Printed circuit board assembly, power converter device, electric axle drive and motor vehicle

Abstract

The invention relates to a printed circuit board assembly (1) comprising a metal-insulating substrate (2), at least one chip (3), and a current conductor (4), wherein the chip (3) is applied to a first layer (5) of the metal-insulating substrate (2), and the chip (3) is electrically contacted by the current conductor (4) on the side facing away from the metal-insulating substrate (2), such that the chip (3) is arranged between the metal-insulating substrate (3) and the current conductor (4), characterized in that the current conductor (4) is connected to the metal-insulating substrate (2) in a thermally conductive manner for heat dissipation. The invention further relates to a power converter device (21), an electric axle drive (22), and a motor vehicle (20) having such a printed circuit board assembly (1).

Description

[0001] The invention relates to a printed circuit board assembly comprising a metal-insulator substrate, at least one chip, and a current conductor. The chip is applied to a first layer of the metal-insulator substrate and the chip is electrically contacted by the current conductor on the side facing away from the metal-insulator substrate, so that the chip is arranged between the metal-insulator substrate and the current conductor. Furthermore, the invention relates to a power converter device, an electric axle drive, and a motor vehicle with such a printed circuit board assembly.

[0002] Printed circuit board arrangements are already known which have chips that are contacted via a current conductor.

[0003] The object of the present invention is to propose a printed circuit board arrangement, in particular for a power module, for example in a power converter device, which enables efficient heat dissipation or cooling of a chip and at the same time keeps the required installation space of the printed circuit board arrangement to a minimum.

[0004] The object underlying the invention is achieved by a printed circuit board assembly having the features of claim 1. Advantageous developments of the invention are described in the subclaims.

[0005] According to the invention, a printed circuit board arrangement is proposed, comprising a metal-insulator substrate, at least one chip and a current conductor, wherein the chip is applied to a first layer of the metal-insulator substrate and the chip is electrically contacted by the current conductor on the side facing away from the metal-insulator substrate, so that the chip is arranged between the metal-insulator substrate and the current conductor, characterized in that the current conductor is connected to the metal-insulator substrate in a thermally conductive manner for heat dissipation.

[0006] In one application, the chip arranged on the circuit board serves as a switch for switching an electrical current. The electrical current can be used, for example, as an electrical signal or as a load current. When switching load currents, the chip serves as a so-called power switch. The chip is preferably a transistor, e.g., a MOSFET or IGBT. A chip is generally constructed of semiconductor materials, such as silicon, silicon carbide, gallium nitride, or gallium oxide.

[0007] The chip essentially has three electrodes: a first, controllable current electrode (drain electrode), a second current electrode (source electrode), and a control electrode (gate electrode). The chip can provide a conductive current path between the two current electrodes when closed, or it can isolate the current path when open. If a load voltage is applied between the two current electrodes, a load current flows through the chip when closed. The switching state of the chip is controlled by a signal voltage applied to the signal electrode. The signal voltage can be provided, in particular, by a so-called driver board.

[0008] In the present printed circuit board assembly, the first layer of the metal-insulating substrate and the current conductor are each electrically contacted with one of the chip's electrodes. Advantageously, the first layer of the metal-insulating substrate is metallic. Preferably, the first layer of the metal-insulating substrate and the current conductor are contacted with the chip's current electrodes, for example, by soldering or sintering. Particularly preferably, the first layer of the metal-insulating substrate is connected to the drain electrode, and the current conductor is connected to the source electrode. In this embodiment, the load current in the printed circuit board assembly would flow through the current conductor, the chip, and the first layer of the metal-insulating substrate. The current conductor can in particular be designed as a so-called leadframe.

[0009] Electrical losses convert the electrical energy of the flowing load current into thermal energy, which heats the components along the load path. This particularly affects the chip, which is built on semiconductor material and therefore usually heats up the most. In addition, the operation of the chip is linked to a maximum operating temperature. Above this maximum temperature, the chip's functionality is limited or it is even destroyed. Effective cooling of the chip is therefore a key task that every printed circuit board arrangement must enable. To achieve this, purely passive cooling of the chip is initially recommended. This is achieved by bringing the chip into contact with bodies whose thermal capacity allows heat to flow away from the chip, thereby cooling it. In the arrangement described, this is initially achieved by heat flowing from the chip into the current conductor and the metal-insulator substrate.For this purpose, the current conductor is thermally contacted with the first layer of the metal-insulator substrate, e.g., by sintering or soldering. This heat flow heats up the current conductor and the metal-insulator substrate, which in turn must be cooled to prevent the chip temperature from rising above a maximum temperature. Further cooling of the metal-insulator substrate is structurally simpler here because it is a planar structure. Additional cooling of the current conductor also has the disadvantage that an additional cooler on the current conductor side further increases the overall height of the circuit board arrangement. Because the current conductor is thermally conductively connected to the metal-insulator substrate in the present invention, the current conductor can be cooled via the metal-insulator substrate, thereby indirectly providing two-sided or double-sided cooling of the chip in between.It should be noted that the current conductor and the metal-insulator substrate are not already thermally connected by the chip, since, as previously described, the chip is usually the warmest component of the circuit board assembly during operation and therefore no heat flow from the current conductor via the chip to the metal-insulator substrate is possible.

