Underfill selection for reducing Cu/low-K delamination risk of flip-chip assembly

Experimental and numerical studies were conducted to investigate Cu/low-k delamination potentials of a flip-chip package assembly implemented with different underfills under an accelerated thermal cycling test condition. A total of six underfills were considered and compared. Their temperature-dependent Young´s moduli, coefficients of thermal expansion, and glass transition temperatures were measured and incorporated in the finite element model. The numerical predictions were benchmarked by actual thermal cycling test results. Results indicate that the first principal stress at the die edge shows a good correlation with Cu/low-k delamination potentials observed from experiments.