WO2001008219A1

WO2001008219A1 - Semiconductor module

Info

Publication number: WO2001008219A1
Application number: PCT/DE2000/002354
Authority: WO
Inventors: Manfred Loddenkötter
Original assignee: eupec Europäische Gesellschaft für Leistungshalbleiter mbH & Co. KG
Priority date: 1999-07-23
Filing date: 2000-07-19
Publication date: 2001-02-01

Abstract

The invention relates to semiconductor modules (1) consisting of a metal support plate (2), a cooling body (8), at least one ceramic substrate (4) and several semiconductor components (6). Mechanical tensions between the ceramic substrates and the metal support plate during assembly on the cooling body are substantially reduced with the insertion of defined elastic points by making recesses in the metal support plate (2) with the purpose of forming small segments. This makes it possible to use large metal support plates having a small thickness.

Description

description

Semiconductor module

The invention relates to a semiconductor module consisting of a metal carrier plate with an upper surface and a lower surface, a heat sink on which the metal carrier plate is fastened via its lower surface, at least one heat-conducting and electrically insulating substrate which fastens on the upper surface of the metal carrier plate is, as well as several semiconductor components that are applied to the substrate.

Such semiconductor modules are generally known. In order to protect semiconductor modules from being destroyed by the resulting heat loss, good heat-conductive contact between the metal carrier plates and the heat sinks is required.

Typically, the metal support plate of the semiconductor module is designed in relation to the flat surface of the heat sink as a convexly curved surface, preferably as a spherical surface, so that when the metal support plate is fixed to the side of the heat sink in question, the metal support plate is pressed and fixed to the heat sink under mechanical tension becomes. In order to reduce the transition heat resistance between the metal support plate and the heat sink, this convex design of the metal support plate has proven to be advantageous. A known method for convex deformation of the metal support plate is e.g. described in DE 39 40 933 AI

In the case of modules with a larger base area, however, mechanical stresses arise between the ceramic substrate and the metal support plate during assembly on the flat heat sink, which in the worst case lead to the destruction of the ceramic substrates. The cause of these negative mechanical stresses when mounting on the flat heat sink is due to the greatly different coefficients of thermal expansion between the metal carrier plates used and the ceramic substrates used. In particular, the thermal expansion coefficients of metals and ceramics are very different, so that the heat which occurs when the ceramic substrates are soldered to the metal support plates leads to the ceramic and the metal support plate expanding to different extents.

The result is that after the arrangement has cooled, there is no longer a plane-parallel metal support plate, but a concavely curved one, based on the position of the ceramic substrates. This means that good contact of the metal support plate with the heat sink is only guaranteed on the lateral surfaces of the arrangement, but the middle part has no or only poor contact, so that the heat dissipation is unsatisfactory.

It has been shown in the past that metal support plates made of copper with a base area of up to 60 x 120 mm can still be formed with a thickness of 3 mm. Contours and recesses required in the metal carrier plate are punched. Convex surface profiles are produced by bending dies.

Larger metal carrier plates have to be machined excitingly. The outer contour is milled, while the holes for attaching the metal support plate are drilled with the heat sink. Convex surface profiles are usually turned. This complex machining process enables metal carrier plates with typical dimensions of approx. 140 x 190 mm. The thickness of the metal support plate is then already 5 mm, which increases the material costs considerably. In addition, the mechanical stresses between the metal support plate and the heat sink increase with the size of the metal support plate. It is therefore an object of the present invention to develop a semiconductor module of the type mentioned at the outset in such a way that simple solder assembly is possible even in the case of modules with large base areas, with perfect thermal contact between the metal support plate and the heat sink being ensured.

According to the invention, this object is achieved by a semiconductor module of the type mentioned at the outset, which is characterized in that one or more recesses are made in the metal carrier plate.

By introducing such exceptions, i.e. From defined elastic points, the mechanical stresses between the ceramic substrate and the metal support plate are drastically reduced when mounted on the heat sink. In particular, the segments formed by the recesses can be individually convexly deformed, so that there is no danger that the ceramic substrates located in the modules will be destroyed by different coefficients of thermal expansion. This makes it possible to manufacture semiconductor modules that have a very inexpensive transition resistance. In addition, the size of the segments can be determined by a corresponding number of recesses, so that the size of the metal support plate can, in principle, be of any size. Another advantage of the invention consists in cost-effective manufacturing processes and materials.

