Affiliations: Graduate School of Meijo University, Nagoya, Japan | Department of Mechanical Engineering, Meijo University, Nagoya, Japan
Note: [] Address for correspondence: Hiromi Ueno, Graduate School of Meijo University, Shiogamaguchi 1-501, Tempaku-ku, Nagoya 468-8502, Japan. E-mail: m0935005@ccalumni.meijo-u.ac.jp.
Abstract: Tin thin films with various thicknesses were electrodeposited on Cu substrate with and without Ni undercoat. The changes of the internal stresses in tin films were measured by the X-ray diffractions. For the case of 2.2 μm thick film without Ni undercoat, the initial internal stress was tension and then gradually changed into compression. After 20 h, the internal compressive stress became around −30 MPa and was remained constant afterward. Filament-type whiskers were formed on the surface after the stress changed into compression. For the case of 2.2 μm thick film with Ni undercoat, the stress maintained in tension and no whisker was observed. For the cases of thicker films with and without Ni undercoat, the stress was compression around −30 MPa just after deposition, and remained constant. Nodule-type and Mount-type whiskers were formed on the surface, but no Filament-type whiskers were observed. The compressive stress applied by bending on 2.2 μm thick film with Ni undercoat resulted in the formation of Mount-type whiskers. The postbake process induced the tensile stresses in 2.2 and 16.5 μm thick films. Whisker formation was prevented in thin film and only Mount-type whiskers were formed in thicker films.
Keywords: Tin whisker, internal stress, electrodeposited tin film, X-ray stress measurement, Ni undercoat, postbake
