Study of the interface reactions between two lead-free solders and copper substrates

Abstract

Traditional Sn-Pb solder alloys are being replaced, because of environmental and health concerns about lead toxicity. Among some alternative alloy systems, the Sn-Zn and Sn- Cu base alloy systems have been studied and reveal promising properties. The reliability of a solder joint is affected by the solder/substrate interaction and type of layers formed at the interface. The solder/substrate reactions, for Sn-Zn and Sn-Cu base solder alloys, were evaluated in what concerns the morphology and chemical composition of the interface layer. The phases formed at the interface between the Cu substrate and a molten lead-free solder were studied, at 250 ºC, with different stage times and alloy compositions. The melting temperatures of the studied alloys, were determined by Differential Scanning Calorimetry (DSC). Identification of equilibrium phases, formed at the interface layer, and the evaluation of their chemical compositions were performed by Scanning Electron Microscopy (SEM/EDS). Results of the studied systems were compared with the interface characteristics obtained for a traditional Sn-Pb solder alloy. Different interface characteristics were obtained, namely for the alloys containing Zn.