Reliability of a stretchable interconnect utilizing terminated, in-plane meandered copper conductor

The pursuit for reliable, deformable electronic systems took two major paths, utilizing either conductive elastomers or metal conductors. In the case of the latter, a mechanical robustness trade-off is made in return for metallic conductor native low resistivity allowing for realization of power demanding and large area applications as well (e.g. conformable lighting and signage). The mechanical trade-off stems from the metal conductor intrinsic inability for significant elongation without failure. One of many present attempts at enabling a metal conductor to perform in an elastomeric medium without failure is the SMI (Stretchable Molded Interconnect), a PCB compatible technology developed at the CMST. Its concept relies on an in-plane, meandered, metal track embedded into a soft, elastomeric material. This work focuses at cyclic, uniaxial elongation endurance and reliability assessment (Weibull analysis) of such interconnect in its most simple form - utilizing unsupported, meandered copper tracks embedded in PDMS (Polydimethylsiloxane). The tracks are evaluated as short interconnects (a few meander wavelengths long) terminating between flexible (non-stretchable) regions to incorporate the effect of flex-stretch transition mechanics on reliability. This is an important assessment for optimizing the interconnect geometry for practical applications where flex-stretch transitions will be inevitable, and reliability under repeated deformation is of interest (e.g. stretchable circuits for integration in textile). An attempt is made to reinforce the meander geometry by tapering the transitions, but a negative impact on reliability is observed. It is clearly demonstrated that the wearout of the interconnect is strongly related to the amount of copper present in the interconnect.