Effect of Sb and Ag Addition and Aging on the Microstructural Evolution, IMC Layer Growth, and Mechanical Properties of Near-Eutectic Sn-Bi Alloys

• Published in: Journal of electronic materials Vol. 53; no. 3; pp. 1284 - 1298
• Main Authors: Fowler, Hannah N., Puttur Lakshminarayana, Sukshitha Achar, Lai, Sean Yenyu, Tay, Sui Xiong, Masaeng, Aleena, Subbarayan, Ganesh, Blendell, John E., Handwerker, Carol A.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-03-2024; Springer Nature B.V
• Subjects: Age hardening; Aging (artificial); Alloy development; Alloying elements; Antimony; Bismuth; Characterization and Evaluation of Materials; Chemistry and Materials Science; Copper; Copper base alloys; Creep strength; Damage accumulation; Electronic Packaging and Interconnections 2023; Electronics and Microelectronics; Eutectic temperature; Evolution; Instrumentation; Lead free; Low temperature; Materials Science; Mechanical properties; Melting points; Optical and Electronic Materials; Silver; Soldered joints; Solders; Solid solutions; Solid State Physics; Thermal cycling; Tin; Tin base alloys; Topical Collection: Electronic Packaging and Interconnections 2023; aging study; Low-temperature solder; lead-free; eutectic Sn-Bi; mechanical testing
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-023-10866-0

Low-melting-point Sn-Bi solder joints (melting point: 139°C) show remarkable resistance to damage accumulation during aggressive thermal cycling. In this study, we used isothermal aging at 85°C of near eutectic Sn-Bi solder joints to determine the effect of Sb in solid solution and Ag
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Sn intermetallic on microstructural evolution and the resulting mechanical properties as a way to explain the thermal cycling behavior. Most importantly, the Sb in solid solution in these alloys resulted in higher strength and improved creep resistance when compared to eutectic Sn-Bi. In contrast to Sn-Pb and Sn-Ag-Cu Pb-free alloys, all the near-eutectic Sn-Bi alloys tested showed significant age hardening. In both the unaged and aged conditions, both Sb and Ag additions individually increased the saturation stress of the eutectic Sn-Bi solder joint, but Ag had a more significant effect. However, when both Sb and Ag were added to eutectic Sn-Bi, the saturation stress was lower than when 1 wt.% Ag alone was added. In terms of relative behavior, the Sb-free 42Sn-Bi-1Ag aged for 250 h had the highest saturation stress of all tested alloys, while as-reflowed eutectic Sn-Bi had the lowest saturation stress. These results suggest that the alloy design strategy for Sn-Ag-Cu alloys, i.e., assuming that the effects of individual alloying elements are additive and independent, is not valid when Sb is added to Sn-Bi low-temperature solder.
Graphical Abstract