Characterization of the Conduction Mechanisms in Adsorbed Electrolyte Layers on Electronic Boards Using AC Impedance

Abstract

The reliability impact of flux residues on electronic assemblies has been traditionally evaluated using surface insulation resistance (SIR) measurement with dc voltages. An ac impedance technique has been investigated to provide detailed information on the conduction mechanisms and electrode reactions in the presence of flux residues on electronic boards. By evaluating different fluxes using a standard comb pattern the relative applicability of the ac impedance and SIR techniques has been made in terms of assessing the reliability of electronic boards. Impedance values at low frequencies, , are close to the SIR results and hence produce similar predictions of reliability. More importantly, the ac impedance spectrum can be used to predict dendrite formation, although the technique itself does not actually promote dendrites. The ac impedance method can distinguish between ionic solution resistance of the thin water layer and impedance from interfacial electrochemical processes. At low contamination levels the solution resistance, between the copper-comb electrodes, dominates the overall impedance. At high contamination levels the impedance from interfacial electrochemical processes becomes significant and increases the potential of dendrite formation. This predictive capability could be developed into a nondestructive test method to provide a more detailed electrochemical characterization and indication of future reliability.