Power module, inverter and method for producing a power module

Abstract

A power module (LM) is disclosed, comprising: - a power semiconductor element (LE) with a sinterable top-side electrical contact surface (KF1); - a bonding element (BE) with a sinterable underside (US) and a bondable upper side (OS) for producing a top-side bond connection (BV1); - a connecting element (VE) which is sinterable on both sides and is provided with a sinterable nanostructure (NS1) on the underside and a sinterable nanostructure (NS2) on the top and is sintered via the nanostructure (NS1) on the underside to the contact surface (KF1) of the power semiconductor element (LE) and via the nanostructure (NS2) on the top to the underside (US) of the bonding element (BE) and thus physically and electrically connects the bonding element (BE) to the contact surface (KF1) of the power semiconductor element (LE). Furthermore, an inverter with a power module (LM) and methods for producing a power module (LM) are described.

Description

Technical area:

[0001] The present invention relates to a power module, in particular for an inverter or a DC-DC converter, especially for an electric drive of a motor vehicle. Furthermore, the invention relates to an inverter with such a power module and a method for producing a power module. State of the art and object of the invention:

[0002] Power modules or power electronics modules with power semiconductor elements are well known and are used, among other things, in power electronics systems such as inverters or DC-DC converters, especially in electric motor vehicles. Such power modules are used, for example, in power inverters (product name: EPF2.8) from Vitesco Technologies GmbH.

[0003] As with almost all technical devices, there is a general requirement for a power module to increase its power density and thus make it more efficient.

[0004] The object of the present application is therefore to provide an efficient power module with a high power density. Description of the invention:

[0005] This problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the subclaims.

[0006] According to a first aspect of the invention, a power module or power electronics module is provided, in particular for an inverter or a DC-DC converter, especially of an electric drive of a motor vehicle.

[0007] The power module comprises a power semiconductor element or a power semiconductor switch with a sinterable top-side electrical contact surface and a bonding element with a sinterable bottom side and a bondable top side, wherein the top side serves as a bonding surface (for bonding a bonding wire or a bonding ribbon) for producing a top-side bond connection for the top-side contact surface of the power semiconductor element.

[0008] The power module further comprises a double-sided sinterable connecting element, which is provided with a sinterable nanostructure on the underside and a sinterable nanostructure on the top. The connecting element is sintered to the top contact surface via the underside nanostructure and to the bonding element via the top nanostructure, thus physically and electrically connecting the bonding element to the power semiconductor element or to its top contact surface.

[0009] For example, the bonding element is shaped like a plate or a metal plate and serves as a bond buffer.

[0010] The connecting element has in particular a central part as well as the underside and the upper side nanostructure, which are each formed distributed on respective opposite sides of the central part.

[0011] The connecting element serves as a joining element between the joining partners: the power semiconductor element and the bonding element, and provides the sintered connection between these two joining partners. After the sintering process, the connecting element thus physically connects the bonding element to the power semiconductor element with low resistance and thermally.

[0012] The connecting element on the top-side electrical contact surface of the power semiconductor element gives the contact surface mechanical strength and thus enables the use of the bonding element as a bond buffer, which, due to its functional requirements, has a significantly higher mechanical strength than the mere contact surface of the power semiconductor element, which could lead to a crack or pre-damage to the contact surface or the structures directly underneath without the said connecting element.

[0013] The nanostructures formed on both sides of the connecting element enable a highly dense microstructure between the joining partners—namely, the connecting element on the one hand, and the top-side electrical contact surface of the power semiconductor element and the bonding element on the other—with high electrical and thermal conductivity as well as high mechanical stability. This ensures reliable electrical contact between the top-side electrical contact surface of the power semiconductor element via the bonding element. This enables the use of a power semiconductor element with a higher power density and / or a smaller contact area, thus reducing the size of the power module.

