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close already to the literature value of a theoretically
possible 420 W/mK for pure silver.
To estimate the accuracy of the method, we have
calculated its sensitivity first. This can then be compared to
the mean accuracy of the temperature measurement δT fitted
for the three sensor values along the Cu-bar.
The sensitivity of the method is expected to depend on the
BLT of the TIM. The simulated curves are given in
figure 21 for different TIM-conductivities and BLTs.
Naturally the sensitivity is higher for the larger BLT and
yields the value of S = 0.0046 mK 2 /W. With δT = 0.045 K
we obtain a resolution of around δλ = ± 10 K for the thicker
BLT.
7-9 October 2009, Leuven, Belgium
introduced by the technological modifications. The accuracy
obtainable at low bond-line thicknesses and highly
conductive interface materials is evaluated and commented
on. More results will follow and be presented soon in
another paper, encompassing also reliability aspects of the
new technologies.
ACKNOWLEDGMENTS
The authors appreciate the support of the EU FP 7
Integrated Project “Nanopack”. Further thanks go to the
authors’ Fraunhofer colleagues A. Gollhardt, S. Huber,
M. Koch, K.-F. Becker, T. Braun and M. von Suchodolez.
∆T [K]
0.12
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
-0.04
BLT = 28 µm
BLT = 71 µm
390 395 400 405 410 415 420
λ Ag
[W/mK]
Fig 21: Sensitivity of measurements for two different BLT
For the thinner BLT we obtain δλ = ± 20 W/mK. This
means that preferably thick BLTs should be used during
characterisation. However, large BLTs of Ag powder are
difficult to realise technologically.
CONCLUSIONS & OUTLOOK
In this paper we have stressed the need for advanced
thermal interface technology and presented two approaches
to process and characterize theses structures. A so-called
“nano-sponge” technology has been introduced with
interesting structural, mechanical and thermal features to
enhance heat transfer across the interface. Nanoindentation
has been used to verify the increased deformability of the
sponge to possibly allow enhanced contact to filler particles.
A second technology using Ag-powder on Ag surface
metallisation has been presented and tested successfully
thermally and mechanically.
It has also been pointed out that usually a variety of
characterisation methods is made necessary as each new
interface technology has to be thermally measured as
processed in the real device. In this vein two test stands have
been designed and developed to measure the effect
REFERENCES
[1] R. Viswanath, V. Wakharkar, A. Watwe and V.
Lebonheur. Thermal Performance Requirements from
Silicon to Systems. Intel Technology Journal Q3, pp. 1-
16, 2000.
[2] S.V. Garimella, Y.K. Joshi, A. Bar-Cohen, R. Mahajan,
K.C. Toh, V.P. Baelmans, J. Lohan, B. Sammakia, and
F. Andros. Thermal challenges in next generation
electronic systems – summary of panel presentations
and discussions. IEEE Trans. Components and
Packaging Technologies, 25(4), pp. 569–575, 2002.
[3] Liu, Y., S. Irving, T. Luk, and D. Kinzer. Trends of
Power Electronics Packaging and Modeling. Proc. 10th
EPTC, 2008.
[4] M. Rencz. Testing interface thermal resistance, Proc.
9th EPTC, 2007.
[5] R. Schacht, D. May, B. Wunderle, O. Wittler, A.
Gollhardt, B. Michel and H. Reichl. Characterization of
Thermal Interface Materials to Support Thermal
Simulation. Proc. 12th Therminic 2006, Sep 27-29,
Nice, Côte d’Azur, France, 2006.
[6] B. Wunderle, J. Kleff, D. May, M. Abo Ras, R. Schacht,
H. Oppermann, J. Keller and B. Michel. In-situ
measurement of various thin Bond-Line-Thickness
Thermal Interface Materials with Correlation to
Structural Features. Proc 14 th Therminic 2008, Rome,
Sept 24-26 2008
[7] R. Kempers, P. Kolodner, A. Lyons and A.J. Robinson.
Development Of A High-Accuracy Thermal Interface
Material Tester. Proc. 10 th Itherm Conf. 2008.
[8] A. Devos, J.-F. Robillard, R. Côte et P. Emery. High
Laser-Wavelength Sensitivity of the Picosecond
Ultrasonic Response in Transparent Thin Films,
Physical Review B 74, 6, 064114, 2006
[9] R. J. Linderman, T. Brunschwiler, U. Kloter, H. Toy,
B.Michel, Hierarchical Nested Surface Channels for
Reduced Particle Stacking and Low-Resistance Thermal
Interfaces, Proc. 23st IEEE SEMI-THERM Symp.,
2007, pp. 87-94.
[10] D.F. Rae and P. Borgesen. Optimising the automated
assembly process for filled polymer-based themal
bondlines. APEX 2009.
[11] B. Wunderle and B. Michel. Lifetime Modeling for
Microsystems Integration – from Nano to Systems. J. of
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