In this study the possibility to apply electrochemical impedance spectroscopy as an alternative method for the characterisation of the intermetallic microstructures of Sn-3.5Ag lead free solder samples was investigated. The aim of the study is to compare the electrochemical impedance spectra of solder samples, reflowed with different heat profiles. A quenching technique was applied in order to solidify the solder samples in cylindrical crucibles. Differences in the microstructures of the solidified alloys were achieved by changing the temperature of the quenching media. The molded and cross sectioned specimens were observed using both optical microscopy and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). The microstructure of the ingots was revealed by selective electrochemical etching. The electrochemical impedance spectrum (EIS) was measured before and also after the selective etching process. The complex impedance spectra contain information regarding the characterized microstructure. Our aim is to determine quantitative parameters which are identical to the characteristics of the microstructure.