Experimental strain energy density dissipated in SAC305 solder joints during different thermal cycling conditions using strain gages measurements
Résumé
Despite being widely investigated for the last two decades, solder joints thermomechanical durability assessment remains a major concern for industries wishing to switch from lead-based (SnPb) to lead-free electronics. Amongst the variety of lead-free solder compositions, 96.5Sn-3.0Ag-0.5Cu (SAC305) solder alloy has become the preferred substitute to classic SnPb solders. However, unlike SnPb assemblies, the return on experience is limited and the microstructure is very different for SAC305 solder joints. The use of SAC305 solder paste requires to understand the mechanical and fatigue behaviors of the soldered interconnects. This paper presents the experimentation based on strain gages measurements, allowing the determination of the shear stress-strain response of SAC305 solder joints subjected to different thermal cycling conditions. The area of the experimental shear strain-stress hysteresis loops gives the values of the strain energy density corresponding to each thermomechanical loading. The finite element modeling of the test assembly showed a good correlation between experimental and numerical strain energy densities. The experimental shear strain-stress curves also provide the necessary data to derive SAC305 solder joints constitutive laws.
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