Semiconductor power module incorporating a temperature sensor and associated manufacturing process

Abstract

Semiconductor power module incorporating a temperature sensor and associated manufacturing process. Power module (31) comprising: - a plurality of semiconductor power components (37), - a substrate (33) comprising an upper metallization (45) receiving the components (37) and a lower metallization (47) opposite the upper metallization (45), - optionally, a base plate (49) fixed to the lower metallization (47) of the substrate (33), - a metallic structure (56) in direct contact with a lower face (54) defined by the base plate (49) or the substrate (33), on a side opposite the components (37), and - at least one elongated temperature sensor (58), at least partially embedded in the metallic structure (56) and extending parallel to the lower face (54). Figure to be published with the abbreviation: 2

Description

Title of the invention: Power module with semiconductor components integrating a temperature sensor and associated manufacturing method Technical field of the invention

[0001] The invention relates to the field of electrical power modules comprising semiconductor components. Such modules are in particular intended for the aeronautical field. State of the prior art

[0002] [Fig.l] illustrates a power module 1 according to the state of the art. The power module 1 comprises a substrate 3 comprising an upper face 5 receiving semiconductor power components 7.

[0003] The components 7 are for example power switches (in particular insulated gate field effect transistors, or insulated gate bipolar transistors), connected to each other by wiring wires 9 and connected to connectors 11 themselves connected to a control card (not shown) configured to control said components 7.

[0004] The substrate 3 is for example a ceramic substrate, which comprises an insulating ceramic layer 13 separating an upper metallization 15, on which the components 5 are soldered, from a lower metallization 17.

[0005] A sole 19 is brazed onto the lower metallization 17 by an upper face 20 of said sole 19, and a housing 21 is fixed onto said metal sole 19 and covers the upper metallization 15 and the components 5. The housing 21 is crossed by the connectors 11.

[0006] In order to have satisfactory heat dissipation for the power module 1, a radiator 23 is fixed to a lower face 24 of the sole 19, to the lower face 9, by means of a layer of thermal interface material 25 covering said lower face 9.

[0007] Indeed, due to their imperfections, the power components 5 are the site of thermal losses by Joule effect and therefore represent a significant source of heat.

[0008] During operation of the power module 1, the electrical properties of the components 3 may vary in different ways (due to premature aging of certain components, manufacturing defects, etc.), leading to significant disparity. This disparity may result in dissipated powers that may be higher in certain components, thus leading to increases in temperature. local temperatures.

[0009] Furthermore, during the life cycles of the module, thermomechanical stresses can lead to the initiation and propagation of cracks in their structure. This cracking can take place in the solder between the components 5 and the substrate 3, in the substrate 3 or in the solder between the substrate 3 and the sole 19. It causes an increase in the thermal resistance of the component below which the crack propagates and, consequently, to a temperature disparity between the components. If these local temperature deviations are not detected quickly, they can lead to thermal runaway of the module, resulting in its total failure.

[0010] Solutions using temperature sensors have been developed to monitor temperature increases in the power module during its operation and thus prevent overheating.

[0011] Integrating such a sensor directly into the semiconductor component limits the possibilities to a small number of components available on the market and greatly reduces the possibilities of adapting the power modules, which must be made to measure, which leads to high prices.

[0012] Attaching the sensor to the component itself or in close proximity to it on the substrate may impact the electrical performance of the component, has limited reliability during thermal cycles of the module, and does not have very good sensitivity to cracking occurring under the component. Presentation of the invention

[0013] The invention aims to remedy these drawbacks by improving temperature control in the power module without significantly reducing the efficiency of heat dissipation or disrupting the operation of the module.

[0014] To this end, the invention relates to a power module comprising:

[0015] - a plurality of semiconductor power components,

[0016] - a substrate comprising an upper metallization receiving the components and a lower metallization opposed to upper metallization,

[0017] - optionally, a sole fixed to the lower metallization of the substrate,

[0018] - a metallic structure in direct contact with a lower face defined by the sole or substrate, on one side opposite the components,

[0019] - a metal structure in direct contact with the lower face, and

[0020] - at least one elongated temperature sensor, at least partially embedded in the metal structure and extending parallel to the underside.

[0021] Such a power module allows temperature monitoring of each component, allowing improved detection and localization of thermal problems in the power module. The number of sensors required to monitor all the The number of components is reduced, and the sensors are embedded in the metal structure, which improves the accuracy of temperature measurement and greatly reduces their impact on heat dissipation.

[0022] The elongated sensor can extend in line with the components, to benefit from improved sensitivity.

[0023] The structure may preferably be made of copper, and alternatively of nickel, silver, or any copper alloy compatible with an electrodeposition method.

[0024] The metal structure may be a plate extending over at least a portion of the lower face, the plate having a thickness, measured perpendicular to said lower face, substantially constant over its extent.

