Power module with substrate, component and moulding material

Abstract

The invention relates to a substrate (10) of a power module, which is provided with a number of conductor tracks (12) and with at least one electronic component. The substrate (10) is surrounded at least on the upper side thereof by a moulding material (46) in which at least one opening (18) is formed. The at least one opening (30, 31) is arranged in the moulding material (46) with stress-optimised regions (50). At least one corner geometry (14) is designed as a circular cutout (32). The invention further relates to the use of the substrate (10) in a power module of power electronics or of an inverter of a vehicle.

Description

[0001] Description

[0002] title

[0003] POWER MODULE WITH SUBSTRATE, COMPONENT AND MOLD MATERIAL

[0004] Technical area

[0005] The invention relates to a substrate of a power module, which is provided with a number of conductor tracks and at least one electronic component and is surrounded by a molding material at least on its upper side, in which at least one opening is formed. Furthermore, the invention relates to the use of the substrate in a power module of a power electronics system or an inverter of a vehicle.

[0006] State of the art

[0007] In the current state of the art, power modules, for example, those installed in a power module bridge, are additionally molded. During molding, the power module is embedded in a rigid protective housing, for example, made of plastic (mold material). The mold material serves to enclose and protect the interior of the power module. However, these mold material enclosures of the power module are not particularly resistant to cracking.

[0008] DE 11 2017 004 390 T5 discloses a power module having the following features: an insulating substrate with a front side to which a power semiconductor element is attached; a base plate connected to a back side of the insulating substrate; a housing attached to the base plate and surrounding the insulating substrate; a cover attached to the housing and forming a sealed area; and a silicone gel serving as a filler element that fills the entire sealed area and has an internal stress that acts as a compressive stress. It has been found that, particularly in power modules overmolded with a molded compound, high stresses occur with certain geometries, which can lead to cracks in the molding compound.These cracks, especially when they extend to a T+ bridge, form a conductive path between two potentials and thus pose a safety risk with regard to the function of the overmolded power module.

[0009] Disclosure of the invention

[0010] According to the invention, a substrate of a power module is proposed, which is provided with a number of conductor tracks with at least one electronic component and is surrounded by a molding material at least on its upper side, in which at least one opening is formed. The at least one opening is designed with stress-optimized regions in the molding material, with at least one corner geometry being formed as a circular cutout.

[0011] The stress-optimized areas proposed according to the invention in the region of at least one opening in the molding material can drastically reduce any notch stress that may occur, significantly reducing the risk of crack formation and crack propagation originating from a corner geometry. This allows the stress-optimized area to be created in a single operation shortly after the molding material is applied, without the need for post-processing or re-clamping the substrate to another workpiece carrier.

[0012] In an advantageous further development, in the substrate proposed according to the invention, the stress-optimized area in the molding material is designed as a laser-cut section.

[0013] Advantageously, the substrate proposed according to the invention is designed such that the lasered-off region is arranged between a horizontal part and a vertical part of a boundary of the at least one opening. The solution proposed according to the invention for the lasered-off regions allows the relevant geometries, in particular the corner regions, to be significantly relieved of the stress levels occurring there. In the substrate proposed according to the invention, the lasered-off region preferably has a transition region formed as a curve that merges into the horizontal part and / or a vertical part of the boundary of the at least one opening in the molding material. The formation of transition regions with curves advantageously serves to generally reduce the stress level that arises in the molding material, which drastically increases its service life.

[0014] In the substrate proposed according to the invention, the laser-removed area is located in the plane of the molding material, which extends above a plane of the substrate. This allows the laser processing of the molding material to take place in the relevant plane, namely that of the molding material, thus eliminating the need to repeatedly traverse the plane of the substrate.

[0015] In the substrate proposed according to the invention, the lasered-off areas extend along opposing corner geometries. This allows all relevant corner geometries of at least one opening in the molding material, designed in any desired geometry, to be optimized in terms of stress-related properties.

[0016] In one embodiment of the substrate proposed according to the invention, the build-up height of a molding material is formed in multiple stages, starting from the top side of the substrate. According to this embodiment, the laser-exposed region can be formed at least in the first stage of the multi-stage build-up height, extending directly above the substrate.

[0017] Furthermore, the invention relates to the use of the substrate in a power module of a power electronics system or an inverter of a vehicle.

