Process for interconnection of electronic power modules of a rotary electrical machine, and assembly of interconnected power modules obtained by means of this process

A method for interconnecting electronic power modules of a polyphase rotary electric machine. The power modules are disposed in open cavities of a heat sink and comprise substrates on which are provided MOSFETs of a synchronous rectifier bridge and integrated control circuits. The method comprises the production of: a planar connector (6) including at least one layer of conductive traces (64); a plurality of interconnection elements (512) arranged in multiple geometric formations and ultrasonically welded or brazed (S2) directly to the substrates (51) and/or the MOSFETs; and openings (65) in the planar connector (6) allowing the free passage of the upper ends (5120) of the connection elements (512) and a mechanical contact with the conductive traces (64). The electrical connections are obtained by means of laser (8) transmission welding (S1) or electric resistance welding.

This application is a national stage application of International Application No. PCT/FR2011/052673 filed Nov. 17, 2011, which claims priority to French Patent Application No. 10/59632 filed Nov. 23, 2010, of which the disclosures are incorporated herein by reference and to which priority is claimed.

The present invention relates in general to the field of rotary electrical machines, in particular for motor vehicles.

More particularly, it applies to alternators with synchronous rectification equipped with electronic power modules, and even more particularly to polyphase alternators.

For the sake of clarity of the concepts, reference will be made hereinafter to the preferred application of the invention, and it will be assumed that the alternator is of the three-phase type, without this limiting in any way the scope of the invention.

By way of example the French patent FR2886477B1 entitled “Interconnection part for a signal for a rotary electrical machine” describes a rotary electrical machine of the alternator-starter type, comprising electronic power means. These electronic power means are in the form of modules of the so-called mechatronic type, including a power transistor bridge which uses MOSFET technology, and ensure a reversible function of an analogue-direct power converter (“AC/DC” according to the terminology commonly used).

In the mode of functioning as an alternator of the rotary electrical machine, the aforementioned converter ensures the rectification of the alternating phase voltages produced by the alternator into a single direct supply voltage (typically of 14 Volts) which supplies an on-board supply network of the motor vehicle. Conversely, as is well known to persons skilled in the art, in the mode of functioning as a motor/starter of the rotary electrical machine, the converter provides phase voltages which supply stator windings of the rotary electrical machine. This therefore gives rise to rotation of the rotor of the rotary electrical machine which has sufficient mechanical torque, such as to ensure the starting of the thermal engine of the vehicle. The phase voltages are obtained by cutting off, by means of the power transistor bridge, the direct voltage of the on-board supply network (direct voltage supplied by an energy storage battery).

The electronic power means described in the aforementioned French patent FR2886477B1 comprise three identical modules, one per branch of the bridge, and a control module which incorporates a specialised integrated circuit known by the acronym “ASIC” (for “Application—Specific Integrated Circuit” according to the terminology commonly used). The branch modules of the bridge each form a branch of the transistor bridge.

The architecture of the branch module of the bridge according to this patent is described for example with reference toFIGS. 4A to 4Eof the aforementioned French patent FR2886477B1. MOSFET transistors in the form of bare electronic chips are soldered onto connection gates known as “leadframes” in the terminology commonly used, which are over-moulded in a mechatronic case. These leadframes are kept placed on a metal base plate by means of an electrically insulating small plate which is sandwiched between the leadframes and the base plate. The small plate has properties of good thermal conduction, such as to transmit the calories generated by the electronic chips to a heat sink which is placed below the metal base plate of the module.

The technology which is disclosed by French patent FR2886477B1 has various applications in rotary electrical machines, and in particular gives very good results in terms of quality and performance in applications of the alternator-starter type which require a reversible rectifier bridge.

However, as previously stated, it is necessary to place the electronic chips in a so-called mechatronic technology case.

These arrangements increase the complexity, in particular that of the interconnection structure which is the main subject of this patent, as well as the number of mechanical parts used, and consequently in particular they increase the cost price.

Whilst maintaining the advantages of the devices according to the known art, in particular those described in French patent FR-2886477B1, the object of the invention is to eliminate the disadvantages of the latter, some of which have just been described.

Whilst proposing an architecture of interconnected electronic power modules for an optimised polyphase rotary electrical machine, the subject of the invention is a process for production of a structure for interconnection of these power modules to one another on the one hand, and also of these power modules to other electrical components of the said rotary electrical machine.

