JPH0354471B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to improvements in semiconductor devices, particularly semiconductor devices incorporating power semiconductor elements.

(b) Prior Art Conventionally, as shown in FIG. 1, a silicon power semiconductor element 4 has been fixed onto a stem 1 made of copper or the like via a copper heat sink 2 and a molybdenum plate 3. This has the disadvantage that the thermal expansion coefficients of copper and silicon are significantly different, and cracks occur in the brazing material that fixes the semiconductor element 4 due to temperature cycles. This prevents the occurrence of

However, although the above-mentioned conventional structure can reduce the occurrence of cracks, it has the drawback that the molybdenum plate 3 is expensive and requires surface treatment such as silver plating so that the semiconductor element 4 can be fixed, resulting in an increase in cost. Another disadvantage is that the presence of the molybdenum plate 3 increases the thermal resistance from the semiconductor element 4 to the stem 1.

Therefore, in order to reduce costs, the inventor of the present invention replaced the molybdenum plate with invar (nickel 36%, iron plate).
64% alloy) was used. That is, as shown in Figure 2,
A structure was adopted in which a silicon power semiconductor element 4 was fixed onto a stem 1 via a heat sink 2 and an invar 5. As is clear from FIG. 8, Invar has a coefficient of thermal expansion that is approximately 1/3 that of molybdenum, and can obtain better results than molybdenum in terms of thermal expansion. However, its thermal conductivity is about 1/10 or less than that of molybdenum, so good heat dissipation effects cannot be expected. If the heat dissipation effect when the semiconductor element 4 is directly fixed on the copper heat sink 2 is 1, then when it is via the molybdenum plate 3, it is 0.75.
If it goes through Invar 5, it becomes 0.28.
Therefore, the structure shown in FIG. 2 cannot be realized in terms of heat dissipation effect.

(C) Objective of the present invention The first objective of the present invention is to realize a buffer plate with a low coefficient of thermal expansion and high thermal conductivity.

A second object of the present invention is to realize a buffer plate with a low coefficient of thermal expansion and high thermal conductivity using inexpensive materials.

(d) Structure of the present invention The semiconductor device according to the present invention is as shown in FIG.
In a structure in which a silicon power semiconductor element 14 is fixed on a metal plate 11 with good thermal conductivity via a heat sink 12 made of copper or the like, a divided metal with good thermal conductivity is surrounded by a metal with a small coefficient of thermal expansion. The feature is that a buffer plate 13 is provided.

(e) Examples of the present invention The cushioning material, which is a feature of the present invention, will be described in detail.
The first embodiment is shown in FIGS. 3 and 4.
In this embodiment, the buffer plate 13 is formed by alternately arranging a metal 21 having good thermal conductivity such as copper and a metal 22 having a small coefficient of thermal expansion such as invar in a concentric manner. Such a buffer plate 13 is manufactured by slicing a cylindrical copper core material into which invar and copper cylinders of different diameters are alternately inserted in close contact with each other. A silicon power semiconductor element 14 is fixed on this buffer plate 13 as shown by dotted lines. In this embodiment, the copper and invar have approximately the same width and have the same area.

A second embodiment is shown in FIGS. 5 and 6. In this embodiment, the buffer plate 13 is formed by arranging metals 21 with good thermal conductivity such as copper in a grid pattern, and metals 22 with a small coefficient of thermal expansion such as invar in a lattice pattern between them. Such a buffer plate 13 is manufactured by fitting copper into a lattice-shaped invar by rolling. A silicon power semiconductor element 14 is fixed on this buffer plate 13 as shown by dotted lines.

As shown in FIG. 7, the above-mentioned buffer plate 13 is embedded in a recess of a heat sink 12 made of copper or the like fixed on a metal plate 11 such as a stem, and a silicon power semiconductor element 14 is fixed onto this buffer plate 13. .

In the above structure, the heat generated from the silicon power semiconductor element 14 is radiated through the divided good heat conductive metal 21 made of copper of the buffer plate 13, while the large thermal expansion of the good heat conductive metal 21 is caused by an inverter. It can be suppressed by surrounding it with a metal 22 having a small coefficient of thermal expansion. As a result, the thermal expansion of the highly thermally conductive metal 21 is limited only in the vertical direction, not in the lateral direction, and the stress applied to the brazing material of the semiconductor element 14 can be kept to a minimum. Specifically, if the heat dissipation effect when the semiconductor element 14 is directly fixed on the copper heat sink 12 is 1, then the structure of the present invention has a heat dissipation effect of 0.85, which is about three times as much as the above-mentioned structure using Invar. can be improved.

(f) Effects According to the present invention, by combining a metal with good thermal conductivity and a metal with low thermal expansion, a cushioning material with good thermal conductivity and low thermal expansion can be easily realized. Moreover, by using Invar, an inexpensive cushioning material can be provided by combining copper and Invar.

Note that even if molybdenum or tungmate is used instead of invar, the object of the present invention can be sufficiently achieved, and the cost will be lower and the heat dissipation will be better than when a molybdenum plate is used.

[Brief explanation of drawings]

1 and 2 are cross-sectional views for explaining the conventional example, FIG. 3 is a top view for explaining one embodiment of the buffer plate used in the present invention, and FIG. 4 is a cross-sectional view taken along the line -- in FIG. 3. , FIG. 5 is a top view illustrating another embodiment of the buffer plate used in the present invention, and FIG.
A line sectional view, FIG. 7 is a sectional view explaining the present invention, and FIG. 8 is a table explaining the coefficient of thermal expansion and thermal conductivity. Explanation of main drawing numbers, 11 is a metal plate with good thermal conductivity, 1
2 is a copper heat sink, 13 is a buffer plate which is a feature of the present invention, and 14 is a semiconductor element.

Claims (1)

[Scope of Claims] 1. In a semiconductor device in which a silicon power semiconductor element is fixed on a metal plate with good thermal conductivity, a metal with good thermal conductivity divided between the metal plate and the power semiconductor element has a coefficient of thermal expansion. A semiconductor device characterized by providing a buffer plate surrounded by a small metal. 2. A semiconductor device according to claim 1, wherein the semiconductor device is a buffer plate in which the metal with good thermal conductivity and the metal with a small coefficient of thermal expansion are alternately arranged concentrically. 3. A semiconductor device according to claim 1, wherein the semiconductor device is a buffer plate in which the metal with good thermal conductivity is arranged in the form of stepping stones and the metal with a small coefficient of thermal expansion is arranged in the form of a lattice. 4. The semiconductor device according to claim 1, wherein copper is used as the metal with good thermal conductivity, and invar is used as the metal with a small coefficient of thermal expansion.