[0025] Such a structure has a simple shape to manufacture, allowing simplified and robust integration of the elongated sensor into the power module.

[0026] A radiator may be attached to the plate, on the side opposite the lower face, for example by means of a layer of thermal interface material.

[0027] The metal structure may be a thermal radiator extending over at least a portion of the lower face.

[0028] Such a feature makes it possible to directly embed the elongated sensor in the structure of the radiator, which can be directly manufactured on the lower face by electrodeposition.

[0029] The presence of the elongated sensor then disrupts the operation of the radiator very little, thanks to its close integration into the material.

[0030] Each elongate sensor may comprise an optical fiber, and in particular is a Bragg grating fiber optic sensor or a Rayleigh backscattering fiber optic sensor.

[0031] Such a feature makes it possible to monitor the temperature at a plurality of points with a single elongated sensor, along its extent, with a spatial resolution of the order of a millimeter.

[0032] Each optical fiber may have an external diameter of less than 100 micrometers and have a profile adapted so that the optical fiber can achieve a radius of curvature of less than or equal to 5 millimeters.

[0033] Such a characteristic makes it possible to make the optical fiber follow a strongly curved contour without generating internal stresses disturbing the signal, to optimize its path on the lower surface and measure the temperature of as many components as possible per fiber.

[0034] Each elongated sensor may comprise at least one thermocouple.

[0035] The power module can include as many thermocouples as power components, each thermocouple being advantageously arranged at right angles of one of the components.

[0036] The invention also relates to a method of manufacturing a power module as above, the method comprising the following steps:

[0037] - provision of a substrate having an upper metallization intended to receive semiconductor power components and a lower metallization opposite the upper metallization, and, optionally, a base plate attached to the lower metallization of the substrate, the base plate or substrate having a lower face opposite the components,

[0038] - installation of at least one elongated sensor on the lower face,

[0039] - formation of the metallic structure by electrodeposition on the lower face and on the elongated sensor.

[0040] The metal structure may be a plate of substantially constant thickness, the method further comprising a step of fixing a radiator to the plate, on the side opposite the components.

[0041] The radiator may be secured via a layer of thermal interface material.

[0042] The metal structure may be a thermal radiator in which each elongated sensor is at least partly embedded, the method comprising steps of:

[0043] - preparation, in particular by additive manufacturing, of a preform suitable for shape the thermal radiator,

[0044] - placing the preform on the lower face and, optionally, a mask on a part of the lower face, and

[0045] - after the formation of the metal structure, removal of the preform and, if applicable, the mask.

[0046] Removal of the mask and preform can be carried out by chemical or thermal dissolution. Brief description of the figures

[0047] [Fig-1] [Fig.l] is a schematic sectional view of a power module according to the state of the art,

[0048] [Fig.2] [Fig.2] is a schematic sectional view of a power module according to a first embodiment of the invention,

[0049] [Fig.3] [Fig.3] is a schematic sectional view from below of the power module of [Fig.l],

[0050] [Fig.4] [Fig.4] is a schematic sectional view from below of a power module according to a second embodiment of the invention,

[0051] [Fig.5] [Fig.5] is a schematic sectional view of a power module according to a third embodiment of the invention, and

[0052] [Fig.6] [Fig.6] is a schematic sectional view from below of the power module of [Fig.5]. Detailed description of the invention

[0053] [Fig. 2] represents a power module 31 according to the invention. In a manner identical to that described above, the power module 31 comprises a substrate 33 defining an upper face 35 onto which semiconductor power electronic components 37 are soldered, connected by wiring wires 39 and connectors 41.

[0054] The substrate 33 comprises a ceramic layer 43 extending between an upper metallization 45, on which the components 37 and the connectors 41 are soldered, and a lower metallization 47.

[0055] The lower metallization 47 is brazed onto a metal sole 49 which carries a housing 51 covering and protecting the components 37.

[0056] The sole 49 has an upper face 50 on which the substrate is brazed and a lower face 54 which extends on the side opposite the substrate 33.

[0057] A metal structure 56 extends in direct contact with the lower face 54 of the sole 49.

[0058] The metal structure 56 is, in the first embodiment, a substantially rectangular metal plate, made of copper deposited on the lower face 54 by electro-formation.

[0059] Alternatively, the metal structure 56 can be made of nickel, silver, copper alloy, or any other metal compatible with electroplating.

[0060] Said metal plate has a thickness that is substantially constant over its extent, measured perpendicular to the lower face 54, for example between 10 micrometers and 10 millimeters.

[0061] The power module 31 comprises at least one elongated temperature sensor 58, at least partly embedded in the metal structure 56, and extending along the lower face 54.

[0062] The elongated sensor 58 includes at least one elongated portion that extends in a curved line through the metal structure 56.

