Power electronics module, method for producing a power electronics module, inverter with a power electronics module

Abstract

Power electronics module, method for producing a power electronics module, inverter with a power electronics module A power electronics module (LM) is disclosed, comprising: - a circuit carrier (ST); - a cooler (KL); - a preformed solder connection part (LF) which is arranged between the circuit carrier (ST) and the cooler (KL) and is soldered to the circuit carrier (ST) and the cooler (KL) under a predetermined soldering temperature and thus physically and thermally connects the circuit carrier (ST) to the cooler (KL); - wherein the solder joint preform (LF) comprises a solder (LT) with 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) embedded in the solder (LT); - where the filler particles (FK) have a higher thermal conductivity than the solder (LT). Furthermore, a method for producing said power electronics module and an inverter with said power electronics module are described.

Description

Technical Field:The present invention relates to a power electronics module, in particular for an inverter or a DCDC converter, and to an inverter or power inverter, in particular for an electric drive of a motor vehicle, having at least one said power electronics module. The invention further relates to a method for producing said power electronics module.STATE OF THE ART AND OBJECT OF THE INVENTIONPower electronics modules as half bridges are known and are used, inter alia, as part of an inverter or a DCDC converter, in particular an electric drive of a motor vehicle. Due to their function, the power electronics modules have a high power loss and have to be cooled during operation with the aid of, in particular, liquid-cooled, coolers which are physically and thermally connected to circuit carriers of the power electronics modules.In this case, there is the general requirement to make the cooling of the power electronics modules and thus of the inverters or the DCDC converters more efficient with the power electronics modules mentioned.The object of the present application is thus to provide a possibility with which a power electronics module and thus an inverter or a DCDC converter can be cooled more efficiently.DESCRIPTION OF THE INVENTIONThis object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.According to a first aspect of the invention, a power electronics module, in particular for an inverter or a DCDC converter, in particular an electric drive of a motor vehicle, is provided.The power electronics module has a circuit carrier and a cooler for cooling the power electronics module.The power electronics module further comprises a preformed soldered connection molding ("solder preform"), which is arranged between the circuit carrier and the cooler and is soldered (in a soldering process) to the circuit carrier and the cooler, and thus connects the circuit carrier to the cooler (purely) mechanically or physically and thermally. The solder joint molding contains a solder (or solder) having a melting temperature that is at or below the soldering temperature. The solder joint molding further includes a plurality of individual thermally conductive filler particles embedded in the solder and having a higher thermal conductivity than the solder.The circuit carrier can be formed, for example, as a ceramic substrate, such as a DBC (Direct Bonded Copper) substrate or an ABM (Active Metal Bonded) substrate, or as a metal core printed circuit board, such as an IMS (Insulated Metal Substrate).The power electronics module can have at least one switchable half bridge with at least one positive-voltage-side semiconductor switch and at least one negative-voltage-side semiconductor switch, which is formed on the circuit carrier. The two semiconductor switches can be formed in particular as silicon carbide (SiC) semiconductor switches, especially as SiC MOSFETs. Alternatively, the two semiconductor switches can also be formed as IGBTs, in particular as GaN (GaN) semiconductor switches or as GaAs (GaAs) semiconductor switches.The cooler may be formed as a cooler having a coolant channel for passing a coolant liquid therethrough and / or having a cooler pin fin structure for increasing the cooler surface area. Further, the cooler may be formed as an aluminum or copper cooler.In this case, the cooler and the circuit carrier can have on their respective upper side facing the moulded soldered connection part and thus the respective other component (circuit carrier or cooler) a solderable layer, such as a copper layer, which is either formed as one piece with the corresponding component by an original component of the respective component (cooler or circuit carrier) or is subsequently formed or coated on the corresponding upper side of the corresponding component.The soldered connection molded part is a solid, independent part which can be transported in a similar manner to a conventional soldered molded part ("solder preform"), in particular in the form of a flat sheet metal part or a wound sheet metal strip, and can be cut or stamped in a corresponding shape, in particular if necessary, before soldering to the circuit carrier and the cooler.The solder joint molding includes a solder (known in the art) which melts and deforms upon soldering to the circuit substrate and the cooler under the action of a predetermined soldering temperature equal to or higher than the melting temperature of the solder.The shaped solder connection part further contains a plurality of individual, thermally highly conductive filler particles which are embedded in the solder (in particular uniformly distributed) and do not melt or deform during soldering under the action of the predetermined soldering temperature, which is lower than the melting temperature of the filler particles.Due to its own mechanical strength or stability, the shaped soldered connection part can hold together the filler particles embedded in the solder. The filler particles likewise have their own mechanical strength or stability and can thus impart additional mechanical strength or stability to the shaped soldered connection part.Unlike conventional soldered connections, which above all produce electrical connections between the electrical components, the soldered connection molded part merely produces a purely mechanical or physical and thermal connection between the circuit carrier and the cooler, wherein a better heat transfer from the circuit carrier