Spatially Resolved Thermal Conductivity of Intermetallic Compounds Measured by Micro-Thermoreflectance Method

Abstract

  Spatially resolved thermal conductivity of Cu₆Sn₅ 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 Cu₆Sn₅ was selectively measured by the TR method considering three-dimensional thermal diffusion model. The estimated thermal conductivity of Cu₆Sn₅ 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.