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Title: Effect of thermal aging on interfacial behaviour of copper ball bonds
Authors: Xu, Hui
Liu, Changqing
Silberschmidt, Vadim V.
Issue Date: 2008
Publisher: © IEEE
Citation: XU, H., LIU, C. and SILBERSCHMIDT, V.V., 2008. Effect of thermal aging on interfacial behaviour of copper ball bonds. IN: 2nd Electronics Systemintegration Technology Conference, Greenwich, London, 1-4 Sept., pp. 891 - 896.
Abstract: Thermosonic copper ball bonding is an interconnection technology that serves as a viable and cost-saving alternative to gold ball bonding. However, the reliability of copper bonds remains to be ascertained. Intermetallic compounds (IMCs) and possible voids and cracks may grow and propagate at the interface of bonds during their service. The proper IMCs formation is beneficial to bonding strength but an excessive growth of IMCs, voids and cracks can induce a mechanical failure and increase a contact resistance. In this study, a 99.99% copper wire with diameter 50.4 mum was bonded to a Al-1%Si-0.5%Cu metallisation pad by thermosonic bonding. Scanning electron microscopy, energy dispersive X-ray spectrometry, dual focused ion bean and transmission electron microscopy (TEM) were used to investigate the interfacial evolution of such formed joints during the thermal ageing, and kinetics of Cu-Al IMCs growth was established. The results showed no IMCs at the initial bonded Cu/Al interface. To study the Cu-Al IMCs growth, the samples were thermally aged for different times at a temperature from 200 degC to 300 degC to accelerate interfacial evolution. The growth of Cu-Al IMCs followed the parabolic law as a function of aging time at a certain aging temperature, and it is more sensitive to temperature compared to time. The activation energy of Cu-Al IMC growth was obtained from the Arrhenius plot. Voids and cracks, which are commonly present in gold ball bonds due to thermal aging, were not observed in copper ball bonds even after aging at 200 degC for 2900 hours. Finally, the structure of Cu-Al IMCs was confirmed to be Cu9Al4 by selected area electron diffraction with TEM.
Description: This is a conference paper [© IEEE]. It is also available at: http://ieeexplore.ieee.org/ Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.
Version: Published
DOI: 10.1109/ESTC.2008.4684470
URI: https://dspace.lboro.ac.uk/2134/5334
ISBN: 9781424428137
Appears in Collections:Conference Papers and Presentations (Mechanical, Electrical and Manufacturing Engineering)

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