POWER MODULE EQUIPPED WITH A RIGIDIFICATION FRAME

Abstract

The present invention relates to a power module (10) comprising: a substrate (11), electronic components (13) mounted on the substrate (11), a stiffening frame (25) assembled, in particular brazed, on the substrate (11) and extending at least partially around the electronic components (13), so as to define an encapsulation space (26), and an encapsulation material (20) disposed within the encapsulation space (26), for encasing the electronic components (13). Figure 2b

Description

Title of the invention: POWER MODULE EQUIPPED WITH A RIGIDIFICATION FRAME

[0001] The present invention relates to a power module equipped with a stiffening frame. The invention finds a particularly advantageous, but not exclusive, application in the field of power modules having an electrical signal conversion function.

[0002] In a manner known per se, power modules allow the integration of several electronic components within the same package to perform more or less complex functions, such as a switch function for a chopper, a rectifier bridge arm function or a complete rectifier bridge function for a set of phases of a polyphase electrical signal.

[0003] Fig. 1 is a schematic cross-sectional view of a power module 10 mounted on a heat sink 15. More specifically, the power module 10 includes a substrate 11 providing various functions, in particular a mechanical holding function for semiconductor chips or other electronic components 13, an electrical connection function, a function for accommodating a protective cover and / or an accommodating an encapsulation solution, as well as a heat exchange function with a cooling device.

[0004] The substrate 11 can be assembled on a base 12, particularly in the case of a ceramic substrate. The base 12 is disposed on the heat sink 15, via a thermal interface material 18. Alternatively, the substrate 11 can be mounted directly on a heat sink 15, for example for an SMI type substrate, an acronym for "Insulated Metallic Substrate".

[0005] The electronic components 13 consist, for example, of semiconductor material chips and / or standard components such as resistors, capacitors, and / or inductors. The electronic components 13 are transferred onto the substrate 11. A standard technique, in particular, consists of transferring the electronic components 13 onto the substrate 11 by soldering.

[0006] Electrical interconnections 14 are made, in particular, between the electronic components 13 and electrical tracks of the substrate 11 and between the electronic components 13 and power terminals 16 and / or control terminals 17.

[0007] The electrical interconnections 14 can, in particular, be made via a wire bonding process. The electrical interconnections 14 can also be made using clips attached by sintering. According to such a technology, an electrical wire, also called a bridge, is welded, for example by ultrasound, between two elements to be electrically connected to each other.

[0008] An assembly thus constituted is embedded in an encapsulation material 20 allowing the electronic components 13 to be protected against aggressions caused by an environment in which the power module 10 is located.

[0009] Classically, the encapsulation material 20 can take the form of a gel, an epoxy resin and / or a coating of an insulating material suitable for application to the electronic components 13. The encapsulation material 20 is also known by the Anglo-Saxon term "coating".

[0010] A housing 21 closes the assembly thus formed. The housing 21 may carry some of the power terminals 16 and / or the control terminals 17.

[0011] The substrate 11 has a general conformation that necessitates the creation of walls to retain the encapsulation material 20 around the electronic components 13 to be protected. A conventional technique for creating these walls involves bonding a retaining ring, particularly made of plastic, also known by the Anglo-Saxon term "ring frame".

[0012] In particular, the SMI type substrate 11 comprises a copper plate of one or more millimeters thick, on which is laminated an insulator, for example of a thickness of about 1000m, on which are metallized electrical tracks, in particular of copper, used for transferring the electronic components 13.

[0013] During the soldering operation of electronic components, the thinness and rigidity of an SMI-type substrate 11 can lead to substrate deformation, also known as "warping." Such deformation of the substrate 11 reduces the heat transfer performance from the substrate 11 to the heat sink 15 due to the deformation of a contact area between the substrate 11 and the heat sink 15.

[0014] Such deformation is difficult to model a priori and is sometimes linked to production parameters that are difficult to control. Thus, unpredictable variabilities may appear during production.

[0015] Furthermore, a bonding process for the retaining ring of the encapsulation material 20 can generate production deviations, such as bubbles in the gel of the encapsulation material 20, adhesion problems, drips, etc...

