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

This paper reports the effect of the addition of 1 wt% 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 degrees C under 2%H(2)98%N-2 forming gas for 5-120 min, 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 eta(2) (AlCu) IMC which was first formed within the bulk of the solder, then migrated towards and gradually replaced the previously formed eta (Cu6Sn5) and epsilon (Cu3Sn) IMCs at the solder/Cu interface, and was finally transformed into delta (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 degrees C under air for 24-2096 h. (c) 2012 Elsevier B.V. All rights reserved.