to the cooler and thus an efficient cooling of the power electronics module is the primary point.For this purpose, the filler particles consist of a material which has a (substantially) higher thermal conductivity than the solder. Due to the high melting temperature, which is higher than the soldering temperature or the melting temperature of the solder, the filler particles retain their original shapes during soldering and thus also after soldering the soldering connection molded part to the circuit carrier and the cooler and act like a "heat bridge" in the soldering connection molded part after soldering, via which the waste heat can be transported away from the circuit carrier to the cooler more quickly than via the solder in the soldering connection molded part. The higher thermal conductivity of the filler particles to the solder enhances the effect of the "thermal bridge". By a uniform distribution of the filler particles in the solder or in the shaped solder connection part, a homogeneous heat transfer over the entire shaped solder connection part can also be achieved.This provides a possibility with which a power electronics module and thus an inverter or a DCDC converter can be cooled more efficiently with a power electronics module.The filler particles have, in particular, a melting temperature which is higher than the brazing temperature.The soldered connection molded part does not establish, in particular, an electrical connection between the circuit carrier and the cooler. The soldered connection via the shaped part of the soldered connection is not provided for the transmission of current. The soldered connection molded part merely physically holds the circuit carrier and the cooler together with one another and (only) transfers the waste heat from the circuit carrier to the cooler.The filler particles can have regular or even irregular shapes as solid particles, in particular in spherical form, egg shape, etc.The solder can be configured, for example, to compensate for unevennesses between the circuit carrier and the cooler during the soldering process by deformation or flow as a result of melting. In this case, the filler particles, the diameter of which is in particular substantially smaller than the solder connection molded part, can move in the liquid solder, so that the distance between the circuit carrier and the cooler can be adapted to the uneven surfaces thereof.The thermal conductivity of the filler particles may be higher than the thermal conductivity of the solder by at least 100%, or at least 200%, or at least 500%, or at least 1000%. In other words, the thermal conductivity of the filler particles may be at least a factor of 2 or more than the thermal conductivity of the solder.The thermal conductivity of the filler particles may be equal to or higher than the thermal conductivity of the cooler.The filler particles may be of the same material as the body material of the cooler. Accordingly, the filler particles may have the same thermal conductivity as the body material of the cooler. If the cooler body consists of copper, the filler particles can likewise consist of copper. The filler particles can be formed as copper spheres. Alternatively, the filler particles may be comprised of one or more copper-like metals or one or more comparable metal alloys.The thermal conductivity of the filler particles can also be (substantially) higher than the thermal conductivity of the circuit carrier.The filler particles may have a melting temperature higher than the brazing temperature (thus higher than the melting temperature of the brazing material), such as at least 10° C. or at least 30° C.As mentioned above, the filler particles may be shaped so as to be able to flow in the melting solder during the soldering operation, thereby compensating for unevenness between the circuit substrate and the cooler.The filler particles have a maximum diameter or maximum extent which is / are in particular below the (minimum) thickness of the soldered connection shaped part.The filler particles also have a minimum diameter or minimum extent, which is / are in particular 1 micrometer or 5 micrometers or 10 micrometers. In particular, the filler particles have different diameters or expansions which lie between the minimum diameter or the minimum expansion of 1 micrometer (or 5 or 10 micrometers) and the minimum thickness of the soldered connection molded part.The filler particles can have a volume fraction of at most 80% or at most 70% or at most 60% or at most 50% in the shaped soldered connection part. Furthermore, the filler particles in the shaped soldered connection part can have a volume proportion of at least 1%, or at least 10%, or at least 20%.According to a second aspect of the invention, a method for producing a power electronics module described above is provided.According to the method, a circuit carrier and a cooler are provided. In this case, the circuit carrier and the cooler are each equipped with a correspondingly solderable surface.Furthermore, a solder joint molding is preformed which comprises solder and a plurality of individual filler particles, for example in the form of copper balls, wherein the filler particles are embedded in the solder. The filler particles are made of a material that conducts heat well, so that they have a higher thermal conductivity than the solder.The soldered connection molded part is placed between the circuit carrier and the cooler and soldered to the circuit carrier and the cooler in a soldering process under the effect of a predetermined soldering temperature on the soldered connection molded part and thus connected to them physically or mechanically and thermally. The soldering temperature is determined in such a way that it is at or above the melting temperature of the solder and at the same time remains below the melting temperature of the filler particles.During the soldering process, the solder deforms or liquifies from the solder connection molded part and in the process physically connects the circuit carrier to the cooler. On the other hand, the filler particles retain their shape and may float in the solder which is being deformed or liquefied, thereby equalizing the unevenness between the circuit substrate and the cooler. After soldering, the soldered connection molded part establishes a pure physical or mechanical and thermal connection between the circuit carrier and the cooler.The soldering process can be carried out under the action of a temperature at which only the solder melts or liquifies and the filler particles do not melt together or still retain their solid form. In this case, the temperature may be, in particular, at or about or more than 10° C. higher than the melting temperature of the solder and at the same time lower, for example, at least 10° C. lower, than the melting temperature of the filler particles.Alternatively, the soldering operation may be performed under a temperature at which both the solder and the filler particles melt, liquify, or deform. In this case, the temperature may be higher than the melting temperature of the solder and the melting temperature of the filler particles.Advantageous configurations of the above-described power electronics module are also to be regarded as advantageous configurations of the method, insofar as otherwise transferable to the above-mentioned method.