Power module comprising semiconductor components with a temperature sensor and associated manufacturing method

Description

Technical field of the invention

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

[0002] There figure 1 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 base 19 is brazed onto the lower metallization 17 by an upper face 20 of said base 19, and a housing 21 is fixed onto said metal base 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, 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 local temperature increases.

[0009] Furthermore, during the module's life cycles, thermomechanical stresses can lead to the initiation and propagation of cracks in their structure. This cracking can occur 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 base plate 19. It causes an increase in the thermal resistance of the component below which the crack propagates and, consequently, 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 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 custom-made, which leads to high prices.

[0012] Attaching the sensor to the component itself or near it on the substrate can impact the electrical performance of the component, has limited reliability during thermal cycling of the module, and does not have very good sensitivity to cracking occurring under the component. GB 2 479 942 A shows a power module consisting of a copper plate supporting ceramic substrates. Presentation of the invention

[0013] The invention aims to overcome 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: a plurality of semiconductor power components, a substrate comprising an upper metallization receiving the components and a lower metallization opposite the upper metallization, optionally, a sole attached to the lower metallization of the substrate, a metal structure in direct contact with a lower face defined by the sole or the substrate, on a side opposite the components, a metal structure in direct contact with the lower face, and at least one elongated temperature sensor, at least partially embedded in the metal structure and extending parallel to the lower face, wherein the metal structure is formed by electrodeposition on the underside and the sensor is elongated.

[0015] 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 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.

[0016] In addition, the electroformed metal structure directly on the underside and the sensor constitutes a continuous link between said underside of the sole or substrate on the one hand and the optical fiber on the other hand. The thermal and mechanical contact is thus continuous between the substrate or sole and the optical fiber, without requiring an intermetallic bonding interface that could disturb the temperature measurements. This also allows for a well-controlled thermal contact resistance, unlike the case where the fiber is inserted into a space formed in the sole for example, thus allowing reproducible and reliable measurement on the different components.

[0017] Furthermore, unlike soldering, the electroforming process is carried out at low temperature (for example around 60°C), which limits the risks of degradation of the optical fiber and its performance.

[0018] The elongated sensor can extend to the right of the components, to benefit from improved sensitivity.

[0019] The structure can be made preferably of copper, and alternatively of nickel, silver, or any copper alloy compatible with an electrodeposition method.

[0020] 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.

[0021] Such a structure has a simple shape to manufacture, allowing a simplified and robust integration of the elongated sensor into the power module.

[0022] A radiator can be attached to the plate, on the side opposite the underside, for example by means of a layer of thermal interface material.

[0023] The metal structure may be a heat radiator extending over at least a portion of the underside.

[0024] Such a feature allows the elongated sensor to be directly embedded in the radiator structure, which can be directly manufactured on the underside by electrodeposition.

[0025] The presence of the elongated sensor then disrupts the operation of the radiator very little, thanks to its close integration into the material.

[0026] Each elongated sensor may comprise an optical fiber, and in particular is a Bragg grating fiber optic sensor or a Rayleigh backscattering fiber optic sensor.

[0027] Such a feature allows temperature monitoring at a plurality of points with a single elongated sensor, along its extent, with a spatial resolution of the order of a millimeter.

[0028] Each optical fiber can have an external diameter of less than 100 micrometers and has a profile adapted so that the optical fiber can achieve a bending radius of less than or equal to 5 millimeters.

[0029] Such a feature allows the optical fiber to follow a strongly curved contour without generating internal stresses that disrupt the signal, to optimize its path on the lower surface and measure the temperature of as many components as possible per fiber. Each elongated sensor can include at least one thermocouple.

[0030] The power module may comprise as many thermocouples as there are power components, each thermocouple being advantageously arranged in line with one of the components.

[0031] The invention also relates to a method of manufacturing a power module as above, the method comprising the following steps: providing a substrate having an upper metallization intended to receive semiconductor power components and a lower metallization opposite the upper metallization, and, optionally, a sole attached to the lower metallization of the substrate, the sole or the substrate having a lower face opposite the components, placing at least one elongated sensor on the lower face, forming the metallic structure by electrodeposition on the lower face and on the elongated sensor.

[0032] 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.

[0033] The radiator may be secured via a layer of thermal interface material. The metal structure may be a thermal radiator in which each elongate sensor is at least partially 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 and, optionally, of a mask on part of the lower face, and after the formation of the metal structure, removal of the preform and, where appropriate, of the mask.

[0034] Removal of the mask and preform can be done by chemical or thermal dissolution.

[0035] The process is simple to implement, unlike the case of creating a channel to embed the fiber under the components (in the substrate or the sole), with a width between 100µm and 500µm. In practice, such a channel often has a fairly complex shape, especially if the components are not aligned, as is often the case, and requires costly technical steps to create it (two plates to be soldered together, very high-precision additive manufacturing techniques, etc.).

[0036] The module obtained by the process according to the invention is thus more reliable by eliminating the brazing used to make the attachment joints between the different constituent elements, and does not require the creation of fragile intermetallic interfaces, with no risk of cracking in the brazing. Brief description of the figures

[0037] [ Fig. 1 ] there figure 1is a schematic sectional view of a power module according to the state of the art, [ Fig. 2 ] there figure 2 is a schematic sectional view of a power module according to a first embodiment of the invention, [ Fig. 3 ] there figure 3 is a schematic sectional view from below of the power module of the figure 1 , [ Fig. 4 ] there figure 4 is a schematic sectional view from below of a power module according to a second embodiment of the invention, [ Fig. 5 ] there Figure 5 is a schematic sectional view of a power module according to a third embodiment of the invention, and [ Fig. 6 ] there figure 6 is a schematic sectional view from below of the power module of the Figure 5 . Detailed description of the invention

[0038] There figure 2represents 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.

