POWER ELECTRONICS MODULE AND A METHOD OF PRODUCING A POWER ELECTRONICS MODULE

Abstract

A power electronics module and a method of producing a power electronics module. The module includes multiple of power electronic semiconductor chips incorporated in a housing, and a heat transfer structure which forms an outer surface of the module and is adapted to receive a surface of a cooling device, wherein the heat transfer structure includes a metallic structure having a soft coating.

Claims

1. A power electronics module comprising a multiple of power electronic semiconductor chips incorporated in a housing, and a heat transfer structure having a surface which forms an outer surface of the module and is adapted to receive a surface of a cooling device, wherein the heat transfer structure comprises a metallic structure having a soft coating.

2. The power electronics module according to claim 1, wherein the soft coating forms an outer surface of the module.

3. The power electronics module according to claim 2, wherein the module comprises a direct bonded copper structure having a top surface and a bottom surface, wherein the power electronic semiconductor chips are attached to the top surface of the direct bonded copper structure and the bottom surface of the direct bonded structure comprises the soft coating.

4. The power electronics module according to claim 2, wherein the module comprises a base plate and a surface of the base plate comprises the soft coating.

5. The power electronics module according to claim 4, wherein the base plate is a copper base plate.

6. The power electronics module according to claim 4, wherein the base plate is a copper base plate and comprises a layer of graphite inside the copper.

7. The power electronics module according to claim 1, wherein the soft coating comprises indium.

8. The power electronics module according to claim 1, wherein the material of the soft coating is indium-based, graphite-based, copper-based, tin-based or polymer material.

9. The power electronics module according to claim 1, wherein the thickness of the soft material layer is in the range of 25 m to 350 m.

10. The power electronics module according to claim 7, wherein the soft coating comprises further diamond or graphite particles for enhancing thermal conductivity of the soft coating.

11. A method of producing a power electronics module, the method comprising providing a power electronics module comprising multiple of power electronics semiconductor chips incorporated in housing and having a heat transfer structure having a surface which forms an outer surface of the module, and applying a soft coating to the outer surface of the provided power electronics module.

12. The method according to claim 11, wherein the material of the soft coating is indium-based, graphite-based, tin-based or polymer material.

13. The method according to claim 11, wherein the coating is applied using PVD coating technology.

14. The power electronics module according to claim 1, wherein the module comprises a direct bonded copper structure having a top surface and a bottom surface, wherein the power electronic semiconductor chips are attached to the top surface of the direct bonded copper structure and the bottom surface of the direct bonded structure comprises the soft coating.

15. The power electronics module according to claim 1, wherein the module comprises a base plate and a surface of the base plate comprises the soft coating.

16. The power electronics module according to claim 15, wherein the base plate is a copper base plate.

17. The power electronics module according to claim 15, wherein the base plate is a copper base plate and comprises a layer of graphite inside the copper.

18. The power electronics module according to claim 8, wherein the soft coating comprises further diamond or graphite particles for enhancing thermal conductivity of the soft coating.

19. The power electronics module according to claim 9, wherein the soft coating comprises further diamond or graphite particles for enhancing thermal conductivity of the soft coating.

20. The method according to claim 12, wherein the coating is applied using PVD coating technology.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

[0018] FIG. 1 shows a known power electronics module with a base plate attached to a heat sink;

[0019] FIGS. 2 shows an embodiment of a power electronics module of the present invention with a base plate;

[0020] FIG. 3 shows an embodiment of a power electronics module of the present invention without a base plate; and

[0021] FIG. 4 shows another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 2 shows a power electronics module of the present invention. In the cross section of FIG. 2, the reference numerals correspond to those of FIG. 1 for the corresponding parts of the module. The power semiconductor chips 11, 12 are soldered to a DBC structure 3, 4 which is again soldered to a base plate 7.

[0023] According to the present invention, a power electronics module comprises multiple of power electronic semiconductor chips 11, 12 incorporated in a housing 6. The module comprises further a heat transfer structure 22 having a surface 21 which forms an outer surface of the module and is adapted to receive a surface of a cooling device, wherein the heat transfer structure 22 comprises a metallic structure 7 having a soft coating 20. In the embodiment of FIG. 2, the heat transfer structure 22 consists of the base plate of the power electronics module and of a soft coating 20 applied to the base plate. The surface 21 of the heat transfer structure forms an outer surface or bottom surface of the power electronics module.

[0024] The surface 21 of the heat transfer structure is adapted to receive a surface of a cooling device such that the heat from the power electronics module is led to the cooling device. According to the invention, a soft coating is formed to directly on the surface of a metallic structure. Thus the power electronics module with a housing comprises a surface that has a soft coating 20.

[0025] When a cooling device, such as a heat sink, is attached to the power electronics module of the invention, the soft coating deforms slightly and fills any gaps that may be present in the surface of the cooling device. In known solutions a separate layer is used for producing a good thermal contact between a power electronics module and the heat sink. Such a separate layer has to fill possible air gaps both in the surface of the module and in surface of the cooling device. As the soft coating is applied to the surface of the module, there cannot be any air gaps between the coating and the surface to which is applied.

