Assembly with a heat sink, as well as its manufacture and use

Abstract

Assembly, comprising: - an electronic power module (13-20) with unpackaged semiconductor chips (13) and a dielectric carrier plate (15, 16) and - an uncoated copper heat sink (10) thermally connected to the power module (13-20) with a base plate (11) for temporarily storing heat emitted by the power module (13-20) and a cooling structure (12) projecting from the base plate (11) for dissipating the heat to a coolant, characterized by the following features: - the cooling structure (12) comprises pins and fins, - the semiconductor chips (13) each have a direct attachment (14) to the carrier plate (15, 16), - the carrier plate (15, 16) comprises a ceramic substrate (15) and a copper layer (16) facing away from the semiconductor chips (13), which is bonded on one side to the ceramic substrate (15) and on the other side to the heat sink (10) by solder (17) and - the carrier plate (15, 16) has copper traces (18) extending from the semiconductor chips (13) and being materially connected to the ceramic substrate (15).

Description

[0001] The present invention relates to an assembly with a heat sink, the use and manufacture of such an assembly.

[0002] In power electronics, power modules (containing semiconductor chips) are used, which are mounted on a heat sink for thermal dissipation. These heat sinks are typically made of copper, aluminum, or corresponding ceramics. Their (absolute) heat capacity is sometimes referred to as thermal mass, and their thermal conductivity as thermal conductivity.

[0003] Particularly well-known are assemblies with liquid-cooled power modules. In relevant specifications, the design-related thermal resistance between the semiconductor junction and the liquid is, for example, denoted by the symbol R. thJ-F provided.

[0004] DE 102008009510 B3 discloses a copper heat sink plate for storing thermal energy. The patent further teaches how to enlarge the plate to increase its heat capacity.

[0005] DE 112005003099 T5 describes an electronic component, for example, for power control of inverters in electric motors. Here too, a copper cooling plate is provided, which can be enlarged if necessary to increase the heat capacity.

[0006] DE 10062108 A1 proposes a copper heat sink for a power electronics module. The module has additional heat capacity to buffer peak thermal power losses.

[0007] DE 102013220591 A1 also concerns a power module with a copper heat sink.

[0008] DE 10205408 A1 discusses a semiconductor module with a copper heat-conducting base for dissipating the waste heat into a cooling fluid.

[0009] DE 19645636 C1 discloses another power module with a copper heat sink.

[0010] DE 102019207012 A1 also describes a power module with a copper heat sink.

[0011] DE 102017222720 A1 proposes a protective-coated substrate made of copper or a copper alloy for cooling power electronics, the heat capacity of which is to be increased by thickening its substrate plate.

[0012] DE 102019001113 A1 relates to a cooling arrangement for power electronics, the base plate of which is thicker in the area of ​​the contact surface with the electronics in order to increase the heat capacity.

[0013] CN 108882499 A discusses a cooling device for a power module in which the thickness of the mainboard in the area of ​​the cooling elements or the power electronics is increased to increase the heat capacity.

[0014] The invention provides an assembly with a heat sink and methods for its use and manufacture according to the independent claims.

[0015] One advantage of using copper here lies in its superior thermal conductivity compared to aluminum. Furthermore, the absence of any protective coating improves heat transfer from the power module being cooled to the heat sink.

[0016] The proposed assembly exhibits numerous positive effects, primarily due to its direct assembly and interconnection technology, a technique known in electronics. This means it is a flat assembly with unpackaged semiconductor chips (dies), which are not housed in discrete plastic or ceramic packages and are attached directly to the substrate. The increased thermal inertia of the overall system with respect to the maximum chip temperature, achieved according to the invention, proves particularly advantageous in such assemblies.

[0017] This makes it possible to subject the semiconductor chips to transient loads while the heat sink's base plate temporarily stores the heat dissipated by the power module, and simultaneously supply the heat sink with a controlled flow of coolant, allowing the cooling structure to dissipate the heat in a controlled manner. A typical chip can thus be subjected to very high currents for short periods (0.5 to 1 s) and to increased currents for medium periods (2 to 20 s), while the increased inertia of the overall system allows the coolant flow to be regulated more slowly and therefore more efficiently.

[0018] This is advantageous, for example, in a modular multi-level converter (MMLC) or other pulse inverter in electrical drive technology, where the corresponding design allows for increased peak power of the overall system. This proves useful, for instance, during the race start of a sports car, where the vehicle accelerates from a standstill to a speed of 350 km / h. A driving function for accessing such peak drive power is marketed by manufacturers, for example, under the name "Launch Control".

[0019] According to the invention, the carrier plate comprises a ceramic substrate and a copper layer facing away from the semiconductor chips, which is bonded to the ceramic substrate (direct copper bonding, DBC) on one side and soldered to the heat sink on the other. Thanks to the proposed approach, the power semiconductors and the layer structure of such an assembly are subjected to lower temperature fluctuations (stress). This significantly increases the service life.