[0010] In one embodiment, the metal-insulator substrate is formed as a DBC substrate with the first layer made of copper. DBC substrates (Direct-Bonded-Copper) have a structure comprising multiple metallic copper layers separated by an insulating ceramic layer. Electronic components such as chips can be applied to the first copper layer, for example by soldering, and electrically contacted. The DBC substrate's thermal properties enable good thermal conductivity, which allows the chips to be cooled particularly well compared to conventional circuit boards. In addition, conductor track structures can be applied to the first copper layer, enabling circuits consisting of multiple chips, for example. The second copper layer is thermally bonded to the first copper layer via the electrically insulating ceramic layer and thus also serves to dissipate heat.

[0011] Preferably, the current conductor is essentially plate-shaped. "Plate-shaped" means, in particular, that the current conductor extends significantly further in two spatial dimensions than in the third spatial dimension. As a result, the current conductor has at least two large surfaces. At least one of these surfaces, which is provided by the plate-shaped design, allows the current conductor to cover a large area and thus provide a large contact surface for thermal coupling. Gradations can also be formed in the plate-shaped structure. These gradations create subsections, which, viewed individually, are themselves plate-shaped.

[0012] Advantageously, the current conductor is arranged parallel to the metal-insulator substrate. This parallel arrangement provides a type of sandwich structure. In this sandwich structure, the chip is located between the current conductor and the metal-insulator substrate. The parallel arrangement of the current conductor to the metal-insulator substrate allows the current conductor to thermally contact both the chip and the metal-insulator substrate in a structurally simple manner. The parallel arrangement of the current conductor and the metal-insulator substrate advantageously makes it possible to achieve the smallest possible spatial distance between the current conductor and the metal-insulator substrate, whereby their stray inductance is as low as possible. Preferably, at least one thermal contact region, which is in particular independent of the at least one chip, is arranged.In the thermal contact area, the current conductor is in direct or indirect contact with the metal-insulator substrate to thermally couple the current conductor to the metal-insulator substrate. Indirect contact is understood to mean, in particular, that a third body is located between the current conductor and the metal-insulator substrate. This is independent of the chip, which also represents indirect contact between the current conductor and the metal-insulator substrate but does not provide thermal coupling, since the chip is generally the hottest spot in the circuit board assembly during operation. Thus, the thermal contact area is a specific sub-area on the metal-insulator substrate.

[0013] Preferably, the conductor is electrically insulated from the rest of the metal-insulator substrate in the thermal contact area. Both the conductor and the metal-insulator substrate or the first layer of the substrate are electrically conductive. If the thermal contact area is not only thermally but also electrically conductive, a short circuit occurs between the conductor and the metal-insulator substrate. Since both the conductor and the metal-insulator substrate are part of a circuit, a short circuit can lead to a malfunction. To prevent a functionally critical short circuit between the conductor and the metal-insulator substrate, the conductor is either completely insulated from the metal-insulator substrate or the short circuit is limited to a portion of the metal-insulator substrate that is not part of an electronic circuit. This means:In particular, the electrical connection between the current conductor and the metal-insulator substrate can be limited to the thermal contact area and separated from the rest of the metal-insulator substrate.

[0014] Preferably, the first layer of the metal-insulator substrate has an interruption for electrical insulation, in particular by etching, which encloses the thermal contact region. A separation of the electrical connection between the thermal contact region and the remaining region of the metal-insulator substrate, which is part of an electronic circuit, can be achieved by interrupting the metallic, electrically conductive layer of the metal-insulator substrate. The interruption provides an insulating effect between the thermal contact region and the remaining region of the first layer of the metal-insulator substrate via a sufficient air and creepage distance. The interruption can be provided, for example, by a trench that extends through the entire first layer of the metal-insulator substrate. Such a trench can be formed, for example, by known etching methods.This interruption preferably encloses the thermal contact area by forming a closed trench around the thermal contact area. This allows the use of an electrically conductive connection technique, such as soldering or sintering, between the current conductor and the metal-insulator substrate in the thermal contact area.

