Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-07-27
2001-07-03
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S430000, C524S440000
Reexamination Certificate
active
06255376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermally conductive compound which is suitable as heat transfer means which rapidly acts to transfer heat generated by the operation of a semiconductor integrated circuit element to a radiation part as well as a semiconductor device using the same.
2. Description of the Related Art
A semiconductor element, for example, semiconductor integrated circuit element, is tightly sealed up, for example, in a semiconductor element housing package to avoid contact with the air when used, and the resulting semiconductor device is connected electrically and mechanically to an outer electric circuit to use.
The semiconductor element housing package generally consists of an insulator body, in which a conductor wiring is formed in a prescribed pattern and on the surface of which a portion for mounting a semiconductor integrated circuit element (element mounting portion) is provided, and a cap which covers the element mounting portion and forms a hollow cut off from the outside between the body and a circumference provided at the part surrounding the element mounting portion on the upper surface of the body. The semiconductor integrated circuit element is then placed in the element mounting portion of the semiconductor element housing package, and then the cap is closely placed on a substrate surrounding the element mounting portion and adhered thereto with a heat curing resin, etc., to form a cell consisting of the insulator body and the cap. The semiconductor integrated circuit element is placed inside the tightly sealed hollow of the cell to make a semiconductor device.
In recent years, high integration of semiconductor integrated circuit elements considerably increases and there is a tendency to increase markedly the heating value during the operation of the semiconductor element, so it becomes an important problem to rapidly release heat generated by the semiconductor integrated circuits outside of the semiconductor device in order to prevent abnormal operation of the element arising from overheating.
In order to avoid this problem, a thermally conductive compound having high thermal conductivity is inserted between the upper surface of a semiconductor integrated circuit and the cap in the airtight sealed-up portion to make a practical structure, and a highly heat conductive material such as copper or aluminum is used as the cap material, or as an alternative method, a material for heat dissipation such as a radiation fin on the upper surface of the cap is provided so that heat generated by the semiconductor integrated circuit element is rapidly transferred to the cap, from which the heat was rapidly released outside.
When a cap made of copper or aluminum is used, however, a shearing stress is repeatedly added to the thermally conductive compound inserted between the semiconductor integrated circuit element and the cap of which the expansion/shrinkage rate is different, by the repeated rise and drop in temperature accompanied by the repeated work and rest of the semiconductor integrated circuit element, because the thermal expansion rate is greatly different between the cap and the semiconductor integrated circuit element mainly made of a silicon material (linear thermal expansion rate at 40° C. is 1.678×10
−5
/deg for copper, 2.313×10
−5
/deg for aluminum, and 2.4×10
−6
/deg for silicon) and in addition the thermally conductive compound is used in a state closely adhesive and chemically or physically linked to the cap and the semiconductor integrated circuit element in order to enhance the thermal conductivity at the surfaces of the thermally conductive compound with the cap and with the semiconductor integrated circuit element. As a result, it is afraid that the thermally conductive compound might be destroyed or the semiconductor integrated circuit might be destroyed by a reaction, or cracks or peeling-off might be produced at the surface of the thermally conductive compound with the circuit element or cap. Accordingly, a variety of thermally conductive compounds and semiconductor devices have been proposed because the merely high thermal conductivity is insufficient.
For example, Japanese Unexamined Patent Publication JP-A 61-29162 (1986) has proposed a semiconductor device that keeps in contact with a thermally conductive material, in which at least one of the upper surface of a pellet (semiconductor integrated circuit element) and the back surface of a cap or the back surface of the pellet and the upper surface of the substrate, to which the pellet is fixed, comprises silicon gel interposed between them, or silicon gel containing a filler consisting of alumina or silicon carbide. According to this device, by making a thermally conductive material comprising silicon gel interposed between the upper surface of the pellet and the backside of the cap, heat generated in the pellet can be released to the cap to effectively prevent overheat of the pellet. Moreover, since the silicon gel has elasticity, mechanical destruction such as occurrence of cracks on the pellet by temperature change can be avoided. Further it is also possible to release the heat more effectively by adding a filler comprising alumina or silicon carbide as a thermally conductive material with high thermal conductivity.
In addition, Japanese Unexamined Patent Publication JP-A 61-36961 (1986) proposes a multi-chip integrated circuit package which comprises a circuit substrate, a plural number of integrated circuit chips (semiconductor element) which are connected electrically or mechanically to the circuit substrate through a plural number of flexible leads provided in advance on the body, a plural number of heat radiating plate fixed to a plural number of integrated circuit chips in one-to-one correspondence through the first thermally conductive adhesive, a heat radiation cover which covers the chip-mounted surface and is fixed to a plural number of heat radiating plates through the second thermally conductive adhesive, and a heat sink fixed on the heat radiation cover. As for the thermally conductive adhesives, an epoxy adhesive containing a highly thermally conductive silver-filler and tin-lead eutectic solder are disclosed. According to this multi-chip integrated circuit package, heat generated by the integrated circuit chips is effectively transferred to the heat sink to effectively cool the chips, and the improvement of radiation characteristics can be attained.
In addition, Japanese Examined Patent Publication JP-B2 6-95557 (1994) has proposed a thermally conductive compound which comprises a liquid carrier selected from the group consisting of mineral oils and poly(&agr;-olefin) oil, thermally conductive filler particles which are dispersed in the liquid carrier so as to wet the particle surface, and a binder which has at least one functional group reacting with the surface of the thermally conductive filler particles and at least one functional group having the same polarity as the liquid carrier, the binder being selected from the group consisting of organosilanes, organotitanates, organoaluminates and organozirconates. According to the patent publication, the thermally conductive compound is a phase-stable and thermally conductive compound that contains a coupling agent (binder) selected from the group consisting of organometals which has at least a dielectric liquid carrier, highly thermally conductive fillers (used for filling) homogeneously dispersed in the carrier, and a functional group reacting with the particle surface and another functional group preferentially moistening the particles by self-coagulation. The compound is adaptable to any chip surface of which the roughness, slope and height are different, is able to moisten the surface, exhibits high filling density, maximizes the thermal conductivity, and maintains a homogeneous suspension to prevent phase separation. As a result, a thermally conductive compound that hardly causes phase separation, though the viscosity is lo
Maeda Toshihiko
Shikata Kunihide
Hogan & Hartson LLP
Kyocera Corporation
Michl Paul R.
LandOfFree
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