Patent Application
20230420334
The instant disclosure relates to a power semiconductor module arrangement and to a method for forming the same, in particular to a power semiconductor module arrangement comprising a thermal interface material.
Power semiconductor modules usually include at least one substrate. The substrate may be arranged on a base plate. A semiconductor arrangement including a plurality of semiconductor components (e.g., two diodes, MOSFETs, JFETs, HEMTs, IGBTs, or any other suitable controllable semiconductor elements in a parallel, half-bridge, or any other configuration) is usually arranged on at least one of the at least one substrates. Each substrate usually comprises a substrate layer (e.g., a ceramic layer), a first metallization layer deposited on a first side of the substrate layer and a second metallization layer deposited on a second side of the substrate layer. The controllable semiconductor components are mounted, for example, on the first metallization layer. The first metallization layer may be a structured layer while the second metallization layer is usually a continuous layer. The second metallization layer may be attached to a base plate.
Heat that is generated by the controllable semiconductor components is dissipated through the substrate and further through an (optional) base plate to a heat sink. A heat-conducting layer is usually arranged between the substrate and the heat sink (in base plate-less modules) or between a base plate and the heat sink (in modules comprising a base plate) to effectively conduct the heat away from the substrate. The heat-conducting layer is required to have adequate heat conducting properties (e.g., high thermal conductivity). At the same time, the heat-conducting layer is required to permanently mount the power semiconductor module to the heat sink (e.g., to form a firm substance-to-substance bond between the power semiconductor module and the heat sink).
There is a need for an improved power semiconductor module which provides for an improved thermal conductivity between the power semiconductor module and a heat sink, and for a method for forming the same.
A power semiconductor module arrangement includes a power semiconductor module, wherein the power semiconductor module includes a substrate, and a heat-conducting layer arranged on a lower surface of the power semiconductor module, wherein the lower surface of the power semiconductor module is a surface that is configured to be mounted to a heat sink, wherein the heat-conducting layer consists of a metallic foam and an eutectic material filling the cavities within the metallic foam.
A method for producing a power semiconductor module arrangement includes forming a heat-conducting layer on a lower surface of a power semiconductor module, wherein the power semiconductor module includes a substrate, the lower surface of the power semiconductor module is a surface that is configured to be mounted to a heat sink, and the heat-conducting layer consists of a metallic foam and an eutectic material filling the cavities within the metallic foam.
The invention may be better understood with reference to the following drawings and the description. The components in the figures are not necessarily to scale, emphasis is instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.
In the following detailed description, reference is made to the accompanying drawings. The drawings show specific examples in which the invention may be practiced. It is to be understood that the features and principles described with respect to the various examples may be combined with each other, unless specifically noted otherwise. In the description as well as in the claims, designations of certain elements as “first element”, “second element”, “third element” etc. are not to be understood as enumerative. Instead, such designations serve solely to address different “elements”. That is, e.g., the existence of a “third element” does not require the existence of a “first element” and a “second element”. A semiconductor body as described herein may be made from (doped) semiconductor material and may be a semiconductor chip or be included in a semiconductor chip. A semiconductor body has electrically connecting pads and includes at least one semiconductor element with electrodes.
Each of the first and second metallization layers 111, 112 may consist of or include one of the following materials: copper; a copper alloy; aluminum; an aluminum alloy; any other metal or alloy that remains solid during the operation of the power semiconductor module arrangement. Optionally, the first and/or second metallization layer 111, 112 may be covered by a thin layer of nickel or silver, for example. Such a layer may be formed using a nickel plating process or a silver plating process, for example. The substrate 10 may be a ceramic substrate, that is, a substrate in which the dielectric insulation layer 110 is a ceramic, e.g., a thin ceramic layer. The ceramic may consist of or include one of the following materials: aluminum oxide; aluminum nitride; zirconium oxide; silicon nitride; boron nitride; or any other dielectric ceramic. For example, the dielectric insulation layer 110 may consist of or include one of the following materials: Al2O3, AlN, or Si3N4. For instance, the substrate 10 may, e.g., be a Direct Copper Bonding (DCB) substrate, a Direct Aluminum Bonding (DAB) substrate, or an Active Metal Brazing (AMB) substrate.
