WO2014063911A1

WO2014063911A1 - Cooing device for a semiconductor component

Info

Publication number: WO2014063911A1
Application number: PCT/EP2013/070713
Authority: WO
Inventors: Harald NÖBAUER; Stephan Schartner; Dietmar PACHINGER; Almedin BECIROVIC
Original assignee: F.+S. Vermögensverwaltungs Gmbh
Priority date: 2012-10-24
Filing date: 2013-10-04
Publication date: 2014-05-01
Also published as: AT513520A1

Abstract

Disclosed is a heat sink (2) for a directly mounted semiconductor component (7), which heat sink comprises at least one metallic base (3, 4) with a mounting surface (6) for said semiconductor component (7). Under the mounting face (6), a mixture (15) is arranged which is enclosed on all sides by the base (3) and is made of metal/graphite, metal/diamond or metal/graphite/diamond. Further disclosed is a laser module (1) which comprises a laser-light-emitting semiconductor component (7) that is arranged on the mounting surface (6) of said heat sink (2). Finally disclosed is an advantageous use of said laser module (26).

Description

Cooling device semiconductor device

The invention relates to a heat sink for a directly applied semiconductor device, comprising at least one metallic base body with a mounting surface for said semiconductor device. Furthermore, the invention relates to a laser module with a laser light emitting semiconductor device. Finally, the invention also relates to an advantageous use of said laser module.

A heat sink or a laser module of the above type are known in principle. For example, DE 101 13 943 B4 discloses a laser module with a heat sink, which has a hollow region, which is filled with graphite, under a mounting surface for a semiconductor component. About the heat sink, the semiconductor laser to be electrically contacted and cooled. In addition, the filled with graphite hollow body to prevent that on the mounting surface too high thermal expansions occur, which could destroy the semiconductor device.

Disadvantages of the known arrangement are the comparatively poor thermal conductivity, the relatively poor electrical conductivity, as well as the coefficient of thermal expansion of the graphite used, which is poorly matched to the thermal expansion coefficient of the semiconductor substrate.

Furthermore, WO200802113A1 discloses a heat sink made of copper / diamond, wherein an additional component for compensating for unevenness of the mounting surface is required. The disadvantage here is that the semiconductor device is not mounted directly on the heat sink but on the component.

Apart from this type of heat sinks, the heat sinks mentioned below for semiconductor components are known, or are widely used. The following list gives an overview of their advantages and disadvantages. When selecting or developing a cooler configuration, it is important to keep in mind the cornerstones of good machinability, thermal expansion adaptation, and minimization of thermal resistance.

(1) Direct soft solder mounting: The semiconductor device is applied by means of soft solder directly to a copper heat sink. The different expansion of the semiconductor component and the heat sink during the soldering process is on the one hand by the low reduced soldering temperature and on the other hand absorbed by the high ductility of the soft solder. Advantages are the low thermal resistance as well as the good machinability mounting surface. A disadvantage is the poorer long-term stability of soft solder assemblies.

(2) Submount-based brazing assembly: The semiconductor device is brazed to a heat-expansion-matched submount (CuW, CuMo), which in turn is soft soldered onto a copper heat sink. By means of the alloying ratio of the submount, while reducing the thermal conductivity, the coefficient of thermal expansion is adapted to that of the semiconductor device. The night part in terms of longevity is improved compared to the soft solder assembly, but at the expense of thermal resistance. Furthermore, the workability of the common submount alloy is reduced, resulting in higher values for flatness and roughness.

(3) Ceramic-based brazing assembly: The heat sink supports a ceramic layer (aluminum nitride, aluminum oxide) beneath a superficial copper layer, providing a surface thermal expansion comparable to that of the semiconductor device and allowing for braze mounting. Advantages are the longevity of the braze as well as the good machinability of the mounting surface. The disadvantage is the poorer heat conduction in the ceramic on the entire thermal resistance.

(4) Layer cooler - brazing assembly: The heat sink is constructed of layers of different metals (for example, Mo and Cu), so that superficially results in a thermal expansion adapted to the semiconductor device. Again, the top layer of copper, resulting in a good workability results. Again, by introducing a poorly heat-conducting layer smears with respect to the thermal resistance to be booked.