For this purpose, according to an important characteristic of the said architecture, the power modules are implemented directly in a heat sink, which in particular eliminates the need to encapsulate them in a case of the so-called mechatronic type, and this will make it possible to simplify the elements of the inter-module interconnection structure.

According to a particular embodiment, the power modules each comprise the electronic power circuits of two branches of a synchronous rectifier bridge, and control circuits of the electronic power circuits.

Preferably, the power circuits are produced on the basis of a MOSFET transistor. The control circuits are preferably produced using so-called “ASIC” technology (acronym for the expression commonly used “Application-Specific Integrated Circuits”). The power modules comprise the actual electronic power circuits and the control circuits present in the form of substrates using so-called “DBC” technology (acronym for the expression commonly used “Direct Bonded Copper”) which has many advantages, in particular good thermal conductivity. The substrate is constituted by three layers comprising a lower layer made of copper, a median insulating layer made of ceramic (alumina, beryllium oxide, etc.), and an upper layer made of conductive material, generally copper. This layer is subdivided into a plurality of conductive tracks, the electronic components of the power module being soldered on these tracks. This technology is well known to persons skilled in the art, and does not need to be described in greater detail hereinafter.

According to another characteristic of the architecture of power models implemented in the present invention, the heat sink comprises cavities open in one of its surfaces which are each designed to receive one of the said power modules. The power modules are bonded directly on the base of the cavities in the sink. Preferably, after assembly, these cavities are filled with gels such as to cover and insulate the power modules.

According to an important characteristic of the process for implementation of the interconnection structure according to the invention, the interconnections between the terminals of the phase windings of the rotary machine, the terminals of the source of direct electrical energy of the vehicle (generally a positive terminal known as B+ and B− or ground) and the power terminals of the branches of the rectifier bridge and for the signal of the control circuits, are produced firstly by means of first interconnection means comprising a plate made of insulating material, for example plastic, comprising a plurality of conductive tracks, which for example are made of copper, and, secondly, a plurality of input-output elements for connection with the electronic circuits of the aforementioned substrates. The first interconnection means will be known hereinafter as flat connectors, for the purpose of simplification of the description.

According to yet another important characteristic of the process according to the invention, the said connection elements are produced simply on the basis of filamentary components made of conductive material, of the type such as tongues, nails, studs or pins, and can have various mechanical and geometric configurations which will be described hereinafter.

According to yet another important characteristic of the process according to the invention, the said connection elements are soldered or welded by ultrasound directly onto the substrates and/or onto the electronic power components of the said power modules, such as to be contained on planes at right angles to the aforementioned substrate planes which are arranged in the cavities in the heat sink.

According to yet another important characteristic of the process according to the invention, the electrical connections between firstly the input-output elements for connection of the electronic circuits, and secondly conductive tracks of the flat connector, are obtained by a step of welding of the electrical type by resistance, or of the laser type by transparency. According to yet another characteristic of the process according to the invention, the first subassembly constituted by the power modules and the heat sink and the flat connector are secured mechanically to one another after carrying out the steps of electrical connections by soldering or welding by ultrasound of the connection elements, firstly onto the substrates and/or the power components, and secondly onto conductive tracks of the flat connector.

The main object of the invention is thus a process for interconnection of at least two electronic power modules of a polyphase rotary electrical machine to one another, and of the said power modules to specific components of the said polyphase rotary electrical machine, the said power modules comprising a substrate comprising a layer constituted by a first plurality of conductive tracks on which there are implemented semiconductor power components and integrated electronic control circuits of these components which are connected electrically by the said conductive tracks, characterised in that it comprises an initial phase comprising a step consisting of arranging the said substrates in open cavities on a so-called upper surface of a support unit, such as to be incorporated in a first plane of the space, a subsequent phase of production of the said interconnections comprising at least the following steps:a step of production of first interconnection means constituting a flat connector comprising at least one layer constituted by a second plurality of conductive tracks which is supported by at least one plate, known as the lower plate, made of insulating material, such as to form a network of electrical connections with a predetermined configuration;a step of production of a plurality of connection elements in each of the said power modules, constituted by filamentary components made of conductive material, with specific geometric forms, and of their electrical connections, by soldering or welding by ultrasound, at a first so-called lower end, on the said conductive tracks of the said substrates and/or on the said electronic power components, such that they are incorporated on planes substantially at right angles to the said first plane of the space;a step of production of recesses in at least one said lower plate of the said flat connector, the spatial distribution of the said recesses corresponding to the spatial distribution of the said connection elements;a step of placing the said flat connector above the said connection elements, on a plane parallel to the said first plane of the space, such that the second, so-called upper ends of the said connection elements can be put into contact with the said conductive tracks of the said connector through the said openings; andthe production of electrical connections between the said upper ends of the said connection elements and the said conductive tracks, by welding.

