Power electronic module

Abstract

The invention relates to a power electronic module (23) comprising a housing (29), a substrate (31), at least one electronic component (33) transferred onto the substrate (31), a gel (35) encapsulating the electronic component (33) on the substrate (31) and in the housing (29), the power electronic module comprising a tapped nut (37) held in a wall (39) of the housing (29), a threaded rod (41) extending through the nut (37) inside and outside the housing (29), and a base (43) transferred onto the substrate (31) and aligned with the longitudinal axis of the rod (41).

Description

[0001] DESCRIPTION TITLE: Power electronics module

[0002] Technical field

[0003] The present invention relates to the field of power electronic modules.

[0004] In particular, the present invention relates to electronic power modules making it possible to provide an energy conversion function.

[0005] Previous techniques

[0006] Power electronic modules are sub-assemblies of power electronics that allow several power electronic components to be integrated within the same housing to perform more or less complex functions, such as energy conversion.

[0007] Figure 1 schematically shows a sectional view of an assembly 1 comprising an electronic power module 3 and a heat sink 5 according to the state of the art.

[0008] A power electronic module 3 generally comprises electronic components 7 assembled on an electrically insulating and thermally conductive substrate 9. These electronic components 7 are attached in the majority of cases by brazed or sintered joints 11 on said substrate 9. The electrical connections between the electronic components 7 are made by the substrate 9 and / or by wires 13, and / or by ribbons, and / or by clips. The power electronic module 3 is positioned against the heat sink 5 so as to evacuate the heat generated by the electronic components 7 during their operation. The power electronic module 3 also comprises a gel 15 encapsulating the electronic components 7 on the substrate 9. A housing 17 makes it possible to maintain and protect the gel 15, the electronic components 7 and the substrate 9.

[0009] The substrate 9 generally comprises a thermal interface 19 with the heat sink 5 so as to be able to dissipate the heat outside the power electronic module 3. The more contact surface there is between the substrate 9 and the heat sink 5 at the thermal interface 19, the more effective the heat dissipation is.

[0010] However, some substrates such as IMS (Insulated Metal Substrate) deform during the operations of assembling the power electronic module, soldering the electronic components, baking or bonding elements of the power module during the manufacture of said power electronic module. This deformation is generally due to the difference in thermal expansion of the layers making up the substrate.

[0011] This deformation usually manifests as a camber, for example concave, which reduces the contact surface between the substrate and the heat sink, thus impairing effective heat dissipation. The deformation is also called warping or "warpage" in Anglo-Saxon terms. The deformation is generally less than 150 microns.

[0012] Statement of the invention

[0013] The present invention therefore aims to overcome the aforementioned drawbacks and to provide an electronic power module which does not exhibit deformation.

[0014] The present invention relates to a power electronics module comprising a housing, a substrate, at least one electronic component attached to the substrate, a gel encapsulating said electronic component on the substrate and in the housing, the power electronics module comprising a threaded nut held in a wall of the housing, a threaded rod extending through the nut inside and outside the housing, and a base attached to the substrate and aligned with the longitudinal axis of the rod.

[0015] The threaded rod thus allows the substrate to be pressed via the base, thereby compensating for deformation and once again guaranteeing optimal heat dissipation.

[0016] Advantageously, the gel covers the substrate over a gel thickness, the length of the base being greater than the gel thickness. In one embodiment, said electronic component and the base are attached to the substrate by a brazed or sintered joint.

[0017] Advantageously, the substrate is fixed to the housing by fixing means positioned at the ends of said substrate.

[0018] Advantageously, the substrate is an electrically insulated and thermally conductive metal substrate.

[0019] In a particular embodiment, the substrate comprises a copper plate 1 to 3 millimeters thick, an insulator 100 to 200 microns thick, and a thin metallized copper track on which said electronic component and the base are attached.

[0020] Advantageously, the case comprises a plastic material.

[0021] The present invention also relates to an assembly comprising a power electronics module as defined above, and a heat sink, the substrate of the power electronics module comprising a thermal interface with the heat sink, the thermal interface promoting the evacuation of the heat generated by the electronic component towards the heat sink.

[0022] The present invention also relates to a method for compensating for a deformation of a substrate of an electrical power module or of an assembly as defined previously, the method comprising a step of measuring the flatness of the substrate, a step of choosing a thread for the rod, a step of determining the number of rotational turns to be applied to the rod, and a step of screwing the threaded rod so as to press on the base with said rod and to reduce the deformation of the substrate.

[0023] Advantageously, the method further comprises a step of verifying the compensation of the deformation by measuring the thermal impedance of the electrical power module.

[0024] Brief description of the drawings

[0025] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0026] [Fig 1] is a schematic sectional view of an assembly comprising an electronic power module and a heat sink according to the state of the art;

[0027] [Fig 2] is a schematic sectional view of an assembly comprising a power electronic module and a heat sink according to the invention, a deformation of the substrate of the power electronic module being visible;

[0028] [Fig 3] is a schematic sectional view of an assembly comprising a power electronic module and a heat sink according to the invention, a deformation of the substrate of the power electronic module being compensated; and

[0029] [Fig 4] is a representation of the steps of the method for compensating for a deformation of a substrate of a power electronic module according to the invention.

