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Considering that the mechanical behavior plays a very important role in the packaging reliability, this study examined the shear deformation properties of pure Sn joints with different substrate materials and various gap sizes. The proeutectic Sn dendrites were refined and the shear strength was increased with a shrunken sample gap. The interfacial intermetallic compounds (IMCs) were thickened slightly when the sample gap was less than 100 mum. A decrease in joint thickness transformed the fracture paths of the Cu/Sn/Cu samples from solder bulk to the boundary between interfacial IMC and the solder. As for the Cu/Sn/Ni sandwich structured joints, they exhibited an asymmetrical structure which resulted from the interaction of substrate elements and thus inferior shear strength compared to the Cu/Sn/Cu samples with the same thickness, as well as the difference in fracture mode.