Effect of adding 0.3 wt% Ni into the Sn–0.7 wt% Cu solder : Part II. Growth of intermetallic layer with Cu during wetting and aging

Abstract

The growth behavior of intermetallic layer with or without adding 0.3 wt% Ni into the Sn–0.7Cu solder was studied during the wetting reaction on Cu-substrate and thereafter in solid-state aging condition. The Cu-solder reaction couple was prepared at 255, 275 and 295 °C for 10 s. The samples reacted at 255 °C were then isothermally aged for 2–14 days at 150 °C. The reaction species formed for the Sn–0.7Cu/Cu and Sn–0.7Cu–0.3Ni/Cu soldering systems were Cu 6Sn 5 and (CuNi) 6Sn 5, respectively. The thickness of the intermetallic compounds formed at the solder/Cu interfaces and also in the bulk of both solders increased with the increase of reaction temperature. It was found that Ni-containing Sn–0.7Cu solder exhibited lower growth of intermetallic layer during wetting and in the early stage of aging and eventually exceeded the intermetallic layer thickness of Sn–0.7Cu/Cu soldering system after 6 days of aging. As the aging time proceeds, a non-uniform intermetallic layer growth tendency was observed for the case of Sn–0.7Cu–0.3Ni solder. The growth behavior of intermetallic layer during aging for both solders followed the diffusion-controlled mechanism. The intermetallic layer growth rate constants for Sn–0.7Cu and Sn–0.7Cu–0.3Ni solders were calculated as 1.41 × 10 −17 and 1.89 × 10 −17 m 2/s, respectively which indicated that adding 0.3 wt% Ni with Sn–0.7Cu solder contributed to the higher growth of intermetallic layer during aging.