Properties of thin layers of Sn62Pb36Ag2

The increasing miniaturisation of surface mount devices(SMD) reveals some new questions concerning the reliability of solder joints. The components become larger and the solder joints smaller. Especially the thickness mainly influences the mean lifetime of surface mount technology (SMT) solder joints, where micro-fracture and damage evolve under thermomechanical cycling. When the electrical power is switched on and off, the solder joints are heavily distorted due to the thermal expansion mismatch of the package and the PCB. The deformation in eutectic Sn-Pb at homologous temperatures close to 1 is known to be strongly related to grain- and phase boundary mechanisms. Therefore, a change of the mechanical behaviour is expected, if the phase size is of the order of the thickness of the solder layer. This paper covers the determination of the deformation behaviour of thin layers, down to 25 μm