[0014] The high thermal conductivity and high mechanical stability of the structure with the power semiconductor element also enable the use of a stiffer and therefore thicker bond connection and consequently also the use of a copper-based bond wire or bond ribbon, which has a higher current-carrying capacity (than an aluminum-based bond connection). In particular, the high mechanical stability enables the bond element to be subjected to a higher bonding force and, in the case of ultrasonic bonding, high ultrasonic energy used for bonding, particularly thanks to the use of the connecting element between the bond element and the top-side contact surface of the power semiconductor element and the stable sintered connection by the connecting element, which compensates for or reduces thermomechanical stress between the bond connection or the bond element on the one hand and the top-side contact surface of the power semiconductor element on the other.This also increases the lifetime of the aforementioned structure with the power semiconductor element and thus of the power module.

[0015] This provides an opportunity for an efficient power module with a high power density.

[0016] For example, the connecting element has a plate-shaped central part, in particular in the form of a metal plate, on the two opposite sides of which the underside and the topside nanostructure are each distributed.

[0017] For example, the underside and / or topside nanostructure each comprise a plurality of sinterable rod- or hair-shaped projections, each of which extends (at least partially or at their respective subsections) from a center plane of the connecting element or from the center part of the connecting element. The center plane of the connecting element is the central surface of the connecting element in which the longitudinal and transverse axes of the connecting element are located.

[0018] During the sintering process between the connecting element or its nanostructures formed on both sides, on the one hand, and the top contact surface of the power semiconductor element and the underside of the bonding element, on the other, the rod- or hair-shaped protrusions deform and diffuse with the contact surface of the power semiconductor element and the underside of the bonding element. This significantly densifies the microstructure and forms a physical connection between the aforementioned joining partners. This connection exhibits high electrical and thermal conductivity as well as high mechanical stability. Furthermore, it exhibits little to no organic contamination and is halogen-free.

[0019] Furthermore, after sintering, the rod- or hair-shaped projections elastically absorb any thermomechanical stresses that may exist between the bonding element and the contact surface of the power semiconductor element and thus contribute positively to the service life of the power module.

[0020] The diameters of the projections can be - with the exception of deviations due to manufacturing technology or manufacturing tolerances - less than 1 micrometer or less than 750 nanometers or less than 500 nanometers or less than 300 nanometers or approximately 100 nanometers.

[0021] The connecting element has, for example, a central part as a carrier body, preferably made of copper or a copper alloy, on both sides of which there is a coating of rod-shaped projections in nanometer size or nanorods.

[0022] The length, diameter, and density of the nanorods are variable and can be selected according to requirements. However, the diameters of the nanorods are in the nanometer range mentioned above. The central part can be made of various electrically conductive materials and can be coated with a metal such as copper, silver, gold, or nickel, or an alloy containing one or more of these metals. The metal coating can be applied by galvanic deposition, for example, after applying a sponge body with appropriate shapes to form the protrusions to the central part.

[0023] The connecting element, for example, is formed in one piece and consists of copper or a copper alloy.

[0024] The bonding element, for example, also consists of copper or a copper alloy.

[0025] The top-side bond connection can be established, for example, using a bond wire or a bond ribbon. The bond wire or bond ribbon can be made of copper or a copper alloy.

[0026] The power semiconductor element or the power semiconductor switch can be formed as a SiC (silicon carbide) semiconductor element or a SiC semiconductor switch or as a Si (silicon) semiconductor element or a Si semiconductor switch, but also as a GaN (gallium nitride) semiconductor element or a GaN semiconductor switch.

[0027] The use of the connecting element for sintering the bonding element or the bond buffer for the top contact surface of the power semiconductor element enables the use of a (significantly) small power semiconductor element with a high current density and current carrying capacity, such as the SiC semiconductor switch.

[0028] The power module may further comprise a substrate with a sinterable electrical contact surface. In this case, the power semiconductor element may have a sinterable electrical contact surface on the underside and be sintered onto the contact surface of the substrate via the underside contact surface and be physically and electrically connected to the contact surface of the substrate.

[0029] The substrate can be formed as a ceramic-based circuit carrier, such as a DCB substrate (Direct Copper Bonded Substrate) or AMB substrate (Active Metal Brazed Substrate), or a metal-based substrate, such as an IMS (Insulated Metal Substrate).

