Stretchable electronic systems

The variety and applications of electronic systems have undergone a considerable evolution during the past century. Paramount milestones have been the introduction of the printed wiring board, which allowed for a rationalized assembly of electronic systems and the fabrication of integrated circuits with still ongoing increase of functional density due to miniaturization. Additionally sensors, micro electro mechanical systems, displays, and light emitting diodes have greatly added application potentials to electronic systems. Miniaturization is still one of the drivers for development in electronic components. On the other hand, however, conformity of the electronic systems to some give shape or space is increasingly requested for future applications. At present a great number of electronic appliances e.g. in mobile communication and medical electronics are manufactured to be foldable by using flexible printed wiring boards for assembly. The flexible printed wiring board restricts the bending to be only around on axis at a time. For a conformity to a truly three dimensional shape the wiring substrate needs to be stretchable to a certain extend. The development of stretchable wiring boards is the aim of the European project STELLA (stretchable electronics for large area applications). In the present paper process technologies for the efficient fabrication of stretchable wiring substrates using printing technology and/or photo structuring will be described. The conductive wiring which has to be as stretchable as the substrate matrix is designed as a meander and was optimized using FEM modelling. The electric contact formation is effected either by soldering techniques using low melting solder alloys or with anisotropic conductive adhesive. The interface between components assembled on the stretchable board and the wiring is mechanically the most fragile point of the wiring. Approaches for the reinforcement of the vicinity of the assembled components and first results a- re presented.