The object of the invention is also an assembly of interconnected power modules obtained by means of this process.

Hereinafter, without in any way limiting the scope of the invention, the context will be the preferred application of it, unless otherwise stated, i.e. the case of an alternator with synchronous rectification of the double three-phase type, comprising three power modules, each comprising the electronic power circuits of two branches of a rectifier bridge and control circuits for these electronic power circuits.

Also hereinafter, elements which are identical or at least similar in the figures bear the same references, and will be described again only if necessary.

Before describing the invention, it is advantageous to recall briefly the general structure of a machine of this type and an example of electronic power circuits of the rectifier bridge and of an electronic circuit for control of these circuits, with reference toFIGS. 1 and 2.

FIG. 1illustrates highly schematically, in longitudinal cross-section, an example of a structure of a rotary electrical machine Mt according to the known art, i.e. in this case a three-phase alternator with synchronous rectification. This alternator comprises in a conventional manner a stator S and a rotor R, as well as an electronic power module, which contains the actual electronic power circuits (rectifier bridge) and control circuits for these power circuits.

FIG. 2illustrates an example of a configuration of electrical and electronic circuits which can be implemented in the three-phase alternator Mt inFIG. 1.

As illustrated inFIG. 2, the alternator-starter Mt is associated with electronic power and control circuits with the general reference1. These circuits comprise a synchronous voltage rectifier bridge2and a voltage regulator3. The rotor R is rotated by a drive shaft which connects it to the crankshaft of the thermal engine5of the vehicle (not illustrated inFIG. 1)

In this embodiment, the alternator Mt is a three-phase machine of the Lundell type.

FIG. 2illustrates schematically an example of a voltage rectifier circuit2of the type with synchronous rectification. This comprises substantially a voltage rectifier bridge constituted by three branches B1to B3and control circuits3of the bridge2.

In the example described, each branch B1to B3of the bridge2comprises two power transistors in cascade of the MOSFET type, T1H-T1B, T2H-T2B, T3H-T3Brespectively. The signs H and B signify arbitrarily the top and bottom of the branch respectively. The top ends of the branches B1to B3are connected to the terminal B+ and the bottom ends are connected to the terminal B− (generally connected to the ground) of a direct electrical energy storage unit (battery of the vehicle, not illustrated inFIG. 2). In a conventional manner, anti-parallel diodes D1Hto D3Bare connected to the source and drain terminals of the MOSFET transistors T1Hto T3B.

The branches B1to B3are connected at their middle points to the three phase outputs φ1to φ3of the stator windings S.

The control circuits3supply to the gates of the MOSFET transistors T1Hto T3Bcontrol signals CG1Hto CG3Brespectively.

The control circuits2comprise circuits for forming the gate control signals (not explicitly illustrated inFIG. 2), which carry out forming adapted to the signals CG1Hto CG3Bsuch as to obtain functioning with synchronous rectification of the MOSFET transistors T1Hto T1Bof the bridge2. This type of functioning with synchronous rectification of the MOSFET transistors T1Hto T1Bis well known to persons skilled in the art, and need not be described in greater detail hereinafter.

The control circuits2also comprise regulation circuits (not explicitly illustrated inFIG. 2), such as to supply a direct voltage with predetermined precision between the terminals B+ and B−, conventionally of +12 V. This type of circuit is also well known to persons skilled in the art, and need not be described in greater detail hereinafter.

Also, these control circuits3supply an excitation current of the winding of the stator S.

Finally, the control circuits3can comprise circuits for detection of errors and/or of malfunctioning of the rectifier bridge2, in particular in order to protect the MOSFET transistors T1H-T1Bif an overload is detected.

In the known art, and in particular that described by patent FR2886477B1, the bridge2is in reality divided into three parts corresponding to the three bridge branches B1to B3. Each branch B1to B3is in the form of a substrate encapsulated in an independent so-called mechatronic case, and the control circuits are produced in the form of an “ASIC” integrated circuit, the assembly being completed by electrical interconnection and mechanical securing means. As stated in the preamble of the invention, this architecture has a certain number of disadvantages which need not be described here.