[0039] 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.

[0040] The lower metallization 47 is brazed onto a metal base 49 which carries a housing 51 covering and protecting the components 37.

[0041] 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.

[0042] A metal structure 56 extends in direct contact with the lower face 54 of the sole 49.

[0043] 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. Alternatively, the metal structure 56 can be made of nickel, silver, copper alloy, or any other metal compatible with electroplating.

[0044] 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.

[0045] 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.

[0046] The elongated sensor 58 includes at least one elongated portion that extends in a curved line through the metal structure 56.

[0047] 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 the figure 3 , which is away from said metal structure 56.

[0048] Each optical fiber 59 is for example surrounded by a copper capillary which is itself integrated into the metallic structure 56 during its formation by electrodeposition.

[0049] The path of the optical fiber 59 along the lower face 54 of the sole is shown in more detail on the figure 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.

[0050] The elongated sensor 58 is, for example, a Bragg grating fiber optic temperature sensor or a Rayleigh backscattering fiber optic sensor.

[0051] According to a variant not shown, the sensor 58 may comprise several optical fibers extending along the lower surface 54 along different paths from one another. 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.

[0052] 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.

[0053] Each network allows for local temperature measurement. It is therefore possible to measure a multitude of temperature points on a single optical fiber.

[0054] 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.

[0055] These two types of fibers are both sensitive to temperature and deformation. The tight integration of the fiber 59 into the metal structure 56 makes it possible to block deformations of the fiber 59, ensuring that the measured signal corresponds only to a temperature variation.

[0056] 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.

[0057] The method comprises a step of fixing a portion of the elongated sensor 58, for example the optical fiber 59, on the lower face 54.

[0058] The optical fiber 59 is advantageously housed in a protective capillary, in particular in a metallic capillary, such as a copper capillary.

[0059] The optical fiber 59 is for example fixed by gluing.

[0060] The optical fiber 59 follows a path on the lower face 54 advantageously passing in line with each of the components 37.

[0061] 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 next step.

[0062] The method then comprises a step of forming the metal structure 56, here a metal plate of substantially constant thickness.

[0063] 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.

[0064] 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.

[0065] A power module 31 according to a second embodiment of the invention is shown in the figure 4 . This power module 31 is identical to that previously described, except as follows.

[0066] 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.

[0067] The manufacturing process of this power module 31 is similar to the previous process, with elongated sensors of a different nature.

[0068] A power module 31 according to a third embodiment of the invention is shown in the Figures 5 and 6 .

[0069] This power module 31 is identical to the module according to the first embodiment of the invention, except for the following.

[0070] 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.

[0071] The metal radiator has an elongated U-shape in a plane parallel to the lower face 54, as shown in the figure 6 , and extends to the right of each of the components 37.

[0072] The radiator has a substantially rectangular external section in a plane transverse to its extent, as shown in the Figure 5 The height of the radiator, measured perpendicular to the lower face 54, is for example between 10 micrometers and 10 millimeters.

[0073] 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.

[0074] The radiator is for example made of copper, or alternatively of copper alloy, or any other metal compatible with electroplating.

[0075] 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.

[0076] The method includes a preliminary step of manufacturing a preform intended to shape the radiator.

[0077] 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.

[0078] The preform is, for example, made by additive manufacturing from a polymer material. The preform is then attached to the underside and covered with a thin layer of metallization. The thin layer has a thickness of a few micrometers and is formed using a conventional method, such as sputtering, evaporation, or vaporization. This thin layer allows the formation of the metal structure on the preform by electrodeposition.

[0079] A mask is then applied to a portion of the lower face 54 over which the radiator is not intended to extend. The mask is, for example, a polymer film, on which electrodeposition is impossible.

[0080] 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.

[0081] 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.

[0082] The preform and mask are then removed, either mechanically when possible, or by chemical and / or thermal dissolution.

[0083] 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

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

2. Power module (31) according to claim 1, wherein the metal structure (56) is a plate spreading over at least one part of the lower surface (54), where the plate has a thickness, measured perpendicular to said lower surface (54), that is substantially constant over the extension thereof.

3. Power module (31) according to claim 1, wherein the metal structure (56) is a thermal radiator extending over at least a portion of the lower surface (54).

4. Power module (31) according to one of the preceding claims, wherein each elongated sensor (58) comprises an optical fiber (59), and in particular is a Bragg network optical fiber sensor or a Rayleigh backscattering optical fiber sensor.

5. Power module (31) according to claim 4, wherein each optical fiber (59) has an outer diameter less than 100 µm and has a suitable profile so that the optical fiber (59) has a radius of curvature less than or equal to 5 mm.

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

7. Fabrication method for a power module (31) according to one of the preceding claims, the method comprising the following steps: - supplying 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 baseplate (49) attached to the lower metallization of the substrate, where the baseplate (49) or the substrate has a lower surface opposite the components (37); - placement of at least one elongated sensor (58) on the lower surface (54); - formation of the metal structure (56) by electrodeposition on the lower surface (54) and on the elongated sensor (58).

8. Method according to the previous claim, wherein the metal structure (56) is a plate of substantially constant thickness, the method further comprising a step of attachment of a radiator (53) to the plate, on the side opposite the lower surface (54).

9. Method according to claim 7 wherein the metal structure (56) is a thermal radiator in which each elongated sensor (58) is at least partially embedded, the method comprising the steps of: - preparation, in particular by additive fabrication, of a preform suited for shaping the thermal radiator; - placement of the preform on the lower surface (54) and, optionally, placement of a mask on a portion of the lower surface (54); and - subsequent to the formation of the metal structure (56), withdrawal of the preform and, as applicable, the mask.