The effects of encapsulation on deformation behavior and failure mechanisms of stretchable interconnects

In this paper, the effect of encapsulation on deformation behavior and failure mechanisms of stretchable interconnects is presented. Extensive numerical modeling is conducted for mechanical analysis of which the results are correlated with in-situ experimental observations. The numerical results reveal that by adding an encapsulation layer of various thickness (from 0.0 to 0.5 mm) on top of the stretchable interconnect, the out-of-plane deformation and in-plane geometrical opening are reduced. Consequently, not only the plastic strain in the metal increases but also the in-plane shear stress at the interconnect/substrate interface. In-situ electromechanical experiments combined with scanning electron micrographs and optical images confirm the numerical analysis. More specifically, it is found that two failure mechanisms are involved during the stretching process: interfacial delamination in a S-shape alongside the metal conductor and metal breakdown at the crests of the metal conductor. The encapsulated stretchable interconnect shows both failure mechanisms at a lower percentage elongation than the non-encapsulated stretchable interconnect. Even so, the onset point of interfacial delamination for the encapsulated stretchable interconnect occurs only at an impressive number of 63% elongation and metal rupture only at 120%. The in-plane shear strain contour, obtained by numerical simulation, agrees well with the delamination failure location observed in the experiment.