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Abstract
Issue Title: Pb-free Solders and Materials for Emerging Interconnect and Packaging Technologies
Alloys from the composition range Sn-(0.7 wt.% to 7.6 wt.%)Cu consist of primary Cu^sub 6^Sn^sub 5^ surrounded by a eutectic Sn-Cu^sub 6^Sn^sub 5^ mixture. The primary Cu^sub 6^Sn^sub 5^ intermetallics commonly adopt a coarse elongated morphology, which is not optimal for the mechanical properties of the soldered joint. This paper investigates the effect of trace elemental additions on the size and morphology of the primary Cu^sub 6^Sn^sub 5^ in Sn-4 wt.%Cu alloy with and without Ni additions. Elements investigated include ppm additions of Al, Ag, Ge, and Pb. It is shown that Al has a marked effect on the solder microstructure and refines the size of the primary Cu^sub 6^Sn^sub 5^, even at very low addition levels, in both binary Sn-Cu alloys and those containing additional Ni. The effect of Al is confirmed using real-time x-radiographic synchrotron observations of solidification.[PUBLICATION ABSTRACT]