Mechanical behaviour of SAC-lead free solder alloys with regard to the size effect and the crystal orientation

Material parameters has to be determined with regard to the influence of the solder volume and the crystal orientation to understand the thermo-mechanical properties and therefore the reliability of small lead free solder joints in microelectronics. The influence of crystal orientation to the reliability is very important because a small solder joint of a 0201 or a 01005 electronic device consists of three to one tin dendrites only. The results of creep and tensile tests were obtained with with very small test specimens (diameter 1 mm) of SAC-alloys with Ag-contents between 2 to 4 wt-% and Cu-contents with 0.5 to 1.2 wt-% and SAC-alloys with Bi, Sb and Ni components at room temperature, 80 and 150degC. The highest strength and creep resistance show alloys with high Ag and Cu content combined with Bi, Sb and Ni. In solder joints the Cu content depends on the solder volume and results in diffusion and intermixture of Cu in the solder material during soldering. Nano hardness measurements in szlig-tin crystals and intermetallic components to determine the hardness, the Young´s Moduli and the Yield strength give information to the size effect on mechanical parameters and the strong influence of the crystal orientation, which was determined using EBSD measurements, and the metallographic structure of the solder joints after reflow soldering. The experimental results and their differences based on differential test methods will be compared with literature date and hints will be given to choose the real material parameters for thermo-mechanical simulations.