Method for producing power electronics

Abstract

The invention relates to a method for producing power electronics comprising at least one electrical circuit carrier (1), on which at least one power-electronics semiconductor module (3) is arranged, which is thermally conductively coupled to a heat sink (4) via a main surface of its housing (2) facing away from the circuit carrier, wherein said method enables a force-free connection between the circuit carrier, which is already fitted with the semiconductor module, and the heat sink. According to the invention, this is achieved, inter alia, by the use of positioning studs (8) on the heat sink and elastomer grommets (6), which are filled with a curable casting compound (10).

Description

[0001] Method for manufacturing power electronics

[0002] The invention relates to a method for manufacturing power electronics comprising at least one electrical circuit carrier on which at least one power electronic semiconductor module provided with a housing is arranged, which is thermally coupled to a heat sink with a main surface of its housing facing away from the circuit carrier.

[0003] For years, power electronics and electric vehicle design have focused on increasing power density to enable ever higher charging capacities for increasingly larger batteries within limited installation space. This brings electric vehicles closer to the range and availability of conventional combustion engine vehicles, both in terms of range and charging times.

[0004] As power density increases, new concepts are constantly being developed for power semiconductors, which generate high power losses. For example, there are isolated semiconductor modules in which several power semiconductors are housed in an insulating package. One advantage of these modules is the short distance to the heat sink, because unlike topside-cooled or bottomside-cooled semiconductors, these are not primarily attached to the circuit board, but directly to a heat sink. For this purpose, the packages have, for example, recesses or holes through which screws can be inserted. These screws allow the packages to be attached to the heat sink in such a way that one of their main surfaces is thermally coupled to the heat sink. In a subsequent process step, a fully assembled circuit board is then blindly mounted onto the solder pads of the semiconductor modules and soldered in place.In this case, the necessary tolerance compensation between the semiconductor module and the circuit board is achieved via the solder pins of the semiconductor module. These are inserted far through the circuit board and only soldered once the semiconductor module and subsequently the circuit board are firmly screwed to the heat sink. This creates an initially force-free solder joint, which is highly desirable from a durability perspective.

[0005] A disadvantage of this solution, however, is the complex and expensive soldering process. While all other components on the circuit board are pre-soldered using SMD or, if applicable, THT technology, the subsequent soldering of the through-hole solder pins requires a selective soldering process on the circuit board, which is already screwed into the housing. This can be a relatively slow and therefore expensive laser soldering process or a selective wave soldering process. However, these methods also have limitations, such as restrictions on housing height. Furthermore, these selective soldering processes require that parts of the assembly be heated and then cooled after soldering, which, among other things, leads to longer process times.

[0006] The method according to the invention has the advantage over the prior art described that the semiconductor modules can be soldered to the circuit board before being connected to the heat sink, preferably in the same process as all other components on the circuit board, and only then attached together with the circuit board in the housing or to the heat sink.

[0007] According to the invention, this is achieved by a method comprising a sequence of process steps according to claim 1. A crucial aspect for the success of the present invention is that it has succeeded in avoiding the mechanical stresses in the solder joints that are practically unavoidable in the case of conventional mounting of the circuit carrier, already pre-equipped with the semiconductor module, to the heat sink using fastening screws, due to the sum of all production tolerances.

[0008] An embodiment of the invention is illustrated and explained in more detail below with reference to the drawing. The drawings show...

[0009] Fig. 1: A power electronics unit manufactured according to the invention in a half-section view

[0010] Fig. 2: A detailed view of the power electronics in Fig. 1

[0011] Fig. 3: a side view of the power electronics in Fig. 1 or 2. Fig. 4: a detail view from Fig. 3 in half-section.

[0012] Figures 1 and 2 show a power electronics assembly manufactured according to the invention in a half-section view from the solder side of the circuit carrier. Figures 3 and 4 show the same power electronics assembly in a side view. The circuit carrier 1 is equipped with electronic components on the side facing away from the viewer. The electronic components include power electronic semiconductor modules 3, each of which is provided with an insulating housing 2 and connecting pins 5 for soldering to the circuit carrier 1. The power electronic semiconductor modules 3 are each thermally coupled to a heat sink 4 via the main surface 2a of their housing 2 facing away from the circuit carrier 1.