Usually one or more semiconductor bodies 20 are arranged on a substrate 10. Each of the semiconductor bodies 20 arranged on a substrate 10 may include a diode, an IGBT (Insulated-Gate Bipolar Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), a JFET (Junction Field-Effect Transistor), a HEMT (High-Electron-Mobility Transistor), or any other suitable controllable semiconductor element. One or more semiconductor bodies 20 may form a semiconductor arrangement on the substrate 10. In
In the example illustrated in
The second metallization layer 112 of the semiconductor substrate 10 in
In the example illustrated in
According to an even further example which is not specifically illustrated, the power semiconductor module 100 comprises a housing, the housing comprising sidewalls, a lid and a bottom or ground plate. One or more substrates 10 may be arranged in the housing. Optionally, the one or more substrates 10 may be arranged on a base plate 32, the base plate 32 also being arranged inside the housing. The lower surface of the power semiconductor module 100 in this case may be provided by the ground plate of the housing. The lower surface of the power semiconductor module 100 may be provided by any other suitable component of the power semiconductor module 100.
An additional heat-conducting layer 42 consisting of the same material as the heat-conducting layer 40 may be arranged between the substrate 10 and the base plate 32, for example. This additional heat-conducting layer 42, however, is optional. The substrate 10 may be mounted to the base plate 32 by means of any other suitable kind of connection layer (e.g., by means of a conventional solder or sinter layer).
The base plate 32 may comprise a metal, for example. According to one example, the base plate comprises at least one of Al and Cu. According to another example, the base plate 32 may be a metal matrix composite (MMC) base plate comprising an MMC material such as AlSiC. Any other suitable materials are possible. The base plate 32, optionally, may also be covered by a thin layer of nickel or silver, for example Such a layer may be formed using a nickel plating process or a silver plating process, for example.
The heat-conducting layer 40 comprises a metal foam 402 and a eutectic material 404. A metal foam is a cellular structure consisting of a solid material with gas filled pores, the gas filled pores constituting a large portion of the volume (e.g., at least 70%, at least 80%, or even at least 90%). The pores may be interconnected for example (open-cell foam). According to one example, only 5-25% of the overall volume of the metal foam 402 is formed by the base metal. That is, the base metal of the metallic foam 402 forms a framework or capillary, open fibre-structure that may be filled by a second material. Exemplary metallic foams are schematically illustrated in
According to one example, the metallic foam 402 is formed first. Methods for forming metallic foams are generally known and will not be described in further detail herein. When the eutectic material 404 is in its liquid state, the metallic foam 402 may easily soak it in and contain the eutectic material 404 such that the eutectic material 404 fills the cavities or pores within the metallic foam 402, resulting in the heat-conducting layer 40. This is exemplarily illustrated in
The metallic foam 402 may consist of or may comprise aluminum, copper, steel, nickel, silver, gold, platinum, or palladium, for example. The eutectic material 404 may comprise at least one of indium, bismuth, tin, zinc, germanium, silver, antimony, or gallium, for example. According to one example, the eutectic material 404 consists of indium, bismuth and tin. For example, the eutectic material 404 may comprise 51 weight % of indium, 32.5 weight % of bismuth, and 16.5 weight % of tin. A material with this specific composition is viscous in a temperature range that corresponds to a typical temperature range (e.g., 70° C.-100° C.) during operation of the power semiconductor module 100. Other examples of suitable eutectic materials 404 for operating temperature ranges between 60° C. and 175° C. include pure indium, or an indium-tin alloy with 52 weight % of indium and 48 weight % of tin.
If even higher temperatures occur during operation of the power semiconductor module 100 (e.g., temperatures of 200° C. or even more), other compositions may be more suitable such as, e.g., a tin-zinc alloy with 13 weight % of tin and 87 weight % of zinc, a tin-zinc-bismuth-germanium alloy with 83.5 to 84 weight % of tin, 12.5 to 13 weight % of zinc, 2.5 to 3 weight % of bismuth and less than 1 weight % of germanium, a tin-bismuth-antimony-silver alloy with 59 weight % of tin, 38 weight % of bismuth, 0.7 weight % of antimony, and 2 weight % of silver, a tin-bismuth alloy with 42 weight % of tin and 58 weight % of bismuth, a tin-silver alloy with 96.5 weight % of tin and 3.5 weight % of silver, a tin-silver, antimony alloy with 65 weight % of tin, 25 weight % of silver and 10 weight % of antimony, or an indium-tin-antimony alloy with 17 weight % of indium, 66 weight % of tin and 17 weight % of antimony. Similar weight % ratios as those mentioned above are generally also possible. Other eutectic materials 404 which become liquid at temperatures typically occurring in power semiconductor modules 100 are also possible.