[0063] In the first embodiment, the elongated sensor 58 is a fiber optic temperature sensor, which comprises an optical fiber 59, embedded in the metal structure 56 and a control module 60, shown in [Fig. 3], which is spaced from said metal structure 56.

[0064] Each optical fiber 59 is for example surrounded by a copper capillary which is itself integrated into the metal structure 56 during its formation by electrodeposition.

[0065] The path of the optical fiber 59 along the lower face 54 of the sole is shown in more detail in [Fig. 3]. The optical fiber 59 follows a curved path advantageously passing directly past each of the semiconductor power components 37, in order to measure their temperature.

[0066] The elongated sensor 58 is for example a Bragg grating fiber optic temperature sensor or a Rayleigh backscattering fiber optic sensor.

[0067] According to a variant not shown, the sensor 58 may comprise several optical fibers extending along the lower surface 54 along paths that are different from each other.

[0068] Each optical fiber 59 advantageously has an external diameter of less than 100 micrometers and has a profile adapted so that the fiber can achieve a radius of curvature of less than or equal to 5 millimeters. This allows the optical fiber 59 to follow a tortuous path closely following the components 37.

[0069] It is recalled that the principle of a Bragg grating fiber consists of locally modifying the refractive index of the fiber core, thus creating a series of gratings (Bragg gratings). Each grating reflects a specific wavelength different from the other gratings. Each grating makes it possible to measure a temperature locally. It is therefore possible to measure a multitude of temperature points on a single optical fiber.

[0070] It is also recalled that a Rayleigh backscattering fiber exploits the imperfections intrinsically present in the fiber (due to heterogeneities generated during manufacturing). These imperfections induce backscattering along the fiber (similar to the presence of weakly reflecting mirrors along the fiber). The exploitation of this backscattering signal makes it possible to measure a physical phenomenon (temperature or deformation) and its location.

[0071] These two types of fibers are both sensitive to temperature and to deformation. The close integration of the fiber 59 in the metal structure 56 makes it possible to block the deformations of the fiber 59, ensuring that the measured signal corresponds only to a variation in temperature.

[0072] A method of manufacturing the power module 31 will now be described. The method comprises a preliminary step of providing and assembling the substrate 33 and the sole 49, which will not be described further because it is well known in the prior art.

[0073] The method comprises a step of fixing a part of the elongated sensor 58, for example the optical fiber 59, on the lower face 54.

[0074] The optical fiber 59 is advantageously housed in a protective capillary, in particular in a metal capillary, such as a copper capillary.

[0075] The optical fiber 59 is for example fixed by gluing.

[0076] The optical fiber 59 follows a path on the lower face 54 advantageously passing in line with each of the components 37.

[0077] In the case where the optical fiber 59 is housed in a non-metallic capillary, the method comprises a step of depositing a thin layer of metallization on said capillary. The thin layer has a thickness of a few micrometers, and is formed according to a conventional method by cathode sputtering, evaporation or vaporization, for example. This thin layer allows the formation of the metallic structure on the capillary in the following step.

[0078] The method then comprises a step of forming the metal structure 56, here a metal plate of substantially constant thickness.

[0079] The metal structure 56 is formed by electrodeposition in an electrolytic bath, on the lower face 54 and the optical fiber 59, in order to embed said optical fiber in said metal structure 56. This makes it possible to have excellent thermal contact between the metal structure 56 and the optical fiber 59, as well as to ensure the mechanical maintenance of the optical fiber 59.

[0080] After the formation of the metal plate 56, a radiator 53 is fixed to said metal plate 56, on the side opposite the sole 49, for example by means of a thermal interface material 55.

[0081] A power module 31 according to a second embodiment of the invention is shown in [Fig.4]. This power module 31 is identical to that previously described, except for the following.

[0082] In this embodiment, the elongated sensor 58 comprises a plurality of thermocouples 62, in particular as many thermocouples as components 37, connected to a control module 64. The thermocouples 62 are advantageously located in line with each of the components 37, in the vicinity of the lower face 54 of the sole 49, and embedded in the electrodeposited metal layer.

[0083] The manufacturing process of this power module 31 is similar to the previous process, with elongated sensors of a different nature.

[0084] A power module 31 according to a third embodiment of the invention is shown in Figures 5 and 6.

[0085] This power module 31 is identical to the module according to the first embodiment of the invention, with the exception of the following.

[0086] In the third embodiment, the metal structure 56 is a thermal radiator directly formed by electrodeposition on the lower face 54 of the sole 49, in which the optical fiber 59 of the elongated sensor 58 is embedded.

[0087] The metal radiator has an elongated U-shape in a plane parallel to the lower face 54, as shown in [Fig.6], and extends in line with each of the components 37.

