Coating processes – Applying superposed diverse coating or coating a coated base
Reexamination Certificate
2000-05-25
2001-08-07
Turner, Archene (Department: 1775)
Coating processes
Applying superposed diverse coating or coating a coated base
C419S010000, C419S011000, C419S023000
Reexamination Certificate
active
06270848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat sink material for releasing heat from a semiconductor component, and to a method for fabricating the same. The present invention also relates to a semiconductor device package or to a heat-release jig equipped with a heat sink formed of the inventive material
2. Background Art
Copper (Cu) is known as a typical material for use as a heat sink. However, although Cu has a relatively high thermal conductivity of 398 W/mK, the coefficient of thermal expansion is also large, having a value of 17 ppm/°C. Thus, when Cu is joined with a semiconductor, such as silicon (Si) having a coefficient of thermal expansion of 4.2 ppm/°C. or gallium arsenide (GaAs) having a coefficient of thermal expansion of from 6 to 7 ppm/°C., both of the joined materials suffer a large thermal stress in the cooling process from the joining temperature to room temperature, or in the cooling process from the maximum temperature achieved during the operation of the semiconductor component to room temperature. In many cases, such a large thermal stress makes the component unfeasible for use. In the light of such circumstances, alloys of Cu with a material having small coefficient of thermal expansion (e.g., W (tungsten) or Mo (molybdenum)), such as CuW and CuMo are used. That is, design of a heat sink material which matches the semiconductor package is made possible by using a material whose coefficient of thermal expansion is controllable. In such cases, however, the alloy becomes inferior to Cu in terms of thermal conductivity, i.e., having a value of about 200 W/mK, because the metals (W or Mo) alloyed with Cu have small thermal conductivity.
Diamond has the highest thermal conductivity in the temperature range of from room temperature to the high temperature region of 200° C. Moreover, the coefficient of thermal expansion thereof in the vicinity of room temperature is about 1.5 ppm/°C., which is smaller as compared with ordinary semiconductor materials such as Si and GaAs.
Therefore, it has been thought of using metallic materials containing particles of diamond embedded therein having such superior characteristics.
The idea of embedding diamond particles is disclosed in, for example, JP-A-Sho62-249462 (the term “JP-A-” as used herein signifies “an unexamined published Japanese patent application”), JP-A-Hei2-170452, JP-A-Hei3-9552, JP-A-Hei4-231436, JP-A-Hei4-259305, JP-A-Hei5-291444, and JP-A-Hei5-347370.
Disclosed in JP-A-Sho62-249462 is a material in which diamond is incorporated in a resin to improve thermal conductivity. However, since a resin generally is a poor conductor of heat, the thermal conductivity as a whole is not much improved.
Disclosed in JP-A-Hei2-170452, JP-A-Hei4-231436, JP-A-Hei4-259305, and JP-A-Hei5-347370 is disclosed a material comprising diamond particles embedded in a metallic matrix. Gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), etc., are used for the metallic matrix.
Also known (see H. L. Davidsonet et al., IEEE (1995), pp. 538) is a material based on diamond, which is prepared by subjecting diamond to special coating with a metal, and then impregnating the resulting material with an alloy of Cu and Ag.
All of the cases described above comprises incorporating diamond particles into a metallic matrix. That is, the diamond particles are separated from each other with a metallic material interposed therebetween. Accordingly, heat should also be transferred by the metallic material, that is, by a material sequence ordered in the order of diamond/metal/diamond/metal/ - - - . This structure is disadvantageous not only because thermal conductivity is impaired by the junction formed between diamond and the metallic material, but also because the sample itself cannot be shaped easily due to the weak bonding at the junction between diamond and the metallic material. In fact, the thermal conductivity achieved by a conventional heat sink was found to be 400 W/mK at best.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a heat sink for use with a semiconductor component, having a coefficient of thermal expansion well comparable to that of a semiconductor material and yet having high thermal conductivity.
Another object of the present invention is to provide a semiconductor device package which effectively releases heat upon its assembly and when the semiconductor component is in operation.
As a result of extensive study of the present inventors, it has been found that, by utilizing a material comprising a plurality of diamond particles previously connected with each other by a metal carbide and having an interstitial metal, a heat sink for use with a semiconductor component having a coefficient of thermal expansion close to that of the semiconductor material and having an extremely high thermal conductivity can be obtained.
Thus, the heat sink material for use with a semiconductor component according to the present invention comprises a plurality of diamond particles, a metal, and a metal carbide, wherein the metal carbide and diamond particles constitute the matrix, and the metal fills the interstices of the matrix.
The phrase “material comprising a metal carbide and diamond particles constituting a matrix” as referred to herein signifies a “material comprising a plurality of diamond particles connected together by a metal carbide”. More specifically, this material maintains the connected structure of diamond particles and metal carbide even when the metal of the heat sink is molten.
The basic concept of the present invention is that the diamond particles are not buried in metal, but that a metal carbide (or a metal carbide and graphite) is formed (grown) on the surface of the diamond particles to connect them together, which combination is then impregnated with a metal (Cu, Ag, Au, or Al). Briefly, the concept is more like a case of forming sintered diamond, and then incorporating an interstitial metal. The only difference is that the diamond particles themselves are not bonded together; thus, this material is different from sintered diamond.
Concerning the structure, the diamond particles are incorporated in the matrix of a metal carbide such as TiC, ZrC, or HfC, and a metal fills the interstices of the matrix comprising the diamond particles and the metal carbide. Thus, it can be seen that the structure of the heat sink for use with a semiconductor component according to the present invention greatly differs from the conventional one in which diamond particles are buried in a metal. More specifically, if metal is removed from a conventional heat sink material for a semiconductor component, the diamond particles become disunited. In contrast to this, the diamond particles remain connected to each other in the heat sink according to the present invention.
In the conventional case, furthermore, a metal is always incorporated between each pair of diamond particles. Although there may partly be such a component in the heat sink of the present invention, many parts consist of a metal carbide alone. That is, many parts consist of only metal carbide incorporated between different diamond particles, and the metal carbide is in contact with the surfaces of the different diamond particles.
In such a material, heat is transferred by lattice vibration alone. Thus, when compared with the conventional case in which heat is transferred by lattice vibration/electron/lattice vibration/electron - - - , it can be readily anticipated that a high thermal conductivity is achieved. Moreover, mechanical bonding strength is increased in such a case.
It is preferred to incorporate graphite in the matrix, because graphite may contribute to the improvement of thermal conductivity.
Preferably, the diamond particles have an average diameter of 60 &mgr;m or larger, but not more than 700 &mgr;m. If the diamond particles are less than 60 &mgr;m in average diameter, the thermal conductivity tends to become too low; if the diamond particles exceed 700 &mgr;m in average diameter
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
Turner Archene
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