Power module

Abstract

The invention relates to a power module (1), the power module (1) having a substrate (2) with a metallization (3), on which at least one power semiconductor switch (4) is arranged, an RC series circuit is provided, which consists of at least one resistor (6) and at least one capacitor (6), the at least one resistor (6) is arranged on the substrate (2), and the at least one capacitor (6) is arranged on the substrate (2). The at least one capacitor (12) is arranged on a separate substrate (8) above the at least one resistor (6).

Description

Technical Field

[0001] The invention relates to a power module, wherein the power module comprises a substrate with a metallization and at least one power semiconductor switch is arranged on the substrate. Background Art

[0002] One area of ​​application for power modules is their use in pulse-controlled inverters, in particular in traction systems for electric vehicles. Other areas of application are, for example, DC / DC converters.

[0003] In pulse-controlled inverters for traction applications, it is always necessary to minimize the commutation inductance. This refers to the inductance in the commutation loop. This loop consists of the intermediate circuit capacitor, the power module, and the interfaces between them. The inductance generated by this loop is the commutation inductance. The greater this commutation inductance, the higher the so-called shutdown overvoltage when the power semiconductors are switched off.

[0004] In mass production, the possibilities for commutation circuits with very low inductance are limited. To address this problem, RC series circuits, also known as RC snubbers, are known. Here, both the resistor and the capacitor can consist of multiple components connected in series or in parallel. The RC series circuit can be connected in parallel with the intermediate circuit capacitor, i.e., in parallel with the half-bridge. However, designs are also known in which the RC series circuit is connected in parallel with the corresponding power semiconductor switches. Due to its relatively small size, it has been proposed to integrate the RC series circuit into the power module. This allows the formation of a very low-inductance commutation unit consisting of the power semiconductor and the RC series circuit (RC snubber).

[0005] The problem is that an RC snubber has electrical power losses in the resistor, which causes the temperature to rise. Most capacitors are not designed for temperatures exceeding 105° C. or 125° C. This in turn limits the possible switching speed.

[0006] US Pat. No. 11,631,974 B2 discloses a snubber circuit in which resistors and capacitors are stacked one on top of another, wherein these are arranged on separate substrates. Summary of the Invention

[0007] The technical problem underlying the present invention is to provide a compact power module with which higher switching speeds can be achieved.

[0008] The solution to this technical problem is provided by the power module according to the invention. Further advantageous embodiments are apparent from the description.

[0009] The power module comprises a substrate with metallization, on which at least one power semiconductor switch is arranged. An RC series circuit is provided, consisting of at least one resistor and at least one capacitor. The at least one resistor is arranged on the substrate, while the at least one capacitor is arranged on a separate substrate above the at least one resistor. The basic concept here is to spatially separate the RC series circuit. The resistor, which generates heat losses, is arranged on a main substrate that has a good thermal connection to a heat sink or cooling device. Conversely, the temperature-sensitive capacitor is spatially separated from the heat-loss components (resistor and power semiconductor switch). This requires only slightly more substrate area for the resistor, while the power module becomes only slightly taller due to the additional substrate with the capacitor. The power semiconductor switch is, for example, an IGBT or a MOSFET, in particular a SiC or GaN MOSFET. The substrate of the at least one capacitor can be designed as a printed circuit board, such as an FR4 PCB or a printed circuit board with a core and prepreg material. The power module can also be cast using molding compound.

[0010] In principle, the substrate or printed circuit board of the at least one capacitor can be placed directly on the resistor. In this case, the contact can also be made via the printed circuit board. However, the resistor and printed circuit board must then be well thermally decoupled.

[0011] In one embodiment, the base of the capacitor is spatially spaced apart from the resistor. This improves thermal decoupling. To this end, the printed circuit board is mechanically held above the resistor by means of projections or the like and then, for example, cast.

[0012] In another embodiment, at least one half-bridge circuit is arranged on a substrate having a resistor, wherein an RC series circuit is arranged in parallel with the half-bridge circuit. This structural form saves components.

[0013] In another embodiment, the electrical connection between the at least one capacitor and the associated connection (resistor and DC+ or DC-) on the substrate is achieved by means of bonding wires. Here, the electrical connection can also have multiple bonding wires connected in parallel, so that the current is divided among the individual parallel bonding wires.

[0014] In another embodiment, each electrical connection to the substrate is realized by at least two bonding wires, wherein the bonding wires of the different electrical connections are arranged alternately with one another, thereby reducing the effective inductance of the bonding wires.

[0015] As an alternative to bonding wires, the electrical connection between the at least one capacitor and the associated connection on the substrate can be achieved by means of a heavy ribbon. The advantages are a higher current carrying capacity and mechanical robustness, but the bonding process is somewhat more complex.

[0016] In another embodiment, the electrical connection to the substrate is realized by at least two bonding ribbons, wherein the electrically connected bonding ribbons are arranged one above the other. This also keeps the overall inductance low.

[0017] In a further embodiment, the at least one resistor is connected to the metallization via a soldered or sintered connection.

