Magnetron Sputtering of Nickel Silicon Alloy as Thin Film UBM for Pb-free Flip-Chip Packaging

摘要

Nonmagnetic nickel silicon alloy thin film was deposited as a new barrier layer for iinder-bump-ruetallization (UBM) by magnetron sputtering. In comparison to the existing NiV thin film, our results showed that in direct contact with molten Pb-free solder NiSi reacts with Sn at much slower rate than NiV. After extended thermal aging, at the NiSi UBM-solder interface the (Ni,Cu)-Sn intermetallic compounds (IMC) form a stable and continuous layer, while in the NiV case, Kirkendall voids form in between the amorphous V-Sn rich layer and IMC, which inevitably leads to UBM interfacial fracture in bump ball shear/pull tests. The excellent performances such as balanced interdiffusion process, reduced Ni-Sn reaction rate, stable interface and desirable solder fracture failure mode that were demonstrated in this study strongly suggest that NiSi is a very promising thin film UBM solution to the challenges presented by the coming age of Pb-free solder flip-chip packaging.