Influence of solder volume on interfacial reaction between Sn-Ag-Cu solder and TiW/Cu/Ni UBM

Solder bump interconnection is a widely accepted approach for high performance and miniaturized packaging. Solder bump pitch of 90 mum or less will be needed to support chip-to-next-level packaging when the integrated circuitry features reach 45 nm by 2010 [ITRS 2004 Update - Assembly & Packaging]. Lead-free solder is expected to be widely implemented by then. Intermetallic compound (IMC) formation is inherent in the soldering process. Excessive IMC is detrimental to interconnection reliability and this is expected to be more pronounced as IC chips get thinner and smaller. In this study, Sn-Ag-Cu (SAC) solder bumps on under-bump-metallization (UBM) comprised of sputtered TiW/Cu and electrolytic plated Cu and Ni were evaluated. Solder bumps with pad diameters of 200, 70 and 40 mum were produced by solder paste printing on matching UBM prepared on silicon wafers and reflowed. SAC solder bump IMC morphology and its growth kinetics, and bump shear strength after isothermal aging were investigated