Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
2000-11-14
2003-02-11
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
C264S429000, C264S437000, C264S612000, C522S003000, C522S004000, C148S108000
Reexamination Certificate
active
06517744
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a curing composition for forming a heat-conductive sheet, a heat-conductive sheet, a process for producing the same, a method of bonding or adhering with the use of the heat-conductive sheet and a heat sink structure.
BACKGROUND OF THE INVENTION
In accordance with the enhancement of the performance of electrical or electronic equipment, there is a trend toward an increase of the number of electrodes used in semiconductor elements and toward an increase of the power consumption by semiconductor elements. Therefore, it is now of importance to efficiently release heat generated by parts of the electrical or electronic equipment.
In order to efficiently carry out the heat sink from semiconductor packages or semiconductors per se, attempts have been made to furnish them with a heat sink device or to effect a heat sink by means of a wiring board having'semiconductor elements mounted thereon. For example, the heat sink from semiconductor packages has generally been performed by natural convection over the surface of heating element body or forced convection by means of a fan disposed in the unit. This system has, however, a drawback in that, when the calorific value is increased in accordance with the enhancement of the function of semiconductor packages, the heat sink capability becomes unsatisfactory to thereby disenable surely preventing any deterioration of the performance of the semiconductor packages. Further, a system comprising a heat sink pressed against the surface of semiconductor packages so as to increase the heat sink by convection has been provided. In this system, however, the contact area of the mutually pressed surfaces of the semiconductor packages and the heat sink is -reduced because of the occurrence of clearance to thereby cause a problem in the exertion of heat sink effect as designed. Accordingly, for example, in the joining of a heat sink to semiconductor packages, it is performed to interpose, for example, a heat-conductive resin sheet therebetween and to, while adhering the semiconductor packages and the heat sink to each other, effectively attain a heat sink. Further, for example, in the joining of a semiconductor element to a heat spreader to be brought into contact therewith, it is performed to interpose a heat-conductive adhesive therebetween and to, while maintaining the bonding of the semiconductor element and the heat spreader to each other, effect the heat sink from the semiconductor element.
As a resin composition for heat conductivity increase or the like to be interposed between the semiconductor element or semiconductor package and the heat sink, for example, a silicone rubber sheet of a claylike thermocuring bonding type is employed in Japanese Patent Laid-open Publication No. 5(1993)-326916. This silicone rubber sheet has a drawback in that the heat conductivity thereof is not satisfactory from the viewpoint of coping with the increase of power consumption being encountered by semiconductor elements. For increasing the heat conductivity, it is performed to randomly disperse metal particles of high heat conductivity in the resin sheet of, for example, silicone rubber. For attaining a further increase of the heat conductivity, it is being tried to load the resin sheet with metal particles in high dispersion and in high filling ratio. However, even if the resin sheet is loaded with metal particles in high dispersion and in high filling ratio, there remain problems not only such that heat is diffused in random directions to thereby disenable satisfactorily increasing the heat conduction between the semiconductor element and the heat sink but also such that the loading with metal particles in high filling ratio causes the resin sheet to have poor tensile strength and poor elasticity and is further likely to cause the resin moldability to deteriorate.
Therefore, there has been a demand for the development of a heat-conductive sheet which is excellent in the anisotropic heat conduction in the direction of the thickness of the sheet (subject 1).
Japanese Patent Laid-open Publication No. 52(1977)-128465 discloses a process for obtaining an electrically conductive sheet while orientating fibers in the direction of the thickness of the sheet by the action of magnetic field.
On the other hand, when a semiconductor package is assembled in, for example, an electronic equipment product and utilized, it has been experienced that the degree of adherence of interposed resin sheet to the semiconductor element and the heat sink is deteriorated because of the suffering of the semiconductor package from vibration, shock, etc. from outside and because of the long-term irregular heat buildup by the semiconductor element, caused by the use of the electronic equipment product, to thereby render the heat sink unsatisfactory. Therefore, it has been demanded for the resin sheet interposed between the semiconductor element and the heat sink or the like to exhibit high heat conductivity and further to not only simply adhere them to each other but also achieve such a satisfactory bonding that these can resist vibration, etc. from outside.
A method of using a resin sheet in combination with an adhesive or a method wherein a highly adherent liquid epoxy resin or the like is applied to adherend surfaces and cured has been tried for improving the bonding between the semiconductor element and the heat sink or the like. However, the former method has a drawback in that the use of an adhesive causes the heat conductivity to deteriorate. The latter method has a drawback in that accurate coating must be effected on minute semiconductor.elements and, in the use of a two-pack epoxy resin, the addition proportion must be controlled to thereby cause the production process to be complex and lack simplicity.
Furthermore, a method comprising thermally curing, for example, a liquid resin for sheet to a semi-cured state, interposing the semi-cured resin sheet between joining surfaces of the semiconductor element and the heat sink or the like and fully curing the semi-cured resin sheet by heating to thereby bond the semiconductor element and the heat sink or the like to each other has been tried. However, this method has a drawback in that it is difficult to control the curing reaction of, for example, highly adherent epoxy resin so that it is terminated at a semi-cured state, thereby causing readily obtaining such a semi-cured product to be practically infeasible.
Therefore, there has also been a demand for the development of a semi-cured resin sheet which not only exhibits a high heat conductivity but also is excellent in the capability of.bonding a semiconductor element or the like and a heat sink means to each other and further can be readily shaped within a short period of time (subject 2).
On the other hand, apart from the demand of the subject 2, if the heat sink or the like is bonded to the semiconductor element to an inseparable degree, there occurs such a problem that, for example, upon finding of any defect in the semiconductor element, the heat sink or the like cannot be easily detached to thereby cause repairing of the semiconductor element to be difficult.
Therefore, there has further been a demand for the development of a heat-conductive sheet which not only exhibits a high heat conductivity but also adheres a semiconductor element or the like and a heat sink means to each other in a separable condition but with a satisfactory adhesive strength, that is, has a sticky surface (subject 3).
As apparent from the above, it is demanded for the heat-conductive sheet to not only exhibit a high heat conductivity but also have various additional functions such as high bonding capability and adherence permitting detachment. Furthermore, besides these demands, there is a demand for a heat-conductive sheet having excellent insulating capability so as to enable protection against electric shock, depending on the type of heating element, which may be experienced when heat sink is conducted on, for example, a circuit board whose sur
Hara Takeo
Iwanaga Shin-ichiro
Sato Hozumi
Setaka Ryoji
JSR Corporation
Kopec Mark
LandOfFree
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