A Comprehensive Methodological Approach Towards the Micromechanical Characterization of Lead-Free Solder Joints

In light of continued trends regarding increased complexity and ongoing miniaturization in microelectronics, advanced characterization approaches for miniaturized components are essential. We present a comprehensive experimental approach combining multiple small-scale mechanical testing techniques to characterize plastic deformation mechanisms in lead-free SAC305 soft solder. The Sn-rich matrix features a highly anisotropic β-Sn body-centered tetragonal crystal structure, resulting in a complex deformation behavior. Our approach integrates advanced nanoindentation methods with in situ microcompression testing to bridge length-scales and deformation regimes. Through nanoindentation, we quantified rate-dependent plasticity, revealing a particularly high stress exponent (n = 15.52), indicating that deformation is strongly hindered by obstacles. The activation volume of ~ 25 b3 corresponds to bcc materials, signifying that deformation is likely controlled by a dislocation-based kinking mechanism. In situ microcompression experiments enabled observation of slip-system activation, documenting the operation of (100)[010] slip-systems with a Schmid factor of m = 0.44 at a critical resolved shear stress of ~ 30 MPa. This favorably aligns with stress–strain curves from spherical nanoindentation. Important experimental details to effectively integrate multiple testing methods are highlighted, facilitating comprehensive scale-bridging understanding of mechanical behavior in solder materials. The presented framework is generally applicable to evaluate mechanical properties and deformation mechanisms in systems where traditional bulk testing is not feasible.