[0020] A heat sink for such a DBC power module can be soldered directly to the heat sink's base plate after milling. This eliminates the otherwise usual coating step during the manufacturing process, which in turn simplifies the soldering of the power modules and thus reduces the manufacturing costs of the resulting assembly in two ways.

[0021] Finally, the use of oil as an operating fluid can be provided, which, in addition to its cooling function, also prevents the oxidation of the cooling element.

[0022] An embodiment of the invention is shown in the drawings and is described in more detail below. Fig. Figure 1 shows a conventional assembly. Fig. Figure 2 shows an assembly according to the invention. Fig. Figure 3 shows the time course of the operating temperature of a chip under maximum load in each of the two assemblies.

[0023] Fig. Figure 1 illustrates an electronic power module (13-20) thermally connected to a heat sink (10). In a conventional design, a heat sink (10) with low thermal mass is used. Additionally, a water-based coolant is employed. This necessitates that the heat sink (10) must either be made of a water-resistant material or undergo a complex coating process. In particular, copper and copper alloys with near-optimal thermal properties can only be used with increased effort (coating).

[0024] The heat sink (10) according to Fig. In contrast, version 2 is designed in such a way that it has a deliberately increased thermal mass and the thermal resistance R thJ-F The heat dissipation into the fluid remains unchanged, thus maintaining a high level compared to the conventional system. The thermal resistance between the semiconductor chip (13) and the base plate (11) of the heat sink (10) is advantageously low.

[0025] While the thermal mass of a heat sink (10) may also be increased by other design measures, e.g., a corresponding thickening of the base plate (11) of the heat sink (10) or the use of coated copper instead of aluminum, if—as in Fig. Figure 2 illustrates that, with a non-aqueous coolant, copper, a material with high specific heat capacity, can be used without incurring the costs associated with its coating. In the illustrated embodiment, therefore, an uncoated copper heat sink (10) is used in combination with oil.

[0026] The cooling structure (12), which extends downwards from the base plate (11) as shown in the illustration and through which the flow is directed, comprises - in accordance with the so-called pin-fin design - a large number of pins which transfer the heat to the controlled supply of oil.

[0027] As an example, the copper traces (18) running along the upper surface of the carrier plate (15, 16) and connected to its ceramic substrate (15) are shown connected to the semiconductor chips (13) and terminals (20) of the power module (13-20) by means of bond wires (19). It should be noted that the inventive approach may also be used, for example, in the context of so-called chip-flip connection technology.

[0028] The time course of the operating temperature of the respective semiconductor chip (13) of the assemblies according to Fig. 1 and Fig. 2 under sustained maximum load is schematically the Fig. 3. As a comparison of the two curves readily reveals, the temperature rise is slower in the case of the construction according to the invention. Accordingly, the proposed approach also delays the transient heating of the semiconductor chips in non-steady-state applications (13 - Fig. 1 and Fig.2) and avoids critical conditions (e.g. high temperature fluctuations) during peak loads.

Claims

[1] Assembly comprising: - an electronic power module (13-20) with unpackaged semiconductor chips (13) and a dielectric carrier plate (15, 16) and - an uncoated copper heat sink (10) thermally connected to the power module (13-20) with a base plate (11) for temporarily storing heat emitted by the power module (13-20) and a cooling structure (12) projecting from the base plate (11) for dissipating the heat to a coolant, characterized by the following characteristics: - the cooling structure (12) comprises pins and fins, - the semiconductor chips (13) each have a direct attachment (14) to the carrier plate (15, 16), - the carrier plate (15, 16) comprises a ceramic substrate (15) and a copper layer (16) facing away from the semiconductor chips (13), which is bonded on one side to the ceramic substrate (15) and on the other side to the heat sink (10) by solder (17) and - the carrier plate (15, 16) has copper traces (18) extending from the semiconductor chips (13) and being materially connected to the ceramic substrate (15). [2] Assembly according to claim 1, characterized by one of the following characteristics: - the assembly is a pulse inverter or - the assembly is an electric drive train. [3] Assembly according to claim 1 or 2, characterized by the following characteristics: - the power module (13-20) has bond wires (19) and terminals (20) and - the bond wires (19) connect the semiconductor chips (13) to the copper traces (18) and terminals (20). [4] Use of an assembly according to any one of claims 1 to 3, characterized by the following characteristics: - the semiconductor chips (13) are subjected to transient loads, while the base plate (11) temporarily stores the emitted heat, and - Oil is supplied to the cooling element (10) in a controlled manner, so that the cooling structure (12) releases the heat to the oil in a controlled manner. [5] Manufacturing an assembly according to any one of claims 1 to 3, characterized by the following characteristics: - the heat sink (10) is milled from copper and - the carrier plate (15, 16) of the power module (13-20) is soldered directly to the base plate (11) of the heat sink (10).

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