An aging study of intermetallic compounds formation in Sn-0.4Co-0.7Cu

Interfacial reactions between Sn-0.4Co-0.7Cu eutectic alloy and immersion Ni/Cu substrate have been investigated after reflow and high temperature storage. The reflow peak temperature at 265degC and a total duration time of 6 minutes were used. The duration time at the peak temperature of the reflow process was approximately 2 min. The aging temperature was 150degC and the duration time was 100 h, 200 h, 550 h and 1000 h, respectively. In the solder matrix of the Sn-0.4Co-0.7Cu alloy, the intermetallic compounds (IMC) CoSn₂ were found. At the interface between the solder alloy and the electroless nickel substrate, a ternary (Cu, Ni)₆Sn₅ intermetallic compound was detected. The intermetallic compound layer became thicker as a function of thermal aging time. The IMCs were continuous and their morphology was faceted at the interface. No voids and gaps were observed at the interface between the nickel layer and the Sn-0.4Co-0.7Cu eutectic alloy after thermal aging.