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Experimental investigation on microstructural influence towards visco-plastic mechanical properties of Sn-based solder alloy for material modelling in finite element simulations

The paper presents experimental results on tinbased solder alloys to their mechanical visco-plastic deformation behaviour under systematically investigation of cooling rates and their micro-structural solidification. We developed a novel process to produce solder bulk specimens in a re-melting process under specific cooling rates up to -300 K/min. The paper shows a comparison of SnAg3.5 and SnAg3.8cuO.75 solidified with -20 Klmin and -200 Klmin as well as a SnSbCu alloy solidified with -20 Klmin and -100 K/min. By contrast to a commonly used passive cooling solution the increased cooling rates are closer to an actual industrial soldering process. The metallographic investigation shows significant changes of the micro-structure with increasing grain quantity while their size decreased. The intermetallic sizes are reduced and the surface roughness of the specimens overall decreased with higher cooling rates. The mechanical comparison of the different produced specimens uses an advanced experimental procedure to determine the material properties for a unified visco-plastic constitutive model initially proposed by Chaboche et al. The constitutive model describes the time-dependent material behaviour in the strain range of primary creep under cyclic load and isothermal conditions. This progress is performed in a temperature range between -40°C up to 150 °C, with varying strain rates between lE-3 to lE-6 per second and relaxation steps. The detailed characterization procedure has been presented in [4] and [5]. In two separate chapters the paper explains the advantages of this modelling approach on lifetime prediction using finite-element simulations.