Iodine-containing thermal interface material

Details Iodine-containing thermal interface material Iodine-containing thermal interface material

2001-09-18

2004-06-22

Bennett, Henry (Department: 3743)

Heat exchange

Heat transmitter

C361S704000, C165S080300

Reexamination Certificate

active

06752204

ABSTRACT:

BACKGROUND OF THE 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 an iodine-containing material.
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 industry. As these goals are achieved, microelectronic dice become smaller. Accordingly, the density of power consumption of the integrated circuit components in the microelectronic device has increased, which, in turn, increases the average junction temperature of the microelectronic device. If the temperature of the microelectronic device becomes too high, the integrated circuits of the microelectronic device may be damaged or destroyed.
Various apparatus and techniques have been used and are presently being used for removing heat from microelectronic devices. One such heat dissipation technique involves the attachment of a heat dissipation device to a microelectronic device.
FIG. 4
illustrates an assembly
200
comprising a microelectronic device
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 device
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 device
202
due to a mismatch between coefficients of thermal expansion (“CTE”) of the heat dissipation device
208
and the microelectronic device
202
as the microelectronic device
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 device
202
, which may cause the failure of the microelectronic device
202
. Furthermore, in order to get the solder materials to adhere to the microelectronic device back surface
212
and the heat dissipation device back surface
216
, a gold coating may have 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 device
222
is placed in a socket
224
mounted on the carrier substrate
204
, wherein pins
226
extending from the PGA device
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 PGA device
222
with a spring clip
234
that spans the heat dissipation device
208
and connects to the socket
224
. A conductive grease
236
is placed between the microelectronic device
202
and the heat dissipation device
208
. This configuration virtually eliminates problems with CTE mismatch. Such materials that are placed between heat dissipation devices and microelectronic devices are generally known as thermal interface materials.
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 is not able to conform to all microwarpages). Therefore, the liquid phase has better contact properties that result in a higher heat dissipation compared to the solid phase.
However, as the size or “footprint” of microelectronic devices decreases, the contact area between the microelectronic device 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 device, heat dissipation from the heat dissipation device becomes less efficient. Furthermore, as the microelectronic device 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 thermal interface material between the microelectronic device and the heat dissipation device. As microelectronic devices become smaller, the heat transfer properties of the thermal interface materials become a greater factor. Thus, currently available thermal interface materials, such as thermally conductive adhesives, greases, and most phase-change materials, are quickly becoming bottlenecks to heat dissipation.
Therefore, it would be advantageous to develop a thermal interface material, as well as apparatus and methods using the same, to improve the efficiency of heat transfer at an interface between a heat source and a heat dissipation device.


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patent: 5168926 (1992-12-01), Watson et al.
patent: 5441918 (1995-08-01), Morisaki et al.
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patent: 5623394 (1997-04-01), Sherif et al.
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