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.The inverter has (at least) one previously described power electronics module which (at least) has a semiconductor switch which is arranged on the circuit carrier of the power electronics module. The inverter further comprises (at least) a driver circuit for operating the (at least) one semiconductor switch.DESCRIPTION OF THE DRAWINGAn exemplary embodiment of the invention is explained in more detail below with reference to the accompanying drawing. In this case, the single FIG. 1 shows a section of a power electronics module LM of a power inverter of an electrical drive device of a motor vehicle in accordance with an exemplary embodiment of the invention in a schematic cross-sectional illustration. In this case, 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 which are electrically connected in accordance with the function of the half-bridge. Alternatively, the power electronics module LM may form the entire three-phase bridge circuit of the power inverter and correspondingly comprise six or more semiconductor switches HS electrically connected according to the function of the three-phase bridge circuit. In this case, the semiconductor switches HS are formed, for example, as SiC (silicon carbide) semiconductor switches, in particular as SiC-MOSFETs ("silicon carbide metal oxide semiconductor field-effect transistors").For operating the power electronics module LM, the power inverter further comprises a driver circuit (not shown in FIG. 1 ) which is electrically or signal-connected to the semiconductor switches for operating the latter.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 which has an upper-side copper layer OS for forming electrical conductor tracks and a lower-side copper layer US for heat dissipation and for forming a physical and thermal connection to a cooler KL to be discussed below, and an electrically insulating and at the same time 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 upper-side copper layer OS and are electrically contacted with the corresponding conductor tracks of the copper layer OS.The power electronics module LM also has 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 conducting a cooling liquid.The cooler KL has a solderable cooling surface KF on which the circuit carrier ST is arranged via its underside, likewise solderable copper layer US, and is soldered to the cooler KL by means of a solder connection molding LF to be described below.Between the circuit carrier ST and the cooler KL, the power electronics module LM has the aforementioned soldered connection molded part LF, which is arranged as a preformed molded part between the circuit carrier ST and the cooler KL and is soldered in one soldering process both to the circuit carrier ST and to the cooler KL and thus physically and thermally connects the circuit carrier ST to the cooler KL.The cooling surface KF of the cooler KL and thus the cooler KL itself also 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 molded part LF establishes a purely mechanical or physical and thermal connection between the circuit carrier ST and the cooler KL, and no electrical connection between these two components.The soldered connection molded part LF is formed as an independent, sheet-like preformed, solid molded part before the soldering process and has a thickness of, for example, 200 micrometers (before the soldering process).The brazing joint molding LF contains a brazing material LT in which a plurality of individual metallic filler particles FK are embedded. The solder LT consists, for example, of a solder customary on the market. The filler particles FK are formed as copper beads having a diameter of 10 to 100 micrometers, in particular at about 30 micrometers.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.The soldered connection to the soldered connection molded part LF has a cost advantage and an advantage during the production process in comparison with a sintered connection.The previously described power electronics module LM is produced as described below:First, the circuit carrier ST with the solderable underside copper layer US and the cooler KL with the likewise solderable cooling surface KF are provided.Further, the brazing joint molded part LF is made of the solder LT and a plurality of individual filler particles FK by embedding the filler particles FK in the solder LT.The preformed shaped soldered 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 soldered to the circuit carrier ST and the cooler KL in a soldering process under the effect of a sufficient soldering temperature.Under the effect of the soldering temperature higher than the melting temperature of the solder LT, the solder LT melts. The filler particles FK in the solder LT maintain their original shapes and flow with the melting solder LT in a cavity between the underside copper layer US and the cooling surface KF, thereby filling the cavity and thus equalizing the asperities between the underside copper layer US and the cooling surface KF and thus between the circuit substrate ST and the cooler KL. Alternatively, the filler particles FK can deform under the effect of the soldering temperature and fill the intermediate spaces between the soldering partners and thereby equalize the local height differences between the connecting surfaces of the two soldering partners.The above-described soldering process with the preformed moulded soldered connection part LF can be carried out without or with a negligibly small additional outlay or cost in a conventional production process on a conventional installation.

