Effect of Impurities of Au and Pd on Tensile Properties of Eutectic Sn-Pb Solder for Aerospace Applications

Abstract

For aerospace applications, eutectic Sn–Pb solder has been used for soldered joints requiring high reliability. However, the use of lead-free electronic components has been spreading and such components have been required. For lead-free electronic components, electrode materials have been changed from Sn–Pb alloys to lead-free materials. In joints with eutectic Sn–Pb solder and Ni/Pd/Au electrodes, degradation of the mechanical properties of the solder due to the dissolution of Au and Pd into the solder is a concern. In this study, the effect of Au and Pd impurities on the tensile properties of eutectic Sn–Pb solder was examined. In solders with Au ranging from 1 to 5 mass%, the tensile strength is stable at approximately 50 MPa, which is 1.25 times that of Sn–37Pb solder. Elongation decreases with increasing Au content. In solders with Pd ranging from 1 to 5 mass%, the tensile strength increases with increasing Pd content. Elongation decreases with increasing Pd content and is less than half that of Sn–37Pb solder. In the addition range investigated, Pd is more harmful than Au for elongation. In solders with both Au and Pd added, in the range less than 1 mass%, the tensile strength increases and elongation decreases with increasing contents of Au and Pd. It was clarified that the contents of Au and Pd should be less than 0.025 and 0.05 mass%, respectively, to prevent significant decrease in elongation.