WO2016156022A1

WO2016156022A1 - Apparatus comprising a power module attached through an isolation layer to an electric machine and corresponding manufacturing method

Info

Publication number: WO2016156022A1
Application number: PCT/EP2016/055420
Authority: WO
Inventors: Aylin BICAKCI; Frank Osterwald; Jacek Rudzki; Ronald Eisele; Tino FILIPIAK-RESSEL; Holger Ulrich; Klaus Olesen; Rüdiger BREDTMANN; Ole MÜHLFELD
Original assignee: Danfoss Silicon Power GmbH
Current assignee: Danfoss Silicon Power GmbH
Priority date: 2015-03-30
Filing date: 2016-03-14
Publication date: 2016-10-06
Anticipated expiration: 2017-09-30
Also published as: DE102015104880A1

Abstract

An apparatus comprises a power module (1) and an electric machine (e.g. a multiphase motor of a vehicle), wherein the power module (1) comprises a plurality of components (4) attached to a circuit layer (5) and wherein the power module (1) and the electric machine (e.g. its end bearing plate (2)) are physically connected by an isolation layer (7), the isolation layer (7) electrically insulating the power module (1) and the circuit layer (5) from the electric machine. The power module (1) is thus an integral part of the electric machine. The circuit layer (5) may be a lead frame. The plurality of components (4) may be attached to the circuit layer (5) by sintering or soldering. The isolation layer (7) may be an epoxy resin filled with thermally conductive fillers. An encapsulation layer may be provided, by filling a resin (12) within additional resin walls (dam) (11). A multi-terminal socket (15) with a plurality of terminals (13) mounted in a plastic holder (14) may be provided, configured perpendicular to the circuit layer (5).

Description

APPARATUS COMPRISING A POWER MODULE ATTACHED THROUGH AN ISOLATION LAYER TO AN ELECTRIC MACHINE AND CORRESPONDING MANUFACTURING METHOD

FIELD OF THE INVENTION

The present invention relates to power modules. In particular, the invention relates to the integration of a power module into an electrical machine.

BACKGROUND OF THE INVENTION

Electric drives, as are required, for example, for the operation of an electric power-steering system in motor vehicles, are often equipped with integrated power output stages and control devices. The power output stage may comprise a power module positioned in the vicinity of a three- phase motor in a separate housing . The control unit, the power module and the motor are often connected to one another by means of cable runs or metal rails. This solution has the disadvantage of an increased level of expenditure for housing parts, cabling and shielding requirements. This results in considerable requirements for installation space and also in additional weight and high production costs on the system level . The present invention seeks to address at least some of the problems outlined above.

SUM MARY OF THE INVENTION

The present invention provides an apparatus (such as a motor drive system) comprising a power module and an electric machine, wherein the power module comprises a plurality of components attached to a circuit layer and wherein the power module and the electric machine are physically connected by a lamination comprising the electric machine, an isolation layer and the circuit layer. Here by the term electric machine is meant an electric machine such as a motor or generator, typically a 3- phase motor or generator. The lamination comprises part of this machine, and this part may conveniently be part of the structure of the machine, such as an endplate (bearing plate) on which is mounted a bearing for the axle of the machine, or a casing of the machine used to shield the machine from the environment or, for example, to reduce the electrical or audible noise emitted by the machine. It is a great advantage to utilise a part of the machine in this manner, since it enables the power module to be positioned close to the machine controlled by it. The use of the machine to mount the power module on allows the power module to be an integral part of the electric machine. By lamination is meant a uniform and material (integral) connection between relatively thin layers of different materials. Such a connection is a permanent one, and not designed for easy disassembly of its components. This provides a highly reliable connection. Thin refers to the dimension of the layer normal to the plane of connection between the layers. The isolation layer typically electrically insulates the power module and the circuit layer from the electric machine.

The circuit layer may be a lead frame. The plurality of components may include a plurality of semiconductors. The plurality of components (e.g. including semiconductors) may be attached to the circuit layer by sintering (soldering is an alternative). In one embodiment, semiconductors (and/or other components) are sintered to a lead frame, with the lead frame being connected to the isolation layer and with the lead frame and isolation layer being laminated with the surface of a motor (or some other electric machine) that is driven by the power module.

The isolation layer may be an epoxy resin filled with thermally conductive fillers. In this way, the isolation layer can be electrically insulating, but with the thermally conductive fillers provide a degree of thermal conductivity. Heat and/or pressure are typically applied to the epoxy resin during the lamination process. Alternatively or additionally, any thermosetting plastic may be suitable as an isolation layer.

The circuit layer may be a copper layer. The copper may be "stamped" to provide the circuit design (e.g. lead frame). Alternatives are possible (such as etching or cutting the copper layer) .