[0030] Detailed description of at least one embodiment

[0031] Figure 2 schematically shows a sectional view of an assembly 21 comprising an electronic power module 23 and a heat sink 25 according to the invention and having a deformation 27. The same assembly 21 is shown in Figure 3, in which the deformation 27 has been compensated.

[0032] The heat sink 25 comprises, for example, metal fins.

[0033] The electronic power module 23 comprises a housing 29, a substrate 31, at least one electronic component 33 attached to the substrate 31, a gel 35 encapsulating said electronic component 33 on the substrate 31 in the housing 29, a threaded nut 37 held in a wall 39 of the housing 29, a threaded rod 41 extending through the nut 37 inside and outside the housing 29, and a base 43 attached to the substrate.

[0034] The housing 29 is for example fixed to the substrate 31 by fixing means (not shown) positioned at the ends of said substrate 31. These fixing means prevent the substrate 31 from deforming convexly when the electronic power module 23 is fixed to the heat sink 25. Alternatively, or additionally, the electronic power module 23 is for example fixed to the heat sink 25 by screws (not shown), thus making it possible to prevent the substrate 31 from deforming convexly.

[0035] The substrate 31 has a thickness of less than one centimeter. It extends in its other dimensions along a plane, for example a polygonal plane. The means for fixing the substrate 31 to the housing 29 are then fixed at the edge of the polygon defining the shape of the substrate 31.

[0036] The housing 29 may comprise a plastic material. It covers, without being in contact with it, a first face 44 of the substrate 31 on which the electronic components 33 are attached.

[0037] The substrate 31 is for example an AMB type substrate (“Active Metam Brazed” in Anglo-Saxon terms), or a DBC type substrate (“Direct Bonded Copper” in Anglo-Saxon terms), or an SMI type, in other words an electrically insulated and thermally conductive metal substrate.

[0038] In a particular embodiment, the substrate 31 comprises a copper plate 45 1 to 3 millimeters thick, an insulator 47 100 to 200 microns thick, and a thin copper track 49, for example less than 100 microns thick. The plate 45 and the insulator 47 extend over the entire plane formed by the substrate 31.

[0039] The copper plate 45 is positioned towards the outside of the electronic power module 23 and constitutes a second face 51 of the substrate 31.

[0040] In one embodiment, the second face 51 of the substrate 31 constitutes a thermal interface 53 with the heat sink 25, the latter being able to be positioned directly against the second face 51 of the substrate 31 in order to dissipate the heat from the power electronic module 23 towards said heat sink 25.

[0041] In another embodiment not shown, the second face 51 of the substrate 31 is covered by a portion of the housing thus constituting the thermal interface 53 with the heat sink 25.

[0042] The insulator 47 is laminated onto the copper plate 45. The insulator 47 is made of an electrically insulating material, in order to electrically isolate the electronic components 33 from the external environment. Conversely, the insulator 47 must promote the extraction of calories from the electronic components 33 to the heat sink 25.

[0043] In this embodiment, the thin copper track 49 comprises the first face 44 of the substrate 31 and accommodates one or more electronic components 33, the electronic components 33 being sintered or soldered onto the first face 44 of the substrate 31. The thin track 49 incorporates conductive tracks allowing the interconnection of the electronic components 33.

[0044] The electronic power module 23 therefore comprises, in one embodiment, a solder 55, also called a soldered joint, or a sintered joint, between the electronic components 33 and the substrate 31.

[0045] The electronic component(s) 33 are, for example, semiconductor chips, and / or diodes, and / or transistors.

[0046] In addition to an interconnection by the substrate 31, the internal connections of the electronic components can be made by wires 57, by ribbons or by clips.

[0047] Additionally, a power connection 59 and a signal connection 61 may be connected to the substrate 31 and exit the housing 29 to a power supply or other electronic component.

[0048] The gel 35 makes it possible to keep the electronic components 33 in contact with the substrate 31, and to protect the thin conductive track 49.

[0049] The nut 37 has the same internal diameter as the external diameter of the rod 41. The tapping of the nut 37 is also complementary with the thread of the threaded rod 41. The nut 37 is for example assembled directly in the material of the housing 29. The thickness of the nut 37 is for example identical to the thickness of the wall 39 in which it is held. The nut 37 is held in the wall 39 so as to create a passage between the interior and the exterior of the electronic power module 23. It is preferably positioned in a wall 39 opposite the first face 44 of the substrate 31. The nut 37 is preferably positioned opposite a central zone of the substrate 31. Indeed, a central zone of the substrate 31 is more likely to be the zone where the deformation 27 of the substrate 31 is the greatest.The nut 37 must not be positioned directly opposite electronic components 33, the base 43 then not being able to be fixed aligned with the nut 37.

