Power module, inverter and method for producing a power module

Abstract

The invention relates to a power module (LM), comprising: - a power semiconductor element (LE) having a sinterable upper electrical contact surface (KF1); - a connecting element (BE) having an upper connecting layer (BS) for producing an upper electrical connection (BV1) and a sinterable nanostructure (NS) on an underside facing away from the connecting layer (BS); - wherein the connecting element (BE) is sintered to the upper contact surface (KF1) of the power semiconductor element (LE) via the lower nanostructure (NS) and is thus physically and electrically connected to the upper contact surface (KF1) of the power semiconductor element (LE). The invention also describes an inverter having an aforementioned power module (LM) and a method for producing a power module (LM).

Description

[0001] Description

[0002] Power module, inverter and method for producing a power module

[0003] Technical area:

[0004] The present invention relates to a power module, in particular for an inverter or a DC-DC converter, especially of an electric drive of a motor vehicle.

[0005] Furthermore, the invention relates to an inverter with a said power module and a method for producing a power module.

[0006] State of the art and task of the invention:

[0007] 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.

[0008] 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.

[0009] The object of the present application is therefore to provide an efficient power module with a high power density.

[0010] Description of the invention:

[0011] This problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0012] 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 for an electric drive of a motor vehicle.

[0013] The power module comprises a power semiconductor element or a power semiconductor switch with a sinterable top-side electrical contact surface and a connecting element with a top-side electrical connecting layer and a sinterable bottom-side nanostructure on a bottom side of the connecting element facing away from the connecting layer, wherein the top-side connecting layer serves as a connecting surface for physically and electrically connecting an "external" electrical connection element, such as a bonding wire or a bonding ribbon, and thus for establishing a top-side electrical connection for the top-side contact surface of the power semiconductor element.

[0014] The connecting element is sintered onto the top contact surface via the underside nanostructure and is thus physically and electrically connected to the power semiconductor element or to its top contact surface.

[0015] The connecting element serves as a connection buffer, such as a bond buffer, and is shaped, for example, in the form of a platelet or a metal plate. The connecting element can be sintered onto the top contact surface via its underside nanostructure in a sintering process, thus physically and electrically connecting it to the power semiconductor element or its top contact surface.

[0016] Furthermore, the connecting element serves as a joining element between itself and the joining partner: the power semiconductor element or its upper contact surface, and establishes the sintered connection between itself and the power semiconductor element. After the sintering process, the connecting element is physically, low-resistance, and thermally connected to the power semiconductor element.

[0017] The connecting element on the top electrical contact surface of the power semiconductor element gives the contact surface and the semiconductor element higher mechanical strength and higher thermomechanical cycle strength.

[0018] The nanostructure formed on the underside enables a highly compacted microstructure between the two joining partners, namely between the top-side electrical contact surface of the power semiconductor element and the connecting element, 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 and the "external" connection element via the connecting 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.

[0019] The high thermal conductivity and the high mechanical stability of the structure for the power semiconductor element also enable the use of a stiffer electrical connection element and consequently also the use of a copper-based bonding wire or bonding ribbon, which has a higher current-carrying capacity than, for example, an aluminum-based bond. In particular, the high mechanical stability enables the effect of a higher connection force, such as a higher bonding force, and a higher connection energy, such as the high ultrasonic energy used in ultrasonic bonding, on the connecting element and thus on the structure consisting of the power semiconductor element and the connecting element. Thanks to the stable sintered connection caused by the nanostructure on the underside of the connecting element, the thermomechanical stress between the electrical connection on the top side orThe contact area between the connecting element on the one hand and the top contact surface of the power semiconductor element on the other hand can be better compensated or reduced. This also increases the service life of the aforementioned structure with the power semiconductor element and thus of the power module.

[0020] With the connecting element as a connection buffer, an upper-side electrical connection surface is created for the power semiconductor element, which is itself sufficiently rigid and mechanically stable and also gives the power semiconductor element or the structure consisting of the power semiconductor element and the connecting element 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.

