Pressure distribution composite film and method for distributing pressure force in a sintering process

Abstract

The invention relates to a pressure distribution composite film (DV) for distributing pressure force on a component (BE1, BE2), to be sintered on an electrical device (LM), during a sintering process, having: - a pressure distribution film (DF) for distributing the pressure force on the component (BE1, BE2) to be sintered; - a blocking layer (SS) on the pressure distribution film (DF), said blocking layer being fixedly joined to the pressure distribution film (DF) and being designed to prevent the deposition of the material of the pressure distribution film (DF) on the component (BE1, BE2) and / or the device (LM). The invention also relates to a method for sintering an electrical device with an above-mentioned pressure distribution composite film. The invention furthermore relates to a power electronics module, and to an inverter and a DC / DC converter, which are produced with the above-mentioned pressure distribution composite film using the above-mentioned method.

Description

[0001] Description

[0002] Pressure distribution film composite and method for distributing compressive force during a sintering process

[0003] Technical area:

[0004] The present invention relates to a pressure distribution film composite for distributing compressive force on an electrical device during a sintering process in which at least one (electrical or electronic) component is sintered onto the device. Furthermore, the invention relates to a method for pressure sintering an electrical device, in which the aforementioned pressure distribution film composite is used to distribute compressive force during the sintering process. Furthermore, the invention relates to a power electronics module, in particular a (power) inverter or a (power) DC-DC converter, specifically for an electric drive device of a motor vehicle, manufactured according to the aforementioned method.

[0005] State of the art and task of the invention:

[0006] Due to various advantages over soldering, such as higher load cycling strength or better thermal conductivity, sintering is becoming increasingly important for (power) electrical devices, especially in the field of power electronics, especially for electric drive technology. Especially for power modules with high-performance semiconductors, such as silicon carbide (SiC) or gallium nitride (GaN) semiconductors with high operating temperatures of more than 200°C, sintered joints provide a permanently stable bond between the semiconductors and the power module carrier thanks to their temperature resistance to temperatures exceeding 250°C.

[0007] In sintering, as in soldering or other known joining processes, the general requirement is for the highest possible yield (in English “First Pass Yield” (FPY)) after the sintering process.

[0008] The object of the present application is therefore to provide a method for a reliable sintering process with which electrical devices, especially power modules, can be manufactured with a high yield. Description of the invention:

[0009] This problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0010] According to a first aspect of the invention, a pressure distribution film composite is provided which is configured to (uniformly) distribute the compressive force (e.g. from a sintering pressure stamp) acting on the device and thus also on the component and consequently on the sintering paste during a sintering process in which at least one (electrical or electronic) sinterable component is sintered onto the device (e.g. a circuit carrier of the device) by means of at least one sintering paste.

[0011] The pressure distribution film composite has a pressure distribution film which is designed to (during the sintering process) distribute the above-mentioned pressure force on the at least one component and thus on the surface of the device (or on the surfaces of the circuit carrier and the component) and thus on the sintering paste (uniformly) on the at least one component and consequently on the surface (in particular over the entire surface) or over the entire area of ​​the sintering paste.

[0012] The pressure distribution film composite further comprises a barrier layer on the pressure distribution film, which is firmly connected to the pressure distribution film and is designed to prevent or at least reduce the evaporation of the material of the pressure distribution film and / or the deposition of the material of the pressure distribution film on the at least one component and / or on the device during the sintering process.

[0013] A sintering process usually takes place under the influence of pressure and temperature on the sintering layer (sintering paste), which is applied to the surface of the circuit carrier before sintering and is thus located between the component and the circuit carrier.

[0014] For a reliable sintering process, a uniform pressure distribution on the component to be sintered (or, in the case of multiple components to be sintered, a uniform pressure distribution across all components) is required during the sintering process. To achieve this, a so-called pressure distribution film made of a plastic, such as a fully fluorinated plastic film or a perfluoroalkoxy polymer film (PFA film), is placed on the component to be sintered (on all components to be sintered) before the actual sintering process. During the sintering process, a pressure stamp with a contour adapted to the component (or all components) is lowered onto this pressure distribution film and thus onto the component (or all components) and printed on the pressure distribution film and the component (or all components) with a predetermined pressure force of e.g. 20 MPa, required to create the sintered bond.At the same time, the sinter layer is heated to a specified temperature of, for example, 210°C. Under the influence of pressure and temperature, sinter particles (e.g., silver or copper particles) of the sinter layer bond with materials on the surfaces of the component and the circuit carrier through diffusion processes and are further compacted, thus forming a material-to-material sintered bond between the component (or components) and the surface of the circuit carrier. After the sintering process, the pressure stamp is moved away from the pressure distribution film, and the pressure distribution film is removed from the component (or components) and the circuit carrier.

