Characterization of Heat Conduction in a Polymer Film

In- and cross-plane thermal diffusivities of a plate like material in the directions parallel to the plane surface and perpendicular to the plane surface can be obtained using an ac-calorimetric distance-variation method and a temperature wave analysis method, respectively. In this study, we carried out the thermal diffusivity measurements of commercially available polyimide films in both direction as a function of thickness. As expected, the in-plane thermal diffusivity is larger than the cross-plane thermal diffusivity. The in-plane thermal diffusivity is larger in an advanced polyimide film with a high tensile strength threshold and a low elongation percentage than in a standard polyimide film with a low tensile strength threshold and a high elongation percentage. The cross-plane thermal diffusivities are almost the same between an advanced polyimide film and a standard polyimide film. Therefore, cross-plane thermal diffusivity is not markedly influenced by the detailed features of a polyimide film. Furthermore, in-plane thermal diffusivity decreases slightly but clearly as the film becomes thicker, but cross-plane thermal diffusivity remains almost constant against the film thickness. The measurement of thermal diffusivity is a useful method of characterizing heat conduction in a polymer film.