POWER ELECTRONIC MODULE

Abstract

The present invention relates to a method for manufacturing a power electronic module comprising a step of applying a protective layer to a face of a substrate opposite to that carrying power electronic components and arranging the substrate in a mold so that the protective layer is applied to the bottom of the mold and then injecting resin. Abstract figure: Figure 5

Description

Title of the invention: ELECTRONIC POWER MODULE Technical field

[0001] The present disclosure relates to the field of electronic power modules for converting electrical energy. Such modules are intended in particular for supplying power to electrical equipment, in particular in the field of aeronautics. Prior art

[0002] Generally speaking, a power electronic module comprises power electronic components which make it possible to supply power to electrical equipment from an electrical network, in particular via electrical conductors in the form of buses. From a structural point of view, a power electronic module 10 ([Fig.l]) conventionally comprises a substrate 12 and power electronic components 14 mounted on a first face 12a of the substrate and electrical connection tracks of the power electronic components 14 to the electrical connectors 16, 18. The whole is conventionally encapsulated in a housing and embedded in an encapsulating material, such as epoxy resin 19.

[0003] Figure 1A illustrates a power electronic module 10 without the resin 19 while the resin 19 surrounding the power electronic components is shown in Figures 1B and 2. In [Fig.2], the power electronic module with encapsulation is observed as obtained after molding. This module comprises electrical conductors 16, 18 comprising power connectors 16 and signal connectors 18. The metal electrical connectors are connected to each other by a metal frame 20, the connectors 16, 18 and the frame 20 being made of the same material.Conventionally, the substrate 12 comprises several successive layers, a lower layer of copper or aluminum serving as a mechanical support, a ceramic layer serving as an electrical insulator and an upper layer of copper or aluminum allowing the formation of the electrical connection tracks for the connection to the signal connectors 18, this upper metal layer also allowing the electrical connection to the power connectors 16.

[0004] The substrate equipped with the electronic components and illustrated in Figure 1B is then plasma cleaned before being placed in a mold ([Fig.3]) and preheated to improve the adhesion between a thermosetting resin that will be used during the encapsulation by transfer molding, and the substrate. As shown in [Fig.3], the mold comprises a lower part 22 and an upper part 24. More pre Specifically, the lower part 22 forms a receiving tray for the module 10. It is observed that the electrical connectors 16, 18 extend outside the mold and beyond the junction plane of the lower 22 and upper 24 parts. The bottom wall 26 of the lower part 22 of the mold comprises a convex wall 28 intended to receive the second face of the substrate 12b, that is to say the one opposite the first face 12a. The upper part 24 of the mold is applied to the upper peripheral edge of the lower part 22 of the mold so as to form a sealed joint plane at which the power connectors 16 and the signal connectors 18 are tightened.

[0005] It is observed that the upper part 24 of the mold comprises support pins 30 making it possible to support the substrate 12 equipped with the electronic components on the convex wall 28 of the lower part 22 of the mold. The addition of a camber is necessary to counter the camber of the substrate 12 following the very manufacture thereof. The convex wall has an amplitude of approximately 200-250 pm in order to obtain a desired final camber of amplitude less than 100 pm for the substrate.

[0006] Despite the presence of support pins 30 and the convex support wall 28, it is observed that air cavities may be present between the substrate 12 and the convex wall 28. These cavities are mainly due to the variability of camber in amplitude and shape between the substrates. It follows that the predetermined shape of the convex wall is not suitable for all substrates.

[0007] Under the effect of pressure and temperature, the resin injected into the mold can penetrate under the substrate and fill the air cavities. This leads to the formation of flash zones 32 which can be observed in [Fig.4]. These flash zones can have a width of approximately 2.4 mm for a substrate with dimensions of approximately 63.5 mm x 35.6 mm.

[0008] To remove these resin burrs, a deburring process is used. Conventional deburring processes generally use chemicals, water, or hard solids immersed in water as agents.

[0009] In the case of chemical treatment, strongly acidic or alkaline chemicals are used to attack the interface between the epoxy and the substrate surface. This process can lead to degradation of the substrate surface if these parameters are not well controlled. After a sufficient chemical reaction time, a water rinse and a water jet can be used to detach the burrs from the substrate surface. It is understood that the use of chemicals is not optimal from an environmental point of view due to the use of chemicals themselves but also the associated water consumption.

[0010] In the case of abrasive blasting treatment, glass or crystal beads mixed with water can also be used for blasting the upper surface of the burrs. However, this method may result in surface defects. (dents or micro-cracks) and additional camber of the power module which can affect its performance and reliability.

