METHOD FOR PRODUCING A HEAT-SPREADING PLATE, HEAT-SPREADING PLATE, METHOD FOR PRODUCING A SEMICONDUCTOR MODULE AND SEMICONDUCTOR MODULE

Abstract

One aspect relates to a method for producing a heat-spreading plate for a circuit carrier. At least one first layer made of a first material having a first coefficient of expansion and at least one second layer made of a second, low-stretch material having a second coefficient of expansion that is smaller than the first coefficient of expansion are bonded to each other at a bonding temperature of 150° C.-300° C. by means of a low-temperature sintering process. At least one bonding layer from a bonding material is formed between the first layer and the second layer and the bonding temperature essentially corresponding to the mounting temperature at which the produced heat spreading plate is connected to at least one circuit carrier.

Claims

1-20. (canceled)

21. A method for producing a heat spreading plate for a circuit carrier, comprising: bonding at least one first layer made of a first material having a first coefficient of expansion with at least one second layer made of a second low-stretch material having a second coefficient of expansion smaller than the first coefficient of expansion to each other; wherein the bonding of the at least one first and second layers is at a bonding temperature of 150° C.-300° C. by means of a low-temperature sintering process; wherein at least one bonding layer from a bonding material is formed between the first layer and the second layer and the bonding temperature substantially corresponds to a mounting temperature at which the produced heat spreading plate is connected to at least one circuit carrier.

22. The method of claim 21, wherein the bonding temperature is between 240°-260° C.

23. The method of claim 21, wherein the bonding material of the bonding layer produces a bond that withstands temperatures above the bonding temperature, and comprises a diffusion metal comprising one of a group comprising silver (Ag), a silver alloy, gold (Au), a gold alloy, copper (Cu), and a copper alloy.

24. The method of claim 21, wherein the first material comprises a metal comprising one of a group comprising copper (Cu), a copper alloy, and the second material comprises one of a group comprising a nickel alloy, Invar (Fe.sub.65Ni.sub.35), Invar 36 (Fe.sub.64Ni.sub.36), Kovar (Fe.sub.54Ni.sub.29Co.sub.17), tungsten (W), an iron-nickel-cobalt alloy (FeNiCo alloy), and molybdenum (Mo).

25. The method of claim 21, wherein bonding the at least first layer to the at least second layer and the at least first bonding layer is effected by means of pressure application at a pressure of between 10 MPa-28 MPa.

26. A heat spreading plate for a circuit carrier, comprising: at least one first layer made of a first material having a first coefficient of expansion bonded to at least one second layer made of a second low-stretch material having a second coefficient of expansion that is smaller than the first coefficient of expansion; wherein at least one first bonding layer is formed between the first layer and the second layer; and wherein the at least one first bonding layer comprises a diffusion metal comprising one of a group comprising silver (Ag), a silver alloy, gold (Au), a gold alloy, copper (Cu), and a copper alloy.

27. The heat spreading plate of claim 26, wherein the at least one first bonding layer is configured as a boundary layer of the first layer and/or the second layer.

28. The heat spreading plate of claim 26, wherein the first material comprises one of a group comprising copper (Cu) and a copper alloy, and the second material comprises one of a group comprising a nickel alloy, Invar (Fe.sub.65Ni.sub.35), Invar 36 (Fe.sub.64Ni.sub.36), Kovar (Fe.sub.54Ni.sub.29Co.sub.17), tungsten (W), an iron-nickel-cobalt alloy (FeNiCo alloy), and molybdenum (Mo).

29. The heat spreading plate of claim 26, wherein at least one third layer made of the first material, which is bonded by means of a second bonding layer from the bonding material to the second layer made of the second low-stretch material.

30. The heat spreading plate of claim 29, wherein at least one fourth layer from the second material, which is bonded by means of a third bonding layer made of the bonding material to the third layer made of the first material.

31. The heat spreading plate of claim 30, wherein the at least one first through fourth layers and the bonding layers are in a symmetrical arrangement such that a planar heat spreading plate is formed.

32. The heat spreading plate of claim 30, wherein the at least one first through fourth layers and the bonding layers are in an asymmetrical arrangement, such that a convexly or concavely shaped heat spreading plate is formed.

33. The heat spreading plate of claim 30, wherein the second layer or the fourth layer is embedded in a layer from the first material.

34. The heat spreading plate of claim 30, wherein the second layer or the fourth layer is shaped one of frame-like, grid-like, and wire-like.

