Microstructural Modification of Sn-0.7Cu Solder Alloys by Fe/Bi-Addition for Achieving High Mechanical Performance

• Published in: Journal of electronic materials Vol. 46; no. 8; pp. 4755 - 4764
• Main Authors: Ali, Bakhtiar, Sabri, Mohd Faizul Mohd, Said, Suhana Mohd, Mahdavifard, Mohammad Hossein, Sukiman, Nazatul Liana, Jauhari, Iswadi
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-08-2017; Springer Nature B.V
• Subjects: Alloying additive; Alloys; Backscattering; Bearing; Characterization and Evaluation of Materials; Chemistry and Materials Science; Copper; Diamond pyramid hardness tests; Dwell time; Electronics and Microelectronics; Emission analysis; Ferrous alloys; Field emission microscopy; Impact strength; Impact tests; Instrumentation; Intermetallic compounds; Materials Science; Mechanical properties; Microstructure; Optical and Electronic Materials; Scanning electron microscopy; Shear strength; Solders; Solid State Physics; Spectroscopic analysis; Tin base alloys; Toughness; X-ray diffraction; shear strength; hardness; Sn-0.7Cu; microstructure; impact toughness; Fe/Bi additives
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-017-5416-x

In this work, we studied the Fe/Bi-bearing tin-copper (Sn-0.7Cu) solders for their microstructural and mechanical properties. The microstructure was studied using field emission scanning electron microscopy (FESEM) with a backscattered electron (BSE) detector, x-ray diffraction (XRD) analysis, and energy-dispersive x-ray spectroscopy (EDX). The microstructure study showed that Fe forms very few FeSn
2
intermetallic compounds (IMCs) and does not significantly alter the microstructure of Sn-0.7Cu, whereas Bi controls the size of inter-dendritic regions containing Cu
6
Sn
5
and Ag
3
Sn IMCs of the alloy, as well as significantly refines its primary β-Sn dendrites. Moreover, Bi atoms dissolve in β-Sn matrix, which in turn strengthen the solder by the Bi solid solution strengthening mechanism. Such microstructural modification leads to significant improvements in various mechanical properties of the alloy, including shear strength, impact toughness, and hardness values. Shear tests were performed with a 0.25 mm/min shear speed. The results showed that shear strength improves from 16.57 MPa to 38.36 MPa with the addition of Fe/Bi to Sn-0.7Cu, raising by about 130%. The energy absorbed during impact tests was measured for samples with the help of a Charpy impact testing machine with a 5.4 m/s impact speed. The results revealed that the addition of Fe/Bi to Sn-0.7Cu improves its impact absorbed energy by over 35%, increasing it from 7.5 J to 10.3 J. Vickers hardness tests were carried out for the test samples with a 245.2 mN applied load and 10 s dwell time. The results showed that the hardness number improves from 9.89 to 24.13 with Fe/Bi to Sn-0.7Cu, increasing by about 140%.