Effect of the bismuth content on the interface reactions between copper substrate and Sn-Zn-Al-Bi lead-free solder

Abstract

Because of environmental and health concerns, some alternative solder alloys, named lead-free ones, are being developed. Among them, the Sn-Zn-Al system has been studied and reveals promising properties. In this work the presence of bismuth, in the range of 0 - 8 wt%, was evaluated in what concerns to the chemical interactions between solder/substrate and the equilibrium phases present at the interface. The phases formed at the interface between the Cu substrate and a molten lead-free solder were studied with different time of stage and alloy compositions. The effect of Bi content on transformation temperatures of a Sn-9Zn-1Al base alloy was studied by Differential Scanning Calorimetry (DSC). For each alloy the solidification range was determined, which is an important characteristic regarding the application of these materials in the electronic industry. Identification of equilibrium phases and their chemical composition evaluation was performed by scanning electron microscopy (SEM/EDS). The interface thickness and chemical composition profiles were also evaluated