35. A method for producing a semiconductor module, comprising: forming a heat spreading plate by bonding at least one first layer made of a first material having a first coefficient of expansion with at least one second layer made of a second low-stretch material having a second coefficient of expansion smaller than the first coefficient of expansion to each other; wherein the bonding of the at least one first and second layers is at a bonding temperature of 150° C.-300° C. by means of a low-temperature sintering process; wherein at least one bonding layer from a bonding material is formed between the first layer and the second layer and the bonding temperature substantially corresponds to a mounting temperature during connection of the produced heat spreading plate to at least one circuit carrier; wherein the at least one circuit carrier supports at least one semiconductor component; wherein the circuit carrier is connected by means of a contacting layer to the heat spreading plate at a mounting temperature of 150° C.-300° C.; and wherein the mounting temperature essentially corresponds to the bonding temperature at which the layers of the heat spreading plate are bonded together.

36. The method of claim 35, wherein the bonding of the layers of the heat spreading plate and the bonding of the circuit carrier to the heat spreading plate is carried out simultaneously.

37. The method of claim 35, wherein the mounting temperature is between 240° C.-260° C.

38. A semiconductor module, comprising a heat spreading plate, comprising: at least one first layer made of a first material having a first coefficient of expansion bonded to at least one second layer made of a second low-stretch material having a second coefficient of expansion that is smaller than the first coefficient of expansion; wherein at least one first bonding layer is formed between the first layer and the second layer; and wherein the at least one first bonding layer comprises a diffusion metal comprising one of a group comprising silver (Ag), a silver alloy, gold (Au), a gold alloy, copper (Cu), and a copper alloy; and at least one circuit carrier supporting at least one semiconductor component.

39. The semiconductor module of claim 38, wherein the circuit carrier is configured as a DCB substrate from at least one of a group comprising aluminium oxide (Al.sub.2O.sub.3), aluminium nitride (AlN), silicon nitride (Si.sub.3N.sub.4), and zirconia toughened alumina (ZTA).

40. The semiconductor module of claim 38, wherein the heat spreading plate is connected to a cooler, and wherein a heat-conducting paste is formed between the heat spreading plate and the cooler.

Description

[0064] The invention will now be explained in further detail with reference to the attached schematic drawings by way of exemplary embodiments, in which

[0065] FIG. 1a shows the arrangement of individual layers of a heat spreading plate in a first embodiment;

[0066] FIG. 1b shows the heat spreading plate of FIG. 1a in a bonded state;

[0067] FIG. 2a shows the arrangement of individual layers of a heat spreading plate according to the invention in a second embodiment;

[0068] FIG. 2b shows the arrangement of individual layers of a heat spreading plat according to the invention in a third embodiment;

[0069] FIGS. 3a and 3b show further embodiments of heat spreading plates according to the invention;

[0070] FIGS. 4a and 4b show the arrangement of individual layers of a heat spreading plate according to the invention with circuit carrier in a first embodiment in an unconnected and in a connected state;

[0071] FIGS. 5a and 5b show the arrangement of individual layers of a heat spreading plate according to the invention with circuit carrier in a further embodiment in an unconnected and in a connected state;

[0072] FIG. 6 shows the arrangement of individual layers of a heat spreading plate according to the invention with circuit carrier in a further embodiment;

[0073] FIGS. 7a and 7b show the arrangement of individual layers of a heat spreading plate according to the invention with circuit carrier in a further embodiment in an unconnected and in a connected state;

[0074] FIGS. 8a-8c show the convex formation of heat spreading plates and circuit carriers arranged thereon in various embodiments; and

[0075] FIG. 9 shows a semiconductor module connected to a cooler.

[0076] In the following identical and functionally identical parts are marked with identical reference symbols.

[0077] FIG. 1a shows the individual layers of a conventional heat spreading plate 10 (see FIG. 1b). Accordingly the heat spreading plate to be produced comprises a first layer 20 made of a first material M1, a second layer 30 made of a second material M2 and a third layer 25 also made of the first material M1. The material M1 is preferably a metal, in particular copper or a copper alloy. Material M2 on the other hand is a low-stretch material with a second expansion coefficient which is smaller than the first expansion coefficient of the first material M1. The second material M2 may be a nickel alloy, in particular Invar or Invar 36 or Kovar and/or tungsten and/or an iron-nickel-cobalt alloy. In the present embodiment material M2 is molybdenum.

[0078] A first bonding layer 40 from a bonding material VM is provided between the first layer 20 and the second layer 30. A second bonding layer 41 from a bonding material VM is provided between the second layer 30 and the third layer 25. The bonding material VM of the bonding layers 40 and 41 creates a bond between the layers 20, 25 and 30, with this bond withstanding temperatures above a bonding temperature. Preferably the bonding layer comprises a diffusion metal, in particular silver and/or a silver alloy and/or gold and/or a gold alloy and/or copper and/or a copper alloy.