In the present invention, whilst retaining the general structure of a rotary machine according to the known art and the configuration of the electronic circuits as such, which represents a certain advantage, an architecture of optimised interconnected modules is adopted which no longer requires the modules to be packed in cases, and permits simplification of the connection means. For this purpose, partitioning and physical implementation of the circuits are provided which avoid the aforementioned disadvantages, and make it possible to achieve the objectives set out, as will now be shown in relation withFIGS. 3 to 6D.

FIG. 3illustrates in space and in exploded view around an axis of longitudinal symmetry A, the main subassemblies of an example of preferred architecture of power modules in which the process for interconnection according to the invention will be implemented.

The architecture illustrated in this figure relates to an alternator of the double three-phase type, and comprises three subassemblies which are specific to the invention, i.e. a heat sink4, a series of power modules5, with references51to53, and means6for electrical interconnection between the series of modules5. The power modules5of the series each comprise the electronic circuits of two rectifier bridge branches and the corresponding control circuits.

According to an important characteristic of the invention, the heat sink4is provided on its upper surface (inFIG. 3), which is substantially flat, with three open cavities41to43with a flat base which are designed to receive the modules51to53. The lower surface of the sink4is provided in a conventional manner with fins45or similar units which are designed to improve the heat exchanges with the ambient air.

The heat sink4is in the general form of a “horseshoe” (arc of a circle) such as to allow free passage of the air in its central part, for the purpose of cooling of the inner units of the rotary machine (windings, etc.), of which only the upper mechanical part7(rear bearing) is represented inFIG. 3. In a habitual manner, the ambient air is aspirated towards the interior of the rotary machine by a fan which rotates with the rotor (not represented inFIG. 3). The part7comprises a plurality of orifices (with no reference) surrounding a central orifice70which is designed to receive a bearing capsule, and lateral orifices71which allow the air to enter the interior of the rotary machine.

In a conventional manner, after final assembly, the three sub-assemblies4to6are secured mechanically to the mechanical part7by any appropriate means (screws, etc.), with the “horseshoe” covering the periphery partially.

Each module51to53comprises a substrate which contains the electronic power circuits themselves (the MOSFET transistors of two branches of the hexaphase rectifier bridge) and control circuits of this bridge.

According to another characteristic of this architecture, the control circuits are distributed in the three modules51to53, and are not centralised as for the example of the three-phase alternator inFIG. 2. They are in the form of integrated circuits which are preferably produced using “ASIC” technology.

Apart from these specific features, the functional diagrams of the power and control circuits implemented in the known art can be retained within the context of the invention, which represents an additional advantage as already indicated, since a new functional design of these circuits is not necessary.

The power and control circuits are arranged on a substrate, all preferably produced using “DBC” technology, and constituting the aforementioned power modules51to53. The substrates of the modules51to53will be described hereinafter with reference toFIG. 4. Connection elements (FIG. 3: under the general references512,522and532) which can have various configurations (and will be described in detail with reference toFIGS. 6A to 6D) are soldered or welded by ultrasound directly on the substrates of the modules51to53, according to one of the important characteristics of the process for interconnection of power modules according to the invention. They make it possible to establish electrical connections with the means6for interconnection between modules5. After the soldering or welding by ultrasound, the connection elements are incorporated on a plane which is substantially at right angles to the substrates.

The means6for interconnection are in the general form of a plate which constitutes a flat electrical connector. This plate comprises one or a plurality of flat layers made of insulating material, for example plastic of the PPS type. This plate supports a plurality of conductive trails or tracks, which for example are made of copper or any other appropriate metal, and can convey firstly so-called “strong” electric currents (connections with the terminals B+ and B− of the battery, the terminals of the branches of the rectifier bridge which are distributed in the modules51to53, and the terminals of the windings of the rotary machine), and secondly so-called “weak” currents (control signals). The conductive tracks can be over-moulded and sandwiched between layers of insulating material of the plate6.

