Abstract:
Nickel or nickel alloys are common materials used in under bump metallization (UBM) in flip chip technology. Nickel is used because of its slow reaction rate with tin-based solder at
elevated temperatures. However, nickel is ferromagnetic at room temperature, hence cannot be easily deposited with magnetron sputtering. In this study, small quantities of titanium and
vanadium were added to nickel via co-sputtering to try to form nonmagnetic binary alloys. BH-looper results showed decrease in saturation magnetization alloys with increasing amount of
the added metal. Impurity addition to nickel in UBM can create reliability issues especially with solder reaction. This may lead to a mechanically unstable film that ultimately results in an electrical open circuit from the die to the package. A solder reflow process is simulated to analyze reactions with SnAgCu lead-free solder via electron microscopy. SEM analysis showed
increased contact angle and serious interfacial separation between Ni(Ti) and solder.
