Direct bump-on-copper process for flip chip technologies

Abstract

Direct bump-on-copper technology provides a direct cost savings, equivalent bumping qualities, and better performance and reliability for products. The bump-on-copper FOC (flexon-cap) technology is modified and derived from the existing high volume, reliable, proven bump-on-aluminum FOC process. A copper compatible adhesion layer, namely, titanium, combined with a NiV barrier layer and a Cu wetting layer for solder are used to construct the tri-metal stack that defines a reliable under bump metallurgy (UBM) for flip chip solder bumps. A proprietary solder deposition technique using solder paste is then applied to form the solder interconnects. Bump quality tests such as bump height and bump shear strength demonstrates an equivalent structure to the existing Al/NiV/Cu based flip chip bump. Wafers constructed as described are tested at both wafer level and in an assembled level. All perform well in the preliminary reliability evaluation including temperature cycle (TC), thermal shock (TS), autoclave test (PCT), high temperature storage (HTS), high temperature operational life (HTOL), and high accelerated stress test (HAST).