Large area processes for 3D shaped electronics

Abstract

Conformable electronic systems consisting of laterally distributed electronic components (typically sensors, actuators or LEDs) have attracted considerable interest during the last years. By using different technology approaches considerable elasticity, repeated stretchability and conformability of such systems has been shown by research groups. Contrary to the expression of interest by many potential industrial manufactures of stretchable electronics, the adaptation of related technologies into fabrication environments is lagging. Among the reasons for the reluctance with respect to industrialization 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. Based on a previously developed technology for stretchable electronics using thermoplastic polyurethane as the matrix material, an approach for three dimensionally shaped electronic systems was developed. In order to fabricate a stable self-supported structure the stretchable system is attached to a thermoplastic polymer sheet (typically polycarbonate) with a thickness between 200 and 800 µm prior to being 3D-deformed by thermo-forming. 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 an underfiller, 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.