Environmental and health concerns of well-established but toxic Pb-containing solder materials force a replacement by newly developed lead-free materials. In order to ensure the required reliability and life-time of microelectronic components the mechanical performance of the solder material needs to be evaluated on real devices under actual loading conditions. This includes plastic deformation and fracture of the individual phases at high homologous temperatures of 0.6 already at 23°C.
In this study, advanced testing methods are applied to evaluate the mechanical behavior of the complex solder microstructure composed of a Sn-Matrix with intermetallic compound layers of Cu3Sn and Cu6Sn5 at the solder-copper interface. In situ micro-pillar compression tests of Sn revealed a strong size dependency, with a power law exponent of n = -1, that follows recently developed models based on e.g. dislocation stochastics (P. Phani, Acta Materialia, 2013, p. 2489) or Taylor strengthening (J. El-Awady, Nature Communications, 2015, p. 5926). The tests also provide valuable data about activated slip systems as well as the size and orientation dependent critical resolved shear stress of tin. The influence of the brittle intermetallic interlayers is assessed by micro fracture bending experiments on cantilevers milled from individual grains or polycrystalline regions to evaluate the fracture toughness. The results will be discussed with respect to life-limiting mechanisms present in each individual phase.