Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1998-11-05
2001-02-20
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S703000, C361S704000, C361S709000, C361S717000, C361S718000, C257S706000, C257S707000, C257S714000, C174S016300, C165S080400, C165S104330
Reexamination Certificate
active
06191944
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heat sink for eliminating heat produced by a device such as an electrical and electronic device, in particular a semiconductor chip such as an integrated circuits, or a casing for such an electric/electronic device.
To date, a conventional cooling apparatus or heat sink is made of metals, metal alloys, metal composites or the like. Concrete examples of materials include aluminum and metal matrix composites. In order to be able to radiate heat produced by the device being cooled as rapidly and completely as possible to the surrounding environment, the heat sink should exhibit a greatest possible contact surface towards the ambient atmosphere. To meet this requirement, conventional heat sinks are formed with a number of contoured areas such as ribs, knobs or like so that the heat sinks receive a relatively large surface at comparable small mass. Still, metallic heat sinks of this type have the drawback of a significant mass and size. Moreover, it should also be taken into consideration that the performance of electronic components steadily increases in modern microelectronics, resulting in an increased production of dissipated heat to be eliminated. At the same time, the mentioned power increase is accompanied by a desire to minimize the size of the components.
In order to reliably and effectively carry away increasing amounts of lost heat by use of a heat sink of the above-stated type, this heat sink must be dimensioned of relatively great size and volume, resulting in greater geometric sizes of the electric and/or electronic devices which incorporate the component to be cooled so that the achievements of the microelectronics, namely the manufacture of particularly small and thus practical devices (e.g. mobile telephones or portable computers) by means of especially small and powerful components are defeated.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved heat sink, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved heat sink which is capable to efficiently absorb dissipated heat generated in particular by semiconductor chips.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by forming the heat sink from a material including whiskers.
Through the provision of whiskers, that heat sink is provided with an especially large surface to enable a particularly rapid radiation of dissipated heat from the heat sink to the ambient atmosphere.
Suitably, the material of the heat sink is identical to the material of the component being cooled. Thus, the coefficient of thermal expansion between heat sink and component being cooled are matched, thereby preventing tensions in the joint between the component and heat sink and effectively eliminating the risk of detachment of the heat sink from the component as a result of temperature fluctuations.
Preferably, the heat sink has a substrate in heat conductive connection with the component being cooled, whereby the whiskers grow on the substrate. A substrate which has whiskers can be effectively and easily connected in a heat conductive manner with the component being cooled.
According to a further feature of the invention, the substrate as well as the whiskers are each made of a semiconductor material.
In practice, e.g. in modern microelectronics, electronic components to be cooled are frequently made of a semiconductor material. A heat sink formed from a semiconductor material is especially suitable for attachment to such components because of matching coefficients of thermal expansion between the heat sink and the component itself. The heat sink can thus be directly attached to the component being cooled, without risking development of tensions in the joint between the component and the heat sink as a result of temperature fluctuations. Suitably, the whiskers are so dimensioned that the ratio of length to diameter of the whiskers is greater than
10
. These geometric dimensions impart the heat sink with a particularly large surface and thus with particularly good heat dissipation properties.
Preferably, a cover is affixed to the substrate to at least partially envelope the whiskers, whereby the substrate and the cover form a space which is filled, at least partially, with a liquid, such as water or alcohol. Thus, the whiskers are in particular capable to eliminate heat absorbed from the component being cooled so that the overall efficiency of the heat sink according to the invention is improved.
According to another feature of the present invention, the heat sink has a first zone for attachment of the component being cooled, and a second zone which is capable of being cooled. The heat sink according to the invention can thus be operated as so-called “heat pipe”, i.e, the liquid is vaporized by heat emitting from the component being cooled, whereby this vapor is moved to the coolable zone of the heat sink to condense there as a result of a cooling action taking place there. By this system, heat can be carried away particularly efficiently from the component being cooled.
Suitably, the area of coolable zone of the heat sink is provided with a fan. This apparatus is of very simple structure and commercially available as a standard piece so that the use of a fan for cooling the heat sink realizes in a particularly simple and cost-efficient manner the above-mention “heat pipe function”.
According to still another feature of the invention, the component to be cooled is a semiconductor chip, such as an integrated circuit, with the heat sink being affixed eutectically upon the semiconductor chip. The provision of a eutectic joint produces a particularly good heat conducting connection between the component being cooled and the heat sink because the joint is largely made from the material of the heat sink, so as to realize as a whole a particularly efficient transport of the dissipated heat from the component to the ambient atmosphere.
It is a further object of the invention to provide a casing for an electric and/or electronic device which has attached thereon a heat sink, with the casing being so constructed as to minimize the impact on the heat transfer from heat sink to the ambient atmosphere.
In accordance with the present invention, this object is attained by providing the casing with an opening in which the heat sink is received at least partially, preferably in its entirety.
Thus, the heat sink is in direct contact to the ambient atmosphere, enabling a direct transfer of lost heat thereto. Consequently, a significant deterioration of the heat transfer efficiency resulting from a multi-staged heat transfer from heat sink to the casing atmosphere, from there to the casing material and from there to the ambient atmosphere, is prevented. Still, the heat sink is effectively protected by the casing from mechanical impacts.
Suitably, the heat sink is made of a semiconductor material. As stated above, the advantages of such a heat sink reside primarily in the fact that the coefficient of thermal expansion of the component to be cooled and oftentimes also made of semiconductor material and the coefficient of thermal expansion of the heat sink are very much alike so that the heat sink can be positioned directly upon the component.
REFERENCES:
patent: 3706127 (1972-12-01), Oktay et al.
patent: 4593661 (1986-06-01), Brander
patent: 4612601 (1986-09-01), Watari
patent: 5368094 (1994-11-01), Hung
patent: 5858537 (1999-01-01), Brown et al.
patent: 046 605 A2 (1982-03-01), None
patent: 718 883 A3 (1990-11-01), None
patent: 362024730 (1987-02-01), None
patent: 90/12769 (1990-11-01), None
Römpp Chemical Dictionary 9, expanded and revised edition, by Prof. Dr. Jürgen Falbe and Prof. Dr. Manfred Regitz, Georg Thieme Verlag Stuttgart-N.Y., vol. 6, p. 5039.
“Whisker Technology”, New York 1970, by A. P. Levitt, publishing house Wiley-Interscience.
“Transactions of the Metallurgical Society of AIME (The Vapor-Liquid-Solid Me
Hammel Ernst
Holzer Hermann
Chervinsky Boris
Electrovac, Fabrikation elektrotechnischer Spezialartikel Gesell
Feiereisen Henry M.
Picard Leo P.
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