Flip-Chip Bonding Using Aerosol Jet Printed Silver Nanoparticles for RF Applications

This work demonstrates a new approach to flip-chip bonding of RF chips using aerosol jet printed silver nanoparticle (NP) microbumps for advanced packaging and heterogeneous integration. Here, chips with gold pads are flip-chip mounted on silver printed microbumps on an alumina substrate at low temperature and pressure. This process is similar to cold-welding in that it joins nanostructures without intense heating or other external forces. While silver NPs have been explored extensively for power electronics bonding, only large bonding pad sizes (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gt 1 \mathrm {mm} ^{2}$ </tex-math></inline-formula>) were possible due to manual application of the NPs, limiting their usefulness for RF structures. We demonstrate miniaturized bonding pad sizes using aerosol jet printing (AJP) to precisely control the application of the NPs. The same printed material is used for both transmission line conductors and the microbump bonds. Thermal cycling (between room temperature and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$125~^{\circ }$ </tex-math></inline-formula>C) over 500 cycles was carried out to demonstrate the first-order reliability of the bonding process. RF performance is presented using a broadband microwave nonlinear transmission line (NLTL).