  Creep of directionally solidified Sn-3Ag-0.5Cu wt.% (SAC305) samples with
near-<110> orientation along the loading direction and different
microstructural lengthscale is investigated under constant load tensile testing
and at a range of temperatures. The creep performance improves by refining the
microstructure, i.e. the decrease in secondary dendrite arm spacing
({\lambda}2), eutectic intermetallic spacing ({\lambda}e) and intermetallic
compound (IMC) size, indicating as a longer creep lifetime, lower creep strain
rate, change in activation energy (Q) and increase in ductility and homogeneity
in macro- and micro-structural deformation of the samples. The dominating creep
mechanism is obstacle-controlled dislocation creep at room temperature and
transits to lattice-associated vacancy diffusion creep at elevated temperature
(T/T_M > 0.7 to 0.75). The deformation mechanisms are investigated using
electron backscatter diffraction (EBSD) and strain heterogeneity is identified
between b/-Sn in dendrites and b/-Sn in eutectic regions containing Ag3Sn and
Cu6Sn5 particles. The size of the recrystallised grains is modulated by the
dendritic and eutectic spacings, however, the recrystalised grains in the
eutectic regions for coarse-scaled samples (largest {\lambda}2 and {\lambda}e)
is only localised next to IMCs without growth in size.