[0021] The material or material composition of the connecting element can be freely selected depending on the need or requirement. The upper connecting layer of the connecting element can also be metallized differently with a suitable metallization depending on the need or requirement. Furthermore, the connecting 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

[0022] A layered composite, such as an aluminum layer, for the top-side contact surface allows the connecting element to be "metallized" as required by the "free" selection of materials to meet the needs or requirements. A costly or technically almost impossible metallization of the top-side contact surface of a standard semiconductor chip, such as with gold, silver, palladium, copper, and / or tin, etc., can be achieved using the comparatively inexpensive 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.

[0023] This provides an opportunity for an efficient power module with a high power density that can still be manufactured cost-effectively, especially with inexpensive “standard” semiconductor chips available on the market.

[0024] The connecting element is formed in one piece.

[0025] The connecting element comprises, for example, a platelet-shaped carrier part, preferably made of copper or a copper alloy, on the upper side of which the upper-side electrical connection layer is formed and on the underside of which, facing away from the upper side, the nanostructure is formed.

[0026] The connecting element is formed, for example, as a bonding element, wherein the upper-side connecting layer in this case is formed as a bonding layer for producing a top-side bond connection.

[0027] For example, the nanostructure has a plurality of sinterable rod- or hair-shaped projections which extend (at least partially or at their respective subsections) away from the upper connecting layer or from the carrier part of the connecting element.

[0028] During the sintered bond between the connecting element and the top contact surface of the power semiconductor element, the rod- or hair-like projections deform and diffuse with the contact surface of the power semiconductor element. This significantly densifies the structure and forms a physical bond between the two joining partners. This bond exhibits high electrical and thermal conductivity as well as high mechanical stability. Furthermore, it exhibits little to no organic contamination and is halogen-free.

[0029] Furthermore, after sintering, the rod- or hair-shaped projections elastically absorb any thermomechanical stresses that may be present between the connecting element and the contact surface of the power semiconductor element and thus contribute positively to the service life of the power module.

[0030] 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.

[0031] The length, diameter, and density of the nanorods in the nanostructure are variable and can be selected according to requirements. However, the diameters of the nanorods are in the nanometer range mentioned above. The carrier part can be made of various electrically conductive materials and can be coated with a metal or a metal alloy, such as copper, silver, gold, or nickel, or an alloy containing one or more of these metals. The metal coating can be applied by electroplating, for example, after applying a sponge body with appropriate shapes to form the projections to the central part.

[0032] The connecting element or the upper connecting layer of the connecting element can be metallized with one or more metallic materials that are different from the base material of the connecting element.

[0033] By metallizing the connecting element or connecting layer, the connecting element or connecting layer can be adapted to the different needs or requirements of the various connection technologies for establishing the top-side electrical connection with different "external" connection elements (or the subsequent module assembly technology). This allows a cost-effective, conventional standard semiconductor chip to be used for different connection technologies for the top-side connection.

[0034] The connecting element can comprise several metal layers made of different metals or metal alloys, which are formed integrally with each other and with the nanostructure. One of the metal layers, or the outer metal layer facing away from the nanostructure, forms the top-side connecting layer.

[0035] The connecting element can be made of copper or a copper alloy (i.e. an alloy with copper as the main component) or a copper-containing alloy (i.e. an alloy with copper as a component but not necessarily as the main component).

[0036] The top-side electrical connection can be established, for example, using a bonding wire or a bonding ribbon. The bonding wire or bonding ribbon can be made of copper or a copper alloy.

[0037] 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.

[0038] The use of the connecting element with the sinterable nanostructure for the top contact surface of the power semiconductor element enables the application of a (significantly) small power semiconductor element with a high current density and current carrying capacity, such as the SiC semiconductor switch.

[0039] 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.

[0040] The substrate can be formed as a ceramic-based circuit carrier substrate, 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).

[0041] According to a second aspect of the invention, an inverter or power inverter, especially for an electric drive of a motor vehicle, is provided.

[0042] 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.

[0043] According to a third aspect of the invention, a method for manufacturing a power module is provided.

[0044] 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.

[0045] Furthermore, a power semiconductor element having 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 onto the sintering paste via its bottom-side contact surface and contacted with the sintering paste.