Each aforementioned connection element, welded on the substrates of the modules51to53, is connected electrically to one or a plurality of conductive tracks, such as to form a network of interconnections with a predetermined configuration which connects the modules51to53to one another and a voltage regulator, which is also present in the alternator on the one hand, and these modules51to53on the other hand, to the rectified output voltage and phase terminals (terminal B+ and ground) of the alternator. For this purpose, the plate6which forms a connector has a geometry similar to that of the heat sink4(form of a “horseshoe”), such that the plate can be secured mechanically on the sink, after assembly of the modules51to53, in the cavities41to43.

The plate6additionally comprises areas under the general reference60which leave free access to the conductive tracks, the dimensions and spatial distribution of which are adapted to those of the connection elements512,522and532which are soldered on the substrates of the modules51to53.

The mechanical connection of the two subassemblies, i.e. the heat sink4and connector6, is carried out by any conventional means well known to persons skilled in the art (screwing, etc.). For the sake of clarity of the concepts,FIG. 3represents schematically means for securing with the general references44(heat sink4) and61(connector6). In addition, as already indicated, this assembly is also secured mechanically on the part7by any conventional means (not represented inFIG. 3).

FIG. 4illustrates schematically, seen from above in space, the mounting of the modules51to53in the cavities41to43of the sink4.

The modules51to53comprise substrates, only the upper layers of which have references,510to530. These substrates are preferably produced using “DBC” technology.FIG. 4also represents integrated circuits511to531which are supported by the substrates. In this embodiment of the invention, a single control circuit511,521or531is provided per module51to530. However, it should be understood that these modules can comprise a plurality of integrated circuits: in particular the bridge control circuits, which are preferably produced using “ASIC” technology, and the MOSFET transistors. Finally, connection elements are represented schematically. These connection elements are soldered directly on conductive tracks and/or on the integrated circuits of the modules51to53, and are designed to establish galvanic contacts with the conductive tracks of the connector6(FIG. 3).

The geometric configurations and the embodiments of these elements, which constitute one of the important characteristics of the invention, will be described hereinafter with reference toFIGS. 6A to 6D.

A single connection element has specifically been given a reference inFIG. 4, i.e. the connection element512of the module51, which is illustrated in greater detail inFIG. 4A.

The element512has the general form of a tongue made of conductive material bent back into a “Z”, with a flat lower surface which is in electrical contact with the substrate of the modules51to53, and a flat upper surface which is designed to be put into electrical contact with one of the tracks of the connector6(FIG. 3). This embodiment corresponds to that which will be described with reference toFIG. 6A.

FIG. 5illustrates another embodiment of connection elements, in the form of vertical cylindrical studs, of the semiconductor diode end type, or similar components (resistor, etc.).

InFIG. 5, only the central part of the heat sink4is shown, i.e. the part corresponding to the cavity42and the module52. With the exception of the embodiment of the connection element522′, the other elements inFIG. 5are identical to those inFIG. 4, and need not be described again. This embodiment of the connection element corresponds to that which will be explained more particularly with reference toFIG. 6B, but it can also be implemented for the elements corresponding to those which will be explained with reference toFIGS. 6C and 6D.

Irrespective of the embodiment of the connection elements selected, the modules51to53are secured in the cavities41to43by bonding on the base of these cavities, directly on the sink4, i.e. without intermediate elements, contrary to the known art described by French patent FR2886477B1. For the sake of clarity of the concepts, a glue of the silicon thermal type can be used for this purpose. After assembly of the modules51to53in the cavities41to43, the latter can be filled with a gel such as, for example, a two-component silicone gel, which makes it possible to insulate the semiconductor components electrically, and to provide mechanical protection.

For the sake of clarity of the concepts, and without this limiting in any way the scope of the invention, a description will now be provided, with reference toFIGS. 6A to 6D, of four main embodiments of connection elements, as well as of the corresponding processes for connection of these connection elements to the conductive tracks of the connector6(FIG. 3).

FIG. 6Aillustrates schematically a connection element512constituted by a flat tongue made of conductive material, which is bent in the manner of an accordion in order to assume the general form of a “Z”. This embodiment corresponds to that which is illustrated inFIG. 4.

FIG. 6Arepresents schematically the substrate of the module51, and it is assumed that it comprises a plate of insulating material511, sandwiched between an underlying plate of conductive material513and conductive tracks510which run on the upper surface. The configuration is identical for the other substrates52or53.

Each connection element512is welded (by means of the lower branch5121of the “Z”) on a conductive track510, or alternatively on a semiconductor element (MOSFET of the rectifier bridge not represented inFIG. 6A) by welding S2. The upper layer510is constituted by a plurality of tracks for interconnection between the input and/or output terminals of the components of the power module (51in the example inFIG. 6A) welded onto this layer.

