Power module having a stiffening frame

Abstract

The present invention relates to a power module (10) comprising: - a substrate (11), - electronic components (13) transferred onto the substrate (11), - a stiffening frame (25) assembled, in particular soldered, onto 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) arranged inside the encapsulation space (26), for coating the electronic components (13).

Description

DESCRIPTION TITLE: POWER MODULE EQUIPPED WITH A RIGIDIFICATION FRAME

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

[0002] As is known per se, power modules allow several electronic components to be integrated within the same housing 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] Figure 1 is a schematic sectional view of a power module 10 mounted on a heat sink 15. More specifically, the power module 10 comprises a substrate 11 providing various functions, in particular a function of mechanically holding semiconductor chips or other electronic components 13, a function of electrical connections, a function of accommodating a protective cover and / or a function of accommodating an encapsulation solution, as well as a heat exchange function with a cooling device.

[0004] The substrate 11 may be assembled on a sole 12, in particular in the case of a ceramic substrate. The sole 12 is arranged on the heat sink 15, by means of a thermal interface material 18. Alternatively, the substrate 11 may be mounted directly on a heat sink 15, for example for an SMI type substrate, acronym for “Insulated Metal Substrate”.

[0005] The electronic components 13 are constituted, for example, by chips made of semiconductor material and / or standard components, such as resistors, capacitors and / or coils. The electronic components 13 are transferred to the substrate 11. A standard technique consists, in particular, of transferring the electronic components 13 to 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 may, in particular, be produced via a wire bonding process. The electrical interconnections 14 may also be produced using clips attached by sintering. According to such 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 making it possible to protect the electronic components 13 against attacks caused by an environment in which the power module 10 is located.

[0009] Conventionally, the encapsulation material 20 can take the form of a gel, an epoxy resin and / or a coating of an insulating material suitable for being applied to the electronic components 13. The encapsulation material 20 is also known by the English term “coating”.

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

[0011] The substrate 11 has a general conformation making it necessary to create walls to hold the encapsulation material 20 around the electronic components 13 to be protected. A conventional technique for producing the walls consists of gluing a retaining ring, in particular made of plastic, also known by the Anglo-Saxon name of “ring frame”.

[0012] In particular, the SMI type substrate 11 comprises a copper plate one or more millimeters thick, on which is laminated an insulator, for example with a thickness of approximately 100 μm, on which are metallized electrical tracks, particularly copper, used for transferring electronic components 13.

[0013] During the soldering operation of electronic components, a low thickness and rigidity of an SMI type substrate 11 can lead to deformation of the substrate, also known as “warping”. Such deformation of the substrate 11 reduces the heat transfer performance of the substrate 11 to the heat sink 15 due to the deformation of a contact zone 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 method of bonding the retaining ring of the encapsulation material 20 may generate production drifts, such as bubbles in the gel of the encapsulation material 20, adhesion problems, drips, etc.

[0016] Preparation of the surface of the substrate 11, application of the glue, as well as polymerization of the glue requiring passages in the oven, increase, 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 cause deterioration 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 transferred to the substrate, - a stiffening frame assembled, in particular soldered, on the substrate, and extending at least partially around the electronic components, so as to delimit an encapsulation space, and - an encapsulation material disposed inside the encapsulation space to coat the electronic components.

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

[0020] Furthermore, the invention makes it possible to simplify and reduce the duration of the manufacturing process by eliminating the steps linked 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 a coefficient of thermal expansion of the substrate. Alternatively, the stiffening frame has a coefficient of thermal expansion close to a coefficient of thermal expansion of the substrate.

[0022] According to another aspect of the invention, the stiffening frame comprises: - at least one horizontal wall, extending parallel to an extension plane of the substrate, 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, arranged 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 produced 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 on the stiffening frame.

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

[0027] According to another aspect of the invention, the substrate is an insulated metal substrate.

[0028] According to another aspect of the invention, the encapsulating material is an encapsulating 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 comprises at least one mounting interface allowing passage of a fixing member ensuring fixing of the power module to the heat sink.

[0031] According to another aspect of the invention, the stiffening frame comprises a support wall against which a snap-in device rests, making it possible to press the power module against the heat sink.

[0032] The present invention will be better understood and other characteristics and advantages will become apparent upon reading the detailed description which follows, comprising embodiments given for illustrative purposes with reference to the appended figures, presented as non-limiting examples, which may serve to supplement the understanding and the description of the embodiment of the present invention and, where appropriate, contribute to its definition, in which: - [Fig. 1] Figure 1, already described, is a schematic sectional view of a power module mounted on a heat sink; - [Fig. 2a] [Fig. 2b] Figures 2a and 2b are respectively top and sectional views along 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 top and sectional views along a section plane BB of a power module according to the invention comprising a stiffening frame; - [Fig. 4] Figure 4 is a schematic sectional view of a power module mounted on a heat sink by snap-fitting; and - [Fig. 5] Figure 5 is a diagram of the steps of a method of manufacturing 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 references. Thus, unless otherwise stated, such elements have identical structural, dimensional and material properties.

[0034] Figures 2a and 2b are respectively top and 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 attached to 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 an insulator is laminated, for example with a thickness of approximately 10Oprn, on which copper tracks are metallized for the transfer of the electronic components 13.

