Electronics of the future—more tightly integrated with freeform 3D design—require rethinking the often bulky, planar design of current circuit boards. Significant size reduction compared to conventional PCBs can be made by working with bare die components over packaged SMDs, and by placing and interconnecting these dies in 3D space. To this end, TNO at Holst Centre has developed a novel multi-material additive manufacturing technique: “3D Additive Lithography for Electronics” (3D-ALE). By combining direct imaging lithography and 3D printing, this system is optimized for the production of electrically interconnected, heterogeneously integrated freeform functional devices. A scanning DMD-based light engine is used to pattern photopolymer and allows printing of electrical features down to 10 µm line spacings. Using industry-standard conductive pastes, electrical components can subsequently be integrated and interconnected within the printed polymer body. A microelectronic demonstrator to enable endoscopic ultrasound imaging via a catheter will be demonstrated. The device features sub-mm sized, bare die ASIC and CMUT chips integrated and interconnected using the 3D-ALE system.
We demonstrate a method combining direct ink writing of a chiral nematic liquid crystal oligomer ink with a photolithography step in a procedure that gives the user great flexibility in the design of striking polymer optics. The printable chiral nematic ink is first made by oligomerizing a reactive nematic liquid crystal monomer with a reactive chiral dopant. This ink can be readily printed using direct ink writing and quickly forms the cholesteric phase after deposition. Increasing the lateral nozzle speed forces the helical chiral nematic alignment into a slanted configuration, which has deviating optical properties compared to conventional planar chiral nematic liquid crystal reflectors—when inspected from the surface normal, these slanted photonics do not display circular polarization dependence, a feature characteristic for chiral nematics. The direction of this slant is determined by the printing direction, and thus highly customizable. For instance, when printing in a single direction, the peak reflected wavelength λmax is only seen at ca. 50° angle of incidence. Writing a back-and-forth pattern turns the object into an “inverse cholesteric” in two dimensions, where the longest reflected wavelength is seen from 50° in either direction. More intricate print path designs lead to more complex appearances. With a two-step photo-crosslinking procedure using masks, two-dimensional designs can be imprinted in direct ink written coatings, resulting in highly complex but programmable reflection patterns.
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