[0030] According to an exemplary embodiment, the bonding element and the connecting element can be formed in one piece.

[0031] According to another exemplary embodiment, the bonding element can be metallized with a metal layer made of a metallic material that differs from the base material of the bonding element. In particular, (only) the top side of the bonding element can be metallized with a metal layer made of a metallic material that differs from the base material of the bonding element.

[0032] According to yet another exemplary embodiment, the bonding element may comprise a plurality of metal layers made of different metals or metal alloys that are formed integrally with one another.

[0033] The connecting element and the bonding element create an upper-side electrical connection surface for the power semiconductor element, which is itself sufficiently rigid and mechanically stable and also provides the power semiconductor element or the structure consisting of the power semiconductor element, the connecting element and the bonding element with sufficient rigidity and mechanical stability so that an "external" electrical connection element, such as a bonding wire or a bonding ribbon, made of copper or comparable stiffer materials with a high current conductivity and a high current flow can be physically and electrically connected to it, without the power semiconductor element or the structure being damaged by mechanical stress on the connection element.

[0034] The material or material composition of the bonding element can be freely selected depending on the need or requirement. The top side of the bonding element can also be metallized differently with a suitable metallization depending on the need or requirement. Furthermore, the bonding element can be formed in one piece from several layers or material layers of different materials or material compositions. Accordingly, a power semiconductor element, which as a cost-effective standard semiconductor chip only has one predetermined material layer (or layer composite), such as an aluminum layer, for the top-side contact surface, can be "arbitrarily metallized" by the "free" material selection for the bonding element adapted to the need or requirement. A costly or technically hardly feasible metallization of the top-side contact surface of a standard semiconductor chip, such aswith gold, silver, palladium, copper, and / or tin, etc., can be realized using the comparatively cost-effective connecting element. Consequently, a commercially available, cost-effective standard semiconductor chip can be used for various technical requirements for the top-side contacting of the power semiconductor element.

[0035] According to a second aspect of the invention, an inverter or power inverter, especially for an electric drive of a motor vehicle, is provided.

[0036] The inverter comprises one or more previously described power modules and one or more driver circuits for operating the power module(s). The driver circuit(s) are (each) electrically or signal-wise connected to the respective power module(s) via one or more control signal connections.

[0037] According to a third aspect of the invention, a method for manufacturing a power module is provided.

[0038] According to the method, a substrate with a sinterable electrical contact surface is provided. A sintering paste is applied, e.g., coated or printed, to the contact surface of the substrate.

[0039] Furthermore, a power semiconductor element with a sinterable top-side electrical contact surface and a sinterable bottom-side electrical contact surface is provided and arranged on the substrate, wherein the power semiconductor element is placed on the sintering paste via its bottom-side contact surface and contacted with the sintering paste.

[0040] Furthermore, a connecting element that is sinterable on both sides is provided, which is provided with a sinterable nanostructure on the underside and a sinterable nanostructure on the top. The connecting element is arranged on the top contact surface of the power semiconductor element, wherein the connecting element is placed onto the top contact surface of the power semiconductor element via its underside nanostructure and contacted with this contact surface.

[0041] Furthermore, a bonding element with a sinterable underside and a bondable top side is provided for establishing a top-side bond connection. The bonding element is arranged on the connecting element, with the bonding element being placed onto the top-side nanostructure of the connecting element via its sinterable underside and contacted with it.

[0042] The following sintered connections are then created between the substrate, the power semiconductor element and the bonding element: - a first sintered connection between the underside contact surface of the power semiconductor element via the sintering paste with the contact surface of the substrate, - a second sintered connection between the top-side contact surfaces of the power semiconductor element via the bottom-side nanostructure of the connecting element with the connecting element; and - a third sintered connection between the underside of the bonding element via the top-side nanostructure of the connecting element with the connecting element.

[0043] In particular, the three sintered compounds mentioned above are produced in the same sintering process (simultaneously).

