METHOD FOR MAKING AN ELECTRICAL CONNECTION

Abstract

The invention relates to a method for making an electrical connection (100) between at least one electronic component (206) and at least one electrically conductive part (204A, 204B, 204C), comprising at least: a contacting step (106) in which at least one electrical conductor (402, 404) is brought into contact with, on the one hand, the electronic component (206) and, on the other hand, the electrically conductive part (204A, 204B, 204C); and an electrolysis step (112) in which an electrically conductive layer (702) is deposited by electrolysis around the electrical conductor (402, 404). Figure for the abstract: Fig. 8

Description

Title of the invention: METHOD FOR PRODUCING AN ELECTRICAL CONNECTION Technical field of the invention

[0001] The invention relates to a method for producing an electrical connection between an electronic component, in particular a semiconductor component, and an electrically conductive part. The invention is also specific to an electronic module and an electrical converter comprising such an electronic module. Finally, the invention also relates to an aircraft comprising such an electronic module and / or such an electrical converter.

[0002] The invention applies in particular to electronic power modules capable of integrating electrical converters necessary for the electrification of propulsion and / or non-propulsion systems on board aircraft, for example voltage converters for converting electrical energy from a main network (115V AC, 230V AC, 540V DC, etc.) into several forms (AC / DC, DC / AC, AC / AC and DC / DC). Technological background

[0003] A power electronic module comprises power semiconductor components, such as diodes and transistors interconnected to perform more or less complex electrical functions.

[0004] Such a power electronic module is usually made up of: • a substrate, or electronic circuit support, • electronic components connected to the substrate by appropriate connections, • connectors to ensure a connection between the electronic power module and its environment, and • a protective box.

[0005] The substrate is usually made of a metallized ceramic layer. However, the substrate can also be a printed circuit board, also referred to by the acronym PCB for "Printed Circuit Board" in English. The electronic components are soldered, welded or glued onto metallized electrical tracks on the substrate.

[0006] Power semiconductor components usually have, on the upper face, a metallization of a few microns thick in aluminum, typically between 4 μm and 10 μm. In the initial state, the metallization is composed of columnar grains of aluminum. In operation, the electronic component undergoes heating and cooling cycles which, through thermomechanical constraints, cause a microstructural reorganization of the grains of the metallization, or work hardening. The crystallographic orientation of the columnar aluminum grains changes under the accumulation of stresses, causing the appearance of sub-grain boundaries in them and a disorientation of the latter, ultimately leading to the multiplication of grains and a significant reduction in their size in the metallization. Such a mechanism allows stress relaxation and further delays the formation of cracks in the metallization, thus delaying the degradation of the metallization and therefore of the electronic component, extending its lifespan.

[0007] It is often necessary to make additional connections to enable the expected electrical circuit to be produced. The connections are usually made by wiring wires. The traditional technology in power electronics for producing wiring wires is ultrasonic wedge wire bonding technology, also known as "Ultrasonic Wedge Wirebonding" in English, with wires, in particular made of aluminum or aluminum-silicon alloy, several hundred microns in diameter, typically 250 qm, to allow the passage of high electric current.

[0008] This technology makes it possible to carry out the wiring by bridging between an electrode of the power electronic component and the electrical track to which it must be connected. The connection is made by applying high pressure, for example a force of 10 N generating a pressure of 37 MPa, on the wiring wire and the metallization of the electronic component coupled with ultrasound to ensure the welding of the wiring wire on the metallization of the electronic component. Such a process is called "cold" since the necessary energy is provided by the ultrasound.

[0009] When welding the wiring wire to the metallization using ultrasonic wedge wire bonding technology, the application of pressure and ultrasound causes premature aging of the aluminum grains located at the base of the wiring wire. In the initial state, the aluminum grains vertical to the wiring wire are therefore already disoriented and small in size, thus limiting the stress relaxation capacity of this area. The solution used by the metallization to release the stresses will be the formation of intergranular cracks. This mechanism causes faster failure of the electronic component. The process using ultrasonic wedge wire bonding technology therefore reduces the lifetime of the metallization of the electronic component and therefore of the system including such an electronic component.

[0010] A limiting point of ultrasonic wedge wire bonding technology is the reconstruction of aluminum from the metallization of electronic components.

[0011] In addition, when a wiring wire transfer process by ultrasonic wedge wire bonding technology is performed improperly, it may cause the area to break. active part of the electronic component located directly above the wiring wires, mainly grid oxide, causing immediate failure of the electronic component.

