Stretchable and deformable electronic systems in thermoplastic matrix materials

Deformable of electronic systems consisting of laterally distributed electronic components (typically sensors, actuators or LEDs) has attracted considerable attention during the last decade. By using different technology approaches considerable elasticity, repeated stretchability and conformability of such systems has been shown by number of research groups. Contrary to the expression of interest by many potential industrial manufactures of stretchable electronics, the adaptation of related technologies into industrial fabrication environments is lagging. Among the reasons for the reluctance to industrialize are concerns with respect to material used in deformable electronics (silicones), reliability issues (repeated stretchability), and (initial) cost. In this paper an approach for “single cycle deformable”-electronic systems and some of its application scenarios will be presented, which is very close to established printed circuit board technologies. Based on a previously developed technology for repeatedly stretchable electronics -using thermoplastic polyurethane as the matrix material, see figure 1- an approach for three dimensionally deformable electronic systems is formed. In order to fabricate a stable self-supported structure the stretchable system is attached to a thermoplastic polymer sheet (typically polycarbonate or a polycarbonate/Acrylonitrile butadiene styrene blend) with a thickness between 200 and 800 μm prior to being 3D-deformed by thermo-compression. Potential applications are any kind of products (consumer electronics, automotive, household appliances), where a need to integrate sensors and actuators into ergonomically or aesthetically 3D-shaped surfaces is identified. The fabrication of deformable electronics is a process fully compatible with a typical printed circuit board manufacturing and electronics assembly line. Also the used materials are well compliant with wet chemical processes used during the processing. Rather complex electronic systems with a number of components like distributed sensors or actuators can be assembled in a conventional way on a flat electronic panel. The low temperature solder SnBi is used for the electronics assembly. Mounted components are typically fixed additionally by a under filler, so that during the thermoforming process when the solder eventually melts components are not released from the contact pads. The stretchable electronics is subsequently fixed to a stiff thermoplasitc support sheet prior to being 3D-deformed by a thermoforming process. Manufacturing aspects and results will be discussed in the presentation.