Experimental Evidence for Formation of Ni-Al Compound in Flip-Chip Joints Under Current Stressing

Abstract

The materials interactions on the under bump metallization (UBM) side of flip-chip solder joints during current stressing were studied by using highresolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM). Flip-chip solder joints with sputtered Al/Ni(V)/Cu UBM were subjected to current stressing at an ambient temperature of 150°C. It was found that a layer of Ni-Al phase, presumably NiAl 3 according to energy-dispersive x-ray spectroscopy (EDX) measurements, was observed at the Al/Ni(V) interface. In addition, evidence for the formation of a nonconductive oxide layer at the NiAl 3 /Ni(V) interface was observed. This nonconductive oxide layer was responsible for diverting electron current away from the porous region.

Sputtered Ni–Zn under bump metallurgy (UBM) for Sn–Ag–Cu solders

“…Pure Ni thin films are not effectively deposited by conventional magnetron sputtering since Ni is a magnetic material [5,7,8]. Ni-V thin films have been widely used as a sputtered UBM [1,3,9] since magnetron sputtering is possible with a non-magnetic Ni-V (7 wt.%) target [7]. However, several problems such as electromigration failure [10,11] and Sn-patch problems [8,12] were reported for the Ni-V UBM.…”