[0015] During the sintering process, with a (pure) plastic-based pressure distribution film, the plastic material of the pressure distribution film evaporates under the aforementioned pressure or temperature influences and deposits uncontrollably on the surfaces of the component (or components) and the circuit carrier, thus contaminating the surfaces. This leads to defective production, as the sintered component-circuit carrier composite with contaminated surfaces is unsuitable for subsequent manufacturing processes or no longer functions properly, especially if the contaminated surfaces are intended for specific functions, e.g., the formation of electrical connections such as bond connections.

[0016] This problem is solved with the pressure distribution film composite described above, consisting of a pressure distribution film (made of a plastic, such as a fully fluorinated plastic film or a perfluoroalkoxy polymer film (PFA film)) and a barrier layer on the pressure distribution film. The pressure distribution film has the function of distributing the compressive force acting on a surface to be sintered over the surface (in particular evenly over the entire surface) (during the sintering process). The barrier layer, which is firmly bonded to the pressure distribution film, holds the material of the pressure distribution film in place during the sintering process and thus, on the one hand, reduces the evaporation of the material of the pressure distribution film during the sintering process and, on the other hand, prevents the evaporated material of the pressure distribution film from settling on the surfaces of the device, thus of the component (or components) and the circuit carrier.Consequently, contamination of the device surfaces and the component is prevented or reduced. The previously described production defects caused by contamination (from the material of the pressure distribution film) can thus be avoided or reduced.

[0017] This provides a possibility for a reliable sintering process with which electrical devices, especially power modules, can be manufactured with a high yield.

[0018] The pressure distribution film can be a fully fluorinated plastic film or a perfluoroalkoxy polymer film (PFA film).

[0019] The barrier layer can be a metallic layer or a layer of aluminum or a layer of an aluminum alloy.

[0020] The barrier layer can be applied to the pressure distribution film by physical vapor deposition (PVD), chemical vapor deposition (CVD), or fine powder coating (FPC) and firmly bonded to the pressure distribution film.

[0021] According to a second aspect of the invention, a method is provided for pressure sintering at least one (electrical or electronic) sinterable component, such as at least one sinterable power semiconductor component, onto an electrical device, e.g. a power electronics module, in particular a (power) inverter or a (power) DCZDC converter, specifically for an electric drive device of a motor vehicle.

[0022] According to the method, an electrical device is provided with a surface on which a sintered layer is formed. The at least one sinterable component is placed on the sintered layer. A previously described pressure distribution film composite is applied to the component and thus also to the device (or to the surface of the device and to a surface of the component facing away from the sintered layer). Depending on the properties of the device and the component, this composite film covers the surface of the component and / or exposed surface areas of the device.

[0023] Under the action of a compressive force via the pressure distribution film composite on the device and on the component, the component is sintered onto the surface of the device via the sintered layer, whereby the sintered layer, under the action of the compressive force, firmly connects the component to the surface of the device and thus to the device (sintered connection).

[0024] After the sintered connection has been established, the pressure distribution film composite is removed from the device and the component.

[0025] When the component is sintered onto the surface of the device, the material of the pressure distribution film of the pressure distribution film composite is at least partially evaporated under the influence of the compressive force. The barrier layer of the pressure distribution film composite prevents the evaporated material of the pressure distribution film from depositing on the component and / or the device or their surfaces.

[0026] In this case, the pressure distribution film composite is placed on the component or on the surface of the component facing away from the sintered layer and on the device or its surface in such a way that the pressure distribution film of the pressure distribution film composite faces the component and the device or their surfaces and the barrier layer of the pressure distribution film composite faces away from the component and the device or their surfaces.

[0027] According to a third aspect of the invention, a power electronics module is provided, in particular for a (power) inverter or a (power) DC / DC converter, especially an electric drive device of a motor vehicle.

[0028] The power electronics module (as the aforementioned at least one component) comprises at least one (sinterable) power semiconductor, such as a power semiconductor switch, specifically a silicon carbide (SiC) semiconductor switch or a gallium nitride (GaN) semiconductor switch, as well as a circuit carrier, e.g., a ceramic substrate, such as a DCB (Direct Copper Bonded Substrate) or AM B (Active Metal Brazed Substrate) substrate, or a metallic substrate, such as an IMS (Insulated Metal Substrate) substrate. The circuit carrier comprises a (sinterable) surface on which the at least one power semiconductor is arranged and sintered via a sinter layer according to the previously described method, thus firmly bonding it to the surface.