In one embodiment of the present invention, a plurality of substrates, which are preferably metallized on both sides, on the one hand to facilitate assembly on the metal support plate and on the other hand to be able to apply the semiconductor components in a structured manner, are fastened to the upper surface of the metal support plate. The attachment is preferably carried out via a soft solder layer. Because of the relationship ΔX = Δα x ΔT x 1, where ΔX denotes the difference of the linear expansion and Δα the difference of the linear expansion coefficients of the ceramic substrate and the metal support plate, and ΔT the temperature difference of the arrangement between the melting temperature of the solder and the room temperature and 1 die Long of the ceramic substrate to be applied, it follows that an inexpensive method for avoiding undesired carrier plate deformations is to reduce ΔX and thus the parameters Δα, ΔT and 1 as much as possible. Δα depends on the material and is therefore not variable if metal carrier plates and ceramic substrates are used. In order to keep the difference in temperature as low as possible during the soldering process and after the arrangement has cooled, a solder must be used which has a low melting temperature, but on the other hand is not so low that the heat of loss which occurs later when the semiconductor module is in operation dissolves the solder melts. Melting temperatures of approx. 180 ° C are common. However, this measure is no longer sufficient if larger ceramic substrates are to be used, since the ceramic substrate lengths 1 likewise enter into the relationship for the difference in the linear expansion of two different materials. It is therefore very convenient to use several smaller ceramic substrates instead of a single large ceramic substrate in order to dimension the length 1 as desired. The size of the ceramic substrates is advantageously adapted to the size or shape of the segments formed by the recess.

Gaps are then typically provided between the individual ceramic substrates. However, it is also conceivable for the individual ceramic substrates to be soldered onto the metal carrier plate in abutting fashion.

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The configurations of the segments are adapted to the arrangement of the holes in the metal support plate for attachment to the heat sink. Advantageously, a screw is provided adjacent to opposite edges of the metal carrier plate between two recesses and / or between a recess and the adjacent, parallel edge.

The invention is illustrated in the drawing, for example, and described in detail below with reference to the drawing. Show it:

1 shows a schematic illustration of a section through a semiconductor module according to the present invention,

FIG. 2 shows a plan view of the semiconductor module according to FIG. 1,

Figure 3 is a plan view of an alternative semiconductor module and

Figure 4 is a plan view of a further semiconductor module.

The basic structure of a semiconductor module 1 shown in FIG. 1 consists of a metal carrier plate 2

Copper, three substrates 4 made of Al ₂ O ₃ ceramic applied by means of a soft solder layer, on which the actual semiconductor components 6 are attached by means of a further solder layer 5. The metal carrier plate 2 is divided into three segments I, II, III by means of two recesses 12 (shown in broken lines). In the present example, each segment I, II, III carries a substrate 4.

The metal carrier plate 2 has an upper surface 11 and a lower surface 10. The metal support plate 2 rests with its lower surface 10 on a heat sink 8 and is screwed (not shown) onto the cooling element. screwed on by 8. Each segment I, II, III of the metal support plate 2 has a lower surface 10 which is convex with respect to the heat sink 8. On the upper surface 11 there are the three thermally highly conductive, electrically insulating substrates 4, between which there are gaps 13 s. The substrates 4 are connected to the upper surface 11 of the metal support plate 2 by a soft solder layer 3. Semiconductor components 6 are in turn fastened on the upper side of the substrate 6 via soft solder layers 5. These can be connected to housing connections (not shown). The top sides of the semiconductor components 6 are typically connected to one another via bond connections (not shown).

These recesses run transversely to the longitudinal direction of the metal carrier plate 2 in the regions 14 of the lower surface 11 of the substrate 4 corresponding to the gaps 13, which can be seen from FIG. 2. However, it is also conceivable to arrange one or more recesses in the longitudinal direction of the metal support plate 2 (FIG. 3).

By introducing the recesses 12 in the metal support plate 2, the mechanical stresses between the ceramic substrates 4 and the metal support plate 2 are significantly reduced during assembly on the heat sink 8. At the same time, good thermal properties are guaranteed. In particular, it should be emphasized that the recesses can accommodate excess thermal paste, so that a further improvement in the transition resistance can be achieved. As a further essential advantage, the corresponding number and size of recesses can in principle be used to make the metal support plate any size without mechanical stresses occurring. Furthermore, the thickness of the metal support plate can be chosen to be small (eg 3 mm), regardless of the size, since there is no need for exciting machining to produce the convex surface. It is therefore a considerable material and compared to the prior art for a large metal support plate Cost savings possible because the metal carrier plate with common manufacturing processes for large series, z. B. can be produced by stamping and shaping.

If a segment of the metal support plate 2 has a much greater length than its width, a convex deformation in the longitudinal direction may not suffice. For segments whose transverse dimensions are quite large and e.g. in the size of the transverse dimensions, a convex deformation in both the longitudinal and transverse directions is very advantageous. In this case, a segment typically has the shape of a spherical cap.

