PhD Student University of Colorado - Boulder Boulder, CO, United States
This work demonstrates fully automatic 3D-fabrication of multi-material and multi-layer Printed-Circuit-Boards (PCBs) with dense integration of print-in-place active and passive electronics including functional-as-printed organic electrochemical transistors (OECTs), resistors and capacitors. Solution-processable materials are increasingly being preferred by the industry for many applications since they are compatible with a wide range of deposition methods including inkjet, aerosol-jet and electro-hydrodynamic printing. Among them, piezo-driven inkjet deposition is highly scalable and well-known, alongside being very accessible. It is inherently suited for multi-material deposition, allowing many different materials to be combined at small scales at the print-site, enabling fabrication of both homogeneous and heterogeneous parts without the need to pre-mix materials.
By developing a palette of low-viscosity UV and heat-reactive materials, we demonstrate full automation in fabricating multi-material 3D structures comprising rigid and flexible regions, highly conductive traces, semiconducting polymers, dielectrics and UV-curing solid and gel-state electrolytes. We also demonstrate via-less interconnects across multiple layers in printed PCBs that have traditional electronic components soldered in place to form working devices. The devices are all printed-in-place on a heated bed at 90\degree C. This includes 3D-printing the flexible substrate itself. Using simultaneous deposition of UV-curing dielectric materials with different mechanical properties, we form the rigid and flexible regions of the structure. Further, we can combine these materials in-situ to form transition regions within the structure that gradually go from rigid-to-flexible in order to reduce mechanical stresses at the interface. Following this, the conductive and semiconductive materials are simultaneously deposited to form the highly-conductive traces and resistors. When printing OECTs, this is followed by printing solid and gel-state electrolytes and a dielectric encapsulation layer to allow subsequent deposition of the next layers to build more devices and traces on top.
This method of manufacturing does not require any manual steps between printing each material or the use of multiple systems to complete the fabrication. It allows fabrication of a variety of heterogeneous materials in true-3D, offering a more elegant solution to electronics manufacturing compared to traditional approaches, screen printing and extrusion-based printing. Moreover, all the materials used are mutually-compatible with all process steps, eliminating the need to sequence steps based on material types. Inkjet deposition does not require the substrate to be flat. Hence, we can make use of trapezoidal side walls between different layers to deposit conductive materials forming interconnects between layers without the need for traditional cylindrical vias or drilling.
The fabrication is performed on a commercial UV-inkjet system, which further demonstrates the ease of adaptability to other piezo-driven inkjet systems.