[0036] Alternatively, the substrate 11 may 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 coils. The electronic components 13 can be transferred by soldering to the substrate 11 or by any other suitable techniques.

[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 may be made via a wire wiring 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 the substrate 11, in particular onto a metal part of the substrate 11.

[0042] The brazing between the stiffening frame 25 and the substrate 11 implies that the metallic connection between the stiffening frame 25 and the substrate 11 is established without melting the elements assembled together. Depending on the case, there may be a use, as required, of a filler metal having a melting temperature lower than that of the elements to be assembled together.

[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 coat or encapsulate the electronic components 13 in order to protect them.

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

[0046] According to the example presented for purely illustrative and non-limiting purposes, the stiffening frame 25 may have a rectangular or square shape. The stiffening frame 25 thus comprises four sides 25.1-25.4. The stiffening frame 25 comprises two sides 25.1, 25.3 parallel to each other, each extending close to and parallel to a corresponding edge of the substrate 11. The stiffening frame 25 also comprises two other sides 25.2, 25.4 parallel to each other, respectively extending close to 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 Figure 2b, in sectional view, the stiffening frame 25 may comprise at least one horizontal wall 29, or first horizontal wall 29, extending parallel to a plane of extension of the substrate 11. The horizontal wall 29 is, in particular, brazed onto the substrate 11. The stiffening frame 25 may also comprise at least one vertical wall 30, or first vertical wall 30, extending in a vertical plane perpendicular to the plane of extension to 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 makes it possible to ensure 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 a height of the highest 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] Alternatively or additionally, as illustrated in Figure 4, the stiffening frame 25 may further comprise a second vertical wall 30' extending parallel to the first vertical wall 30 so as to have a U-shaped cross-section.

[0053] Alternatively or additionally, as illustrated in Figure 4, the stiffening frame 25 may further comprise a second horizontal wall 29' parallel to the horizontal wall 29 so as to have a C-shaped or inverted C-shaped cross-section.

[0054] Alternatively or additionally, as illustrated in Figure 4, the second horizontal wall 29' extends between the first vertical wall 30 and the second vertical wall 30' so as to have 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 to or close to a coefficient of thermal expansion of the substrate 11. More specifically, the material of the stiffening frame 25 has a coefficient of thermal expansion identical to 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 thermal expansion coefficients 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 aluminum or stainless steel.

[0060] It is then possible that a surface treatment is necessary so that the stiffening frame 25 is 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 presented 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" is meant a brazing or welding area of ​​small size, for example a surface of 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 may be perpendicular and mechanically connected to at least one of the two sides of the stiffening frame 25.

[0066] In 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 arranged, in particular a significant degree of pollution, a protective cover 44 may be arranged to protect the electronic components 13, in particular the sensitive electronic components 13, in particular against dust and dirt from the external environment, as shown in FIG. 4.

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

[0070] The protective cover 44 advantageously comprises shapes, such as, for example, dovetail shapes, intended to cooperate with complementary shapes produced on the stiffening frame 25. The protective cover 44 can thus be mounted by snap-fastening 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 fixing means, in particular by screwing or gluing or any other suitable fixing means.

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

[0073] For this purpose, the stiffening frame 25 may comprise at least one mounting interface 45, capable of allowing passage of a fixing member 46, such as a screw, in order to ensure fixing of the power module 10 on the heat sink 15.

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

[0075] According to an alternative or complementary mounting method, the stiffening frame 25 may comprise a support wall 49 against which a snap-fastening device 50 bears, making it possible to press the power module 10 against the heat sink 15.

[0076] For this purpose, the support wall 49 can be constituted by the second horizontal wall 29', capable of 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 90 degrees, relative to the first vertical wall 30.

[0078] The snap-on device 50 comprises at least one flexible blade 51 intended to come into contact with 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 installing 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 bear against the support wall 49, exerting a pressing 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] Figure 5 is a flow chart of a method of manufacturing the power module 10 according to the present invention.

[0083] The manufacturing method comprises 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 method also comprises at least one assembly step 101, during which the stiffening frame 25 and the electronic components 13 are assembled, in particular soldered, on 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 soldered, on the substrate 11 at the same time as the electronic components 13. During the assembly, in particular the soldering, of the stiffening frame 25 on 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 over the entire periphery of the stiffening frame 25.

[0087] The manufacturing method also comprises 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 method may also include at least one covering step 103, during which the protective cover 44 is mounted on the stiffening frame 25.

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

[0090] Of course, the various features, variants and / or embodiments of the present invention may be combined with each other in various combinations to the extent that 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 may be envisaged by those skilled in the art 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

CLAIMS 1. Power module (10) comprising: - a substrate (11), - electronic components (13) transferred onto the substrate (11), the power module (10) further comprising: - a stiffening frame (25) assembled, in particular soldered, 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) arranged inside the encapsulation space (26) to coat the electronic components (13), - characterized in that the substrate (11) is an insulated metal substrate, and in that the stiffening frame (25) is made of a metal material having a thermal expansion coefficient identical to or close to a thermal expansion coefficient 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) comprises at least one assembly point (35) arranged 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 produced 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) comprises shapes intended to cooperate with complementary shapes produced on the stiffening frame (25), so as to allow snap-fitting 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) comprises at least one mounting interface (45) allowing passage of a fixing member (46) ensuring fixing 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-fastening device (50) bears, making it possible to press the power module (10) against the heat sink (15).

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