Intel-metallic Compound Formation and Morphology Evolution in the 95Pb5Sn Flip-Chip Solder Joint with Ti/Cu/Ni Under Bump Metallization during Reflow Soldering

摘要

Intermetallic compound formation and morphology evolution in the 95Pb5Sn flip-chip solder joint with the Ti/Cu/Ni under bump metallization(UBM)during 350 deg C reflow for durations ranging from 50 sec to 1440 min were investigated.A thin intermetallic layer of only 0.4 mum thickness was formed at the 95Pb5Sn/UBM interface after reflow for 5 min.When the reflow was extended to 20 min,the intermetallic layer grew thicker and the phase identification revealed the intermetallic layer comprised two phases,(Ni,Cu)_3Sn_2 and(Ni,Cu)_3Sn_4.The detection of the Cu content in the intermetallic compounds indicated that the Cu atoms had diffused through the Ni layer and took part in the intermetallic compound formation.With increasing reflow time,the(Ni,Cu)_3Sn_4 phase grew at a faster rate than that of the(Ni,Cu)_3Sn_2 phase.Meanwhile,irregular growth of the(Ni,Cu)_3Sn_4 phase was observed and voids formed at the(Ni,Cu)_3Sn_2/Ni interface.After reflow for 60 min,the(Ni,Cu)_3Sn_2 phase disappeared and the(Ni,Cu)_3Sn_4 phase spalled off the Ni layer in the form of a continuous layer.The gap between the(Ni,Cu)_3Sn_4 layer and the Ni layer was filled with lead.A possible mechanism for the growth,disappearance,and spalling of the intermetallic compounds at the 95Pb5Sn/UBM interface was proposed.