Power electronics module, method for producing a power electronics module, and inverter having a power electronics module

Abstract

Disclosed is a power electronics module (LM), comprising: - a circuit carrier (ST); a cooler (KL); - a solder preform (LF) which is arranged between the circuit carrier (ST) and the cooler (KL) and which is soldered to the circuit carrier (ST) and to the cooler (KL) at a specified soldering temperature and thus physically and thermally connects the circuit carrier (ST) to the cooler (KL); - wherein the solder preform (LF) comprises a solder (LT) having a melting temperature equal to or lower than the soldering temperature, and - the solder preform (LF) also has a plurality of individual filler particles (FK) embedded in the solder (LT); - wherein the filler particles (FK) exhibit greater thermal conductivity than the solder (LT). Also described are a method for producing the aforementioned power electronics module, and an inverter having an aforementioned power electronics module.

Description

[0001] Description

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

[0003] Technical area:

[0004] The present invention relates to a power electronics module, in particular for an inverter or a DC / DC converter, as well as to an inverter or power inverter, in particular for an electric drive of a motor vehicle, comprising at least one power electronics module. Furthermore, the invention relates to a method for producing said power electronics module.

[0005] State of the art and task of the invention:

[0006] Half-bridge power electronics modules are well-known and are used, among other things, as part of an inverter or a DC / DC converter, especially in the electric drive of a motor vehicle. Due to their functionality, these power electronics modules exhibit high power dissipation and must be cooled during operation using coolers, particularly liquid-cooled ones, that are physically and thermally connected to the circuit boards of the power electronics modules.

[0007] The general requirement is to make the cooling of the power electronics modules and thus the inverters or DCDC converters with the aforementioned power electronics modules more efficient.

[0008] The object of the present application is therefore to provide a possibility with which a power electronics module and thus an inverter or a DCDC converter can be cooled more efficiently.

[0009] Description of the invention:

[0010] This object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the subclaims. According to a first aspect of the invention, a power electronics module is provided, in particular for an inverter or a DCDC converter, specifically for an electric drive of a motor vehicle.

[0011] The power electronics module has a circuit carrier and a cooler for cooling the power electronics module.

[0012] The power electronics module further comprises a preformed solder joint (in English, a "solder preform"), which is arranged between the circuit carrier and the cooler and is soldered to the circuit carrier and the cooler (in a soldering process), thus (purely) mechanically, or physically and thermally, connecting the circuit carrier to the cooler. The solder joint contains a solder (or solder) with a melting temperature at or below the soldering temperature. The solder joint further comprises a plurality of individual thermally conductive filler particles embedded in the solder and having a higher thermal conductivity than the solder.

[0013] The circuit carrier can be formed, for example, as a ceramic substrate, such as a DBC substrate (Direct Bonded Copper substrate) or an ABM substrate (Active Metal Brazed substrate), or as a metal core circuit board, such as an IMS (Insulated Metal substrate).

[0014] The power electronics module can comprise at least one switchable half-bridge with at least one positive-voltage-side semiconductor switch and at least one negative-voltage-side semiconductor switch formed on the circuit carrier. The two semiconductor switches can be formed, in particular, as silicon carbide (SiC) semiconductor switches, specifically as SiC MOSFETs. Alternatively, the two semiconductor switches can also be formed as IGBTs, specifically as gallium nitride (GaN) semiconductor switches or as gallium arsenide (GaAs) semiconductor switches.

[0015] The cooler can be formed as a cooler with a coolant channel for conducting a cooling liquid and / or with a cooler pin-fin structure to enlarge the cooler surface. Furthermore, the cooler can be formed as an aluminum or copper cooler. The cooler and the circuit carrier can have a solderable layer, such as a copper layer, on their respective upper sides facing the solder connection preform and thus the respective other component (circuit carrier or cooler). This solderable layer can either be an original component of the respective component (cooler or circuit carrier) formed in one piece with the corresponding component or can be subsequently formed or coated on the corresponding upper side of the corresponding component.

[0016] The solder connection preform is a solid, independent part that can be transported similarly to a conventional solder preform, particularly in the form of a flat sheet metal part or a wound sheet metal strip, and can be cut or punched into the appropriate shape, especially if necessary, before soldering to the circuit board and the cooler.

[0017] The solder connection preform contains a solder (of a known type) which melts and deforms when soldered to the circuit carrier and the cooler under the influence of a predetermined soldering temperature which is equal to or higher than the melting temperature of the solder.

[0018] The solder joint preform further contains a plurality of individual, thermally highly conductive filler particles which are embedded in the solder (especially evenly distributed) and do not melt or deform during soldering under the influence of the predetermined soldering temperature, which is lower than the melting temperature of the filler particles.

