Microwave Characterisation of the Coefficient of Thermal Expansion and the Thermal Evolution of Electric Conductivity for Metallised Substrate

This paper presents a new microwave characterisation technique to obtain the coefficient of thermal expansion (CTE) using a cylindrical resonator. This technique is non-destructive and can be applied to any kind of solid material. With the help of a metallised sample insert in the middle of the resonator, two cavities are formed, with one side made of the unknown metallisation of the sample. By monitoring resonant frequencies and the quality factor of these cylindrical sub-cavities, the dimensions of the sample and its conductivity can be extracted. Performing this technique with temperature tracking allows us to calculate a thermomechanical parameter, the coefficient of thermal expansion. The realised measurements on different samples and metallised substrates show a micrometre resolution for the thickness and a resolution of approximately 5 μm with other measurement techniques. Several electric conductivities in terms of temperature are also presented at different frequencies related to their uncertainties.