The temperature response of the thermal conductivity (lambda) of metal thin films has been investigated by the thermoreflectance (TR) method. The phase lag of the TR signals depends on the thermal diffusivity when the heating area is small, while on the thermal effusivity when the heating area is large. This enables us to evaluate lambda by analyzing the three-dimensional thermal propagation in the film on the substrate. We show that by analyzing the TR signals, lambda of Cu-Pt alloy thin films formed on glass substrates can be estimated. The estimated lambda drastically decreases with an increase in the Pt concentration. Furthermore, we discuss these results by considering the crystallographic properties of the abovementioned thin films investigated by transmission electron microscopy and x-ray diffraction.
Spatially resolved thermal conductivity of Cu 6 Sn 5 intermetallic compounds (IMCs) formed in Sn Ag Cu lead free solder has been investigated by using a periodically modulated thermoreflectance (TR) method. The high spatial resolution has been achieved by focusing a modulated laser beam. The temperature response on the irradiated surface has been analyzed by calculating the phase lag of the TR signal as a function of the thermal diffusion length. We found that the boundary of IMCs influences the phase lag. Furthermore, the thermal conductivity of Cu 6 Sn 5 was selectively measured by the TR method considering three dimensional thermal diffusion model. The estimated thermal conductivity of Cu 6 Sn 5 is 39 W/(mK) which is lower than 54 W/ (mK) of Sn 3.5Ag 0.5Cu. Thus the micro TR method is a powerful method to characterize the thermal conductivity of not only IMCs but also various complex materials.
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