[0019] Due to its inherent mechanical strength and stability, the solder joint preform can hold the filler particles embedded in the solder together. The filler particles also have their own mechanical strength and stability and can thus provide the solder joint preform with additional mechanical strength and stability.

[0020] Unlike conventional solder joints, which primarily establish electrical connections between electrical components, the preformed solder joint creates a purely mechanical, or physical, and thermal, connection between the circuit board and the cooler. The primary focus is on improved heat transfer from the circuit board to the cooler, and thus efficient cooling of the power electronics module. For this purpose, the filler particles are made of a material with a (significantly) higher thermal conductivity than the solder. Due to the high melting temperature, which is higher than the soldering temperature or the soldering temperature,The melting temperature of the solder means that the filler particles retain their original shape during soldering and thus also after the soldering of the solder joint preform to the circuit board and the cooler. After soldering, they act like a "thermal bridge" in the solder joint preform, through which the waste heat from the circuit board can be transported to the cooler more quickly than via the solder in the solder joint preform. The higher thermal conductivity of the filler particles compared to the solder reinforces the effect of the "thermal bridge." Furthermore, by evenly distributing the filler particles in the solder or in the solder joint preform, homogeneous heat transfer can be achieved across the entire solder joint preform.

[0021] This provides a way to cool a power electronics module and thus an inverter or a DCDC converter with a power electronics module more efficiently.

[0022] The filler particles in particular have a melting temperature that is higher than the soldering temperature.

[0023] The solder joint preform does not establish an electrical connection between the circuit board and the cooler. The solder joint via the solder joint preform is not intended for power transmission. The solder joint preform merely physically holds the circuit board and the cooler together and (only) transfers the waste heat from the circuit board to the cooler.

[0024] As solid particles, the filler particles can have regular or irregular shapes, in particular spherical, egg-shaped, etc.

[0025] The solder can, for example, be designed to compensate for unevenness between the circuit board and the cooler by deforming or flowing as a result of melting during the soldering process. The filler particles, whose diameter is particularly much smaller than the solder connection preform, can move in the liquid solder, allowing the distance between the circuit board and the cooler to be adjusted to their uneven surfaces. The thermal conductivity of the filler particles can be at least 100%, or at least 200%, or at least 500%, or at least 1000% higher than the thermal conductivity of the solder. In other words, the thermal conductivity of the filler particles can be at least a factor of 2 or more higher than the thermal conductivity of the solder.

[0026] The thermal conductivity of the packing particles can be the same as the thermal conductivity of the cooler or higher than the thermal conductivity of the cooler.

[0027] The filler particles can be made of the same material as the cooler's body material. Accordingly, the filler particles can have the same thermal conductivity as the cooler's body material. If the cooler body is made of copper, the filler particles can also be made of copper. The filler particles can be formed as copper spheres. Alternatively, the filler particles can be made of one or more copper-like metals or one or more comparable metal alloys.

[0028] The thermal conductivity of the filler particles can also be (significantly) higher than the thermal conductivity of the circuit carrier.

[0029] The filler particles may have a melting temperature that is higher than the soldering temperature (thus higher than the melting temperature of the solder), such as at least 10°C or at least 30°C.

[0030] As previously mentioned, the filler particles can be shaped in such a way that they can flow in the melting solder during the soldering process and can compensate for unevenness between the circuit board and the cooler.

[0031] The filler particles have a maximum diameter or a maximum extension which is in particular below the (minimum) thickness of the brazed joint component.

[0032] The filler particles also have a minimum diameter or minimum dimension, which is typically 1 micrometer, 5 micrometers, or 10 micrometers. In particular, the filler particles have different diameters or dimensions, which lie between the minimum diameter or minimum dimension of 1 micrometer (or 5 or 10 micrometers) and the minimum thickness of the solder joint preform.

[0033] The filler particles in the brazed joint preform may have a volume fraction of a maximum of 80%, a maximum of 70%, a maximum of 60%, or a maximum of 50%. Furthermore, the filler particles in the brazed joint preform may have a volume fraction of at least 1%, at least 10%, or at least 20%.

[0034] According to a second aspect of the invention, a method for manufacturing a power electronics module as described above is provided.

[0035] According to the method, a circuit carrier and a cooler are provided. The circuit carrier and the cooler are each provided with a correspondingly solderable surface.

[0036] Furthermore, a preformed solder joint component is preformed, comprising solder and a plurality of individual filler particles, for example, in the form of copper beads, with the filler particles embedded in the solder. The filler particles are made of a material with good thermal conductivity, so that they have a higher thermal conductivity than the solder.

[0037] The solder joint preform is placed between the circuit board and the cooler and, in a soldering process, is soldered to the circuit board and the cooler at a specified soldering temperature, thus physically, mechanically, and thermally bonding them. The soldering temperature is determined such that it is at or above the melting temperature of the solder while remaining below the melting temperature of the filler particles.

