Electronic module and method for manufacturing an electronic module

Abstract

Electronic module (1) comprising at least one substrate (2) with at least one electronic component (4) and contacts (5), wherein the electronic component (4) and at least partially the substrate (2) are covered with at least one molding compound (8), wherein at least one contact (5) is not completely covered by the at least one molding compound (8), wherein a top surface (10) of the at least one molding compound (8) is structured, characterized in that the top surface (10) of the at least one molding compound (8) has at least one convex protrusion (11) and / or the top surface (10) of the at least one molding compound (8) has a rib structure (12) that is arranged completely around the edges of the top surface (10).

Description

[0001] The invention relates to an electronic module and a method for manufacturing an electronic module.

[0002] From DE 10 2012 112 738 A1, a generic electronic module is known which has at least one substrate with at least one electronic component and contacts, wherein the electronic component and at least partially the substrate are covered with at least one molding compound, and wherein at least one contact is not completely covered by the at least one molding compound. The molding compound can also be understood as an encapsulation and typically consists of plastic. The molding compound also has, among other things, a protective function for the electronic component.

[0003] A similar electronic module is known from WO 2019 / 219650 A1. This document describes that it is preferably provided that the electronic module and / or the support substrate is thermomechanically symmetrical, in particular along a stacking direction that runs perpendicular to a principal extension plane of the support substrate. Thermomechanical symmetry means, in particular, that the thermomechanical coefficients of expansion are symmetrical when viewed in the stacking direction. The thermomechanical coefficient of expansion is a measure of the expansion of the respective layer during a temperature change.Preferably, the electronic module can be divided into virtual sub-substrates, in particular with a virtual primary substrate, a virtual secondary substrate, and a virtual intermediate layer, wherein the coefficients of thermal expansion of the virtual sub-substrates are symmetrically distributed in the stacking direction. The symmetrical design of the coefficients of expansion advantageously provides an electronic module that exhibits comparatively low torsional rigidity under operational or environmental temperature fluctuations. Consequently, defects or cracks that would otherwise be caused by thermally induced mechanical stresses can be avoided. In particular, in conjunction with a support substrate having a comparatively thick metallic intermediate layer, especially one thicker than 1 mm, it is possible to provide a comparatively high coefficient of thermal expansion for the entire support substrate.

[0004] Consequently, adjusting the coefficient of thermal expansion for the encapsulation of the electronic module is simplified, as the effort required to reduce the typically high coefficient of thermal expansion of the encapsulation itself can be reduced. To lower the coefficient of thermal expansion, a filler material is incorporated into the encapsulation material. The increased coefficient of expansion for the substrate allows for a reduction in the amount of filler material, which in turn reduces the manufacturing costs of the electronic module. The filler material is, for example, SiO2 or Al2O3.

[0005] Such metallic interlayers are not always desirable. Furthermore, the problem is exacerbated by the connection to a cooling structure, such as a metallic plate on the underside of the substrate, which can lead to warping between the substrate and the metallic plate. Depending on the specific design of the electronic module, this warping can be convex or concave.

[0006] A generic electronic module is known from US 2013 / 0121000 A1.

[0007] US patent 2004 / 0012099 A1 discloses another electronic module in which a heat sink is applied to the top surface of a molding compound. The top surface of the molding compound and the bottom surface of the heat sink are roughened to improve the connection.

[0008] The invention is therefore based on the technical problem of creating an electronic module that compensates for thermal stresses that occur, and of providing a method for manufacturing such an electronic module.

[0009] The solution to the technical problem is achieved by an electronic module having the features of claim 1 and a method having the features of claim 8. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0010] The electronic module comprises at least one substrate. At least one electronic component with contacts is arranged on the substrate, the electronic component and at least partially the substrate being covered with at least one molding compound, wherein at least one contact is not completely covered by the molding compound. One surface of the molding compound is structured.

[0011] The structuring of the top surface of the molding compound clearly defines centers of mass. The position, size, and shape of these centers of mass are preferably designed so that, under typical operating conditions of the electronic module and the resulting temperature distribution, the thermal expansion on the top and bottom surfaces of the module is as equal as possible. This is achieved by considering the thermal conductivity and coefficient of thermal expansion of the molding compound. This reduces bending stresses in the electronic module and converts them into shear stresses, which are significantly less critical for component load. Simultaneously, the position of the centers of mass, resulting from the structuring, creates a stiffness profile that reduces deformation caused by remaining bending stresses. Additional centers of mass can also be molded onto the sides.

[0012] The upper surface has at least one convex protrusion. Embodiments are possible where concave indentations and convex protrusions are combined. In a preferred embodiment, the at least one molded mass has a central convex protrusion, so that the center of mass is also centrally located.

[0013] Alternatively or cumulatively, the top surface of the at least one mold mass has a rib structure arranged around the edges of the top surface, so that the mass centers of gravity are located on the outside, analogous to the concave indentation.

