Mechanical behaviour of typical lead-free solders at high strain rate conditions

3D packaging is one of the main emerging markets especially for mobile application within the last view years. Mobile devices are exposed and hence need to be reliable under to vibration or mechanical shock conditions. Therefore, material properties covering strain rate dependency have to be at hand within reliability studies. Miniature bulk specimens were utilized to gain stress and strain data at strain rates from 20 s^-1 to 600 s^-1. Specimens consist of SnAg1.3Cu0.5Ni, SnAg3.0Cu0.5 and SnAg3.5 solder compositions. Ultimate strain, ultimate transversal contraction and fracture surfaces were analysed to determine the deformation and fracture behaviour. The strain rate dependent yield stress was determined and introduced into a material description feasible for finite element analysis (FEA). Finite element simulations were conducted for all solders at strain rates of 100 s^-1 to 600 s^-1. Results on fracture behaviour agreed well to the experiments. All studied solder compositions revealed ductile deformation behaviour changing only little with strain rate. A higher silver content as well as copper presence lead to higher yield stress level. The sensitivity to the strain rate alters with the copper presence only.