Effect of trace Al on growth rates of intermetallic compound layers between Sn-based solders and Cu substrate

Abstract

This paper reports the effect of the addition of 1wt% Al into 100Sn, 96.5Sn–3.5Ag (SA) and 95.5Sn–3.8Ag–0.7Cu (SAC) solders, on growth rates of intermetallic compound (IMC) layers between the solders and a Cu substrate. During reflow at 260°C under 2%H298%N2 forming gas for 5–120min, the most pronounced reduction in IMC growth was observed in the SAC–1Al/Cu system. This was accompanied with the evolution of a layer of η2 (AlCu) IMC which was first formed within the bulk of the solder, then migrated towards and gradually replaced the previously formed η (Cu6Sn5) and ε (Cu3Sn) IMCs at the solder/Cu interface, and was finally transformed into δ (Al2Cu3) IMC and dispersed into the bulk of the solder again. A similar reduction in growth and associated evolution of IMCs was observed in the SAC–1Al/Cu samples subjected to thermal ageing at 170°C under air for 24–2096h.