Análise do eutético ternário na liga Sn-3%Ag-0,7%Cu (SAC 307)

Abstract

The effects of the thermal parameters on the processing of brazed joints in electronic components and especially in the final microstructure, is extensively reported in the literature. However, the characterization of ternary eutectics present in lead-free brazing alloys is something scarce. In this sense, the present work has as objective the study the influence of the cooling rate (ṪE) and the velocity of displacement of the eutectic front (VE) in the microstructure of the Sn-3%Ag-0,7%Cu (SAC307) alloy, directionally solidified under transient heat flow conditions, especially in the tertiary nutrient Sn+Cu6Sn5+Ag3Sn. The characterization of the eutectic regions was performed by Scanning Electron Microscopy (SEM) together with the Electron Backscatter Diffraction (EBSD) technique taking into account the size, appearance and morphology of the phases present in the eutectic. The results indicated a microstructure composed of a dendritic matrix rich in Sn surrounded by a ternary eutectic mixture composed of the β-Sn, Cu6Sn5 and Ag3Sn phases, besides primary intermetallic particles of Cu6Sn5 distributed heterogeneously. According to the MEV-EBSD images and the laws of microstructural growth, more refined eutectic structures were obtained for larger values of VE, having an exponent of -1/2 describing the variation of interphase spacing (λCu6Sn5 e λAg3Sn).