[0014] In one embodiment, a lattice structure is arranged cumulatively within the at least one molding compound. This structure lies between the electronic component and the top surface of the molding compound and is completely surrounded by the at least one molding compound. The lattice structure is preferably an aluminum lattice structure. The lattice structure increases the bending stiffness. If a metal plate is arranged as a base plate below the substrate, the lattice structure also compensates for the high thermal expansion of the base plate, so that the overall structure is primarily subjected to shear stress. The lattice structure preferably has holes to facilitate overmolding. Furthermore, the lattice structure can have openings for control pins.

[0015] In another embodiment, at least two molding compounds are used that have different coefficients of thermal expansion.

[0016] Preferably, the electronic module comprises several electronic components. The molding compound can be applied, for example, by injection molding or compression molding processes such as transfer molding or low-pressure casting. Therefore, the terms injection molding and casting will no longer be used interchangeably.

[0017] In one embodiment with at least two molding materials, these are layered on top of each other, with the resulting top surface potentially being flat. However, the lower molding material can also have indentations, raised areas, and / or ribbed structures. In this layered structure, the lower molding material is completely covered by the upper molding material.

[0018] In an alternative embodiment, the first (lower) molding compound only partially covers the substrate with the at least one electronic component, with the second (upper) molding compound covering the remaining part of the substrate and the first (lower) molding compound.

[0019] In another embodiment, a metal plate is arranged below the substrate, which is partially embedded in the molding compound. This base plate is preferably made of copper and can be used for connection to a cooling device.

[0020] In another embodiment, fillers such as SiO2 or Al2O3 are inserted into the at least one molding mass.

[0021] Regarding the procedural details, full reference is made to the preceding statements.

[0022] The electronic components are preferably power semiconductors, wherein the electronic module preferably forms a half-bridge of an inverter or a complete inverter.

[0023] The invention is explained in more detail below with reference to preferred embodiments. The figures show: Fig. 1 a schematic representation of an electronic module before the application of at least one molding compound, Fig. 2 a perspective view of an electronics module with a concave indentation, Fig. 3 a cross-sectional view through the electronics module according to Fig. 2, Fig. 4 a cross-sectional view through an electronics module with a convex protrusion, Fig. 5 a perspective view of an electronics module with a rib structure, Fig. 6 a schematic representation of an electronic module before the application of at least one molding compound with a grid structure, Fig. 7 a sectional view of an electronic module according to Fig. 6 after casting with the molding compound, Fig. 8 a schematic sectional view of an electronic module with two molding compounds in a first embodiment and Fig. 9 a schematic sectional view of an electronic module with two molding compounds in a second embodiment.

[0024] In the Fig. Figure 1 schematically depicts an electronic module 1 before the application of a molding compound. The electronic module 1 has a substrate 2 on which a metallization layer 3 is applied. The substrate 2 is preferably a ceramic, and the metallization layer 3 is preferably made of copper and is structured accordingly to form conductive traces. Four electronic components 4 are arranged on the metallization layer 3. The electronic components 4, in the form of chips, are, for example, power transistors. Furthermore, contacts 5, which form the outer contacts of the electronic module 1, are arranged on the metallization layer 3. Finally, control pins 6 are also arranged on the metallization layer 3. A metal plate 7, preferably made of copper, is arranged on the underside of the substrate 2. The metal plate 7 forms the base of the electronic module 1.

[0025] In the Fig. Figure 2 shows the electronic module 1 after being encapsulated with at least one molding compound 8. The upper surface 10 of the molding compound 8 has a concave depression 9, such that the center of mass of the molding compound 8 lies at the edge of the upper surface 10. These centers of mass at the edge stiffen the electronic module 1 in that area, thus counteracting any upward curvature of the substrate 2 at the edges. The concave depression 9 is centric.

[0026] In the Fig. Figure 3 shows the corresponding sectional view, whereby the section was made in such a way that the electronic components 4 cannot be seen, as they are completely surrounded by the molding mass 8.

[0027] In the Fig. Figure 4 shows an alternative embodiment, wherein the upper surface 10 of the molding compound 8 has a convex protrusion 11. This places the center of mass centrally in the middle of the electronic module 1.

[0028] It should be noted that the concave depressions 9 or the convex elevations 11 can be conical or spherical.

[0029] The choice of whether the center of mass is located at the edge or centrally of the electronic module 1 preferably depends on the specific design of the electronic module 1, i.e., for example, what type of substrate 2 is used, how thick the metal plate 7 is, what electronic components 4 are used, and how they are arranged. It can be empirically determined beforehand whether bulges primarily occur at the edge or in the center of the electronic module 1.

[0030] In the Fig. Figure 5 shows an alternative embodiment, wherein the molding compound 8 has a ribbed structure 12 on the upper surface 10 at the edge. Here, too, the center of mass is located at the edge, as with the concave indentation 9. The ribbed structure 12 is in the Fig. 5 is shown as a continuous rib structure 12. However, the rib structure 12 can also have several isolated ribs that protrude as elevations from the upper surface 10.