[0011] Deburring processes are therefore very delicate and also expensive. It is therefore desirable to have an alternative that is simpler to implement, less polluting and makes it possible to guarantee the integrity of the substrate while avoiding the formation of resin burrs on the substrate, i.e. on the face opposite that carrying the power electronic components. Summary

[0012] The present disclosure relates to a manufacturing method comprising: a. Obtaining a substrate comprising a first face on which electronic components are arranged and a second free opposite face, b. Obtaining an injection mold of a thermosetting resin comprising an upper part and a lower part, a convex wall being formed on a bottom wall of the lower part of the mold, c. Forming a protective layer on the second face of the substrate, this layer being capable of retaining its original mechanical structure up to a temperature of at least 200°C, d. Arrange the substrate obtained from step d) so that the protective layer comes into contact with the convex wall of the lower part of the mold, e. Close the mold by placing the upper part of the mold on the lower part of the mold, f. Inject resin under pressure into the mold to cover the electronic components.

[0013] According to the invention, a protective layer is formed on the second substrate face which prevents the resin from coming into contact with the second face of the substrate. This protective layer has a certain flexibility allowing it to be crushed without dislocating, thus allowing perfect contact with the convex wall of the lower part of the mold. In this way, no air cavity is formed between the substrate and the convex surface which avoids the introduction of resin. It is thus possible to do without the chemical or mechanical deburring step, which makes the manufacturing process of a power module simpler, faster, less expensive and more environmentally friendly.

[0014] The protective layer may have a Young's modulus of between 0.5 and 2 GPa. This range of values ​​allows good mechanical strength of the protective layer because it achieves a good compromise between flexibility and resistance to dislocation, thus making it possible to protect the rear face of the substrate against overflow of the epoxy.

[0015] According to another characteristic of the invention, the protective layer can cover the entire second surface of the substrate.

[0016] The peripheral edge of the protective layer may be applied to a peripheral edge of the second face of the substrate.

[0017] The protective layer may have a thickness less than or equal to 100 μm, preferably between 50 and 100 μm.

[0018] The protective layer may comprise an adhesive film allowing it to be held on the second face of the substrate.

[0019] The resin may be thermosetting and is chosen from an epoxy resin, a polyimide (PI) resin such as Kapton®, polyamide such as Nomex® paper (type 410) or polytetrafluoroethylene such as Teflon®.

[0020] After injecting the resin, the following steps can be carried out:

[0021] - the upper part of the mold is removed,

[0022] - the protective layer is then removed from the second face of the substrate.

[0023] A cleaning operation of the second face of the substrate can also be carried out after removal of the protective layer. This operation makes it possible to remove any residues, in particular adhesive when the protective layer comprises an adhesive film. A visual inspection of the second face of the substrate can also be carried out. Brief description of the drawings

[0024] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0025] [Fig. 1] illustrates a power module according to the known technique and comprising a substrate carrying electronic components, the upper part A illustrating the power module with encapsulation and the lower part B illustrating the same power module without encapsulation;

[0026] [Fig.2] illustrates a power module after resin injection;

[0027] [Fig.3] illustrates the overflow of the epoxy resin on the face of the substrate opposite to the one carrying the electronic components;

[0028] [Fig.4] schematically illustrates the epoxy resin injection device according to the prior art;

[0029] [Fig.5] and [Fig.6] schematically illustrate the manufacturing process of a module of power according to the invention. Description of the embodiments

[0030] Reference is now made to Figures 5 and 6 which represent a resin injection mold 34 according to the present disclosure. In [Fig.5], the mold 34 is in the open state before resin injection and in [Fig.6], the mold 34 is in the open state after resin injection 36.

[0031] The mold 34 comprises a lower part 34a and an upper part 34b and is intended to receive the substrate 37 equipped with the electronic components and the electrical power connectors 38 and signal 40. The substrate 37 comprises a first face 37a carrying the electronic power components and a second opposite face 37b.

[0032] The lower part 34a of the mold 34 comprises a bottom wall 42 and a side wall 44 connected to a peripheral edge of the bottom wall 42. The side wall 44 comprises an upper peripheral edge 44a intended to receive a lower peripheral edge 46 of the upper part 34b of the mold 34. The upper part 34b of the mold 34 is in the form of a cover intended to close the upper opening of the lower part 34a of the mold 34.

[0033] The lower part 34a of the mold 34 comprises a boss 48 having a convex upper wall 50 oriented towards the opening of the lower part 34a of the mold 34. This boss 48 has a dimension in width and length such that the substrate 37 will be applied entirely on the convex wall 50. In practice, it is observed that the surface of the convex wall 50 is substantially equal to the second surface 37b of the substrate 37.