[0018] In a further embodiment, the at least one capacitor is contact-connected by means of a reflow soldering connection on a separate substrate, in particular a printed circuit board, which can be realized very cost-effectively.

[0019] In a further embodiment, a metal base plate is arranged below the substrate, which, in addition to mechanical stability, simplifies the thermal connection to the cooling device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be described in more detail below based on preferred embodiments, wherein:

[0021] Figure 1 A schematic diagram showing the structure of the power module,

[0022] Figure 2 A schematic diagram showing the alternating guidance of the bonding wires, and

[0023] Figure 3 A schematic diagram of two joined ribbons is shown. DETAILED DESCRIPTION

[0024] exist Figure 1 The layer structure of a power module 1 is schematically shown in FIG. A metallization 3, preferably composed of copper, is applied to a substrate 2. At least one power semiconductor switch 4 is applied to the metallization 3 by means of a solder layer 5. The power semiconductor switch 4 is, for example, designed to be bare. Similarly, a resistor 6 is applied to the metallization 3 by means of a solder layer 5, with the solder layer 5 being connected to a contact region 7 of the resistor 6.

[0025] Arranged above resistor 6 is another substrate 8 in the form of a printed circuit board 9, with the bottom side of substrate 8 at a distance d from the top side of resistor 6. Arranged on substrate 8 is at least one capacitor 10, with contact areas 11 each connected to a solder layer 12. Resistor 6 and capacitor 10 are electrically connected in series, with the electrical connection being achieved via at least one bonding wire 13. Resistor 6 is then connected to DC+ or DC- on substrate 2. Accordingly, capacitor 10 is connected to DC- or DC+ via another bonding wire (not shown), resulting in an RC series circuit between DC+ and DC-. This structure allows capacitor 12 and resistor 6, which generates heat losses, to be largely thermally decoupled due to their spatial separation. Arranged beneath substrate 2 is a metal base plate 16, which is connected to each other via a solder layer 17 or a sintered connection.

[0026] exist Figure 2 The bonding wire 13 between the capacitor 12 and the resistor 6 and the bonding wire from the capacitor 12 to the substrate 2 (see FIG. Figure 1 ) on the DC+ or DC- connection of the bonding wire 14. In this case, the bonding wires 13, 14 are routed alternately with one another, wherein the current directions in the bonding wires 13, 14 are opposite.

[0027] exist Figure 3 , an electrical connection between the resistor 6 and the capacitor 12 is shown, which is formed by two bonding ribbons 15 arranged one above the other.

[0028] List of Reference Numerals

[0029] 1 Power Module

[0030] 2 base

[0031] 3 Metallization

[0032] 4 Power semiconductor switches

[0033] 5 welding layer

[0034] 6 resistors

[0035] 7 Contact area

[0036] 8 Underside of the base

[0037] 9. Printed Circuit Board

[0038] 10 Capacitors

[0039] 11 Contact area

[0040] 12 Capacitors

[0041] 13 Bonding wire

[0042] 14 Bonding wire

[0043] 15. Joining Strips

[0044] 16 Metal base

[0045] 17 welding layer

[0046] d spacing.

Claims

1. A power module (1), wherein: The power module (1) comprises a substrate (2) with a metallization (3), on which at least one power semiconductor switch (4) is arranged, wherein an RC series circuit is provided, which consists of at least one resistor (6) and at least one capacitor (12). It is characterized by: The at least one resistor (6) is arranged on the substrate (2), wherein the at least one capacitor (12) is arranged on a separate substrate (8) above the at least one resistor (6).

2. The power module according to claim 1, wherein: The substrate (8) of the capacitor (12) is arranged spatially spaced apart from the at least one resistor (6).

3. The power module according to any one of the preceding claims, characterized in that At least one half-bridge circuit is arranged on the substrate (2), wherein the RC series circuit is arranged in parallel with the half-bridge circuit.

4. The power module according to any one of the preceding claims, characterized in that The electrical connection between the at least one capacitor (12) and an associated connection on the substrate (2) is realized by means of bonding wires (13, 14).

5. The power module according to claim 4, characterized in that: Each electrical connection to the substrate (2) is realized by at least two bonding wires (13, 14), wherein the bonding wires (13, 14) of different electrical connections are arranged alternately with each other.

6. The power module according to any one of claims 1 to 3, characterized in that: The electrical connection between the at least one capacitor (12) and an associated connection on the substrate (2) is achieved by means of a bonding strip (15).

7. The power module according to claim 6, characterized in that: The electrical connection to the substrate (2) is respectively realized via at least two bonding strips (15), wherein the electrically connected bonding strips (15) are arranged one above the other.

8. The power module according to any one of the preceding claims, characterized in that The at least one resistor (6) is connected to the metallization (3) via a solder connection or a sintered connection.

9. The power module according to any one of the preceding claims, characterized in that The at least one capacitor (12) is contacted on the separate substrate (8) by means of a reflow soldering connection.

10. The power module according to any one of the preceding claims, characterized in that A metal bottom plate (16) is arranged below the base (2).

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