[0026] FIG. 3 shows another embodiment of the power electronics module of the invention in which the soft coating 20 is applied to a copper layer of the DPC structure. In the embodiment the heat transfer structure is thus formed from the copper layer 3 and the soft coating 20. The module of FIG. 3 is a module without a base plate. Thus the bottom surface of the module is formed of the soft coating applied to a metallic structure which is the copper layer 3. The bottom surface is adapted to receive a cooling device for removing and spreading the heat from the module.

[0027] According to an embodiment in which the power electronics module comprises a base plate, the base plate comprises a heat spreading graphite structure 41 as shown in FIG. 4. The heat spreading graphite structure is preferably formed as a layer or as several layers inside the metallic base plate 7. The purpose of the graphite structure is to spread the heat in a lateral direction of the base plate as indicated by the arrows in FIG. 4. Graphite structures may have different heat conduction properties in different directions. When the heat from the power semiconductor chips is led through the base plate, the graphite layer spreads the heat such that the base plate is heated more evenly. When the base plate heats uniformly, the heat transfer from base plate to the cooling device is more efficient than in the case the base plate has warmer and cooler areas. Further, when the thermal mass of the base plate is used efficiently with the aid of the graphite layer, the soft coating of the bottom surface produces efficient cooling properties when a cooling device is attached to the module.

[0028] According to an embodiment the material of the soft coating is indium, copper, tin, graphite or polymer. The material of the soft coating may also consist primarily of one of the mentioned materials. When the material consist primarily of the mentioned materials, the material comprises one or more additional materials which may be included to the coating to further enhance the thermal properties or mechanical properties of the coating, for example.

[0029] Preferably the coating material is indium based material having a thickness in the range of 25 m to 350 m in uncompressed state. The indium based material coating is processed into the power electronics modules baseplate. In case the power semiconductor has no baseplate the indium material layer is processed into the bottom surface of DBC structure.

[0030] The natural softness and thickness of the indium allows it to adapt and fill sufficiently (air) gaps between surfaces of power electronics modules base plate and a cooling device during the attachment of the module. Power electronics modules operation and power cycling during the operation causes base plate to bend and/or twist. This means that some new gaps occur in varying locations in between the base plate with Indium coating layer and the cooling surface of the attached external cooling device. However, the indium based material has a relatively high thermal conductivity (k82 W/mK) compared to conventional thermal interface material layers.

[0031] According to the invention, the soft coating is pre-applied into the component DBC substrate's or baseplate's bottom. The coating can be applied by using PVD coating technology and especially with low process temperature DIARC FCAPAD coating method, for example. PVD coating is suitable for very thin coating thicknesses (up to 25 m) while other known methods may be more suitable for thicker coatings.

[0032] When the soft coating is applied to the surface of the power electronics module, it allows easy and fast work in the production of devices employing power electronics modules. When the module of the invention is used, separate thermal interface materials are not needed.

[0033] The soft coating has a sufficiently low hardness (approx. Mohs 1.2). The low hardness allows the initial thickness of the coating to reduce and adapt to the cooling surface's surface profile during mounting to its designated value. When a cooling device is properly attached to a power electronics module of the invention, the thickness of the coating is reduced from the above mentioned range of 25 m to 350 m.

[0034] The soft coating allows further to provide patterns or textures to the metallic surface. That is, the soft coating can be applied in a non-uniform manner if desired. Such a pattern may include dots or lines, for example. Further, the coating may be applied in desired portions of the metallic surface. For example, when the power electronic module is attached with screws or bolts to a cooling device, such as heat sink, it may be desirable that the soft coating is not applied near the holes provided for the screws or bolts. The such areas are left without the soft coating, the pressure between the module and the cooling device may be more desirable in the center areas of the modules base plate.

[0035] With the indium based soft coating approximately 16 to 40 times higher thermal conductivity can be achieved when compared to conventionally used thermal interface material layers. Naturally the different alloys of indium can be processed that allows tailoring of physical properties including thermal conductivity and hardness.

[0036] According to an embodiment, the indium coating may contain small enough (nano/micro) additive substances, like diamond or graphite, which enhance the materials thermal conductivity and/or its mechanical properties. The first is beneficial for reducing thermal resistance and the latter for the rigidity of the soft coating against mechanical forces during component operation and thermal cycling. The coating's additive or filler substances physical form may be for example particle, fiber, mesh or net.

[0037] In the above, the soft coating is referred specifically to be indium based material. However, tin, copper, polymers and graphite have similar benefits when used as a coating for a bottom surface of the power electronics module. It should be noted, that all the materials can be applied to a metallic surface in a known manner and that the coating is a solid coating in the operating temperatures of the power electronics module.

[0038] In the method of producing a power electronics module, the method comprises providing a power electronics module comprising multiple of power electronics semiconductor chips incorporated in housing and having a heat transfer structure having a surface which forms an outer surface of the module, and applying a soft coating to the outer surface of the provided power electronics module. The method of the invention enables to modify an existing power electronics module to module which has better thermal properties.

[0039] In the above description embodiments of power electronics module are described quite generally as power electronics modules as such are known in the art. It is, however, clear that such modules have a quite large footprint area and the length of the module is typically in the range of 6 to 25 cm:s. The drawings show cross sections of power electronics modules seen from one end of the module. The modules are shown to be cut in the positions of power electronic to semiconductor chips.

[0040] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.