[0015] In one embodiment of the invention, an insulating element is arranged between the conductor and the first layer of the metal-insulating substrate in the thermal contact area. To prevent a critical short circuit between the conductor and the metal-insulating substrate, the conductor can also be completely electrically insulated from the metal-insulating substrate. By placing an additional insulating element between the conductor and the metal-insulating substrate, only an indirect connection exists between the conductor and the metal-insulating substrate in the thermal contact area, which is thermally but not electrically conductive.

[0016] The insulation element is preferably designed as a gap pad and / or ceramic and / or insulating paper and / or insulating foil. Gap pads can be made of silicone, for example, and provide a plasticity that additionally compensates for tolerances.

[0017] In one embodiment of the invention, the current conductor has a bending region which shortens the distance between the current conductor and the metal-insulating substrate in the thermal contact region. If the current conductor is completely flat and designed without a bending region, the height of the chip determines the distance between the current conductor and the metal-insulating substrate. In order to form a thermal contact region, this distance between the current conductor and the metal-insulating substrate must be bridged. This can be achieved by a bending region which forms a step in the current conductor. This step allows the current conductor to stretch towards the metal-insulating substrate in sections, thereby reducing the distance between the metal-insulating substrate and the current conductor. This makes it possible to reduce the thickness of the insulation element, thereby increasing the thermal conductivity of the thermal contact.The bending area and the resulting step do not change the fundamentally plate-shaped design of the current conductor.

[0018] In one embodiment of the invention, a heat sink is arranged on the side of the metal-insulating substrate facing away from the current conductor in order to dissipate heat from the metal-insulating substrate. The flat surface of the unpopulated side of the metal-insulating substrate allows for a simple design and good thermal contact with the substrate. This allows for effective heat dissipation from the metal-insulating substrate. The additional heat introduced into the metal-insulating substrate via the current conductor and the thermal contact area can be effectively dissipated. In such a design, the side of the chip in contact with the current conductor is also thermally coupled to the cooler. This enables double-sided cooling of the chip without the need for an additional cooler on the current conductor side.

[0019] The current conductor is preferably arranged as a DC+, DC-, or AC current conductor. The current conductor can, for example, provide a DC+ or DC- input potential for the chip, with the metal-insulator substrate carrying the AC output potential. Conversely, the current conductor can also carry the AC output potential of the chip, with the metal-insulator substrate providing the DC+ or DC- input potential for the chip. The current conductor can further be contacted with a DC+, DC-, or AC busbar. Furthermore, the current conductor can be contacted with an intermediate circuit capacitor and / or an energy storage device, for example, a battery.

[0020] The invention further relates to a power converter device comprising a printed circuit board arrangement designed as described above. The power converter device comprises, in particular, a plurality of switching elements for converting an input voltage into an output voltage by means of targeted switching of the switching elements. The power converter device preferably comprises at least one power module that combines a plurality of switching elements. In this case, the power module is designed with a printed circuit board arrangement as described above. The power converter device is preferably a DC / AC inverter. In this case, the input voltage is a DC voltage provided by a DC voltage source, which generates a DC input current. The output voltage is an AC voltage that generates a plurality of phase currents of an AC output current. Alternatively, the power converter device can be a DC / DC rectifier.In this case, the input voltage is a DC input voltage provided by a DC power supply (e.g., a DC charging station), and the output voltage is a DC output voltage. The power converter device comprises at least one, preferably several phases, each of which has a half-bridge with a high side and a low side, with a switch each assigned to the high side and the low side.

[0021] The invention further relates to an electric axle drive, comprising an electric machine, a transmission, and a power converter device designed as described above. The electric machine can be designed as a permanent or separately excited synchronous machine or asynchronous machine, which is supplied with a power current via the power converter device. In addition, the electric machine can provide a voltage in generator mode, which is converted by the power converter device into a charging current for a battery storage device. The traction torque provided by the electric machine can be converted by means of a transmission, for example by converting a rotational speed or distributing a torque to various drive axles. For this purpose, the transmission can be designed as a single-stage or multi-stage spur gear transmission, as a planetary gear and / or differential gear.The gearbox can in particular be arranged coaxially or axially parallel to the electric machine.

