A Combined Aerosol Jet Printing and Electrodeposition Process for Fabrication of Multi-Layer Inductors and Transformers on Iron-Nitride Substrates

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The manufacturing of planar spiral transformers and inductors by direct write additive manufacturing is an attractive approach because they are lighter, less brittle, and have the added customizability of a digital design process compared with conventional wire-wound inductors. Aerosol jet printing (AJP) is a direct write process capable of printing structures with less than 10 µm lateral resolution. However, the nanoparticle Ag inks used in AJP of conductive parts typically only have 35-40% of bulk conductivity. A hybrid electroless deposition of Cu and electrodeposition of Cu and Ni process can decrease the resistance of AJP printed silver spiral inductors by a factor of 45x while maintaining linewidths of 50 µm.[1] We have recently demonstrated the use of this hybrid method to manufacture a coreless flyback transformer with a primary inductance of 206-208 nH and a secondary inductance of 19.4-23.1 µH. This inductor converted an input of 17 V at 400 kHz to an output of 1250 V.[2]Forming the transformer on a magnetic layer of Fe4N can increase the inductance of the primary and secondary inductors, and ultimately the output of the transformer. Transformers (Figure 1) were manufactured on polyimide covered Fe4N substrates by aerosol jet printing of Ag seed layers, electrodeposition of Cu and Ni, and ultrasonic spraying or aerosol jetting of dielectric polymer separation layers. A new plating fixture which contacts both the interior and exterior of the secondary inductors enables the electrodeposition of Cu without the need for an intermediate electroless deposition step. For the same inductor configuration, the inductance increased to 561-809 nH for the primary and 63-82 µH for the secondary when sandwiched between Fe4N layers. Finally, a flyback transformer of this design converted an input voltage of 15V to an output voltage of greater than 2100V.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2024-04161A.