The apparatus may further comprise an encapsulation layer applied to the circuit layer and the plurality of components. The encapsulation layer may be formed by applying a resin within defined boundaries. The boundaries may be defined by additional resin walls (e.g. providing a so- called "dam and fill" encapsulation). Alternatives exist, such as providing a cheap plastic frame to define the boundaries or by using the electric machine itself to define the boundaries (e.g . by building up part of the electric machine, or by etching or machining a recess into the electric machine) .

The components may include one or more terminals configured perpendicular to the circuit layer. In an encapsulated system, the terminals may extend beyond the encapsulation and allow for connections to be made to the encapsulated circuit. A plurality of terminals may be provided. The terminals may be arranged as an array of terminals forming a multiterminal socket. The present invention also provides a method of generating an integral power module comprising a power module and an electric machine (such as a motor), wherein the power module comprises a plurality of components (such as semiconductors) attached to a circuit layer, the method comprising laminating the electric machine (e.g . the casing or the bearing plate of the electric machine), an isolation layer (such as an epoxy resin filled with thermally conductive fillers) and the circuit layer. In this way, the power module can become an integral part of the electric machine. The process of lamination comprises the forming of a uniform and material (integral) connection between relatively thin layers of different materials. Such a lamination process may enable the adhesive properties of an organic insulating material forming the isolation layer, and thus provide the material connection between the layers to be joined. The process may involve the application of specific pressures and temperatures for specific times. The exact pressures, temperatures and times depend upon the materials involved. The use of quasi-hydrostatic pressure may ensure a uniform connection .

Attaching the plurality of components to the circuit layer may include sintering at least one of said plurality of components to the circuit layer.

The method may further comprise applying an encapsulation layer to the circuit layer and the plurality of components. The encapsulation layer may, for example, be formed by applying a resin within defined boundaries. The boundaries may be defined by additional resin walls (e.g. providing a so-called "dam and fill" encapsulation) . Alternatives exist, such as providing a cheap plastic frame to define the boundaries or by using the electric machine itself to define the boundaries (e.g . by building up part of the electric machine, or by etching or machining a recess into the electric machine) .

The method may further comprise providing one or more terminals configured perpendicular to the circuit layer. In an encapsulated system, the terminals may extend beyond the encapsulation and allow for connections to be made to the encapsulated circuit. A plurality of terminals may be provided (for example to provide a multiterminal socket).

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in further detail with reference to the following schematic drawings, in which :

Figure 1 is a plan view of an embodiment of the present invention ; Figure 2 is a cross-section of an embodiment of the present invention ;

Figure 3 shows a detail of a further embodiment of a power module and electric machine in accordance with an aspect of the present invention ;

Figure 4 is a cross-section of a further feature of the present invention ; and

Figure 5 shows a flow diagram for exemplary embodiments of the method of the current invention . DETAILED DESCRIPTION OF THE INVENTION

Figure 1 is a plan view of an embodiment of the present invention, and in figure 2 a cross-section of the same embodiment is shown . Illustrated here is a section of a motor drive system comprising a power module 1 and an electric machine, here a multiphase motor. Only the end bearing plate 2 of the motor is shown in figure 1. This end plate 2 is part of the casing of the electric machine and is preferably of rugged construction . In this case the end plate 2 is made of cast aluminium with a thickness and form capable of withstanding the forces required for the motor assembly. Other materials and constructions are also suitable for the construction of an end bearing plate, such as the drawn aluminium or aluminium alloy, or metal castings. This end bearing plate 2 supports the end bearing of the motor axle, and for this purpose a recess 3 is created in the centre of the plate 2. When in use, a bearing will be fitted into this recess. In other embodiments the axle may pass through the bearing plate and a hole will be created for that purpose. Integrated into this bearing plate 2 is a power module comprising a plurality of components 4 mounted on a circuit layer 5. The components may include power switching transistors, or other semiconductors. The circuit layer 5 comprises conductor paths which enable current and control signals to pass from power terminals and/or signal terminals 6. The circuit layer 5 forms part of a multilayer lamination 18, that is uniform and material (integral) connection between relatively thin layers of different materials. Such a connection is a permanent one, and not designed for easy disassembly of its components. This provides a highly reliable connection . Thin refers to the dimension of the layer normal to the plane of connection between the layers. The multilayer lamination 18 comprises the circuit layer 5, an isolation layer 7 and the bearing plate 2. The isolation layer 7 has good thermal conducting properties and is thus able to efficiently conduct heat away from the heat generating components 4 and into the bearing plate 2.