[0022] Finally, the invention relates to a motor vehicle comprising an electric axle drive as described above.

[0023] Advantageous embodiments and further features are explained in more detail in the form of exemplary embodiments and with reference to figures.

[0024] It shows: Fig. 1 a circuit board arrangement in a perspective view, Fig. 2 a sectional view of a printed circuit board arrangement in a first embodiment, Fig. 3 a sectional view of a printed circuit board arrangement in a second embodiment and Fig. 4 a schematic representation of a motor vehicle.

[0025] Fig. 1 shows a schematic representation of a printed circuit board assembly 1 in one embodiment. The basis of the printed circuit board assembly 1 is a metal-insulator substrate 2. The metal-insulator substrate extends in the plane spanned by the axes X and Y. Two chips 3 are applied to the metal-insulator substrate with their undersides. On their upper sides, the chips 3 are contacted by a current conductor 4. This enables a current to flow from the current conductor 4 via the chip 3 into the first layer 5 of the metal-insulator substrate 2. The metal-insulator substrate comprises a first layer 5 made of, for example, copper, which is electrically conductive, and a second layer 51 made of an insulating material, for example, ceramic. A third layer 52 is again made of copper and is shown in the perspective view in Fig. 1 not visible. In addition to the chips 3, insulation elements 8 are applied with their underside to the first layer 5 of the metal-insulator substrate 2 and form a thermal contact region 6 there. The insulation elements 8 are contacted on their upper side by the current conductor 4. This enables heat to flow in the thermal contact regions 6 from the current conductor 4 via an insulation element 8 into the metal-insulator substrate 2. The current conductor 4 is essentially plate-shaped, i.e. it extends essentially in the X and Y directions and is thin in comparison in the direction Z oriented perpendicular thereto. Furthermore, the current conductor 4 is aligned parallel to the metal-insulator substrate 2. This results in a sandwich structure made up of the metal-insulator substrate 2 and the current conductor 4, with the chips 3 and the insulation elements 8 being arranged between these layers.Furthermore, the current conductor 4 has a plurality of bending regions 10, forming steps in the current conductor 4 that extend in the Z direction. The steps allow for different heights in the Z direction of the chips 3 and the insulation elements 8. Furthermore, the height of the insulation elements in the Z direction can be minimized to provide better thermal coupling between the metal-insulator substrate 2 and the current conductor 4.

[0026] Fig. Figure 2 shows a section of a conductor arrangement 1 in a sectional view taken in the XZ plane. The structure in the Z direction, which enables effective heat dissipation of the chip 3, is particularly evident here. The lowest level is formed by the metal-insulator substrate 2, consisting of a first layer 5, which is electrically conductive, a second layer 51, which is electrically insulating, and a third layer 52, which is again electrically conductive. The chip 3 is applied to the first layer 5 and electrically contacted via the first layer 5. In addition to the chip 3, electrically non-conductive insulation elements 8 are applied to the first layer 5 of the metal-insulator substrate. The top level of the circuit board arrangement is the current conductor 4, which contacts both the insulation elements 8 and the chip 3 on their upper side. The contact between the chip 3 and the current conductor 4 is electrically conductive and allows current to flow from the current conductor to the chip 3.The current conductor 4 has two bending regions 10, whereby the distance in the Z direction between the current conductor 4 and the metal-insulating substrate 2 in the region of the insulating elements 8 or the thermal contact region 6 is reduced. This reduces the thickness of the insulating elements 8. This leads to better thermal coupling between the current conductor 4 and the metal-insulating substrate 2, since the metallic current conductor 4 has better thermal conductivity than the insulating elements 8. On the underside, the metal-insulating substrate 2 is connected to a heat sink 9 by the third layer 52. The metal-insulating substrate 2 and thus the entire printed circuit board arrangement 1 can be effectively cooled via this heat sink 9. The heat flow 11 is indicated by arrows. It is evident that, thanks to the illustrated structure, the chips 3, which are generally the hottest components during operation, are cooled both from the underside and the top.The heat flows from the top side of the chip 3 via the current conductor 4, the insulation element 8, and the metal-insulator substrate 2 into the heat sink 9. Thus, the top side of the chip 3 is also indirectly connected to a heat sink without the need for a second heat sink on the top side of the chip 3 or the current conductor 4. This allows the overall height in the Z direction to be kept low.

