Demonstration of Inkjet Printed Nanoparticle-based Inks for Solder Bump Replacement

摘要

Conventional eutectic solders suffer from scaling limitations related to their relatively poor conductivity,electrochemical and thermochemical stability, and toxicity/regulatory restrictions. Novel materials and systems thataim to replace conventional eutectic solders for future packaging applications must be able to meet both thethroughput and the thermal demands of standard bumping processes while simultaneously providing the electricaland mechanical properties characteristic of high performance and extended lifetimes. Inkjet printing is a fastgrowingdeposition technique aptly suited for wafer bumping processes because the feature sizes and pitchescapable are appropriate for solder bumps and the droplet-on-demand functionality is an attractive alternative toblanket films processing. Metallic nanoparticle-based inks represent the functional material for eutectic solderreplacement, and these inks are attractive due to their relative ease in synthesis and dispensation, their low thermalbudget, and electrical conductivities that routinely exceed those of even the best lead-based solders. Furthermore,such material systems have been shown to deliver very good reliability due to their bulk-like properties andavoidance of intermetallic complications as seen in eutectic systems. In this work, we present the capability ofprinting three dimensional features with nanoparticle inks and demonstrate the critical processing parameters thatdictate size control. We fabricate micropillars using a commercially available gold nanoparticle ink, demonstratingfeature sizes and techniques appropriate for solder bump replacement. Further, we investigate, for the first time, theprocess of sintering in three-dimensional nanoparticle features. Using extracted conductivity and mechanicalstrength measurements, we suggest a model for the sintering in three-dimensional features using our printedmicropillars as test structures.