Selective Deposition of Copper Traces onto Additively Manufactured All-Aromatic Polyimides via Laser Induced Graphene to Enable Conformal Printed Electronics

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Virginia Tech


The hybridization of direct write (DW) and additive manufacturing (AM) technologies to create additively manufactured electronics (AME) has enabled the integration of electrical functionality to form multifunctional AM components. Current work in AME has demonstrated the integration of conductive traces into and onto geometries and form factors that are not possible through traditional electronics packaging processes. This has largely been accomplished by using AM and DW technology to deposit conductive inks to form interconnects on the surface of AM substrates or within multimaterial AM geometries. However, the requisite thermal post-processing and high resistivity of the conductive inks and the limitations in thermal and dielectric performance of printable substrates commonly used in AME restrict the capabilities of these parts. This thesis proposes an alternative process for the conformal deposition of low resistivity traces on additively manufactured all-aromatic polyimides (AM-PI) without the use of conductive inks. This is accomplished through the selective patterning of laser induced graphene (LIG), a porous 3D graphene fabricated via laser irradiation, onto the AM-PI. While the resultant LIG is conductive, its resistivity is further reduced by the electrodeposition of copper (Cu-LIG). In this thesis, the synthesis of LIG on AM-PI, thermally post processed to 240℃, 300℃, and 450℃, is demonstrated and characterized through sheet resistance measurements and Raman spectroscopy. AM-PI post-processed to 300℃ demonstrated the lowest resistivity LIG formation (13.8 Ω/square). The resistivity of Cu-LIG is compared to an industry standard silver ink (Micromax CB028) used in direct write hybrid manufacturing applications. Cu-LIG was found to have a measured resistivity (1.39e-7 Ω·m), two orders of magnitude lower than the measured resistivity of the CB028 silver ink (1.62e-5 Ω·m). Additionally, the current capacity of the Cu-LIG was demonstrated and Joule heating of the material was observed via IR thermography. Cu-LIG demonstrated no failure of conductive trace or substrate under 5A of current for 2 minutes, heating to a maximum recorded temperature of 76.3℃. Several multifunctional components were fabricated as case studies to further validate the process. Several small passive electronic devices (e.g., a heater and an interdigitated capacitor) are fabricated to demonstrate selective deposition of complex copper traces. The fabrication of an Archimedes spiral on a hemispherical substrate via Cu-LIG is completed to demonstrate the ability to use the process to fabricate conformal conductive traces. An LED circuit is fabricated on a face-center cubic AM-PI lattice which demonstrates multi-planar fabrication on geometrically complex 3D printed substrates.



Additive Manufacturing, 3D printing, printed electronics, electroplating, Laser Induced Graphene, LIG, All-Aromatic Polyimides