Microstructural modeling of a stretchable electronic device: towards shape optimization

Stretchable electronic devices are electronic circuits embedded in a flexible and stretchable substrate. The advantage of such devices is the flexibility in all directions. Stretchable and bendable displays, body sensors and wearable electronics are only a little selection of the many applications that become possible with this technique. There are many designs to achieve stretchability in electronic circuits. In this project a horseshoe pattern metal connection is investigated using 3D numerical modeling, incorporating actual geometries and material models, in order to guide the design of such micro structures. For the 3D model an RVE (Representative Volume Element) is used, containing one period of metal connector track. In order to analyze many different shapes a code is written that can generate different patterns for the model. The model incorporates a material model for the copper track and for the rubber-like substrate. Periodic boundary conditions are applied. Different RVE’s are subjected to a in-plane uniaxial stretch load case through finite element simulations. By varying the radius and track width an optimum shape is sought. A relatively broad track can handle more deformation than a narrow one because the strain is better distributed in the copper track. Thereafter the response on different load cases, such as bending, is investigated in order to see which load case is most critical. It turns out that in-plane stretching is more critical than bending, in-plane shearing and twisting. The model and the simulation framework developed within this project can be used for further design improvements of stretchable electronic microstructures. J.J.C.M. van Dun CONTENTS page 2