[0029] According to a fourth aspect of the invention, a (power) inverter, in particular for an electric drive device of a motor vehicle, is provided. The inverter has at least one previously described power electronics module and at least one driver circuit for operating the at least one power electronics module, which is electrically or signal-wise connected to the at least one power electronics module via at least one signal connection.

[0030] According to a fifth aspect of the invention, a (power) DC / DC converter is provided, in particular for an electric drive device of a motor vehicle. The DC / DC converter comprises at least one previously described power electronics module and at least one driver circuit for operating the at least one power electronics module, which is electrically or signal-wise connected to the at least one power electronics module via at least one signal connection.

[0031] Short description of the drawings:

[0032] An exemplary embodiment of the invention is explained in more detail below with reference to the accompanying drawings. In the drawings:

[0033] Figure 1 shows a schematic cross-sectional view of a section of a power module with a conventional pressure distribution foil during a sintering process; and

[0034] Figure 2 shows a further schematic cross-sectional view of the section of the power module from Figure 1 with a pressure distribution film composite according to an exemplary embodiment of the invention during the sintering process. Detailed description of the drawings:

[0035] Figure 1 shows a schematic cross-sectional view of a section of a power module LM with a conventional pressure distribution foil DF1 during a sintering process in which two power semiconductors BE1, BE2 are sintered onto a circuit carrier ST of the module LM.

[0036] For sintering, the circuit carrier ST or its surface OF intended for sintering—in this case, the surfaces of conductor tracks LB on the circuit carrier ST—is pre-coated with sintering pastes SP, which form the sintering layers onto which the power semiconductors BE1, BE2 are sintered. The sinterable power semiconductors BE1, BE2 with the corresponding sinterable surface are applied to the sintering pastes SP.

[0037] The subsequent sintering process takes place under pressure and temperature influences on the sinter layers or the sinter pastes SP.

[0038] The subsequent sintering process takes place under pressure on the sintered layers or the sintered pastes SP, by means of a pressure stamp (not shown in the figure) (shaped according to the top contour of the power module LM and all components located on it, including the two power semiconductors BE1, BE2) indirectly via the power semiconductors BE1, BE2, as well as under the influence of temperature. For this purpose, a so-called pressure stamp is provided, which is shaped according to the top contour of the (entire) power module LM and all components located on it, including the two power semiconductors BE1, BE2. During the sintering process, it is lowered onto the power module LM and thus the two power semiconductors BE1, BE2 and presses them onto these parts with a predetermined pressure force of, for example, 20 MPa.Furthermore, the power module LM and thus the two power semiconductors BE1, BE2 are heated to a predetermined temperature of, for example, 210°C.

[0039] For a reliable sintering process, a uniform pressure distribution on the sinter layers or the sinter pastes SP is required, which acts indirectly via the power semiconductors BE1, BE2 to be sintered on the corresponding sinter layers SP. For this purpose, before the actual sintering process, a so-called pressure distribution film DF1 made of a fully fluorinated plastic film, such as a perfluoroalkoxy polymer film, is placed on the power module LM and thus on the two power semiconductors BE1, BE2. During the sintering process, the pressure stamp is lowered onto this pressure distribution film DF1 and thus onto the power module LM and thus onto the two power semiconductors BE1, BE2 and printed with the specified pressure force onto the pressure distribution film DF1 and onto the power module LM including the two power semiconductors BE1, BE2. At the same time, the sintered layer is heated to the specified temperature.Under this pressure and temperature influence, the sintered particles of the sintered layers SP bond with the materials of the conductor tracks LB and the surfaces of the two power semiconductors BE1, BE2 through diffusion processes and become even more dense, thus forming integral sintered bonds between the conductor tracks LB on the one hand and the power semiconductors BE1, BE2 on the other. After the sintering process, the pressure stamp is moved away from the pressure distribution film, and the pressure distribution film DF1 is removed from the power module LM or the two power semiconductors BE1, BE2.

[0040] In the case of a (pure) pressure distribution film DF1 based on plastic, such as the previously mentioned fully fluorinated plastic film or the perfluoroalkoxy polymer film, it can happen during the sintering process that the plastic material of the pressure distribution film DF1 evaporates under the aforementioned pressure or temperature influence and deposits uncontrollably on the (exposed) surfaces OF, OF3 of the components, e.g. a component BE3, and the conductor tracks LB and the circuit carrier ST of the power module LM and thus on the (exposed) surfaces OF1, OF2 of the two power semiconductors BE1, BE2 and thus contaminates the surfaces LB, OF, OF1, OF2, OF3. This leads to defective production, since the power module LM with the contaminated surfaces LB, OF, OF1, OF2, OF3 is unsuitable for subsequent production processes or no longer functions properly, in particularif the contaminated surfaces LB, OF, OF1, OF2, OF3 are intended for certain (electrical) functions, for example for the formation of electrical connections such as bonds.