[0079] Preferably the bonding layer is formed as a sintering layer, in particular a sintering paste. This sintering paste, which preferably comprises one of the named diffusion metals, may for example be applied by means of a printing process.

[0080] Preferably the layers 20, 25 and 30 are bonded to each other by a low-temperature method at a bonding temperature of 150° C.-300° C. Especially preferably the bonding temperature is 250° C. The bonding temperature for bonding the layers 20, 25 and 30 with the aid of the bonding layers 40 and 41 substantially corresponds to the mounting temperature during connecting the produced heat spreading plate 10 to a circuit carrier to be mounted.

[0081] FIG. 1b shows the produced heat spreading plate 10. The bonding layers 40 and 41 can be recognised. It is possible that bonding layers 40 and 41 are designed as boundary layers of the first layer 20, the third layer 25 and the second layer 30.

[0082] Bonding of the first layer 20 to the second layer 30 and the third layer 25 is preferably effected by means of the application of pressure, in particular at a pressure of 5 MPS-30 MPa, in particular 10 MPa-28 MPa, in particular 25 MPa.

[0083] As can be recognised from FIGS. 1a and 1b, the layer thicknesses d1 of the first layer 20, d2 of the second layer 30 and d3 of the third layer 25 are identical. With the aid of the symmetry axis S plotted in FIG. 1b it can be seen that the heat spreading plate 10 is built-up symmetrically from individual layers 20, 25 and 30 as well as the bonding layers 40 and 41. The symmetry axis S halves the overall thickness D of the heat spreading plate 10. The overall thickness D is formed by totaling the layer thicknesses d1, d2 and d3. Above and below the symmetry axis S a symmetrical structure of the heat spreading plate 10 is obvious. Using such a heat spreading plate permits a planar structure/a planar shaping of the heat spreading plate 10.

[0084] FIG. 2a by contrast shows an asymmetrical arrangement of individual layers 20, 25 and 30 and bonding layers 40 and 41. With regard to materials and bonding options of individual layers 20, 25 and 30 reference should be made to the above explanations in conjunction with FIGS. 1a and 1b.

[0085] It can be seen that the layer thickness d1 of the first layer 20 is larger than the layer thickness d2 of the second layer 30 as well as the layer thickness d3 of the third layer 25. A hinted at symmetry axis S which halves the overall thickness D of the heat spreading plate 10, shows that the heat spreading plate 10 to be formed, comprises an asymmetrical arrangement of individual layers above and below the symmetry axis S. Preferably the layer thickness d1 is between 0.2 mm and 3.0 mm, whereas the layer thickness d2 is between 0.1 mm and 2.0 mm. The thickness of the first bonding layer 40 and/or the second bonding layer 41 is for example between 1 μm and 50 μm. The layer thickness d3 may be between 0.2 mm and 3.0 mm.

[0086] FIG. 2b by contrast shows a symmetrical structure/a symmetrical arrangement of individual layers 20, 25, 26, 30, 35 and bonding layers 40, 41, 42, 43. It can be recognised that the heat spreading plate 10 to be produced may also comprise two layers made of the second low-stretch material M2. These are the second layer 30 and the fourth layer 35. Above and below the second layer 30 and the fourth layer 35 a layer from a first material M1 is respectively provided, which is, respectively, the first layer 20, the third layer 25 as well as the fifth layer 26. The individual layers which consist of the first material M1, i.e. layers 20, 25 and 26, are bonded to the layers consisting of the second low-stretch material M2, i.e. the second layer 30 and the fourth layer 35, by means of bonding layers 40, 41, 42 and 43. The bonding layers 40, 41, 42 and 43 preferably comprise the same bonding material VM. Preferably this is a sintering material, in particular a sintering paste, which for example comprises silver and/or silver oxide and/or silver carbonate.

[0087] The symmetry axis S hinted at shows that the embodiment shown in FIG. 2b depicts a symmetrical arrangement of the layers 20, 25, 26, 30, 35 and the bonding layers 40 to 43. With the aid of a heat spreading plate 10, as shown in FIG. 2b, it is possible to achieve a reduction in stretch of the marginal layers 20 and 26 which preferably consist of copper. This is done with the aid of two spaced-apart layers 20 and 35, which consist of a low-stretch material, in particular molybdenum.

