Influence of sodium chloride and weak organic acids (flux residues) on electrochemical migration of tin on surface mount chip components

摘要

The electrolytic properties of sodium chloride and no-clean solder flux residue, and their effects on electrochemical migration and dendrite growth on surface mount chip capacitors were investigated. The leakage current dependency on concentration of contaminants was measured by a solution conductivity method and compared with current measurements using DC voltage. The effect of electrolyte concentration and potential bias on the probability of electrochemical migration was investigated using a water droplet method on chip capacitors. The results from leakage current and conductivity measurement showed a difference which is caused by polarization effects, and demonstrated existing issues when indexing contamination levels on printed circuit board assemblies using a standardised solvent extract method. The experimental results showed that dendrite growth was dependent on the type and amount of contamination. The probability of migration becomes less dependent on the amount of contamination for sodium chloride at high concentrations. However, for organic acids from flux residues the migration probability shows an abrupt decrease with increasing concentration, which is attributed to a pH change in the condensed electrolyte phase.