at one of said upper ends (31) and lower end (32), said thermal conduction element (8) being configured to be in contact with an external cold source (80).

12. Capacitive element according to the preceding claim, characterized in that it further comprises an external insulating layer (72) surrounding said coil (2) and said thermal conduction element (8) so as to electrically isolate said thermal conduction element (8) from said external cold source (80).

13. Assembly for power module comprising at least one capacitive element (1) according to any one of the preceding claims.

14. A method for manufacturing a capacitive element (1) according to any one of claims 1 to 12, the method comprising the following successive steps: forming the coil (2) by superimposing and winding said first film (20) and second film (21) around said mandrel (3) so that said first insulating portion (200) is against said second insulating portion (210) and said first conductive portion (201) and said second conductive portion (211) are opposite along a longitudinal axis (X) of said capacitive element (1); projecting metallic particles at said first end of said coil (2) so as to form a first metallized layer (40), and at said second end of said coil (2) so as to form a second metallized layer (41);formation of a first electrical bond between one of said two radial outlets (50) and said first metallized layer (40), and of a second electrical bond between the other of said two radial outlets (51) and said second metallized layer (41).;

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