[0016] A preparation of the surface of the substrate 11, a deposition of the glue, as well as a polymerization of the glue requiring oven passages, increases, in particular by several hours, the duration of the manufacturing process of the power module 10.

[0017] Since the glue has a limited lifespan, aging of the glue can generate degradation of the mechanical strength of the power module 10, or of its sealing.

[0018] The invention aims to effectively remedy the aforementioned drawbacks by proposing a power module comprising: - a substrate, - electronic components mounted on the substrate, - a stiffening frame assembled, notably brazed, onto the substrate, and extending at least partially around the electronic components, so as to delimit an encapsulation space, and - an encapsulation material placed inside the encapsulation space to encase the electronic components.

[0019] The invention thus makes it possible, thanks to the presence of the stiffening frame, to reduce the deformation effects of the substrate which decrease the thermal conductivity of the power module with the heat sink.

[0020] In addition, the invention makes it possible to simplify and reduce the duration of the manufacturing process by eliminating the steps related to the bonding of the retaining ring of the encapsulation material, which are a preparation of the supports, an application of an adhesive and a polymerization phase.

[0021] According to one embodiment of the invention, the stiffening frame has a coefficient of thermal expansion identical to that of the substrate. Alternatively, the stiffening frame has a coefficient of thermal expansion close to that of the substrate.

[0022] According to another aspect of the invention, the stiffening frame comprises: - at least one horizontal wall, extending parallel to a plane of substrate extension, and / or - at least one vertical wall, extending in a vertical plane relative to the substrate.

[0023] According to another aspect of the invention, the stiffening frame comprises at least one assembly point, in particular a brazing or welding point, disposed between two opposite sides of the stiffening frame.

[0024] According to one embodiment of the invention, the assembly point, in particular the brazing or welding point, is made on a contact portion originating from a branch of the stiffening frame extending at least partially between the two opposite sides of the stiffening frame.

[0025] According to another aspect of the invention, a protective cover is fixed to the stiffening frame.

[0026] According to another aspect of the invention, the protective cover comprises shapes intended to cooperate with complementary shapes made on the stiffening frame so as to allow snap-fit ​​mounting of the protective cover onto the stiffening frame.

[0027] According to another aspect of the invention, the substrate is an isolated metallic substrate.

[0028] According to another aspect of the invention, the encapsulation material is an encapsulation gel.

[0029] The invention also relates to an assembly comprising: - a power module as previously defined, and - a heat sink.

[0030] According to another aspect of the invention, the stiffening frame includes at least one mounting interface allowing passage of a fastening element ensuring the fastening of the power module onto the heat sink.

[0031] According to another aspect of the invention, the stiffening frame comprises a support wall against which a snap-fit ​​device rests, allowing the power module to be pressed against the heat sink.

[0032] The present invention will be better understood and other features and advantages will become apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the accompanying figures, presented by way of non-limiting examples, which may serve to complete the understanding and explanation of the embodiment of the present invention and, where appropriate, contribute to its definition, on which: - [Fig.l] The [Fig.l], already described, is a schematic cross-sectional view of a power module mounted on a heat sink; - [Fig. 2a] [Fig. 2b] Figures 2a and 2b are respectively views of top and in section according to a section plane AA of a power module according to the invention comprising a stiffening frame; - [Fig. 3a] [Fig. 3b] Figures 3a and 3b are respectively views of top and in section according to a BB section plane of a power module according to the invention comprising a stiffening frame; - [Fig. 4] Fig. 4 is a schematic cross-sectional view of a module of power mounted on a snap-on heat sink; and - [Fig. 5] [Fig. 5] is a diagram of the steps in a manufacturing process of a power module according to the invention.

[0033] It should be noted that, in the figures, the structural and / or functional elements common to the different embodiments have the same reference numerals. Thus, unless otherwise stated, such elements have identical structural, dimensional and material properties.

[0034] Figures 2a and 2b are respectively top and cross-sectional views along a section plane AA of the power module 10 according to the invention comprising a stiffening frame 25. More particularly, Figures 2a and 2b show a power module 10 comprising the substrate 11 and electronic components 13 mounted on the substrate 11. In particular, the substrate 11 has a plate shape.

