A METHOD FOR MANUFACTURING AN ELECTRONIC POWER MODULE

Abstract

A method for manufacturing a power electronic module by additive manufacturing includes the step of depositing a layer of an electrically conductive nanoporous material on a substrate that includes an electrically insulating layer and at least one layer of conductive metal material, called a metallized substrate. The method further includes the step of placing an element for example an active component of the semiconductor power component type, on the layer of nanoporous material and sintering the layer of nanoporous material, so as to ensure a mechanical and electrical connection between said element and the metallized substrate.

Claims

1. A method of manufacturing a power electronic module by additive manufacturing, comprising the steps of: depositing in a single step, by electrodeposition, a layer of electrically conductive nanoporous material directly on a substrate comprising an electrically insulating layer and at least one layer of conductive metal material, called a metallized substrate, placing an element on the layer of nanoporous material and sintering the layer of nanoporous material to ensure a mechanical and electrical connection between said element and the metallized substrate, making or fixing preforms of polymer material on at least one face of the metallized substrate, depositing a first metal layer on the preform, and depositing a second metal layer on the first metal layer by electroforming.

2. The method according to claim 1, wherein the layer of nanoporous material is deposited on the second metal layer.

3. The method according to claim 1, further comprising a step of dissolving the preforms of polymeric material by chemical or thermal means.

4. The method according to claim 1, further comprising a step of covering at least one area of the conductive layer of the metallized substrate with a protective film made of non-conductive material, before deposition of the first metal layer and of the second metal layer.

5. The method according to claim 4, further comprising a step of carrying out the removal of at least one zone of the protective film to form an opening, a spike being obtained by depositing the first and second metal layers in the said opening.

6. The method according to claim 1, wherein the substrate comprises at least one insulating layer of ceramic.

7. The method according to claim 1, wherein the first metal layer has a thickness of less than 5 microns.

8. The method claim 1, wherein the power electronic module comprises a housing in which the metallized substrate and the active component are housed, the method further comprising a step of at least partially filling the housing, with an insulating material.

9. The method according to claim 1, wherein the element is an active component of the semiconductor power component type.

10. The method according to claim 7, wherein the first metal layer has a thickness of less than 1 micron.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0068] FIG. 1 is a schematic view illustrating a power electronic module of the prior art,

[0069] FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8 and FIG. 9 illustrate various steps of a method of manufacturing a power electronic module according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0070] FIGS. 2 to 6 schematically illustrate the various manufacturing steps of a power electronic module 1 according to one embodiment of the invention.

[0071] In a first step illustrated in FIG. 2, preforms 15 of polymeric material are made by additive manufacturing on two opposite sides of a first metallized substrate 2a and a second metallized substrate 2b. The preforms 15 may be made directly on each metallized substrate 2a, 2b or may be attached to said metallized substrate 2a, 2b after making the preforms 15. In the latter case, the preforms 15 may be bonded to the corresponding metallized substrate 2a, 2b.

[0072] Each metallized substrate 2a, 2b comprises an electrically insulating layer 2c of ceramic material coated on each of its opposite sides with a metal layer 2d, 2e, for example of copper. The metal layers 2d, 2e of the metallized substrate 2a, 2b can be joined to the insulating layer 2c by soldering (or “Active Metal Brazing” or “AMB”), by direct bonding of copper (or “DBC”), or by direct bonding of aluminum (or “DBA”).

[0073] Alternatively, the electrically insulating layer 2c may be made of a polymeric material (in the case of an IMS or Insulated Metal Substrate).

[0074] The metal layers 2d form electrically separate tracks from each other.

[0075] Protective films 16 of polymeric material cover at least a portion of the conductive tracks of the top layer 2d.

[0076] As shown in FIG. 2, a first metal layer 17, for example of silver or copper, is deposited on the preforms 15, for example by chemical reduction via spraying. The first layer 17 has a thickness of less than 1 micron for example. Other deposition techniques can be used, such as spray coating or dip coating.

[0077] Some of the preforms 15 may be pre-metallised, i.e. coated with the first metal layer 17 before assembly on the corresponding metallised substrate 2a, 2b.

[0078] openings 18a, 18b are formed in the protective film 16 covering the second substrate 2b, some of these openings (i.e. openings 18b) being covered with an auxiliary protective film 19.

[0079] A second metal layer 20, for example of copper, is then deposited on the first metal layer 17, as shown in FIG. 4. Such a deposit is made by electroforming.

[0080] The second layer 20 has a thickness of between a few microns and a few millimetres, as required. The thickness of the second layer 20 can be varied as a function of the applied voltage and bias time applied during the electroforming deposition step.