According to one example, the eutectic material 404 comprises or consists of:
The metallic foam 402 may be completely soaked with the eutectic material 404. That is, the eutectic material 404 may fill at least 95% of the cavities and hollow spaces within the metallic foam 402.
A heat-conducting layer 40 comprising a metallic foam 402 filled with a eutectic material 404 is a very flexible layer that provides good gap-filling properties at temperatures occurring during the operation of the power semiconductor module 100. In particular, the metallic components comprised in the eutectic material bond to the metallic surfaces (e.g., copper or nickel surfaces) of the power semiconductor module 100 and the heat sink 30, but do not form any alloys with the neighboring metallic surfaces. The eutectic material 404, when in its fluid state, fills any roughness or unevenness of the neighboring metallic surfaces (e.g., lower surface of power semiconductor module 100 or heat sink 30). That is, a thermal contact between the heat-conducting layer 40 and its neighboring components is excellent during operation of the power semiconductor module 100. The metallic foam 402 prevents the eutectic material from losing its shape when in its fluid state. That is, a pump-out of the eutectic material 404 does not occur even at higher temperatures. The main heat-conducting capability of the heat-conducting layer 40 is provided by the eutectic material 404, while the metallic foam's 402 main function is to contain the eutectic material 404 and prevent the eutectic material 404 from pumping out. The metal comprised in the metallic foam, therefore, may have a melting temperature that is significantly higher than the melting temperature of the eutectic material 404 and that is also significantly higher than the typical operating temperatures such that the metallic foam keeps its form during operation of the power semiconductor module 100. The heat-conducting layer 40 as described herein reduces or even dissolves any thermal bottlenecks of conventional power semiconductor modules 100.
The eutectic material 404 of the heat-conducting layer 40 being solid at temperatures below the threshold temperature (below the typical operating temperatures) allows to easily handle the power semiconductor module 100 with the heat-conducting layer 40 attached thereto, e.g., during shipping.
The heat-conducting layer 40 may be formed on or attached to the lower surface of the power semiconductor module 100 by means of different alternative processes.
According to one example, the power semiconductor module 100 may be completely assembled before the heat-conducting layer 40 is formed thereon/attached thereto. That is, all steps that are performed during the assembly of the power semiconductor module 100 which may require applying heat to the power semiconductor module 100 may be performed while the heat-conducting layer 40 has not yet been formed thereon/attached thereto. As has been described above, the power semiconductor module 100 may be a power semiconductor module 100 comprising a base plate 32, or may be a base plate-less power semiconductor module 100.
According to one example, the heat-conducting layer 40 may be produced separately as a foil or plate. Such a foil or plate may be easily handled at temperatures below the first threshold temperature (e.g., at room temperature). According to one example, a layer of eutectic material 404 may be formed and a metallic foam 402 may then be pressed on the layer of eutectic material 404. The layer of eutectic material 404 may be heated such that it becomes liquid and the metallic foam 402 may easily penetrate into the layer of eutectic material 404. The resulting heat-conducting layer 40 may subsequently be cooled down again such that the eutectic material 404 becomes solid again and the heat-conducting layer 40 may be easily handled. The pre-produced foil or plate may then be applied to the lower surface of the power semiconductor module 100. For example, the foil or plate may be tacked, hot rolled, or laminated on the lower surface of the power semiconductor module 100. According to one example, temperature may be applied to the heat-conducting layer 40 during the process of attaching it to the lower surface of the power semiconductor module 100. For example, the temperature applied may just be high enough for the eutectic material 404 contained in the heat-conducting layer 40 to become slightly liquid. When the temperature is reduced again, the eutectic material 404 becomes solid again and permanently attaches to the lower surface of the power semiconductor module 100. Optionally, a certain amount of pressure may also be applied when attaching the heat-conducting layer 40 (i.e., the pre-produced foil or plate) to the lower surface of the power semiconductor module 100.