The object of the invention is therefore to provide an improved heat sink and an improved laser module. In particular, the thermal conductivity is to be optimized, and the thermal expansion coefficient at the mounting surface should better match the applied semiconductor Adapted component and a good workability of the mounting surface are made possible.

The object of the invention is achieved with a heat sink of the type mentioned above, by arranging under the mounting surface, a mixture which is enclosed on all sides by the main body and made of metal / graphite, metal / diamond or metal / graphite / diamond. It is advantageous in this case that the outer regions of the heat sink remain as an excellently workable metal.

Preferably, aluminum or copper is selected for the metal of the mixture. Likewise, aluminum or copper is also preferably chosen for the basic body.

If the mixture contains a proportion of diamond, the thermal conductivity with respect to graphite is markedly improved. Finally, by varying the proportions of the mixture, the thermal expansion coefficient at the mounting surface can be excellently adapted to the applied semiconductor device. This is also an exact adaptation of the coefficient of thermal expansion of various other semiconductor materials whose thermal expansion coefficient between those of graphite / diamond and a metal is possible.

The following table (Table 1) shows the thermal conductivity and coefficient of thermal expansion for graphite, diamond, gallium arsenide (GaAs), copper-tungsten (CuW) in a conventional alloy ratio Cu: Wo (85:15 wt%, aluminum nitride (AIN) , Copper (Cu) and aluminum (AI):

AIN 180 4,6 10 ^"6

Cu 151 16.5 10 ^"6

AI 211 23 10 ^"6

Tab. 1: Thermal conductivity values and thermal expansion coefficients of participating materials.

The above table makes it clear that the thermal conductivity is significantly improved by the specified mixture compared to the materials used in the prior art.

In this context, it is particularly advantageous if the resulting coefficient of thermal expansion of the mixture and the part of the basic body which lies between the mixture and the mounting surface corresponds essentially to the thermal expansion coefficient of the semiconductor component at the mounting surface. In this variant of the heat sink, the geometric properties of the base body and the mixture and their material properties are coordinated so that the thermal expansion at the mounting surface substantially corresponds to the thermal expansion of the semiconductor device mounted thereon. As a result, no dangerous mechanical stresses can arise in the semiconductor, which could destroy it or reduce its performance.

It is advantageous if the thickness of the base body between the mixture and the mounting surface has a thickness in the tenth-mm range, in particular 0.1-0.3 mm. This distance has proven to be particularly advantageous to meet the requirements of the heat sink with respect to power and heat dissipation, as well as setting a suitable for the semiconductor device thermal expansion coefficient.

It is also advantageous if the heat sink comprises a stepped projection, which is upstream of the mounting surface in the direction of the boundary of the heat sink. In particular, the projection offers in addition to an additional heat spreading diverse possibilities for the assembly of one or more optical elements. In addition, cooling channels can be provided, for example, with which the cooling effect of the heat sink is further improved by heat transport with a heat carrier conducted through the cooling channels. In general, the cooling effect of a heat sink can be improved if it has at least one cooling channel extending in its interior, which optionally can also run through the mixture. Thus, a guided in the cooling channel heat transfer medium can be brought very close to the heat source (= semiconductor device).

It is also advantageous if the mixture is connected on all sides cohesively to the base body. In this way, on the one hand thermal stresses between the body and the sintered body are well transferred and the body is inhibited in its expansion, on the other hand, an optimal heat transfer is possible and prevents any accumulation of heat in the mixture. Cohesive connections are all compounds in which the connection partners are held together by atomic or molecular forces. They are at the same time non-detachable connections, which can only be separated by destruction of the connecting means. In particular, soldering, welding, sintering and gluing are included.

The object of the invention is further achieved with a laser module in which a laser light emitting semiconductor device is arranged on the mounting surface of the heat sink according to the invention.

Although the heat sink may generally be used for semiconductor devices, use thereof to construct a laser module is particularly advantageous. It is furthermore particularly advantageous if such a laser module is used for material processing, for example for laser welding and laser cutting, since due to the power required for material processing the properties of the heat sink with respect to its electrical conductivity, its cooling effect and in terms of its thermal expansion particularly come into play.

