JPH077810B2 - Semiconductor device - Google Patents

Description

The present invention relates to a novel semiconductor device, and more particularly to a connection structure using SiC or AlN ceramics having a low coefficient of thermal expansion for insulation as an insulating substrate for mounting a semiconductor element.

[Conventional technology]

The conventional connection between ceramics and metallic materials is disclosed in JP-A-56-13.
As described in 5948, etc.
After metalizing metal such as o, W, Ni, Mo-Mn alloy by vapor deposition or screen printing, connect it to the surface of the metal material to be the heat sink through solder material such as solder or silver solder. The method is taken. However, in ceramics with a low coefficient of thermal expansion such as SiC and AlN, the compatibility with metallic materials is poor, and due to the stress remaining inside the ceramics due to heat treatment during brazing, reliability tests such as the subsequent thermal cycle test are performed. This caused cracking, which caused problems such as leaking of airtightness and reduction of insulation resistance.

[Problems to be solved by the invention]

The above-mentioned prior art does not give sufficient consideration to the coefficient of thermal expansion of SiC or AlN ceramics, and there is a problem in constructing a package of a semiconductor device such as insulation failure or airtightness due to destruction of the ceramics.

An object of the present invention is to provide a semiconductor device connected to a material having a different thermal expansion coefficient, in particular, a metal material serving as a heat sink, without breaking ceramics having a low thermal expansion such as SiC and AlN.

[Means for solving problems]

The present invention relates to a semiconductor device in which a high thermal conductive ceramics is inserted between a semiconductor element and a heat sink metal made of a metal for insulation separation, and the ceramics end portion is covered with a metal frame, and the frame is used as the heat sink. In the semiconductor device, the ceramics are connected to a heat sink by connecting them.

Furthermore, the present invention resides in that pure copper or a metal foil softer than pure copper is interposed between the ceramic and the heat sink.

Ceramics such as silicon carbide, silicon nitride, aluminum nitride, etc., which have a thermal conductivity of 0.05 cal / cm, sec · ° C or higher at room temperature, and a coefficient of thermal expansion at room temperature of 5 × 10 ^-6 / ° C or lower. Is preferred. Particularly, it is preferable that the thermal conductivity is 0.2 cal / cm, sec. ° C. or higher. Further, it may be an alumina or zirconia sintered body. In particular, the thickness of the ceramic is preferably 0.4 to 1 mm, and the effect of the present invention is greatly exhibited when the ceramic has a size of 10 mm square or more. Therefore, preferable results are obtained especially for 10 to 30 mm square.

The heat sink is preferably made of metal, particularly preferably copper or aluminum. The plate-shaped or heat-dissipating fin, and the metal foil interposed between the ceramic and the heat sink are made of pure copper or a softer material. Specifically, Cu, Al, Sn, Pb,
Au, Ag, Ni, Zn and the like are preferable, and a thickness of 0.01 to 0.5 mm is preferable. Particularly, 0.1 to 0.2 mm is preferable.

The above-mentioned problem is caused by residual stress caused by directly connecting ceramics such as SiC and AlN having a small coefficient of thermal expansion to a metal material having a large coefficient of thermal expansion with solder or Ag solder.

On the other hand, in a large power semiconductor device, one electrode is connected to a main electrode (Cu) by connecting a buffer plate such as Mo or W, which has a thermal expansion coefficient relatively close to that of silicon, with a brazing material. Generally, a method is used in which the spaces are electrically connected by pressure welding.

Therefore, the inventors have focused on the connection method in order to solve the above-mentioned object. That is, the ceramics on which the metallized layer is formed and the semiconductor element are connected by using solder, brazing material or the like as in the conventional method, but the ceramics are connected by pressure welding to the metal material such as the heat sink.

[Function] Since the coefficient of thermal expansion of ceramics such as SiC and AlN is almost the same as that of the material silicon of the semiconductor device, the conventional method can be used as it is for connecting them, and there is no particular problem.

On the other hand, when connecting ceramics such as SiC and AlN with heat sink materials, generally Cu-based and Fe-based metallic materials through solder or Ag solder, residual stress is different from conventional Al ₂ O ₃ stress. This causes a crack. The larger the size of the ceramics, the higher the rate of occurrence of this phenomenon, and in reliability tests such as the heat cycle test, the occurrence of cracks was observed in the early stage. Therefore, by connecting the heat sink material and the ceramics with a pressure welding structure without using a brazing material or the like, a soft metal material such as Al or Cu foil is inserted between the metallized SiC or AlN ceramics and the heat sink material, and the ceramics end is connected. Higher adhesion between the ceramic and the heat sink can be obtained by connecting the frame itself configured to cover the part to the heat sink. According to this method, even if the metal material is heated and stretched, it does not affect the ceramics and cracks do not occur. On the other hand, this method slightly lowers the thermal conductivity between the ceramics and the heat sink, but since SiC and AlN ceramics are 4 to 8 times higher than Al ₂ O ₃ , it does not cause a problem.

〔Example〕

FIG. 1 is a sectional view of a semiconductor device showing an embodiment of the present invention. In an insulating semiconductor device in which the semiconductor chip 15 is insulated and separated by a sintered body 12 such as SiC or AlN, a soft metal that is deformed and relaxed by thermal stress such as Al or Cu foil in the ceramics 12 and the heat sink 10. Insert a buffer plate 11 consisting of, and connect the ceramics 12 and the heat sink 10 with a metal frame.
The end portion 14 of 13 is pressure-contacted and fixed by adhering the end portion 14 to the heat sink 10 by a percussion method, solder or the like.
Although a solderable metallization layer is formed on the main surface of the ceramic on which the semiconductor chip 15 is mounted, it is not necessary to solder the back surface in contact with the buffer plate 11 in the present invention. The buffer plate 11 is not limited to the two types of Al and Cu foils, and may be any soft, good heat conductor full-layer foil such as Ag or solder foil. On the other hand, the material of the heat sink may be any of Cu, Fe, Al and the like which are generally used in semiconductor devices.

