A novel experimental configuration is devised to measure the evolution of the deformation field and the corresponding toughness in solder joints for microelectronic packaging. The material system utilized comprised ductile layer of Tin based solder, encapsulated within relatively hard copper shoulders. The experimental configuration provides pure shear state within the constrained solder layer. Different Pb/Sn compositions are tested with grain size approaching the film thickness. The in-plan strain distribution within the joint thickness is measured by a microscopic digital image correlation system. The toughness evolution within such highly gradient deformation field is monitored qualitatively through a 2D surface scan with a nano-indentor. The measurements showed a highly inhomogeneous deformation field within the film with discreet shear bands of concentrated strain. The localized shear bands showed long-range correlations of the order of 2–3 grain diameter. A size-dependent macroscopic response on the layer thickness is observed. However, the corresponding film thickness is approximately 100–1000 times larger than those predicted by non-local continuum theories and discreet dislocation.

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