Hybrid Aerosol Jet Printing and Electrodeposition of Ferrite-Sandwiched Inductors

Abstract

The additive manufacturing (AM) of inductors of suitable size to be integrated into packaged electronics is attractive to customize the device characteristics for the specific application. Magnetic ferrite cores are widely used in conventional inductors, however, wire wound inductors can be brittle, heavy, bulky. Planar spiral inductors in a sandwich configuration present a promising alternative. Aerosol jet printing, a direct write AM technology, can deposit metal inks at a resolution of < 10 µm. Metal nanoparticle inks have limited conductivity at < 40% bulk. Building a higher profile may result in loss of resolution. Electrodeposition offers the ability to plate thick layers of highly conductive metals, including copper and nickel which are normally hard to access as nanoparticle inks compatible with aerosol jetting. We have previously shown the construction of a multi-layer flyback transformer with this hybrid aerosol jet and electrodeposition method. [1]We present a three-layer planar inductor with the first layer being a 1.3mm stack of ferrite sheets (Fair-Rite) with a 9 mm x 9 mm footprint integrated onto a circuit board. The intermediate layer consists of a spiral inductor made by aerosol jet printing UTDots Ag40X silver nanoparticle ink as the seed layer. To achieve high accuracy, the inductor was printed with a rotary axis stage. Electrodeposition in an acidic CuSO4 plating bath on top of the Ag seed layer resulted in thicknesses of 50 µm. A submicron layer of Ni is added for oxidation protection by electrodeposition from a Ni-Sulfamate bath. Lastly, a top 1.3 mm ferrite stack, with laser cut holes, is added to provide pass throughs for wire bonding. Figure 1 shows a micrograph of an inductor as printed, after electrodeposition, and with the top ferrite layer. Electrical measurements including impedance characteristics will be presented.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. The SAND No. is SAND2023-14571A.Figure 1. Construction of a ferrite-sandwiched inductor with (a) the aerosol jet printing of an Ag seed layer, (b) after electroplating of Cu and Ni.