Design and analysis of Cu circuit for stretchable electronic circuits using finite element analysis

Stretchable electronic devices are desirable for the next application of electronic devices such as stretchable sensors, stretchable energy storage devices, and humanmachine interfaces. Also, stretchable electronic systems require a stretchable metal circuit on the elastomeric substrate for electrical connection to components. The stretchable circuits fabricated by Cu foil lamination on the thermoplastic polyurethane (TPU) film are investigated with various zigzag-patterned circuit designs. The various circuit designs are simulated by finite element analysis (FEA) for fatigue life prediction and the simulation results are compared with experimental results. The 6 types of zigzag-shaped circuit designs with different corner patterns are investigated. The thicknesses of the Cu electrode and TPU substrate are 18 mu m and 50 mu m, respectively. The stretchability of Cu stretchable circuits is evaluated by the uniaxial tensile test with 10% elongation. Also, the equivalent plastic strain is calculated for fatigue life prediction. The number of stretch cycles to failure increased as decreasing the equivalent plastic strain obtained by FEA. The tendency of crack propagation and fatigue life prediction are well agreed with FEA results. Thus, it is considered that modifying the circuit patterns of the strain concentration area is the most important to enhance the mechanical reliability of stretchable circuits.