[0088] FIG. 3a shows a further embodiment of the heat spreading plate 10. Here a second layer 30 is configured as a grid. The grid would be visible when looking from the top onto a first side 15 of the first layer 20. The second layer 30 is embedded into in the first layer 20 made of the first material M1. Semi-circular recesses 22 are formed on the side 16 opposite the first side 15 of the heat spreading plate 10.

[0089] According to the embodiment depicted in FIG. 3b of the heat spreading plate 10 it is again provided that the second layer 30 is embedded in the first layer 20. On the side 16 opposite the first side 15 of the heat spreading plate 10 both recesses 22 and bulges 23 are formed. The second layer 30 is formed from an upper portion 36 and a lower portion 37. The lower portion 37 is formed like a wire. The cross-sections of the wires can be recognised. The wires of the lower portion 37 are positioned in the bulges 23. The upper portion 36 by contrast is shaped like a plate, but comprises a smaller width than the first layer 20.

[0090] In FIG. 4a the individual layers/components of a semiconductor module to be produced are depicted. The heat spreading plate 10 is thus formed from a first layer 20 of a first material M1 and a second layer 30 from a second material M2. A bonding layer 40 is formed between the first layer 20 and a second layer 30. This bonding layer is preferably a sintering layer which comprises a bonding material VM, i.e. silver.

[0091] On the first side 31 of the second layer 30 a bond-enhancing layer 50 is applied. The first side 31 of the second layer 30 is the side of the second layer 30 facing the first layer 20. The bond-enhancing layer 50 is preferably applied by electroplating onto the second layer 30. The bond-enhancing layer 50 is for example a nickel-silver layer. With the aid of the bond-enhancing layer 50 the adhesion between the second layer 30 and the bonding layer 40 can be improved. In the bonded state (see FIG. 4b) a combined bonding layer 45 is created. The bonding layer 40 and the bond-enhancing layer 50 are pressed together using a low-temperature sintering process so that the combined bonding layer 45 is formed.

[0092] The hinted-at symmetry axis S in FIG. 4b helps to recognise that the heat spreading plate 10 has an asymmetrical structure. With regard to the symmetry axis S the preceding explanations apply. The asymmetrical structure is achieved by different layer thicknesses of the first layer 20 and the second layer 30. The layer thickness d1 of the first layer 20 is larger than the layer thickness d2 of the second layer 30.

[0093] The circuit carrier 80 is for example a so-called DCB substrate. This may be configured as a substrate plate made of aluminium oxide and/or silicon nitride and/or zirconia-toughened alumina.

[0094] A contacting layer 60 is provided for connecting the circuit carrier 80 to the heat spreading plate 10. This contacting layer 60 may for example be a sintering paste. It is also feasible for the contacting layer 60 to be an adhesive layer or a solder layer. The circuit carrier 80 is attached by means of the contacting layer 60 to the side 15 of the heat spreading plate 10 which faces the circuit carrier 80. The surface 15 of the heat spreading plate 10 to be connected to the circuit carrier 80 is the first side 15 of the first layer 20, wherein the first side 15 of the first layer 20 is configured so as to face away from the second layer 30.

[0095] Connecting the circuit carrier 80 to the heat spreading plate 10 is carried out by applying a mounting temperature of 150° C.-300° C. to the arrangement, wherein the mounting temperature substantially corresponds to the bonding temperature when bonding the layers 20 and 30 of the heat spreading plate 10. It is possible that both the layers 20 and 30 as well as the circuit carrier 80 are connected together in a single step, i.e. simultaneously.

[0096] The embodiment of the invention depicted in FIGS. 4a and 4b represents the smallest possible thermal stack with regard to a heat spreading plate 10, which can be connected to a circuit carrier 80.

[0097] FIGS. 5a and 5b also show an asymmetrical structure of a heat spreading plate 10. In contrast to the embodiments of FIGS. 4a and 4b the heat spreading plate 10 here consists of a first layer 20, a second layer 30 and a third layer 25. The first layer 20 and the third layer 25 comprise a first material M1. The material is preferably copper. Between these two layers 20 and 25 which have different layer thicknesses d1 and d3, a second layer 30 from a second material M2 is formed. The second material M2 consists of a low-stretch material/the expansion coefficient of the second material M2 is smaller than the expansion coefficient of the first material M1. The asymmetrical heat spreading plate 10 again has a circuit carrier 80 formed on it and therefore can, together with a semiconductor component 90 (not shown), form a semiconductor module 100.

