In this paper we extract the characteristic impedance of Back End Of Line (BEOL) interconnections from radio frequency (RF) scattering parameter measurements. Quantification of the electric interconnection performance on a broad frequency band requires a good knowledge of the characteristic impedance Zc and the propagation exponent γ. Propagation exponent is easily obtained by measuring two interconnections with different lengths. However, because of the complex test structure with mismatched ports where interconnections are embedded, the extraction of Zc from scattering parameter measurements remains challenging. To solve this problem, we propose an approach based on the Winkel method without using simplified assumptions. Limits of validity for our de-embedding procedure to extract characteristic impedance are also analyzed.