[0050] The base 43 is transferred to the substrate 31, for example on the thin copper track 49, and optionally by a brazed or sintered joint 55. The base 43 is positioned aligned with the longitudinal axis of the threaded rod 41.

[0051] The base 43 is configured to receive one end of the threaded rod 41. In one embodiment, the base is a stud of similar cross-sectional size to the cross-section of the rod 41.

[0052] Thus, the threaded rod 41 is held axially by its thread in the nut 37, the thread functioning as a brake. The rod 41 can nevertheless be manipulated in rotation so as to move along its longitudinal axis. For this purpose, the rod 41 comprises a gripping head 63 by which the rotation can be applied by a tool or an operator.

[0053] In the embodiment illustrated in Figure 2, a concave deformation 27 of the substrate is shown, the deformation 27 preventing optimal contact between the substrate 31 and the heat sink 25. A longitudinal movement of the threaded rod 41 then makes it possible to press said rod 41 against the base 43, and finally to push the substrate 31 in the opposite direction to the deformation 27. The deformation 27 is thus reduced, as illustrated in Figure 3. An advantage of the threaded rod 41 is to be able to reduce the deformation 27 after the assembly of the power electronic module 23: the deformation 27 can be compensated at any time by a few turns of the threaded rod 41. The threaded rod 41 is chosen according to its thread, the latter having to allow sufficient axial movement to move the rod 41 longitudinally without too many turns during the rotation of the rod 41 being necessary.In particular, the pitch of the thread can be chosen as a function of the extent of the deformation 27. Preferably, the pitch of the thread is less than twice the deformation 27 measured so as to apply at least half a turn of the rod 41 to compensate for the deformation 27.

[0054] Preferably, the gel 35 covers the substrate 31 over a thickness of gel not filling the entire volume of the housing 29, the base 43 having a length greater than the thickness of the gel. This makes it possible to avoid degradation of the lifetime of the gel 35 by creation of air bubbles.

[0055] Figure 4 shows the steps of the method for compensating for the deformation of a substrate 31 of an electrical power module 23 according to the invention.

[0056] First, a step 65 is carried out for measuring the flatness of the substrate 31, in other words a step 27 for measuring the deformation.

[0057] A step 67 is then carried out for choosing a thread for the rod 41, then a step 69 for determining the number of rotations to be applied to the rod 41, and finally a step 71 for screwing the threaded rod 41 so as to press on the base 43 with said rod 41 and to reduce the deformation 27 of the substrate 31.

[0058] Optionally, a step 73 is carried out to verify the compensation of the deformation 27 by measuring the thermal impedance of the electrical power module 23. A thermal impedance showing an improvement in heat dissipation means that the deformation 27 has been reduced.

Claims

CLAIMS 1. Power electronics module (23) comprising a housing (29), a substrate (31), at least one electronic component (33) attached to the substrate (31), a gel (35) encapsulating said electronic component (33) on the substrate (31) and in the housing (29), characterized in that it comprises a threaded nut (37) held in a wall (39) of the housing (29), a threaded rod (41) extending through the nut (37) inside and outside the housing (29), and a base (43) attached to the substrate (31) and aligned with the longitudinal axis of the rod (41), the electronic component (33) and the base (43) being attached to the substrate (31) by a brazed or sintered joint (55).

2. Module according to claim 1, in which the gel (35) covers the substrate (31) over a thickness of gel, the length of the base (43) being greater than the thickness of gel.

3. Module according to one of claims 1 and 2, in which the substrate (31) is fixed to the housing (29) by fixing means positioned at the ends of said substrate (31).

4. Module according to any one of claims 1 to 3, in which the substrate (31) is an electrically insulated and thermally conductive metal substrate.

5. Module according to any one of claims 1 to 4, in which the substrate (31) comprises a copper plate (45) 1 to 3 millimeters thick, an insulator (47) 100 to 200 microns thick, and a thin track (49) of metallized copper on which said electronic component (33) and the base (43) are attached.

6. Module according to any one of claims 1 to 5, in which the housing (29) comprises a plastic material.

7. Assembly (21) comprising a power electronics module (23) according to any one of claims 1 to 6 and a heat sink (25), the substrate (31) of the power electronics module (23) comprising a thermal interface (53) with the heat sink (25), the thermal interface (53) promoting the evacuation of the heat generated by the electronic component (33) towards the heat sink (25).

8. Method for compensating for a deformation (27) of a substrate (31) of an electrical power module (23) according to any one of claims 1 to 6, or of an assembly (21) according to claim 7, comprising a step (65) of measuring the flatness of the substrate (31), a step (67) of choosing a thread for the rod (41), a step (69) of determining the number of rotational turns to be applied to the rod (41), and a step (71) of screwing the threaded rod (41) so as to press on the base (43) with said rod (41) and to reduce the deformation (27) of the substrate (31).

9. Method according to claim 8, further comprising a step (73) of verifying the compensation of the deformation (27) by measuring the thermal impedance of the electrical power module

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