During the past two decades a number of product concepts electronic build-ups have been developed, which inherently demand a certain degree of stretch (elongation, extension) to be accommodated within the electronic systems.
Fraunhofer IZM developed a technology to fabricate “stretchable printed circuits”. The dielectric carrier material of these circuitries is thermoplastic polyurethane as opposed to the glas-fibre-epoxy compound of rigid or Polyimid (PI), Polyethylenterephtalat (PET) or Polyethylenenephtalat (PEN) for flexible circuits.
Conductor tracks on the stretchable circuits are similar to the conventional printed circuits made of copper. However, depending on the use case a more or less pronounced meandering design is used in the stretchable circuits, in order to allow for an extension of these tracks.
Automated assembly of commercially available components onto these circuits is possible. As solder alloy tin bismuth is used, which has a melting temperature of around 142 °C.
Electronic systems thus fabricated withstand repeated extension and release cycles until fatigue failures of the conductor tracks occur. Depending on the layout, up to 300 % extension is possible until the first tensile break.
Typical application areas of stretchable electronic systems are medical devices (electronic band-aid), textile electronics and electronic skin as part of future robotics.