Optionally, the heat-conducting layer 40 may be protected by a protecting foil 44 after applying the heat-conducting layer 40 to/forming the heat-conducting layer on the power semiconductor module 100. In this way, the heat-conducting layer 40 is well protected during shipping of the power semiconductor module 100 and before mounting the power semiconductor module 100 to a heat sink 30. A protective foil 44 may protect the heat-conducting layer 40 from any kind of environmental influences such as, e.g., dust, foreign particles, or oxygen. A heat-conducting layer 40 that is protected by a protective foil 44 is schematically illustrated in
If a protective foil 44 is applied to the heat-conducting layer 40, this protective foil 44 may be removed again before mounting the power semiconductor module 100 to a heat sink 30. The power semiconductor module 100 may be mounted to the heat sink 30 with the heat-conducting layer 40 arranged between the power semiconductor module 100 and the heat sink 30. The power semiconductor module 100 may be pressed onto the heat sink 30. According to one example, heat may be applied during the step of mounting the power semiconductor module 100 to the heat sink 30. In this way, the heat-conducting layer 40, i.e. the eutectic material 404 comprised in the heat-conducting layer 40, may become viscous. When the arrangement is subsequently cooled down again, the heat-conducting layer 40 attaches the power semiconductor module 40 to the heat sink 30. The step of mounting the power semiconductor module to the heat sink 30 is exemplarily illustrated in
During subsequent operation of the power semiconductor module 100, heat may be generated (e.g., by the semiconductor bodies 20) which is conducted away through the heat-conducting layer 40 to the heat sink 30. The heat-conducting layer 40 is heated to temperatures of above the threshold temperature. The eutectic material 404, therefore, becomes liquid during operation of the power semiconductor module 100. In the liquid state of the eutectic material 404, the heat-conducting layer 40 still forms a firm substance-to-substance bond between the power semiconductor module 100 and the heat sink 30. The material of the heat-conducting layer 40, i.e. the eutectic material 404, does not leak out from under the power semiconductor module 100 due to the metallic foam 402 preventing the leak-out and the heat-conducting layer 40 remains essentially in its desired shape.
According to another example, it is also possible to form the heat-conducting layer 40 directly on the lower surface of the power semiconductor module 100, e.g., by applying the eutectic material 404 by means of a pattern-dispensing process or by means of stencil printing. Other suitable processes can also be used to form a layer of the eutectic material 404. This is schematically illustrated in
The lower surface of the power semiconductor module 100 may be prepared before applying the heat-conducting layer 40/the eutectic material 404. The surface of the heat sink 30 to which the power semiconductor module 100 is mounted may be prepared in a similar way. In particular, every surface that comes into direct contact with the heat-conducting layer 40 may be prepared correspondingly. A main aspect of surface preparation may be to ensure the wettability of the concerned surfaces. A thin oxide layer may form on a metal surface when it comes into contact with oxygen. For a sufficient wettability of a metal surface, for example, such an oxide layer may be removed before forming the heat-conducting layer 40 thereon. The oxide layer may be removed by means of a plasma reduction process, for example. Alternatively, it is also possible, for example, to plate the respective surface with a thin layer of a noble metal, or to use a preform (e.g., a pre-produced foil or plate) that is coated with a flux layer. This flux layer may comprise or consist of a reducing agent, for example, which activates the respective metallic surface when it comes into contact with the metallic surface. “Activating” in this context means that an oxide layer that has formed on the surface is reduced to pure metal. According to another example, the respective surface may be plated with a diffusion layer consisting of Ni (nickel), Ni—Ti (nickel-titanium), or any other suitable metal.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
The expression “and/or” should be interpreted to include all possible conjunctive and disjunctive combinations, unless expressly noted otherwise. For example, the expression “A and/or B” should be interpreted to mean only A, only B, or both A and B. The expression “at least one of” should be interpreted in the same manner as “and/or”, unless expressly noted otherwise. For example, the expression “at least one of A and B” should be interpreted to mean only A, only B, or both A and B.
It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22181245.6 | Jun 2022 | EP | regional |
