Optimized Thermoforming Process for Conformable Electronics

3D conformable electronic systems have attracted considerable attention lately. New technologies to realize such 3D electronics not only save weight and volume in known applications - e.g. car interior. They also allow completely new functionalities and systemic changes as the new smart structures and surfaces enable a novel interaction with the environment as well as with human beings through integrated sensors, actuators and electronics. The technology is and will be used in very different applications: Home appliances, Automotive, Robotics and Medical. Examples of first functionalities are operating elements such as switches or sliders in the form of capacitive sensors which can be integrated into three-dimensional surfaces. Conformable Electronics is largely based on established two-dimensional process technologies for the realization of the circuit carriers (printed circuit boards) as well as for the assembly of components as established in recent decades. Conformable electronics is manufactured in the same way as conventional electronic systems. It is endowed with the 3D shape, which goes beyond the typical properties of rigid and flexible printed circuit board in the last manufacturing step (thermoforming or injection molding). Flexible circuits cannot fully meet the requirements as they are only designed to bend and fold conductors around a single axis. A spherical surface, for example, cannot be covered without folds by a flat flex circuit. Therefore new materials and geometries for substrates and conductor lines have to be developed and investigated. To achieve the maximum freedom of design high levels of deformation are required. If realized with conventional thermoforming processes the deformation of base material and conductor tracks is very inhomogeneous which limits the geometries. In order to get predictable and homogeneous results which allow higher degrees of deformation a novel high resolution ceramic heater array for thermoforming has been developed. It allows controlled temperature distribution over the thermoformed area with lower temperatures where deformation has to be reduced. In combination with this heating technology a novel processing to produce conformable electronics is conceivable where first the circuit carriers will be applied and then the 3D geometry is formed.