Mechanical Shock Behavior of Bulk Pure Sn Solder

Abstract

With the increasing focus on developing environmentally benign electronic packages, Pb-free alloys have received a great deal of attention. Mishandling of packages during manufacture, assembly or by the user may cause failure of the solder joint. A fundamental understanding of the behavior of Pb-free solders under mechanical shock conditions is lacking. Reliable experimental stress–strain data over a range of strain rates needs to be obtained for reliability models. In this paper we report on the intermediate strain rate behavior of pure Sn solder. The first part of the paper discusses modeling and analysis of the specimen geometry to obtain a relatively uniform stress (and strain) distribution within the gage section. Analysis by the finite element method (FEM) showed that a modified specimen geometry, with 10 mm gage length, provided a homogeneous strain distribution, similar to the American Society for Testing and Materials (ASTM) E8 specimen geometry. The second part describes microstructural characterization and experimental results on pure Sn at intermediate strain rates (~10/s). Ultimate tensile strength and strain to failure in the 10 mm specimen were quite similar to those of the ASTM specimen. A double necking phenomenon was observed in the ASTM specimen, which was not observed in the 10 mm specimen. FEM modeling of the dynamic behavior of the solder correlated very well with the experimental observations.