[0038] During the soldering process, the solder from the solder joint preform deforms or liquefies, physically connecting the circuit board to the cooler. The filler particles, however, retain their shape and may float in the deforming or liquefied solder, thereby compensating for any unevenness between the circuit board and the cooler. After soldering, the solder joint preform establishes a purely physical, mechanical, and thermal connection between the circuit board and the cooler.

[0039] The soldering process can be carried out at a temperature at which only the solder melts or liquefies, leaving the filler particles unmelted or still retaining their solid form. In this case, the temperature can be at or approximately 10°C higher than the melting temperature of the solder, while at the same time being lower, such as at least 10°C lower, than the melting temperature of the filler particles.

[0040] Alternatively, the soldering process can be carried out at a temperature at which both the solder and the filler particles melt, liquefy, or deform. In this case, the temperature can be higher than the melting temperature of the solder and the melting temperature of the filler particles.

[0041] Advantageous embodiments of the power electronics 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.

[0042] According to a third aspect of the invention, an inverter, in particular a power inverter for an electric drive of a motor vehicle, is provided.

[0043] The inverter comprises (at least) one previously described power electronics module, which comprises (at least) one semiconductor switch arranged on the circuit carrier of the power electronics module. The inverter further comprises (at least) one driver circuit for operating the (at least) one semiconductor switch.

[0044] Description of the drawing:

[0045] An exemplary embodiment of the invention is explained in more detail below with reference to the accompanying drawing. The only figure 1 shows a schematic cross-sectional view of a section of a power electronics module LM of a power inverter of an electric drive device of a motor vehicle according to an exemplary embodiment of the invention. The power electronics module LM forms, for example, one of three switchable half-bridges of a three-phase bridge circuit of the power inverter and has two semiconductor switches HS that are electrically connected according to the function of the half-bridge. Alternatively, the power electronics module LM can form the entire three-phase bridge circuit of the power inverter and accordingly have six or more semiconductor switches HS that are electrically connected according to the function of the three-phase bridge circuit. The semiconductor switches HS are, for example,as SiC (silicon carbide) semiconductor switches, in particular as SiC MOSFETs (in English “silicon carbide metal oxide semiconductor field-effect transistors”).

[0046] To operate the power electronics module LM, the power inverter also has a driver circuit (not shown in Figure 1) which is electrically or signal-wise connected to the semiconductor switches to operate them.

[0047] The power electronics module LM has a circuit carrier ST on which the semiconductor switches HS are arranged and electrically connected. In this embodiment, the circuit carrier ST is formed as a DBC substrate having a top-side copper layer OS for forming electrical conductor tracks and a bottom-side copper layer US for heat dissipation and for forming a physical and thermal connection to a cooler KL, which will be discussed below, as well as an electrically insulating and simultaneously thermally conductive ceramic layer KS, which is arranged between the two copper layers OS, US and physically connects the two copper layers OS, US to one another. The semiconductor switches HS are arranged on the top-side copper layer OS and are electrically contacted with the corresponding conductor tracks of the copper layer OS.

[0048] The power electronics module LM further comprises the aforementioned cooler KL for cooling the power electronics module LM, which in this embodiment is formed as a liquid-cooled copper cooler with cooling channels for passing a cooling liquid.

[0049] The cooler KL has a solderable cooling surface KF, on which the circuit carrier ST is arranged via its underside, also solderable copper layer US, and is soldered to the cooler KL by means of a solder connection preform LF, which will be described below. Between the circuit carrier ST and the cooler KL, the power electronics module LM has the aforementioned solder connection preform LF, which is arranged as a preformed part between the circuit carrier ST and the cooler KL and is soldered to both the circuit carrier ST and the cooler KL in a single soldering process, thus physically and thermally connecting the circuit carrier ST to the cooler KL.

[0050] The cooling surface KF of the cooler KL, and thus the cooler KL itself, as well as the underside copper layer US of the circuit carrier ST, have no electrical function. In particular, the cooling surface KF and the underside copper layer US do not form a potential surface. Accordingly, the solder connection preform LF establishes a purely mechanical, physical and thermal connection between the circuit carrier ST and the cooler KL, and not an electrical connection between these two components.

[0051] The solder joint preform LF is formed as a separate, pre-formed, sheet-like, solid part before the soldering process and has a thickness of, for example, 200 micrometers (before the soldering process).

[0052] The preformed solder joint (LF) contains a solder (LT) in which a large number of individual metallic filler particles (FK) are embedded. The solder (LT) consists, for example, of a commercially available solder. The filler particles (FK) are formed as copper spheres with a diameter of 10 to 100 micrometers, especially around 30 micrometers.