[0044] The connecting element, like the sintering paste (as a joining element between the joining partners: the substrate and the power semiconductor element), serves as a joining element between the joining partners: the power semiconductor element and the bonding element during sintering. After the sintering process, the connecting element physically connects the bonding element to the power semiconductor element with low resistance and thermally.

[0045] Advantageous embodiments of the power module described above are, insofar as they are otherwise transferable to the above-mentioned method, also to be regarded as advantageous embodiments of the method. Short description of the drawings:

[0046] An exemplary embodiment of the invention is explained in more detail below with reference to the accompanying drawings. Fig. 1 shows a schematic exploded view of a part of a power module according to an exemplary embodiment of the invention; and Fig. 2 in a schematic cross-sectional view the part of the power module from Fig. 1. Detailed description of the drawings:

[0047] Fig. 1 shows a schematic exploded view of a part of a power module LM according to an exemplary embodiment of the invention, which is intended to symbolically represent the power module LM before assembly, in particular before a sintering process to be described below. Fig. 2 shows the part of the power module LM from Fig. 1 after its assembly or after the sintering process in a schematic cross-sectional view.

[0048] The power module LM has a substrate ST, e.g. a DCB or AMB substrate, with a sinterable electrical contact surface KF0, which is formed, for example, as a copper conductor track.

[0049] The power module LM also has a sintering paste SP (e.g. DTF, in English “Die Transfer Film”), which is printed or applied to the contact surface KF0 of the substrate ST.

[0050] The power module LM also has a power semiconductor element LE, which is formed as a SiC semiconductor switch and has a sinterable top-side electrical contact surface KF1 (possibly with a corresponding coating for sintering), which forms a source terminal of the semiconductor switch, a bondable top-side electrical contact surface KF2 (possibly with a corresponding coating for bonding), which forms a gate terminal of the semiconductor switch, and a sinterable bottom-side electrical contact surface KF3 (possibly with a corresponding coating for sintering), which forms a drain terminal of the semiconductor switch. The sinterable contact surfaces KF1, KF3 are possibly provided with a corresponding coating for sintering. Accordingly, the bondable contact surface KF2 is possibly provided with a corresponding coating for bonding.

[0051] The power semiconductor element LE or the SiC semiconductor switch rests on the sintering paste SP via its sinterable underside contact surface KF3 and is physically and electrically connected to the contact surface KF0 of the substrate ST via the sintering connection of this sintering paste SP.

[0052] The power module LM also has a connecting element VE made of copper or a copper alloy, which is sinterable on both sides and has a platelet-shaped central part MT, a sinterable nanostructure NS1 formed on the underside of the central part MT, and a sinterable nanostructure NS2 formed on the upper side of the central part MT. The lower-side nanostructure NS1 has a plurality of sinterable rod- or hair-shaped projections VS, each extending from the underside of the central part MT and thus from a central plane ME of the connecting element VE. Analogously, the upper-side nanostructure NS2 has a plurality of sinterable rod- or hair-shaped projections VS, each extending from the upper side of the central part MT and thus from a central plane ME of the connecting element VE and consequently also from the projections VS of the lower-side nanostructure NS1.The projections VS of the two nanostructures NS1, NS2 each have a diameter of less than 1 micrometer and an average diameter of approximately 700 - 800 nanometers.

[0053] The power module LM also has a bonding element BE made of copper or a copper alloy, which is formed in the form of a copper plate and has a sinterable underside US (if necessary with a corresponding coating for sintering) for producing a sintered connection and a bondable upper side OS (if necessary with a corresponding coating for bonding) for producing a top-side bonding connection BV1.

[0054] The connecting element VE is sintered onto the top contact surface KF1 of the power semiconductor element LE via the underside nanostructure NS1. The connecting element VE is further sintered to the bonding element BE or its underside US via the top nanostructure NS2, thus physically and electrically connecting the bonding element BE to the top contact surface KF1 of the power semiconductor element LE.