[0034] The upper part 34b of the mold 34 comprises support pins 52 making it possible to press on the first face 37a of the substrate 37 and thus constrain the substrate 37 according to the shape of the convex wall 50 of the bottom wall 42 of the lower part 34a of the mold 34. These pins 52 are positioned on the upper part 34b of the mold 34 so as to press directly on the substrate 37 and not on the power electronic components. These pins 52 extend projecting relative to the upper part 34a of the mold 34. The upper part 34b of the mold 34 also comprises ejectors 54 making it possible to press on the hardened resin after injection and hardening of the resin.

[0035] The method of manufacturing an electronic power module according to the invention takes place as follows: a. Obtaining a substrate 37 comprising a first face 37a on which electronic components are arranged and a second free opposite face 37b, b. Obtaining a mold 34 for injecting a thermosetting resin comprising an upper part 34b and a lower part 34a, c. A convex wall 50 being formed on a bottom wall 42 of the lower part 34a of the mold 34, d. Forming a protective layer 56 on the second face of the substrate 37, this layer 56 being capable of retaining its original mechanical structure up to a temperature of at least 200°C, e. Arrange the substrate 37 obtained at the end of step d) so that the protective layer 56 comes into contact with the convex wall of the lower part of the mold, f. Close the mold 34 by placing the first part 34b of the mold on the second part, g. Inject resin 36 under pressure inside the mold 34 so as to cover the electronic components.

[0036] Unlike the prior art, a layer 56 of a material resistant to the temperatures to which the resin is subjected is provided, which may be epoxy. The layer may be Teflon ADEZIF TE205. The layer of protective material could be a polyimide (PI) such as Kapton®, polyamide such as Nomex® paper (type 410) or even Polytetrafluoroethylene such as Teflon®, in particular Teflon® ADEZIF TE205.

[0037] In practice, the layer 56 should have a thickness less than 100 pm and preferably between 50 and 100 pm.

[0038] The protective layer 56 may be electrically insulating so as not to have residues at the end of the process which may be a source of partial discharge in the module and a source of short circuit. This layer 56 may be applied to the second face 37b of the substrate 37 by gluing. For this purpose, it may thus comprise an adhesive film. It must have a mechanical strength enabling it to withstand the bearing force produced by the pins 52.

[0039] After injection of the resin 36, the upper part 34b of the mold 34 is removed using the ejectors 54. The layer 56 is then removed from the second face 37b of the substrate 37. Cleaning is also carried out to remove any glue residue and a visual inspection of the second face 37b of the substrate 37 is carried out.

[0040] At the end of these steps, the substrate 37 encapsulated in resin 36 is thus obtained, this substrate being free of inclusion of resin 36 on the second face thereof. This avoids long and complicated mechanical or chemical deburring operations.

Claims

Claims

1. A method of manufacturing a power electronic module comprising: a. Obtaining a substrate (37) comprising a first face (37a) on which electronic components are arranged and a second free opposite face (37b), b. Obtaining an injection mold (34) of a thermosetting resin (36) comprising an upper part (34b) and a lower part (34a), a convex wall (50) being formed on a bottom wall (42) of the lower part (34a) of the mold (34), c. Forming a protective layer (56) on the second face (37b) of the substrate (37), this layer (56) being capable of retaining its original mechanical structure up to a temperature of at least 200°C, d. Arrange the substrate obtained at the end of step d) so that the protective layer comes into contact with the convex wall (50) of the lower part (34a) of the mold (34), e.Close the mold by placing the upper part (34b) of the mold (34) on the lower part (34a) of the mold (34), f. Inject resin (36) under pressure inside the mold (34) so ​​as to cover the electronic components.

2. The method of claim 1, wherein the protective layer (56) covers the entire second surface (37b) of the substrate (37).

3. A method according to claim 2, wherein the peripheral edge of the protective layer (56) is applied to a peripheral edge of the second face (37b) of the substrate (37).

4. Method according to one of claims 1 to 3, in which the protective layer (56) has a thickness less than or equal to 100 pm, preferably between 50 and 100 pm.

5. Method according to one of claims 1 to 4, in which the protective layer (56) comprises an adhesive film allowing it to be held on the second face of the substrate.

6. A method according to any one of claims 1 to 5, wherein the resin is thermosetting and is chosen from an epoxy resin, a polyimide resin, polyamide or even polytetrafluoroethylene.

7. Method according to one of the preceding claims, in which the layer (56) is electrically insulating.

8. Method according to one of the preceding claims, in which the protective layer has a Young's modulus of between 0.5 and 2 GPa.

9. Method according to one of the preceding claims, in which after injection of the resin (36), the following steps are carried out: - the upper part (34b) of the mold 34 is removed, - the protective layer (56) is then removed from the second face (37b) of the substrate (37).

10. A method according to claim 9, wherein an operation of cleaning the second face of the substrate (37b) is carried out.

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