The circuit layer 5 is formed from a flat plate or film of metal such as copper into which a pattern of conductor paths has been introduced by etching . Alternative methods of forming such a pattern of conductor paths are known in the art and include stamping . Alternatively the circuit layer 5 can be formed as a lead frame structure, also known in the art.

In traditional constructions, such a power switching unit may comprise one or more encased power modules which are individually bolted to a cooled base plate with a thermal interface material (TIM), such as a heat conducting paste or glue, between the module on the base plate. This construction suffers from the disadvantage that the greasy paste is difficult to handle, and can suffer from being "pumped out" in a system with thermal cycling under use. The use of a multilayer lamination 18 including an isolation layer 7 ensures a material connection directly between the circuit layer 5 and the bearing plate 2. Such a connection is permanent, solid and highly reliable. The disadvantages of the use of a TIM paste are therefore avoided .

The isolation layer 7 comprises a planar film with very low electrical conductivity but high thermal conductivity. A suitable material for the isolation layer is an epoxy resin filled with thermally conductive fillers.

In the embodiment shown in figures 1 and 2, the components 4 that form the power switching circuit are attached to the circuit layer 5 by the use of a sintering method . Such a method comprises the application of sintering paste to one or both of the component 4 and/or the circuit layer 5 before positioning the component 4 and applying pressure and/or heat to complete the sintering . This yields an extremely reliable and electrically conducting attachment between the components 4 and the circuit layer 5. Sintered connections are capable of withstanding the high service temperatures that are found in some applications, in particular the use of such circuits within vehicles.

An alternative to the use of sintering is soldering . However, if high service temperatures are expected, then such solders may need to have high lead content. The environmental disadvantages of the use of such lead containing materials make them ecologically disadvantageous. Sintering materials do not contain lead, and therefore help to meet modern environmental standards.

Figure 3 shows a detail of the encapsulation feature of a further embodiment of a power module and electric machine in accordance with an aspect of the present invention . It is often necessary to further protect a circuit formed of components 4 from the environment in which the circuit is used . Such an environment may yield dust, moisture, solvent or corrosion problems from which the circuit should be protected . In figure 3 is shown part of the casing 8 of the electric machine which the power module forms an integral part of. The laminated structure comprising the casing 8, the isolation layer 7 and the circuit layer 5 are similar to that shown in figures 1 and 2. One component 4 is shown, and this is attached to the circuit layer 5 using a sintering process. The sintered layer 9 is shown between the component 4 and the circuit layer 5. Also shown is a wire or ribbon bond 10 making an electrical connection between the top connector of the component 4 and the circuit layer 5.

The component 4 is encapsulated by the use of a two-stage process, sometimes known as "dam and fill". In this process, a wall 11 of a significant vertical extent is laid around the outer circumference of the area for encapsulation . This is achieved by dispensing an epoxy resin which is sufficiently viscous in its uncured state to enable the creation of a "wall" structure. The wall structure 11 defines a boundary, and after the completion of the wall structure 11, a second epoxy resin is dispensed within this boundary to fill the reservoir created and to create an encapsulation layer 12 which covers the components 4 that require protection . The viscosity of this second epoxy resin is designed to be low enough so that the resin will fill any cavities including spaces underneath bond wires 10. After curing, the encapsulation layer 12 forms a solid encapsulation of the components 4. In an alternative embodiment, the wall structure 11 may be created by a low-cost plastic form which is placed around the components 4 before the dispensing of the second epoxy resin or a silicone potting gel .

In further alternative embodiments, the wall structure 11 may be formed by protrusions of the casing 8, or by placing the circuitry within a depression cast, machined or stamped within the casing 8. "Dam and fill" encapsulations are particularly suitable for components within a vehicle, since power supply voltages available (around 12V - 48V) limit the maximum voltages found within vehicle power modules. The requirements (in terms of insulation for example) that an encapsulation material has to fulfil are therefore lower than for power modules working from mains voltages, and these are easily met by the encapsulation materials typically used in "dam and fill" applications.

Figure 4 is a cross-section of a further feature of the present invention . In figure 4 is shown part of the casing 8 of the electric machine which the power module forms an integral part of. The laminated structure comprising the casing 8, the isolation layer 7 and the circuit layer 5 are similar to that shown in figures 1 and 2. One component 4 is shown, and this is attached to the circuit layer 5 using a sintering process. The sintered layer 9 is shown between the component 4 and the circuit layer 5. Also shown in this figure is a terminal 13 for making electrical contact with external apparatus. Such electrical contact could be used for signalling purposes (the input or output of control signals and/or timing, housekeeping or other necessary signals for controlling the power module or for passing information from the power module to external apparatus) or for the conduction of power in or out of the power module. In a similar way to the component 4, the terminal 13 is sintered to the circuit layer 5. A sintered layer 9 is shown between the terminal 13 and the circuit layer 5. In alternative embodiments of the means of attachment could be used (such as soldering), however, as stated above, sintering has the advantage of forming a reliable, heat-resistant attachment without the use of high-lead-content solder.