[0055] The connecting element VE, like the sintering paste SP, serves as a joining element for joining the bonding element BE with the top contact surface KF1 of the power semiconductor element LE.

[0056] A bonding wire or a bonding ribbon made of copper or a copper alloy, or a copper round wire or a copper ribbon, is bonded to the bondable upper surface OS of the bonding element BE. This bonding wire or ribbon establishes the bond connection BV1 to the bonding element BE and thus to the upper contact surface KF1 of the power semiconductor element LE with another electrical component (not shown in the figures) provided according to the function of the power module LM. The bond connection BV1 serves to transmit a load current with a current intensity of several amperes, even up to 20 amperes.

[0057] The power module LM shown here can, for example, be part of an inverter of an electric motor vehicle drive, wherein the inverter, in addition to three or more such power modules LM, also has a driver circuit for operating these power modules LM, which is electrically or signal-technically connected to the power modules via control signal connections and further via a second bond connection BV2 in the form of a bond wire made of aluminum or an aluminum alloy to the respective power semiconductor element LE or their respective bondable top-side contact surfaces KF2.

[0058] The production of the Fig. 2 shown power module LM or its assembly is carried out as follows: First, the substrate ST with the sinterable electrical contact surface KF0 is prepared. The sintering paste SP is printed or applied onto the contact surface KF0 and dried if necessary. The power semiconductor element LE is placed onto the sintering paste SP via its sinterable underside contact surface KF3. The connecting element VE is placed onto the sinterable top-side contact surface KF1 of the power semiconductor element LE via its sinterable underside nanostructure NS1. The bonding element BE is placed onto the sinterable top-side nanostructure NS1 of the connecting element VE via its sinterable underside US. This creates a visible structure consisting of the substrate ST, the sintering paste SP, the power semiconductor element LE, the connecting element VE, and the bonding element BE, which lie loosely on top of one another.

[0059] Sintered connections are then made in one and the same sintering process - between the underside contact surface KF3 of the power semiconductor element LE via the sintering paste SP with the contact surface KF0 of the substrate ST; - between the top-side contact surfaces KF1 of the power semiconductor element LE via the bottom-side nanostructure NS1 of the connecting element VE with the connecting element VE; and - between the underside US of the bonding element BE via the top-side nanostructure NS2 of the connecting element VE with the connecting element VE, manufactured at the same time.

[0060] The joint sintering process takes place under a compressive force acting on the entire layer structure and at a temperature of over 200°C for a specified period of time. This results in a (bilateral) diffusion process of the rod- or hair-like projections VS of the two nanostructures NS1, NS2 of the connecting element VE with the surfaces of the corresponding joining partners, i.e., the sinterable underside US of the bonding element BE and the sinterable upper contact surface KF1 of the power semiconductor element LE. The temperature of over 200°C accelerates this diffusion process.

[0061] In a subsequent bonding process or in a subsequent bonding operation or several subsequent bonding operations, the two bond connections BV1, BV2 are bonded or formed onto the bondable top side OS of the bonding element BE or the bondable top-side contact surface KF2 of the power semiconductor element LE.