[0041] This problem is solved with a pressure distribution film composite DV from Figure 2. The pressure distribution film composite DV has a pressure distribution film DF, such as a fully fluorinated plastic film or a perfluoroalkoxy polymer film, and a barrier layer SS made of aluminum or an aluminum alloy, which lies on the pressure distribution film DF and is firmly bonded to it. The pressure distribution film DF has the same function as the pressure distribution film DF1 from Figure 1. The barrier layer SS, which is firmly bonded to the pressure distribution film DF, holds the material of the pressure distribution film DF during the sintering process and thus, on the one hand, reduces the evaporation of the material of the pressure distribution film DF during the sintering process and, on the other hand, also prevents the evaporated material of the pressure distribution film DF from settling on the surfaces OF, OF1, OF2, OF3 of the components LB, BE1, BE2, BE3.Consequently, contamination of the surfaces OF, OF1, OF2, and OF3 is prevented or reduced. The previously described production defects caused by contamination from the material of the pressure distribution film DF can thus be avoided or reduced.

[0042] This provides a possibility for a reliable sintering process with which the LM power modules can be manufactured with a high yield.

[0043] The pressure distribution film composite DV can be produced, for example, by physical vapor deposition or chemical vapor deposition or by fine powder coating of aluminum particles or aluminum-containing particles onto a pressure distribution film, such as a fully fluorinated plastic film or a perfluoroalkoxy polymer film.

Claims

Patent claims 1 . Pressure distribution film composite (DV) for distributing compressive force on a component (BE1, BE2) to be sintered on an electrical device (LM) during a sintering process, comprising: - a pressure distribution foil (DF) for distributing the pressure force on the component to be sintered (BE1, BE2); - a barrier layer (SS) on the pressure distribution film (DF), which is firmly connected to the pressure distribution film (DF) and is designed to prevent the material of the pressure distribution film (DF) from being deposited on the component (BE1, BE2) and / or the device (LM).

2. Pressure distribution film composite (DV) according to claim 1, wherein the pressure distribution film (DF) is a fully fluorinated plastic film or a perfluoroalkoxy polymer film.

3. Pressure distribution film composite (DV) according to claim 1 or 2, wherein the barrier layer (SS) is a metallic layer or a layer of aluminum or a layer of an aluminum alloy.

4. Pressure distribution film composite (DV) according to one of the preceding claims, wherein the barrier layer (SS) is applied to the pressure distribution film (DF) by physical vapor deposition or by chemical vapor deposition or by fine powder coating.

5. Method for sintering a component (BE1, BE2) onto an electrical device (LM), comprising the following method steps: - Providing the electrical device (LM) with a sintered layer (SP); - Placing the component (BE1, BE2) on the sintered layer (SP); - placing a pressure distribution film composite (DV) according to one of the preceding claims on the component (BE1, BE2); - sintering the component (BE1, BE2) via the sintered layer (SP) onto the device (LM) under the action of a compressive force via the pressure distribution film composite (DV) onto the component (BE1, BE2); - removing the pressure distribution film composite (DV) from the component (BE1, BE2) after the joining step; - wherein, during the sintering step, the material of the pressure distribution film (DF) of the pressure distribution film composite (DV) is at least partially evaporated; - wherein the barrier layer (SS) of the pressure distribution film composite (DV) prevents the evaporated material of the pressure distribution film (DF) from being deposited on the component (BE1, BE2) and / or on the device (LM).

6. Method according to claim 5, - wherein the step of applying further provides that the pressure distribution film composite (DV) is placed on the component (BE1, BE2) in such a way that the pressure distribution film (DF) of the pressure distribution film composite (DV) faces the component (BE1, BE2) and the barrier layer (SS) of the pressure distribution film composite (DV) faces away from the component (BE1, BE2).

7. Power electronics module (LM), comprising: - at least one power semiconductor (BE1, BE2); - a circuit carrier (ST) with a surface (OF) on which the at least one power semiconductor (BE1, BE2) is arranged and firmly connected; - wherein the at least one power semiconductor (BE1, BE2) is sintered on the surface (OF) using a method according to one of claims 5 to 6 and is firmly connected thereto.

8. Inverter, comprising: - at least one power electronics module (LM) according to claim 7; - at least one driver circuit for operating the at least one power electronics module (LM), which is electrically connected to the at least one power electronics module (LM) via at least one signal connection.

9. DC / DC converter, comprising: - at least one power electronics module (LM) according to claim 7; - at least one driver circuit for operating the at least one power electronics module (LM), which has at least one Signal connection with at least one Power electronics module (LM) is electrically connected.

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