One feature of the terminal 13 in this embodiment is its large vertical extent which extends well above the other components mounted on the circuit layer 5. This carries the terminal connection region clear of other components, facilitating easy access for making connections to it. In an alternative embodiment, where an encapsulation layer 12 is utilised, such a terminal 13 with a large vertical extent brings the connection region of the terminal well above the surface of the encapsulation layer 12. In this way connections to the terminal 13 may be made without any particular modifications to the encapsulation layer 12 to accommodate them .

The terminal 13 is shown in figure 4 mounted within a plastic holder 14. This plastic holder 14 holds a plurality of terminals 13 arranged as an array of terminals, thus forming a multi-terminal socket 15. Two such multiterminal sockets 15 are illustrated in figure 1. The use of such as socket is of a great advantage, since it simplifies the electrical connection of other apparatus to the power module. A simple plug may be used, instead of wiring, bolting or soldering of connections. Another feature of the terminal 13 is that it can be optimally placed on the circuit layer 5. This placement can ta ke account of the need to reduce the inherent inductance of the circuit, bringing about improvements in the electrical characteristics of the power module. In traditional power modules it is often the case that terminals are placed around the edge of the module, and this restriction can often lead to longer circuit connecting elements and hence to larger inductance.

Figure 5 shows a flow diagram for exemplary embodiments of the method of the current invention, illustrating also an alternative step.

In a first step of the method 16, a circuit layer 5 and an isolation layer 7 are laminated together with the casing 8 of the electric machine. The circuit layer 5 is formed from a conducting material preferably a metal . Alternatively the circuit layer 5 can be formed as a lead frame structure. The isolation layer 7 comprises a planar film with very low electrical conductivity but high thermal conductivity. The process of forming the laminated structure 18 out of these individual materials the application of specific pressures and temperatures for specific times. The exact pressures, temperatures and times depend upon the materials involved . The use of quasi-hydrostatic pressure ensures a uniform connection. In an optional second step of the method 17, at least one of the plurality of electrical components 4 are attached to the circuit layer 5 by a process of sintering .

The embodiments of the invention described above are provided by way of example only. The skilled person will be aware of many modifications, changes and substitutions that could be made without departing from the scope of the present invention. The claims of the present invention are intended to cover all such modifications, changes and substitutions as fall within the spirit and scope of the invention.

Claims

CLAIMS :

1. An apparatus comprising a power module and an electric machine, wherein the power module comprises a plurality of components attached to a circuit layer and wherein the power module and the electric machine are physically connected by a lamination comprising the electric machine, an isolation layer and the circuit layer.

2. An apparatus as claimed in claim 1, wherein the isolation layer electrically insulates the power module and the circuit layer from the electric machine.

3. An apparatus as claimed in claim 1 or claim 2, wherein the circuit layer is a lead frame.

4. An apparatus as claimed in any preceding claim, wherein the plurality of components are attached to the circuit layer by sintering.

5. An apparatus as claimed in any preceding claim, wherein the isolation layer is an epoxy resin filled with thermally conductive fillers.

6. An apparatus as claimed in any preceding claim, wherein the circuit layer is a copper layer.

7. An apparatus as claimed in any preceding claim, further comprising an encapsulation layer applied to the circuit layer and the plurality of components.

8. An apparatus as claimed in claim 7, wherein the encapsulation layer is formed by applying a resin within defined boundaries.

9. An apparatus as claimed in claim 8, wherein the boundaries are defined by additional resin walls.

10. An apparatus as claimed in any preceding claim, wherein the components include one or more terminals configured perpendicular to the circuit layer.

11. An apparatus as claimed in claim 10, wherein the terminals are arranged as an array of terminals forming a multiterminal socket.

12. A method of generating an integral power module comprising a power module and an electric machine, wherein the power module comprises a plurality of components attached to a circuit layer, the method comprising laminating the electric machine, an isolation layer and the circuit layer.

13. A method as claimed in claim 12, wherein attaching the plurality of components to the circuit layer includes sintering at least one of said plurality of components to the circuit layer.

14. A method as claimed in claim 12 or claim 13, further comprising applying an encapsulation layer to the circuit layer and the plurality of components.

15. A method as claimed in any one of claims 12 to 14, further comprising providing one or more terminals configured perpendicular to the circuit layer.