Claims

[1] Power module (LM), comprising: - a power semiconductor element (LE) with a sinterable top-side electrical contact surface (KF1); - a bonding element (BE) with a sinterable underside (US) and a bondable upper side (OS) for producing a top-side bond connection (BV1); - a connecting element (VE) which is sinterable on both sides and is provided with a sinterable nanostructure (NS1) on the underside and a sinterable nanostructure (NS2) on the top and is sintered via the nanostructure (NS1) on the underside to the contact surface (KF1) of the power semiconductor element (LE) and via the nanostructure (NS2) on the top to the underside (US) of the bonding element (BE) and thus physically and electrically connects the bonding element (BE) to the contact surface (KF1) of the power semiconductor element (LE). [2] Power module (LM) according to claim 1, wherein the connecting element (VE) has a platelet-shaped central part (MT), on the two opposite sides of which the lower side (NS1) and the upper side (NS2) nanostructure are each formed in a distributed manner. [3] Power module (LM) according to claim 1 or 2, wherein the lower-side (NS1) and / or upper-side (NS2) nanostructure each have a plurality of sinterable rod-shaped projections (VS) which each extend away from a center plane (ME) of the connecting element (VE). [4] Power module (LM) according to claim 3, wherein the diameters of the projections (VS) are less than 1 micrometer or less than 750 nanometers or less than 500 nanometers or less than 300 nanometers or approximately 100 nanometers. [5] Power module (LM) according to one of the preceding claims, wherein the connecting element (VE) consists of copper or a copper alloy and is formed in one piece. [6] Power module (LM) according to one of the preceding claims, wherein the bonding element (BE) consists of copper or a copper alloy. [7] Power module (LM) according to one of the preceding claims, wherein the top-side bonding connection (BV1) is produced by means of a bonding wire or a bonding ribbon, wherein the bonding wire or the bonding ribbon consists of copper or a copper alloy. [8] Power module (LM) according to one of the preceding claims, wherein the power semiconductor element (LE) is a Si semiconductor element or a SiC semiconductor element or a GaN semiconductor element. [9] Power module (LM) according to one of the preceding claims, further comprising: - a substrate (ST) with a sinterable electrical contact surface (KF0); - wherein the power semiconductor element (LE) has a sinterable underside electrical contact surface (KF3) and is sintered onto the contact surface (KF0) of the substrate (ST) via the underside contact surface (KF3) and is physically and electrically connected to the contact surface (KF0) of the substrate (ST). [10] Power module (LM) according to one of the preceding claims, wherein the bonding element (BE) and the connecting element (VE) are formed in one piece. [11] Power module (LM) according to one of the preceding claims, wherein the bonding element (BE) or its upper side (OS) is metallized with a metal layer made of a metallic material which differs from the base material of the bonding element (BE). [12] Power module (LM) according to one of the preceding claims, wherein the bonding element (BE) has a plurality of metal layers made of different metals or metal alloys which are formed integrally with one another. [13] Inverter, comprising: - a power module (LM) according to one of the preceding claims; - a driver circuit for operating the power module (LM), which is electrically connected to the power module (LM) via a control signal connection. [14] Method for producing a power module (LM), comprising the steps of: - Providing a substrate (ST) with a sinterable electrical contact surface (KF0); - Applying a sintering paste (SP) to the contact surface (KF0) of the substrate (ST); - Arranging a power semiconductor element (LE) with a sinterable top-side electrical contact surface (KF1) and a sinterable bottom-side electrical contact surface (KF3) on the substrate, wherein the power semiconductor element (LE) is placed on the sintering paste (SP) via its bottom-side contact surface (KF3); - Providing a connecting element (VE) which is sinterable on both sides and is provided with a sinterable nanostructure (NS1) on the underside and a sinterable nanostructure (NS1) on the top side; - arranging the connecting element (VE) on the power semiconductor element (LE), wherein the connecting element (VE) is placed on the top contact surface (KF1) of the power semiconductor element (LE) via its underside nanostructure (NS1); - Providing a bonding element (BE) with a sinterable underside (US) and a bondable upper side (OS) for producing a top-side bond connection (BV1); - arranging the bonding element (BE) on the connecting element (VE), wherein the bonding element (BE) is placed via its sinterable underside (US) onto the top-side nanostructure (NS2) of the connecting element (VE); - producing a first sintered connection between the underside contact surface (KF3) of the power semiconductor element (LE) via the sintering paste (SP) with the contact surface (KF0) of the substrate (ST); - producing a second sintered connection between the top-side contact surfaces (KF1) of the power semiconductor element (LE) via the bottom-side nanostructure (NS1) of the connecting element (VE) with the connecting element (VE); and - Producing a third sintered connection between the underside (US) of the bonding element (BE) via the top-side nanostructure (NS2) of the connecting element (VE) with the connecting element (VE). [15] The method of claim 14, wherein the first, second and third sintered joints are produced in the same sintering process.

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