Nucleation and shrinkage of defects on the surface of tin induced by local strain distribution

This paper discusses nucleation of stress-induced defects on a tin surface finish. The spring back effect was used to generate compressive stresses in the tin layer. In-situ observation was carried out by means of atomic force microscopy (AFM). Nucleation of defects was found in the observed area. AFM revealed that not only nucleation but also shrinkage of defects took place. Cross-section profiles revealed that defects are classified into hillocks. Since the tin crystal structure has anisotropic properties, local stress distribution was developed by compressive stresses. The digital image correlation (DIC) approach revealed that defects were located at areas of severe strain gradient. The strain gradient corresponds with the nucleation and shrinkage of defects in in-situ observation. The surface energy based model is employed to explain the hillock formation.