Thermal interface material on a mesh carrier

Details Thermal interface material on a mesh carrier Thermal interface material on a mesh carrier

2000-07-31

2003-02-25

Au, Spe (Department: 3743)

Heat exchange

Heat transmitter

C165S080300, C361S708000

Reexamination Certificate

active

06523608

ABSTRACT:

BACKGROUND OF TEE INVENTION
1. Field of the Invention
The present invention relates to apparatus and methods for removal of heat from electronic devices. In particular, the present invention relates to a thermal interface comprising a grid frame coated with a thermal interface material, wherein the coated grid frame is disposed between a heat generating source, such as a microelectronic die, and a heat dissipation device, such as a heat spreader or heat sink.
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 microelectronic and 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 heat dissipation device to a microelectronic die.
FIG. 4
illustrates an assembly
200
comprising a microelectronic die
202
(illustrated as a flip chip) physically and electrically attached to a carrier substrate
204
by a plurality of solder balls
206
. A back surface
216
of a heat dissipation device
208
may be attached to a back surface
212
of the microelectronic die
202
by a thermally conductive adhesive or solder
214
. The heat dissipation device
208
may be a heat pipe, as known in the art, or a heat slug constructed from a thermally conductive material, such as copper, copper alloys, aluminum, aluminum alloys, and the like.
However, the use of a rigid thermally conductive adhesive or solder
214
can cause stresses in the microelectronic die
202
due to a mismatch between coefficients of thermal expansion (“CTE”) of the heat dissipation device
208
and the microelectronic die
202
as the microelectronic die
202
heats to a normal operating temperature when on and room temperature when off. Stresses due to CTE mismatch increase the probability that cracks will initiate and propagate in the microelectronic die
202
, which may cause the failure of the microelectronic die
202
. Furthermore, in order to get the solder materials to adhere to the microelectronic die back surface
212
and the heat dissipation device back surface
216
, a gold coating may to be applied to both surfaces, which is prohibitively expensive.
In another known embodiment as shown in
FIG. 5
, a pin grid array-type (“PGA”) microelectronic die
222
is placed in a socket
224
mounted on the carrier substrate
204
, wherein pins
226
extending from the PGA microelectronic die
222
make electrical contact with conductive vias
228
in the socket
224
. The socket
224
is, in turn, in electrical contact (not shown) with the carrier substrate
204
. The heat dissipation device
208
(shown as a finned heat sink having a plurality of fins
232
) is kept in contact with the microelectronic die
222
with a spring clip
234
which spans the heat dissipation device
208
and connects to the socket
224
. A conductive grease
236
is placed between the microelectronic die
202
and the heat dissipation device
208
. This configuration virtually eliminates problems with CTE mismatch.
It is also known that the conductive grease
236
of
FIG. 5
may be replaced with a phase-change material or matrix. Such materials are in a substantially solid phase (paste-like consistency) when cool (i.e., room temperature). When heated (brought to operating temperatures), the phase-change material changes to a substantially liquid phase (grease-like consistency) which allows the phase-change material to conform to surface irregularites of mating surfaces (when in a solid phase the phase change material is not able to conform to all microwarpages). Therefore the liquid phase has better contact properties which results in a higher heat dissipation compared to the solid phase. One such material is Thermflow™ T443, consisting of a phase-change material within a fiberglass carrier (mat/pad) available from Chomerics, Woburn, Mass., USA.
However, as the size or “footprint” of microelectronic dice decreases, the contact area between the microelectronic die and the heat dissipation device decreases, which reduces the area available for conductive heat transfer. Thus, with a decrease of the size in the microelectronic die, heat dissipation from the heat dissipation device becomes less efficient. Furthermore, as the microelectronic die power is increased, the heat source upper temperature specifications decreases, or the external ambient temperature specification increases. Thus, every area of thermal performance must be examined for any possible enhancement. One such area is the interface between the microelectronic die and the heat dissipation device. As microelectronic dice become smaller, the heat transfer properties of the interface becomes a greater factor. Thus, currently available thermally conductive adhesives, greases, and phase-change materials generally are quickly becoming bottlenecks to heat dissipation.
Therefore, it would be advantageous to develop techniques and apparatus to improve the efficiency of heat transfer at an interface between a heat source and a heat dissipation device.


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“Grid Matrix Thermal Interface Material Carrier,” IBM Technical Disclosure Bulletin, IBM Corp., vol. 38, NR. 10, Oct. 1995, pp. 407-408, XP000540542.
ISSN: 0018-8689, New York, USA.
International Search Report, European Patent Office, Date of Mailing: May 16, 2002, International Application No.: PCT/US 01/22960, International Filing Date: Jul. 20, 2001, pp. 1-4.

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