Reducing out-of-plane deformation of metal interconnects in structural electronics

This paper presents a novel approach for removing out-of-plane deformation in metal interconnects by adding a fractional structure to the original meander shape and using the optimised fabrication stack. In thermoformed electronics in cases where copper is used as the conductor, the twisting of meander-shaped structures caused by excessive mechanical stress can cause a non-uniform surface, delamination of the metal interconnect from the substrate, and in some cases, a short circuit to the adjacent tracks. Typically, stretchable electronics designers use various shapes and widths of the copper interconnect to tackle this issue. Using conventional meander shapes such as horseshoes and U shapes is not universally practical, especially when stretching is higher than 30 percent leading to significant out-of-plane deformation. Limiting this out-of-plane deformation by reducing the track width is not always applicable, as a minimum width is needed from a technology and conductivity perspective. The presented approach is inspired by computational and experimental studies of multiple meander shapes and fabrication methods. A geometry-based and fabrication-based approach is presented, which can reduce the mechanical stress of almost all possible meander shapes by increasing the meander’s path length to accommodate the metal track’s produced torque during stretching. An analytical approach is provided for calculating the optimal meander parameters, and the optimal fabrication stack is achieved based on simulation results. Experiments and finite-element modeling for an industrial case study show the improvement in the stress distribution and reduction of out-of-plane.