FIG. 2 is a sectional view showing an example of another power semiconductor device. The concave portion 20 of the heat sink 10 is provided, and the cushion plate 11 and
The ceramics 12 is dropped and the frame is adhered to the ceramics so as to press the ceramics.

The recess 20 facilitates positioning of the ceramic 12, and the depth thereof may be such that the ceramic can be positioned.

Although the embodiment of the present invention has been described with reference to the example of the power semiconductor device (thyristor), a semiconductor module or hybrid IC or high voltage IC, LSI, in which other electronic components such as a resistor or a capacitor other than the semiconductor chip are mixedly mounted, It can be used as a board on which VLSI, ECL, etc. are mounted.

All of the SiC or AlN sintered bodies used as the ceramics 12 contained 2% by weight of BeO and were manufactured by hot press sintering. The former is about 0.7 cal / cm, sec ・ ° C at room temperature.
And the latter has a thermal conductivity of 0.3 cal / cm, sec · ° C. As these sintered bodies, those having a thickness of 0.6 mm and a size of 15 mm square were manufactured.

In the metal frame 13, the end of the sintered body 12 is 2 mm in the metal frame.
As described above, the contact is made over the entire circumference, and the cushion plate 11 made of Al having a thickness of 0.1 mm and the same size as the ceramics 12 is interposed so that the pressure is slightly increased. Connected. Therefore, the ceramic 12 can be brought into close contact with the heat sink 10 and the heat radiation effect can be improved. The metal frame 13 may be both ends of the sintered body. The semiconductor element 12 is a metal frame made of Au-Si solder, Au-Ge solder, Au-Sn solder, Pb-Sn solder, etc.
It can be bonded on the ceramic either before or after connection of 13. When the semiconductor element 15 is joined to the SiC ceramics 12 by soldering, a reaction layer is formed by metallizing with a Cr paste, and then Ni and Cu are plated on the reaction layer and joined by soldering. Further, in the case of joining with an Au-based alloy, it can be joined directly by containing 10% or less of Cd.

FIG. 3 is a sectional view of a power semiconductor device showing another embodiment of the present invention. SiC, AlN The portion of the main surface of the ceramic such as the aforementioned sintered body that contacts the metal frame 13 and the entire back surface
A metal film 30 having a soft thickness of 5 to 30 μm such as Al is formed. This metal film 30 is provided on the back surface to efficiently transfer the heat of the ceramic surface to the buffer plate 11, and Al or the like that does not react with the buffer plate 11 is preferable. Further, the metal film 30 provided on a part of the main surface is for effectively contacting the metal frame 13 and the ceramic 12 and may be basically the same as the Al on the back surface. It may be a Cu-based or Au-based soft metal that is formed.

The buffer plate 11 in FIG. 2 of the present invention can also be implemented by using a low melting point metal that is solid at room temperature to 50 ° C. and then becomes a fluid. In this case, when the semiconductor device is in operation, the buffer plate 11 becomes a liquid, and similar to the boiling cooling structure, it can be a medium for efficiently transmitting the heat of the semiconductor device mounted on the ceramic to the heat sink.

On the other hand, the buffer plate 11 important for carrying out the present invention is Pb, Sn, In, B.
A low melting point alloy composed of a metal selected from i, Cd, etc., having a liquidus point in the range of 65 to 150 ° C. is preferable. Specifically, Bi42.5-67 wt%, Pb17.2-40.2 wt%, Sn0-5
Any alloy selected from 0% by weight, In0 to 50% by weight, and Cd0 to 12.5% by weight may be used.

By using the insulating substrate made of the material as described above, it is possible to effectively radiate heat from the semiconductor device that generates heat.

〔The invention's effect〕

According to the present invention, since a pressure contact structure that avoids a direct connection between the ceramics and a metal material having a relatively large coefficient of thermal expansion is adopted, even a ceramic having a relatively small coefficient of thermal expansion such as SiC or AlN can be easily connected. And large ceramics can be used. This also has the effect of facilitating the design related to heat dissipation of the semiconductor module in which a different number of electronic components are mounted together.

[Brief description of drawings]

1, 2 and 3 are vertical sectional views of a power semiconductor device showing an embodiment of the present invention. 10 ...... Heat sink, 11 ...... Buffer plate, 12 ...... Ceramics, 13 ...... Frame, 14 ...... End part (joint part), 15 ...... Semiconductor chip, 16 ...... Cathode terminal, 17 ...... Gate terminal,
18 …… Anode terminal, 20 …… Concave, 30 …… Metal film.

Front Page Continuation (72) Inventor Koichi Inoue 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture, Hitachi Research Laboratory Ltd. In the laboratory (56) Bibliography Showa 60-79752 (JP, U) Showa 59-3580 (JP, Y2)

Claims (2)

[Claims] 1. In a semiconductor device in which a high thermal conductivity ceramic is inserted between a semiconductor element and a heat sink metal made of metal to be insulated and separated, the end portion of the ceramic is covered with a metal frame, and the frame is used as the heat sink. A semiconductor device, wherein the ceramics is connected to a heat sink by connecting. 2. In a semiconductor device in which a ceramic having a high thermal conductivity is inserted between a semiconductor element and a heat sink made of metal for insulation separation, pure copper or a metal foil softer than pure copper is interposed between the ceramic and the heat sink. And cover the ceramic end with a metal frame,
A semiconductor device, wherein the ceramics is connected to a heat sink by connecting the frame to the heat sink.