FIG. 2 shows a plan view of the semiconductor module according to the invention according to FIG. 1. In particular, the arrangement of the substrates 4, the recesses 12 and the bores 7 is shown in an advantageous form. The recesses 12 divide the area of the metal support plate 2 into three segments I, II, III of approximately the same size. Each segment has two bores 7 lying adjacent to the edges 13b, 13d. The bores 7 are advantageously arranged centrally in the respective segment with respect to the segment edge. In the present plan view, each segment contains only one substrate 4. However, it is also conceivable that one segment accommodates several substrates.

FIG. 3 shows a further exemplary embodiment of a top view of the semiconductor module according to the invention. In the present figure, 7 recesses 12 are provided which divide the surface of the metal support plate 2 into six segments I ... VI of approximately the same size. The recesses 12 are designed as elongated slots which are introduced in the longitudinal and transverse directions, ie approximately parallel to the edges of the metal carrier plate. The recesses end adjacent to the edges 13a ... 13d. Defined elastic points A are thus created along the edges. Such elastic points B are likewise in the interior of the metal carrier plate 2 formed the intersection of the imaginary extensions of the recesses 12. The arrangement of the bores 7 is chosen in accordance with FIG. 2.

FIG. 4 shows a further exemplary embodiment in which the bores 7 are placed adjacent to the corner points of the ceramic. Thus, larger substrates can be used in the respective segments compared to FIG. 3 without changing the external dimensions of the metal carrier plate. In the present figure, eight holes are provided, three substrates being applied in each segment.

In a practical exemplary embodiment, the metal carrier plate 2 has a length of 162 mm and a width of 122 mm. Its thickness is 3 mm. Typically, two recesses at a distance of 54 mm from one another then run symmetrically on the lower surface of the metal carrier plate in the transverse direction. The recesses end a few millimeters in front of the respective edges of the metal carrier plate.

Such a metal support plate is then attached to the heat sink, for example by six screws.

The exemplary embodiments shown in the figures are usually used in a plastic housing. This is filled with a casting compound in order to ensure mechanical stability of bond connections of the semiconductor components and to increase the insulation capability. In order to prevent the casting compound from leaking out over the recesses, the plastic frame is advantageously designed such that struts (on the plastic frame) cover the recesses.

Claims

claims

1. Semiconductor module (1) consisting of a metal support plate (2) with an upper surface (11) and a lower surface (10), a heat sink (8) on which the metal support plate (2) is fastened via its lower surface (10) is characterized, at least one heat-conducting and electrically insulating substrate (4), which is attached to the upper surface (11) of the metal carrier plate (2), and several semiconductor components (6), which are applied to the substrate (4), that one or more recesses (12) are made in the metal support plate (2).

2. Semiconductor module according to claim 1, that a plurality of substrates (4) are attached to the upper surface (11) of the metal carrier plate (2).

3. Semiconductor module according to claim 2, d a d u r c h g e k e n e z e i c h n e t that gaps (13) are provided between the substrates (4).

4. Semiconductor module according to one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that the lower surface (10) of the metal support plate (2) is convex at the locations of the substrates to be fastened (4).

5. Semiconductor module according to claim 4, d a d u r c h g e k e n n z e i c h n e t that the convexity in the longitudinal and transverse directions is designed such that it corresponds to a spherical surface.

6. The semiconductor module according to claim 5, characterized in that the recesses (12) are made in the regions (14) of the lower surface (10) corresponding to the gaps (13).

7. The semiconductor module as claimed in claim 5, so that the recesses (12) are made in the regions of the lower surface (10) which are approximately below the edges (16) of the substrates (4).

8. Semiconductor module according to one of claims 1 to 7, d a d u r c h g e k e n n z e i c h n e t that at least some of the recesses (12) end adjacent to the edges of the metal support plate (2).

9. Semiconductor module according to one of claims 1 to 8, so that the substrates (4) are attached to the metal carrier plate (2) via a soft solder layer (3).

10. The semiconductor module according to one of claims 1 to 9, that the semiconductor components (6) are attached to the substrates (4) via a further solder layer (5).

11. Semiconductor module according to one of claims 1 to 10, d a d u r c h g e k e n n z e i c h n e t that the metal support plate (2) on the heat sink (8) with screws (9) are attached.

12. Semiconductor module according to one of claims 1 to 11, characterized in that in each case a screw (9) adjacent to opposite edges (13a, 13c; 13b, 13d) of the metal support plate (2) between two recesses (12) and / or between a recess and the adjacent, approximately parallel edge is provided

13. Semiconductor module according to one of claims 1 to 12, characterized in that ceramic substrates are provided as substrates (4), in particular A1 ₂ 0 ₃ - or AIN substrates.

14. Semiconductor module according to one of claims 1 to 13, d a d u r c h g e k e n n z e i c h n e t that a copper plate is provided as the metal carrier plate.