Chip-size packaging (CSP) attracts largely attentions due to its lighter, thinner and smaller size. In this study, the deformations and the stresses in the CSP fabricated by non-conductive film stud-bump direct interconnection (NSD) were analyzed. The reliability evaluation of single-sided CSP and both-sided CSP were investigated for heat cycles. The material parameters, i.e. stresses, strains and deformations, for achieving a high reliability of CSP were investigated using a finite element method and experiment. The dependency of the life in single-sided CSP and both-sided CSP on the thicknesses of IC and substrate could be expressed using a normal stress in the thickness direction and shear stress in the vertical cross section, respectively.