The invention lies in the field of power circuit technology and relates to a power semiconductor arrangement comprising, for example, a heat sink or a heat-dissipating substrate for mounting, making contact with and cooling electrical devices, in particular power semiconductor devices.
DE 199 42 915 A1 discloses a substrate, also referred to as DCB (Direct Copper Bonding), comprising a ceramic carrier material metalized (e.g. coated with copper) on both sides, which carries a plurality of devices (Power Semiconductor Modules) on the one top side, the so-called layout or placement side. The devices are electrically connected to conductor track structures formed in the top-side metalization.
The metalized underside of the substrate is in physical contact with a cooling element in order to be able to dissipate heat loss occurring during operation of the devices. Said heat loss could otherwise lead to damage to devices or components or shorten the service life thereof.
It is necessary in this case to electrically insulate the devices from one another and/or from conductive components (e.g. a cooling element) provided on the underside. Particularly in the case of discrete power components, such as e.g. power transistors in TO 220 packages, there is often no electrical insulation with respect to the heat dissipation contact area of the package. In principle, it is conceivable in these cases to use films or mica laminae for insulation. However, these have to be handled and positioned individually during mounting, resulting in complicated mounting. Moreover, this electrical insulation also leads to an undesired thermal insulation.
Besides good thermal coupling to the cooling element with sufficient electrical insulation, a high mechanical strength of the substrate is also desired. There are mutually conflicting requirements in this respect: on the one hand, a small substrate thickness (carrier material thickness) is desirable for a good thermal conductivity. On the other hand, a high mechanical stability (breaking strength) is desired, which decreases, however, in the case of ceramic substrate materials with reduced layer thickness of the brittle substrate material.
The use of much less brittle and therefore breaking-insensitive plastic as carrier material metalized on both sides for the substrate using so-called IMS technology is conceivable as an alternative. The fields of application are limited owing to the considerably poorer thermal stability of plastics. Moreover, the way in which plastics are applied requires higher layer thicknesses. Since plastic has a much poorer thermal conductance in comparison with ceramics, however, a larger layer thickness leads to a significantly poorer heat dissipation with the problems outlined in the introduction.
Furthermore, there is also the problem of electrically interconnecting the components and also electrically connecting them externally. These connections are usually performed at the side of the component opposite to the heat sink, by means of so-called bonding technology. For this purpose, connecting wires are fixed by means of ultrasound to the components to be connected. Besides the increased susceptibility to faults during production and in operation, what are highly disadvantageous are primarily also the large structural height, current constrictions and the practically impossible cooling of the top side of the components on account of the connecting wires situated there.
According to an embodiment, a power semiconductor arrangement may comprise a heat-dissipating basic body having at least one exterior side formed in planar fashion, the basic body comprising metallic material or being provided with a layer made of metallic material and, at its one exterior side, an electrically insulating oxide layer being at least partly formed on the metallic material. Furthermore, at least one power semiconductor device is provided which is arranged on said one exterior side of the basic body in such a way that it is electrically insulated from the basic body by the oxide layer. An electrically insulating film is at least partly laminated onto said one exterior side across said one power semiconductor device, the film having cutouts for making contact with the power semiconductor device in the region of said one power semiconductor device. Finally, an upper metalization is applied to the film and, in the cutouts thereof, also to the power semiconductor device in large-area fashion or in patterned fashion.
The invention is explained in more detail below on the basis of the exemplary embodiments illustrated in the figures of the drawing, in which:
According to different embodiments, a heat dissipating insulation layer that may serve as a substrate or heat sink, for example, is provided, with a basic body that comprises metallic material or is provided with a layer made of metallic material, at least one electrical device being intended to be arranged on the top side thereof, and with an electrically insulating oxide layer that is formed on the basic body over the whole area or partly in the form of oxide layer islands and insulates at least one active or passive device (transistor, IGBT, resistor, busbar, conductor track, etc.), the oxide layer being formed by oxidation of the metallic material.
A first aspect consists in the fact that the electrical insulation of the device is realized by means of an oxide layer that is produced from the basic body material or from a suitable oxidizable coating of the basic body. The oxide layer can be produced directly on the basic body. A thermal conductivity which, in terms of its quality, entirely corresponds to the DCB technology mentioned in the introduction is thus ensured.
A further aspect consists in the fact that very small insulation layer thicknesses can be realized without mechanical stability problems arising. This is because the mechanical strength and stiffness are advantageously ensured independently of the insulation layer thickness by the basic body, which can be dimensioned depending on the mechanical loading to be expected.
A further aspect brings about the reduction of the structural volume, the improvement of the thermal impedance of electrical components and connecting conductors and also the reduction of the static and dynamic electrical losses by the utilization of planar metalization levels at the top side of the components, which are applied in particular by means of metal spraying technology.
In the case of this solution path, the construction inductances and also the connecting resistances can again be reduced and the electrical losses occurring in the module can thus be reduced. A low-resistance and low-inductance construction technology is highly advantageous precisely in the automotive sector, given the high currents. Since the static power losses are involved quadratically with the current, the low-resistance electrical connection is crucial in the case of low-voltage applications.
