Assessment methods for the characterization of flux material systems toward water absorption

Evaluation of electrochemical migration (ECM) on printed circuit boards (PCB) is becoming increasingly important for the reliability of electronic systems in automotive applications. This is triggered by the miniaturization of electronic systems and the increasing electrical loads. Consequently, the strength of electrical fields is rising. The demand for material solutions that are resistant to combined moisture and electrical loads is growing. There is a strong demand for further analytical methods to characterize the materials with respect to ECM-risks. Up to now, surface insulation resistance (SIR) measurement has been used as the standard method for assessing the ECM-risk. AC-Impedance measurement offers a more sensitive resolution of the condensation process. The resolution of initial dew states is better using AC-Impedance than SIR, since the latter only detects water adsorption if a closed water film is present. In addition, it does not trigger any electrochemical migration. Thus, AC-Impedance works non-destructively in contrast to SIR. The advantage is that materials can be characterized in terms of their hygroscopic properties without being superimposed by the corrosion effect. With a frequency sweep, the electrical properties of the microstructure system can be analyzed by the Electrochemical Impedance Spectroscopy (EIS). EIS can display interfacial processes at electrodes, kinetic reaction, and mass transfer in the solution. The EIS-method works non-destructively by using low amplitudes in the range of mV. Compared to SIR, EIS is more sensitive in terms of detecting physicochemical changes in the ECM process. Both, AC-Impedance and EIS methods, can help to pre-assess the ECM-risk of PCB materials used in the fabrication process. In this work, solder flux residues from different materials will be evaluated in terms of water absorption and dielectric properties.