Electrochemical Migration Inhibition of Tin by Disodium Hydrogen Phosphate in Water Drop Test

The inhibition effect of Na2HPO4 on the electrochemical migration (ECM) of pure tin was investigated by means of water drop testing and surface characterizations. The effects of concentration of Na2HPO4 and applied direct current (DC) bias voltage on the ECM were also studied. Results showed that the mean time to failure caused by ECM decreased with the increasing bias voltage. Upon addition of relative high concentrations of Na2HPO4, Na2HPO4 can react with metallic tin or tin ions to form a protective film on the surface of anode and increase the pitting potential. The rate of anodic dissolution can be slowed down and thus ECM of tin was retarded. Fractal-like dendrites formed after ECM tests in the absence and presence of low concentrations of Na2HPO4 mainly consisted of tin elements. Relevant reactions were proposed to explain the inhibitory effect of Na2HPO4 on the ECM of tin.