Electrochemical migration (ECM), which is a form of corrosion influenced by bias voltage, occurs when two oppositely biased and closely spaced electrodes are connected by an aqueous electrolyte and may result in the growth of metallic dendrites between the conducting parts to form short circuits. It has been one of the major failure mechanisms in electronic packaging. Due to the fact that no significant decomposition of fluxes and acids takes place within the temperature regime of soldering process, the potential acceleration of corrosion caused by flux residues has been found to create reliability issues in electronic assemblies, especially under humid condition. In this case, the effect of representative solder flux residue weak organic acids (WOAs) on ECM of tin in thin electrolyte layer (TEL) were studied using a technique based on the coupling of in situ electrochemical measurements and optical observations. The results showed that the increasing amount of WOA decreased the probability of tin migration and the dendrites formed are mainly composed of metallic tin. Tin ions reacted with organic compound ions from hydrolysis of WOA to form complexes with electronegativity. The formation of complexes with electronegativity retarded the migration of tin ions and some complexes can be oxidized to the insoluble tin oxide on the anode surface. The anodic tin-oxide acted as a barrier layer and blocked dissolution of anode during tin ECM process. The rate of dendrite growth was found to be limited by dissociation of tin oxalate complexes. Mechanisms were proposed to explain the role of WOA in the ECM of tin.
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