The structural volume is likewise reduced by the small layer thickness. By means of suitable materials, heat dissipation on both sides can furthermore be realized since the surface is now approximately planar and the distances between the metalization surface and the second heat-dissipating structure (for example heat sink) can thus be kept small, with the result that the component's heat dissipation is improved.
The achievement, therefore, is to produce the electrical connections between the electrical components and to the terminal elements in the next higher system level by means of a suitable metalization layer (for example by means of metal spraying technology or laminating technology) in order to enable an improved heat dissipation, to obtain a lower power loss of the module and also to realize a smaller structural volume. Furthermore, with the utilization of electrical insulation films, the area to be oxidized is decreased and this reduces the process outlay during the oxidation method.
With regard to the different thermal expansion properties of oxide layer and metallic starting material, it may be advantageous, particularly in the case of large-area heat-dissipating insulation layers, if the oxide layer covers only one region or—as it were in insular fashion—a plurality of regions of the heat-dissipating insulation layer or the metallic layer, to be precise at the locations at which devices or assemblies are intended to be mounted in an electrically insulated manner.
The thickness of the insulating oxide layer can advantageously be controlled by the process parameters during the oxidation operation (e.g. in the case of the anodizing method known per se by the choice of voltage, current intensity, temperature and/or oxidation duration) and be optimally adapted to the respective electrical insulation requirements. Further known oxidation methods are plasma electrolytical oxidation (PEO) or Micro Arc Oxidation (MAO). This advantageously opens up the possibility of local optimization of the insulation layer thickness depending on the voltage to be insulated (potential difference). In other words: the oxide layer can be formed with different thicknesses depending on the voltage to be insulated from the device.
In order to further optimize the properties of, in particular, relatively large insulation layer thicknesses, one embodiment provides for further material for increasing the electrical insulation properties and/or the mechanical strength and/or the thermal conductivity additionally to be applied to and/or introduced into the oxide layer. Materials of this type are also known by the term “filler”.
Thus, by way of example, epoxy material may be provided as an additional insulation layer. For increasing the thermal conductivity, material having a good thermal conductivity—e.g. ceramic material or carbon—may be introduced into the epoxy material.
An embodiment provides for a top-side metalization for mounting and making contact with the device to be provided on the oxide layer.
Said metalization may be produced by various methods. It may be applied e.g. galvanically, chemically, by sputtering or by hot dipping. A high-temperature-resistant substrate is thus produced.
The metalization—both before and after it has been applied—may be patterned by, e.g. photolithographic, methods known per se in order to form in said metalization conductor tracks which serve for making contact with and/or interconnecting the devices mounted on the heat-dissipating insulation layer. The devices can be soldered, welded, adhesively bonded or clamped onto the conductor tracks for this purpose.
An embodiment provides for an initialization layer to be applied to the oxide layer, the metalization being produced on said initialization layer by growth (e.g. by electrodeposition).
One preferred variant for producing the metalization on the oxide layer provides for the metalization to be laminated onto the oxide layer. In this case, it is possible to provide a thin plastic layer which is preferably admixed with “fillers” for improving the thermal conductivity. The plastic layer serving as an adhesion promoter may be very thin, so that it does not impair the thermal conductivity of the substrate; it additionally also has the positive side effect of additional electrical insulation.
It is also possible for the metalization or conductor tracks to be adhesively bonded on, screwed on or else soldered on or welded on as individual elements if a corresponding metalization is present.
It is possible to produce a multilayer substrate by multilayered application of metalizations.
An embodiment that is cost-effective and advantageous in terms of production engineering provides for the basic body preferably to comprise aluminum or aluminum alloy (e.g. silicon-aluminum, aluminum-silicon) or titanium, tantalum or magnesium and the oxide layer to be a substrate metal oxide layer. However, it is also possible to apply to a basic body made of a different material—e.g. made of copper—an oxidizable layer—e.g. an aluminum layer—which at least partly (layer by layer) serves as insulation layer after its (anodic) oxidation (e.g. to form Al2O3).
A further embodiment provides for the basic body to be a cooling element. The cooling element may be formed e.g. as an air cooler or as a liquid cooler. The basic body, in a dual function, thus performs both a mechanically stabilizing function and a heat-dissipating function, there advantageously being no additional thermal interface between heat-dissipating insulation layer and cooling element.
As already discussed, oxide layer and metallic starting material have different thermal expansion properties. The latter may lead to mechanical stresses which, in the worst case, cause cracking in the oxide layer. Against this background, one embodiment provides for the oxide layer or the oxide layer islands to have a rounded edge profile.
The mechanical stresses may preferably also be reduced (further) by virtue of the oxide layer or the oxide layer islands having a layer thickness that decreases toward the edges thereof.
As an alternative or in addition, the oxide layer or the oxide layer islands, for mechanically decoupling from the basic body, may preferably be surrounded by a peripheral trench. The trench may advantageously have rounded corner regions.
