Impact Testing of Sn-3.0Ag-0.5Cu Solder with Ti/Ni(V)/Cu Under Bump Metallization After Aging at 150°C

Abstract

Nonmagnetic Ni(V) metal and low consumption rate with solders are the advantages of sputtered Ti/Ni(V)/Cu under bump metallization (UBM). However, a Sn-rich phase (''Sn-patch'' herein) can form in the Ni(V) layer after reflow and aging. In lead-free solder, Sn-patches form and grow more quickly than in Sn-Pb solder. Thus, the effect of Sn-patches on solder joint reliability becomes critical. In this study, Sn-3.0Ag-0.5Cu solder was reflowed with Ti/Ni(V)/Cu UBM at 250°C for 60 s, and then aged at 150°C for various durations. A high-speed impact test was introduced to evaluate solder joint reliability. After impact testing, it was found that, the larger the Sn-patch, the greater the propensity of the solder joint to suffer brittle fracture. The correlation between Sn-patch and solder joint reliability is discussed.