Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
1999-09-29
2001-11-13
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S706000, C257S711000, C257S713000
Reexamination Certificate
active
06316826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor mounting package for mounting one or a plurality of high power semiconductor chips such as high power transistors and microwave monolithic ICs (MMIC).
2. Description of the Background Art
As output power and operation frequency of a semiconductor chip have been improved, amount of heat generated from the semiconductor chip has been increasing. Further, there is a strong demand in the market to reduce the size and weight of electronic equipments, and therefore packaging density of semiconductor chips has been made higher and higher. Therefore, devices mounting semiconductor chips have been required to satisfy severe conditions of heat radiating characteristic.
In a device of which heat radiating characteristic is required, a material having high thermal conductivity is used as a heat sink to form a substrate, the semiconductor chip is mounted thereon, and heat generated from the semiconductor chip is effectively diffused to prevent overheating of the semiconductor device.
Conventionally, AlN (aluminum nitride) and BeO (beryllium oxide) have been widely used as materials of the heat sink. BeO is disadvantageous in that it has an insufficient heat radiation characteristic and poor machinability, as well as strong toxicity. Though AlN is not toxic, its heat radiation characteristic is poor, and therefore it is not a satisfactory substitute for BeO.
Japanese Patent Laying-Open No. 7-99268 discloses a ceramic package having improved heat radiation characteristic, by adhering a Cu plate on a BeO or AlN substrate. It has been difficult, however, to ensure sufficient heat radiation even by this ceramic package.
Among substances, diamond has the highest thermal conductivity, and hence it is an ideal material to be used as a substrate for the semiconductor chip to lower heat resistance of the device mounting the semiconductor chips such as described above. The problem is that diamond is too expensive for this use.
Chemical vapor deposited diamond which has been under development recently is advantageous in that it allows synthesis over a large area as compared with natural diamond or diamond grown by high pressure and high temperature method and that it is inexpensive. Coefficient of thermal expansion of chemical vapor deposited diamond, however, is smaller than that of the semiconductor chips to be mounted on the substrate formed of the chemical vapor deposited diamond, leading to a problem that after the semiconductor chips are mounted by brazing on the substrate formed of the chemical vapor deposited diamond, the chip cracks.
In view of the foregoing, the inventors of the present invention have proposed in Japanese Patent Application No. 10-6238 (filed on Jan. 16, 1998), a heat spreader in which a substrate of Si (silicon), SiC (silicon carbide) or AlN (aluminum nitride) is coated with thin diamond. The heat spreader two-dimensionally diffuses heat generated film the semiconductor chips through the thin film of diamond, whereby the heat can be dissipated. Further, as the diamond is formed in the form of a thin film, manufacturing cost of diamond is low and effective coefficient of thermal expansion at the surface of the diamond increases, which prevents destruction of the chip at the time of brazing of the semiconductor chips.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor mounting package which can improve heat radiating characteristic of a package utilizing diamond, improve cost efficiency and meet increase output of the semiconductor chips to be mounted thereon.
The semiconductor mounting package in accordance with an aspect of the present invention includes one or a plurality of diamond members having one surface (e.g. a first surface) on which one or a plurality of semiconductor chips are mounted and the other surface (e.g. a second surface) opposed to the first surface, and a high thermal conductivity metal member adhered on the aforementioned second surface of the diamond member.
According to another aspect of the present invention, the semiconductor mounting package includes one or a plurality of diamond coated members having one surface (e.g. a first surface) at least partially formed of diamond and on which one or a plurality of semiconductor chips are mounted, and the other surface (e.g. a second surface) opposed to the first surface, and a high thermal conductivity metal member adhered on the aforementioned second surface of the diamond coated member.
In the semiconductor mounting package in accordance with the present invention as described above, the high thermal conductivity metal member is used in order to assist heat spreading effect of diamond. This contributes to reduced amount of diamond used, and maintains or improves heat radiation characteristic of the package as a whole. Therefore, the cost efficiency of the overall semiconductor mounting package can be improved, allowing for increased heat radiation from the semiconductor chips mounted thereon.
When the diamond coated member is used as the member on which the semiconductor chips are to be mounted, it is preferred that the diamond coated member includes a base material and a diamond coating layer formed on a surface of the base material. Here, it is preferred that one surface of the diamond coated member is formed of the diamond coating layer.
In the semiconductor mounting package in accordance with the present invention, preferably, the diamond member or the diamond coating layer is manufacture or formed by chemical vapor deposition method. Chemical vapor deposition method enables formation of diamond having high thermal conductivity over large area at a low cost. Though there are various methods of chemical vapor deposition proposed, any method may be adopted provided that diamond of sufficient area and preferably having thermal conductivity of at least 1000W/m·K can be obtained. For example, microwave plasma assisted CVD method, combustion flame method and hot-filament CVD method may be used.
When the diamond member is used as the member on which the semiconductor chips are to be mounted, it is preferred that the diamond member has the thickness of at least 100 &mgr;m and at most 500 &mgr;m. When the diamond coated member is used as the member on which the semiconductor chips are to be mounted, it is preferred that the diamond coated layer has the thickness of at least 10 &mgr;m and at most 200 &mgr;m.
The base material on which the diamond coating layer is formed preferably includes at least one selected film the group consisting of silicon, aluminum nitride, silicon carbide, copper-tungsten alloy, copper-molybdenum alloy and copper-tungsten-molybdenum alloy.
In the semiconductor mounting package in accordance with the present invention, as to the thermal conductivity of the high thermal conductivity metal member, the higher the better. Preferably, it is at least 300W/m·K and, more preferably, 350W/m·K for sufficient effect.
In the semiconductor mounting package in accordance with the present invention, preferably, the high thermal conductivity metal member includes at least one selected from the group consisting of copper, copper alloy, gold and gold alloy. Further, the material of the high thermal conductivity metal member preferably includes a sintered body. Among the materials listed above, the most preferable is copper, which has highest thermal conductivity and low cost, to be used as the high thermal conductivity metal member.
If the thickness of the high thermal conductivity metal member is too thin, the effect of heat spreading cannot sufficiently be exhibited. When the thickness of the high thermal conductivity metal member is too thick, heat resistance in thickness direction will be too high, degrading heat radiating characteristic of the overall package. Therefore, preferable thickness of the high thermal conductivity metal member is at least 20 &mgr;m and at most 3 mm and, more preferably, at least 40 &mgr;m and at most 1 mm.
In the semiconductor mou
Imai Takahiro
Yamamoto Yoshiyuki
Fasse W. F.
Fasse W. G.
Flynn Nathan
Sefer Ahmed N.
Sumitomo Electric Industries Ltd.
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