[0018] Advantages of the invention

[0019] The design of the substrate proposed according to the invention, in particular its mold coating on its upper side, makes it possible to prevent crack formation or crack propagation. The stress-optimized regions proposed according to the invention, in particular in the corner geometry of the boundary of the at least one opening in the mold material, drastically reduce the notch stress that occurs in the corner geometries, in particular due to rounding. This extends the service life of the mold material because cracks do not even occur due to the drastically reduced stress level. This also takes into account the aspect that, if a crack occurs, current paths could form between the potentials, which can represent a safety-relevant aspect when using substrates or power modules, for example in electrically powered vehicles.The solution proposed according to the invention significantly increases the service life of the molding material and its protective function for the components covered by it, in particular the conductor tracks or at least one electronic component, on the upper side of the substrate.

[0020] If the stress-optimized areas are manufactured, for example, by laser-cutting cutouts, it becomes possible shortly after the mold material has cured to machine all areas in one and the same substrate setup and to create cutouts in corner geometries. These preferably transition into horizontal or vertical parts of openings in the mold material at transition areas with curved curves, so that overall, the stress level occurring in the boundary of at least one opening can be reduced, which is extremely advantageous with regard to service life.

[0021] Furthermore, the stress-optimized areas in the mold material created by laser manufacturing allow for low manufacturing costs in large-scale production. The mold materials used are, in particular, mold materials that provide effective protection for the conductor track or electronic component arranged on the top side of the substrate and, at the same time, are amenable to post-processing after curing, for example, using a laser cutting process.

[0022] Brief description of the drawings Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0023] They show:

[0024] Figure 1 shows a substrate with a crack running through its molding material,

[0025] Figure 2 is an enlarged view of a stress-optimized area according to the present invention in the plane of the molding material,

[0026] Figure 3 is a perspective view of a build-up height of the molding material on the top side of the substrate and

[0027] Figure 4 is a perspective view of the molding material with an enlarged circular cutout in the area of ​​a corner geometry.

[0028] The illustration in Figure 1 shows that a substrate 10 is formed with a number of conductor tracks 12 running parallel to one another with different courses. An opening 18 in a molding material 46 has at least one corner geometry 14, which is illustrated as a rounding 16. The at least one opening 18 in the molding material 46 is defined by a boundary 22. A crack 24 extends from the base of the corner geometry 14 according to a crack course 26 in the molding material 46. The crack 24 and its crack course 26 in the molding material 46 can create a conductive path between two potentials, which can represent a safety risk for the use of the substrate 10 as part of a power module on a vehicle, in particular an electrically powered vehicle.

[0029] Embodiments of the invention

[0030] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only represent the subject matter of the invention schematically. The illustration in Figure 2 shows an enlarged illustration of a corner geometry 14 of a molding material 46 designed according to the invention. According to the plan view in Figure 2, the molding material 46 is located in a plane 34 above a plane 36 in which the substrate 10 with its conductor tracks 12 lies, of which only one is shown in the plan view in Figure 2. The plan view in Figure 2 shows that a voltage-optimized region 50 shown here in the region of the corner geometry 14 is designed as a circular cutout 32 which has a rounding radius 30.The stress-optimized area 50, as shown in Figure 2, is produced by laser processing as a laser-cut cutout 52 in the mold material 46. Depending on the laser travel speed, different rounding radii 30 can be set, which can result in larger or smaller circular cutouts 32. The corner geometry 14 lies between a horizontal part 42 and a vertical part 44, extending perpendicularly thereto, of the boundary 22 of the at least one opening 18 in the mold material 46.

[0031] Figure 2 further shows that, for example, a transition region 38 can be formed on the horizontal part 42 of the boundary 22. Within the transition region 38, the molding material 46 has a curvature 40, whereby a gradual transition into the stress-optimized region 50 in the form of the laser-cut cutout 52 can be achieved. The smoother or more uniform the transition regions 38 between the horizontal part 42 and the vertical part 44 are formed, the more favorable the stress distribution results in the molding material 46. A reduction in the stress level in the molding material 46 leads to a significant increase in its service life and thus its protective function.Furthermore, safety-relevant errors, such as the occurrence of crack formation and the associated electrically conductive paths, can be prevented, which brings with it an additional safety aspect over the service life of the substrate 10 proposed according to the invention, which is protected at least on its upper side with a molding material 46.

[0032] Although only one corner geometry 14 of the at least one opening 18 is shown in the illustration according to Figure 2, all corner geometries 14 of an opening 18, which can be formed in any desired cross-section, can advantageously be provided with precisely those stress-optimized regions 50, so that the stress increase due to the notch effect in the roundings 16 of the corner geometries 14 can be considerably reduced by the solution proposed according to the invention.

