Copper pillar bump design optimization for lead free flip-chip packaging

Abstract

The interfacial delamination between the under bump metallurgy and the aluminum (Al) pad was observed in a copper (Cu) pillar bump evaluation in the work. The finite element analysis was employed to investigate the failure mechanism and the cu pillar bump geometry designed optimization. The finite element simulation result shows that the Cu pillar bump sustains the largest tensile stress at the temperature cycling test. The larger diameter Cu pillar bump can reduce the tensile stress significantly at the high temperature stress environment. Besides, an experiment confirms the finite element simulation result. Furthermore, an underfill with high glass transition temperature (T g) and high modulus also improve the flip-chip ball grid array packaging reliability.