Thermal Transport Properties of Ag-Based Nanocomposites Containing MWCNTs
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Thermal Transport Properties of Ag-Based Nanocomposites Containing MWCNTs M. Inoue1, Y. Hayashi2 and H. Takizawa2 1 The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan 2 Graduate School of Engineering, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579, Japan
ABSTRACT Variation in thermal conductivity of Ag-based composites by introduction of multi-walled carbon nanotubes (MWCNTs) was investigated. The Ag/MWCNT nanocomposite powder was successfully prepared when appropriate surfactants were used via a sonoprocess. The nanocomposite powder was subsequently cured at 280-300 ºC in air. After curing, the thermal conductivity of the nanocomposites was compared with the electronic contribution to thermal conductivity that was estimated from experimental values of the electrical conductivity. The thermal conductivity of Ag/MWCNT nanocomposites was much higher than the electronic contribution. Therefore, the increase in thermal conductivity of the Ag-based nanocomposites is attributed to phonon transfer along the percolation network of MWCNTs.
INTRODUCTION In the last decade, Ag-based low temperature joining technologies [1,2] have attracted great interests as a candidate for thermal interface materials (TIMs) in power electronics modules. From the start, Ag nanoparticles with sufficient sinterability below 250-350 °C have been studying as the processing avoids the risk of damage associated with severe joining conditions. Recently, novel joining processes using micro-particles of Ag and Ag2O under moderate pressure or no pressure were proposed as a method for die-attachment [3,4]. In these joining processes, the Ag and Ag2O particles are suspended in organic solvents to prepare printable pastes. After printing, the pastes are subsequently cured at low temperatures (below 250-350 °C). Highly conductive electrical and thermal interconnections are observed after curing because the joint formed through Ag porous sintered body independent of the state of the starting materials (typically Ag nanoparticles, Ag micro-particles and Ag2O micro-particles). However, the electrical and thermal conductivities of the Ag porous bodies can be sensitively varied depending on degree of sintering. The thermal conductivity of the porous bodies is usually much lower than that of bulk Ag (429 Wm-1K-1) because their electrical conductivity is lower than that of bulk Ag. To improve the thermal conductivity of the Ag-based TIMs, the present authors propose
introduction of percolation network composed of carbon-based materials, such as carbon nanotubes (CNTs) and diamond, for phonon transfer into the Ag matrix. In the previous work, we have successfully developed Ag/MWCNT nanocomposite powder via a sonoprocess [5]. This work aims to quantify the thermal conductivity of the nanocomposite products obtained by sintering the powder.
EXPERIMENTAL DETAILS The sonoprocess for preparing Ag/MWCNT nanocomposite powders has two steps (the dispersion of MWCNTs in ethanol
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