FIG. 6Aalso represents a portion of the connector6overhanging the module51and the connection element512. It is assumed in the example described that the connector6comprises a single layer64of tracks of conductive material, sandwiched between two plates of insulating material, i.e. an upper62and a lower63plate. It will be appreciated that it must be understood that the invention is not limited to a single layer of conductive tracks. In fact, according to a variant embodiment not represented, it is possible to provide a plurality of superimposed layers of conductive tracks which are separated by plates of insulating material.

Recesses65are provided in the areas of the insulating plates62and63which overhang the upper branches5120of the connection elements512.

According to this embodiment, as a result of their form in the shape of a “Z” and the resilient properties of the material which constitutes the tongue, the connection elements512are provided with a “spring” function, which makes it possible to ensure good mechanical contact by exerting a support force when the connector6is put into place.

The tracks64of the connector6are welded on the connection element512(on the upper branch5120of the “Z”) by laser welding by transparency, i.e. through the conductive track64by welding S1. The laser8which makes possible this operation is illustrated schematically inFIG. 6A, as is the beam emitted f1which converges on the upper branch5120of the “Z”.

A laser weld has the advantage of requiring less energy than welding by resistance. There is therefore less risk of damaging the soldering on the substrates and the semiconductor components (MOSFETS).

For the sake of clarity of the concepts, the characteristics of the process for production of the electrical connections are typically as follows:ideally, the thickness of the track63to be passed through should not exceed 0.6 mm;the thickness of the track situated below (i.e. the upper branch5120of the “Z”) must be at least equal to the thickness of the track passed through64;the maximum play admissible between the tracks64and5120for a through weld is approximately 20% of the thickness passed through, i.e. 0.12 mm in the example selected;a pressure force on the connector6is necessary and must be calculated so as not to damage the substrate52and its components;in order to obtain a good laser weld by transparency, the track above64must be subjected to a mat surface treatment of the nickel plating type in order to limit the reflection of the laser beam (for example by using the nickel plating technology known as “Sulfamat”—registered trademark). On the other hand, tin and phosphorus are not acceptable because they are liable to create cracks in the weld.

FIG. 6Billustrates schematically a connection element522′ constituted by a cylindrical stud made of conductive material, perpendicular to the plane of the upper layer520of the substrate52(or of the other substrates51or53). The stud522′ comprises a base5220′ with a larger diameter soldered directly (by welding S2) on the upper layer520of the underlying substrate52(or alternatively on a power component i.e. MOSFET, not represented). The upper layer520is constituted by a plurality of tracks for interconnections between the input and/or output terminals of the components of the power module (52in the example inFIG. 6B) welded on this layer. This embodiment corresponds to that which is illustrated inFIG. 5.

According to this embodiment, and in the example described inFIG. 6B, the connector, which henceforth has the reference6′, is assumed to comprise, as in the example inFIG. 6A, a single layer of conductive tracks64′, sandwiched between two plates of insulating material62′ and63′. On the other hand, again in this embodiment, it is necessary for the conductive track64′, and not only the insulating plates62′ and63′, also to be provided with a receptacle65′ in order to allow free passage at the upper end of the connection element522′ through the stack of layers62′-64′-63′. One of the ends640′ of the conductive track64′ is extended into the recess area65′. It is bent back by 90° upwards. The latter comprises a dish6400′ which is designed to be put into contact with the connection element522′ in its upper part.

In this embodiment, the weld between the track64′ and the connection element is produced by a process of welding by resistance at the level of the dish6400′. This is a process well known to persons skilled in the art. It is commonly used, in particular in order to weld ends of semiconductor diodes or equivalent components.

For the sake of clarity of the concepts, according to this variant, the characteristics of the process for production of the electrical connections is typically as follows:the process of welding by resistance is well controlled, and does not pose a particular problem if the elements to be welded (studs522′ and track64′) have dimensions similar to those of the aforementioned semiconductor diodes;typically, the studs522′ have a diameter of 1.2 mm;as a variant, instead of being cylindrical, the studs522′ can be provided with a square or rectangular cross-section, if the bent-back tongue640′ of the track64′ comprises a dished pin;typical parameters of the welding are as follows: force of 35 DaN, electric current of approximately 8000 A with 2 V for a period of time of 20 to 30 ms. The electrodes must descend to a minimum of 1.5 mm below the boss6400′ of the track64′.

