Study improves stretchable interconnect reliability

IMEC has studied the deformation behavior and failure mechanisms of horseshoe-patterned stretchable interconnects. The study has further resulted in a design guideline for deciding on the optimal pitch between the conductors, and in a model for predicting their fatigue life. These results contribute to an improved reliability of the stretchable interconnects.

Two different failure mechanisms are involved in the stretching process: interfacial delamination and metal rupture.

Electronic systems with flexibility and stretchability have great potential in biomedical applications such as implantable devices and wearable health monitoring systems. Since these systems need to withstand high deformations (>10 percent), hybrid systems are proposed that consist of rigid or bendable elements connected through stretchable electrical conductors. A promising and cost-effective technology to realize these stretchable conductors makes use of a co-planar horseshoe-patterned metallic connector encapsulated in a stretchable polymeric substrate. IMEC and its associated laboratory at Ghent University have now investigated the reliability performance of these interconnects through both experimental analysis and numerical modeling.

The experimental part of the study makes use of a commercially available 0.018mm thick Cu foil encapsulated in a polydimethylsiloxane or PDMS substrate. A commercial finite element code was used for the numerical analysis. The results indicate that the crest of the meander is the weakest point where potential metal failure will occur during stretching. The maximum elongation before electrical failure occurs depends on the conductor line-to-line pitch: a sample with fine pitch (i.e. 1.8mm) can be stretched up to 123 percent, a similar sample with coarse pitch (i.e. 3.0mm) up to 135 percent. Based on these results, the researchers proposed a design guideline for the optimal pitch between the conductors, including a highly risky zone in terms of plastic strain.