Abstract
This study aims to investigate the interfacial reaction and the impact reliability of Sn-3.0Ag-0.5Cu/Cu-15Zn (wt.%; SAC/Cu-Zn) solder joints. The Cu-Zn under bump metallization (UBM) was developed to replace the traditional Cu UBM in the Pb-free solder joints. In the Sn-Ag-Cu/Cu solder joint, thick Cu 6 Sn 5 and Cu 3 Sn intermetallic compounds (IMCs) formed at the interface after thermal aging at 150 C for 1000 h. In contrast, the SAC/Cu-Zn solder joint shows a thinner Cu 6 (Sn,Zn) 5 layer, and the growth of Cu 3 Sn IMC was absolutely suppressed at the SAC/Cu-Zn interface. To evaluate the bonding energy, the high speed shear testing was carried out to correlate the microstructure of solder joints. It is noteworthy that the SAC/Cu-Zn solder joint can enhance the impact toughness. The higher impact toughness of SAC/Cu-Zn is attributed to the thinner and tougher Cu 6 (Sn,Zn) 5 IMC at the joint interface. Accordingly, Cu-Zn alloy is a potential UBM material for Pb-free solder joints to improve the impact reliability. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.