[0012] The surface condition of the wiring wires and the metallization of the electronic component before assembly can also induce particular defects. In particular, there may be a presence of bubbles, also called "voids" in English, oxidized at the wiring wire / metallization interface of the electronic component and a preferred cracking zone at this interface.

[0013] It is thus desired to provide a method for producing an electrical connection between an electronic component and an electrically conductive part which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0014] A method is therefore proposed for producing an electrical connection between at least one electronic component and at least one electrically conductive part, which comprises at least: • A contacting step during which at least one electrical conductor, for example of the wire type, is brought into contact with, on the one hand, the electronic component and, on the other hand, the electrically conductive part; and • An electrolysis step during which an electrically conductive layer is deposited by electrolysis around the electrical conductor.

[0015] Thanks to the invention, it is possible to use a small diameter electrical conductor, which is then widened or extended by an electrically conductive layer. The use of a small diameter electrical conductor allows the use of low-constraint techniques to bring it into contact, in particular with the electronic component, which makes it possible to avoid the disadvantages of techniques for laying wires with large diameters, such as the so-called “Ultrasonic Wedge Wirebonding” technique.

[0016] In addition, the method for producing an electrical connection may also further comprise, advantageously before the electrolysis step, a deposition step during which a coating, in particular a coating compatible with electrolysis, is deposited on the electrically conductive part and / or the electronic component.

[0017] Furthermore, the method of making an electrical connection may comprise one or more of the following characteristics: • the electrically conductive layer has a thickness of at least 10 pm, in particular at least 35 pm, in particular at least 50 pm; • the electrical conductor is a wire having a diameter of less than 250 pm, preferably between 10 pm and 50 pm; • the electrically conductive layer has a thickness at least equal to the diameter of the electrical conductor; • the electrical conductor is made of a material having a ductility of at least 3, advantageously at least 5, in particular 10; • the electrical conductor is made of copper or gold; • the coating has a thickness of at most 1 pm; and / or • the conductive part is made of aluminum, copper, gold, silver or nickel.

[0018] An electronic module is also proposed comprising at least: • an electronic component; • an electrically conductive part; and • an electrical connection between the electronic component and the electrically conductive part, this electrical connection comprising: • an electrical conductor in contact with, on the one hand, the electronic component and, on the other hand, the electrically conductive part, in particular produced using a wired wiring technique, and • an electrically conductive layer deposited by electrolysis around the electrical conductor.

[0019] The invention also relates to a voltage converter comprising at least one electronic module as previously defined.

[0020] An aircraft comprising at least one electronic module according to the invention or a voltage converter according to the invention is also proposed.

[0021] Of course, the different characteristics, variants and / or embodiments of the invention can be associated with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0022] The invention will be better understood and other characteristics and advantages will become apparent upon reading the detailed description which follows, comprising embodiments given for illustrative purposes with reference to the appended figures, presented as non-limiting examples, which may serve to supplement the understanding of the invention and the description of its implementation and, where appropriate, contribute to its definition, in which:

[0023] [Fig-1] [Fig.l] is a block diagram illustrating the steps of a production method of an electrical connection according to the invention,

[0024] [Fig.2] [Fig.2] is a perspective view of a substrate and a component electronics on which the method of [Fig.l] is intended to be applied,

[0025] [Fig.3] [Fig.3] is a perspective view of the substrate with the electronic component mounted thereon according to the invention,

[0026] [Fig.4] [Fig.4] is a perspective view, similar to [Fig.3], illustrating a contacting step according to the invention,

[0027] [Fig.5] [Fig.5] is a perspective view, similar to [Fig.4], illustrating a polarization step according to the invention,

[0028] [Fig.6] [Fig.6] is a perspective view, similar to [Fig.5], illustrating the immersion step according to the invention,

[0029] [Fig.7] [Fig.7] is a perspective view, similar to [Fig.5], of the substrate with the electronic component mounted thereon resulting from the steps of the method for producing an electrical connection according to the invention, and

[0030] [Fig.8] [Fig.8] is a sectional view of one of the electrical connection conductors resulting from the steps of the method for producing an electrical connection according to the invention. Detailed description of the invention

[0031] It should be noted that, in the figures, the structural and / or functional elements common to the different embodiments may have the same references. Thus, unless otherwise stated, such elements have identical structural, dimensional and material properties.

[0032] [Fig.l] is a block diagram illustrating the steps of a method for producing an electrical connection 100 according to the invention.

[0033] The method for producing an electrical connection 100 comprises a obtaining step 102, during which a substrate 202 and an electronic component 206, for example a power electronic component, in particular a semiconductor component, in particular a power semiconductor component, are obtained. The substrate 202 is designed to support power electronic components 206 and to allow them to be electrically connected to each other. The “power” qualification for the electronic component and the electrical connection means in particular that they are respectively designed to be crossed by a current of at least one ampere and / or to withstand a voltage of at least one hundred volts and / or to receive an electrical power of at least one kilowatt.

