Microstructural development and mechanical properties of a near-eutectic directionally solidified Sn-Bi solder alloy

Author(s)

Silva, Bismarck Luiz ^[1] ; Reinhart, Guillaume ^[2] ; Nguyen-Thi, Henri ; Mangelinck-Noel, Nathalie ^[3] ; Garcia, Amauri ^[4] ; Spinelli, Jose Eduardo ^[1]

Affiliation

^[1] Univ Fed Sao Carlos, Dept Mat Engn, BR-13565905 Sao Carlos, SP - Brazil

^[2] Aix Marseille Univ, CNRS, IM2NP UMR 7334, F-13397 Marseille - France

^[3] Henri Nguyen-Thi, Aix Marseille Univ, CNRS, IM2NP UMR 7334, F-13397 Marseille - France

^[4] Univ Estadual Campinas, Dept Mfg & Mat Engn, BR-13083970 Campinas, SP - Brazil

• Document type: Journal article
• Source: MATERIALS CHARACTERIZATION; v. 107, p. 43-53, SEP 2015.
• Web of Science Citations: 22

Abstract

Sn-Bi solders may be applied for electronic applications where low-temperature soldering is required, i.e., sensitive components, step soldering and soldering LEDs. In spite of their potential to cover such applications, the mechanical response of soldered joints of Sn-Bi alloys in some cases does not meet the strength requirements due to inappropriate resulting microstructures. Hence, careful examination and control of as-soldered microstructures become necessary with a view to pre-programming reliable final properties. The present study aims to investigate the effects of solidification thermal parameters (growth rate VI, and cooling rate TO on the microstructure of the Sn-52 wt%Bi solder solidified under unsteady-state conditions. Samples were obtained by upward directional solidification (DS), followed by characterization through metallography and scanning electron microscopy (SEM). The microstructures are shown to be formed by Sn-rich dendrites decorated with Bi precipitates surrounded by a complex regular eutectic mixture, with alternated Bi-rich and Sn-rich phases. Experimental correlations of primary (lambda(1)), secondary (lambda(2)), tertiary (lambda(3)) dendritic and eutectic spacings (lambda(coarse) and lambda(fine)) with cooling rate and growth rate are established. Two ranges of lamellar eutectic sizes were determined, described by two experimental equations lambda = 1.1 V-L(-1/2) and lambda = 0.67 V-L(-1/2). The onset of tertiary branches within the dendritic array along the Sn-52 wt.%Bi alloy DS casting is shown to occur for cooling rates lower than 1.5 degrees C/s. (C) 2015 Elsevier Inc. All rights reserved. (AU)

• FAPESP's process: 13/13030-5 - Microstructure, thermal parameters, segregation and mechanical properties of lead-free Sn-based, Zn-based and Bi-based solder alloys
• Grantee: José Eduardo Spinelli
• Support Opportunities: Regular Research Grants
• FAPESP's process: 13/08259-3 - Microstructure and mechanical behavior of Sn-Bi-Cu and Sn-Bi-Ag lead-free solder alloys
• Grantee: Bismarck Luiz Silva
• Support Opportunities: Scholarships in Brazil - Doctorate