[0035] The substrate 11 is, in particular preferably, an SMI type substrate comprising a copper plate, in particular having a thickness of one or more millimeters, on which is laminated an insulator, for example of a thickness of about 1000m, on which are metallized copper tracks for transferring the electronic components 13.

[0036] Alternatively, the substrate 11 can take the form of a ceramic substrate or any other suitable type of substrate.

[0037] The electronic components 13 may comprise semiconductor chips and / or standard components, such as resistors, capacitors, and / or inductors. The electronic components 13 may be transferred to the substrate 11 by soldering or by any other suitable technique.

[0038] The electrical interconnections 14 are made, in particular, between the electronic components 13 and electrical tracks 19 of the substrate 11 and between the electronic components 13 and the power terminals 16 and / or the control terminals 17.

[0039] The electrical interconnections 14 can be made via a wire cabling process.

[0040] The power module 10 may also include a connector 22.

[0041] The power module 10 further comprises the stiffening frame 25, in particular brazed onto substrate 11, in particular onto a metallic part of substrate 11.

[0042] The brazing between the stiffening frame 25 and the substrate 11 implies that the metallic bond between the stiffening frame 25 and the substrate 11 is established without melting the elements being joined together. Depending on the circumstances, a filler metal with a melting point lower than that of the elements to be joined together may be used as needed.

[0043] The stiffening frame 25 extends, at least partially, around the electronic components 13 so as to delimit an encapsulation space 26. The encapsulation space 26 may advantageously have a closed circumference.

[0044] The encapsulation material 20 is arranged inside the encapsulation space 26 delimited by the stiffening frame 25 to encase or encapsulate the electronic components 13 in order to protect them.

[0045] The encapsulation material 20 is preferably an encapsulation gel. Alternatively, the encapsulation material 20 may be in the form of an epoxy resin or a coating of an insulating material suitable for such an application.

[0046] According to the example given by way of illustration only and not limitation, the stiffening frame 25 may have a rectangular or square shape. The stiffening frame 25 thus has four sides 25.1-25.4. The stiffening frame 25 has two parallel sides 25.1, 25.3, each extending close to and parallel to a corresponding edge of the substrate 11. The stiffening frame 25 also has two other sides 25.2, 25.4 parallel to each other extending respectively near and parallel to a corresponding edge of the substrate 11. The sides 25.1-25.4 are mechanically connected to each other.

[0047] Alternatively, the stiffening frame 25 may have a round, oval, triangular, hexagonal, more generally polygonal shape or any other shape adapted to the shape of the substrate 11 and / or to the shape of the encapsulation space 26 to be filled by the encapsulation material 20.

[0048] According to the example illustrated in [Fig. 2b], in cross-sectional view, the stiffening frame 25 may include at least one horizontal wall 29, or first horizontal wall 29, extending parallel to an extension plane of the substrate 11. The horizontal wall 29 is, in particular, brazed to the substrate 11. The stiffening frame 25 may also include at least one vertical wall 30, or first vertical wall 30, extending in a vertical plane perpendicular to the extension plane of the substrate 11.

[0049] A brazing zone 31 extends along each side 25.1-25.4 of the stiffening frame 25.

[0050] The vertical wall 30 provides a barrier to the flow of the encapsulation material 20. For this purpose, the vertical wall 30 has a height greater, for example, by a few millimeters than the height of the tallest electronic component 13 to be encapsulated.

[0051] In the example shown, the stiffening frame 25 has an L-shaped cross-section corresponding to an angle-shaped profile.

[0052] As an alternative or in addition, as illustrated in [Fig.4], the stiffening frame 25 may further comprise a second vertical wall 30' extending parallel to the first vertical wall 30 so as to present a U-shaped cross-section.

[0053] As an alternative or in addition, as illustrated in [Fig.4], the stiffening frame 25 may further comprise a second horizontal wall 29' parallel to the horizontal wall 29 so as to present a cross-section in the shape of a C or inverted C.

[0054] Alternatively or in addition, as illustrated in [Fig.4], the second horizontal wall 29' extends between the first vertical wall 30 and the second vertical wall 30' so as to present a rectangular or square cross-section.