[0034] The electronic component 206 is, for example, a transistor electronic component, such as a metal-oxide field effect transistor, also designated by the acronym MOSFET for “Metal Oxide Semiconductor Field Effect Transistor” in English.

[0035] [Fig. 2] is a perspective view of the substrate 202 and an electronic component on which the method of [Fig. 1] is intended to be applied. More specifically, the substrate 202 has several conductive parts, including in particular the electrically conductive parts designated by the references 204A, 204B and 204C between which the electronic component 206 is intended to be electrically connected.

[0036] According to one embodiment, the substrate 202 may comprise an electrically insulating layer 208 and an electrically conductive layer 210 in which the electrically conductive parts 204A, 204B and 204C are cut. For example, the substrate 202 is a metallized ceramic substrate, such as a directly bonded copper substrate, also designated by the acronym DBC for “Direct Bonded Copper” in English. In such a latter case, the electrically insulating layer 208 is made of ceramic, such as alumina, and the electrically conductive layer 2010 is made of copper. The electrically conductive parts 204A, 204B and 204C are thus formed by conductive tracks carried by the electrically insulating layer 208.The electrically conductive parts 204A, 204B and 204C will thus be called hereinafter “conductive tracks”. Alternatively, the substrate 202 can be any other substrate conventionally used in power electronic modules.

[0037] The electronic component 206 may be integrated in the form of a chip. In particular, in such a case, the electronic component 206 may be in the form of a plate having an upper face and a lower face. The upper face may, in particular, have a power electrode, such as a source electrode, for example in the case of a MOSFET, and a control electrode, such as a gate electrode, for example in the case of a MOSFET. The lower face may, in particular, have another power electrode, such as a drain electrode, for example in the case of a MOSFET. The electronic component 206 may be of any shape used in the production of electronic devices.

[0038] The upper face of the electronic component 206, in particular the power electrode that it presents, may present, in the example described, a metallization, such as a metallization of a few microns of thickness in aluminum, in particular between 4 μm and 10 μm.

[0039] As shown in [Fig.l], the method for producing an electrical connection 100 also comprises an assembly step 104, the result of which is illustrated in [Fig.3], during which the electronic component 206 is surface-mounted on one of the electrically conductive tracks 204A, 204B and 204C, in this case the electrically conductive track 204B according to the example shown in [Fig.3], in order to be electrically connected to the latter. For example, the lower face of the electronic component 206 may be mounted so as to electrically connect the power electrode that it presents to the electrically conductive track 204B. Any technique traditional may be used. For example, the electronic component 206 may be soldered, welded or glued onto the electrically conductive track 204B.

[0040] Furthermore, the method for producing an electrical connection 100 also comprises a contacting step 106, the result of which is illustrated in [Fig. 4], during which at least one electrical conductor 402, 404 is brought into contact with, on the one hand, the electronic component 206 and, on the other hand, the desired conductive part. Advantageously, during the contacting step 106, several electrical conductors 402, 404 are respectively brought into contact with, on the one hand, the electronic component 206 and, on the other hand, one or more of the desired conductive parts 204A, 204B and 204C.

[0041] In the example presented in [Fig. 4], three electrical conductors 402 connect the electronic component 206, in particular the power electrode of the upper face of the electronic component 206, to the electrically conductive track 204A, while an electrical conductor 404 connects the electronic component 206, in particular the control electrode of the upper face of the electronic component 206, to the electrically conductive track 204C. The electrical conductors 402, 404 may have several forms, in particular those of conductive strips or conductive wires, according to the embodiment of [Fig. 4], the electrical conductors 402, 404 are electrically conductive wires having a diameter of less than 250 μm, preferably between 10 μm and 50 μm, in particular 15 μm.

[0042] Preferably, the electrical conductors 402, 404 have a ductility of at least 5. In particular, the electrical conductors 402, 404 are made of gold.

[0043] Thus arranged, such electrical conductors 402, 404 can be produced by a technology that is not very restrictive for the electronic component 206. Thus, it is possible to use a technology usually used in microelectronics. For example, a ball bonding technology, also called a ball bonding technology, designated by "Bail Bonding" in English, can be used to produce the electrical conductors 402, 404.

