Integrated circuit package with diamond heat sink

Details Integrated circuit package with diamond heat sink Integrated circuit package with diamond heat sink

1994-07-01

2002-10-15

Thompson, Gregory (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C257S675000, C361S723000

Reexamination Certificate

active

06466446

ABSTRACT:

BACKGROUND OF THE INVENTION
The ever-increasing demand for smaller, higher performance information systems has lead to the adoption of the integrated circuit (“IC”) as the information processing center of the modern computer. These integrated circuits, or chips, are typically housed within standard ceramic, plastic or metal packages and carry information between the chip and other information processing units within the system.
In one type of plastic encapsulated dual in-line package, such as the package
1
shown in
FIG. 1
, an integrated circuit chip
2
having a plurality of wire bonding pads
3
at its perimeter is fastened to a die substrate
4
which is held by two tie bars
5
embedded in thermoplastic molding compound
6
, such as a polyimide. A plurality of metal legs, or leads
7
are also embedded in the plastic compound
6
with (typically) nickel-plated wire bonding pads
8
at their inner ends. The leads
7
and substrate
4
are parts which have been separated from a lead frame in the course of assembly of the package
1
. Lead wires
9
are bonded to the pads
3
and the bonding pads
8
of the leads
7
to connect the chip
2
to the leads
7
, which provide electrical connection means to other circuit components.
Because electrical inefficiencies in the chip generate heat, the temperature of both the chip
2
and other parts of the package supporting the chip
2
significantly rise during use. It is known that such elevated temperatures can degrade the IC's performance. For example, because many of the IC's critical processes rely on electron kinetic phenomena which become accelerated by increased temperature, failures in metallization and bonded interfaces occur during extended use. Accordingly, heat production by the chip, often termed “thermal density”, has become a significant design consideration which threatens to limit the further miniaturization of information systems within reasonable cost constraints.
Conventional treatment of the thermal density problem has met with limited success. For example, in the prior art design shown in
FIG. 1
, heat generated by the chip is dissipated through the plastic molding, the die pads and the bonding wires connecting the chip and the legs of the lead frame. However, each of these thermal conduits is only marginally effective. In particular, the wires are poor thermal conduits because they have a small cross section (i.e., about 0.002 inch thickness). The die pads, while having a good cross section (i.e., about 0.010 inch thickness) are ineffective thermal conduits because they are truncated at each end of the IC package, and so there are no metal thermal paths available to the outside after the IC molding process. The plastic molding has an extremely low thermal conductivity. One present improvement in thermal dissipation connects a more thermally conductive, high surface area material (known as a “heat spreader”) to the chip. Although embedded heat spreaders succeed in dissipating hot spots on the chip, they do not significantly assist in removing heat from the package as a whole. Another present improvement involves blowing air across either the chip or attached heat spreader, thereby removing heat convectively from the package. Although this improvement succeeds in removing more heat from the package, it adds cost and requires geometry changes in the area around the package.
Therefore, it is the object of the present invention to provide a package which can provide electrical connection between the chip and the lead frame, yet still maintain the chip at low temperatures.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a plastic encapsulated integrated circuit package comprising:
a) a thermally conductive, electrically insulating resistive base,
b) an integrated circuit mounted on the base,
c) a plurality of legs in electrical connection with the integrated circuit, and wherein the base is in intimate thermal contact with both the integrated circuit and the plurality of legs of the lead frame.
Also in accordance with the present invention, there is provided an integrated circuit package comprising:
a) an integrated circuit,
b) a lead frame having a plurality of legs in electrical connection with the integrated circuit, and
c) a diamond film base, wherein the diamond film base is in intimate thermal contact with both the integrated circuit and the plurality of legs of the lead frame.


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Research Disclosure, “Electrical Resistive, Thermally Conductive Diamond Coating For Integrated Circuit Chips”, 4/88, No. 288, Kenneth Masch Publications Ltd, England, (361/713).*
Masato Tanaka, Yukiharu Takeuchi, Advanced Package Development, SHINKO Electric Industries Co., Ltd., 80, Oshimada-machi, Nagano City, 381-22 Japan,Thermal Analysis of Plastic QFP With High Thermal Dissipation, 1992 IEEE, pp. 332-339.

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