[0033] The illustration in Figure 3 shows a perspective top view of a substrate 10, onto which a molding material 46 has been applied at a construction height 48. The perspective illustration in Figure 3 shows that the molding material 46 has a stepped structure. Starting from a first step 54, which is located directly above the conductor tracks 12 of the substrate 10, a second step 56 and a final third step 58 are made of molding material 46, with the latter third step 58 forming the top side of the construction height 48. The stress-optimized regions 50 proposed according to the invention are located as lasered cutouts 52 in the corner geometries 14, which delimit the opening 18 shown in Figure 3 in a perspective top view.The illustration in Figure 3 shows that, for example, on the long side of the first step 54, the stress-optimized regions 50 are designed as circular cutouts 32 with a rounding radius 30, whereby the stress level in the opposing corner geometries 14 of the at least one opening 18 in the molding material 46 can be drastically reduced. The perspective top view in Figure 3 further shows that a number of conductor tracks 12 with different geometries run on the substrate 10. Although the illustration in Figure 3 shows the stress-optimized regions 50 in the region of the first step 54, they could also be formed at the corner geometries 14 of the second step 56 or the third step 58.The build-up height 48 of the molding material 46 results from requirements and depends on how many electronic components are arranged or electrically contacted in addition to the conductor tracks 12 on the top side of the substrate 10.

[0034] From the illustration according to Figure 3 it can also be seen that the opening 18 shown here in perspective is defined by the boundary 22, which has horizontal parts 42 and vertical parts 44 extending from the respective corner geometries 14.

[0035] Figure 4 shows that the stress-optimized region 50 is designed as a circular cutout 32, from which a transition region 38 extends. Compared to the corner geometry 14 as shown in Figure 1, the stress level in the area of ​​the corner geometry 14 in the embodiment according to Figure 4 is at least approximately 30% lower, so that the stress level prevailing at the notch root of the fillet 16 of the corner geometry 14 is considerably reduced and crack formation originating from the notch root of the fillet 16 of the corner geometry 14 can be largely ruled out in the design proposed according to the invention.

[0036] The at least one opening 18 in the molding material 46 shown in Figures 2, 3 and 4 can, for example, be a signal pad area that is defined by the boundary 22. In the illustrated embodiment according to Figures 2 to 4, the at least one opening 18 is rectangular or square. The solution proposed according to the invention makes it possible to create a free cut 32 in critical areas, in particular in the area of ​​the corner geometries 14 of the molding material 46, whereby the high notch stresses that otherwise occur in the corner geometries 14 are drastically reduced. The stress-optimized areas 50 in the form of the laser-cut cutouts 52 make it possible to reduce the stresses that occur in the molding material 46 over the service life, and thus the occurrence of cracks 24 can be prevented.

[0037] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of expert practice.

Claims

Claims 1 . Substrate (10) of a power module, which is provided with a number of conductor tracks (12) and with at least one electronic component and is surrounded by a molding material (46) at least on its upper side, in which at least one opening (18) is formed, characterized in that the at least one opening (18) is designed with at least one voltage-optimized region (50) in the molding material (46) and at least one corner geometry (14) is designed as a circular free cut (32).

2. Substrate (10) according to claim 1, characterized in that the at least one stress-optimized region (50) in the molding material (46) is designed as a laser-cut section (52).

3. Substrate (10) according to claims 1 and 2, characterized in that the lasered area (52) is positioned between a horizontal part (42) and a vertical part (44) of a boundary (22).

4. Substrate (10) according to claim 3, characterized in that the lasered-off region (52) has a transition region (38) which, as a curvature (40), merges into the horizontal part (42) and / or the vertical part (44) of the boundary (22).

5. Substrate (10) according to claims 1 to 4, characterized in that the lasered-off region (52) in the molding material (46) is formed in a plane (34) of the molding material (46) which extends above a plane (36) of the substrate (10).

6. Substrate (10) according to claims 1 to 5, characterized in that the lasered areas (52) run in mutually opposite corner geometries (14) of the at least one opening (18).

7. Substrate (10) according to claims 1 to 6, characterized in that a construction height (48) of the molding material (46), starting from the top side of the substrate (10), contains a plurality of steps (54, 56, 58).

8. Substrate (10) according to claim 7, characterized in that the lasered-off region (52) runs at least in the first step (54) of the molding material (46) running above the substrate (10).

9. Use of the substrate (10) according to one of claims 1 to 8 in a power module of a power electronics system or an inverter of a vehicle.

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