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Nowadays, multi-material systems can be realised in and on 3D components by means of sequential coating technology (dispensing/aerosol jet). In addition to the additive manufacturing of the basic body, the integration of electrical conductors and optical fibres can thus also be implemented additively and with a high degree of freedom of form. 3D opto-electro MIDs offer the possibility for intrinsic galvanic isolation, excellent electromagnetic compatibility and novel applications in sensor technology. The complete integration of electronics and optics on 3D base bodies therefore leads to an increase in the functionalisation of MIDs. Current manufacturing processes do not currently allow industrial scaling of 3D components with integrated electrical circuits and complex optical networks. In the “3DOptronic MID” project, a highly productive process chain for manufacturing 3D hybrid systems with integrated optical networks and electronic conductors will therefore be researched. For this purpose, (multilayer) hybrid systems will first be produced on planar foils, which contain both conductor paths for controlling diodes (optical sources and receivers) and optical waveguides for information transmission and energy supply. In the flexographic printing process used, both electrically conductive and light-conductive materials can be applied. Subsequently, thermoforming is used to give the planar hybrid system the spatial characteristics corresponding to the functional geometry. The main research question is how the hybrid systems and the moulding parameters are to be designed in order to guarantee a reliable function in the product. For this purpose, the individual processes must be optimised for productivity and quality in order to increase the economic potential. For process development, the temperature stability and formability relevant for thermoforming must be characterised. This applies to the substrate as well as to the optical and electrical materials.
Figure 1: Solution approach; Source: Leibniz University – ITA
Subsequently, geometric limit values for the forming process (radii of curvature, elongations) are determined with the help of mechanical process simulations. At the same time, the process limits and geometry specifications are prototypically validated and implemented with 3D-printed stamp bodies. Depending on the determined forming requirements, different layer thicknesses and printed layouts of hybrid systems are produced in flexographic printing. For this purpose, the sub-processes are tested with thermoformable substrates (PMMA, PC, PET). UV-curable polymers are printed to produce the optical fibres. For the electrical conductors, metal-containing (Cu or Ag) pastes or inks are applied, dried and optionally sintered using flash light. A comprehensive investigation of the mechanical properties such as adhesive strength, geometry (confocal microscope, SEM) and temperature stability (temperature cycling tests) of the generated systems is carried out. Likewise, a validation of the characteristic properties, such as the optical attenuation or transmittable bandwidth for optical fibres and the electrical resistance for electrical conductors, is carried out. Finally, the multi-stage flexographic printing and thermoforming of the entire system is validated. Several demonstrators are to be realised with the generated 3D hybrid systems to illustrate the advantages for sensor technology and for the design of functional lighting elements.
The aim of the project is to produce 3D components with fully integrated electrical conductors and optical networks. The focus of the investigations is to determine the technically possible parameter range for flank angles, radii of curvature and height of the generated 3D geometry while minimising optical attenuation. A particularly innovative aspect is that thermoforming should simplify the assembly of components, as the optical components are aligned with the waveguide by creating pockets and compensating for any height differences that occur. In the project, we are aiming for a maximum signal attenuation between transmitter and receiver of 10 dB. With an attenuation of 0.2 to 1 dB/cm (literature values for planar optical systems), this results in a maximum transmission length of 10 to 50 cm. With the targeted optical power of 50 mW on the transmitter side, a power of 5 mW is thus available to the sensor units. The research objectives are to be achieved by empirically checking process parameters and determining the valid process windows.
Benefits and economic significance for SMEs
The project enables SMEs to produce novel products such as housings or packaging with integrated optical waveguides and sensors. This is a competitive advantage for safety-relevant components. In addition, needs in Industry 4.0 can be met through the development of “smart” components. Other examples of application on formable substrates also include the distribution of light in lighting applications such as car interiors. The additive manufacturing option of the moulded bodies in thermoforming also enables adaptive design adjustment, which offers particular advantages for medical technology, which is characterised by individualisation. The unique selling point of scalable production of electro-optical EMFs, which enables cost-effective mass production, is a particular competitive advantage for SMEs. The project results should enable SMEs to realise completely optically coupled sensor nodes that have a purely optical data and energy connection in an optical network.