Heat-dissipating device for integrated circuit package

Details Heat-dissipating device for integrated circuit package Heat-dissipating device for integrated circuit package

1999-12-22

2001-06-19

Picard, Leo P. (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S688000, C361S707000, C361S709000, C257S706000, C257S707000, C257S796000, C165S080200, C165S185000

Reexamination Certificate

active

06249433

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to integrated circuit (IC) packaging technology, and more particularly, to a heat-dissipating device for use in an integrated circuit package for heat dissipation.
2. Description of Related Art
An integrated circuit package is used to enclose one or more semiconductor chips therein for easy handling and utilization. During operation of the semiconductor chips, however, electricity will cause the semiconductor chips to produce heat. If the heat is not effectively dissipated, it can cause damage to the internal circuitry or electronic components of the semiconductor chips. Therefore, there is a need for providing internal heat-dissipating means in the integrated circuit package for heat dissipation during operation. Conventionally, this can be achieved by embedding a heat sink or a heat block within integrated circuit package, or by directing a stream of cooled air or liquid against the semiconductor chips. When using a heat sink or a heat block, it is required to expose a part of the heat sink or heat block to the outside of the encapsulant for enclosing the semiconductor chip so that the heat can be dissipated to the atmosphere or another externally linked heat-dissipating means. In design, it is desired to increase the exposed area to the atmosphere and shorten the heat-conducting path from the heat-generating source to the exposed area for the purpose of increasing the heat-dissipating efficiency.
One drawback to the use of heat sink or heat block, however, is that, since such heat-dissipating devices are molded through stamping, the edges there of would be undesirably rolled over, which would cause the encapsulating resin used in the molding process to flash through these rounded corners to the exposed area of the heat-dissipating device and thereby covers a considerable part of the exposed area of the heat-dissipating device. This would degrade the heat-dissipating efficiency. Moreover, the flashed resin would cause the exposed area of the heat-dissipating device to lose planarity, making the heat-dissipating device unable to be linked securely to the external heat-dissipating means. The flashed resin can be removed through sanding or laser polishing, but such post-treatment would undesirably increase the overall manufacture cost and may easily cause surface damage to the integrated circuit package.
FIG. 6
is a schematic sectional diagram of an integrated circuit package incorporating a conventional heat-dissipating device. As shown, the heat-dissipating device
16
is a molded piece of a heat-conductive material, having a top side exposed to the outside of the encapsulant
17
. Further, the heat-dissipating device
16
is formed with a cutaway part
16
a
at the edge thereof. During the molding process, the cutaway part
16
a
can help prevent the melted encapsulation resin from flashing onto the exposed surface of the heat-dissipating device
16
. When the melted resin enters the cutaway part
16
a,
it would be increased in viscosity and thus reduced in flowability so that it would hardly flash. One drawback to this heat-dissipating device
16
, however, is that the cutaway part
16
a
is flat and narrow, which would nevertheless allow a small but considerable part of the melted resin to flash onto the exposed surface of the heat-dissipating device
16
.
One solution to the foregoing problem is depicted in FIG.
7
. As shown, in this heat-dissipating device, a metal layer
31
of silver or platinum is coated over the cutaway part
16
a.
The flashed encapsulation resin adheres to this metal layer
31
with a less strength than to the heat-dissipating device
16
; and therefore, the flashed resin over the exposed surface of the heat-dissipating device
16
, if any, can be easily removable during post-treatment. One drawback to this solution, however, is that the coating of the metal layer
31
over the cutaway part
16
a
of the heat-dissipating device
16
would make the overall manufacture process more complex, and thus would undesirably increase the manufacture cost. In addition, it would not prevent the flashing of the encapsulation resin over the exposed surface of the heat-dissipating device
16
.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide a heat-dissipating device for integrated circuit package, which can prevent the melted encapsulation resin from flashing over the exposed area of the heat-dissipating device.
It is another objective of this invention to provide a heat-dissipating device for integrated circuit package, which can help prevent outside moisture from entering into the integrated circuit package that would otherwise cause delamination in the integrated circuit package.
It is still another objective of this invention to provide a heat-dissipating device for integrated circuit package, which can help increase the heat-dissipating efficiency.
In accordance with the foregoing and other objectives, the invention provides an improved heat-dissipating device for integrated circuit package. The heat-dissipating device of the invention is made of a heat-conductive material, having an exterior side which is to be exposed to the outside of the integrated circuit package. The heat-dissipating device of the invention is characterized in the forming of a staircase-like cutaway part at the edge of the exterior side thereof, which is formed with a plurality of stepped surfaces.
During the molding process, when the resin flow enters into the first stepped surface, the resin flow would absorb the heat from the mold, thereby being increased in viscosity and thus reduced in flowability. Onwards, the resin flow flows into the next stepped surface, where, since the next stepped surface is smaller in depth than the first stepped surface, the resin flow would be further slowed down; and similarly, when the resin enters into the next stepped surface, it would be still further slowed down. Since the resin flow is reduced in flowing speed at the successive stepped surfaces, it would hardly flash onto the exterior side of the heat-conductive device. Therefore, the invention can prevent the resin flow from flashing onto the exterior side of the heat-conductive device. Compared to the prior art, since the resin would hardly flash, the exposed surface of the heat-conductive device would not be covered by flashed resin, thus ensuring the heat-dissipating efficiency. The staircase-like cutaway part preferably has a total width of from 0.6 mm to 1.5 mm and a total depth of from 0.06 mm to 0.15 mm; and more preferably, the staircase-like cutaway part has a total width of from 1.0 mm to 1.3 mm and a total depth of from 0.10 mm to 0.13 mm.


REFERENCES:
patent: 5041902 (1991-08-01), McShane
patent: 5455462 (1995-10-01), Marrs
patent: 5705851 (1998-01-01), Mostafazadeh et al.
patent: 5773886 (1998-06-01), Rostoker et al.
patent: 5892278 (1999-04-01), Horita et al.
patent: 5977626 (1999-11-01), Wang et al.

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