[0044] In the context of a ball connection, the contacting step 106 may, for example, comprise the following steps consisting of: • a wire generation step, in which the electrical conductor 402, 404 is generated through a nozzle from which one end of the electrical conductor 402, 404 emerges; • an electrical discharge step, in which an electrical discharge is applied to the end of the electrical conductor 402, 404 causing a ball to form; and • a crushing step, in which the ball is crushed with a certain pressure against the desired support, in particular the conductive track electrical component 204A or the electronic component 206, advantageously combined with a generation of ultrasounds applied to the ball thus crushed.

[0045] Due to the small diameter of the electrical conductor 402, 404 and / or the ductility of the material used, the pressure may be low, preferably less than 100 MPa. Similarly, the ultrasonic power may also be low, preferably less than 100 kHz. Thus, the production of the electrical conductors 402, 404 is not very restrictive for the support, in particular for the electronic component 206.

[0046] In addition, the method for producing an electrical connection 100 may also comprise a deposition step 108 during which a coating, in particular a metal coating, may be deposited on the electronic component 206 and / or on at least one of the electrically conductive tracks 204A, 204B and 204C. The coating may be used when the surface material of the electronic component 206 and / or of the electrically conductive track 204A, 204B and 204C is not compatible with the material electro-deposited during the electrolysis which will be described later in the electrolysis step 112. Such an incompatible material is, for example, aluminum.

[0047] The metal coating is generally thin. It has, for example, a thickness of at most 1 μm. The type of deposition is generally called “re-metallization” or “flash metallization”.

[0048] Such a “re-metallization” or “flash metallization” can be carried out to make the material compatible with the material of the electrical conductors 402, 404. Indeed, for the electronic components 206 and / or the electrically conductive tracks 204A, 204B and 204C made of aluminum, aluminum oxide is formed natively on the surface, which prevents the adhesion of the electro-deposited material during electrolysis. By carrying out a flash metallization, with gold for example, the aluminum oxide on the surface is eliminated. Thus, the electro-deposited material is capable of being fixed on the electronic components 206 and / or the electrically conductive tracks 204A, 204B and 204C. If the electronic components 206 and / or the electrical conductive tracks 204A, 204B and 204C comprise a native metallization of gold or copper, it is not necessary to carry out a “re-metallization” or “flash metallization”. The removal step 108 is optional.

[0049] The deposition step 108 may be carried out prior to the contacting step 106, in order to facilitate implementation of the ball bonding technology, and / or prior to the assembly step 104, in order to facilitate metallization on the substrate 202 and / or on the electronic component 206 before assembly.

[0050] The method for producing an electrical connection 100 may also comprise a masking step 110 during which a masking of the area where the deposition of electro-deposited material is not desired may be carried out. The masking step 110 thus makes it possible to limit unwanted short circuits. The masking is, for example, carried out by depositing a polymer on the areas in question. In the absence of specific masking needs, the masking step 110 may be optional.

[0051] The method for producing an electrical connection 100 also comprises an electrolysis step 112 during which an electrically conductive layer 702 is deposited by electrolysis. The deposition of the electrically conductive layer is carried out on all the unmasked areas and can be carried out by bringing the unmasked areas subjected to an electrical potential into contact with an electrolysis bath. Advantageously, the deposition of the electrically conductive layer is carried out around each electrical conductor 402, as well as, preferably, at the feet of each of them, on the electronic component 206 and / or on one or more of the electrically conductive tracks 204A, 204B and 204C. The electrolysis step 112 can be, for example, broken down into several sub-steps 112A to 112C.

[0052] The electrolysis step 112 may comprise a polarization step 112A during which, as illustrated in [Fig. 5], at least one of the electrically conductive tracks 204A, 204B and 204C is polarized.

[0053] In addition, the electrolysis step 112 may comprise an immersion step 112B during which, as illustrated in [Fig. 6], the assembly consisting of the substrate 202 with the electronic component 206 mounted thereon and the electrical conductors 402 is immersed in a polarized electrolytic bath.

[0054] Finally, the electrolysis step 112 may comprise a deposition step 112C during which the deposition is carried out, in particular by migration of ions towards the polarized electrical conductors 402.

[0055] The result thus obtained is illustrated in Figures 7 and 8. An electrically conductive layer 702, according to the example described, extends not only around each electrical conductor 402 but also on at least one of the electrically conductive tracks 204A, 204B and 204C, more particularly the electrically conductive track 204A as shown in [Fig. 8], and on the power electrode of the upper face of the electronic component 206. Preferably, the electrically conductive layer 702 has a thickness of at least 10 μm.

[0056] Thus, each electrical conductor 402 surrounded by the conductive layer 702 forms an electrical connection 802 between the electronic component 206 and the electrical conductive track 204A. The electrical connection 802 has a large cross-section allowing use in power electronics, without the production of the electrical connection 802 imposing / generating significant stress on the electronic component 206.