In a preferred manner in terms of production engineering, the trench may be produced by embossing and subsequent heat treatment of the basic body or the layer made of metallic material, by casting—e.g. by aluminum die-casting—, by erosion, milling or by deep-drawing of the basic body material, in which case the planes of trench and/or island may lie at the same level as the surface of the basic body or alternatively above or below that.
The cooling element, which comprises metal for the purpose of good thermal conduction, is electrically insulated from the device or the metalization for technical circuitry reasons. An electrical insulator 9 is provided for this purpose.
As shown in
The layer thickness d is dimensioned according to the voltages that are operationally to be expected and are to be reliably insulated and can be adapted or formed as required by correspondingly setting the process parameters (e.g. oxidation current, temperature, etc.). It is thus possible to realize an oxide layer thickness which overall is only very small but is sufficiently voltage-resistant and which impairs the thermal conductivity only to an insignificant extent.
The oxide layer 12b may contain “fillers” 15, which further improve the thermal and/or electrical conductivity of the insulation layer 14. By virtue of the solid basic body 10, the substrate can be subjected to high mechanical loading and is mechanically durable. In this case, too, the basic body may preferably be formed as a cooling element.
The substrate is thus optimized with regard to a minimum insulation layer thickness and at the same time ensures a very good thermal coupling of the electronic devices applied on the metalization to a cooling element in conjunction with very high mechanical stability.
In addition, as shown in
Afterward (as shown in step B on the basis of the enlarged detail I), the substrate is dipped into an electrolyte bath. In the process, in the region of the cutouts 56 of the film 51, the desired oxide islands 57 are produced on the metallic material of the substrate 53 (step B). The masking, i.e. the film 51, is then removed or stripped away again (step C) to leave the substrate top side provided with oxide islands.
In this respect,
The invention thus provides a substrate which, by known means and tried and tested technologies, has only the oxide layer thickness which is required according to the electrical dimensions and which hardly impairs the thermal conductivity and the very thin formation of which nevertheless does not cause mechanical instabilities.
In the case of the power semiconductor module according to an embodiment in accordance with
An insulating film 84 is laminated on over this arrangement comprising heat sink 80, oxide layer 81, conductor tracks 82 and also MOS transistor 83. The film 84 has cutouts at specific locations of the conductor track 82 and of the MOS transistor 83. In this case, the film may comprise for example a specific plastic material such as, for instance, polyamide, polyethylene, polyphenol, polyether ketone and/or epoxide. In this case, the cutouts can be introduced into the film as early as prior to the lamination, or else preferably after the lamination by opening the laminated-on film at the corresponding locations. A metalization 85 is then applied to the film 84 and also, in the cutouts, to the conductor track 82 and the MOS transistor 83. In this case, the film 84 simultaneously serves as masking for the metalization 85 and may alternatively also be embodied as a hard material mask or resist mask, in particular photoresist mask. A metal spraying technology is preferably used for producing the metalization 85. Afterward (not illustrated in the drawing for the sake of simplicity) an insulating film, a photoresist or the like may in turn be applied and serve as a mask and also electrical insulation for further metalizations. The use of metal spraying technologies is distinctly advantageous compared with customary galvanic metalizations, for example, with regard to the outlay in respect of time, materials and apparatus. What is more, thicker layers (greater than 1 mm) can be produced thereby. Application of a metalization in conjunction with insulating films being laminated on achieves, in a simple manner, an electrical contact-connection at the top side of the components and conductor tracks which is distinguished by a small structural height, a low susceptibility to faults and by extended possibilities for use.
The result is a low-resistance and low-inductance connecting structure of the electrical components both at the top side and at the underside. The contact areas can be larger by a multiple in relation to the typical bonding wire connections. Moreover, the structural volume is considerably reduced since bonding wire geometries no longer stand out from the carrier material.
The coupling piece 89 is coupled to the metalization 85 and the metalization 88 by pressing on (soldering, welding, adhesive bonding etc. also possible), the pressing-on pressure being obtained by means of a pressing-on apparatus—only parts of which are shown in
What is achieved, then, by the use of the heat spreader 86 is that the electrical component (the MOS transistor 83 in the exemplary embodiment) is cooled and electrically contact-connected on both sides. This means that the thermal resistance of the component is considerably reduced and the performance of the power semiconductor module is significantly increased. What is more, it is also possible to realize more extensive electrical interconnections in the heat spreader level. In this case, the further electrical insulation layer (oxide layer 87) situated at this level enables the electrical insulation between the conductor tracks of the metalization 88 and the heat spreader body. In order to mechanically couple the two levels, the arrangement is held—as shown—by means of a spring, heat spreader 86 and heat sink 80 being positioned and fixed.
Number | Date | Country | Kind |
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DE102004 018475.5 | Apr 2004 | DE | national |
This application is a continuation of co-pending International Application No. PCT/EP2005/003617 filed Apr. 6, 2005, which designates the United States, and claims priority to German application number DE 10 2004 018 475.5 filed Apr. 16, 2004.
Number | Date | Country | |
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Parent | PCT/EP05/03617 | Apr 2005 | US |
Child | 11549765 | Oct 2006 | US |