[0031] In the Fig. Figure 6 shows a further embodiment, wherein the basic structure of the embodiment is as follows: Fig. 1 corresponds to. Additionally, a grid structure 13 is provided. The grid structure 13 is preferably made of aluminum and is formed as a plate with holes 14 and elongated slots 15. The holes 14 and elongated slots 15 allow the grid structure 13 to be better embedded in the molding compound 8 (not yet shown). The control pins 6 pass through the elongated slots 15 on one side. The elongated slots 15 on the other side serve for symmetry. To prevent the grid structure 13 from creating short circuits, it must be held in the mold above the metallization layer 3 and / or the electronic components 4.

[0032] In the Fig. 7 is the electronics module 1 according to Fig. Figure 6 shows the structure after casting with the molding compound 8. The grid structure 13 acts as a stiffener and also compensates for the thermal expansion of the metal plate 7, so that the overall structure is primarily subjected to shear stress. In the example shown, the top surface 10 of the molding compound 8 is flat. However, it can also have structures as described previously (e.g., depressions 9, protrusions 11, or rib structures 12).

[0033] In the Fig. Figure 8 shows a further alternative embodiment of an electronic module 1 in a sectional view. The difference from the previous embodiments is that two different molding compounds 8 are used, namely a first molding compound 8.1 and a second molding compound 8.2, wherein the first molding compound 8.1 is the lower molding compound 8 and the second molding compound 8.2 is the upper molding compound 8. The two molding compounds 8.1 and 8.2 have different coefficients of thermal expansion. The top surface 10 of the second molding compound 8.2 forms the top surface of the electronic module 1. In the illustrated example, the top surface of the first molding compound 8.1 has a depression, while the top surface 10 of the second molding compound 8.2 is flat. However, as indicated by the dashed lines, the top surface 10 of the second molding compound 8.2 can also have a protrusion 11 or a depression 9. Preferably, the first molding compound 8.1 has the higher coefficient of thermal expansion. In the . Fig. In section 8, the two molding masses 8.1 and 8.2 are completely layered on top of each other. The two molding masses 8.1 and 8.2 are applied sequentially.

[0034] In the Fig. Figure 9 shows an alternative embodiment in which the first molding compound 8.1 only partially covers the substrate 2 or the overlying metallization layer 3. The overlying second molding compound 8.2 can then again have a flat top surface 10 or, as shown by dashed lines, a raised area 11 or a recessed area 9. Likewise, the second molding compound 8.2 can have ribbed structures 12 (see Figure 9). Fig. 5) exhibit. Reference symbol list 1 electronic module 2 Substrat 3 Metallization layer 4 electronic component 5 Contact 6 Control pins 7 metal plate 8 Molding compound 8.1 First molding compound 8.2 second molding compound 9 In-depth study 10 Top 11 Survey 12-rib structure 13 Lattice structure 14 holes 15 elongated holes

Claims

Electronic module (1) comprising at least one substrate (2) with at least one electronic component (4) and contacts (5), wherein the electronic component (4) and at least partially the substrate (2) are covered with at least one molding compound (8), wherein at least one contact (5) is not completely covered by the at least one molding compound (8), wherein a top surface (10) of the at least one molding compound (8) is structured, characterized in that the top surface (10) of the at least one molding compound (8) has at least one convex elevation (11) and / or the top surface (10) of the at least one molding compound (8) has a rib structure (12) that is arranged completely circumferentially at the edges of the top surface (10). Electronic module according to claim 1, characterized in that a grid structure (13) is arranged in the at least one molding compound (8), which lies between the electronic component (4) and the top surface (10) of the at least one molding compound (8) and is completely surrounded by the at least one molding compound (8). Electronic module according to claim 1 or 2, characterized in that at least two molding materials (8.1, 8.2) are present, wherein the two molding materials (8.1, 8.2) have different coefficients of thermal expansion. Electronic module according to one of the preceding claims, characterized in that the at least two molding masses (8.1, 8.2) are layered on top of each other. Electronic module according to one of claims 1 to 3, characterized in that a first molding compound (8.1) only partially covers the substrate (2) with the electronic component (4), wherein the second molding compound (8.2) covers the remaining part and the first molding compound (8.1). Electronic module according to one of the preceding claims, characterized in that a metal plate (7) is arranged below the substrate (2), which is partially embedded in the molding compound (8). Electronic module according to one of the preceding claims, characterized in that fillers are inserted into the at least one molding mass (8). Method for manufacturing an electronic module (1), wherein at least one electronic component (4) and contacts (5) are applied to a substrate (2), wherein the electronic component (4) and at least partially the substrate (2) are subsequently covered with at least one molding compound (8), wherein at least one contact (5) is not completely covered by the at least one molding compound (8), wherein a top surface (10) of the at least one molding compound (8) is structured during injection molding, characterized in that the top surface (10) of the at least one molding compound (8) has at least one convex elevation (11) and / or the top surface (10) of the at least one molding compound (8) has a ribbed structure (12) that is arranged completely around the edges of the top surface (10).

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