For a better understanding of the invention, this will be explained in more detail with reference to the following figures.

Each shows in a highly schematically simplified representation: 1 shows an exemplary laser module in an oblique view. Fig. 2 shows the laser module of FIG. 1 in cross section and

Fig. 3 shows another exemplary laser module with a cooling channel in cross section.

By way of introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference numerals or the same component designations, unless otherwise stated, the disclosures contained in the entire description can be analogously applied to the same parts with the same reference numerals or component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and are to be transferred to the new situation mutatis mutandis when a change in position. Furthermore, individual features or combinations of features from the different exemplary embodiments shown and described can also represent independent, inventive or inventive solutions.

All statements on ranges of values in the description of the present invention should be understood to include any and all sub-ranges thereof, e.g. is the statement 1 to 10 to be understood that all sub-areas, starting from the lower limit 1 and the upper limit 10 are included, ie. all subregions begin with a lower limit of 1 or greater and end at an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1 or 5.5 to 10.

FIGS. 1 to 3 now show a laser module 1, FIG. 1 an oblique view, FIGS. 2 and 3 a cross-section. The laser module 1 comprises a heat sink 2, which has a metallic base body 3 and an upper body 4 connected thereto by the screw 5. Preferably, the upper base body 4 is made of metal, in particular of the same metal as the lower base body 3, manufactured. For example, copper or aluminum come into question. The heat sink 2 furthermore has a mounting surface 6 for a semiconductor component 7. Specifically, in this example, a semiconductor laser 7 is arranged on the mounting surface 6. Between the upper base body 4 and the semiconductor laser 7, a ductile contact plate 8 is additionally provided for forming the electrical contact. Furthermore, the laser module 1 comprises two insulators 9 and 10, which are arranged between the lower base body 3 and the upper base body 4. Likewise, the insulators 9 and 10 may also be formed by an insulator plate, which correspondingly has a recess for the screw 5 and an end-side recess for lateral positioning. The insulator is preferably also embodied such that the distance between the base bodies 3 and 4 can be adjusted via its thickness. Also, the laser module 1 comprises a step-shaped projection 11, which is the mounting surface 6 upstream in the direction of the boundary of the heat sink 2 on the base body 3, mounting holes 12, two electrical connections 13 and 14 and at least one recess for a thermocouple - as in Fig. 2 and 3 shown in the main body 3. The connection of the laser module 1 to an electrical power supply takes place via the electrical connections. By the insulators 9 and 10, the two poles are electrically isolated from each other. The lower main body 3 preferably forms the positive pole and the upper main body 4 forms the negative pole. Accordingly, the screw 5 has insulation, so that an electrical short circuit is prevented. The stepped projection 11 is designed for mounting not shown optical elements, which is arranged downstream of the semiconductor laser 7 in the beam direction. In particular, the projection 11 offers a variety of mounting options for different optical elements.

In FIG. 2 it can now be seen that the lower base body 3 has an area enclosed on all sides below the mounting surface 6, which is filled with a mixture 15 of metal / graphite, metal / diamond or metal / graphite / diamond. Preferably, the metal is copper or aluminum. A mixture of copper and diamond has proved to be particularly advantageous, since in this case, with adapted thermal expansion, a high, at least comparable or higher, thermal conductivity of copper sets.

The mixture 15 is materially connected to the mounting surface 6 and to the base body 3, that is enclosed on all sides by the base body 3. As a result, heat accumulation is avoided and thermal stresses are well transferred between the base body 3 and the mixture 15 and an expansion of the base body 3 is inhibited by the mixture 15 at least in the region of the mounting surface 6, so that the base body 3 and the semiconductor 7 expand substantially the same. This is especially true during assembly of the semiconductor 7 important, because the temperatures are much higher than during operation. Thus, a stress and / or destruction of the semiconductor 7 during assembly is prevented.