[0055] Preferably, the stiffening frame 25 is made of a metallic material. The material of the stiffening frame 25 has a coefficient of thermal expansion identical or close to that of the substrate 11. More specifically, the material of the stiffening frame 25 has a coefficient of expansion thermal identical or close to a coefficient of thermal expansion of the metal plate of the substrate 11 in the case of an SMI type substrate.

[0056] Such a configuration makes it possible to limit a differential expansion effect between the stiffening frame 25 and the substrate 11.

[0057] Preferably, for an SMI type substrate comprising a copper plate, the stiffening frame 25 is also made of copper.

[0058] It is also possible to use different materials but having coefficients of thermal expansion close to the metal plate of the substrate 11.

[0059] For example, for an SMI type substrate 11 comprising a copper plate, the stiffening frame 25 can be made of aluminium or stainless steel.

[0060] It is then possible that a surface treatment may be necessary to make the stiffening frame 25 compatible with the metallic material of the substrate 11.

[0061] Figures 3a and 3b are respectively top and sectional views along a section plane BB of the power module 10 according to the invention comprising the stiffening frame 25 capable of being provided with at least one assembly point 35, in particular a brazing or welding point 35. In the embodiment shown in Figures 3a and 3b, the assembly point 35 is arranged between two opposite sides of the stiffening frame 25.

[0062] By "brazing or welding point 35", it is understood that there is a small brazing or welding area, for example an area on the order of ten to one hundred square millimeters.

[0063] The assembly point 35 can be made on a contact portion 36 originating from a branch 37 of the stiffening frame 25. The branch 37 of the stiffening frame 25 extends, for example, longitudinally between two opposite sides of the stiffening frame 25.

[0064] In particular, the branch 37 of the stiffening frame 25 is able to extend at least partially between the two opposite sides of the stiffening frame 25.

[0065] In particular, the branch 37 of the stiffening frame 25 can be perpendicular and mechanically connected to at least one of the two sides of the stiffening frame 25.

[0066] In cross-sectional view, the contact portion 36 has a horizontal wall 40, on which the assembly point 35 is made, and a vertical wall 41, originating from the horizontal wall 40 and connected to the branch 37 of the stiffening frame 25.

[0067] The contact portion 36 may have, for example, a T-shaped cross-section or an L-shaped cross-section.

[0068] Depending on the external environment in which the power module 10 is located, particularly a high degree of pollution, a protective cover 44 may be provided to protect the electronic components 13, in particular the 13 sensitive electronic components, particularly with regard to dust and dirt from the external environment, as shown in [Fig.4].

[0069] The protective cover 44 is suitable for being fixed to the stiffening frame 25.

[0070] The protective cover 44 advantageously has shapes, such as, by For example, dovetail shapes, designed to cooperate with complementary shapes made on the stiffening frame 25. The protective cover 44 can thus be snapped onto the stiffening frame 25 to simplify the assembly operation.

[0071] Alternatively, the protective cover 44 can be fixed to the stiffening frame 25 by other means of fixing, in particular by screwing or gluing or any other suitable means of fixing.

[0072] Fig. 4 is a schematic cross-sectional view of the power module 10 mounted on a heat sink 15.

[0073] For this purpose, the stiffening frame 25 may include at least one mounting interface 45, suitable for allowing the passage of a fastening element 46, such as a screw, in order to secure the power module 10 to the heat sink 15.

[0074] The mounting interface 45 can take the form of protruding ears provided with a through hole for the fixing member 46.

[0075] According to an alternative or complementary mounting method, the stiffening frame 25 may include a support wall 49 against which a snap-fit ​​device 50 rests, allowing the power module 10 to be pressed against the heat sink 15.

[0076] For this purpose, the support wall 49 can be constituted by the second horizontal wall 29', suitable for forming the square or rectangular cross-section of the stiffening frame 25.

[0077] More generally, the support wall 49 is a wall forming a non-zero angle, preferably of 90 degrees, with respect to the first vertical wall 30.

[0078] The snap-fit ​​device 50 includes at least one flexible blade 51 intended to bear against the support wall 49 of the stiffening frame 25.

[0079] Thus, an operator is likely to move the flexible blade 51 away from the heat sink 15 by elastic deformation, so as to free up space for the installation of the power module 10.

