Creep Behaviors Along Characteristic Crystal Orientations of Sn and Sn-1.8Ag by Using Nanoindentation

The creep mechanisms of Sn and Sn-1.8Ag along specific orientations are investigated by the constant-strain-rate nanoindentation method. Due to the anisotropy of Sn, the mechanical behaviors could be very different along different crystal orientations. For microelectronic applications, Ag is often added to Sn to increase its strength. Data from creep test show that Ag addition increases the stress exponent by 3, which indicates that the rupture time could be extended by Ag addition. Moreover, the creep rate of Sn (100) grain is lower than that of Sn (001) grain in a low stress regime, namely, that [100] in Sn would have better creep resistance for usual applications. After indentation, transmission electron images of Sn samples show that the slip systems are $$ (1\bar{1}0) $$ $$ [11\bar{1}] $$ in (100) grain and (101) $$ [1\bar{1}\bar{1}] $$ in (001) grain. Lastly, Sn-1.8Ag has better performance along [100] in creep resistance due to greater hindrance of Ag atoms on dislocation motion and its critical threshold stress.