[0027] Fig. 3 shows analogous to Fig. 2 shows a further embodiment of the circuit board arrangement. In contrast to the design in Fig. 2, the insulating elements 8 are omitted here and are replaced by interruptions 7 in the first layer 5 of the metal-insulator substrate 2. This has the advantage that the structure contains fewer components. In addition, the thermal coupling between the current conductor 4 and the metal-insulator substrate 2 can be improved compared to the structure with insulating elements 8, since the insulating element 8 generally has poorer thermal conductivity than a direct connection by soldering or sintering. The interruptions 7 are necessary because, without insulating elements 8, insulation must be provided between the thermal contact region 6 and the remaining region of the metal-insulator substrate 2, on which in particular the chip is applied. This insulation is achieved by removing the first layer 5 of the metal-insulator substrate, for example by etching in the Z direction down to the second layer 51.The thermal contact area is electrically insulated from the remaining metal-insulator substrate 2 by a clearance and creepage distance provided by the interruptions 7. For this purpose, the interruption encloses the thermal contact area, particularly in the XY plane.

[0028] Fig. 4 schematically shows a motor vehicle 20 with an electric axle drive 21, wherein the electric axle drive comprises a power converter device 22, an electric machine 23 and a transmission 24. Reference symbol 1 PCB layout 2 Metal insulator substrate 3 chips 4 conductors 5 First layer of the metal insulator substrate 51 Second layer of the metal insulator substrate 52 Third layer of the metal insulator substrate 6 Thermal contact area 7 Interruption 8 Insulation element 9 heat sinks 10 Bending area 11 Heat flow 20 motor vehicles 21 Electric axle drive 22 Power converter device 23 Electric machine 24 gearboxes

Claims

[1] Printed circuit board arrangement (1) comprising a metal-insulator substrate (2), at least one chip (3) and a current conductor (4), wherein the chip (3) is applied to a first layer (5) of the metal-insulator substrate (2) and the chip (3) is electrically contacted by the current conductor (4) on the side facing away from the metal-insulator substrate (2), so that the chip (3) is arranged between the metal-insulator substrate (2) and the current conductor (4), characterized by that the current conductor (4) is thermally conductively connected to the metal-insulator substrate (2) for heat dissipation. [2] Printed circuit board arrangement (1) according to claim 1, characterized by that the metal-insulator substrate (2) is designed as a DBC substrate with the first layer (5) made of copper. [3] Printed circuit board arrangement (1) according to one of claims 1 to 2, characterized by that the current conductor (4) is essentially plate-shaped. [4] Printed circuit board arrangement (1) according to claims 1 to 3, characterized bythat the current conductor (4) is arranged parallel to the metal-insulator substrate (2). [5] Printed circuit board arrangement (1) according to one of claims 1 to 4, characterized by that at least one thermal contact region (6), which is in particular independent of the at least one chip (3), is arranged. [6] Printed circuit board arrangement (1) according to claim 5, characterized by that in the thermal contact area (6) the current conductor (4) is electrically insulated from the rest of the metal-insulator substrate (2). [7] Printed circuit board arrangement (1) according to claim 6, characterized by that the first layer (5) of the metal-insulator substrate (2), in particular by etching, has an interruption (7) for electrical insulation, which encloses the thermal contact area (6). [8] Printed circuit board arrangement (1) according to claim 6, characterized bythat in the thermal contact area (6) an insulating element (8) is arranged between the current conductor (4) and the first layer (5) of the metal-insulator substrate (2). [9] Printed circuit board arrangement (1) according to claim 8, characterized by that the insulation element (8) is designed as a gap pad and / or ceramic and / or insulation paper and / or insulation film. [10] Printed circuit board arrangement (1) according to one of the preceding claims, characterized by that the current conductor (4) has a bending region which shortens the distance between the current conductor (4) and the metal-insulator substrate (2) in the thermal contact region (6). [11] Printed circuit board arrangement (1) according to one of the preceding claims, characterized by that a heat sink (9) is arranged on the side of the metal-insulator substrate (2) which faces away from the current conductor (4) in order to dissipate heat from the metal-insulator substrate (2). [12] Printed circuit board arrangement (1) according to one of the preceding claims, characterized by that the current conductor (4) is arranged as a DC+, DC- or AC current conductor. [13] Power converter device (22) comprising a printed circuit board arrangement (1) which is designed according to one of claims 1 to 12. [14] Electric axle drive (21) comprising an electric machine (24), a transmission (23) and a power converter device (22) which is designed according to claim 13. [15] Motor vehicle (20) comprising an electric axle drive (21) according to claim 14.

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