Process for forming molded heat dissipation devices

Details Process for forming molded heat dissipation devices Process for forming molded heat dissipation devices

2000-12-27

2003-07-01

Ortiz, Angela (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

To produce composite, plural part or multilayered article

C264S272170, C264S328700, C264S328800, C264S328180

Reexamination Certificate

active

06585925

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to heat dissipation devices and methods for fabricating the same. In particular, the present invention relates to a multiple step injection molding technique used to form a heat dissipation device comprising at least two separate conductive material regions.
2. State of the Art
Higher performance, lower cost, increased miniaturization of integrated circuit components, and greater packaging density of integrated circuits are ongoing goals of the computer industry. As these goals are achieved, microelectronic dice become smaller. Accordingly, the density of power consumption of the integrated circuit components in the microelectronic die has increased, which, in turn, increases the average junction temperature of the microelectronic die. If the temperature of the microelectronic die becomes too high, the integrated circuits of the microelectronic die may be damaged or destroyed.
Various apparatus and techniques have been used and are presently being used for removing heat from microelectronic dice. One such heat dissipation technique involves the attachment of a high surface area heat sink to a microelectronic die.
FIG. 12
illustrates an assembly
300
comprising a microelectronic die
302
(illustrated as a flip chip) physically and electrically attached to a substrate carrier
304
by a plurality of solder balls
306
. A heat sink
308
is attached to a back surface
312
of the microelectronic die
302
by a thermally conductive adhesive
314
. The heat generated by the microelectronic die
302
is drawn into the heat sink
308
(following the path of least thermal resistance) by conductive heat transfer.
High surface area heat sinks
308
are generally used because the rate at which heat is dissipated from a heat sink is substantially proportional to the surface area of the heat sink. The high surface area heat sink
308
usually includes a plurality of projections
316
extending substantially perpendicularly from the microelectronic die
302
. It is, of course, understood that the projections
316
may include, but are not limited to, elongate planar fin-like structures and columnar/pillar structures. The high surface area of the projections
316
allows heat to be convectively dissipated from the projections
316
into the air surrounding the high surface area heat sink
308
. A fan
318
may be incorporated into the assembly
300
to enhance the convective heat dissipation.
The heat sinks
308
may be fabricated by molding, such as injection or extrusion, or by forming the projections
316
from a block of conductive material (such as by skiving) or attaching projections (such as folded fins) to a conductive block. Furthermore, the heat sinks
308
may be constructed from a thermally conductive material, such as copper, silver, gold, aluminum, and alloys thereof. However, although copper, gold, and silver have excellent thermal conductivity (e.g., greater than about 300 J/(s*m*° C.) between about 0° C. and 100° C.), they are heavy (e.g., specific gravities of greater than about 8.0), such that the weight of the heat sink
308
could damage the microelectronic die
302
to which it is attached. Furthermore, they are expensive (prohibitively so with gold and silver) relative to other conductive materials. Thus, less expensive and lighter materials such as aluminum (i.e., a specific gravity of about 2.7) could be used. However, since aluminum and other lighter materials generally have lower thermal conductive properties lower than gold, silver, and copper (less than about 300 J/(s*m*° C.) between about 0° C. and 100° C.), they may not have sufficient thermal conductive properties to adequately cool a high heat producing microelectronic die
302
.
Thus, some heat sinks are a combination of highly thermally conductive materials and lightweight, relatively, less thermally conductive material to form multiple conductive material designs.
FIG. 13
illustrates such a heat sink
320
comprising a highly thermally conductive plate portion
322
(such as copper) and a lightweight thermally conductive, high surface area portion
324
(such as aluminum) having projections
326
thereon. The plate portion
322
and the high surface area portion
324
are attached to one another by any known connection method. This design allows the highly thermally conductive plate portion
322
to thermally contact the microelectronic die
302
for effective heat removal and to conduct the heat to the lighter, high surface area portion
324
for convective dissipation to the surrounding air.
Another design of a heat sink
330
comprises an extruded, lightweight, high surface area portion
332
having a plurality of projections
334
and a highly conductive plate portion
336
which has been pressed into the high surface area portion
332
, as shown in FIG.
14
. Both multiple metal designs of
FIGS. 13 and 14
result in lightweight heat sinks; however, the interface between the high surface area portions and the plate portions may not have an efficient contact. Surface variations between the high surface area portion and the plate portion may result in very small voids/air spaces, which reduces the efficiency of the thermal contact therebetween.
Therefore, it would be advantageous to develop techniques to fabricate a multiple material heat sink that has efficient thermal contact between the various materials in the heat sink.


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