It has proved to be particularly advantageous if the resulting coefficient of thermal expansion of the mixture 15 and of the part of the base body 3 which lies between the mixture 15 and the mounting surface 6 corresponds essentially to the thermal expansion coefficient of the semiconductor 7 at the mounting surface 6. In this case, the geometric properties (ie shape and size) of the main body 3 and the mixture 15 and their thermal expansion coefficients are adjusted so that the resulting thermal expansion at the mounting surface 6 substantially corresponds to that of the semiconductor laser 7. In the proposed manner dangerous mechanical stresses in the semiconductor laser 7 can be effectively avoided. It has proved to be particularly advantageous in the above context if the thickness of the main body 3 between the mixture 15 and the mounting surface 6 is 0.1-0.3 mm. This thickness in the tenth-mm range is correspondingly sufficient for the processing of the mounting surface 6.

Furthermore, the optical properties of the emitted radiation are also improved if the mounting surface 6 is manufactured with high precision, so that the mounting surface 6 has at least a high flatness, small roughness depth and edge rounding. This is achieved in particular by the good machinability of the material used - ie copper or aluminum - of the base body 3.

The adaptation of the thermal expansion of the heat sink to the semiconductor allows the semiconductor assembly to the mounting surface 6 by means of brazing, whereby the long-term stability is significantly improved.

FIG. 3 now shows a cross section through a laser module 1, which is very similar to the laser module 1 shown in FIGS. 1 and 2. In contrast, in the base body 3 but also a cooling channel 16 is arranged, through which a heat transfer medium is guided and thus the cooling effect of the heat sink 2 is further improved. Accordingly, the cooling channel 16 is arranged in the region of the mixture 15 so that a good heat dissipation is achieved. Although the heat sink 2 has been illustrated with respect to a semiconductor laser 7, it is of course also generally suitable for other semiconductor devices. It is also particularly advantageous if the laser module 1 is used for material processing, for example for laser welding, laser cutting, engraving, marking, etc. Of course, the laser module 1 can also be used in conjunction with welding or cutting robots.

The embodiments show possible embodiments of a heat sink 2 according to the invention and a laser module 1 according to the invention, it being noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments are possible with each other and this variation possibilities due the doctrine for technical action by the subject invention in the skill of those working in this technical field is the expert. So are all conceivable embodiments, which are possible by combinations of individual details of the illustrated and described embodiment variant, includes the scope of protection.

In particular, it is noted that the heat sink 2 and the laser module 1 are not necessarily shown to scale and therefore may have other proportions. Furthermore, the cited devices may also comprise more or fewer components than shown.

The task underlying the independent inventive solutions can be taken from the description.

Claims

Patent claims

1. heat sink (2) for a directly applied semiconductor device (7), comprising at least one metallic base body (3, 4) with a mounting surface (6) for said semiconductor device (7), characterized in that below the mounting surface (6) a mixture (15) is arranged, which is enclosed on all sides by the base body (3) and made of metal / graphite, metal / diamond or metal / graphite / diamond.

2. Heatsink (2) according to claim 1, characterized in that as metal for the base body (3, 4) aluminum or copper is provided.

3. heat sink (2) according to one of claims 1 to 2, characterized in that as metal for the mixture (15) aluminum or copper is provided.

4. heat sink (2) according to claim 3, characterized in that the resulting coefficient of thermal expansion of the mixture (15) and the part of the base body (3) which lies between the mixture (15) and the contact surface (6), on the mounting surface ( 6) essentially corresponds to the thermal expansion coefficient of the semiconductor component (7).

5. heat sink (2) according to one of claims 1 to 4, characterized in that the base body (3) between the mixture (15) and the mounting surface (6) has a thickness in the tenth-mm range, in particular 0, 1-0.3 mm.

6. heat sink (2) according to one of claims 1 to 5, characterized by a step-shaped projection (11), which is the contact surface (6) in the direction of the boundary of the heat sink (2) upstream.

7. heat sink (2) according to one of claims 1 to 6, characterized by at least one extending in its interior cooling channel (16).

8. Laser module (1), comprising a laser light emitting semiconductor component (7), characterized in that this is arranged on the mounting surface (6) of the heat sink (2) according to one of claims 1 to 7.

9. Laser module (1) according to claim 8, characterized by a heat sink (2) according to claim 6 and at least one on the step-shaped projection (11) arranged optical element.

10. Use of a laser module (1) according to one of claims 8 to 9 for material processing.