[0046] Furthermore, a connecting element is provided with a top-side electrical connection layer for establishing a top-side electrical connection and a sinterable nanostructure on a bottom side facing away from the connection layer. The connecting element is arranged on the power semiconductor element, wherein the connecting element is placed onto the likewise sinterable top-side contact surface of the power semiconductor element via its sinterable nanostructure and contacted therewith.

[0047] The following sintered connections are then produced between the substrate, the power semiconductor element and the connecting element:

[0048] - 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,

[0049] - 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.

[0050] In particular, the two sintered joints are produced in the same sintering process (simultaneously). 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 connecting element during sintering. After the sintering process, the connecting element is physically, low-resistance, and thermally connected to the power semiconductor element.

[0051] 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.

[0052] Short description of the drawings:

[0053] An exemplary embodiment of the invention is explained in more detail below with reference to the accompanying drawings. In the drawings:

[0054] Figure 1 shows a schematic exploded view of a part of a power module according to an exemplary embodiment of the invention; and

[0055] Figure 2 shows a schematic cross-sectional view of part of the power module from Figure 1.

[0056] Detailed description of the drawings:

[0057] Figure 1 shows a schematic exploded view of a portion 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. Figure 2, in turn, shows the portion of the power module LM from Figure 1 after its assembly or after the sintering process in a schematic cross-sectional view.

[0058] The power module LM comprises a substrate ST, e.g. a DCB or AMB substrate, with a sinterable electrical contact surface KFO, which is formed, for example, as a copper conductor track.

[0059] The power module LM further comprises a sintering paste SP (e.g. DTF, in English “Die Transfer Film”), which is printed or applied onto the contact surface KFO of the substrate ST. The power module LM also comprises a power semiconductor element LE, which is formed as a SiC semiconductor switch and has a sinterable top-side electrical contact surface KF1 (if necessary with a corresponding coating for sintering), which forms a source connection of the semiconductor switch, a bondable top-side electrical contact surface KF2 (if necessary with a corresponding coating for bonding), which forms a gate connection of the semiconductor switch, and a sinterable bottom-side electrical contact surface KF3 (if necessary with a corresponding coating for sintering), which forms a drain connection of the semiconductor switch. The sinterable contact surfaces KF1, KF3 are if necessary provided with a corresponding coating for sintering. Accordingly, the bondable contact surface KF2 is if necessary.provided with appropriate coating for bonding.

[0060] The power semiconductor element LE or the SiC semiconductor switch rests on the sinter paste SP via its sinterable underside contact surface KF3 and is physically and electrically connected to the contact surface KFO of the substrate ST via the sintering connection of this sinter paste SP.

[0061] The power module LM also has a bonding element BE made of copper or a copper alloy as a connecting element, which has a platelet-shaped carrier part TR with a bondable bonding layer BS (if necessary with a corresponding coating for bonding) as a top-side connecting layer on its upper side and a sinterable nanostructure NS (if necessary with a corresponding coating for sintering) on ​​its underside.

[0062] The underside nanostructure NS has a multitude of sinterable rod- or hair-like protrusions VS that extend from the underside of the carrier part TR of the bonding element BE. The protrusions VS each have a diameter of less than 1 micrometer, or an average diameter of approximately 700–800 nanometers.

[0063] The bonding element BE is sintered onto the top-side contact surface KF1 of the power semiconductor element LE via the bottom-side nanostructure NS and is thus physically and electrically connected to the top-side contact surface KF1 of the power semiconductor element LE.

[0064] The bonding element BE, like the sintering paste SP, serves as a joining element for joining itself to the top-side contact surface KF1 of the power semiconductor element LE. 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 top-side bonding layer BS of the bonding element BE. This bonding wire establishes the bond connection BV1 to the bonding element BE and thus to the top-side 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.

[0065] 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.

[0066] The production and assembly of the LM power module shown in Figure 2 is carried out as follows:

[0067] 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 bonding element BE is placed onto the sinterable top-side contact surface KF1 of the power semiconductor element LE via its sinterable underside nanostructure NS. This creates a visible structure consisting of the substrate ST, the sintering paste SP, the power semiconductor element LE, and the bonding element BE, which lie loosely on top of one another.

