Bump structure e.g. ladder-bump structure, for bump-on-trace assembly, has copper pillar provided on metallurgy structure and including tapering arc-shaped profile, and metal cap mounted on pillar, where solder structure is mounted on cap

摘要

The structure i.e. ladder-bump structure (10), has an under bump metallurgy structure (14) arranged over a substrate (12). A copper pillar (16) is arranged on the metallurgy structure, and includes a tapering arc-shaped profile (22). A metal cap (18) is mounted on the pillar, and a solder structure (20) is mounted on the metal cap. A lower side (24) of the pillar is broader than an upper side (26) of the pillar. A ratio of a width (34) of the pillar on half height of the pillar to a width (36) of the lower side of the pillar is ranged between approximately 0.9 and 0.93. An independent claim is also included for a method for forming a bump structure.