[0098] The embodiment of a semiconductor module depicted in FIG. 6 is also based on an asymmetric heat spreading plate 10. A first layer 20 from a first material M1, such as copper, is bonded to a second layer 30 from a second low-stretch material M2. To this end a bonding layer 40 is provided between the two layers 20 and 30. The layer thickness d1 of the first layer 20 is six times that of the layer thickness d2 of the second layer 30. Again, a circuit carrier 80 can be attached on the first side 15 of the first layer 20 with the aid of a contacting layer 60.

[0099] The second layer 30 also has a smaller width than the first layer 20. The width of the second layer 30 corresponds approximately to the width of the contacting layer 60.

[0100] In the embodiment shown in FIGS. 7a and 7b a further arrangement consisting of a heat spreading plate 10 and a circuit carrier 80 is depicted. FIG. 7a shows the two components in an unconnected state.

[0101] The heat spreading plate 10 comprises a first layer 20 as well as a second layer 30. The second layer 30 is embedded in the first layer 20 which consists of the first material M1. The geometrically smaller layer 30 is thus placed into a hollow of the first layer 20 and connected by means of a bonding layer 40. The width b1 of the second layer 30 substantially corresponds to the width b2 of the contacting layer 60. The circuit carrier 80 is arranged above the second layer 30 such that the circuit carrier 80, in particular the contacting layer 60, is configured congruently with the second layer 30.

[0102] The heat spreading plate 10 also comprises a raised plateau 29. The circuit carrier 80 can be attached to the topmost side 15 on this plateau 29. The raised plateau 29 may serve as a mounting aid. Moreover this plateau 29 contributes to an asymmetrical arrangement of the individual layers of the heat spreading plate 10. The plateau may for example be produced by pressing the layers 20 and 30 shown in FIG. 6 together.

[0103] FIG. 8a shows a semiconductor module 100, wherein the heat spreading plate 10 has a concave shape. The concave shape of the heat spreading plate 10 is the result of the asymmetrically structure of the heat spreading plate 10. The layer thickness d3 of the third layer 25 is smaller than the layer thickness d1 of the first layer 20, so that the heat spreading plate 10 is generally bent in direction of the third layer 25. A circuit carrier 80, which has a semiconductor component 90 attached to it, is connected to the first side 15 of the first layer of the heat spreading plate 10, i.e. the topmost side 15 of the heat spreading plate 10. The circuit carrier 80 is connected to the heat spreading plate 10 such that the indentation 70 created because of the concave shape of the heat spreading plate 10 marks the central position of the circuit carrier 80.

[0104] FIG. 8b shows a further semiconductor module 100. The heat spreading plate 10 in this embodiment comprises cooling fins 110. In other respects the structure of the semiconductor module 100 of FIG. 8b is the same as the structure of the embodiment shown in FIG. 8a.

[0105] FIG. 8c shows that a heat spreading plate 10 may comprise a number of concave hollows thereby forming three indentations 70 in the example shown, wherein the three circuit carriers 80 are each arranged centrally to the indentation 70 on the first side 15 of the first layer 20. The concave hollows/curved sides 75 of the heat spreading plate 10 are formed in that three portions of second layers 30 are embedded in the first layer 20 consisting of a first material M1. The second layers 30 are arranged such that the curved sides/the indentations 70 are formed above/below the position of the respectively second layer 30.

[0106] It would be possible to split the arrangement of FIG. 8c up, so that three mutually independent semiconductor modules 100 are formed.

[0107] FIG. 9 shows a semiconductor module 100, which comprises a concavely shaped heat spreading plate 10, a circuit carrier 80, a cooler 120 as well as a semiconductor component 90 placed on and connected to the circuit carrier 80. A heat-conducting paste 130 is applied between the heat spreading plate 10 and the cooler 120. The heat-conducting paste 130 is preferably a plastic paste, which is applied as thinly as possible and free from air inclusions between the heat spreading plate 10 and the cooler 120. The curved side 75/the side of the heat spreading plate 10 opposite the indentation 70 is mounted onto the surface 125 of the cooler 120.

[0108] The heat spreading plate 10 is pressed onto the surface 125 of the cooler 120 with the aid of screws 140 which act as a clamping device. As the mounting pressure rises, the heat-conducting paste 130 is squeezed from inside to outside and in this way fills the gap between the heat spreading plate 10 and the surface 125 of the cooler 120.

[0109] FIG. 9 merely shows a partially mounted state. In the fully mounted state the heat spreading plate 10 is preferably fully supported against the surface 125 of the cooler 120. A rough surface 125 or a contour error of the heat spreading plate 10 and the cooler 120 are compensated for by the heat-conducting paste 130. The cooler 120 shown is a so-called air cooler.