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7142253 
Journal Article 
Novel Bi-containing Sn-1.5Ag-0.7Cu lead-free solder alloy with further enhanced thermal property and strength for mobile products 
El-Daly, AA; El-Taher, AM; Gouda, S; , 
2015 
1 
Materials & Design
ISSN: 0264-1275
EISSN: 1873-4197 
ELSEVIER SCI LTD 
OXFORD 
65 
796-805 
WOS:000345520000099 
In this study, the low Ag-content Sn-1.5Ag-0.7Cu (SAC157) lead-free solder was modified for advance electronic components with minor additions of Bi. The microstructure, melt properties and tensile behavior after and before compositional modifications were investigated. From microstructures evaluation, 1 wt% Bi addition to SAC157 significantly enhanced the solid solution effect of Bi and refined needle-like Ag3Sn and plate-like Cu6Sn5 particles as well as extended the eutectic area, which raised the mechanical strength and Young's modulus to about 1.5 times of SAC157 solder. With increasing Bi addition to 3 wt%, the cubic-shaped Bi precipitates and enlarged eutectic area cause a dramatic increase of ultimate tensile strength, yield strength and Young's modulus to about 2.2-2.6 times of the SAC157 alloy, although the elongation was maintained at the SAC157 level. The peak flow stress during deformation can be correlated with temperature and strain rate by a hyperbolic-sine equation. The activation energy for SAC157 alloy was increased from 58.2 kJ/mol to 101.7 and 109.0 kJ/mol when doped with 1.0 and 3.0 wt% of Bi, indicating the change of dominant deformation mechanism from dislocation pipe diffusion to lattice self-diffusion. Besides, the addition of Bi not only reduced the solidus temperature (T-onset) and eutectic temperature (T-m), but also decreased the undercooling even though the pasty rang is slightly increased. (C) 2014 Elsevier Ltd. All rights reserved. 
Lead-free solders; Microstructure; Mechanical properties