[0068] Sintered connections are then made in one and the same sintering process

[0069] - 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; and

[0070] - between the top-side contact surfaces KF1 of the power semiconductor element LE via the bottom-side nanostructure NS of the bonding element BE with the bonding element BE, produced simultaneously. 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 diffusion process between the rod- or hair-like projections VS of the nanostructure NS of the bonding element BE and the surface of the joining partner, i.e., the sinterable top-side contact surface KF1 of the power semiconductor element LE. The temperature of over 200°C accelerates this diffusion process.

[0071] In a subsequent bonding process or in a subsequent bonding process or several subsequent bonding processes, the two bond connections

[0072] BV1, BV2 are bonded or formed onto the top-side bonding layer BS of the bonding element BE or onto the bondable top-side contact surface KF2 of the power semiconductor element LE.

Claims

Patent claims 1. A power module (LM), comprising: a power semiconductor element (LE) with a sinterable top-side electrical contact surface (KF1); a connecting element (BE) with a top-side connecting layer (BS) for establishing a top-side electrical connection (BV1) and a sinterable nanostructure (NS) on a bottom side facing away from the connecting layer (BS); - wherein the connecting element (BE) is sintered via the underside nanostructure (NS) to the top-side contact surface (KF1) of the power semiconductor element (LE) and is thus physically and electrically connected to the top-side contact surface (KF1) of the power semiconductor element (LE).

2. Power module (LM) according to claim 1, wherein the connecting element (BE) has a plate-shaped carrier part (TR), on the upper side of which the upper-side connecting layer (BS) is formed and on the underside of which, facing away from the upper side, the nanostructure (NS) is formed.

3. Power module (LM) according to claim 1 or 2, wherein the connecting element (BE) is formed as a bonding element (BE), wherein the top-side connecting layer (BS) is formed as a bonding layer for producing a top-side bond connection.

4. Power module (LM) according to one of the preceding claims, wherein the nanostructure (NS) has a plurality of sinterable rod-shaped projections (VS) extending away from the connecting layer (BS).

5. Power module (LM) according to claim 4, 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.

6. Power module (LM) according to one of the preceding claims, wherein the connecting element (BE) or the upper-side connecting layer (BS) of the connecting element (BE) is metallized with a metallic material that differs from the base material of the connecting element (BE).

7. Power module (LM) according to one of the preceding claims, wherein the connecting element (BE) comprises several metal layers made of different metals or metal alloys which are formed integrally with each other and with the nanostructure (NS), wherein one of the metal layers forms the top-side connecting layer (BS).

8. Power module (LM) according to one of the preceding claims, wherein the top-side connection (BV1) is made 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.

9. 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.

10. Power module (LM) according to one of the preceding claims, further comprising: a substrate (ST) with a sinterable electrical contact surface (KFO); - wherein the power semiconductor element (LE) has a sinterable underside electrical contact surface (KF3) and is sintered onto the contact surface (KFO) of the substrate (ST) via the underside contact surface (KF3) and is physically and electrically connected to the contact surface (KFO) of the substrate (ST).

11. An inverter comprising: a power module (LM) according to any 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.

12. Method for producing a power module (LM), comprising the following steps: Providing a substrate (ST) with a sinterable electrical contact surface (KFO); - Applying a sintering paste (SP) to the contact surface (KFO) 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 (BE) with a top-side connecting layer (BS) for producing a top-side electrical connection (BV1) and a sinterable nanostructure (NS) on a bottom side facing away from the connecting layer (BS); - Arranging the connecting element (BE) on the power semiconductor element (LE), wherein the connecting element (BE) is placed via its nanostructure (NS) on the upper contact surface (KF1) of the power semiconductor element (LE); - Producing a first sintered connection between the lower Contact surface (KF3) of the power semiconductor element (LE) via the sintering paste (SP) with the contact surface (KFO) of the substrate (ST); Producing a second sintered connection between the top-side contact surfaces (KF1) of the power semiconductor element (LE) via the nanostructure (NS) of the connecting element (BE) with the connecting element (BE).

13. The method according to claim 12, wherein the first and second sintered joints are produced in the same sintering process.

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