In this paper, we demonstrate electroplating copper and nickel selectively onto traces printed in a highly conductive thermoplastic composite filament and use of the resulting bulk metal conductors for 3D printed electronics packaging. Electroless plating has long been used for metallization of polymer 3D printed parts [9,10] to obtain superior mechanical and electrical properties, but results in blanket deposition of metal over the entire part. Since most 3D printable plastics are difficult to directly electrolessly plate, metallization through this technique is typically a multistep process requiring roughening [11] and surface activation [12] for proper plating. Creating separate electrodes using electroless plating requires additional steps to define the conductors, for instance through laser ablation, [13] variable swelling, [14] or mechanical polishing. [15] In 2017, researchers demonstrated that conductive polymer composites can be used as a conductive seed layer for electroplating. [16] Based on this finding, we demonstrated selective electroplating of a 3D printed fused filament fabrication (FFF) part, combining conductive composite filament to define plated regions with a nonconductive plastic as a mechanical support. [17] Fused filament fabrication, the extrusion of melted thermoplastics to build a part, is a cheap and widely available 3D printing technology. [18] While successful, the composite we used was resistive relative to traditional electroplating seed layers, requiring electrical contact near the region being plated and therefore strongly limiting the complexity of the resulting parts and preventing use for electronics packaging. Building on our work, a group at Southeast University in China subsequently demonstrated the use of a similar dual filament FFF 3D printing process to define regions for selective electroless plating through selective adhesion onto two different printable polymers and showed its use for 3D printed electronic packaging. [19] Electroless plating is however significantly slower than electroplating, [20] limiting possible deposition thickness, and also unlike electroplating lacks the ability to selectively plate different thicknesses or materials on the same part. A more detailed survey of past work on electro-and electroless plating of 3D printed parts was also given in ref. [17].Here, we use a very low resistivity filament to plate centimeters from the contact point and demonstrate the ability to selectively plate complex 3D parts such as electronic packages and 3D printed circuit boards (PCBs). A very low resistivity copperbased FFF filament developed at Duke University and commercialized under the name Electrifi [21] was recently demonstrated Creating 3D-printed parts with embedded circuitry is the next frontier in additive manufacturing, but printing of conductors with performance comparable to bulk metals such as copper is a difficult challenge. A hybrid process based on 3D printing followed by electroplating on highly conductive thermoplastic filament is used to ma...

A 100-element varactor sideband generator array for operation at 1.6 THz has been designed and fabricated. The array consists of varactor Schottky diodes fabricated on GaAs and integrated into an array of bowtie antennas. An integrated transmission line stub is included to tune the diode parasitic capacitance. Harmonic balance simulations predict the array to have a sideband conversion loss of 8.3 dB.

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