[0053] The filler particles FK have a thermal conductivity of 385 W / m*K, while the solder LT has a thermal conductivity of 51 W / m*K.

[0054] The soldered connection with the LF solder joint preform has a cost advantage as well as an advantage in the manufacturing process compared to a sintered connection.

[0055] The production of the previously described power electronics module LM is carried out as follows:

[0056] First, the circuit carrier ST with the solderable underside copper layer US and the cooler KL with the likewise solderable cooling surface KF are prepared. Furthermore, the solder connection preform LF is manufactured from the solder LT and a plurality of individual filler particles FK by embedding or mixing the filler particles FK into the solder LT.

[0057] The preformed solder connection part LF is placed between the circuit carrier ST and the cooler KL or between the underside copper layer US of the circuit carrier ST and the cooling surface KF of the cooler KL and is soldered to the circuit carrier ST and the cooler KL in a soldering process under the influence of a sufficient soldering temperature.

[0058] Under the influence of the soldering temperature, which is higher than the melting temperature of the solder LT, the solder LT melts. The filler particles FK in the solder LT retain their original shape and flow with the melting solder LT into a cavity between the underside copper layer US and the cooling surface KF, filling the cavity and thus compensating for the unevenness between the underside copper layer US and the cooling surface KF, and thus between the circuit carrier ST and the cooler KL. Alternatively, the filler particles FK can deform under the influence of the soldering temperature and fill the gaps between the soldering partners, thereby compensating for the local height differences between the connecting surfaces of the two soldering partners.

[0059] The soldering process described above with the pre-formed LF solder connection component can be carried out in a conventional production process on a conventional system with no or negligible additional effort or cost.

Claims

Patent claims 1. A power electronics module (LM), comprising: a circuit carrier (ST); a cooler (KL); a preformed solder connection preform (LF) arranged between the circuit carrier (ST) and the cooler (KL) and soldered to the circuit carrier (ST) and the cooler (KL) at a predetermined soldering temperature, thus physically and thermally connecting the circuit carrier (ST) to the cooler (KL); - wherein the solder joint preform (LF) comprises a solder (LT) having a melting temperature which is at or below the soldering temperature, and the solder joint preform (LF) further comprises a plurality of individual filler particles (FK) which are embedded in the solder (LT); - where the filler particles (FK) have a higher thermal conductivity than the solder (LT).

2. Power electronics module (LM) according to claim 1, wherein the filler particles (FK) have a melting temperature which is higher than the soldering temperature.

3. Power electronics module (LM) according to one of the preceding claims, wherein the solder connection preform (LF) does not establish an electrical connection between the circuit carrier (ST) and the cooler (KL).

4. Power electronics module (LM) according to one of the preceding claims, wherein the thermal conductivity of the filler particles (FK) is at least a factor of 2 or more than the thermal conductivity of the solder (LT).

5. Power electronics module (LM) according to one of the preceding claims, wherein the thermal conductivity of the filler particles (FK) is equal to or higher than the thermal conductivity of the cooler (KL).

6. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) consist of the same material as the body material of the cooler (KL).

7. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) have a melting temperature which is higher than the soldering temperature.

8. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) are shaped such that they flow in the melting solder (LT) during the soldering process and thereby compensate for unevenness between the circuit carrier (ST) and the cooler (KL).

9. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) have a maximum extension which is below the minimum thickness of the solder connection preform (LF).

10. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) have a minimum dimension of more than 1 micrometer or more than 5 micrometers or more than 10 micrometers.

11. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) in the solder connection molding (LF) have a volume fraction of a maximum of 80% or a maximum of 70% or a maximum of 60% or a maximum of 50%.

12. Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) in the solder connection molding (LF) have a volume fraction of at least 1% or at least 10% or at least 20%.

13. A method for producing a power electronics module (LM) according to one of the claims, comprising the following method steps: Providing a circuit carrier (ST) and a cooler (KL); Forming a solder joint preform (LF) with a solder (LT) and a plurality of individual filler particles (FK) by embedding the filler particles (FK) in the solder (LT), wherein the filler particles (FK) have a higher thermal conductivity than the solder (LT); - Arranging the pre-formed solder connection part (LF) between the circuit carrier (ST) and the cooler (KL); Physical and thermal connection of the circuit carrier (ST) and the cooler (KL) by soldering the solder connection part (LF) to the Circuit carrier (ST) and the cooler (KL) in a soldering process under a predetermined soldering temperature which is at or above the melting temperature of the solder (LT) and at the same time below the melting temperature of the filler particles (FK).

14. An inverter comprising: a power electronics module (LM) according to one of claims 1 to 12, wherein a semiconductor switch (HS) is arranged on the circuit carrier (ST) of the power electronics module (LM); - a driver circuit for operating the semiconductor switch (HS), which is electrically connected to the one semiconductor switch (HS).

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