Claims

A power electronics module (LM) comprising: - a circuit carrier (ST); - a cooler (KL); - a preformed solder joint molding (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 and thus physically and thermally connects the circuit carrier (ST) to the cooler (KL); - wherein the solder joint molding (LF) comprises a solder (LT) having a melting temperature that is at or below the soldering temperature, and - the solder joint molding (LF) further comprises a plurality of individual filler body particles (FK) embedded in the solder (LT); wherein the filler particles (FK) have a higher thermal conductivity than the solder (LT).The power electronics module (LM) according to claim 1, wherein the filler particles (FK) have a melting temperature that is higher than the soldering temperature.Power electronics module (LM) according to one of the preceding claims, wherein the moulded soldered connection part (LF) does not produce an electrical connection between the circuit carrier (ST) and the cooler (KL).The power electronics module (LM) according to any 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).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).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).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.Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) are shaped in such a way that they flow in the melting solder (LT) during the soldering process and in the process compensate for unevennesses between the circuit carrier (ST) and the cooler (KL).Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) have a maximum extent which is below the minimum thickness of the soldered connection shaped part (LF).Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) have a minimum extent of more than 1 micrometer or more than 5 micrometers or more than 10 micrometers.Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) in the moulded soldered connection part (LF) have a volume proportion of at most 80% or at most 70% or at most 60% or at most 50%.Power electronics module (LM) according to one of the preceding claims, wherein the filler particles (FK) in the shaped soldered connection part (LF) have a volume proportion of at least 1% or at least 10% or at least 20%.Method for producing a power electronics module (LM) according to one of the claims, having the following method steps: - providing a circuit carrier (ST) and a cooler (KL); - forming a solder connection shaped part (LF) with a solder (LT) and a plurality of individual filler body particles (FK) by embedding the filler body particles (FK) in the solder (LT), wherein the filler body particles (FK) have a higher thermal conductivity than the solder (LT); - arranging the pre-formed solder connection shaped 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 soldered connection shaped 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).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), said driver circuit being electrically connected to the one semiconductor switch (HS).

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