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

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)(3)Sn-4 IMC was significantly retarded by adding Zn into UBM. (C) 2012 Elsevier B.V. All rights reserved.This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korea government (MEST) (No.2011-0015735)