[0088] The radiator has a substantially rectangular external section in a plane transverse to its extent, as shown in [Fig. 5]. The height of the radiator, measured perpendicular to the lower face 54, is for example between 10 micrometers and 10 millimeters.

[0089] The radiator defines a central channel 66 designed to receive the circulation of a cooling fluid, and improve heat dissipation. The internal channel 66 has, for example, a square or rectangular cross-section. The dimensions of the section of the internal channel 66 are, for example, between 10 micrometers and 10 millimeters.

[0090] The radiator is for example made of copper, or alternatively of copper alloy, or any other metal compatible with electroplating.

[0091] The method of manufacturing the power module 31 according to the third embodiment will now be described, identical to the method of manufacturing the power module according to the first embodiment except for the following.

[0092] The method comprises a preliminary step of manufacturing a preform intended to shape the radiator.

[0093] The preform is for example an elongated element which reproduces the shape of the internal channel 66, so that the preform constitutes a negative of the final shape of the radiator.

[0094] The preform is for example produced by additive manufacturing from a polymer material.

[0095] The preform is then fixed to the lower face and covered with a thin layer of metallization. The thin layer has a thickness of a few micrometers, and is formed according to a conventional method by cathode sputtering, evaporation or vaporization, for example. This thin layer allows the formation of the metallic structure on the preform by electrodeposition.

[0096] A mask is then applied to a portion of the lower face 54 on which the radiator is not intended to extend. The mask is for example a polymer film, on which electrodeposition is impossible.

[0097] The elongated sensor 58 is then placed on a region of the lower face on which the radiator will be formed, and possibly metallized if necessary, as previously described.

[0098] The radiator is then formed by electrodeposition in an electrolytic bath on the unmasked region of the lower face 54, on the preform and on the elongated sensor 58, until the desired thickness of metal is deposited to form the radiator of the desired height.

[0099] The preform and the mask are then removed, either mechanically when possible, or by chemical and / or thermal dissolution.

[0100] According to a variant, the methods according to the two embodiments described can be implemented on a power module not comprising a base, the deposition of the metallic structure 56 taking place directly on the lower metallization 47 of the substrate 33.

Claims

Claims

1. Power module (31) comprising: - a plurality of semiconductor power components (37), - a substrate (33) comprising an upper metallization (45) receiving the components (37) and a lower metallization (47) opposite the upper metallization (45), - optionally, a sole (49) fixed to the lower metallization (47) of the substrate (33), - a metal structure (56) in direct contact with a lower face (54) defined by the sole (49) or the substrate (33), on a side opposite the components (37), and - at least one elongated temperature sensor (58), at least partially embedded in the metal structure (56) and extending parallel to the lower face (54), wherein the metal structure (56) is formed by electrodeposition on the lower face (54) and the elongated sensor (58).

2. Power module (31) according to claim 1, in which the metallic structure (56) is a plate extending over at least a portion of the lower face (54), the plate having a thickness, measured perpendicular to said lower face (54), substantially constant over its extent.

3. The power module (31) of claim 1, wherein the metal structure (56) is a heat sink extending over at least a portion of the lower face (54).

4. A power module (31) according to any preceding claim, wherein each elongate sensor (58) comprises an optical fiber (59), and in particular is a Bragg grating fiber optic sensor or a Rayleigh backscattering fiber optic sensor.

5. Power module (31) according to claim 4, in which each optical fiber (59) has an external diameter less than 100 micrometers and has a profile adapted so that the optical fiber (59) can achieve a radius of curvature less than or equal to 5 millimeters.

6. Power module (31) according to one of claims 1 to 3, wherein each elongated sensor (58) comprises at least one thermocouple.

7. A method of manufacturing a power module (31) according to one of the preceding claims, the method comprising the following steps: - providing a substrate (33) having an upper metallization (45) intended to receive semiconductor power components (37) and a lower metallization (47) opposite the upper metallization, and, optionally, a sole (49) fixed to the lower metallization of the substrate, the sole (49) or the substrate having a lower face opposite the components (37), - placing at least one elongated sensor (58) on the lower face (54), - forming the metallic structure (56) by electrodeposition on the lower face (54) and on the elongated sensor (58).

8. Method according to the preceding claim, in which the metal structure (56) is a plate of substantially constant thickness, the method further comprising a step of fixing a radiator (53) to the plate, on the side opposite the lower face (54)

9. Method according to claim 7, in which the metal structure (56) is a thermal radiator in which each elongated sensor (58) is at least partly embedded, the method comprising steps of: - preparation, in particular by additive manufacturing, of a preform suitable for shaping the thermal radiator, - placement of the preform on the lower face (54) and, optionally, of a mask on a part of the lower face (54), and - after the formation of the metal structure (56), removal of the preform and, where appropriate, of the mask.

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