FIG. 6Cillustrates an additional variant embodiment of the connection elements, which henceforth have the reference512″.

As previously, the connection element512″ is constituted by a cylindrical stud made of conductive material, perpendicular to the plane of the upper layer510of the substrate51(or of the other substrates52or53). The base5121″ of the latter, which can be constituted by bending back at 90°, is soldered (weld S2) on the upper layer510of the underlying substrate51(or alternatively on a power component: MOSFET, not represented inFIG. 6C). It is assumed, as previously, that there is a single conductive track64″ sandwiched between two plates made of insulating material62″ and63″. Also as previously, this conductive track64″ is pierced by an orifice65″, and is extended into the recess area whilst allowing the end of the stud512″ to pass through. The upper part5120″ of the element of the stud512″ is bent back by 90°, such as to come into contact with the upper surface of the end of the conductive track64″.

As for the connection embodiment described with reference toFIG. 6A, the weld is of the laser weld by transparency type, and has the advantages previously described. It is therefore the bent-back part5120″ of the pin which the laser beam passes through (not explicitly represented inFIG. 6C) and which is welded on the conductive track64″ by welding S1.

For the sake of clarity of the concepts, the characteristics of the process for production of the electrical connections are typically as follows:the track which the laser beam must pass through, i.e. the bent-back part5120″ of the stud512″, can be finer, with a thickness which can be as little as 0.3 mm, which makes possible;a lower level of energy necessary for welding;a conductive track thickness64″ of 0 8 mm to 1 mm, in order for the current to pass through;no need to resort to nickel plating of the tracks64″ of the connector6″;the contact between the tracks64″ and studs512″ is ensured simply by the bending operation.

FIGS. 6Dillustrates an additional variant embodiment of the connection element, henceforth with the reference512′″. The latter is similar to the connection element512″ as far as its spatial configuration is concerned, but it has a rectangular or square cross-section, and is not bent in its upper part. Its base5121′″, which can be bent back to a horizontal position, is soldered (weld S2) on the upper layer510of the underlying substrate51(or alternatively on a power component: MOSFET, not represented).

As previously, it is assumed that the connector6′″ comprises only a single layer of conductive tracks64′″, sandwiched between two insulating plates62′″ and63′″. It is also firstly necessary to provide a total opening65′″ in the insulating plates62′″ and63′″, and in the conductive track64′″, such as to allow the upper end of the stud512′″ to pass through, and secondly a track end640′″ which is bent back by 90° upwards, and is put into contact with the upper end of the stud ′″.

The welding is also carried out according to the laser process by transparency, using a laser similar to that represented inFIG. 6A. The relative arrangement of the two elements makes it possible to carry out laser welding (weld S1) with raised edges on the respective ends of the conductive track64′″ and of the stud512′″.

For the sake of clarity of the concepts, the characteristics of the process for production of the electrical connections according to this variant are typically as follows:this solution requires tooling in order to place the conductive track64′″ against the stud512′″, since the maximum play in order to weld these elements correctly must not exceed 5% of the thicknesses of the elements in contact;the laser must be equipped with a vision adjustment system, or it must be mounted on the aforementioned placing tool, in order to ensure correct welding at the junction of the conductive track64′″ and the stud512′″;nickel plating is possible on one or the other of the surfaces of the elements to be welded, or on both, but is no longer necessary;for a track64′″ of the connector6with a thickness of 0.8 mm, the soldered connection element5121′″ must have a minimum thickness of 0.4 mm, and its thickness should preferably be identical to that of the conductive track64′″ at its end640′″.

Reading the preceding description easily shows that the invention achieves well the objectives set out by it, and which need not be recalled in full.

However, the process for interconnection of power modules according to the invention is not limited simply to the embodiments explicitly described with reference toFIGS. 3 to 6D. Similarly, the assembly of electronic power modules obtained by means of the interconnection process according to the invention does not apply only to an alternator with a bridge with synchronous rectification, which constitutes the preferred application of it, but more generally to any polyphase rotary electrical machine comprising at least two power modules to be interconnected via connection elements, one of the ends of which is soldered or welded by ultrasound on these modules, and the other end of which is welded on a conductive track of a connector comprising at least one layer of conductive tracks supported by at least one insulating plate.