Improved Stretchable Electronics Technology for Large Area Applications

Abstract

AbstractA novel technology for stretchable electronics is presented which can be used for the realization of wearable textile electronics and biomedical implants. It consists of rigid or flexible component islands interconnected with stretchable meander-shaped copper conductors embedded in a stretchable polymer, e.g. PDMS. The technology uses standard PCB manufacturing steps and liquid injection molding techniques to achieve a robust and reliable product. Due to the stretchable feature of the device, conductors and component islands should be able to withstand a certain degree of stress to guarantee the functionality of the system. Although the copper conductors are meander-shaped in order to minimize the local plastic strain, the lifetime of the system is still limited by the occurrence of crack propagation through the copper, compromising the connectivity between the functional islands. In order to improve the lifetime of the conductors, the most important feature of the presented technology is the use of spin-on polyimide as a mechanical support for the stretchable interconnections and the functional flexible islands. In this way, every stretchable copper connection is supported by a 20μm layer of polyimide being shaped in the same manner as the above laying conductor. The grouped SMD components and straight copper tracks on the functional islands are also supported by a complete 20 μm polyimide layer. By use of the polyimide, the reliability of the stretchable interconnections, the straight interconnections on the flexible islands and the transitions between the stretchable and non-stretchable parts is improved. This approach results in a significant increase of the lifetime of the stretchable interconnections as it is doubled. In this contribution, the different process steps and materials of the technology will be highlighted. Initial reliability results will be discussed and the realization of some functional demonstrators containing a whole range of different components will further illustrate the feasibility of this technology. The advantages and disadvantages in terms of processability, cost and mechanical strength of the photo-definable polyimide will be covered.