In the Eco Solder project, which is a cooperation between industry and academia within the IC-MPPE Comet framework, a lead-free soldering system is being investigated that ensures the reliable connection between microelectronic components and the board. The aim is to understand the damage mechanism and thus be able to estimate and improve the lifetime. Due to the complicated microstructure, which consists of a beta-tin matrix and differently sized intermetallic compounds, the mechanical properties cannot be investigated with conventional macroscopic tests, hence micromechanical examinations are carried out. Stresses of everyday life are simulated with temperature cycling of the samples, which makes it possible to investigate the potential evolution of the microstructure step by step.
The first experiments are conducted with continuous stiffness measurement nanoindentation, which provides the significant advantage of measuring the stiffness, and thus hardness and modulus, over the whole indentation depth. This is enabled by a miniature superimposed oscillating displacement of the indenter tip. With adapting this method, strain-rate jump tests for investigating the strain-rate sensitivity and activation volumes are possible, which act like the fingerprint of the material and directly connect hardness, stress and the microstructural length scale.
As a next step, in-situ micropillar experiments for determining the critical resolved shear stress of differently oriented single crystal samples will be conducted, as such information is important for computational modeling approaches due to the high anisotropy of the beta-tin matrix.