[0080] Once the power module 10 is in place against the heat sink 15, the operator releases the flexible blade 51, so that the flexible blade 51 comes to rest against the support wall 49 by exerting a clamping force on the power module 10.

[0081] The power module 10 is then held pressed against the heat sink 15 by the flexible blade 51.

[0082] Fig. 5 is a diagram of the steps of a manufacturing process for the power module 10 according to the present invention.

[0083] The manufacturing process includes at least one positioning step 100, during which the electronic components 13 and the stiffening frame 25 are positioned on the substrate 11.

[0084] The manufacturing process also includes at least one assembly step 101, during which the stiffening frame 25 and the electronic components 13 are assembled, in particular brazed, onto the substrate 11. The assembly step 101 may in particular be by a reflow soldering technique or any other suitable technique.

[0085] The stiffening frame 25 can be assembled, in particular brazed, onto the substrate 11 at the same time as the electronic components 13. During the assembly, in particular brazing, of the stiffening frame 25 onto the substrate 11, it is possible to keep the substrate 11 flat to impose a zero curvature on it.

[0086] In the case of assembly by brazing, the latter is preferably carried out on the entire periphery of the stiffening frame 25.

[0087] The manufacturing process also includes at least one encapsulation step 102, during which the encapsulation material 20, such as gel, is deposited, and in particular polymerized, in the encapsulation space 26 delimited by the stiffening frame 25.

[0088] The manufacturing process may also include at least one capping step 103, during which the protective hood 44 is mounted on the stiffening frame 25.

[0089] The manufacturing process may also include at least one fixing step 104, during which the power module 10 is assembled onto the heat sink 15, in particular by screwing and / or snapping.

[0090] Of course, the different features, variants and / or embodiments of the present invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive.

[0091] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms, and other variants that a person skilled in the art may consider within the scope of the present invention, and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination.

Claims

Demands

1. Power module (10) comprising: - a substrate (11), - electronic components (13) mounted on the substrate (11), the power module (10) further comprising: - a stiffening frame (25) assembled on the substrate (11) and extending at least partially around the electronic components (13), so as to delimit an encapsulation space (26), and - an encapsulation material (20) disposed inside the encapsulation space (26) to encase the electronic components (13), characterized in that the substrate (11) is an insulated metallic substrate, and in that the stiffening frame (25) brazed onto the substrate is made of a metallic material having a coefficient of thermal expansion identical or close to a coefficient of thermal expansion of the substrate (11).

2. Power module (10) according to claim 1, characterized in that the stiffening frame (25) comprises - at least one horizontal wall (29), extending parallel to an extension plane of the substrate (11), and / or - at least one vertical wall (30), extending in a vertical plane relative to the substrate (11).

3. Power module (10) according to any one of the preceding claims, characterized in that the stiffening frame (25) has at least one assembly point (35) disposed between two opposite sides of the stiffening frame (25).

4. Power module (10) according to claim 3, characterized in that the assembly point (35) is made on a contact portion (36) originating from a branch (37) of the stiffening frame (25) extending at least partially between the two opposite sides of the stiffening frame (25).

5. Power module (10) according to any one of the preceding claims, characterized in that a protective cover (44) is fixed to the stiffening frame (25).

6. Power module (10) according to claim 5, characterized in that the protective cover (44) has shapes intended to cooperate with complementary shapes made on the frame of stiffening (25), so as to allow snap-fit ​​mounting of the protective cover (44) onto the stiffening frame (25).

7. Power module (10) according to any one of the preceding claims, characterized in that the encapsulation material (20) is an encapsulation gel.

8. Assembly comprising a power module (10) according to any one of claims 1 to 7 and a heat sink (15).

9. Assembly according to claim 8, characterized in that the stiffening frame (25) includes at least one mounting interface (45) allowing passage of a fastening member (46) ensuring a fastening of the power module (10) on the heat sink (15).

10. Assembly according to claim 8 or 9, characterized in that the stiffening frame (25) comprises a support wall (49) against which a snap-fit ​​device (50) is pressed to allow the power module (10) to be pressed against the heat sink (15).

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