TY - JOUR
T1 - The influence of Ni and Zn additions on microstructure and phase transformations in Sn-0.7Cu/Cu solder joints
AU - Zeng, Guang
AU - McDonald, Stuart D.
AU - Gu, Qinfen
AU - Terada, Yasuko
AU - Uesugi, Kentaro
AU - Yasuda, Hideyuki
AU - Nogita, Kazuhiro
N1 - Funding Information:
We gratefully acknowledge financial support from the University of Queensland (UQ)–Nihon Superior collaborative research program. Synchrotron X-ray radiography experiments and micro-XRF mapping experiments were performed at the Japan Synchrotron Radiation Research Institute (JASRI) on BL20XU , BL20B2 and BL37XU of SPring-8 synchrotron ( 2011B1048 , 2012B1440 , 2013B1524 , 2014A1540 , 2014A1541 ), funded by the Australian Synchrotron International Synchrotron Access Program ( AS/IA114/4743 , AS/IA124/6235 , AS/IA142/8198 ). PXRD experiments were performed at the Australian Synchrotron Powder Diffraction Beamline ( AS131/PD/5784 ). This work is also supported in part by a Grant-in-Aid for Scientific Research (S) (24226018) from JSPS, Japan. The authors thank Mr. J. Read of UQ for valuable discussions; Dr. J. Khan of the Queensland Node of the Australian National Fabrication Facility (ANFF-Q) at UQ for use of the DSC facility; and support staff/students from the Department of Adaptive Machine Systems of Osaka University, and Department of Materials Science and Engineering of Kyoto University for experimental assistance at SPring-8. The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis of UQ. G.Z. is financially supported by a University of Queensland International (UQI) Scholarship, a Graduate School International Travel Award (GSITA) of UQ, and a China Scholarship Council (CSC) Scholarship.
Publisher Copyright:
© 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
PY - 2015/1/15
Y1 - 2015/1/15
N2 - Microalloying, in which the solidification structure is preferably and significantly modified by trace elements, is a key method for improving Pb-free interconnections in electronic devices. Microalloying Ni or Zn is expected to modify the Sn-0.7Cu alloy in different ways. This research examines the influences of minor/trace additions of Ni and Zn concurrently on the development of the microstructure, the interfacial reactions and the stability of the intermetallics in Sn-0.7Cu solder alloys and associated joints, using X-ray radiography, X-ray florescence analysis, X-ray diffraction and electron microscopy. It shows that minor Zn additions (∼0.15 wt.%) result in the formation of a CuZn intermetallic in the interdendritic region during solidification, whereas a small amount of Ni completely changes the solidification mode and a eutectic microstructure is obtained. When Ni is added, small particles of primary (Cu,Ni)6Sn5 intermetallic forms in advance of the solidification front. Microalloying Ni and Zn concurrently refines the microstructure and leads to a more continuous, finer-grained and stable interfacial Cu6Sn5 intermetallic and suppresses the growth of Cu3Sn. The Ni and Zn are homogeneously distributed in interfacial Cu6Sn5 and inhibit the polymorphic phase transformation of Cu6Sn5. This stabilizing effect minimizes the thermal expansion mismatch between interfacial Cu6Sn5 and the Cu substrate. The findings have important implications for the manufacture of high-reliability lead-free microjoints.
AB - Microalloying, in which the solidification structure is preferably and significantly modified by trace elements, is a key method for improving Pb-free interconnections in electronic devices. Microalloying Ni or Zn is expected to modify the Sn-0.7Cu alloy in different ways. This research examines the influences of minor/trace additions of Ni and Zn concurrently on the development of the microstructure, the interfacial reactions and the stability of the intermetallics in Sn-0.7Cu solder alloys and associated joints, using X-ray radiography, X-ray florescence analysis, X-ray diffraction and electron microscopy. It shows that minor Zn additions (∼0.15 wt.%) result in the formation of a CuZn intermetallic in the interdendritic region during solidification, whereas a small amount of Ni completely changes the solidification mode and a eutectic microstructure is obtained. When Ni is added, small particles of primary (Cu,Ni)6Sn5 intermetallic forms in advance of the solidification front. Microalloying Ni and Zn concurrently refines the microstructure and leads to a more continuous, finer-grained and stable interfacial Cu6Sn5 intermetallic and suppresses the growth of Cu3Sn. The Ni and Zn are homogeneously distributed in interfacial Cu6Sn5 and inhibit the polymorphic phase transformation of Cu6Sn5. This stabilizing effect minimizes the thermal expansion mismatch between interfacial Cu6Sn5 and the Cu substrate. The findings have important implications for the manufacture of high-reliability lead-free microjoints.
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U2 - 10.1016/j.actamat.2014.10.003
DO - 10.1016/j.actamat.2014.10.003
M3 - Article
AN - SCOPUS:84908425738
SN - 1359-6454
VL - 83
SP - 357
EP - 371
JO - Acta Materialia
JF - Acta Materialia
ER -