Lookup NU author(s): Dr Stevin Pramana
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Nanoscale interfacial evolution in Cu-Al wire bonds during isothermal annealing from 175 °C to 250 °C was investigated by high resolution transmission electron microscopy (HRTEM). The native aluminum oxide film (∼5 nm thick) of the Al pad migrates towards the Cu ball during annealing. The formation of intermetallic compounds (IMC) is controlled by Cu diffusion, where the kinetics obey a parabolic growth law until complete consumption of the Al pad. The activation energies to initiate crystallization of CuAl2 and Cu9Al4 are 60.66 kJ mol-1 and 75.61 kJ mol-1, respectively. During IMC development, Cu9Al 4 emerges as a second layer and grows together with the initial CuAl2. When Al is completely consumed, CuAl2 transforms to Cu9Al4, which is the terminal product. Unlike the excessive void growth in Au-Al bonds, only a few voids nucleate in Cu-Al bonds after long-term annealing at high temperatures (e.g., 250 °C for 25 h), and their diameters are usually in the range of tens of nanometers. This is due to the lower oxidation rate and volumetric shrinkage of Cu-Al IMC compared with Au-Al IMC. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Author(s): Xu H, Liu C, Silberschmidt VV, Pramana SS, White TJ, Chen Z, Acoff VL
Publication type: Article
Publication status: Published
Journal: Acta Materialia
Print publication date: 01/08/2011
Online publication date: 16/06/2011
ISSN (print): 1359-6454
Publisher: Pergamon Press
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