Solidification Behaviour of Sn-40Pb Lead Solder and Sn-0.7Cu Lead-free Solder

Abstract

Lead-free solder, especially Sn-0.7Cu has been evolving due to the restriction of the lead solder usage which is environmental and health unfriendly. However, most of the lead solder properties show a better result compared to the lead-free solder. To further improve the properties of lead-free solder, the solidification state of Sn-40Pb and Sn-0.7Cu, which is one of the important behaviour in thermal analysis that affects the solder properties and performance, was investigated and compared in this study by natural cooling curve method. The result showed that Sn-40Pb has two nucleation phase while Sn-0.7Cu has only one during the solidification. The primary lead-rich phase was first nucleated in Sn-40Pb following by the secondary tin-rich phase when cooling; while the phase of Cu6Sn5 was nucleated in Sn-0.7Cu. In addition, it is found that the undercooling of Sn-40Pb is lower than Sn-0.7Cu in the cooling curve.