Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2002-04-25
2003-12-09
Fabahy, Wael (Department: 2814)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S118000, C438S122000
Reexamination Certificate
active
06660566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat conductive molded body requiring a high thermal conductivity, a manufacturing method thereof and a semiconductor device. Particularly, it relates to a heat conductive molded body effectively radiating heat generated from semiconductor elements, power supply or light source used for electric apparatuses, a manufacturing method thereof and a semiconductor device that has excellent heat radiation qualities.
2. Prior Art
Conventionally, soft sheet heat conductive molded bodies made of silicone rubber or the like have been used for conducting heat transmission between heat generating semiconductor devices or electronic components, and heat transmission members for radiating. In order to enhance the thermal conductivity, these heat conductive molded bodies are made by blending with high heat conductive metals such as silver, copper, gold, aluminum, nickel or their alloys and compounds, powder fillers made of ceramics such as aluminum oxide, magnesium oxide, silicon oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, or power particle form or fiber form heat conductive fillers such as carbon black or diamond.
A sheet heat conductive molded body wherein graphite carbon fiber, as heat conductive filler, is blended with silicon rubber or the like is known. On the other hand, the Japanese Patent Laid-Open No. HEI 9-283955 proposes a heat radiation sheet wherein graphite carbon fiber having the average aspect ratio of less than 3 is dispersed in a matrix such as silicon rubber. As ordinary graphite carbon fiber presents the an isotropy, this invention resolves the an-isotropic thermal conductivity in thickness and in plane direction, by specifYing a small aspect ratio of graphite carbon fiber and thus dispersing its fiber direction at random. However, though this method reduces the an isotropy, its thermal conductivity in the thickness direction has been insufficient. Moreover, as raw material, graphite carbon fiber having an aspect ratio of less than 3 could not always be produced easily at a low price.
On the other hand, the Japanese Patent Publication No. SHOU 50-29939 discloses a manufacturing method of a fiber reinforced complex for orientating the magnetic field using the diamagnetic anisotropy of graphite whisker or carbon fiber. The method of the present invention consists in improving the tensile strength and the elastic module of a rigid complex, namely in enhancing its mechanical strength.
Moreover, a manufacturing method wherein a high polymeric composite made of ferromagnetic material and a high polymeric substance is heat molded under a magnetic atmosphere, and its sheet molded product are known. For instance, the Japanese Patent Laid-Open No. SHOU 49-51593 discloses a basic manufacturing method for hardening a mixture of electric conductive magnetic powder and insulation material in fluid state by applying an external magnetic field. According to the Japanese Patent Laid-Open No. SHOU 53-53796, an an-isotropic electric conductive sheet can be obtained by a manufacturing method for magnetically orientating magnetic linear elements in the sheet thickness direction. The Japanese Patent Publication No. HEI 4-74804 relates to an an-isotropic electric conductive rubber sheet of specific hardness and specific thickness wherein an unhardened complex containing, as major constituents, electric conductive ferromagnetic particle of specific particle diameter and insulate high-polymer .elastic element, is magnetically treated and cross-linked.
However, any of molded bodies obtained by these conventional methods using the magnetic field does not intend to improve the thermal conductivity, and they have been applied mainly to the high strength complex, an-isotropic electric conductive pieces or pressure-sensitive electric conductive pieces.
In other words, various problems such as electrochemical migration acceleration, wiring or pad portion corrosion acceleration provoked by large heat generation from electronic components including semiconductor devices, component material cracking or destruction provoked by the thermal stress, and damaging of the electronic component reliability or life by peeling of the interface of component material junctions, have been occurring, because heat conductive molded bodies presenting a good thermal conductivity in any direction such as thickness direction or plane inside direction have not been developed.
EMBODIMENTS OF THE INVENTION
In order to resolve problems mentioned above, the present invention presents a heat conductive molded body effectively radiating heat generated from semiconductor devices, a power supply, a light source or other components used for electric apparatuses, a manufacturing method thereof and a semiconductor device that has excellent heat radiation qualities.
In other words, the present invention relates to a heat conductive molded body, wherein a diamagnetic filler having a thermal conductivity of 20 W/m·K or more is orientated in a fixed direction in high polymer.
In addition, it relates to a manufacturing method of the heat conductive molded body, wherein a magnetic field is applied to high polymer composition containing the diamagnetic filler having a thermal conductivity of 20 W/m·K or more, and a diamagnetic filler contained in the composition is orientated and hardened in a fixed direction.
Another invention relates to a semiconductor device, wherein a heat conductive molded body, composed by orientating a diamagnetic filler having a thermal conductivity of 20W/m, K or more in a fixed direction in high polymer, is interposed between a semiconductor elements and a heat conductive member. The diamagnetic filler means a filler of negative specific magnetic susceptibility, namely a filler whose magnetism is magnetized in a direction opposite to the magnetic field when a magnetic field is applied. To be more specific, there are bismuth, copper, gold, silver, mercury, quartz and their alloys or compounds, water, graphite, carbon fiber, salts, and many organic compounds. Among metals, it is known that bismuth presents the maximum diamagnetism; however, it is not preferable as diamagnetic filler used for the present invention, because bismuth thermal conductivity is less than 20W/m*K. Water, salts and organic compounds are also inappropriate.
The diamagnetism of diamagnetic filler is very weak compared to the magnetism of ferromagnetic material; however, the heat conductive molded body and semiconductor device of the present invention are characterized by that a diamagnetic filler having a thermal conductivity of 20 W/m° K. or more is orientated in a fixed direction in high polymer. As diamagnetic filler having a thermal conductivity of 20 W/m·K or more, especially copper, gold, silver, mercury and graphite are preferable. Among them, the use of a graphite having a thermal conductivity of 200 W/m·K or more at least in a fixed direction makes it possible to obtain an excellent heat conductive molded body having an especially high thermal conductivity and a semiconductor device excellent in heat radiation characteristics.
The diamagnetic filler having a thermal conductivity of 20 W/m·K or more, when filled abundantly in high polymer matrix and orientated in a fixed direction, increases the high heat conductivity of the diamagnetic filler orientated in the heat conductive molded body in the orientated direction. However, in practice, such abundant filling may provoke the increasing of the compound viscosity excessively, or the difficulty to eliminate mixed bubbles. At higher levels of the compound viscosity, it is more difficult to orientate the diamagnetic filler.
Consequently, though it can be decided arbitrarily according to the nature of diamagnetic filler and high polymer matrix or compounding agents to be used, and the characteristics of the intended final product, the concentration of diamagnetic filler in the heat conductive molded body is preferably 5 to 80% in volume. If the concentration is less than 5% in
Fabahy Wael
McGlew and Tuttle , P.C.
Pizarro-Crespo Marcos D.
Polymatech Co. Ltd.
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