Abstract
We developed a new sputtered under bump metallurgy (UBM) based on Ni-20wt% Zn thin films for Pb-free solders. This study focuses on the interfacial reactions between two Pb-free solders (Sn3.0Ag0.5Cu and Sn1.0Ag0.7Cu) and a Ni–Zn alloy UBM. By adding Zn to Ni UBM, Zn is incorporated into intermetallic compounds (IMCs) to form a quaternary Cu–Ni–Zn–Sn phase at the solder/Ni–Zn interface after reflow and subsequent isothermal aging. The Ni–Zn UBM sufficiently reduces the interfacial reaction and IMCs formation rates as well as UBM consumption rates compared to a Ni UBM. In particular, the formation of (Ni, Cu)3Sn4 IMC was significantly retarded by adding Zn into UBM.
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