Sn concentration effect on the formation of intermetallic compounds in high-Pb/Ni reactions

Abstract

The reaction between high-Pb solders and Ni substrate was investigated to understand the Sn concentration effect on the formation of intermetallic compounds. Three PbxSn solders ( x = 1, 3, and 5 wt.%) were reacted with Ni substrates at 400 °C for 2–240 min. The reaction products formed at the interface were related to the Sn concentration in the solders. When the Sn concentration was 5 wt.%, Ni 3Sn 4 formed first and followed by the formation of Ni 3Sn 2. When the Sn concentration decreased to 3 wt.%, Ni 3Sn 2 formed first and followed by the formation of Ni 3Sn. When the Sn concentration became 1 wt.%, only Ni 3Sn 2 was. This fascinating concentration dependency was rationalized by using the Pb–Sn–Ni isotherm. In addition, the deep penetration of Pb into the Ni substrate along the grain boundaries was observed. It was likely that the low interfacial energy between high-Pb and Ni caused such an unusual grain boundary penetration.