At the Budapest University of Technology and Economics, Department of Electronics Technology a method for the investigation of lead-free solder microstructures was developed recently. The method is based on the selective electrochemical removal of the tin phase from the solder joint. My task was to investigate an electrochemical technique called Electrochemical Impedance Spectroscopy (EIS) as a possible quatitative characterization method for the solder joint microstructures revealed by the etching process. For this purpose I systematically designed and executed measurement series which were aiming to optimize the EIS method for this application. Various electrolytes and measurement parameters were tested on solder joint microstructures prepared with different soldering conditions. Based on the result I found that EIS could be successfully utilized for the identical characterization and differentiation of significantly different solder joint microstructures. In my work I discuss the possible connection between the solder joint microstructures and the shape of the measured EIS spectra in detail.