Online proceedings - EDA Publishing Association

RA (m 2 K/W)
0.0008
0.0007
0.0006
0.0005
0.0004
0.0003
0.0002
0.0001
0
C2
A3
C1
B3
D2
A1
B1
0 0.5 1 1.5 2 2.5 3
Pressure @ 50% Strain (MPa)
D1
F3
7-9 October 2009, Leuven, Belgium
measurements will be required. Future work will also involve
validating the simultaneous thermal-mechanical numerical
model developed by Kempers et al. [6] with this data.
Additionally, characterization the thermal contact resistance
of these MMT-TIMs as they deform is essential to
understating their performance and for the design of optimum
MMT-TIMs for a given application. Present work revolves
around understanding the relationship between electrical and
thermal contact resistance for these deformable metal
structures in order to develop a simple electrical
measurement to estimate the thermal contact resistance of
MMT-TIMs.
ACKNOWLEDGMENTS
This work was supported by IDA Ireland. Special thanks
to Paul Ahern of Alcatel-Lucent for the SEM imaging.
Fig. 9: Variation of specific thermal resistance with pressure at 50%
strain for each MMT-TIM
resistances of the bulk MMT-TIM are extremely small
compared to the resistance at the contact surfaces. For these
MMT-TIMs, it has been proposed that a relatively
straightforward electrical resistance measurement be
employed to characterize the thermal contact resistance [6,7].
Work is presently being carried out in order to characterize
the relationship between thermal and electrical contact
resistance of deformable metal structures for this purpose.
V. CONCLUSIONS & FUTURE OUTLOOK
Several different hollow conical MMT-TIM structures
were characterized experimentally. The results explore the
effect of various geometrical parameters such as metal
thickness, feature height, size, density and shape on both the
mechanical and thermal response of the MMT-TIM. Overall,
these parameters can exhibit a definite influence both the
thermal and mechanical response of the TIM.
Generally speaking, MMT-TIMs with thicker metal
plating (foil thickness) exhibit a stiffer mechanical response
and a slightly higher effective thermal conductivity.
Additionally, stiffer structures and MMT-TIMs with high
density feature arrays can exhibit higher effective thermal
conductivities but also higher thermal resistances due to
lower compressibility in the structure.
The best overall TIM performance was achieved
through a trade-off between effective thermal conductivity
and mechanical compliance. This was achieved with sample
“D2” where a dense array of conical features formed an
interface of multiple, redundant, thermal contacts. Due to the
thin metal plating, the features plastically deform relatively
easily providing good compliance and a large interfacial
contact area. Thicker metal plating does further reduce
thermal resistance of the MMT-TIM, but only at the price of
significantly higher assembly pressures.
The present work represents an initial exploration into
the effects of various MMT-TIM geometries on the
mechanical and thermal properties. Although some
performance trends were demonstrated, the tested structures
are far from optimal. Additional experimental structures and
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©EDA Publishing/THERMINIC 2009 215
ISBN: 978-2-35500-010-2