[0057] Preferably, as is the case in the example described, the electrically conductive layers 702 deposited respectively around the electrical conductors 402 join together so as to form an electrically conductive ribbon or an electrically conductive wire of large diameter, of at least 10 pm, in particular at least 35 pm, in particular at least 50 qm.

[0058] Thus, the method of producing an electrical connection 100 makes it possible to obtain an electronic module, in particular a power module, comprising: • at least one electronic component 206; • at least one electrically conductive part 204A; and • an 802 electrical connection; the electrical connection 802 comprising an electrical conductor 402 surrounded by an electrically conductive layer 702 deposited by electrolysis.

[0059] In particular, this electrically conductive layer 702 has a crystallographic structure generally specific to the electrolytic deposition process used and different from that of the electrical conductor 402, making it possible to distinguish it from an electrical connection obtained by a traditional technology, in particular by ultrasonic wedge wirebonding technology.

[0060] It clearly appears that the method for producing an electrical connection 100 such as that described previously makes it possible to produce an electrical connection between at least one electronic component 206 and at least one electrically conductive part 204A in a manner that places little strain on the electronic component 206.

[0061] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the description which has just been made, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

[0062] Obviously, it will also be noted that the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms and other variants that may be envisaged by those skilled in the art within the scope of the invention and in particular all combinations of the different operating modes described above, which may be taken separately or in association, in the light of the teaching which has just been disclosed to him.

Claims

Claims

1. Method for producing an electrical connection (100) in an electrical module of an aircraft, between at least one electronic component (206) of this electrical module and at least one electrically conductive part (204A, 204B, 204C) of this electrical module, characterized in that it comprises at least: - A contacting step (106) during which at least one electrical conductor (402, 404) is brought into contact with, on the one hand, the electronic component (206) and, on the other hand, the electrically conductive part (204A, 204B, 204C); and - An electrolysis step (112) during which an electrically conductive layer (702) is deposited by electrolysis around the electrical conductor (402, 404).and in that it further comprises, before the contacting step (106), a deposition step (108) during which a coating, in particular a coating compatible with electrolysis, is deposited on the electrically conductive part (204A, 204B, 204C) and / or the electronic component (206), the coating having a thickness of at most 1 μm.

2. Method for producing an electrical connection (100) according to claim 1, characterized in that the electrically conductive layer (702) has a thickness of at least 10 pm, in particular at least 35 pm, in particular at least 50 pm.

3. Method for producing an electrical connection (100) according to claim 1 or 2, characterized in that the electrical conductor (402, 404) is a wire having a diameter of less than 250 pm, preferably between 10 pm and 50 pm.

4. Method for producing an electrical connection (100) according to claim 3, characterized in that the electrically conductive layer (702) has a thickness equal to at least the diameter of the electrical conductor (402, 404).

5. A method of making an electrical connection (100) according to any one of the preceding claims, characterized in that the electrical conductor (402) is made of a material having a ductility of at least 3, advantageously at least 5, in particular 10.

6. Method for producing an electrical connection (100) according to any one of the preceding claims, characterized in that the electrically conductive part (204A, 204B, 204C) is made of aluminum, copper, gold, silver or nickel.

7. Aircraft comprising an electronic module characterized in that it comprises at least: - an electronic component (206); - an electrically conductive part (204A); - an electrical connection (802) between the electronic component (206) and the electrically conductive part (204A) comprising: • an electrical conductor (402) in contact with, on the one hand, the electronic component (206) and, on the other hand, the electrically conductive part (204A), and • an electrically conductive layer (702) deposited by electrolysis around the electrical conductor (402); and - a coating, in particular a coating compatible with electrolysis, deposited on the electrically conductive part (204A, 204B, 204C) and / or the electronic component (206), but not on the electrical connection (802), the coating having a thickness of at most 1 μm.

8. Aircraft comprising a voltage converter characterized in that it comprises an electronic module characterized in that it comprises at least: - an electronic component (206); - an electrically conductive part (204A); and - an electrical connection (802) between the electronic component (206) and the electrically conductive part (204A) comprising: • an electrical conductor (402) in contact with, on the one hand, the electronic component (206) and, on the other hand, the electrically conductive part (204A), and • an electrically conductive layer (702) deposited by electrolysis around the electrical conductor (402) a coating, in particular a coating compatible with electrolysis, deposited on the electrically conductive part (204A, 204B, 204C) and / or the electronic component (206), but not on the electrical connection (802), the coating having a thickness of at most 1 μm.

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