[0013] In the course of the production according to the invention of the illustrated

[0014] In the power electronics assembly, the circuit carrier 1 is first populated with the power electronic semiconductor modules 3 and other electronic components, which are then directly connected to the circuit carrier 1 via a standard soldering process, ideally SMD or THT. Next, elastomer grommets 6 are inserted into corresponding bores 7 of the circuit carrier 1. These elastomer grommets 6 can be made of rubber or another elastic material and are designed to be easily compressible and deformable. They form hollow bodies that are approximately cylindrical in their lower part and essentially frustoconical in their upper part, with a waist formed between these two parts, each positioned within the bores 7 of the circuit carrier 1.They are open on the underside and provided with a sealing surface into which a correspondingly shaped positioning dome 8 of the heat sink 4 can engage. There is also an opening on the top side of each elastomer grommet 6.

[0015] The fully soldered circuit carrier 1, fitted with the elastomer grommets 6, is then placed onto the heat sink 4, engaging the elastomer grommets 6 with their respective positioning domes 8 on the heat sink 4. After placing the circuit carrier 1 onto the heat sink 4, screws 9, which connect the semiconductor modules 3 to the heat sink 4, are inserted through designated openings T, 2' in the circuit carrier 1 and the housings 2 of the semiconductor modules 3 and screwed into corresponding internal threads in the heat sink 4. This brings each semiconductor module 3 into close contact with the surface of the heat sink 4 via a main surface 2a of its housing 2, thus thermally coupling it. The elastomeric nozzles 6 are slightly compressed, resulting in a fluid-tight closure of the elastomeric nozzles 6 by the positioning domes 8 assigned to them.

[0016] The position of the circuit carrier 1 relative to the heat sink 4 is now indirectly determined via the solder lugs 5 by the screw connections. The elastomer grommets 6 are sufficiently flexible that no forces are generated between the circuit carrier 1 and the heat sink 4.

[0017] The elastomer grommets 6 are then filled from their open top side with a potting compound 10 to such an extent that the surface of the potting compound 10 lies above the waist of the elastomer grommet 6 located within the bore 7 in the circuit carrier 1. The potting compound 10 is then cured. The potting compound 10 is, for example, a two-component material which, after the two components are mixed and a predetermined open time has elapsed, cross-links and bonds to the surfaces of the positioning domes 8 of the heat sink 4, forming a material-bonded connection. This creates a material-bonded or form-fit connection between the heat sink 4 and the circuit carrier 1, effectively "freezing" the predetermined relative position of these two components without generating any undesirable forces.

Claims

Patent claims 1. A method for manufacturing power electronics comprising at least one electrical circuit carrier (1) on which at least one power electronic semiconductor module (3) provided with a housing (2) is arranged, the module being thermally coupled to a heat sink (4) by means of a main surface (2a) of its housing facing away from the circuit carrier (1), comprising the following process steps: a) connecting the terminals (5) of the semiconductor module (3) to conductor tracks of the circuit carrier (1) by means of a standard soldering process, b) inserting elastomer grommets (6) into associated bores (7) of the circuit carrier (1), c) placing the assembled circuit carrier (1) onto the heat sink (4), wherein the elastomer grommets (6) are engaged with associated positioning domes (8) on the heat sink (4), d) fastening the semiconductor module (3) to the heat sink (4) by means of at least one screw (9) through openings (T,2') is guided in the circuit carrier (1 ) and the housing (2) of the semiconductor module (3) and is screwed into the heat sink (4) via an associated internal thread, e) Filling the elastomeric nozzles (6) with a curable potting compound (10) and curing the potting compound (10).

2. Method according to claim 1, characterized in that the standard soldering process comprises an SMD and / or THT process.

3. Method according to claim 1 or 2, characterized in that the potting compound (10) is a two-component material which cross-links after the mixing of its two components and after a predetermined open time.

4. Method according to claim 3, characterized in that the potting compound (10) bonds to the surfaces of the positioning domes (8) of the cooling body (4) in a materially bonded manner after crosslinking.

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