[0081] During electroforming, all or part of the metallized substrate 2a, 2b and the first metal layer 17 is immersed in an electrolytic bath comprising metal ions, for example copper in ionic form. The bath may be a low-temperature bath, i.e., a temperature below 100° C. An electrode is electrically connected to some of the conductive tracks of the layers 2d of the substrates 2a, 2b and the metal layers 2e of the substrates 2a, 2b. The conductor tracks or layers connected to the electrode are shown with crosses in FIG. 4. An electrical potential is applied to these areas, via said electrode, so as to deposit the filler metal of the electrolytic bath on the first metal layer 17. The non-metallic areas of the substrate 2a, 2b, the areas covered by the protective film 16 or the metallic areas which are not at the electrode potential, are then not covered with filler metal.

[0082] The second metal layer 17 can in particular delimit connectors 5, housing parts, cooling channels 21 of heat sinks or radiators 11 and spikes 22.

[0083] The deposition of the second layer 20 can be performed in several steps, as illustrated in FIGS. 4 and 5. In a first step illustrated in FIG. 4, the openings 18b are covered by the auxiliary protective film 19, so that only the opening(s) 18a whose corresponding conductor track(s) is (are) at the desired electrical potential are progressively filled with filler metal 20. In a second step illustrated in FIG. 5, the auxiliary protective film 19 is removed, uncovering the openings 18b, so that filler metal can also be deposited in these openings 18b, provided that the corresponding conductor tracks are at the desired electrical potential. In this way, it is possible to make spikes 22 of different lengths, depending on the tracks connected to the electrode and/or depending on the openings 18a, 18b covered by the auxiliary film 19.

[0084] A layer of electrically conductive nanoporous material 23 is then deposited on certain tracks of the metal layers 2d of the first and second metallized substrates 2a, 2b, as shown in FIG. 6.

[0085] The layer of nanoporous material 23 has, for example, a thickness between 1 and 100 microns. The nanoporous material has pores with dimensions of less than 1 micron.

[0086] The nanoporous layer 23 is produced by dipping in an electrolytic bath, the relevant tracks being connected to a potential via an electrode, as illustrated schematically by crosses in FIG. 6. The nanoporous material is obtained in a single step by adding additives to the electrolyte bath and/or by using current pulses, as is known per se.

[0087] As shown in FIG. 7, the preforms 15 are then removed in a chemical or thermal dissolution step.

[0088] In the case of chemical dissolution, ABS preforms 15 can be dissolved in an acetone bath at a temperature of 50° C. using ultrasound.

[0089] Alternatively, in order to dissolve PLA preforms 15, a 35% soda bath can be used at a temperature of 60° C. and stirring can be carried out to promote dissolution.

[0090] It is thus possible to create recessed areas, connectors 5 or channels 21 intended to facilitate heat exchange for the purpose of cooling the assembly, for example by means of a flow of air or a liquid coolant.

[0091] The protective films 16 may also be removed during the dissolving step.

[0092] Active components of the semiconductor power component type 3 are deposited on the layer of nanoporous material 23 deposited on the first metallized substrate 2a (FIG. 8). Said layer of nanoporous material 23 is then sintered so as to provide a mechanical and electrical bond between a first face of said components 3 and the first metallized substrate 2a.

[0093] The second metallized substrate 2b is then placed opposite the first metallized substrate so that the layer of nanoporous material 23 deposited on the ends of the spikes 22 are in contact with the second face of said components 3 and with one of the tracks of the first metallized substrate 2a, respectively (FIG. 9). The said layer of nanoporous material 23 is then sintered so as to ensure a mechanical and electrical connection between the spikes 22, the second face of the said components 3 and the corresponding track of the first metallized substrate 2a. The sintering is carried out at a temperature between 200° C. and 300° C., with the application of a pressure between 1 and 10 MPa, in the case of a nanoporous copper layer. This allows a good mechanical bond to be achieved without impacting the properties of the components 3 and the substrates 2a, 2b to be joined. In order to avoid oxidation, sintering can be carried out in an inert atmosphere or by rapid laser sintering.

[0094] A single simultaneous sintering operation of all the layers of nanoporous material 23 may be considered.

[0095] A housing attached to the substrates 2a, 2b is then filled with an electrical encapsulant or insulator, such as a gel or epoxy, to provide mechanical and electrical protection for the power components 3.

[0096] In particular, such a method has the following advantages: [0097] realization of a practically finished structure by a method for easy industrialization, [0098] attachment of power components 3 with small electrodes without risk of short circuiting by means of sintering, [0099] good thermal performance, due in particular to the reduction of interfaces between the power components 3 and the heat sinks 11 and to the fact that it is possible to produce heat sinks 11 with complex geometrical shapes [0100] possibility to use the power module 1 at very high temperatures, thanks in particular to the elimination of thermal interface materials whose use is limited in temperature, or thanks to the absence of solder, [0101] improvement of the reliability due to the absence of soldering, [0102] increase in the power density of the converters due to the reduction in the mass of the heat sinks 11, [0103] reduction of the residual stresses compared to the same realization by additive manufacturing techniques requiring very high local temperatures for the fusion or sintering of metallic powders, [0104] sealing of the channels 21 of the heat sinks 11 thanks to the absence of porosity and gaps in the electro-deposited material 20.